Pentax ist ds infinity focus problem

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

Thanks for the info---this is my first SLR digital---guess I have alot
to learn.

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

<grevillea@ozemail.com.au> wrote in message
news:1116232293.445981.30530@f14g2000cwb.googlegroups.com...
> Pentax ist ds---camera repaired for autofocus problem---reverted to
> closest focus most of the time.
>
> Now infinity seems to be out---infinity is slightly off the far right
> turn stop---tested using the landscape mode and autofocus and confirmed
> with manual focus. expected infinity to be as far to the right as I
> could go.
>
> Is this a problem? does it need to go back for more repairs (the last
> set took 4 weeks!!!)?
It is normal for lenses to focus slightly beyond infinity (if that makes
sense). If the lens was designed so that infinity fcous was at it's extreme
position of operation, you would find situations where you wouldn't be able
to achieve infinity focus. For example temperature changes or even a bit of
crud on the lens mount would be sufficient to stop the lens focussing to
infinity. Therefore they design the lens to focus a little beyond infinity
so that there is enough provision left in it to allow for temp changes etc.
>
> anyone else have this problem?
it ain't a problem - every single SLR lens is designed like this, if it
wasn't then you would have problems.
>

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

grevillea@ozemail.com.au wrote:

> Pentax ist ds---camera repaired for autofocus problem---reverted to
> closest focus most of the time.
>
> Now infinity seems to be out---infinity is slightly off the far right
> turn stop---tested using the landscape mode and autofocus and confirmed
> with manual focus. expected infinity to be as far to the right as I
> could go.
>
> Is this a problem? does it need to go back for more repairs (the last
> set took 4 weeks!!!)?
>
> anyone else have this problem?


I heard people talk about carefully manually focusing on the moon. WTF?
I don't get that? Shouldn't infinity be good enough???? I think they
were dead serious though. I have no clue.


--
Paul Furman
http://www.edgehill.net/1
san francisco native plants

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

"Justin Thyme" <pleasedontspamme@nowhere.com> wrote in message
news:12_he.302$q33.4289@nnrp1.ozemail.com.au...
>
> <grevillea@ozemail.com.au> wrote in message
> news:1116232293.445981.30530@f14g2000cwb.googlegroups.com...
>> Pentax ist ds---camera repaired for autofocus problem---reverted to
>> closest focus most of the time.
>>
>> Now infinity seems to be out---infinity is slightly off the far right
>> turn stop---tested using the landscape mode and autofocus and confirmed
>> with manual focus. expected infinity to be as far to the right as I
>> could go.
>>
>> Is this a problem? does it need to go back for more repairs (the last
>> set took 4 weeks!!!)?
> It is normal for lenses to focus slightly beyond infinity (if that makes
> sense). If the lens was designed so that infinity fcous was at it's
> extreme position of operation, you would find situations where you
> wouldn't be able to achieve infinity focus. For example temperature
> changes or even a bit of crud on the lens mount would be sufficient to
> stop the lens focussing to infinity. Therefore they design the lens to
> focus a little beyond infinity so that there is enough provision left in
> it to allow for temp changes etc.
>>
>> anyone else have this problem?
> it ain't a problem - every single SLR lens is designed like this, if it
> wasn't then you would have problems.
>>
>
>

I've always heard this and it does make sense, but all my older Pentax and
Nikkors would stop right at infinity. These lenses seemed to be much finer
quality (and very sharp) optical instruments with tight tolerances. Now
everything has lots of plastics in the design and some of the lenses feel
somewhat loose. I'd say the extra focus adjustment past infinity is
allowance for slop in the design and possible the extra coefficient of
thermal expansion of plastics as compared to metals.

John

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

grevillea@ozemail.com.au wrote:
>
> Pentax ist ds---camera repaired for autofocus problem---reverted to
> closest focus most of the time.
>
> Now infinity seems to be out---infinity is slightly off the far right
> turn stop---tested using the landscape mode and autofocus and confirmed
> with manual focus. expected infinity to be as far to the right as I
> could go.
>
> Is this a problem? does it need to go back for more repairs (the last
> set took 4 weeks!!!)?
>
> anyone else have this problem?

Autofocus needs the 'beyond infinity' space to operate properly.

Colin