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09-05-2009, 03:02 PM   #1
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35mm FOV rear converter impossible?

I don't really need a full frame camera (except for the big viewfinder, shallower DOF and the prestige) - but what I really miss (not technically as I've never used film cameras) is using my lenses like intended - meaning using a 28mm lens for wide angles, 50mm as a normal lens and so on.
Finding a fast normal lens for APS-C sensor cameras isn't cheap - for FF it is.
So I was asking myself why it isn't possible to built a wideangle (rear!) converter which gives you the "original" field of view.
It would work just like a teleconverter only that it doesn't in- but decrease focal length (FL/1.54).
With my limited thinking capabilites I came to the conclusion that resolution would even be increased because you concentrate the lens' image circle onto a smaller area.
So what is the problem here?
I'd pay good money for such a thing since I don't really care for the long but the wide end so my choices are pretty limited now.


09-05-2009, 03:23 PM   #2
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Most basic way is something like another macro lens and another direct projection "viewfinder"/ground glass youre photographing:
YouTube - cheapest 35 mm DOF adapter
Almost like shooting trough a film camera viewfinder. Advanced ones shake the ground glass to increase "resolution" (or average out the glass grain actually). Still i think the quality achieved this way is usable only for motion, not still images.

Last edited by ytterbium; 09-05-2009 at 03:31 PM.
09-05-2009, 05:36 PM   #3
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Either 35mm is completely the wrong term for it or you are missunderstanding but what I actually meant was an adapter that gives you the same field of view for a lens on an APS-C camera like on a full frame "35mm" camera
09-05-2009, 07:30 PM   #4
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I agree and have felt this way for a while. Indeed, the thought of a APS-C equivalent* to a 28mm f2 (or even a 35mm f2 equivalent that isn't the size of a car) is rather wishful. These use to be common.

With regard to the specific tool you're looking for, I've read (here, I believe, but elsewhere as well) that it as called a focal reducer and has been commonly paired with telescopes for some time. They even have the added benefit of increasing a lens's f-number. Why they are not used photographically, I do not know (I.Q.? Flange distances?).

(*I mean field of view equivalent--if someone comes in here crying about depth of field equivalents, I'm going home)

09-06-2009, 02:58 AM   #5
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QuoteOriginally posted by Egg Salad Quote
I don't really need a full frame camera (except for the big viewfinder, shallower DOF and the prestige) - but what I really miss (not technically as I've never used film cameras) is using my lenses like intended - meaning using a 28mm lens for wide angles, 50mm as a normal lens and so on.
I so know what you are talking about. I hope this gets solved in a common way, through a release of K-mount FF camera.

And I used and keep using a film camera so I`m desperately spoiled here.
09-06-2009, 06:20 AM   #6
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A FF camera isn't very likely to be released anytime soon - so I'm not waiting for one.
Also, a FFcamera will probably be more expensive than some "simple" converter.
I really like my old primes but a 43mm f/4.5 lens (when comparing the 3.5/28 to a FF equivalent) isn't very useful. Almost any 50mm lens on a converter would be.
09-06-2009, 08:29 AM   #7
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The obvious answer is to realize that an APC-C format DSLR camera is a different format from a 35mm camera and get on with life. That they happen to share a lens mount is a happy coincidence, since it means one does have usable lenses if they owned a 35mm camera system.
To say that a 50mm lens has to be a "standard" lens completely ignores the fact that it is a different format.
If you put a 50mm lens onto a Pentax 6x7 you have a wide angle lens. Would you say that you need an adapter of some sort to arbitrarily make it behave like the normal lens for that format?

The issue most people seem to have isn't with the new field of view that their lenses give them, it seems more so that they are always trying to do mental gymnastics to figure out what lens in one format equals a focal length in a different format.
People who shot multiple film formats don't have as much trouble with this. They seem better able to make the transition from film to digital, simply because they learned not to play numbers games, but rather to learn what their glass would do for them on the format they were shooting.
09-06-2009, 11:17 AM   #8
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No, that's not the point.
I haven't even worked with film at all so I'm not comparing.
I don't try to mentally transfer my lenses into FF equivalents - since APS-C is the only format I'm familiar with.

What I mean is that 35mm lenses were designed for FF so their apertures don't make sense on a crop-cam.
Originally my 3.5/28 was a wideangle lens - so speed isn't that important as you most likely will use it above f/5.6 anyways.
On APS-C however it is an awfully slow wideangle lens which is pretty limited in its usage.
Having a fast telephoto lens (1.7/50) is nice but absolutely worthless to me since I prefer normal to wide lenses.

If I had any medium format lenses I would ask for a medium format converter (probably not because medium format uses pretty slow lenses) to use them on my camera like the were designed to be used.

I don't have a problem with going on but I have a problem with paying big money only to get a fast normal (for crop) lens - so why not use what we already have?



09-08-2009, 10:28 AM   #9
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So is there a logical reason why there isn't such a thing or is it just something nobody wants so nobody makes it?
09-08-2009, 12:34 PM   #10
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My guess would be, if it were possible, and reasonably cheap to do it and not degrade quality too much, it would have been done by now. There are any numbr of *front* "wide converters out there, and these tend to be either terrible in quality, or else at best mediocre in quality and still more expensive than just buying a wide angle lens. If it could be done better or cheaper using a rear converter, again, I have to believe somepne would have already done so.
09-08-2009, 02:26 PM   #11
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Hmmm, good point.

But I don't agree on buying a wide angle lens is cheaper than buying one of these front wideangle converters: the cheapest really wide lens for APS-C right now is the Zenitar 16 (I think) which costs ~ $170+ (or ?), these converters sell for roughly the same (I mean the higher grade Raynox adapters).

Now it takes its toll I'm not an optics engineer (if that's a word)...
So still no solution in sight.
09-08-2009, 06:28 PM   #12
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QuoteOriginally posted by Egg Salad Quote
[FONT="Tahoma"][SIZE="2"]
But I don't agree on buying a wide angle lens is cheaper than buying one of these front wideangle converters: the cheapest really wide lens for APS-C right now is the Zenitar 16 (I think) which costs ~ $170+ (or ?), these converters sell for roughly the same (I mean the higher grade Raynox adapters).
I'm not familiar with the Raynox adapters specifically, nor was I thinking only of ultrawides like the Zenitar for comparison. Some of the wide converters are more like several hundred dollars. There are *lots* of normal and wide lenses available for that kind of budget, including 20, 24, 28, 30, and 35mm lenses.
09-09-2009, 09:50 AM   #13
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Ok, if you mean wide for film cameras you are right but I was thinking of wide for APS-C - don't know why as my starting point actually was a fast normal lens...

And if you had several hundert dollars in mind, yes there are lenses that are cheaper. However your options for a fast (f/2 or faster) are rather limited (like I wrote in my other thread).
Unfortunately if you want to go fast it gets exponentially more expensive but that is true for every lenght.
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