Stopping Down Enlarger Lens Focus Question Newbie

Discussion in 'Darkroom Developing and Printing' started by SofaKing, Apr 17, 2004.

  1. SofaKing

    SofaKing Guest

    I'm a beginner. So go easy. I'm printing B&W (first prints done this week in
    fact). When I stop down my enlarger lens (exposure around 20secs. at f22)
    does focusing becoming less critical, ie. is it similar to a camera in that
    I'm increasing depth of field therefore I can be out a bit? What are the
    advantages to stopping down as opposed to using lower f-stop values (f5.6).
    Am I losing contrast or sharpness in the print? Any grain issues? Does
    leaving the light on that long change any of the characteristics of tone
    distribution? Thx.
     
    SofaKing, Apr 17, 2004
    #1
    1. Advertisements

  2. Yes; it increases the depth of field of the projected image in exactly the
    same way as with a camera taking a picture. Smaller aperture = greater depth
    of field = more latitude in misfocusing.
    Just what was described above: increased overall sharpness.
    Only that what grain is visible will be more sharply in focus. That could be
    good or bad, depending.
    Nope; you're apparently thinking of reciprocity failure characteristics. I
    don't think this becomes a problem with photo paper until your exposures are
    into the range of several minutes or more.


    --
    I was quickly apprised that an "RSS feed" was not, as I had naively
    imagined, some new and unspeakable form of sexual debauchery practised
    by young persons of dubious morality, but a way of providing news
    articles to the cybernetic publishing moguls of the World Wide Wait so
    they can fill the airwaves with even more useless drivel.

    - Cynical shop talk from comp.publish.prepress
     
    David Nebenzahl, Apr 17, 2004
    #2
    1. Advertisements

  3. SofaKing

    SofaKing Guest

    So maybe other than being slower to print no real disadvantages mostly
    advantages, good. I also like stopping down because it's a little bit more
    forgiving when I want to increase or descrease exposure too. Thx.
     
    SofaKing, Apr 17, 2004
    #3
  4. SofaKing

    Bruce Guest

    When I stop down my enlarger lens (exposure around 20secs. at f22)
    No, all the image focus is in the negative, your enlarger will not make focus
    where there is none. Oft time a grain focuser is used to focus on the grain of
    the negative which has nothing to do with image focus. If you missed focus at
    the camera stage you will not get it back of come close at the printing stage.
    In the darkroom all you can do focuse the negative to sharpness and let the
    image fall where it will.
    values (f5.6).

    Every lens has a "sweet spot". It is usually mid way between max and min
    apature, maybe 5.6 or 8. Enlarging lenses are flat focus lenses in that they
    project a flat negative image onto a flat piece of paper, unlike camera
    lenses.. All the DOF the image has in in the negative, closing the apature
    will not increase image DOF. It will lengthen exposure time which is a good
    thing. I personally like exposures of more than 30 seconds and if burning or
    dodging is involved I will stop down as much as possible to insure enough time
    for burning or dodging.


    _________________
    Ready, Fire, AIM.
    Bruce
    Brooklyn, N.Y.
     
    Bruce, Apr 18, 2004
    #4
  5. SofaKing

    jjs Guest

    With my 35mm printing (on a focomat), stopping down to F22 decreases
    sharpness and blurs grain.
     
    jjs, Apr 18, 2004
    #5
  6. You missed my point, or maybe I didn't state it clearly enough: I'm not
    claiming that greater depth-of-field at the enlargement state can make up for
    poor focus in the picture-taking stage. (That would be quite a feat, with
    metaphysical and quantum-mechanics implications.) What I meant is that
    stopping down an enlarging lens gives greater depth of field so far as the
    negative being projected is concerned, and will allow more focusing errors to
    still result in a sharp image of the negative (which may well be out of focus,
    but that's another story).


    --
    I was quickly apprised that an "RSS feed" was not, as I had naively
    imagined, some new and unspeakable form of sexual debauchery practised
    by young persons of dubious morality, but a way of providing news
    articles to the cybernetic publishing moguls of the World Wide Wait so
    they can fill the airwaves with even more useless drivel.

    - Cynical shop talk from comp.publish.prepress
     
    David Nebenzahl, Apr 18, 2004
    #6
  7. Whoops: realized too late that you weren't replying to *my* reply. But the
    point remains, since I don't believe the O.P. was asking whether stopping down
    an enlarging lens could increase depth of field *in the original negative*.
    (At least I hope they weren't.) In other words, when he asked "does focusing
    become less critical?", he was referring to focusing the enlarging lens, not
    the camera lens.


    --
    I was quickly apprised that an "RSS feed" was not, as I had naively
    imagined, some new and unspeakable form of sexual debauchery practised
    by young persons of dubious morality, but a way of providing news
    articles to the cybernetic publishing moguls of the World Wide Wait so
    they can fill the airwaves with even more useless drivel.

    - Cynical shop talk from comp.publish.prepress
     
    David Nebenzahl, Apr 18, 2004
    #7
  8. So you're encountering diffraction effects, right? Or focus shift, one.


    --
    I was quickly apprised that an "RSS feed" was not, as I had naively
    imagined, some new and unspeakable form of sexual debauchery practised
    by young persons of dubious morality, but a way of providing news
    articles to the cybernetic publishing moguls of the World Wide Wait so
    they can fill the airwaves with even more useless drivel.

