Strange light leak from enlarger

Discussion in 'Enlarging' started by kmallick, Jun 28, 2012.

  1. kmallick

    kmallick Subscriber

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    I am having a hard time identifying what is causing this light leak from my enlarger. I am using a LPL Saunders 6700 with color head. The picture below shows the light leaks which shows up around the image projected from a 6x4.5 or 6x6 negative. I have checked the bellows and negative stage but cannot seem to identify the leak path.

    light_leak_2.JPG

    It doesn't seem like a reflection or light leaking out from any gap in the enlarger above the lens. The problem seems to be coming directly from the lens. I am using a Rodenstock Rodagon-S 80mm f/4 lens. I don't have another 80mm lens to compare with. But I did switch it to a Nikon 50mm lens. It causes vignetting on the 6x4.5 and 6x6 negative but I didn't see the lines of light leak.

    I could fix the light leaks by putting a dark skirt all around the lens or by hanging some black foam down from the negative carrier platform. But I am not very thrilled about this make shift fix as it gets in the way of reaching the lens aperture etc.

    I am still puzzled as to what these lines that are being projected by the lens? Is it some sort of internal reflection or flare from the lens? I would be hard pressed to believe that the Rodagon lens is the culprit. But could it be? I have put my head on the baseboard to look up through the lens and I don't see anything suspicious to cause these lines. The lens is also mounted securely to the lens board without any gap.

    Any tips or suggestions to help me identify the problem will be appreciated.
     
  2. Worker 11811

    Worker 11811 Member

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    Does your aperture plate or film holder properly mask the negative? Are you using the correct film holder for the negative you are using?

    Are you cropping in on the image, thus leaving some of the image (and some of the enlarger's light beam) outside the borders of the four-bladed easel you are using?

    'Cause here's what I see in the image.. I see that you are using a piece of paper that's larger than the blades as you have them set on your four-blade easel and some of that paper that's peeking out between the gaps in the blades is getting exposed by the "excess" light that comes from the lens because you are cropping too tight.

    Use smaller paper or readjust the blades of the easel so that they don't let some of it peek out.
    OR... Place a piece of cardboard masking on the easel around the blades where the paper peeks out.
    OR... Readjust and re-crop your picture so that light doesn't spill out.
    OR... Check to be sure you have the right aperture and/or film holder in place to match the aspect ratio and/or format of film you are using.
     
  3. kmallick

    kmallick Subscriber

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    I am using the standard glass less carriers made for LPL 6700 like here:

    220666.jpg

    Also, here is a picture of the head on LPL 6700 (not mine, shamelessly copied from Google image search):

    2908177012_1526dcc7a5_z.jpg

    I am not cropping the image. The projected image is exactly what I see from the 6x4.5 or 6x6 negative. The stray lines of light are beyond the projected image on baseboard alone (no easel). The lines stay there no matter what aperture I choose on the lens.
     
  4. Worker 11811

    Worker 11811 Member

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    Is the film holder inserted all the way into the gate?

    Does your enlarger have a "beam spread" adjustment used to optimize the lamp position for different film formats? (e.g. You raise it up for 35mm and lower it for 120.)
    Even if your lamp is out of adjustment for the film you are projecting, there still shouldn't be any stray light getting by the film holder. You would just have vignetting or a hot spot/

    There shouldn't be any light getting around the negative. The film holder blocks that from happening unless it's not fitted properly or if the gate isn't closed all the way.

    What if you got a large piece of cardboard, cut a hole in it just big enough for the lens and held it up to the bottom of the enlarger? Would the marks still be there?
    That would prove whether the light is or isn't coming out of the lens.

    I'm a little confused by this... You say that there are four sharply focused rectangles bordering the image? Right? Sharply focused?

    If they are sharply focused, they couldn't be just any old stray light coming from the enlarger.
    I can think of two things would cause a sharply focused edge:
    1) Something AT THE FILM PLANE.
    2) Something ON THE EASEL.

    The blades of the easel, lying flat on the paper, would make any stray light look sharply focused. The only other thing I know that would make sharp edges would be something at the film plane that's letting light through which is being focused by the lens. Even an internal reflection from the lens is likely to be blurry. (Unless the easel blades sharpen it.)

