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An ISO Quality question

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Anonymous
August 11, 2005 2:17:02 AM

Archived from groups: rec.photo.digital.slr-systems (More info?)

My Canon 300D has ISO settings from 100 to 1600 and test shots on
dpreview.com show very little difference at 400 and below.

Is there *any* reason to use 100 if 200 has imperceptably more noise
and one stop faster shutter speed is apt to result in a sharper
picture ?

??

Thanks

--
a d y k e s @ p a n i x . c o m

Don't blame me. I voted for Gore.

More about : iso quality question

Anonymous
August 11, 2005 3:49:31 AM

Archived from groups: rec.photo.digital.slr-systems (More info?)

In article <ddeceu$dv0$1@panix5.panix.com>, Al Dykes <adykes@panix.com> wrote:
>
>My Canon 300D has ISO settings from 100 to 1600 and test shots on
>dpreview.com show very little difference at 400 and below.
>
>Is there *any* reason to use 100 if 200 has imperceptably more noise
>and one stop faster shutter speed is apt to result in a sharper
>picture ?

Well ... you've already gotten one followup concerining the
ability to select aperture for proper depth of field. I have another
(rather unusual) factor which makes me wish that my Nikon D70 would go
down to 100 ASA/ISO

Not a consideration on the Cannon, but my Nikon D70 has a
minimum ISO of 200, and this prevents me from shooting at the highest
magnification range of the old 200mm Medical Nikkor (with the built-in
ring flash). It does the exposure calculation based on an ISO (actually
marked as ASA) setting ring, and a magnification ratio ring, resulting
in setting of the aperture ring.

The lens is capable of going down to a 3X magnification ratio,
but the closest that I can get at present is a 2/3X magnification ratio
because of the exposure situation.

I really need to modify the power pack to reduce the flash power
enough for those closer shots.

Enjoy,
DoN.
--
Email: <dnichols@d-and-d.com> | Voice (all times): (703) 938-4564
(too) near Washington D.C. | http://www.d-and-d.com/dnichols/DoN.html
--- Black Holes are where God is dividing by zero ---
Anonymous
August 11, 2005 8:32:57 AM

Archived from groups: rec.photo.digital.slr-systems (More info?)

In article <ddehsb$mma$1@Fuego.d-and-d.com>, dnichols@d-and-d.com
says...
> The lens is capable of going down to a 3X magnification ratio,
> but the closest that I can get at present is a 2/3X magnification ratio
> because of the exposure situation.
>
> I really need to modify the power pack to reduce the flash power
> enough for those closer shots.

ND filter?
--
http://www.pbase.com/bcbaird
Related resources
Anonymous
August 11, 2005 1:03:47 PM

Archived from groups: rec.photo.digital.slr-systems (More info?)

In message <ddehsb$mma$1@Fuego.d-and-d.com>,
dnichols@d-and-d.com (DoN. Nichols) wrote:

> Not a consideration on the Cannon, but my Nikon D70 has a
>minimum ISO of 200, and this prevents me from shooting at the highest
>magnification range of the old 200mm Medical Nikkor (with the built-in
>ring flash). It does the exposure calculation based on an ISO (actually
>marked as ASA) setting ring, and a magnification ratio ring, resulting
>in setting of the aperture ring.

Have you tried shooting with the manual flash for 100 when the camera
was set to 200?

That might not be a problem at all, if you're shooting RAW. 100% matte
reflectance would probably not clip; only specular highlights, which
should be subdued by the ring, anyway (and which would generally even
out the lighting, in your favor).
--

<>>< ><<> ><<> <>>< ><<> <>>< <>>< ><<>
John P Sheehy <JPS@no.komm>
><<> <>>< <>>< ><<> <>>< ><<> ><<> <>><
Anonymous
August 11, 2005 1:31:47 PM

Archived from groups: rec.photo.digital.slr-systems (More info?)

In article <ddeceu$dv0$1@panix5.panix.com>, Al Dykes <adykes@panix.com> wrote:
>
>My Canon 300D has ISO settings from 100 to 1600 and test shots on
>dpreview.com show very little difference at 400 and below.
>
>Is there *any* reason to use 100 if 200 has imperceptably more noise
>and one stop faster shutter speed is apt to result in a sharper
>picture ?

You have to test dynamic range as well. It is very likely that ISO 100
results in 2 stops more dynamic range compared to ISO 400.


--
That was it. Done. The faulty Monk was turned out into the desert where it
could believe what it liked, including the idea that it had been hard done
by. It was allowed to keep its horse, since horses were so cheap to make.
-- Douglas Adams in Dirk Gently's Holistic Detective Agency
Anonymous
August 11, 2005 1:31:48 PM

Archived from groups: rec.photo.digital.slr-systems (More info?)

In message <7cmgnb801l78apn6bnpv0k93l3@inews_id.stereo.hq.phicoh.net>,
philip@pch.home.cs.vu.nl (Philip Homburg) wrote:

>In article <ddeceu$dv0$1@panix5.panix.com>, Al Dykes <adykes@panix.com> wrote:
>>
>>My Canon 300D has ISO settings from 100 to 1600 and test shots on
>>dpreview.com show very little difference at 400 and below.
>>
>>Is there *any* reason to use 100 if 200 has imperceptably more noise
>>and one stop faster shutter speed is apt to result in a sharper
>>picture ?
>
>You have to test dynamic range as well. It is very likely that ISO 100
>results in 2 stops more dynamic range compared to ISO 400.

That would only be true if ISO 100 were limited in DR only by noise, but
it's major limitation is the 12 bits of digitization, which may sound
like a lot, but is actually quite poor for shadows, as linear data.

The difference between ISOs generally shows most when the exposures
under-utilize the 12 bits of RAW data. The closer you get to using the
full range at all ISOs, the less difference there is between them.
--

<>>< ><<> ><<> <>>< ><<> <>>< <>>< ><<>
John P Sheehy <JPS@no.komm>
><<> <>>< <>>< ><<> <>>< ><<> ><<> <>><
Anonymous
August 11, 2005 6:26:29 PM

Archived from groups: rec.photo.digital.slr-systems (More info?)

In article <MPG.1d649f03bfc8c7639897e8@news.verizon.net>,
Brian Baird <no@no.thank.u> wrote:
>In article <ddehsb$mma$1@Fuego.d-and-d.com>, dnichols@d-and-d.com
>says...
>> The lens is capable of going down to a 3X magnification ratio,
>> but the closest that I can get at present is a 2/3X magnification ratio
>> because of the exposure situation.
>>
>> I really need to modify the power pack to reduce the flash power
>> enough for those closer shots.
>
>ND filter?

