Focusing

Discussion in 'Enlarging' started by Prime, Oct 30, 2002.

  1. Prime

    Prime Member

    Messages:
    158
    Joined:
    Sep 7, 2002
    Once I started enlarging 4x5 negatives I had trouble using grain focusers because there wasn't much grain. Is there a technique or a special type of focuser that could make it easier? Thanks.
     
  2. William Levitt

    William Levitt Member

    Messages:
    214
    Joined:
    Sep 7, 2002
    Location:
    Nuernberg, G
    Fine grained film and LF negs will have this effect on anyone and just about any grain magnifier. You might want to try one that has a higher magnification such as 25X. The average ones use around a 6 or 7X I believe.

    When I have this problem of not being able to see the grain, I usually look for an area of the negative that will give me a small, fine and delineated sorce to judge the sharpness such as eyelashes, a zipper works well too.
     
  3. Jorge

    Jorge Inactive

    Messages:
    4,532
    Joined:
    Sep 6, 2002
    Shooter:
    Large Format
    I look for straight edges. The Peak enlarging focusing gizmo is great....expensive though.
     
  4. BobF

    BobF Member

    Messages:
    205
    Joined:
    Sep 7, 2002
    Location:
    Pikes Peak
    I find that a Magna Site image magnifier is adequate for most negatives that have detail and contrast. I also have a Peak 2 that I don't often use because while it works well (more accurate on neg with little detail) I find it harder to use and have found that the results from the Mag are mostly equal. I am glad I found a deal on a used Peak as new they are very very expensive and I would be kicking myself.
     
  5. Les McLean

    Les McLean Subscriber

    Messages:
    1,609
    Joined:
    Oct 18, 2002
    Location:
    Northern Eng
    Shooter:
    Multi Format
    I look for an area of the image where the highlight and shadow meet and straddle the focussing tool across both. This is particularly efficient if this happens to fall on a straight edge as suggested by Jorge.
     
  6. dancqu

    dancqu Member

    Messages:
    3,684
    Joined:
    Sep 7, 2002
    Location:
    Willamette V
    Shooter:
    Medium Format
    </span><table border='0' align='center' width='95%' cellpadding='3' cellspacing='1'><tr><td>QUOTE (Prime @ Oct 29 2002, 10:28 PM)</td></tr><tr><td id='QUOTE'>Is there a technique or a special type of focuser that could make it easier?</td></tr></table><span id='postcolor'>
    Try a pair of the strongest reading glasses available. They are handy for
    cleaning and close inspections. Nice to have around. Ditto handled
    magnafiers. Dan
     
  7. edz

    edz Member

    Messages:
    685
    Joined:
    Dec 4, 2002
    Location:
    Munich, Germ
    Shooter:
    Multi Format
    </span><table border='0' align='center' width='95%' cellpadding='3' cellspacing='1'><tr><td>QUOTE (Prime @ Oct 29 2002, 08:28 PM)</td></tr><tr><td id='QUOTE'>Once I started enlarging 4x5 negatives I had trouble using grain focusers because there wasn't much grain. &nbsp;Is there a technique or a special type of focuser that could make it easier? &nbsp;Thanks.</td></tr></table><span id='postcolor'>
    The kind of focuser assist appropriate are those with a focusing screen and less the, albeit fashionable, microscope variety. Durst and Linhof had made some excellent units with built-in magnification and Paterson once upon a time had a low cost focuser with a large screen and no magnification. They tend--- even with films and formats where the grain is more clearly defined--- to be more accurate than the arial projection designs. The microscope units I think are appropriate for less than solid enlargers with glass-less negative carriers that by virtue of their construction are ill-suited to the use of focusing negatives.
     