    And, at the risk of sounding like a pain, are you sure you are using the right film holder that has the right sized hole in it which matches the size of the image on the negative?
    If the film holder doesn't match the size of the image on the negative... if the hole in the holder is too large... you will have light leaking around the negative and it could possibly be sharply focused.

    More questions: You are absolutely sure your paper isn't getting fogged by room light or your safelight?
    Are you using a red "safety filter" under the enlarger to focus the image? (Or some setting of the enlarger?)
    I never do that. I always sacrifice a sheet of paper (fix, wash and dry without exposing it so that it's pure white) to put under my enlarger to focus on. I never take my paper out of the box until I'm ready to burn it.

    Are you sure that there is no stray light in the room? No gaps in the safelights? No holes in widow coverings or doors?
    You're not turning on a light in the room or using a flashlight? (Even if it's filtered red.)

    You are using a four-blade easel. Right?
     
  5. Rick A

    Rick A Subscriber

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    I agree with Randy. Looks as though your 4 blade easel is cropped too tight on the size paper you are using. A mask around the easel will alleviate the problem, or make a larger print for that size paper(or smaller paper).
     
  6. kmallick

    kmallick Subscriber

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    Thanks for all the help again.

    Yes

    Not that I know of. The lamp position in LPL 6700 is fixed.



    I tried that. I still see the stray lines of lights. Thats why I thought that the light is coming out of the lens.

    Let me clarify a few things.

    The picture I posted with stray lights is just for illustration purpose only. This is how I roughly see the enlarged image together with the stray light when I am in the dark room with the enlarger light on. The stray lines of light are being seen on the baseboard (without any easel). They are not sharply focused. The image from the negative is sharply focused but not the stray lines of light.

    I am yet to test a paper after exposing and developing.
     
  7. Overkill-F2

    Overkill-F2 Member

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    Try this, place a negative in the carrier, and lay a strip of black paper on top of the carrier, along one edge of the carrier so it just covers a tiny portion of the negative along it's edge.
    Does the stray light leaks change at all?
    ...Terry
     
  8. Worker 11811

    Worker 11811 Member

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    Well, I'm flummoxed...

    If the film holder is inserted correctly and it is properly locked into the gate, no light should be able to get around the image aperture. (of the film holder.)

    Vignetting from a misaligned lamp is eliminated. The lamp holder is fixed.

    If you have blocked the light from coming out of the enlarger except for what comes out of the lens (using cardboard) then there should be no stray light coming out of the enlarger, itself. All the light hitting the paper must be coming through the lens and, by extension, through the film.

    If you had internal reflections from the lens, hitting the paper where it shouldn't, it isn't very likely that they would form rectangular bars. Most likely, they would be oblong blobs. Neither would they be likely to be evenly spaced on all four edges of the image proper.

    If the bars are blurry along the edges, that tends to rule out gaps between the easel blades but it doesn't completely eliminate the possibility.
    If the blades were down, tight against the paper, they would form sharp-edged shapes. But not all easels hold their outboard edges perfectly flat to the paper, either. Even if they are a millimeter above the paper surface, they'd form "mostly sharp" lines but they might be a hair bit blurry. Regardless, blurry-edged lines score a point against this theory.

    So, what's left? Stray light from the enlarger is eliminated. A misaligned film holder is eliminated. Enlarger blades are partially eliminated. There's not a whole lot left that I can think of.

    Does the size and shape of the rectangular aperture in the negative carrier exactly match the size and shape of the negative? It can be a millimeter or so larger but that's it. Otherwise rectangular bars of light might escape around the edges of the image and they might, very well, have blurry edges.

    I assume that this is what Terry is getting at. No?

    A scan or a digi-photo of an actual print that exhibits this problem would be very helpful at this stage of the game.
     
  9. Bill Burk

    Bill Burk Subscriber

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    If you follow the stray light with a stick does it take you into the lens?

    If you put black paper in the negative carrier and completely cover the opening for film. Do the lines go away as the negative carrier opening is blocked out?

    If so, what happens if you show just a sliver of one edge of the negative carrier? Does one line come back?

    I was thinking it might be reflections off the opening edges of the negative carrier. If the carrier is a full-frame carrier (like a filed carrier would be), then around the negative will be four (or eight) bright lines that can reflect around.
     