I've considered that, but it is an uncommon diameter (IIRC,
38.7mm or something close), and it would have to go into the middle of
the stack because the most powerful lens of the set has only the male
threads, as it is designed to always be the greatest distance from the
prime lens. All combinations which are documented for the lens have one
or two close-up lenses from the kit on the front of the prime lens,
never three.

I think that simply adding a switch to the power supply to allow
reducing the capacitance supplying the flashlamp power to produce about a
two stop reduction would work nicely. And, IIRC, there is physical room
for such a modification.

I have read that there was a special cord to go from the power
supply to the lens to allow operation at higher ASAs, but I have never
found such a cord, and no information on how to construct one. I would
guess (since there is no capacitance at the flash head) that it would
consist of a resistor in series with the high voltage lead, and a
smaller capacitor closer to the flash head.

And, since I have only the AC powered supply, I might be better
off to design and build a battery powered one which works from normal
batteries -- ideally NiMH rechargeable ones, or perhaps even the same
LiON ones used by the camera itself. Certainly if I were to find the
original battery power supply for it, I would be stuck purchasing 350V
batteries (or are they 277V ones? In any case, rare and expensive in
today's market. :-)

Enjoy,
DoN.
--
Email: <dnichols@d-and-d.com> | Voice (all times): (703) 938-4564
(too) near Washington D.C. | http://www.d-and-d.com/dnichols/DoN.html
--- Black Holes are where God is dividing by zero ---
Anonymous
August 11, 2005 6:28:27 PM

Archived from groups: rec.photo.digital.slr-systems (More info?)

In article <3o4mf1hnsfmeqrt42rormfdc27jupdgo3v@4ax.com>, <JPS@no.komm> wrote:
>In message <ddehsb$mma$1@Fuego.d-and-d.com>,
>dnichols@d-and-d.com (DoN. Nichols) wrote:
>
>> Not a consideration on the Cannon, but my Nikon D70 has a
>>minimum ISO of 200, and this prevents me from shooting at the highest
>>magnification range of the old 200mm Medical Nikkor (with the built-in
>>ring flash). It does the exposure calculation based on an ISO (actually
>>marked as ASA) setting ring, and a magnification ratio ring, resulting
>>in setting of the aperture ring.
>
>Have you tried shooting with the manual flash for 100 when the camera
>was set to 200?

I did while shooting jpegs, and there were blown highlights.

>That might not be a problem at all, if you're shooting RAW. 100% matte
>reflectance would probably not clip; only specular highlights, which
>should be subdued by the ring, anyway (and which would generally even
>out the lighting, in your favor).

Hmm ... it is worth a try. But I think that I would prefer
getting the right amount of light to start with.

Thanks,
DoN.

--
Email: <dnichols@d-and-d.com> | Voice (all times): (703) 938-4564
(too) near Washington D.C. | http://www.d-and-d.com/dnichols/DoN.html
--- Black Holes are where God is dividing by zero ---
Anonymous
August 11, 2005 6:33:00 PM

Archived from groups: rec.photo.digital.slr-systems (More info?)

> Is there *any* reason to use 100 if 200 has imperceptably more noise
> and one stop faster shutter speed is apt to result in a sharper
> picture ?
> a d y k e s @ p a n i x . c o m

As I see it you would adjust ISO to have a desired effect on depth of field.
If you set aperture lower to get a shorter depth if field (to get background
blurred out) then you'll need a slower shutter speed unless you select a
higher ISO allowing a faster shutter speed

Toa
Anonymous
August 11, 2005 9:16:03 PM

Archived from groups: rec.photo.digital.slr-systems (More info?)

"Al Dykes" <adykes@panix.com> wrote in message
news:D deceu$dv0$1@panix5.panix.com...

> Is there *any* reason to use 100 if 200 has imperceptably more noise
> and one stop faster shutter speed is apt to result in a sharper
> picture ?

I did a few portrait tests at ISO 100 to 1600 on my Canon 350D. Between ISO
100 and 200 the difference was minimal - but still detectable. In the end I
decided that if I was to take a portrait that was going to be enlarged and
hung on the wall, then it would have to be @ ISO 100.

I'm having trouble finding a compromise between ISO and shutter speed to
freeze a moving scene - being a picky/fussy bastard I'm going to invest in a
faster lens to get around the problem (present lens has max aperture of 5.6
@ 55mm).

Hope this helps.
Anonymous
August 11, 2005 9:16:04 PM

Archived from groups: rec.photo.digital.slr-systems (More info?)

In article <H8BKe.1938$iM2.165766@news.xtra.co.nz>,
Cockpit Colin <spam@nospam.com> wrote:
>
>"Al Dykes" <adykes@panix.com> wrote in message
>news:D deceu$dv0$1@panix5.panix.com...
>
>> Is there *any* reason to use 100 if 200 has imperceptably more noise
>> and one stop faster shutter speed is apt to result in a sharper
>> picture ?
>
>I did a few portrait tests at ISO 100 to 1600 on my Canon 350D. Between ISO
>100 and 200 the difference was minimal - but still detectable. In the end I
>decided that if I was to take a portrait that was going to be enlarged and
>hung on the wall, then it would have to be @ ISO 100.
>
>I'm having trouble finding a compromise between ISO and shutter speed to
>freeze a moving scene - being a picky/fussy bastard I'm going to invest in a
>faster lens to get around the problem (present lens has max aperture of 5.6
>@ 55mm).

Hmm ... I got a 50mm f1.4 AF lens for about $200.00 -- used.
You might look for the same -- or perhaps the 50mm f1.8 would serve as
well for you. (The above are Nikon lenses, and I see that you have a
Cannon, so you will have to see what is available to fit your camera.

Does your local camera store stock used lenses? Do they have
reasonable prices?

Good Luck,
DoN.

--
Email: <dnichols@d-and-d.com> | Voice (all times): (703) 938-4564
(too) near Washington D.C. | http://www.d-and-d.com/dnichols/DoN.html
--- Black Holes are where God is dividing by zero ---
Anonymous
August 11, 2005 11:45:58 PM

Archived from groups: rec.photo.digital.slr-systems (More info?)