    - Cynical shop talk from comp.publish.prepress
     
    David Nebenzahl, Apr 18, 2004
    #8
  9. Your questions are very good. Some of the replies are not.
    Small aperature will increase depth of field, but not enough to overcome
    poor initial focus.

    What are the
    (f5.6).

    None, as to the resulting image.
    You are loosing sharpness because of optical defraction when you use your
    lens much below f8.0. This a matter of light itself, not lens design or
    construction. The only way a close comparision would not clearly show this
    for you would be if you were using a very low quality lens or were out of
    focus.
    No. If you want longer print times, which can be useful, use a lower output
    bulb or insert neutral density filtration above the negative, and [assuming
    35mm printing with a 50mm lens] keep the lens aperature in the 5.6 - 8.0
    range.
     
    Randy Stewart, Apr 18, 2004
    #9
  10. SofaKing

    jjs Guest

    Yes, diffraction. I can watch the grain go soft through the focusing
    scope. Refocusing has no effect. So I always print stopped down two from
    wide open. If the exposure is too short to comfortably dodge and burn, I
    use an ND filter.
     
    jjs, Apr 18, 2004
    #10
  11. I always refocus after stopping down. Ctein, I think it was, once wrote
    in the journal Photo Techniques about focus shifts that occur after the
    addition of filtration. He stated that by adding yellow or magenta
    filtration, you effectively alter the average wave length of the light
    going through the enlarger, thus affecting the plane of sharpest focus
    and causiong a slight focus shift to occur. While I am not sure that he
    is right, I do find that once I have added filtration and stopped down,
    I do need to refocus to get the sharpest possible image.


    Francis A. Miniter
     
    Francis A. Miniter, Apr 18, 2004
    #11
  12. Use f/5,6 to f/ 8,0, no smaller. That is the optimum aperture for most
    enlarging lenses.
     
    Michael Scarpitti, Apr 18, 2004
    #12
  13. SofaKing

    CCDee Guest

    Yes I was referring to focussing the enlarger.

     
    CCDee, Apr 18, 2004
    #13
  14. SofaKing

    CCDee Guest

    F8. Got it. So my print times will be shortening as well. If I was printing
    20 seconds at F22 is there a rule of thumb of calculating how much time
    opening the aperture by three stops...um let me guess 20, 10, 5, 2.5 secs?
    sound about right?

     
    CCDee, Apr 18, 2004
    #14
  15. SofaKing

    CCDee Guest

    What are the visible artifacts of diffraction, what will I see or not see,
    in my prints if I compare one printed at say f5.6 to one printed at f22? Why
    does Rodenstock make lens that stop down that far then? Will anyone but me
    notice?
     
    CCDee, Apr 18, 2004
    #15
  16. Yes. It's an actual rule, not a rule of thumb.


    --
    I was quickly apprised that an "RSS feed" was not, as I had naively
    imagined, some new and unspeakable form of sexual debauchery practised
    by young persons of dubious morality, but a way of providing news
    articles to the cybernetic publishing moguls of the World Wide Wait so
    they can fill the airwaves with even more useless drivel.

    - Cynical shop talk from comp.publish.prepress
     
    David Nebenzahl, Apr 18, 2004
    #16
  17. Stopping down any lens reduces optical abberations, increases depth of
    field, depth of focus, contrast and resolution, but only to a point.
    After that point, resolution, contrast, and "sharpness" degrades due to
    diffraction. Most lenses, enlarger or taking, obtain the "best"
    balance between the improvements gained by stopping down and the
    degradation due to diffraction 2 to 3 stops down from wide open.

    Most b&w papers perform best in the 10 to 60 second range. With longer
    exposures, they begin to suffer from reciprocity failure -- loose
    speed, change contrast -- just like film does with exposures longer
    than they were designed for.

    To obtain critical focus, buy a grain magnifying focusers. It needn't
    be an expensive one. (I use a 20 year old Patterson that I bought new
    for about $20 and it works just fine.) After composing and focusing
    wide open, stop down to your printing aperture and check the focus to
    be sure there has been no focus shift. Most modern Plasmat type
    enlarging lenses, that is, 6 elements in 4 groups, don't suffer from
    this, but cheaper lenses with less elements are more apt to.
     
    Stefan Patric, Apr 18, 2004
    #17

  18. If you have a high-mangification grain focusser, you can see which is
    the optimum aperture by looking at a projected image and running the
    aperture scale from wide open to minimum. If it is a good lens, the
    optimum will be about 5,6 to 8,0 (for a 50mm).
     
    Michael Scarpitti, Apr 18, 2004
    #18
  19. SofaKing

    Dan Quinn Guest

    Or, stop down, add filtration, then refocus?
    It's been some time since this subject has come up. As
    I recall stopping down was in itself the matter of concern.
    I think a case MAY be made for refocus due to one or the
    other or both togeather; that is filtration and/or stopping
    down.
    I use graded paper; no filters needed. I am concerned though
    with focus shift on stopping down. Off hand I can't think of any
    reason a smaller aperature would change the focal length of a lens.
    I know I don't worry about it when a camera lens is involved.
    Perhaps a LARGE format user could shed some light. And some dark
    for that matter. Dan
     
    Dan Quinn, Apr 19, 2004
    #19
    1. Advertisements

Ask a Question

Want to reply to this thread or ask your own question?

You'll need to choose a username for the site, which only take a couple of moments (here). After that, you can post your question and our members will help you out.