  10. Overkill-F2

    Overkill-F2 Member

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    Negative Carrier.JPG
    I agree with Bill about the neg carrier edges reflections.
    I have filed the edges of my carriers to an angle around 45 degrees and painted them black to stop this very thing. See the image above.
    ...Terry
     
  11. Overkill-F2

    Overkill-F2 Member

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    I was thinking if you covered one edge of the neg carrier and one of the light streaks dissappeared, then we would get an idea of where they are coming from.
    ...Terry
     
  12. Worker 11811

    Worker 11811 Member

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    The exact same thing is done in cinema projectors. You bevel the edge of your aperture plate at about 45º.
    Cinema projector aperture plates are hard brass so, as long as they are smooth, you don't need to worry about stray reflections. Beveling is done, mainly, to make the edges of the image appear cleaner.
     
  13. kmallick

    kmallick Subscriber

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    I appreciate all the help and suggestions. I spent a lot of time tonight investigating the problem without luck. I am still pulling my hair out to solve it.

    I covered the opening in the negative carrier with black paper and checked. All the stray edges disappeared. It was pitch black on baseboard.
    Also, the intensity of the stray lines increase and decrease as I open and close the aperture on the lens. Both of these tell me that these stray lines are definitely coming through the lens.

    I am using standard carriers for 120 films. The window openings are slightly smaller than the actual film frames. The rim of the window is not filed.

    Here are a couple of pictures showing the projected image fom a 6x6 negative and stray lights. I shot these in darkroom with my DSLR.

    20120628233848-5543c5a8.jpg

    20120628233846-76840866.jpg

    20120628233841-7b0cfdb4.jpg

    Here are some pictures I took of my enlarger.

    20120628233839-2a1840a6.jpg

    20120628233833-278259b6.jpg

    20120628233835-5e86b986.jpg

    20120628233837-67cbb388.jpg


    I also took the Dichroic chamber off and took some closeup shots.

    A couple of views of the bottom of the Dichroic chamber:

    20120628233819-3f2eb119.jpg

    20120628233826-8191f450.jpg

    A few views from the top of the negative stage (without the Dichroic chamber):

    20120628233832-f12b4ebb.jpg

    20120628233821-e21a8da9.jpg

    20120628233822-ae86651d.jpg

    20120628233824-3470d878.jpg
     
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  15. M. Lointain

    M. Lointain Member

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    Seems to me that it is coming from the grey edge of the frame below the negative carrier (last few pictures). Flock or paint that edge and it should take care of the problem.
     
  16. Ian C

    Ian C Member

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    I got to thinking about the problem and that jarred my memory. I do recall (vaguely) a discussion about the bright bands you observed. I believe it involved an LPL enlarger. The conclusion—which seemed to make sense—was that the negative carrier is reflecting light from the 4 edges of the film aperture of the carrier into the bright bands that you see projected onto the baseboard.

    But why haven’t I ever observed this on my enlargers? The film apertures on my carriers are similar.

    I looked at the images you sent.

    http://kaushix.com/album/index.php?/category/18

    What they show contradicts the above idea. When you projected a 6 x 4.5cm image you got the same bright bands arranged in the SAME SIZE SQUARE as was the case with the 6 x 6cm projection. Clearly, the edges of the film aperture in the negative carrier are not the cause because they are of obviously different aspect ratio (3:2 vs 1:1).

    I notice that the LPL uses a thick black piece with a handle below the film holding plates (photos 9 and 10). I think that this plays a role in the problem on this LPL enlarger because it provides greater that usual distance from the negative to the opening in the negative stage. This makes it easier for the light to illuminate the edges.

    Photos 2 and 4 show the light colored aluminum opening in the negative stage. Notice that the opening is SQUARE and that the vertical edges are relatively reflective. The size relation between the film aperture in the carriers and the opening in the film stage is about the same as the relation as between the projected image though the carriers and the bright bands. (Lightbulb comes on).

    Here is what I think is happening. The light that passes through the back-illuminated negative radiates in every direction from the bottom surface. Some of it hits the 4 vertical sides of the square opening in the negative stage.

    The edges are “lit up” and are slightly within the image pickup circle of the lens at the magnification that you’re using. Recall that the bands disappear at the corners. That’s because the image pickup circle is too small to include the corners.

    The lens sees these bright bands and does what all good lenses do. It projects them faithfully onto the baseboard. I think this is the most likely explanation of your observation.

    You said

    That makes sense. The 50mm lens has a smaller diameter pickup circle, so it doesn’t see the bright reflections from the edges of the opening in the negative stage.