In article <155mf1l9hhh2btdf8b49pileh23t838g35@4ax.com>, <JPS@no.komm> wrote:
>In message <7cmgnb801l78apn6bnpv0k93l3@inews_id.stereo.hq.phicoh.net>,
>philip@pch.home.cs.vu.nl (Philip Homburg) wrote:
>>You have to test dynamic range as well. It is very likely that ISO 100
>>results in 2 stops more dynamic range compared to ISO 400.
>
>That would only be true if ISO 100 were limited in DR only by noise, but
>it's major limitation is the 12 bits of digitization, which may sound
>like a lot, but is actually quite poor for shadows, as linear data.

Except that as far as I can tell, there are not enough photons at ISO 100
to get 12 bits of S/N.

For a 12-bit signal to noise ratio, you need at least 24-bits worth of
electrons. Assuming a 16Mpixel 35mm full frame sensor and 540 THz light,
and 100% quantum efficiency we can compute the required power that has
illuminate the sensor:

The energy of one photon is 6.626e-34 * 540e12 = 3.57804e-19 J.
Energy per sensor element: 3.57804e-19 * 16.78e6 = 6.00395e-12 J.
Energy for the entire sensor: 6.00395e-12 * 16e6 = 9.60632e-5 J.
Energy per unit of area: 9.60632e-5 / (24e-3 *36e-3) = 0.1112 J/m2

Assuming an exposure of 1 second we get 0.1112 W/m2 or 76 cd/m2

On the other hand, ISO 100 results in an exposure of about 0.08 lx.

There is probably a factor of 2pi involved, but I don't know in which
direction.

This is not the whole story, but the calculation suggests that noise
levels (certainly in the shadow areas) should be better at ISO 100 than
at ISO 400.


--
That was it. Done. The faulty Monk was turned out into the desert where it
could believe what it liked, including the idea that it had been hard done
by. It was allowed to keep its horse, since horses were so cheap to make.
-- Douglas Adams in Dirk Gently's Holistic Detective Agency
Anonymous
August 11, 2005 11:45:59 PM

Archived from groups: rec.photo.digital.slr-systems (More info?)

Philip Homburg wrote:
[]
> Except that as far as I can tell, there are not enough photons at ISO
> 100
> to get 12 bits of S/N.
>
> For a 12-bit signal to noise ratio, you need at least 24-bits worth of
> electrons.

Were your calculation to be for a 12-bit S/N at full exposure, you might
be correct, but you are ignoring the fact that the noise is light-level
dependant.

Top of the head figures:

- well size 40,000 electrons (white)
- 12-bit digitisation, step size 10 electrons
- RMS quantisation noise 3 electrons
- smallest signal (black) 1 electron
- noise on smallest signal 1 electron
- therefore quantisation noise exceeds shot-noise
- 12-bits isn't enough

(OK, lots of assumptions, particularly about scene contrast level....)

David
Anonymous
August 12, 2005 1:22:59 AM

Archived from groups: rec.photo.digital.slr-systems (More info?)

In message <ddg5cb$el4$1@Fuego.d-and-d.com>,
dnichols@d-and-d.com (DoN. Nichols) wrote:

>In article <3o4mf1hnsfmeqrt42rormfdc27jupdgo3v@4ax.com>, <JPS@no.komm> wrote:
>>In message <ddehsb$mma$1@Fuego.d-and-d.com>,
>>dnichols@d-and-d.com (DoN. Nichols) wrote:
>>
>>> Not a consideration on the Cannon, but my Nikon D70 has a
>>>minimum ISO of 200, and this prevents me from shooting at the highest
>>>magnification range of the old 200mm Medical Nikkor (with the built-in
>>>ring flash). It does the exposure calculation based on an ISO (actually
>>>marked as ASA) setting ring, and a magnification ratio ring, resulting
>>>in setting of the aperture ring.
>>
>>Have you tried shooting with the manual flash for 100 when the camera
>>was set to 200?
>
> I did while shooting jpegs, and there were blown highlights.
>
>>That might not be a problem at all, if you're shooting RAW. 100% matte
>>reflectance would probably not clip; only specular highlights, which
>>should be subdued by the ring, anyway (and which would generally even
>>out the lighting, in your favor).
>
> Hmm ... it is worth a try. But I think that I would prefer
>getting the right amount of light to start with.

I consider the ISO numbers on the camera to be pretty arbitrary. My
first DSLR, the Canon 10D, had a reputation for blowing out JPEGs unless
the contrast parameter was set to -2, or you used negative exposure
compensation. Upon further investigation, I found out that the camera
was actually metering for ISO 64, when it was set to ISO 100. I also
found out that I could use an external incident meter, or spot-meter on
a grey card, and expose for ISO 40, and no white that was purely matte
would blow out.

IOW, the minimum of ISO 200 on your camera might only be for big
headroom, and may actually work as ISO 100 like slide film. Try it, but
you must do it in RAW. With RAW, even if you blow one channel out, if
it is a white highlight or specular highlight from the light source,
some converters will treat areas where one or two color channels are
clipped as greyscale. The D70, like the 20D and 10D, are most sensitive
to green, and least sensitive to red, so the red channel often contains
extra greyscale highlight detail.
--

<>>< ><<> ><<> <>>< ><<> <>>< <>>< ><<>
John P Sheehy <JPS@no.komm>
><<> <>>< <>>< ><<> <>>< ><<> ><<> <>><
Anonymous
August 12, 2005 1:45:53 AM

Archived from groups: rec.photo.digital.slr-systems (More info?)

In article <%GMKe.86939$G8.25357@text.news.blueyonder.co.uk>,
David J Taylor <david-taylor@blueyonder.co.not-this-bit.nor-this-part.uk.invalid> wrote:
>- well size 40,000 electrons (white)
>- 12-bit digitisation, step size 10 electrons

Which means that quantisation noise corresponds to 0.5 * 40e3 / 2**12 = 4.88
electrons. At 25 electrons or more, shot-noise exceeds quantisation noise.


--
That was it. Done. The faulty Monk was turned out into the desert where it
could believe what it liked, including the idea that it had been hard done
by. It was allowed to keep its horse, since horses were so cheap to make.
-- Douglas Adams in Dirk Gently's Holistic Detective Agency
Anonymous
August 12, 2005 1:46:15 AM

Archived from groups: rec.photo.digital.slr-systems (More info?)

