How do you focus you enlarger?

Discussion in 'Enlarging' started by Mainecoonmaniac, Oct 21, 2013.

  1. Mainecoonmaniac

    Mainecoonmaniac Subscriber

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    I've been printing for over 33 years. I learned in college how to print. I was taught to focus with the lens wide open then stop down to the desired f stop. I just recently tried to focus with the lens stopped down. I don't notice a difference. How do you focus. Does it really matter?
     
  2. polyglot

    polyglot Member

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    Wide open will give you a better idea that it really is focused, i.e. small errors are more apparent. You can get it right focusing stopped down but it's a little harder, especially with a dim negative.

    Focusing wide open is bad if your lens has focus shift but no decent enlarger lens will.
     
  3. Mainecoonmaniac

    Mainecoonmaniac Subscriber

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    So good lenses..

    So all good lenses will hold the same focus throughout different magnifications?
     
  4. Rom

    Rom Member

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    I don't know if it's a good idea but i just use a piece of film where i made some scratches with my scissors. Then i focus wide open till i get the scratches focused.

    After i just gently put the neg that i want to enlarge.

    Seems to work for me. I never enlarge more than 30x40cm
     
  5. miha

    miha Member

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    I focus wide open but then I use no focusing aid.
     
  6. Rafal Lukawiecki

    Rafal Lukawiecki Subscriber

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    I can't speak for too many enlarger lenses, but the ones I use hold their focus as you stop down, that is, they seem to show no focus shift: El-Nikkor 150 (both the old, knurled one, and the superior new one), Rodagon 150, Rodagon 135, and Apo-Rodagon 80. Like others here, I find it easier to focus wide open, in my case with a Peak magnifier, then to stop down. This way I can see if anything is not parallel, for example, focus at one edge might be off while the other is fine if I titled the lens stage without returning it properly to zero, or if there's an issue with the way I inserted the carrier. I also re-check focus after stopping down and before making exposures, in case anything has shifted etc.
     
  7. wildbill

    wildbill Member

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    I use the focussing knob.
     
  8. Thomas Bertilsson

    Thomas Bertilsson Member

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    Dense negatives are focused with the lens wide open, and thinner ones at whatever aperture is appropriate with the grain focusing device.

    Using the grain focusing device it's best to focus on an area with lots of grain, high mid-tones to highlights. For someone like me, with eye sight that is steadily declining, the grain focusing device is an amazing resource.
     
  9. Ghostman

    Ghostman Member

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    My eyes are perfect and I still use a grain magnifier. I wouldn't bother printing without one.
     
  10. RalphLambrecht

    RalphLambrecht Subscriber

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    wide-open, no filtration and grain focuserthenfiltration and stopping down to tthe sweet spot.
     
  11. BMbikerider

    BMbikerider Member

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    The late Canadian photographer Gene Nocon wrote a book about printing and focussing the lens on the baseboard. He explained that because B&W images are only really interested in the blue end of the spectrum the focussing should be made with a grain magnifier which has a blue filter. He has images in his book demonstrating the difference between a non-blue filter focusing image and one where a blue filter is used. It does apper quite dramatic. The focussing magnifyer is one that used to sold in UK under the Peak name but was available under different names.

    I happen to have one of these grain magnifiers but sadly no blue filter, so I use the colour gead on the LPL enlarger and dial in 50Y and 50C which gives a good blue light source. And yes I can support his theory that a blue filter does improve the focus point when using B&W. Obviously with colour neg there is no use for the blue filtration.

    I focus wide open using my Nikkor 2.8/50 and then stop down to f11 for normal negatives and F8 for those a little denser. Corner to corner sharpness guaranteed.
     
  12. darkosaric

    darkosaric Subscriber

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    Wide open with grain focuser on maximum size, then wide open on some small size (like 15x20cm) with grain focuser to check if autofocus is ok (V35 focomat).
     
  13. baachitraka

    baachitraka Subscriber

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    Perhaps, it is good to consider the focus with paper.
     
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  15. michael_r

    michael_r Subscriber

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    Not buying that. It may depend on how crap one's enlarging lens it, but I've tested it with graded paper and found no difference. Furthermore, variable contrast paper is sensitive to blue and green. So I would advise against the blue filter thing.
     
  16. ic-racer

    ic-racer Member

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    How do you focus your enlarger? -- Just like I focus a view camera!

    Method for critical focus when negative is not held flat or lens is not perfectly flat field. Focus the enlarger by moving the head on the column and focus like a view camera. Focus on the corner of the image and note where the column is. Then focus on the center of the negative without touching the focus knob, by moving the enlarger head. Then set the head to the point exactly half-way between the extremes. This will optimize your depth of field at any aperture.

    If you want, you can actually calculate the aperture to get it all in focus based on the focus spread (based on view camera focus equation of Hansma).

