Improved Wide Angles for 35mm

[savagegibson]

Would it be possible to build a series of wide angle lenses for 35mm cameras, specifically the Canons, that are non-retrofocus lenses? Now that the 1D MIII has live view, could you build a lens where you locked the shutter up, mounted the lens and then worked of the LCD on the back?

It is my understanding that it is much easier to build sharp non-retrofocus lenses than it is to build them in a retrofocus design. Could we get better wide angles this way?

Patent Pending

[dobson]

It's my understanding that such lenses used to exist for SLRs. Contax, maybe? You have to make sure not to use them with most cameras because they would hit the mirror.

Phillip

[macgyver]

Would it be possible to build a series of wide angle lenses for 35mm cameras, specifically the Canons, that are non-retrofocus lenses? Now that the 1D MIII has live view, could you build a lens where you locked the shutter up, mounted the lens and then worked of the LCD on the back?

It is my understanding that it is much easier to build sharp non-retrofocus lenses than it is to build them in a retrofocus design. Could we get better wide angles this way?

Patent Pending
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Who want's to be teathered to live view though?  That knocks out many uses for such lenses.

[jjlphoto]

Retro-focus also works better for digital sensors. Tests I have seen with symmetrically designed rangefinder ultra-wides (like the Voightlanders) custom mounted into a Canon full frame digital body with the mirror up show huge amounts of light fall-off towards the edges. The rear element is too close to the sensor for the edge pixels to see them as good as th center pixels.

The Leica digital M rangefinder is a crop sensor, and even those edge pixels show edge fall off with wides. Leica provides an "in-camera" digital compensation by darkening the center area, while lightening the outer areas.

Zeiss is the master of the retro-focus wide angle lens. There are many Contax Distagons and Vario-Sonnars in CY and N mounts that can be adapted to use on a Canon DSLR.

[savagegibson]

Retro-focus also works better for digital sensors. Tests I have seen with symmetrically designed rangefinder ultra-wides (like the Voightlanders) custom mounted into a Canon full frame digital body with the mirror up show huge amounts of light fall-off towards the edges. The rear element is too close to the sensor for the edge pixels to see them as good as th center pixels.
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That is true in the sense that there is a light fall off problem, but that could be compensated through with software. I was thinking more in terms of corner sharpness and less CA with a non-retro focus lens.

[gehle]

Would it be possible to build a series of wide angle lenses for 35mm cameras, specifically the Canons, that are non-retrofocus lenses?

Sure, if you remove the mirror

If you are familar a wide angle lens on a 4x5, say a 75mm lens, the rear element is very close to the film plane at infinity. Retro focus lenses are a general rule for an SLR design because there is a fixed distance needed to allow for the mirror. A non retro focus lens would have to be much closer to the film plane (or is it imaging plane??) than the mirror allows.

So the answer is no to a non-retro focus wide angle for a camera such as the Canon.

Ken Gehle

[savagegibson]

Sure, if you remove the mirror

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That is what I'm saying. If you lock the mirror up, mount the lens, and then use the LCD live preview on the back for compostion and focusing. Then you could get that back element all the way back there without the mirror being in the way.

[Tim May]

Great advice.  Thanks!

[gehle]

That is what I'm saying. If you lock the mirror up, mount the lens, and then use the LCD live preview on the back for compostion and focusing. Then you could get that back element all the way back there without the mirror being in the way.
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Well there is one more problem because the mirror is actually minor. Read on:

A non-retro focus lens uses a much shorter flange distance, which your good old Canon doesn't have due to the mirror box depth (because of the mirror   ).So even though you could lockup the mirror and use a live preview, a non retro focus lens isn't going to work - the lens flange to image surface distance is way too far. A non retro focus lens needs to be much closer to the imager than the flange distance in modern 35 slrs will allow.

OK?

I now have a headache from past RIT M&P classes

Ken Gehle

[gehle]

Now that is cheating. That ain't a wide angle. Hell for that lens to work it HAS to be that way!

[jjlphoto]

That is true in the sense that there is a light fall off problem, but that could be compensated through with software. I was thinking more in terms of corner sharpness and less CA with a non-retro focus lens.
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That is what Leica does for its Digital M (rangefinder) with symmetrical wide angle lenses. The Hasselblad H3 and the new 28 (which is retrofocus) also uses its software to even out the illumination)

the lens flange to image surface distance is way too far. A non retro focus lens needs to be much closer to the imager than the flange distance in modern 35 slrs will allow.
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Not necessarily- you can use Voightlanders with MLU on a 5D. The flange mount is really arbitrary. The lens can sit as deep as it needs to be, heck, it could sit all the way behind the body's bayonet if it is an AF lens. (Because it would then be quite difficult to operate the lens barrel focusing ring if it were manual focus.) Just imagine a deep and steeply beveled mounting flange that allows the lens to sit deep. (could be trickey mounting and unmounting it if you have fat fingers.)

[gehle]

Not necessarily- you can use Voightlanders with MLU on a 5D. The flange mount is really arbitrary. The lens can sit as deep as it needs to be, heck, it could sit all the way behind the body's bayonet if it is an AF lens. (Because it would then be quite difficult to operate the lens barrel focusing ring if it were manual focus.) Just imagine a deep and steeply beveled mounting flange that allows the lens to sit deep. (could be trickey mounting and unmounting it if you have fat fingers.)
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Well that is still getting "super special" in my book. A day in/day out non-retro wide angle that can be used on any slr type camera, whether 35 or MF, is going to have to have the mirror flipped out of the way. I would love a non-retro wide angle lens on my 1Ds and be able to use the viewfinder but it just not going to happen.

Ken Gehle

[jjlphoto]

Well that is still getting "super special" in my book. A day in/day out non-retro wide angle that can be used on any slr type camera, whether 35 or MF, is going to have to have the mirror flipped out of the way. I would love a non-retro wide angle lens on my 1Ds and be able to use the viewfinder but it just not going to happen.

Ken Gehle
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One of the things that made the Zeiss Biogon 38mm on the Hasselblad SWC so spectacular was its symmetrical design. (The lead in the glass may have had something to do with it as well   )

The Leica Digital M sells out as fast as produced, but that system has been frought with difficulties, the rear element being so close to the sensor has created issues. Also, the sensor was designed with minimal IR filtering, no AA filter as far as I can tell, both so the sensor could take advantage off all that the Leica glass could deliver. But again, there have been problems.