In message <vsdlktt3bqvcl5gcu5t0r77km4@inews_id.stereo.hq.phicoh.net>,
philip@pch.home.cs.vu.nl (Philip Homburg) wrote:

>In article <%GMKe.86939$G8.25357@text.news.blueyonder.co.uk>,
>David J Taylor <david-taylor@blueyonder.co.not-this-bit.nor-this-part.uk.invalid> wrote:
>>- well size 40,000 electrons (white)
>>- 12-bit digitisation, step size 10 electrons
>
>Which means that quantisation noise corresponds to 0.5 * 40e3 / 2**12 = 4.88
>electrons. At 25 electrons or more, shot-noise exceeds quantisation noise.

Arithmetically, perhaps, but things are more complex in the realm of
human perception. Noise doesn't really hide detail as much as the
arithmetic would suggest.

The kinds of things that you seem to be taking into consideration are
the kinds of things that determine the usefulness of single pixels as
accurate measurement devices, not necessarily the usefulness of arrays
of such pixels as "imaging" devices, especially in light of the brain's
abilities in the area of pattern recognition and rejection.
--

<>>< ><<> ><<> <>>< ><<> <>>< <>>< ><<>
John P Sheehy <JPS@no.komm>
><<> <>>< <>>< ><<> <>>< ><<> ><<> <>><
Anonymous
August 12, 2005 4:23:13 AM

Archived from groups: rec.photo.digital.slr-systems (More info?)

In article <3pfnf11jsscctau4havunc9nu4qh20hjlp@4ax.com>, <JPS@no.komm> wrote:
>In message <ddg5cb$el4$1@Fuego.d-and-d.com>,
>dnichols@d-and-d.com (DoN. Nichols) wrote:
>
>>In article <3o4mf1hnsfmeqrt42rormfdc27jupdgo3v@4ax.com>, <JPS@no.komm> wrote:

[ ... Medical Nikkor with D70 & ISO 200 minimum snipped ... ]

>>>Have you tried shooting with the manual flash for 100 when the camera
>>>was set to 200?
>>
>> I did while shooting jpegs, and there were blown highlights.
>>
>>>That might not be a problem at all, if you're shooting RAW. 100% matte
>>>reflectance would probably not clip; only specular highlights, which
>>>should be subdued by the ring, anyway (and which would generally even
>>>out the lighting, in your favor).
>>
>> Hmm ... it is worth a try. But I think that I would prefer
>>getting the right amount of light to start with.
>
>I consider the ISO numbers on the camera to be pretty arbitrary. My
>first DSLR, the Canon 10D, had a reputation for blowing out JPEGs unless
>the contrast parameter was set to -2, or you used negative exposure
>compensation. Upon further investigation, I found out that the camera
>was actually metering for ISO 64, when it was set to ISO 100. I also
>found out that I could use an external incident meter, or spot-meter on
>a grey card, and expose for ISO 40, and no white that was purely matte
>would blow out.

O.K. Note that the chart which comes with the lens suggest that
for 2:1 reproduction ratio, a maximum ASA (now ISO) of 50 is suggested
for color, and 25 for B&W. (This is an old lens system, of course.)
The chart is incomplete, but it looks like it will require an ASA of 25
(or perhaps 32) with the full 3:1 ratio, so I may have to cut the
illumination anyway. I can't see pushing it that far down.

>IOW, the minimum of ISO 200 on your camera might only be for big
>headroom, and may actually work as ISO 100 like slide film. Try it, but
>you must do it in RAW. With RAW, even if you blow one channel out, if
>it is a white highlight or specular highlight from the light source,
>some converters will treat areas where one or two color channels are
>clipped as greyscale. The D70, like the 20D and 10D, are most sensitive
>to green, and least sensitive to red, so the red channel often contains
>extra greyscale highlight detail.

Well ... we'll see what experimentation with RAW shows. But I
suspect that I'll still have to perform an capacitor-ectomy to get to
the maximum close-up with the built in ring flash.

Thanks,
DoN.
--
Email: <dnichols@d-and-d.com> | Voice (all times): (703) 938-4564
(too) near Washington D.C. | http://www.d-and-d.com/dnichols/DoN.html
--- Black Holes are where God is dividing by zero ---
Anonymous
August 12, 2005 12:23:22 PM

Archived from groups: rec.photo.digital.slr-systems (More info?)

Philip Homburg wrote:
> In article <%GMKe.86939$G8.25357@text.news.blueyonder.co.uk>,
> David J Taylor
> <david-taylor@blueyonder.co.not-this-bit.nor-this-part.uk.invalid>
> wrote:
>> - well size 40,000 electrons (white)
>> - 12-bit digitisation, step size 10 electrons
>
> Which means that quantisation noise corresponds to 0.5 * 40e3 / 2**12
> = 4.88
> electrons. At 25 electrons or more, shot-noise exceeds quantisation
> noise.

Yes, in the lighter areas of the picture 12 bits is enough, agreed. But
where you see the quantisation noise is in the dark shadow regions.
Remember that the eye's response isn't linear, but more like log.

David
Anonymous
August 12, 2005 1:32:07 PM

Archived from groups: rec.photo.digital.slr-systems (More info?)

"DoN. Nichols" <dnichols@d-and-d.com> wrote in message
news:D dg5jh$ep6$1@Fuego.d-and-d.com...

> Hmm ... I got a 50mm f1.4 AF lens for about $200.00 -- used.
> You might look for the same -- or perhaps the 50mm f1.8 would serve as
> well for you. (The above are Nikon lenses, and I see that you have a
> Cannon, so you will have to see what is available to fit your camera.

I've decided to get the 100mm F1.2 L series lens - 50mm has proven to be too
short for me, in addition to the other limitations :( 

> Does your local camera store stock used lenses? Do they have
> reasonable prices?

Local stores don't have anything - it's all online auction sites for me. In
any case, I prefer to buy new - it's just the "picky/bastard" bit in me
coming out again! :) 
Anonymous
August 12, 2005 1:32:08 PM

Archived from groups: rec.photo.digital.slr-systems (More info?)

In article <FrPKe.2059$iM2.185097@news.xtra.co.nz>,
Cockpit Colin <spam@nospam.com> wrote:
>
>"DoN. Nichols" <dnichols@d-and-d.com> wrote in message
>news:D dg5jh$ep6$1@Fuego.d-and-d.com...
>
>> Hmm ... I got a 50mm f1.4 AF lens for about $200.00 -- used.
>> You might look for the same -- or perhaps the 50mm f1.8 would serve as
>> well for you. (The above are Nikon lenses, and I see that you have a
>> Cannon, so you will have to see what is available to fit your camera.
>
>I've decided to get the 100mm F1.2 L series lens - 50mm has proven to be too
>short for me, in addition to the other limitations :( 
>
>> Does your local camera store stock used lenses? Do they have
>> reasonable prices?
>
>Local stores don't have anything - it's all online auction sites for me. In
>any case, I prefer to buy new - it's just the "picky/bastard" bit in me
>coming out again! :) 
>

ebay.


