Red filter in enlarger throwing off sharpness

Discussion in 'Enlarging' started by heespharm, May 4, 2010.

  1. heespharm

    heespharm Member

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    I have a durst m301 and I noticed I can focus sharply with the red filter in place and it'll be tack sharp under the grain focuser... But when I move the red filter away I'll have to refocus to get it sharp on the paper...

    Has anybody ran into this problem as well??? I think I'll just focus without a red filter on a piece of paper that will be the "sacrificial lamb" then turn off the lamp and switching out the paper then expose it... Any other suggestions??
     
  2. Sparky

    Sparky Member

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    Hi. It's called 'chromatic aberration'. But the truth is all lenses focus different colors at different distances. But it's hardly surprising here - since it's the light at the OTHER end of the spectrum that does the work in exposing your paper. If anything - I'd use a blue filter- if you're going to use any at all...
     
  3. Neal

    Neal Subscriber

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    Dear heespharm,

    Do not bother adding a piece of paper when focusing. The thickness will make no difference. Save the red filter for organizing multiple dodges and burns.

    Neal Wydra
     
  4. Steve Smith

    Steve Smith Member

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    Yes. Don't bother with the sacrificial paper... unless you have a dark easel base.

    Gene Nocon's book Darkroom Printing has a section relating to focusing with different colours of light. He suggests using a blue filter over the eyepiece of the grain focuser as that is the colour the paper is most sensitive to.


    Steve.
     
  5. Worker 11811

    Worker 11811 Member

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    I never used the filter.

    I took one piece of paper and developed it without exposing it. I put it on my easel and traced the outline of the image area with a Sharpie marker. I did that for each of the favorite print sizes that I like to make.

    So, now, when I want to make a print I can put that piece of paper on the easel and quickly move the blades to the size I want and I don't have to fuss. Then I can focus on that same piece of paper. The ink outlines also help me be sure I am composing to the print size I want. If my easel blades aren't set right it will show up immediately, even in the dark.

    When I am ready, I put my special piece of paper away then get out a fresh piece to make my print with.

    BTW: My Saunders easel is all black so I need something to focus on or I can't see the image.
     
  6. RalphLambrecht

    RalphLambrecht Subscriber

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    Our eyes work best with white light, and that's why I recommend moving all filters (even VC filters) out of the light path for focusing.

    Sparky is correct about chromatic aberration, and theoretically, his recommendation to work with a blue filter makes a lot of sense. However, there is very little blue in incandescent enlarger light sources, and therefore, the blue filter will absorb most of the light, leaving only a dim image to focus with. That makes accurate focusing harder than focusing with a bright white light.
     
  7. RalphLambrecht

    RalphLambrecht Subscriber

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    I agree with Randy. A black easel is a good easel (no surface fog). A white piece of paper is a good idea for focusing, not because of its thickness (depth of field takes care of that with ease), but because of its reflective qualities.
     
  8. fschifano

    fschifano Member

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    Do yourself a favor. Remove that red filter and throw it away. If those things aren't the most useless bits of darkroom accessory ever devised, they're right up there near the top of the list. The issue of red light focusing at a different plane as blue light is valid, but a modern (not more than 50 years old) enlarging lens will be corrected for that and it's not much of a concern. Stopping the lens down will cover the focusing error if not completely, then nearly so.

    The problem with that red "safety filter" isn't that it's red, it's that it's not optically flat. Anything you place in the optical path will introduce it's own refractive index into the equation and that's probably what's screwing you up more than anything else. These safety filters are not made to the standards of filter designed to be used over a lens. Even the best made camera lens filters introduce a bit of error into the focus point, but it's so small that the effect is not noticeable.

    I'm sure you have some scrap prints around. Take one and with and mark it off on the back into a grid using a T-square and a with a Sharpie. Mark off the borders if you like too. Use that for focusing and composing with the lens wide open. Stop the lens down and replace the guide sheet with a fresh sheet of unexposed paper only when you're ready to expose the print. You'll be surprised at how easy it is to get everything lined up the way you want it when you have a grid pattern superimposed over the image. Do not take paper out of its light proof package until you're ready to expose it. Safe lights are not completely safe, and I've not seen the enlarger yet that does not leak some light when it's turned on. All these seemingly little things add up to rob that certain sparkle from your prints by adding just a little bit of fog.
     
  9. bsdunek

    bsdunek Subscriber

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    Guess I'm surprised at this discussion. I always learned you focus without the red filter and lens wide open. I use a piece of printing paper under my grain focuser to put it at the right height. I use an easel so I know where the actual print paper is going to go. If I have a doubt, I use the red filter while positioning my paper. Then stop down, remove the red filter (after turning off the enlarger). Then make your exposure.
    Any filters, such as contrast control, should be in place while focusing just in case they have a focus shift effect.

    Just the way I do it.
     
  10. David A. Goldfarb

    David A. Goldfarb Moderator Staff Member Moderator

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    I always focus with a scrap piece of paper under the grain focuser. Why bother with something that has the precision of a grain focuser and not compensate for the thickness of the paper? The focus sheet is reusable. It's not as if it costs money to do it properly.
     
  11. RalphLambrecht

    RalphLambrecht Subscriber

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    Steve

    Your statement needed repetition.
     
  12. tkamiya

    tkamiya Member

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    David,

    It doesn't cost money but it isn't necessary. I did some experiment a while back. I focused sharply using grain focuser onto a white sheet of paper in easel. Then, I raised my easel by 5mm. Then rechecked focus. It was STILL in focus. This is with 50mm EL-Nikkor 2.8 at wide open.
     
