HUGE Image Circles (lens coverage)

[MichaelBriggs]

Jorge, distortion is one of several of lens abberations. You will find it listed on manufacturer's datasheets under that term. It can be either positive or negative, causing squares to be rendered either as barrels or pin cushions.

Sparky, the effects that you find unpleasant on your least two examples can be obtained with an extreme wide angle lens without using any camera movements, so in that sense the issues aren't the same as in your first post which asserted that coverage is overrated -- unless you want to take photos with the corners missing.

(And of course, front rise and rear fall are the same except for the slight change in the view point of the lens.)

 

[Jorge]

As I said, distortion is not confined to lens aberrations only. It is also known as the unequal spatial image formation.

OTOH I agree with you the distortion seen in the photographs would have been present regardless of wether there was any rise used or not.

 

[Sparky]

Michael,
I do not find the 'optical rendering' (I'll call it) in either or any of the photographs unpleasant. I don't find the images unpleasant. I think they are superb given the working space I had to shoot in. The last set of photos were posted because Jorge asked me to post something to illustrate an aspect of this - not the actual point of the original post... we were just having a discussion about possible designers' intent vs. perspectival rendering. And yes, it is a perspectival phenomenon - not to do with distortion. Jorge was the one who posited that it was a result of distortion. I guess something good has come out of all this for me though. It's gotten me to pinpoint PERHAPS what it is that I don't like about that whole 'look'... which is perhaps imbalanced 'perspectival field' to coin a term. Anyway - it's absoulutely nothing I need solved... I was just wondering if there were others out there who felt as I do. I was not looking to have my opinion 'corrected'. Clearly, if I think something doesn't look right to my eye - it's my responsibility to take steps with my composition and technique to solve it in a way that suits ME. As we all ought to. And that was more the gist of the original point. I wanted to see how embedded this etiquette actually was. Pretty embedded, I'd say.

 

[Jorge]

Now see, perspective does not apply to the apparent spatial distortion. Perspective when we talk about lenses is when you move back and forth, for example a 75 mm lens and a 150 mm lens will have the same perspective when when the 150 mm lens is placed at twice the focal lenght of the 75 mm. While they both might have the same perspective, both can suffer from spatial distortion, such as if both cameras were pointed up.

 

[Murray@uptowngallery]

I think the etiquette is as embedded as other 'parochial' views like photos having to be sharp...my wife refers to pinhole photographers as pinheads :O(

I only know enough about converging vertical lines to feign arrogance, for example, looking at a local 35mm RF photogs architectural shots with such bad convergence (I'll guess 30% difference in top width vs. bottom width), that they look like bad amateur snapshots. I'm sure it was intentional, but when I look a them, I wonder...why bother to mat & shrink wrap those? I could do that...oops, I also refer to 'I can do that syndrome' with gallery visitors and photography, and now I'm guilty.

Murray

 

[scootermm]

MASSIVELY overrated. What do you think? Everyone's so hung up on this. I spent COUNTLESS hours trying to figure out which lenses had the biggest coverage - even to the point of considering a 150 grandagon for my normal lens on 4x5. I'm an architectural photographer, too - so you'd think it would be important to me. When I do lens rises - they tend to be pretty subtle - rarely more than 10-20mm. And QUITE often I use 5mm or less. I even think it's quite refreshing not to use ANY. More than 10mm on 4x5 just starts to look kind of silly IMHO. Others' opinions?

thought maybe Id spark the initial flames on this conversation...
speaking from my experience in 4x5, then 8x10, and now 7x17 (along with much 8x10) I like lens coverage. one of the downfalls of my one and only 7x17 lens (14" Kodak Commercial Ektar) just doesnt give me the coverage I wish it would. although Im fine working within the constraints but having some more of an image circle would be gladly appreciated. so to state its massively overrated is something I couldnt disagree with more. Id much prefer to have excess coverage thats never used then not enough coverage that vignettes negs.

 

[Murray@uptowngallery]

If it's typical for edge resolution to be worse than central resolution with many lenses, is 'excessive' coverage a blessing in disguise with regard to resolution deterioration at edges?

I suppose degree of enlargement trumps this supposition. Is there any connection between physical aperture diameter and edge resolution? It would seem that they necessarily interact but might be independent in theory. Diffraction-limitation and ab errations are discussed in totally different 'chapters' both both coexist in an exposure.

Murray

 

[Sparky]

Well, I don't know QUITE how to answer that except that the extra image circle only seems to be available with increasing aperture number - and the trade off is image circle vs. diffraction - the greater your image circle the greater the amount of diffraction overall. Apart from inherent aberrations/effects native to off-axis use, the entrance pupil seen from the edges is distorted (american football shaped) and I suspect you're getting increased diffractive effects there in addition to off-axis aberrations. But anyway - that part of the image would not exist at a lower aperture number. So I suppose it is what it is - and there's no improving on it that I can see - but yes, lower magnification enlargements would certainly help matters!