--
a d y k e s @ p a n i x . c o m

Don't blame me. I voted for Gore.
Anonymous
August 12, 2005 1:45:26 PM

Archived from groups: rec.photo.digital.slr-systems (More info?)

DoN. Nichols wrote:

> Not a consideration on the Cannon, but my Nikon D70 has a
> minimum ISO of 200, and this prevents me from shooting at the highest
> magnification range of the old 200mm Medical Nikkor (with the built-in
> ring flash). It does the exposure calculation based on an ISO (actually
> marked as ASA) setting ring, and a magnification ratio ring, resulting
> in setting of the aperture ring.
>
> The lens is capable of going down to a 3X magnification ratio,
> but the closest that I can get at present is a 2/3X magnification ratio
> because of the exposure situation.
>
> I really need to modify the power pack to reduce the flash power
> enough for those closer shots.
>

ND filter.

--
-- r.p.e.35mm user resource: http://www.aliasimages.com/rpe35mmur.htm
-- r.p.d.slr-systems: http://www.aliasimages.com/rpdslrsysur.htm
-- [SI] gallery & rulz: http://www.pbase.com/shootin
-- e-meil: Remove FreeLunch.
Anonymous
August 12, 2005 4:50:19 PM

Archived from groups: rec.photo.digital.slr-systems (More info?)

In article <_%YKe.87228$G8.18745@text.news.blueyonder.co.uk>,
David J Taylor <david-taylor@blueyonder.co.not-this-bit.nor-this-part.uk.invalid> wrote:
>Philip Homburg wrote:
>> Which means that quantisation noise corresponds to 0.5 * 40e3 / 2**12
>> = 4.88
>> electrons. At 25 electrons or more, shot-noise exceeds quantisation
>> noise.
>
>Yes, in the lighter areas of the picture 12 bits is enough, agreed. But
>where you see the quantisation noise is in the dark shadow regions.
>Remember that the eye's response isn't linear, but more like log.

Except that according to this calculation, quantisation noise exceeds
photon shot noise only at output levels 0, 1, and 2. At level 3 you have
3 * 40e3/4095 = 29.3 electrons, which gives a photon shot noise of 5.41
electrons. Which is more than 0.5 LSB.


--
That was it. Done. The faulty Monk was turned out into the desert where it
could believe what it liked, including the idea that it had been hard done
by. It was allowed to keep its horse, since horses were so cheap to make.
-- Douglas Adams in Dirk Gently's Holistic Detective Agency
Anonymous
August 12, 2005 4:50:20 PM

Archived from groups: rec.photo.digital.slr-systems (More info?)

Philip Homburg wrote:
> In article <_%YKe.87228$G8.18745@text.news.blueyonder.co.uk>,
> David J Taylor
> <david-taylor@blueyonder.co.not-this-bit.nor-this-part.uk.invalid>
> wrote:
>> Philip Homburg wrote:
>>> Which means that quantisation noise corresponds to 0.5 * 40e3 /
>>> 2**12 = 4.88
>>> electrons. At 25 electrons or more, shot-noise exceeds quantisation
>>> noise.
>>
>> Yes, in the lighter areas of the picture 12 bits is enough, agreed.
>> But where you see the quantisation noise is in the dark shadow
>> regions. Remember that the eye's response isn't linear, but more
>> like log.
>
> Except that according to this calculation, quantisation noise exceeds
> photon shot noise only at output levels 0, 1, and 2. At level 3 you
> have 3 * 40e3/4095 = 29.3 electrons, which gives a photon shot noise
> of 5.41
> electrons. Which is more than 0.5 LSB.

Yes, but level 3 corresponds to the sensor output of 87, so there is quite
a lot lost. People have measured this (but not me).

David
Anonymous
August 12, 2005 7:38:04 PM

Archived from groups: rec.photo.digital.slr-systems (More info?)

In article <ddi95i$ieg$1@inews.gazeta.pl>,
Alan Browne <alan.browne@FreeLunchVideotron.ca> wrote:
>DoN. Nichols wrote:
>
>> Not a consideration on the Cannon, but my Nikon D70 has a
>> minimum ISO of 200, and this prevents me from shooting at the highest
>> magnification range of the old 200mm Medical Nikkor (with the built-in
>> ring flash). It does the exposure calculation based on an ISO (actually
>> marked as ASA) setting ring, and a magnification ratio ring, resulting
>> in setting of the aperture ring.
>>
>> The lens is capable of going down to a 3X magnification ratio,
>> but the closest that I can get at present is a 2/3X magnification ratio
>> because of the exposure situation.
>>
>> I really need to modify the power pack to reduce the flash power
>> enough for those closer shots.
>>
>
>ND filter.

As I already mentioned elsewhere in this thread, this lens is a
bit weird. Start off with a 200mm f5.6 lens, but mount it so it is
fixed focus, at a 1:15 ratio (10' 11.9" or 3.35 meters.

Now -- supply a set of close-up lenses which must screw into the
front of the lens -- defined as 1/8X, 1/6X, 1/4X, 1/2X, 1X & 2X.

To get the intermediate values, stacking specific CU lens pairs
is defined:

1/3X = 1/4 + 1/6

2/3X = 1/2 + 1/4

1.5X = 1 + 1/2

3 X = 2 + 1

The only place where I need the reduced light is in the range
from 1 to 3.

Note that the 2X CU lens has a rather pronounced front element
curvature, and thus also has no front female filter thread.

This means that the ND filter must be placed between the prime
lens and the first CU lens, or between the two CU lenses for the 2X or
3X settings. I'm not sure about stacking that many elements, and flare
would be lower with the ND filter as the frontmost element, which is not
an option when the 2X CU lens is in use.

Also -- the filter thread is a bit weird. IIRC, I measured it
at something like 37.6 mm, so I'm not at all sure that I could get such
a filter, except as a custom, or with a reducing ring, which would mean
that I would need the opposite converter ring to continue on to the 2X
element.

So -- overall, I think that I would get better shots with a
modification to the flash power supply.

If you want to see what this is like, here is one which just
closed on eBay:

Auction #: 7536353068

Full URL: http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=7536...

