D70 viewfinder real life image size

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

Hi folks,

I am getting into digital photography and recently bought a D70 DSLR
with the kit lens (18-70mm f/3.5-4.5 G-AFS ED-IF DX Autofocus Lens).

The question I have is related to the size of the image as I see it
through the viewfinder.
Now, my understanding is that this lens will produce images that are
similar (size wise at least) to those coming out of a 27-105mm SLR (due
to the 1.5x crop factor).

When I look through the viewfinder the image that is the closest to
what I see in reality "happens" somewhere between 60-65mm.

Here's where I get confused, please bare with me.

I remember reading it somewhere that the "unit" lens for 35mm would be
42mm (the diagonal measurement of a 35mm frame) so the numbers don't
quite add up.

The diagonal measurement of the CCD sensor would be ~28mm. Multiplying
it with 1.5 you get (after less than 7.5 mil years of calculation -
42. Doing it again you'll get 63mm indeed but this is cargo cult math
and I would like to understand more exactly how this things work.

Thanks in advance!
Sebastian

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

<sebif@yahoo.com> wrote in message
news:1121711139.746121.138240@o13g2000cwo.googlegroups.com...
> Hi folks,
>
> I am getting into digital photography and recently bought a D70 DSLR
> with the kit lens (18-70mm f/3.5-4.5 G-AFS ED-IF DX Autofocus Lens).
>
> The question I have is related to the size of the image as I see it
> through the viewfinder.
The viewfinder shows 92% of the image.
> Now, my understanding is that this lens will produce images that are
> similar (size wise at least) to those coming out of a 27-105mm SLR (due
> to the 1.5x crop factor).
>
> When I look through the viewfinder the image that is the closest to
> what I see in reality "happens" somewhere between 60-65mm.
At what focal length of the zoom lens?
>
> Here's where I get confused, please bare with me.
Your confusion started far sooner....
>
> I remember reading it somewhere that the "unit" lens for 35mm would be
> 42mm (the diagonal measurement of a 35mm frame) so the numbers don't
> quite add up.
Your number don't because yours are incorrect. The film diagonal of a 35mm
frame (size = 24x36) is 43.266. The diagonal of the D70 sensor (size =
15.6x23.7) is 28.429. If you divide 43.266 by 28.429 you will find the
answer to be 1.52. The posted factor of 1.5 is close enough.
Jim

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

Thanks for your responses guys,

I guess my question should have been:

How do you calculate the focal length for which you get objects to
*appear* life-size in the viewfinder? Is this important in any way?

Looking through the viewfinder the objects appear to be life-size at
aprox. 70mm.
This happens for both DSLR (D70 - 18-70 lens) and 35mm SLR (Elan7 28-90
lens - which has a bigger viewfinder).

I thought the focal length for real life-size would be 50mm (well..
43mm) for 35mm camera and somewhat proportional(1.5x) for the DSLR,
hence my confusion when I actually got 70mm for each one of them.

I hope my question is somewhat clearer this time. It could be that I am
looking at the problem from a weird perspective as I am learning these
things. If so please let me know.

Again, thanks for your time,
Sebastian