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Pardon my ignorance ...
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PostPosted: Sun Jul 17, 2011 3:29 pm    Post subject: Pardon my ignorance ... Reply with quote
Can anyone tell me why an ultra wide angle lens for a rangefinder cam such as leica has zero or almost zero distortion (even perspective!) than ultra wide angle lens for a SLR camera?

Please pardon my ignorance..


PostPosted: Sun Jul 17, 2011 3:54 pm    Post subject: Re: Pardon my ignorance ... Reply with quote
Ash wrote:
Can anyone tell me why an ultra wide angle lens for a rangefinder cam such as leica has zero or almost zero distortion (even perspective!) than ultra wide angle lens for a SLR camera?

Please pardon my ignorance..


Whats the Lens in question?


PostPosted: Sun Jul 17, 2011 3:59 pm    Post subject: Reply with quote
This has something to do with lens design. For rangefinders, wide lenses can be designed using a symmetrical formula, distortion is much easily controlled, but the rear lens elements are much closer to the focus plane. Lenses of this designed thus cannot provide sufficient reflex mirror movement on a SLR. An alternative design of rectrofocus can provide much needed clearance for mirror movement on a SLR, however the distortion correction is much more difficult and lens element combinations are much more complicated, Hope this would provide some ideas on the difference between the two...


PostPosted: Sun Jul 17, 2011 4:33 pm    Post subject: Reply with quote
I you looking for a 'zero' distortion lens for SLR, take Flektogon 20mm f4.


PostPosted: Sun Jul 17, 2011 5:23 pm    Post subject: Reply with quote
Attila wrote:
I you looking for a 'zero' distortion lens for SLR, take Flektogon 20mm f4.

I'd love to take one! If you have an extra Flek20, my birthday is coming soon, hint hint. Wink

But with wide-ish lenses on an APS-C camera, I see *some* distortion with any focal length shorter than 28mm, the 'normal' focal length. I look through the viewfinder, pan the camera, and watch the image edges stretch more-or-less. I see the same with lenses shorter than 35mm on a FF camera. Does the Flek20 transcend this?


PostPosted: Mon Jul 18, 2011 6:38 am    Post subject: Reply with quote
RioRico wrote:
But with wide-ish lenses on an APS-C camera, I see *some* distortion with any focal length shorter than 28mm, the 'normal' focal length. I look through the viewfinder, pan the camera, and watch the image edges stretch more-or-less. I see the same with lenses shorter than 35mm on a FF camera. Does the Flek20 transcend this?


It sounds like you're talking about volume anamorphosis. See: http://www.dxo.com/us/photo/dxo_optics_pro/optics_geometry_corrections/anamorphosis


PostPosted: Mon Jul 18, 2011 4:04 pm    Post subject: Reply with quote
Hello Ash!

"Perspective distortion" will always be the same for a given format and focal length irrespective of whether a lens is on a SLR or rangefinder body . It has to with the angle of view and not the individual lens design.

The distortion of straight lines - I guess you mean their bending - is indeed linked to the optical design, but it doesn't necessarily follow that a rangefinder type will have less than than one for a SLR. I'm no expert on optical design, but from what's easily available to read, trading-off some distortion against other aberrations can let a designer get certain benefits in (for instance) how well the lens stays sharp getting away from the centre of the field. Reducing ALL the aberrations will bump up the complexity and cost so designers are often hemmed-in by the target-budget for their design.

As most rangefinder lenses are often pretty (even very!!!) high priced, maybe that goes part way to explaining some differences in the distortion department.


PostPosted: Mon Jul 18, 2011 5:14 pm    Post subject: Reply with quote
AhamB wrote:
RioRico wrote:
But with wide-ish lenses on an APS-C camera, I see *some* distortion with any focal length shorter than 28mm, the 'normal' focal length. I look through the viewfinder, pan the camera, and watch the image edges stretch more-or-less. I see the same with lenses shorter than 35mm on a FF camera. Does the Flek20 transcend this?

It sounds like you're talking about volume anamorphosis. See: http://www.dxo.com/us/photo/dxo_optics_pro/optics_geometry_corrections/anamorphosis

Yes, that looks like what I see. And damn, now I'll have to buy dxo warez for correction! But I wonder if this is strictly a property of the lens, or a function of the lens projection onto a specific frame size. Just as the image from a Zenitar 16/2.8 is very fishy on FF and only slightly fishy on HF/APSC. If I crop the Zen16 image down to 110/m43 frame size, it's even less fishy. And as I mentioned above, I see edge-stretching / volume anamorphosis with lenses <35mm on FF. So does the Flek20 have some magickal cure?


PostPosted: Mon Jul 18, 2011 5:36 pm    Post subject: Reply with quote
Apparently there are plugins too, for example here.....
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