  8. Ed Sukach

    Ed Sukach Member

    Messages:
    4,519
    Joined:
    Nov 27, 2002
    Location:
    Ipswich, Mas
    Shooter:
    Medium Format
    </span><table border='0' align='center' width='95%' cellpadding='3' cellspacing='1'><tr><td>QUOTE (Prime @ Oct 29 2002, 08:28 PM)</td></tr><tr><td id='QUOTE'>Once I started enlarging 4x5 negatives I had trouble using grain focusers because there wasn't much grain. &nbsp;Is there a technique or a special type of focuser that could make it easier? &nbsp;Thanks.</td></tr></table><span id='postcolor'>
    I might suggest the obvious:

    It may help to focus with the enlarging lens aperture wide open. In addition to providing the most illumination possible, it will make the apparent field of focus narrower and the ideal focus will be more easily seen.

    Second, there is always the option of using a "Substiitute - Test" negative, either/ or a coarse-grained image or gray field (read: Fast film developed in Rodinal) or one with a fine pattern (lines, dots, resolution target, etc.) to be used for focusing and then replaced with the "real" negative.
     
  9. Thilo Schmid

    Thilo Schmid Member

    Messages:
    357
    Joined:
    Sep 10, 2002
    Location:
    France
    Shooter:
    Multi Format
    </span><table border='0' align='center' width='95%' cellpadding='3' cellspacing='1'><tr><td>QUOTE (Ed Sukach @ Dec 13 2002, 03:08 PM)</td></tr><tr><td id='QUOTE'>It may help to focus with the enlarging lens aperture wide open. &nbsp;In addition to providing the most illumination possible, it will make the apparent field of focus narrower and the ideal focus will be more easily seen.</td></tr></table><span id='postcolor'>
    Ed,

    although your suggestion is based on common experience, you will find that more than a few enlarger lenses will show a significant focus shift when stopped down. Although enlarger lenses are designed for flat field projection, the practical performance is always a compromise within the variety of possible magnification factors and apertures.

    Apart from that, the performance of an enlarger lens can be bad wide open making it difficult to find any sharp grain. In my experience, it is always better to use the grain magnifier at working apertures. If the grain is sharp, your picture will be sharp, too, no matter how many degrees you can turn your focus knob around this. However, if you check the edges, too, you will see that there is usually not that much tolerance.

    Regarding the original question: if your magnification ratio is too small to get any aid from a grain magnifier, you will not need one. You will need neither the resolution nor the brightness (shorter times) of larger apertures. Simply focus with your eyes and stop down 3-4 f-stops. If your image is intentionally out of focus (i.e. contains no reference details), judge case by the case. Small magnification ratios reduce the visual impact of unsharpness and you may find it useful to add some defocus while printing. In this case, the use of a grain magnifier may even deteriorate your results.
     
  10. David A. Goldfarb

    David A. Goldfarb Moderator Staff Member Moderator

    Messages:
    17,919
    Joined:
    Sep 7, 2002
    Location:
    Honolulu, Ha
    Shooter:
    Large Format
    I agree--you should always double check for focus shift at working apertures. You would be surprised, but some otherwise very good lenses have this problem.
     
  11. Ed Sukach

    Ed Sukach Member

    Messages:
    4,519
    Joined:
    Nov 27, 2002
    Location:
    Ipswich, Mas
    Shooter:
    Medium Format
    </span><table border='0' align='center' width='95%' cellpadding='3' cellspacing='1'><tr><td>QUOTE (tschmid @ Dec 13 2002, 07:30 AM)</td></tr><tr><td id='QUOTE'>Ed,

    although your suggestion is based on common experience, you will find that more than a few enlarger lenses will show a significant focus shift when stopped down. Although enlarger lenses are designed for flat field projection, the practical performance is always a compromise within the variety of possible magnification factors and apertures.

    Apart from that, the performance of an enlarger lens can be bad wide open making it difficult to find any sharp grain. In my experience, it is always better to use the grain magnifier at working apertures. If the grain is sharp, your picture will be sharp, too, no matter how many degrees you can turn your focus knob around this. However, if you check the edges, too, you will see that there is usually not that much tolerance.

