Correcting barrel distortion in wide angle lenses

[cotdt]

Some of my wide angle lenses have some distortion, probably 2% barrel distortion. How do I correct for this distortion when I am printing in the darkroom?

 

[David A. Goldfarb]

Well, I suppose you could try pinning the paper to a pincushion shaped pillow, but I've never heard of anyone trying to correct this kind of distortion at the enlarging stage.

 

[cotdt]

Well, I suppose you could try pinning the paper to a pincushion shaped pillow, but I've never heard of anyone trying to correct this kind of distortion at the enlarging stage.

wouldn't that make the corners out of focus?

 

[David A. Goldfarb]

That's probably why no one tries to correct this at the enlarging stage, though you could stop down and try your luck.

Another option might be to enlarge through a lens that has the opposite degree of pincushion distortion, but enlarging lenses are usually designed to be free of distortion, and a lens that isn't designed as an enlarging lens could have other problems when used in this way (e.g., impractical to mount, falloff of illumination, not terribly sharp, etc.).

 

[fschifano]

Do what the old timers did. Use the taking lens as an enlarging lens. This was not an uncommon practice. Of course, mounting a modern SLR lens to an enlarger might pose some problems. Easier, but not necessarily easy, to do with prime lenses. Forget about doing it with a zoom lens.

 

[cotdt]

Do what the old timers did. Use the taking lens as an enlarging lens. This was not an uncommon practice. Of course, mounting a modern SLR lens to an enlarger might pose some problems. Easier, but not necessarily easy, to do with prime lenses. Forget about doing it with a zoom lens.

cool i'll try that!!! i'm a DIY guy so mounting an SLR lens isn't an issue for me.

 

[David William White]

OMG, you MUST post these. Print with your normal enlarging lens and again with your camera lens.

It's real late, and half my brain says it will cancel out and the other half says it will make it worse.

 

[AgX]

The procedure of using the taking lens as enlarging lens could compensate for light fall off in a n/p process.

However any distortion would get stronger...

 

[Jim Noel]

Printing a negative made with a lens having barrel distortion with an enlarging lens (or same camera lens) having barrel distortion will only double the effect. The only real solution is to replace the camera lens with one not having this problem. If is is an extreme wide angle lens, the barrel distortion is expected.

 

[cotdt]

any enlarging lenses that have pincushion distortion? maybe that would cancel the barrel distortion.

 

[AgX]

As David indicated in the design of enlarger/reprographic lenses lack of distortion is a major objective.

 

[RobC]

It's a myth that using the taking lens for enalrging will work. People may have done it if it was the only lens they had but you are not reproducing what happened at the taking stage unless you were doing macro photography.
An enlarger is a macro camera which uses macro lenses. It takes a photograph of the negative and uses paper for its output film.

Will your lens focus on the film? If you use it the same way round as in your camera, then it would, but how far away would the paper need to be, to be in focus. And if you did it that way round you would magnify the barrel distortion as has alread been pointed out. If you reverse the lense would you be able to focus on the film? All depends on the type of lens but it won't work as well as a properly designed enlarging lens.

 

[cotdt]

bah! too bad that it just so happens that when it comes to wide angle lenses, the higher the distortion the sharper the lens and flatter the field.

 

[richard ide]

Wide angle lenses are available which exhibit practically zero distortion, extreme sharpness and very flat field. They are used for aerial photography. Unfortunately they are very expensive.

 

[Murray@uptowngallery]

Consider the discussion of a meniscus lens and whether the stop is fore or aft. One situation is supposed to have barrel distortion and the other pincushion. Hence the recommendation for one configuration as being less objectionable.

Now, if you had a symmetrical enlarger lens like a Componon or Rodagon, would this work? My Rodagon lens will allow me to unscrew one cell (the back?). Not sure about the front. The Componon is either uncooperative or too tight for me to tell.

Would this work, or would you gain more aberrations than would fix your 2% distortion? I don't know. Just an idea.

About a non-flat 'paper plane' (no pun) below your enlarger...some enlargers had accessory tilt tables...so is the projected field of an enlarger more tolerant of 'DOF' like the object side of a taking lens is compared to the image side ('depth of focus'), for the same reason film plane flatness is more critical than DOF?

 

[Andrey]

Printing a negative made with a lens having barrel distortion with an enlarging lens (or same camera lens) having barrel distortion will only double the effect.

That's only true if you mount the lens the "wrong way" - negative facing the front element of the lens and the print facing the rear/mount end of the lens.

I'd use a rangefinder lens. They are usually free of pincushion distortion.

 

[AgX]

Yes Andrey,

You are right. I was puzzled for a moment, then realizing that at least I have been looking at the wrong side of the issue, eh lens...



However in case of an enlarger lens (to which Jim was referring) the distortion would be referred to concerning the print side. Thus with an larger lens being reported to have barrel distortion a negative showing barrel distortion could not be compensated...

 

[cotdt]

I'd use a rangefinder lens. They are usually free of pincushion distortion.

that would solve the problem if only rangefinder lenses could focus closer. a lot of the photography i do has a nearby foreground object and its background. but you're right, rangefinder lenses do have an advantage when it comes to distortion.