Curious Lens Faults

A couple months ago, I posted that a homemade tripod had collapsed,

causing the base of my Yashica-Mat to indirectly strike the floor

with moderate force, enough to bend the tripod socket at an slight

angle. There weren't any light leaks or film flatness issues after

the accident, but pictures I've made since then have revealed strange

lens problems. There's a lot of coma at f/5.6 or lower (with light

sources and images around the corners of the picture enlongating

and "bleeding out"), and even at f/11 and f/16, the edges are still

slightly soft. The centers of every picture are moderately crisp,

though not as sharp as they used to be. The Yashica-Mat used to

produce very sharp images even wide open, with no noticeable

abberations. These problems never showed up in any of the negatives

or slides made before the accident.

 

Could it be that the lens elements are out of alignment? If so, would

be possible to realign them to produce the sharp, crisp original

images, or is the Yashica-Mat now going to be relegated to occasional

portrait work only? Thanks!

 

JW

The camera could just be out of square, so that the lens isn't parallel to the film. Or, the lens barrel itself may have been distorted, or the elements put out of center. Or, perhaps it's just out of collimation, and not focusing right.

 

Sounds like you may have generated an "parts donor", sad to say.

Have it checked out.

Mark Hama is great with mats, he used to built them.

www.markhama.com

I have no connection with him, other than having repair work

done by him.

When I was a kid, my Mat-124 rolled out of its case onto the pavement. It looked fine, but the impact cracked the body casting. It isn't as strong as it looks. Go over all the visible parts of the body, inside and out, looking for cracks. Something is definitely out of alignment. Lens elements typically can't move in their bores, but they can fracture. Look through the lens with the shutter open at a bare bulb and see if you see any lines or discontinuities. Unfortunately, it may well have become a parts doner.

My yashica-D had a visible dent on the bottom of the lens board, when i got it. Focusing was also a bit tight. The board was not fully parallel with the camera body. On the test roll, the photos were out of focus. Checkled with a groundglass on the film plane and a strong loupe: whenever i focused for the centre of the frame, the top and bottom were out of focus in the opposite direction. I mean, i had to focus closer for the top, and further for the bottom, compared to the center. I opened up the camera body; the focusing arms were a bit bent. Compensated the difference inserting thin metal rings before putting the lens board back. It is perfectly good working now.

 

You might have a similar problem; i've heard lots of stories about unparallel lens boards on TLR's since i had my own. After the pain of removing the leatherette/vulcanite, it's a piece of cake to repair it. Good luck!

By the way, i did not see increased coma; however, i've read in literature (e.g. Sidney Ray, Applied photographic optics) that the coma is the most sensitive aberration to misaligned lenses, so your observation might be spot on.