    </td></tr></table><span id='postcolor'>
    I have heard this idea of focus "shifting" at different apertures many times, but from my training in physical optics it is difficult to explain. It is interesting to note that few claim that that phenomenon also applies to camera lenses, and the last time I looked the same optical principles applied.

    My experience does not cover every enlarger lens ever made; it is largely restricted to Rodenstocks and Schnieder (on the turret of my Omega now) and in times past, Elgeet [​IMG], Federal (Rodenstock??) and a few others ... I have never observed that "focus shift" in any of them, although I will be the first to admit to the possiblity of having "lucked out" to a major degree.

    Also, in a few (actually more than a "few") hours of lens testing on the Optical Bench (dating myself here!) I've found various optical flaws and manufacturing errors - but I cnnot recall a "shifting of focus" as one of them - and come to think of it - I cannot ever remember a criteria of "Stability" (?) of Focus at Various Apertures.

    I am familar - very - with the difficulties of lens design, and just why it is that large-aperature capacity lenses are optimized for certain apertures (read: best compromize) but the parameters existing for enlarger lenses are far more restricted.

    Personally, if I ever did find an enlarger lens with anything aproaching a "focus shift", I might conduct an experiment: find out how many times I could make it "skip" across the water of my local pond.
     
  12. David A. Goldfarb

    David A. Goldfarb Moderator Staff Member Moderator

    Messages:
    17,919
    Joined:
    Sep 7, 2002
    Location:
    Honolulu, Ha
    Shooter:
    Large Format
    I've seen it with a Componon-S and old Dagors have a notorious shift.

    I think the explanation is not that the focal length of the lens actually changes, but that it is an illusion resulting from uncorrected spherical abberation being corrected when the lens is stopped down.
     
  13. clay

    clay Subscriber

    Messages:
    1,124
    Joined:
    Nov 21, 2002
    Location:
    Asheville, N
    Shooter:
    Multi Format
    >>>It is interesting to note that few claim that that phenomenon also applies to camera lenses, and the last time I looked the same optical principles applied.

    Actually quite a few of the old dagors and protars (view camera lenses) will shift focus significantly as you stop down. I have a box full of negatives to prove it. This has been discussed ad nauseum in many of the online discussion groups.

    Clay
     
  14. Ed Sukach

    Ed Sukach Member

    Messages:
    4,519
    Joined:
    Nov 27, 2002
    Location:
    Ipswich, Mas
    Shooter:
    Medium Format
    </span><table border='0' align='center' width='95%' cellpadding='3' cellspacing='1'><tr><td>QUOTE (David A. Goldfarb @ Dec 13 2002, 03:23 PM)</td></tr><tr><td id='QUOTE'>
    I think the explanation is not that the focal length of the lens actually changes, but that it is an illusion resulting from uncorrected spherical abberation being corrected when the lens is stopped down.</td></tr></table><span id='postcolor'>
    I agree. Having worked in Optical Quality Control, I have been *very* sensitive to careful identifcation of optical properties and specific errors. *Apparent* quality can shift significantly as the parameters of testing change. A smaller aperture will significanly increase the
    "depth" of focus- properly known as "hyperfocal distance", and edge-to-edge resolution, by restricting the area open to both spherical and chromatic abberations, curvature of field... (and a few other factors) until diffraction effects kick in.

    Incidentally, one of the most valuable accessories I own are 40.5mm "Soft" filters. I bought two of them solely out of curiosity from a "bargain box" as they were the precise size to fit my Rodenstock enlarging lenses. Indispensable for printing Portraits... they do a remarkable job in eliminating minor (and some not-so-minor) skin flaws. I *do* have to remember to remove them when I focus.

    I prefer to keep the sharpness in the negative (i.e. not using "Softars") and "adjust" as necessary in the enlarger.
     
