grain focuser questions

Discussion in 'Enlarging' started by JeffD, Feb 23, 2005.

  1. JeffD

    JeffD Member

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    I am new to enlarging 4x5. I have a grain focuser left over from my 35mm enlarging days which seemed to work fine way back when.

    I now have a 4x5 enlarger, and, when projecting a 16x20 image, in no way can I check the edges or corners- the view in the scope goes from a small "ufo" saucer shaped image, to no image at all at the edges.

    I guess my old cheap grain focuser is not good for this.

    I am now using a 135mm lens.

    Is this the fault of my focuser, my lens, or what?

    Is there a feature in a grain focuser I should look for to be able to check the edges of my print?
     
  2. martin@jangowski.de

    martin@jangowski.de Member

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    Most grain focusers are made to be used only in the center of the print. I know only the different models of the Peak enlarger that are useable in the edges, notably the Peak #1 (usable 30 deg. off axis)

    Martin
     
  3. edz

    edz Member

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    Correct.
    Does not matter.
    Its not a fault but (a shortcomming of) the design of your grain focuser. The only grain focuser to my knowledge that allows for view outside of the center is the Z. Koana concept focusers with rotating ocular sold as the Peak#1 (2000) or Micromega. If your enlarger, however, is properly aligned then the center focus should be quite sufficient-- if not most appropriate--- to the task. In a properly designed system, afterall, if the negative is correctly focused in the center then it'll be focused as best as can be at the edges---and, if not, there's hardly much one can do beyond trying to align things and maybe turning the aperature down. I view the Peak more as a diagnostic, aligment and test instrument than as a grain focuser. In focusing I see sometimes advantages to using my (historical) Tourret Scoponet due to his higher form or one of my mirror boxes.
     
  4. Claire Senft

    Claire Senft Member

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    Not a consideration for me

    I use a Scoponet. It is not any good when used very far off axis. I enlarge with glass carriers on an enlarger that stays in alignment. I use an enlarging lens whose field is adequately flat...for 35mm I use a 63mm 2.8 EL Nikkor N. It is an exceeding satisfactory lens. Because of this I do not find the lack of ability to view the edges or corners of the field to be any short coming whatsoever. When the negative is put into the carrier I use a light table and check the negative for sharpness and for dust with a 7 power loupe.

    There are, however, a few cautions to be observed in using magnification in focussing the enlarger.

    Firstly there are two types of devices for doing so. I). A ground glass device that functions similar to looking at a focussing screen on a camera.
    Generally a dimmer image and lesser magnification is used with this type of device.

    Secondly, an Aerial image magnifyer that is used to judge an aerial image of the projected negative. Generally, thes devices use more magnification than the ground glass variety. One must use care to not focus using this type of device with filters in the light path. Your results can be compromised by the nature of human visual response. Patrick Gainer, in Photo Techniques magazine wrote a very worthy article about this. He is to be commended.

    Either type of device is capable of being a very large improvement in achieving proper focus with an enlarger.
     
  5. JeffD

    JeffD Member

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    Thanks! I was given an old Beseler 4x5 enlarger, and I did my best to adjust it to where the negative carrier plane, lens plane, and baseboard are parallel.

    I guess I was hoping for a verification that I did this correctly by seeing nice grain, when focused, all across the image, when projected moderately large (16x20).

    Looks like most grain focusers won't do this.

    I suppose I could get some kind of 4x5 test negative, with a fine test pattern across it, and print it, to see if I get much "fuzziness" near the edges.
     
  6. Claire Senft

    Claire Senft Member

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    misaligment

    Misalignment will not take the form of having soft or out of focus edges. It will take the form of one side of the print being sharp when another side is visibly less sharp but that you know is sharp all over. Even if you are not going to use glass carriers, putting a negative between glass will at least get negative buckling removed from your evaluation. Care is required in determining if the misalignment is due to the enlarger or if it is due to a lens with misaligned element(s). Ctein's book Post Exposure will tell you how to test for both. I believe that any top qualty enlarging lens made for 4x5 use should have an optimum aperture of no more than 1 stop down from wide open.
     
  7. gainer

    gainer Subscriber

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    There are times when a substitute target is useful. A cleared piece of film with a scratch or two on the emulsion side is easily focused. It is more useful when you are using a glass carrier. You can scribe a line with a razor blade or Xacto knife.

    I wrote that article for Photo Techniques because there was a lot of discussion about errors of focusing due to supposed inadequate correction of lenses for blue and near UV light. Astronomers have known for years that the chromatic aberration of the eye makes the telescope objective look bad. What I found in my experiments is that there are two effects of chromativ aberration of the eye. One is due to the fact that the resolving power of the eye is best with green or white light. As a consequence, the spread of focusing errors is greater as the light is either bluer or redder than the color of best resolution. This being the case, one would expect and indeed finds that there is a bias away from the point of best focus when the focusing light is not green or white. You can demonstrate what causes this bias by viewing a printed page through deep red and deep blue filters in succession, bringing the material each time to the position of closest clear vision. You may be surprised at the difference in position of clearest focus.
     