Thanks,
DoN.
--
Email: <dnichols@d-and-d.com> | Voice (all times): (703) 938-4564
(too) near Washington D.C. | http://www.d-and-d.com/dnichols/DoN.html
--- Black Holes are where God is dividing by zero ---
Anonymous
August 13, 2005 1:06:58 AM

Archived from groups: rec.photo.digital.slr-systems (More info?)

In message <ddh87h$p02$1@Fuego.d-and-d.com>,
dnichols@d-and-d.com (DoN. Nichols) wrote:

>In article <3pfnf11jsscctau4havunc9nu4qh20hjlp@4ax.com>, <JPS@no.komm> wrote:
>>In message <ddg5cb$el4$1@Fuego.d-and-d.com>,
>>dnichols@d-and-d.com (DoN. Nichols) wrote:

>>>In article <3o4mf1hnsfmeqrt42rormfdc27jupdgo3v@4ax.com>, <JPS@no.komm> wrote:

> [ ... Medical Nikkor with D70 & ISO 200 minimum snipped ... ]

>>>>Have you tried shooting with the manual flash for 100 when the camera
>>>>was set to 200?

>>> I did while shooting jpegs, and there were blown highlights.

>>>>That might not be a problem at all, if you're shooting RAW. 100% matte
>>>>reflectance would probably not clip; only specular highlights, which
>>>>should be subdued by the ring, anyway (and which would generally even
>>>>out the lighting, in your favor).

>>> Hmm ... it is worth a try. But I think that I would prefer
>>>getting the right amount of light to start with.

>>I consider the ISO numbers on the camera to be pretty arbitrary. My
>>first DSLR, the Canon 10D, had a reputation for blowing out JPEGs unless
>>the contrast parameter was set to -2, or you used negative exposure
>>compensation. Upon further investigation, I found out that the camera
>>was actually metering for ISO 64, when it was set to ISO 100. I also
>>found out that I could use an external incident meter, or spot-meter on
>>a grey card, and expose for ISO 40, and no white that was purely matte
>>would blow out.

> O.K. Note that the chart which comes with the lens suggest that
>for 2:1 reproduction ratio, a maximum ASA (now ISO) of 50 is suggested
>for color, and 25 for B&W. (This is an old lens system, of course.)
>The chart is incomplete, but it looks like it will require an ASA of 25
>(or perhaps 32) with the full 3:1 ratio, so I may have to cut the
>illumination anyway. I can't see pushing it that far down.

I suggest that you try putting some magenta filters cut out from clear
magenta sheets of file folders or something. I use "Flomo" folders; two
sheets thick of their magenta folder over my Canon 550EX gives the flash
almost the exact color that is native to the camera's channel
sensitivities. The noise is less chromatic when you do this, and weaker
to boot, so the shadows are much quieter. A neutral density on the lens
will cut all three color channels equally, but ideally, for the D70, you
want to cut the green the most, and the red the least. If the lighting
is mixed with daylight or tungsten ambient, then a filter on the lens
may do the trick. I shoot in daylight with a Hoya FLD filter, which
doesn't get white balance perfectly native, but gets it closer. A
double-strength FLD would probably be perfect for the 20D, 10D, D70, or
any other DSLR with the same general color channel sensitivity. I
haven't experimented with the Tiffen magenta filters or the Cokins yet
(of course, the Cokins wouldn't work with your specialty lens).

If you want to see what's really going on, get a matte white target, and
take a picture at each ISO with it, at the magnifications in question,
in RAW, and then load the RAW files into IRIS which will show the exact
RAW values, and you can calculate how much headroom you have at a given
ISO. Do this both with and without a magenta filter over the flash.
--

<>>< ><<> ><<> <>>< ><<> <>>< <>>< ><<>
John P Sheehy <JPS@no.komm>
><<> <>>< <>>< ><<> <>>< ><<> ><<> <>><
Anonymous
August 13, 2005 1:06:59 AM

Archived from groups: rec.photo.digital.slr-systems (More info?)

In article <pn2qf1l5q4ihhes3ahtkdoelthe87n6c04@4ax.com>, <JPS@no.komm> wrote:
>In message <ddh87h$p02$1@Fuego.d-and-d.com>,
>dnichols@d-and-d.com (DoN. Nichols) wrote:

[ ... Medical Nikkor flash overexposure on Nikon D70 ... ]

>> O.K. Note that the chart which comes with the lens suggest that
>>for 2:1 reproduction ratio, a maximum ASA (now ISO) of 50 is suggested
>>for color, and 25 for B&W. (This is an old lens system, of course.)
>>The chart is incomplete, but it looks like it will require an ASA of 25
>>(or perhaps 32) with the full 3:1 ratio, so I may have to cut the
>>illumination anyway. I can't see pushing it that far down.
>
>I suggest that you try putting some magenta filters cut out from clear
>magenta sheets of file folders or something. I use "Flomo" folders; two
>sheets thick of their magenta folder over my Canon 550EX gives the flash
>almost the exact color that is native to the camera's channel
>sensitivities.

Now *this* makes sense. Filtering at the flash output, instead
of in the stack of close-up lenses at the input makes a *lot* more
sense here.

I'm not familiar with the "Flomo" folders. Would I find them at
my local "Staples" or some similar office supply store?

The next trick would be to find some form of neutral density
filter material in a similar cuttable form.

> The noise is less chromatic when you do this, and weaker
>to boot, so the shadows are much quieter. A neutral density on the lens
>will cut all three color channels equally, but ideally, for the D70, you
>want to cut the green the most, and the red the least. If the lighting
>is mixed with daylight or tungsten ambient, then a filter on the lens
>may do the trick.

As explained elsewhere, a filter on the lens seems to not be an
option, but the exposure problem only occurs in the extreme close-ups,
between 0.66:1 and 3:1 ratios, and there, even with the filtering, the
flash will predominate. The lens stops down to about f45, and that is
where we are with the extreme close-ups.

> I shoot in daylight with a Hoya FLD filter, which
>doesn't get white balance perfectly native, but gets it closer. A
>double-strength FLD would probably be perfect for the 20D, 10D, D70, or
>any other DSLR with the same general color channel sensitivity. I
>haven't experimented with the Tiffen magenta filters or the Cokins yet
>(of course, the Cokins wouldn't work with your specialty lens).

Hmm ... perhaps make a mount at the *rear* of the lens? If
there is enough room so the mirror won't hit it?

