75mm lens vignetting

[sergiofigliolia]

Hi all,
thanks everyone for the responses.
This is the image where the effect is stronger:

I did not use any filter at all and it was shot at f/22

[xkaes]

Thanks for the picture. To me, it shows that it just comes down to personal preference and subject matter. In your example, I don't find it offensive at all, in fact, what little optical fall-off there is actually helps. But that's just my personal preference. Here's an example of a little TOO much for my taste:



I have no idea if it was intentional -- but it certainly could be.

I should add that with wide lenses, it becomes more important to make sure your image falls on the middle of the ground glass. I don't mean the subject. I mean the optical (or mechanical) light fall-off will be minimized if the optical center of the lens is in the dead center of the GG. There has been a discussion on this issue going on lately on this forum. I encourage you to check it out.

[Dan Fromm]

I have a 75mm Congo that is attached to a Cambo recessed lens board.

Does anyone here know if a neutral density central filter is available for it?

Before anyone asks, right now I can't remember the thread pitch. I will go look in my notes.

Terry, read my article. Link to it in post #4 in this thread.

Short answer, Yamasaki didn't make center filters but there may be one that will fit and is the right density.

[Emmanuel BIGLER]

Terry, read my article. Link to it ...

[sergiofigliolia]

... it becomes more important to make sure your image falls on the middle of the ground glass. I don't mean the subject. I mean the optical (or mechanical) light fall-off will be minimized if the optical center of the lens is in the dead center of the GG.

You mean to not use much rise/fall/shift of the front standard, I guess

[xkaes]

Back in grandpa's day, there were a couple of accessories that were not intended to solve optical light fall-off, but just might help. I know a little about a couple of them. There might be other ones, and it appears that it would be easy to make one yourself.

The first is the PICTROL. It was designed to create soft-focus images on camera or on-enlarger.



The adjustable blades could be moved in or out, and were clear (but not too clear). It just created as much fuzziness -- as desired -- without impacting the exposure. However, if the blades were simply painted black and used on an enlarging lens with a negative "suffering" for unexposed edges, this might decrease the exposure under the enlarger, and achieve a more consistent tonality.

There may have been different versions of the PICTROL.

Similarly, there were a few versions of the VIGNETTER. Here's four of them in an old ADORAMA catalog. One was similar to the PICROL. It was adjustable but it had opaque blades.



These items might be useful "as is" or modified, and useful in reducing the impacts of optical light fall-off. In any event, they were all REALLY cheap. I'll have to check EBAY.

Any thoughts?

[Dan Fromm]

You mean to not use much rise/fall/shift of the front standard, I guess

Almost exact. No decentering movements at either end.

But this isn't a firm rule and you shouldn't follow it slavishly. For example, converging verticals can be a worse problem than dark corners.

[xkaes]

You mean to not use much rise/fall/shift of the front standard, I guess

Yes.

Many wide-angle lenses have lots of optical light fall-off AND a very small image circle. If your GG is not perfectly centered on the lens axis, you will be closer to the edge of the image circle where the optical light fall-off will be at its maximum. Making sure your lens and GG are aligned will decrease -- as much as possible -- the optical light fall-off.

[Dan Fromm]

Um, Joe, you may be remembering the extremely extreme wide angle versions of the Goerz Hypergon, which came with a mechanical center filter. See http://web.archive.org/web/201612041....com/hyper.htm for a full explanation.

http://web.archive.org/web/201605060...lens-i-promise has a clearer image of the star in place, ready to be spun.

The devices you described won't, unfortunately, do the job. When the Hypergon's star spins it acts like a disk who density is highest at the center. Your devices don't spin.

There really is no substitute for a center filter.

I didn't discuss the center filters supplied with Metrogon lenses in my article. These are clear filters with a pattern of small dots deposited on them. Dot density is highest at the center, falls off away from the center and there are no dots at all towards the edge. Its been a while, but I've seen discussions (here, I think) about how to calculate and lay down the dot pattern.

I'm a tinkerer but I've found searching for used CFs a better use of my time than trying to make my own. Others who are better and more serious tinkerers may go the other way.

[xkaes]

Hi Dan,

I was not trying to suggest that any of these tools could solve the optical light fall-off problem -- just simply minimize its appearance, AKA "make it less obvious" to the viewer. The Adorama Vignetter #2 simply dodges the edges of the paper so they won't come out as dark. You could do the same thing with your hand, but the Vignetter #2 covers the entire image at once, has an opening that is adjustable -- even more so than a typical aperture -- and is moveable during the exposure -- up & down, or rotating -- to minimize the edges of the tool. A longer exposure of the paper makes this easier.

I've used a hand-made tool -- just a hole in a piece of cardboard to lighten the edges of portraits -- using camera lenses with no optical light fall-off. Anyone who has done a lot of portrait work has done that. I never thought of it before, but it seems to me that it can do the same thing in reverse -- lighten edges that would otherwise come out too dark due to optical light fall-off. Of course, it would not bring back detail that was no there, but tonality would be improved.