Lens board light leak / lens board question

[smeylan]

Hi, I just received my first large format camera (an Intrepid 4x5 Mark IV) after reading this board for several months and am trying to track down an issue with a light leak: In bright sunlight, on the gg I see an annulus that looks exactly like a "ring of fire" solar eclipse, though it's pretty dim (I tried to draw it in photoshop, got frustrated, and realized it's the same as this sort of eclipse). So it looks like light is coming around the edges of the lens/shutter. If I put my finger to anywhere on the circumference that the shutter meets the lensboard, it darkens the annulus in that position.

Logically this seems like it could only be that I have not seated the lens (a Rodenstock 75mm f1:4.5, Copal 0 shutter) properly in the lensboard (Copal 0, from Intrepid, not recessed). I can see that there is about a very small (.5 - 1) mm space between the lens board and the lens (seems bad). But I don't know what I did wrong in terms of the combination of equipment or placement — shouldn't the two fit flush if both are Copal 0? What am I missing?

Any help greatly appreciated!

[Dan Fromm]

First of all make sure that the shutter is properly seated. Unscrew the lens' rear cell, unscrew the retaining ring, make sure that the back of the shutter level on the front of the board, reattach retaining ring and rear cell. If the shutter won't sit flat on the board, look for a small screw protruding from the back of the shutter. Remove it.

If all's well and you still have the leak, get some darkroom tape -- black masking tape -- and put it on the retaining ring and board. You'll have to unscrew the rear cell to do this.

[Bob Salomon]

First of all make sure that the shutter is properly seated. Unscrew the lens' rear cell, unscrew the retaining ring, make sure that the back of the shutter level on the front of the board, reattach retaining ring and rear cell. If the shutter won't sit flat on the board, look for a small screw protruding from the back of the shutter. Remove it.

If all's well and you still have the leak, get some darkroom tape -- black masking tape -- and put it on the retaining ring and board. You'll have to unscrew the rear cell to do this.

Or return the board to the seller.

[Alan9940]

Depending how precisely the hole for the shutter has been drilled into the board, I sometimes find it a bit tricky and fiddly to ensure that the retaining ring is seated properly into the board. If you look closely, you'll see that the retaining ring has a slight lip on the side that fits into the shutter hole. What I've started doing in recent years when mounting a lens is to: 1) remove rear element and retaining ring, 2) place retaining ring into shutter hole on back of board with the board back facing up, then 3) while holding the ring with a finger, screw the lens into the ring from the bottom. The weight of the lens will keep the ring in place. Hope this makes sense the way I wrote it. If all else fails, contact Intrepid and get a replacement board.

[grat]

Suggest reviewing this video to make sure you have it installed correctly:

https://www.youtube.com/watch?v=2JjzwjO5ZSE

[smeylan]

After re-seating my two lenses four times each and trying all combinations of electrical tape, I put a flashlight in the bellows and lo and behold the whole lens board glows. I feel slightly gaslit. This can't be normal, right?

[Tin Can]

Not normal

I made a lens board yesterday with hole saw and hobby saw out of 3 mm plywood

Then blacked it with magic marker

no leaks the clamp ring fits perfectly and snugly

[Dan Fromm]

After re-seating my two lenses four times each and trying all combinations of electrical tape, I put a flashlight in the bellows and lo and behold the whole lens board glows. I feel slightly gaslit. This can't be normal, right?

Thanks for showing us. You may have a board drilled for a #1 shutter. If so, the hole's diameter will be 39 mm. Whether or not this is so, get a board (ask Intrepid) drilled for a #0.

[smeylan]

Thanks for showing us. You may have a board drilled for a #1 shutter. If so, the hole's diameter will be 39 mm. Whether or not this is so, get a board (ask Intrepid) drilled for a #0.

It is a #0. The light ring in the above photo is the space between the shutter and the circular stand-off in the front standard. The material of the lensboard seems weirdly translucent with a thin layer of black paint on top. I will try taping over the whole board and see if that fixes it (I also ordered a new one).

[Keith Pitman]

How about posting some pics in good light showing how the lens sits on the lensboard when mounted—both from front and rear? The lensboard should be aluminum and will not pass light.

Look again as Dan suggested to see if there is a tiny screw protruding from the back of the shutter. If so remove it. Then try remounting the lens.

Report back.