Speaking about design, what does close to zero distortion imply?

Juan Valdenebro

Juan Valdenebro

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I'm just curious: I'd love a 35mm lens without distortion, yet very very small, for f8 shooting only, because when light is lower, it's another lens the one I put on my camera, so I don't really need a 35mm lens faster than f8... I know that lens doesn't exist, but I wonder what sacrifice, if we talk about lens design, would be necessary to make a 35mm lens get rid of its distortion... For example, what would we lose in other optical aspects if we wanted to make the CV 35 2.5 and the CV 35 1.4 have zero distortion keeping their size? Or would it be just impossible to keep their size?
I see some of the smallest 35mm lenses have low distortion, like the Nikkors 35 1.8 and 2.5, or the Leica Summicron v3...
Thanks for your help!
Cheers,
Juan
 
I think it come down to the optical formula mostly..
many older lenses (I am thinking 1980's in my sample), mine has near "0" distortion when the camera is plum and level (most be a good copy)
The Nikon 24mm f/2.8 Ais with Close-Focus-Correction" though it was not a "true" wide angle design because the registration needed to clear the mirror.

But, true wide angle design are symmetrical with the front and rear block element lens designs. I would think they have a better chance to have less distortion.

Now, the VC wides also may be a non true wide angle design because most, if not all, were made to clear the Leica M5/CL meter arm.

Our Head Bartender should have some info on the more technical specks of the CV lens being a US distributor.
 
I use my asph 'cron at any f-stop but rarely above f8.
I never worried about distortion.
I use it for photography and not for any scientific purpose :D.
 
icebear said:
I use my asph 'cron at any f-stop but rarely above f8.
I never worried about distortion.
I use it for photography and not for any scientific purpose :D.
Click to expand...

I agree sometimes it doesn't matter at all. Other times, an image can be horrible (to my taste) if an important line gets curved close to the border and cropping that part is not a good option.
Maybe I see it as a relevant thing in those cases because I've done Architecture Photography with large format for many years... There are a few lines I prefer straight as they are in reality.
That's why there are designers thinking of it, and major brands' lenses without distortion: for those of us who care sometimes.
Cheers,
Juan
 
Unless you allow slight correction with post processing software, then you should stick with large format for critical architectural photography. RF is not developed for this specific application. You can use it with good results but if you are that picky, you just might end up frustrated as your expectation can't be met.
 
Hmm,
I use my favorite Contax IIa with 35/2.8 Biogon and 21/4.5 Biogon, and have never noticed any distortion, but then, these two lenses are known for it.
Usually, I don't pay attention to any distortion, but if I happen to see it, then, I will start looking for it.
 
icebear said:
Unless you allow slight correction with post processing software, then you should stick with large format for critical architectural photography. RF is not developed for this specific application. You can use it with good results but if you are that picky, you just might end up frustrated as your expectation can't be met.
Click to expand...

No doubt I do stick with large format for architecture.
And for street my expectations are met with rf lenses too, contrary to what you say... My CV15 is very well corrected, and I like my CV28 too... And again, there are plenty of other great rf lenses in this regard too, from Nikon, Leica and Zeiss.
Cheers,
Juan
 
distortion is mostly determined by the geometrical layout of the lens (location of the aperture!, optical construction). symmetrical constructions usually show less distortion, but even modern biogons are not 'strictly' symmetrical.

as far as i understand, you do not balance one property with exactly one other, but all of them come into the game at the same time. still i guess (guess!), that for lack of distortion, you mainly pay with vignetting.

i hope that someone more knowledgeable than me chimes in.

by the way, a very simple distortion free imager works without any glass: pinholes. very compact, too, but your requirement of f/8 is impossible to meet.

cheers,
s.
 
I have 20mm which is suppose to be linear, but when it comes down to it it isn't. I also have a Nikkor f2.5 35mm which to me is the best I've seen. Too bad, it is on a Nikonos. This is a uninteresting image but things are straight.

10423654745_59e3f99727.jpg


Here is my 35mm Serenar which is also pretty straight, but with other problems.

9509880317_f362b8e25d.jpg


EDIT, I'm like you I don't like curves. I'm using my 35mm FA Pentax f 2.0 for the first time on a 35mm camera. I'll see if it is any better.
 
Distortion is one of the 5 Seidel Aberrations, Juan, which are usually optimized together. If speed is of no concern, the simplest design that can correct all of the Seidel Aberrations is the Cooke triplet (see, for instance, http://spie.org/x33126.xml; also explains how the optimization is done). Distortion depends on focus distance, some lenses are rectilinear at infinity but noticeably distort up close. Also, wrt distortion, 35mm on 35mm is a good focal length for Leica mount lenses, because the registration distance is short enough to not have to use a retro-focal design. So, if you want small, high contrast + low flare (few elements) and little distortion, you might want to look into the MS Optical Super Triplet Perar 3.5/35. Forgot where, but MiyazakiSan has a write-up somewhere detailing how the lens was optimized.

