60mm Hexanon on Baby Speed Graphic,,,,Puzzled by light leak.

[Steve S]

I had a 60mm f5.6 lens from a Koni Omega which nominally was made to cover 6x7. I decided to take the elements and put them in a size 0 Syncro Compur shutter to use on my Baby Pacemaker Speed graphic (6x9). I can just get focus on infinity so that was so far so good.
I shot 3 test frames using a Graphic film back and I have a very odd effect visible. See attached pics.
At first I thought vignetting from the lens hood but if that was the case it would be on both sides and anyway it would be darker, not lighter.
Then I thought light leak in the film back. But this hasn't happened before and the other shots taken on two different lenses on the same film were OK.
The lens and shutter are good and tightly secured on the lens board.
The only other conclusion I can think of is that I am getting light in around the lensboard itself. Unlikely but it seems the only explanation.
Any other ideas that I may have missed?

 

[shutterfinger]

The symmetrical curvature suggest that the cells are cross threaded, cell and shutter threads are a mismatch but close enough that they appear to work. There is enough swing to cause the right side of the photos to be softer than the left side in the correctly exposed area whether it be from misinstalled cells or front standard movement.
Are you sure the cell spacing is correct in the Compur shutter? It should be the same as when they were in the Koni Omega.

 

[wombat2go]

Looks like a light leak.
I would suggest to go into your darkroom with a little led flashlight (like a key ring one) inside the camera, and a cap on the lens , and the back on the camera with the darkslide in. When your eyes adjust, wobble things; you might see the leak.
Hope you fix it any way !

 

[Dan Fromm]

Steve, I reshuttered a 60/5.6 Konica Hexanon (ex-Koni-Omega) in a normal Copal #0. No problems, and the hood causes no problems.

The cock-and-shoot Copal #0 should have the same tube length, threading and diaphragm position as the Compur #0. See, e.g., http://www.suaudeau.eu/memo/pratique/Les_obturateurs_centraux.html

Do as Wombat suggested and look for a light leak. Also make sure that y'r lens' hood is lined with felt. If it isn't, and is shiny black paint or metal, that might cause the flare you have.

 

[Steve S]

Thank you all for your helpful responses. I have glued some velvet light-trap to the inner edges of the lens board. This makes the board a very tight fit and should exclude any light incursion from that area.
Dan, I actually tried fitting this lens into two separate copal press 0 shutters and found that the rear element when screwed in fully was fouling the diaphragm operation. About half a turn was enough to free it but I assumed it needed to be fully screwed in for best performance. Maybe I will try a shim on the copal press if I get further problems after the next test.
By the way, lens boards for these cameras are like gold-dust. I have had to buy some 1.2 mm thick aluminium sheet in order to fabricate my own in future. Looks to be pretty difficult to get these right.

 

[Dan Fromm]

Thank you all for your helpful responses. I have glued some velvet light-trap to the inner edges of the lens board. This makes the board a very tight fit and should exclude any light incursion from that area.
Dan, I actually tried fitting this lens into two separate copal press 0 shutters and found that the rear element when screwed in fully was fouling the diaphragm operation. About half a turn was enough to free it but I assumed it needed to be fully screwed in for best performance. Maybe I will try a shim on the copal press if I get further problems after the next test.
By the way, lens boards for these cameras are like gold-dust. I have had to buy some 1.2 mm thick aluminium sheet in order to fabricate my own in future. Looks to be pretty difficult to get these right.

In the Compur/Prontor/Copal/Seiko shutter standard, press shutters' diaphragms are closer to the rear than are cock-and-shoot shutters' diaphragms. See, e.g., http://www.skgrimes.com/products/new-copal-shutters/standardcopals

The 60/5.6 Konica Hexanon's design is similar to the f/8 Super Angulon. This class of lens' performance is very sensitive to cell spacing. Don't put yours in a #0 Copal Press and shim the rear cell so it clears the diaphragm, put it in the right shutter. Cock-and-shoot #0, Copal or Compur makes no difference.

There used to be an eBay seller located in eastern Europe who sold carbon fiber 2x3 Pacemaker Graphic boards for quite reasonable prices. I haven't looked for a while, b'lieve he's still selling boards for 4x5ers. If you find them, ask him about 2x3ers. skgrimes offers metal 2x3 Pacemaker boards. Midwest (www.mpex.com) used to have 'em, may still; asking is cheap.

 

[Steve S]

Just an update. I am pleased to say this was an issue with a leaky lens board. Maybe the weight of the lens was a factor. Anyway the velvet light trap solved the problem. I developed another test roll today and this lens is a fine performer. Focused on10 feet at f8 everything is crisp and in focus from ten feet (and maybe closer) to infinity. It should be very useful as a point and shoot solution as I will probably only need to mark the 5 feet and 10 feet focus positions on the rail.
I do need to remember to drop the lens bed though as it just catches it even in landscape format.
Once again, thanks for all the contributions