  15. Thilo Schmid

    Thilo Schmid Member

    Messages:
    357
    Joined:
    Sep 10, 2002
    Location:
    France
    Shooter:
    Multi Format
    </span><table border='0' align='center' width='95%' cellpadding='3' cellspacing='1'><tr><td>QUOTE (Ed Sukach @ Dec 13 2002, 11:01 PM)</td></tr><tr><td id='QUOTE'>I have heard this idea of focus "shifting" at different apertures many times, but from my training in physical optics it is difficult to explain.</td></tr></table><span id='postcolor'>
    Ed,

    this is not a real focus shift, it is an apparent focus shift. Some aberrations can actually be diminished by a slight defocus (i.e. an offset to the extension computed by the exact focal length and the exact magnification ratio/subject distance). Some of these aberrations are influenced by the aperture diameter. So stopping down a lens can shift the apparent focus towards real focus (usually not the other way round). David probably meant the same thing. Depending on design goals, lenses show different behaviors here. The primary design goals of enlarger lens are: resolution and flat field. Camera lenses usually have other or additional design goals, resulting in different focus-shift behavior, too
     
  16. Ed Sukach

    Ed Sukach Member

    Messages:
    4,519
    Joined:
    Nov 27, 2002
    Location:
    Ipswich, Mas
    Shooter:
    Medium Format
    </span><table border='0' align='center' width='95%' cellpadding='3' cellspacing='1'><tr><td>QUOTE (tschmid @ Dec 14 2002, 02:26 AM)</td></tr><tr><td id='QUOTE'>
    This is not a real focus shift, it is an apparent focus shift. Some aberrations can actually be diminished by a slight defocus (i.e. an offset to the extension computed by the exact focal length and the exact magnification ratio/subject distance). ...</td></tr></table><span id='postcolor'>
    Again, I agree.

    You may have noticed that I wrote about "Optical Bench" testing - that dates me... I think the last lens testing I did was around 1990. Now, most lens quality is defined in terms of Modulation Transfer Function (MTF).

    An excellent article is "Understanding Lens Contrast And the Basics of MTF", by Mike Johnstone, available at The Luminous Landscape web site, http://www..luminous-landscape.com under "Tutorials", "Understanding Series"...

    Luminous Landscape is a good site, but strongly tilted towated "digital" imaging.
     
  17. Ed Sukach

    Ed Sukach Member

    Messages:
    4,519
    Joined:
    Nov 27, 2002
    Location:
    Ipswich, Mas
    Shooter:
    Medium Format
    </span><table border='0' align='center' width='95%' cellpadding='3' cellspacing='1'><tr><td>QUOTE (Ed Sukach @ Dec 14 2002, 05:54 AM)</td></tr><tr><td id='QUOTE'></span><table border='0' align='center' width='95%' cellpadding='3' cellspacing='1'><tr><td>QUOTE (tschmid @ Dec 14 2002, 02:26 AM)</td></tr><tr><td id='QUOTE'>
    This is not a real focus shift, it is an apparent focus shift. Some aberrations can actually be diminished by a slight defocus (i.e. an offset to the extension computed by the exact focal length and the exact magnification ratio/subject distance). ...</td></tr></table><span id='postcolor'>
    Again, I agree.

    You may have noticed that I wrote about &quot;Optical Bench&quot; testing - that dates me... I think the last lens testing I did was around 1990. Now, most lens quality is defined in terms of Modulation Transfer Function (MTF).

    An excellent article is &quot;Understanding Lens Contrast And the Basics of MTF&quot;, by Mike Johnstone, available at The Luminous Landscape web site, http://www..luminous-landscape.com under &quot;Tutorials&quot;, &quot;Understanding Series&quot;...

    Luminous Landscape is a good site, but strongly tilted towated &quot;digital&quot; imaging.</td></tr></table><span id='postcolor'>
    Correction: One too many periods in the address - Should be:
    http://www.luminous-landscape.com.
     
  18. clogz

    clogz Subscriber

    Messages:
    2,842
    Joined:
    Dec 28, 2002
    Location:
    Rotterdam, T
    Shooter:
    Multi Format
    An old trick to help you to focus: take an old, preferably dense, negative; take a ruler and a needle and make a nice scratch on the emulsion. You can focus on that.