Basically, for classic lenses, any nr. elements above 3 are there to add speed. The classic Nikkor 35/1.8 distorts noticeably, much like its modern descendants (UC Hexanon, Hexar AF). I'm surprised you mention the 35 Color Skopar, which I found quite rectilinear, see example below.

If you want a classic lens that is distortion free and faster than f3.5, in 35mm, look for 6 element symmetric, like Nikkor 35/2.5, Canon 35/2.8 or Summaron. The 6 element Summicron v3 is pretty good, too (much better than the Nikkor 35/1.8, for instance), but not as good as the f2.8 lenses. Also, for fast fstop, you usually pay with vignetting and/or loss in edge performance.

For modern lenses, check out Diagrams before you buy. High speed is not necessarily an indicator of higher distortion. For example, the ZM 35/2.8 distorts more than the ZM 35/2 (see http://www.zeiss.com/content/dam/Ph...loadcenter/datasheets_zm/cbiogon_28_35_zm.pdf vs. http://www.zeiss.com/content/dam/Ph...oadcenter/datasheets_zm/biogon2_35mm_zm_e.pdf).

In 35mm SLR, the classic shift lenses are optimized for low distortion (Nikkor or OM Zuiko 35/2.8, etc.).

Roland.

PS: Distortion "test" of the 35/2.5 Color Skopar PII I had. For close focus, this is pretty good, IMO:

ColorSkopar-X2.jpg
 
As Roland said, low distortion is part of the design. From the lenses I use, the Biogons usually have little distortion, and also the Summaron. I also use Summicron v3, but have actually not noticed it is so distortion free. A lens that was noticeably rectilinear which I sold, is the Elmarit 28 asph - I wanted an extra stop.
 
A good light wide angle planar/double gauss design should be able to overcome most of distortions the planar was designed to be distortion free. The problem is that the faster the lens is the more compromises the lens designer has to make. An f4 planar type lens should be pretty much completely distortion free (except some very minor ones). I believe the size of the front element also plays a role but I could be wrong. Biogons, Flektogons and Hologons are very good at giving very low distortions. The best wideangle design is probably the Hologon which has very littly distortion but unfortunately it tends to vignette heavily at faster speeds than f8 (one of the compromises, in LF we use a center filter to overcome that drawback)
 
Thank you all for the interesting comments.
It's mostly barrel and pincushion/mustache distortions what I don't like, and for wet printing there's no software solution...
When a horizontal line close to negative's lower border gets curved, I just dislike it.
Sebastel, I like the idea of vignetting being the price for very low or zero distortion, because I really love vignetting! I consider it positive for most images in general...
Roland, great post, thanks for the Skopar shot... And I’ll try to get some information on Perar’s distortion: it seems both the Skopar and the Perar are the closest ones to what I want.
If someone has an image done with the skopar 35 2.5 (or the Perar) to check the amount of barrel/pincushion distortion it has, maybe a simple bricks wall?, or a link to any test or comparison, I'd really appreciate it... Thanks!
Or if someone knows about a lens like the Zeiss Biogon 35 f/2 but really small, like f/4 or f/5.6... :) I know some dreams never come true...
Cheers,
Juan
 
Rockwell has distortion examples of several 35mm-- 35/2 Biogon appears to be at the top of the heap, although 35/2 Summicron and Summaron are described as having 'invisible' distortion. Not sure there would be any practical difference between them
 
As always, on the web there's huge contradiction: I see it's common to consider high the barrel distortion on the CV 35 1.4 (I agree from images I've seen), but when it comes to the CV 35 2.5 some people say it's got little distortion, while other people say its distortion is similar to the 1.4 Nokton... I know from comments and images the 1.7 Ultron has very low distortion, but it's a bit big for the size I'm looking for right now...
It would be great to see the same image, one with a straight horizontal line from left to right, at the bottom of the frame, close to its lower border, at least with the skopar...
Any examples or links? Sorry for insisting one last time...
Can't this at least be read in any data diagram or table from Voigtlander?
Thanks again.
Cheers,
Juan
 
Totally out of my price range, but I see the 35 lux pre-aspherical has no distortion (aspherical lux and cron have some) AND is really small... It's what I want, but fast and expensive! :) I'd buy that lens if I could. Good for those who can and have it!
Cheers,
Juan
 
hi juan,

i think the summaron is really a pretty good recommendation. since you did not ask for big apertures, the f/3.5 version might fit the bill best. very compact, too.

cheers,
sebastian
 
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