  13. fschifano

    fschifano Member

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    I agree that the thickness of the paper has no practical effect on the focus, but I find it a LOT easier to see what I'm doing when there's a white piece of paper under the enlarger as a focusing and composing aid. Yellow easels aren't too bad. Anything darker makes the job almost impossible.
     
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  15. David A. Goldfarb

    David A. Goldfarb Moderator Staff Member Moderator

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    Then you might as well toss the grain focuser and eyeball it.
     
  16. Sparky

    Sparky Member

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    I've always found eyeballing amazingly effective... not like my eyesight is all that great or anything. I've always learned to trust the eyes. The only problem is stopping down. That's what the grain focuser is for... just in case.
     
  17. RalphLambrecht

    RalphLambrecht Subscriber

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    I'm not surprised, looking at the attached depth of field table. Placing a piece of paper under the grain focuser to compensate for the missing paper thickness is theoretically correct but practically pointless. Placing it on a dark easel as a focusing aid is valuable.
     

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  18. RalphLambrecht

    RalphLambrecht Subscriber

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    Now, you're throwing out the baby with the bath water.
     
  19. David A. Goldfarb

    David A. Goldfarb Moderator Staff Member Moderator

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    Why bother to align the enlarger? Why bother to use a glass negative carrier? Why worry about what kind of lens to use?
     
  20. RalphLambrecht

    RalphLambrecht Subscriber

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    David

    You are mixing issues! Enlager alignment and glass negative carriers make sure, you can live with limited depth of focus (see the next table attached). Depth of focus (tolerance at the negative stage) is critically sensitive for an enlargement, depth of field (tolerance at the baseboard) is not.
     

    Attached Files:

  21. tkamiya

    tkamiya Member

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    David,

    I didn't expect such a reply from you. If my commenting on the subject was inappropriate, I apologize. May I recommend you try what I did and see it for yourself? What I'm finding is that the distance between the film and the lens is very critical to focus. However, distance between lens and the paper is not so much so. My grain focuser helps me bring the image into sharp focus. But once in focus, I can raise or lower the paper by about 5mm without losing focus.

    I was very curious about this myself so I conducted my own experiment using my own equipment. Now I don't even bother with sacrificial paper.
     
  22. Monophoto

    Monophoto Member

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    The red filter isn't for focusing!

    You should focus using the light that will be used for making the enlargement - including any variable contrast filters that you want to use. Then, leaving the enlarger light on, swing the red filter into the light path, and then load paper into the easel. Finally, turn off the light, swing the red filter out of the way, and start the clock.

    This does two things. First, leaving the lamp on with the filter in place as you load the paper into the easel allows you to see the final composition. More importantly, it allows you to leave the enlarger light on right up to a point a few seconds before you start the print exposure. That means that if there is a tendency for the negative to 'pop' due to heat from the lamp, it won't have a chance to cool and change the focus.

    Yes, to focus most accurately, you should focus on a sacrificial piece of paper. There are two equivalent tricks that avoid wasting a sheet of paper. One is to use a fixed, thoroughly washed and dried test print - just focus on the back. Or, for those who use a grain focuser, glue a scrap of a test print to the bottom of the grain focuser. That elevates the grain focuser by an amount equal to the thickness of a sheet of paper, and has the same effect as focusing on a sacrificial sheet of paper, but without wasting a sheet of paper.
     
  23. 2F/2F

    2F/2F Member

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    Nice chart. Thank you. Makes me feel batter about FB paper bowing up a little bit in the middle without a vacuum easel. Do you mind if I print it out?

    I thought that the red filter was simply a compositional aid for doing multiple-negative printing, a la Jerry Uelsmann.
     
  24. David A. Goldfarb

    David A. Goldfarb Moderator Staff Member Moderator

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    I can see the difference in the grain focuser between having the paper under the grain focuser and not, and that's enough to convince me that given all the trouble we go to to avoid other very slight errors and sources of image degradation, like the difference between using an APO lens and an otherwise adequate modern 6-element lens, or choosing one film developer over another, or the possibility (suggested by Ctein in Post-Exposure if I remember correctly) that multigrade paper tends to be slightly less sharp than graded paper perhaps due to the difference in the spectral sensitivity of the paper depending on the contrast grade and that of human vision, that there is no reason to introduce an easily avoidable source of error by focusing without a focus sheet under the grain focuser.
     
  25. Sparky

    Sparky Member

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    BIZARRE. I NEVER heard that before... nor noticed it (which isn't to say that it's not happening)... interesting...
     
  26. patrickjames

    patrickjames Member

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    I can't even remember the last time I even had the red filter mounted on the enlarger.

    The most important thing you can do to your enlarger is to make everything parallel. Then make sure your lens is good. Then get a good focussing aid. When you have it dialed in you only have to check it periodically.

    That blue filter thing that Nocom puts forward is a bunch of hokum. I think the biggest problem is standard enlarging lenses just aren't that good.

    The most important thing to say here is that you have to find out what works for you. I recommend you read Thornton's book "Edge of Darkness" in which he describes his chase for sharp prints. Let's just say there are a lot of variables.

    I use a Saunders enlarger with a Zeiss S-Orthoplanar lens aligned with a Versalab Parallel laser alignment tool focussed with either a Microsight or a Peak Critical Grain Enlarging Focuser.

    That works really well for me. You are already understanding that focussing through a red filter doesn't work for you, so congrats. Onwards and upwards as they say.