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05-12-2010, 09:43 AM   #16
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QuoteOriginally posted by Canada_Rockies Quote
Not when the lens is in the mount. I know this theory about the "normal" lens being the diagonal of the format, but my personal take is that the lens + finder optics should make the image appear the same size as the other eye sees. With my early, early, early Asahi Pentax the 55mm did just that. There is a third theory that the lens should approximate the field of view - but that appears to be my 12mm lens, and seems a tad wide.
Actually, with a lens of focal length same as the diagonal of the format, the perspective size of objects near and far is the same as the perspective sizes seen by the eye; through a longer focal length lens, farther objects appear larger in relation to size of closer object, through shorter focal length, farther objects appear smaller in relation to size of closer object. Of course, that is true only with the same [edit]framing[/edit].

As for field of view, a 16mm lens on 35mm/FF camera gives the same wide angle view as the eye, and a 135mm lens on 35mm/FF camera gives the same narrower angle view as the fovea, the part of the eye with best focus.


Last edited by rhodopsin; 05-13-2010 at 08:30 AM.
05-12-2010, 10:49 AM   #17
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QuoteOriginally posted by rhodopsin Quote
through shorter focal length, farther objects appear smaller in relation to size of closer object. Of course, that is true only from the same taking position.
You may want to think it over. And edit your post.
05-12-2010, 03:17 PM   #18
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QuoteOriginally posted by Canada_Rockies Quote
Not when the lens is in the mount.
Sorry, you right as you were talking about a "thin lens" (element) at the mount position. I just read "lens" and assumed you meant a camera lens that can be focused.

QuoteOriginally posted by Canada_Rockies Quote
I know this theory about the "normal" lens being the diagonal of the format, but my personal take is that the lens + finder optics should make the image appear the same size as the other eye sees.
I see the merit in your personal take but note that than the definition of a "normal" lens depends on the viewfinder magnification. The later varies a lot between cameras. What really counts is the perspective captured in the final image, not the temporary view through the viewfinder. If one can make the latter coincide with what your other eye sees while taking the shot, all the better, but this is a question of getting the viewfinder magnification right, not of adapting a focal length to an arbitrary viewfinder magnification.

QuoteOriginally posted by Canada_Rockies Quote
There is a third theory that the lens should approximate the field of view...
The AOV of the human eye is very difficult to define (irregular shape, both eyes or just one?, area of sharp vision or peripheral vision included?, individual differences in broadness of vision) that's why I think that trying to define a "normal" lens in terms of the eye's AOV is futile.

QuoteOriginally posted by rhodopsin Quote
Of course, that is true only from the same taking position.
When you don't change the position, the perspective distortion doesn't change. Different focal lengths don't influence perspective. Only the change in position that makes them capture the same image does.
05-12-2010, 04:37 PM   #19
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"btw, 74.1 - 45.46 = 28.64"

Yeah thanks you're right, I must have hit the wrong button in calculator.

Can I also assume that the 45.46mm registry is the same for Pentax digital and film cameras ?

I had thought about the shifted image and also thought that cropping might be good enough. I guess that will depend on how far I shift it and it might end up a pretty small image.
So is the Pentax 6x7 image, 6cm x 7cm ? That’s huge, and would give ample scope over an *ist-DL sensor. Could it be way larger than I need ?

Chromo


Last edited by chromo; 05-12-2010 at 05:46 PM.
05-12-2010, 04:51 PM   #20
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QuoteOriginally posted by chromo Quote
Can I also assume that the 45.46mm registry is the same for Pentax digital and film cameras ?
It depends on which side of the film you're referring to. 0.01mm difference to consider!
05-12-2010, 04:55 PM   #21
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QuoteOriginally posted by falconeye Quote
It depends on which side of the film you're referring to. 0.01mm difference to consider!
Yeah I know, but to the top or the underside of the emulsion?
05-13-2010, 08:26 AM   #22
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QuoteOriginally posted by falconeye Quote
You may want to think it over. And edit your post.
OMG! Thanks Falk. (I can't believe I wrote that!)
05-13-2010, 03:31 PM   #23
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Someone once suggested using a projector lens.
I haven't a clue about them. I don't know what brand, what size or type etc.

Can anyone elaborate with this ?

Any ideas on this post will be helpful as I don't have much money but I do have a pretty good machinery workshop.

Chromo

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