  8. Bob Carnie

    Bob Carnie Subscriber

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    Jeff
    When I want to see if my set up is ok on any 4x5 enlarger I do the following.
    1. use glass carrier
    2. 35 mm negative
    3. 12x18 image size
    4. make a print, focus on the center
    5. If the grain is sharp in the middle , middle top/bottom, edges middle/top/bottom, then you know your enlarger is aligned. If you do not see grain in these 9 points then leveling the negstage and film stage to baseboard is due.
    There is lots of past threads on this issue , where you can get some good tips.
    I have peak and other cheaper grainscopes and I always focus on the middle area . try to find a contrast difference area for best results.
     
  9. dancqu

    dancqu Member

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    Four. I find correct focus is best determind using both eyes
    wide open. For that I use high diopter reading glasses.

    A fourth device is a two to four power magnifying glass. Lets
    be resonable. With either of the two devices I've mentioned
    one is very closely and at some magnification seeing a full
    sized projected image.

    I've a grain magnifier and think it good for checking grain. Dan
     
  10. Terry Hayden

    Terry Hayden Member

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    plane of focus

    My .02 -

    Since we use large negatives here at work ( 9x9 ) and make fairly large
    enlargements ( up to 40 x 50) a an observation may be in order:

    We have not found any ( componon-s, el nikkor, etc) enlarger lenses that project on a truly flat plane. In other words, when the center is in focus, the edges are not as sharp.

    Generally we have found a "dome" of sharp focus. When the edges are sharp, the center point of sharp focus is above the easel.

    This is true when all four edges are sharp. It's not an alignment issue since we use a restitutional enlarger that allows for tip and tilt of the lens stage to maintain proper scheimpflug (sp?) orientation.

    The negatives are in a glass carrier so it's also not a flatness issue.

    Of course stopping down takes mostly takes care of it. Out of habit now, we get the edges sharp, then refocus off center ( the old adage of a 1/3 in front of the plane of focus and 2/3 behind for depth of field).

    Just a bit of info from experience.
     
  11. Bob Carnie

    Bob Carnie Subscriber

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    Hi Terry
    A bit confused with your post, are you suggesting a flat field enlarging lens works the same way as a camera lens. ie stopping down the lens will give you depth of field??
    In my experience this is not the case, maybe you could let me know what lens does this magical feat for enlarging and sharpness issues. I would be extremely happy to find this lens.
     
  12. Terry Hayden

    Terry Hayden Member

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    dof enlarging

    Hello Bob,

    Well, any lens with an aperture offers more d.o.f. at a smaller f stop.

    That doesn't have anything to do with a "flat field" or not flat field lens.

    It's basic optics.

    My point was that these flat field lenses aren't all that flat. The d.o.f.
    effect does indeed apply, and alleviate some of this problem.

    Anyone else want to chime in- I'm pretty sure that I'm right on this,
    Butt Hay - maybe I'll learn something new...
     
  13. Ed Sukach

    Ed Sukach Member

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    You are absolutely right. I often wonder why some think that an enlarging lens is somehow - magically - subject to different optical laws. A Lens is a lens is a lens...

    Try it ... focus, using a grain focuser, with the lens wide open, and, first shifting so that you are again out, re-focus at a smaller f/stop. The grain will "snap" into focus much more decisively with the large aperture. That is the major source for the myth that there is a focus shift with different apertures - the lens is focused non-critically at a small f/stop, and when opening up to a larger one seems to be out-of-focus due the the reduced depth of ... not field, since this is a projection lens - but focus.
     
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  15. gbroadbridge

    gbroadbridge Member

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    A lense is a lens :smile: DOF effects are the same i.e. smaller aperture will always help with any focus issues in relation to the negative and the projected image especially if you have a lense whose focus varies across the projected plane.

    The problem of course is that the smaller the aperture, the longer the exposure - so you end up with blurring caused by unstable enlarger mountswhen using 30 sec exposures at f32

    Graham.
     
  16. gainer

    gainer Subscriber

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    Every lens has an optimum aperture for resolution. When the lens opening is too large, lens aberrations are apparent. When the opening is too small, diffraction limits resolution. It is impossible to design a perfect glass lens that will have diffraction limited resolution at all openings, no chromatic aberration, no astigmatism, perfect flatness of field, etc. The best we can do is close enough, and sometimes that costs much coin of the realm, depending on how close is close enough. I don't have a 50 mm enlarging lens that is better at f/8 than it is at f/5.6 or better at 2.8 than at 5.6.
     