>If you want to see what's really going on, get a matte white target, and
>take a picture at each ISO with it, at the magnifications in question,
>in RAW, and then load the RAW files into IRIS which will show the exact
>RAW values, and you can calculate how much headroom you have at a given
>ISO. Do this both with and without a magenta filter over the flash.

O.K. IRIS is probably not an option, as I am using unix
machines, not Windows or Macs, but the capability exists in other
programs which I *do* have.

And this all started out in answering a question as to why you
would want to shoot at ISO 100 (if possible). :-)

Thanks much,
DoN.
--
Email: <dnichols@d-and-d.com> | Voice (all times): (703) 938-4564
(too) near Washington D.C. | http://www.d-and-d.com/dnichols/DoN.html
--- Black Holes are where God is dividing by zero ---
Anonymous
August 13, 2005 1:17:26 AM

Archived from groups: rec.photo.digital.slr-systems (More info?)

In message <hjo4r089j4s77uq50ujg4hohl0@inews_id.stereo.hq.phicoh.net>,
philip@pch.home.cs.vu.nl (Philip Homburg) wrote:

>In article <_%YKe.87228$G8.18745@text.news.blueyonder.co.uk>,
>David J Taylor <david-taylor@blueyonder.co.not-this-bit.nor-this-part.uk.invalid> wrote:
>>Philip Homburg wrote:
>>> Which means that quantisation noise corresponds to 0.5 * 40e3 / 2**12
>>> = 4.88
>>> electrons. At 25 electrons or more, shot-noise exceeds quantisation
>>> noise.
>>
>>Yes, in the lighter areas of the picture 12 bits is enough, agreed. But
>>where you see the quantisation noise is in the dark shadow regions.
>>Remember that the eye's response isn't linear, but more like log.
>
>Except that according to this calculation, quantisation noise exceeds
>photon shot noise only at output levels 0, 1, and 2. At level 3 you have
>3 * 40e3/4095 = 29.3 electrons, which gives a photon shot noise of 5.41
>electrons. Which is more than 0.5 LSB.

If you have noise that fills a bell curve 20 RAW levels wide, you can
still see images that add only 2 or 3 RAW levels of signal to the noise.
There is no concrete threshold; the image simply gets less and less
detailed and more noisy as the noise-to-signal ratio increases.
--

<>>< ><<> ><<> <>>< ><<> <>>< <>>< ><<>
John P Sheehy <JPS@no.komm>
><<> <>>< <>>< ><<> <>>< ><<> ><<> <>><
Anonymous
August 13, 2005 2:12:10 AM

Archived from groups: rec.photo.digital.slr-systems (More info?)

In message <ddj5el$ho8$1@Fuego.d-and-d.com>,
dnichols@d-and-d.com (DoN. Nichols) wrote:

> I'm not familiar with the "Flomo" folders. Would I find them at
>my local "Staples" or some similar office supply store?

They are common at "99 cent" stores here in the NYC area. Staples
stores only carries Staples folders, and I haven't seen anything
equivalent there.
--

<>>< ><<> ><<> <>>< ><<> <>>< <>>< ><<>
John P Sheehy <JPS@no.komm>
><<> <>>< <>>< ><<> <>>< ><<> ><<> <>><
Anonymous
August 13, 2005 3:01:25 AM

Archived from groups: rec.photo.digital.slr-systems (More info?)

In article <ddehsb$mma$1@Fuego.d-and-d.com>,
DoN. Nichols <dnichols@d-and-d.com> wrote:
> Not a consideration on the Cannon, but my Nikon D70 has a
>minimum ISO of 200, and this prevents me from shooting at the highest
>magnification range of the old 200mm Medical Nikkor (with the built-in
>ring flash). It does the exposure calculation based on an ISO (actually
>marked as ASA) setting ring, and a magnification ratio ring, resulting
>in setting of the aperture ring.

What may work is to set the shutter speed sufficiently high that only part
of the flash output is captured . This works on the D1 (though I didn't try
it with a medical Nikkor), and I think that it is also supposed to work with
a D70.


--
That was it. Done. The faulty Monk was turned out into the desert where it
could believe what it liked, including the idea that it had been hard done
by. It was allowed to keep its horse, since horses were so cheap to make.
-- Douglas Adams in Dirk Gently's Holistic Detective Agency
Anonymous
August 13, 2005 3:01:26 AM

Archived from groups: rec.photo.digital.slr-systems (More info?)

In article <ro0u11hketp1d8q69vme383vu1@inews_id.stereo.hq.phicoh.net>,
Philip Homburg <philip@pch.home.cs.vu.nl> wrote:
>In article <ddehsb$mma$1@Fuego.d-and-d.com>,
>DoN. Nichols <dnichols@d-and-d.com> wrote:
>> Not a consideration on the Cannon, but my Nikon D70 has a
>>minimum ISO of 200, and this prevents me from shooting at the highest
>>magnification range of the old 200mm Medical Nikkor (with the built-in
>>ring flash). It does the exposure calculation based on an ISO (actually
>>marked as ASA) setting ring, and a magnification ratio ring, resulting
>>in setting of the aperture ring.
>
>What may work is to set the shutter speed sufficiently high that only part
>of the flash output is captured . This works on the D1 (though I didn't try
>it with a medical Nikkor), and I think that it is also supposed to work with
>a D70.

I'll try that. That sounds like a good option, as does the
suggestion of cutting out filters to fit over the ring flash instead of
over the lens itself.

Thanks,
DoN.


--
Email: <dnichols@d-and-d.com> | Voice (all times): (703) 938-4564
(too) near Washington D.C. | http://www.d-and-d.com/dnichols/DoN.html
--- Black Holes are where God is dividing by zero ---
Anonymous
August 13, 2005 3:01:26 AM

Archived from groups: rec.photo.digital.slr-systems (More info?)

In article <ro0u11hketp1d8q69vme383vu1@inews_id.stereo.hq.phicoh.net>,
Philip Homburg <philip@pch.home.cs.vu.nl> wrote:
>In article <ddehsb$mma$1@Fuego.d-and-d.com>,
>DoN. Nichols <dnichols@d-and-d.com> wrote:
>> Not a consideration on the Cannon, but my Nikon D70 has a
>>minimum ISO of 200, and this prevents me from shooting at the highest
>>magnification range of the old 200mm Medical Nikkor (with the built-in
>>ring flash). It does the exposure calculation based on an ISO (actually
>>marked as ASA) setting ring, and a magnification ratio ring, resulting
>>in setting of the aperture ring.
>
>What may work is to set the shutter speed sufficiently high that only part
>of the flash output is captured . This works on the D1 (though I didn't try
>it with a medical Nikkor), and I think that it is also supposed to work with
>a D70.
>
>


According to what I'm reading my new 420EX flash on my 300D can sync
at "any" speed if a switch on the flash is set to "FP". It does
this by doing a 50KHz (I think) strobe effect and the power is
reduced as a byproduct.