    You can cover the edges of the opening in the negative stage with black tape to test the idea. If you cover them with black tape and the bright bands disappear, then you have positively found the problem and can easily devise a permanent fix.

    The important things to realize are: there is nothing wrong with your enlarger or lens.

    The projected bands, while annoying, are of modest intensity and are well outside of the image area. They won’t affect the enlargement quality and I don’ think they will affect the contrast of the main image.
     
  17. ic-racer

    ic-racer Member

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  18. kmallick

    kmallick Subscriber

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    Ian, Hats off to you for doing the thorough analysis. :whistling: This makes total sense and I was getting suspicious of this late last night as well. I will try putting black tape around the perimeter of the opening in the negative stage just above the bellows and see if I can get rid of the stray light.

    Am I missing something in the negative stage? How come others with LPL 6700 doesn't experience this?
     
  19. kmallick

    kmallick Subscriber

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    You are correct, the reflections of the bellows are showing up when the negative holder is not in place. I have tried masking the stray lights out, but I have not been happy with the not-so-good Dmax I am getting with this enlarger because of the stray lights bouncing on to the paper. My prints from a Leica Focomat V35 are much contrastier in comparison. This is what led me to do the investigation.
     
  20. Ian C

    Ian C Member

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    As I pointed out, I have heard of this several years ago. Used with a 50mm lens the problem isn’t evident. Other owners might simply ignore it as it won’t affect the prints. It’s just a design idiosyncrasy of no real consequence, possibly annoying, but the prints that result will still be of excellent quality. Most owners probably ignore it.
     
  21. kmallick

    kmallick Subscriber

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    Interesting. :confused:


    Yes, the prints are still of excellent quality. I am not sure if I am being too anal, but I would prefer to get the best out of enlarging without any loss of Dmax due to stray light leaks. I can imagine that many don't notice or prefer to mask it out. So did I until this puzzling problem to figure out the stray lights took over me. Hopefully I am getting close to nailing it with all of your help and support. :D
     
  22. Bill Burk

    Bill Burk Subscriber

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    Great! You found it.

    I think a careful painting job using matte black paint under the negative stage base and maybe even inside top of lens stage would be a good move to reduce the internal reflections in the area between the negative and lens.

    Some "flare" is expected. You should be able to get good Dmax without the modification. But I still recommend the paint job. Also if you were using a condenser enlarger before, this is a diffusion enlarger which requires "harder" negatives to get the same results as before.

    Your 50mm lens doesn't show it up because it's angle of view doesn't cover the entire stage.
     
  23. ic-racer

    ic-racer Member

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    How are you determining one enlarger prints with more contrast than the other? Same lens on both enlargers and graded paper, right?
     
  24. kmallick

    kmallick Subscriber

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    This is a stubborn problem. I put black tape over the edges of the opening in the negative stage. See pictures of the mod below. The stray lights didn't go away.

    20120629221320-e8e57428.jpg

    20120629221322-6089bf31.jpg

    I put a paper mask on half of the negative carrier (above the negative) and the stray lines disappear on one half of the baseboard.

    I also tried moving the bellows up and down and that didn't move the stray lines. Therefore it doesn't seem like the bellows causing it.

    I also checked the inside of the bellows carefully. Its matt black with no real shiny edges.

    Is this some sort of diffraction?
     
    Last edited by a moderator: Jun 30, 2012
  25. Bill Burk

    Bill Burk Subscriber

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    Notice how the bellows show up in the two pictures. They would be pitch black if they didn't reflect. It's images of the bellows that you see. Light goes down through the negative and bounces off the inside of the lens stage which "lights up" the flats of the bellows.
     
  26. kmallick

    kmallick Subscriber

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    Thats what I was suspecting too. But with the enlarger on, negative in the stage and room dark I tried poking and moving the bellows up and down from outside from different sides to see if that would move or shake the stray lines. It didn't.

    The bellows do show up in the two pictures when there is no negative and the opening "lights up" the flats of the bellows. I don't see the parallel lines reflecting off the bellows when I have the negative in. I see just 4 stray lines in a square pattern no matter what size of negative I put in, 6x4.5, 6x6 or 6x7.

    However when I mask half of the negative off, the stray lines disappear from one side. This definitely points to the fact that the light is reflecting off of some edge on the negative stage, doesn't it?