Stray light

Pieter12 · May 14, 2021

I noticed a bit of stray light today coming from my Omega D5 condenser enlarger with a Schneider 135mm lens. It seems to be coming off the edge of the lens--when I put my finger along the rim of the lens it goes away. Putting the sheet of paper close to the lens, it looks like it has the shape of the diaphragm. It does not seem to affect the prints, and I don't recall every seeing it before. I thought it might be the lens, so I swapped it out for my 90mm and still had the stray light in about the same place. Not the same shape, though, but that could be because the rim of the 90 protrudes a tiny bit more than the 135. Since this happened with 2 different lenses and I checked the seating in the lens board and enlarger, The bellows and upper condenser are in the proper position for each lens. I am a bit befuddled.

saman · May 14, 2021

That curved shadow below the stray light patch looks suspicious. Are you sure it's not coming from below the main condenser (rounded) and above the neg carrier? Or above the lower condenser? Or finally, from between the lamp house and upper condenser assembly?

Pieter12 · May 14, 2021

I don't see how light from above the negative carrier could reach that area, but I will check.

saman · May 14, 2021

the round shape is kind of odd. What's the square light spot in the middle? Isthat the light from the opening in the neg carrier? If that's the case, it makes me want to check above or below the main condenser, or below the lamp house.

Pieter12 · May 14, 2021

The square light is the negative in the carrier. The size of the carrier and the negative stage would kind of eliminate any light that close to the image. It seems to be coming from the lens mount or the lens itself.

saman · May 14, 2021

I see. It's crazy that its happening with two lenses though. I mean, unlikely to be the lens in that case right?

MattKing · May 14, 2021

Do you have illuminated apertures in that/those lenses?

Pieter12 · May 14, 2021

I know. They are both Schneider lenses, the 135 a Componon-S and the 90 an APO Componon HM. I ended up removing the lens board from the enlarger and readjusting the bellows, replaced the lens board/lens and the problem seems to be gone. Without the negative carrier in place, I can clearly see the corrugated edges of the condenser assembly projected on the easel. I can only conclude that the lens board was not seated properly and somehow a stray reflection was produced in the lens--it definitely had a polygonal shape when the sheet of paper was a few inches from the lens, and it went away when I put my finger along the edge of the lens housing. The curve showing in the photo I posted was most probably the protruding lens rim blocking part of that reflection.

Pieter12 · May 14, 2021

MattKing said:
Do you have illuminated apertures in that/those lenses?

Only the 90.

Bill Burk · May 14, 2021

Maybe it’s the light bouncing off the rear lens cell up towards the negative carrier and something is shiny. Aluminum negative carrier? Paint it black.

Pieter12 · May 14, 2021

Black carrier.

Bill Burk · May 14, 2021

Can you see anything if you look up with the lens off? Maybe it’s getting around the negative carrier, or maybe the upper section of the interior where the bellows attaches to the negative stage has a shiny surface. Shine a light up maybe something will shine back

Pieter12 · May 14, 2021

Bill Burk said:
Can you see anything if you look up with the lens off? Maybe it’s getting around the negative carrier, or maybe the upper section of the interior where the bellows attaches to the negative stage has a shiny surface. Shine a light up maybe something will shine back

Nothing there except the shiny screw heads on the bottom of the carrier. But I checked 5 of my carriers and they all have the same more or less shiny screw heads. If that were the problem, others would have discovered it long before me. My theory as of now is the card I was holding up to the lens was at such an angle that it reflected light back into the lens, where it bounced off a lens surface and to the side of the projected negative image. If that is true, there is nothing to worry about. I was just concerned that something might be happening that would affect the print, and it doesn't seem that way.

gone · May 15, 2021

My old Lentar enlarger has 6 dime sized holes in the top for vents, and it was quite a shock to see it lighting up the ceiling like a flying saucer or something the first time I made an enlargement. The filter drawer is broke on one end too, and it has quite a light leak there as well. However, none of these light leaks are on the print easel, and I've seen no sign of fogging on the prints. I guess that's the determining factor w/ these things, not so much where a light leak is, but where the light ends up going.

M Carter · May 15, 2021

Can you stick a strip of white card in that stray spot, and lift it up - keep it in the path of the light. Keep moving it up towards the enlarger and keep it lit by that spot, and you should eventually reach the source and see where it's coming from.

I had some odd issues doing small prints with an MXT enlarger - found it was light reflecting off the flat gearing thing that sticks straight down from the enlarger.

wiltw · May 15, 2021

M Carter said:
Can you stick a strip of white card in that stray spot, and lift it up - keep it in the path of the light. Keep moving it up towards the enlarger and keep it lit by that spot, and you should eventually reach the source and see where it's coming from.

I had some odd issues doing small prints with an MXT enlarger - found it was light reflecting off the flat gearing thing that sticks straight down from the enlarger.

Do this!

Stray light

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