It's recommended for fill flash in bright sun. I haven't played with
it.


--
a d y k e s @ p a n i x . c o m

Don't blame me. I voted for Gore.
Anonymous
August 13, 2005 3:01:27 AM

Archived from groups: rec.photo.digital.slr-systems (More info?)

In article <ddjlom$rs6$1@panix5.panix.com>, Al Dykes <adykes@panix.com> wrote:
>In article <ro0u11hketp1d8q69vme383vu1@inews_id.stereo.hq.phicoh.net>,
>Philip Homburg <philip@pch.home.cs.vu.nl> wrote:
>>In article <ddehsb$mma$1@Fuego.d-and-d.com>,
>>DoN. Nichols <dnichols@d-and-d.com> wrote:
>>> Not a consideration on the Cannon, but my Nikon D70 has a
>>>minimum ISO of 200, and this prevents me from shooting at the highest
>>>magnification range of the old 200mm Medical Nikkor (with the built-in
>>>ring flash). It does the exposure calculation based on an ISO (actually
>>>marked as ASA) setting ring, and a magnification ratio ring, resulting
>>>in setting of the aperture ring.
>>
>>What may work is to set the shutter speed sufficiently high that only part
>>of the flash output is captured . This works on the D1 (though I didn't try
>>it with a medical Nikkor), and I think that it is also supposed to work with
>>a D70.
>>
>>
>
>
>According to what I'm reading my new 420EX flash on my 300D can sync
>at "any" speed if a switch on the flash is set to "FP". It does
>this by doing a 50KHz (I think) strobe effect and the power is
>reduced as a byproduct.
>
>It's recommended for fill flash in bright sun. I haven't played with
>it.

Intersting -- though how it can be applied to the situation
above, a Nikon D70 camera body, and a truly antique Medical Nikkor with
a built-in ring flash (old enough so the only semiconductor in it is
the rectifier in the HV power supply.)

If this were a modern enough flash so it could be set to reduced
output, the whole problem would go away. :-)

Enjoy,
DoN.

--
Email: <dnichols@d-and-d.com> | Voice (all times): (703) 938-4564
(too) near Washington D.C. | http://www.d-and-d.com/dnichols/DoN.html
--- Black Holes are where God is dividing by zero ---
Anonymous
August 13, 2005 5:13:53 PM

Archived from groups: rec.photo.digital.slr-systems (More info?)

In message <ddjlom$rs6$1@panix5.panix.com>,
adykes@panix.com (Al Dykes) wrote:

>According to what I'm reading my new 420EX flash on my 300D can sync
>at "any" speed if a switch on the flash is set to "FP". It does
>this by doing a 50KHz (I think) strobe effect and the power is
>reduced as a byproduct.

>It's recommended for fill flash in bright sun. I haven't played with
>it.

It's not really like flash at all; it's like an ambient light that is
strobing invisibly, unless something moves quickly, in which case you
will get non-contiguous sub-exposures.

I think of it as extra light, not "flash" per se. On your 300D, the
flash will be up to 4x as strong, and/or up to 1/40 the duration at
1/200 than at 1/250. In other words, at 1/200, you could use a 600mm
lens, hand-held, and the flash part of the exposure will be sharp, and
punctuate the image, even if the ambient is slightly blurry. At 1/250,
when fp kicks in, you will have a blurry image. I used to leave my
550EX set to fp mode, with the safety of knowing that it disabled if the
10D is set to 1/200 or slower, or 1/250 on the 20D, but what wound up
happening is that I'd use faster shutter speeds and get blurrier images,
so I now only enable it on a per-need basis.
--

<>>< ><<> ><<> <>>< ><<> <>>< <>>< ><<>
John P Sheehy <JPS@no.komm>
><<> <>>< <>>< ><<> <>>< ><<> ><<> <>><
Anonymous
August 19, 2005 11:17:29 AM

Archived from groups: rec.photo.digital.slr-systems (More info?)

On 10 Aug 2005 23:49:31 -0400, dnichols@d-and-d.com (DoN. Nichols)
wrote:

>
> The lens is capable of going down to a 3X magnification ratio,
>but the closest that I can get at present is a 2/3X magnification ratio
>because of the exposure situation.
>
Why not try to diffuse and/or partially block the flash to control the
light. I have no idea what your lens flash looks like but I have an
old Viviitar ring light and I can tape a thin paper ring on it to cut
the output in half.

Dave
East Englewood
---------------------
The proof is in the print.
Anonymous
August 19, 2005 9:41:45 PM

Archived from groups: rec.photo.digital.slr-systems (More info?)

In article <3qebg1ds1u7gfdkebekqjdt0ketsps8dj0@4ax.com>,
<dave6134@verizon.net> wrote:
>On 10 Aug 2005 23:49:31 -0400, dnichols@d-and-d.com (DoN. Nichols)
>wrote:
>
>>
>> The lens is capable of going down to a 3X magnification ratio,
>>but the closest that I can get at present is a 2/3X magnification ratio
>>because of the exposure situation.
>>
>Why not try to diffuse and/or partially block the flash to control the
>light. I have no idea what your lens flash looks like but I have an
>old Viviitar ring light and I can tape a thin paper ring on it to cut
>the output in half.

The ring flash is built into the lens body. If you want some
excellent photos and drawings, take a look at the following recently
closed eBay auction:

Auction Number: 7536353068

Full URL: http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=7536...

I have already received such a suggestion, and essentially a
ring cut from a neutral density filter gel would work nicely for the
purpose.

I also, while examining an older separate ring flash which I had
stored away discovered that it had a rheostat between the lamp and the
capacitor, which adjusts the output through perhaps a 4:1 ratio (I'm not
sure, as I don't have a flash meter.) At the very bottom of the range,
the flash will not trigger -- but a 4:1 ratio should be sufficient for
my purposes. And that could be put in a cord between the power supply
and the flash head.

Enjoy,
DoN.
--
Email: <dnichols@d-and-d.com> | Voice (all times): (703) 938-4564
(too) near Washington D.C. | http://www.d-and-d.com/dnichols/DoN.html
--- Black Holes are where God is dividing by zero ---
!