    N = 20/(1+M) * square root of 'dv'

    N = Aperture number
    20 = user dependent constant (circle of confusion 0.15mm for me)
    M = magnification
    'dv' = millimeters of focal depth on the enlarger column.
     
    Last edited by a moderator: Oct 21, 2013
  17. miha

    miha Member

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    This puzzles me, care to explain.
     
  18. cliveh

    cliveh Subscriber

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    What a load of tosh. Full aperture, no filtration, focus by eye the check with magnifier.
     
  19. Mainecoonmaniac

    Mainecoonmaniac Subscriber

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    I wonder if filtration is one of the factors in focusing since it changes the wavelength of the light?
     
  20. michael_r

    michael_r Subscriber

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    I posted a thread a few years back in which I tested this with different filters, moving the easel up/down etc. It was based on Ctein's focusing "gotcha" thing. I found no difference. Generally one focuses with white light or whatever filter is in place.
     
  21. summicron1

    summicron1 Subscriber

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    I focused my leitz focomat Ic once, using a grain magnifier.

    Since then, set it and forget it, as they say... (self-satisfied grin) :tongue:
     
  22. Mainecoonmaniac

    Mainecoonmaniac Subscriber

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    You lucky dude..

    But can you print anything bigger than 35mm :wink:

    Your enlarger is scary sharp. The Mercedes of enlargers.
     
  23. pentaxuser

    pentaxuser Subscriber

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    Wow! Two pages and as yet no-one seems to be saying that you should always focus at the aperture at which you intend to expose the paper. I seem to recall that in the past when this question was asked there were those who insisted that there was always focus shift from wide open to a smaller aperture irrespective of how good the lens was

    Maybe we have lost those members who believe that :D

    I must try BMbikerider's suggestion on simulating a blue "look" to see if there is any difference. I had read the same G Nocon book and while he uses a set of "before and after" examples in that book I must confess to not being able to see any difference. Gene did concede that in the book's limited reproduction range it might not be apparent and it certainly wasn't apparent to me.

    No less a printer than Tim Rudman in his book said, if I recall correctly and if I understood his meaning, that he remained unconvinced of the blue filter's value

    pentaxuser
     
  24. MattKing

    MattKing Subscriber

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    I focus at maximum aperture.

    Sometimes I check the corner focus at the exposing aperture.
     
  25. polyglot

    polyglot Member

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    No, filtering removes a selection of wavelengths by absorption. Absolutely no photons have their wavelengths changed.

    If you had a spectacularly crap lens with severe longitudinal chromatic aberration, the focus points will differ with wavelength, which means you can focus either the blue, green or red parts of the spectrum. However, a good modern enlarging lens does not suffer from such stupidity, so no filter is needed.

    You can focus with a blue filter and it will be perfectly accurate, but then so will focusing with no filter. Focusing with no filter will be far easier because our eyes are much more sensitive to the yellow/green part of the spectrum because we've evolved to see by sunlight. Note also that a VC paper can see well into the green part of the spectrum, so if you had such an example lens (maybe Gene's?) then focusing with a blue filter would give a sharp image in the high contrast layer and a defocused image in the lower-contrast layers.

    The issue is further confused by people hearing about "chemical focus", which is the problem wherein a lens with poor chromatic correction focuses UV light differently from visible light. So if you're shooting old UV processes with an ancient lens, being visually focused is slightly wrong. People then apply the same principle to enlarging, which is erroneous IMHO because:
    - longitudinal CA is mostly caused by wavelength-dependence of refractive index, so chromatic focus shift is approx proportional to wavelength ratio
    - the wavelength ratio between UV (300nm) & yellow (580nm) light is far larger than that between blue (480nm) and yellow light
    - lenses are far better chromatically corrected than they were in the 19th century
    - VC paper can see green too, so you need to focus the whole 380-570nm band

    So quit worrying, open the lens and filters up and let your eyes see properly. Once you've stopped down enough to make the corners sharp, the DOF in the print will more than cover any errors you would have made. And while there might be a measurable focus shift on stopping down, it will be much less than the DOF gained.

    Don't be confused that the grain looks softer when you stop down. It's true, it does get noticeably softer but this is a demonstration of diffraction and not focus shift.

    Edit: focus shift on stopping down is an issue caused by light being focused differently in the centre of the lens compared to the edges, i.e. the lens design is such that the middle of the lens has one focal length and the edges have a slightly different focal length, so they focus on slightly different points. I've never heard of an enlarger lens suffering from that problem, it seems to be an issue with some older retrofocus (wideangle for SLR) lenses, probably also some soft-focus lenses.
     
    Last edited by a moderator: Oct 21, 2013
  26. Mainecoonmaniac

    Mainecoonmaniac Subscriber

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    Hey Polyglot. You're a wealth of knowledge. I guess one can over obsess on focusing.

    Best,
    Don