  17. Bob Carnie

    Bob Carnie Subscriber

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    Hi Tom Ed
    sorry guys, I dissagree.
    Your post said depth of field, which is associated with the 1/3-2/3 principle associated in a camera taking Lens.
    In enlarging we are concerened with depth of focus which is extremely minimal with an apo chromatic enlarging lens.
    I have done tests with different f stops from wide open to fully closed and I can assure you that there is no difference.
    Simple test , glass carrier, focus wide open ,, then adjust density for each apeture click from wide to close down .. make a print and tell me that the focus is better on any of the prints.
    I doubt it very much.
    In fact I have found the lens at minimum apeture to be a percieved softer not sharper ,only due to the light bouncing around trying to get through this minimum diaghram.
    My position is from practical experience and some optic theory I took years ago , I am certain their are others on this forum who can clarify this , in a thoretical manner.Better than my description.
     
  18. Terry Hayden

    Terry Hayden Member

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    dof

    Okay, it's true, in enlarging we are indeed talking depth of focus.

    However, the same principals apply.

    Try this web site -

    http://www.matter.org.uk/tem/depth_of_field.htm

    Read it with an english accent - makes it more authoritative...

    Later,
    Terry
     
  19. gainer

    gainer Subscriber

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    That's not the test you want. You should focus stopped down and then open up. You will see the depth of field-focus when you try to focus stopped down, as the uncertainty will be greater stopped down. Also, when doing these tests, you should leave the lens-film distance constant and move the head on the column to sharpen the focus visually. Use a meter stick to measure the position of the head. After each trial, move the head on the column a small amount to disturb the focus, then see if it returns to its previous position when you sharpen the focus by moving the head.
    The depth of field and depth of focus are interrelated. You cannot change one without changing the other. If you do enough of these trials at each f-stop, you can get an idea of the mean and standard deviation of the head positions. You can repeat the whole series of tests with a different color of focusing light. There is among some an idea that one should focus by the color of light you plan to use in making the print. Unless this is green or white, you will find it is not true. Green or white is best to use for focusing no matter what color you plan to use for the print. Any lens you are likely to have on your enlarger is much better than your eye. If it is not, then you have a real problem.
     
  20. Ed Sukach

    Ed Sukach Member

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    Please re-read my post. I was very careful to choose the term "Depth of Focus" - applying to a projection lens.

    You say you focus "wide open" and then stop down, and there is "no improvement". Of course, but that is not a measure of acceptable resolution at varying apertures, given focusing distances other than "ideal" - a.k.a. "Depth of Focus".

    Projection or Taking lens, the same optical theories apply ... unless there Is another set I don't know about. Could you be more specific?
     
  21. Bob Carnie

    Bob Carnie Subscriber

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    Ok, maybe I am not understanding something here and without getting pissed I will make a statement and I would like someone to tell me in practical terms why my statement is incorrect.
    When printing I focus at wide open apeture. I see grain and I know that I am sharp , I then stop down two stops to print , mainly for time applications. I also see grain when I close down.
    Is someone here saying that I am sharper at f8 than at f4????
    If I close down and focus at f16 and see grain then open up to f4 and see grain am I decreasing my sharpness.

    Sorry to be a pain in the neck here , but just do this simple test and I assure you the grain is the same at any fstop when enlarging.
    One of the posters suggested that focusing on the edges and then closing down the image would snap into place. > the only way I could see this happen is if the poster was not using a glass carrier and this snapping into focus is the negative popping out of position as the negative heats up( therefore the practice of glass carriers)

    I would like someone to give a practical explanation to this so called DOF experience using an enlarger . To be honest I have never seen it and I have printed a few negatives in my time.
     
  22. gainer

    gainer Subscriber

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    Don't be too upset about getting pissed. Just don't do it on us. Let me tell you a story. One day when working at NASA, a colleague and I were in a conference room engaging in an attempt to solve a technical program. We would get quite excited about some point or another and our voices would rise. Outside the room the secretary was thinking, as I found out later, that we were about to engage in fisticuffs. Then we went down to the Coke machine, flipped a coin, drank our cokes, came back and went at it again.

    Just pretend we are together in the same room having it out about some technical point.

    With regard to the technical point, I doubt that you will be able to focus as exactly as you think with the lens stopped down. With most lenses nowadays, the resolution will go down from 4 to 8. I can't see how the grain will look as sharp at 8 as at 4 with a 2.8 lens. I can tell the difference between 4 and 2.8 with my 50 mm APO Rodagon. 5.6 is about as good as it gets.

    Each lens is designed to be optimum at a particular magnification. Most 50 mm enlarging lenses are optimized at 10, I believe. Try your experiment at 10X magnification. Focus on a nice, grainy Rodinal negative wide open and watch the definition of the grain as you stop down. It should get sharper, then fuzzier as you pass through the aperture where diffraction takes over.
     
  23. Bob Carnie

    Bob Carnie Subscriber

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    hi Gadget

    Actually I am not getting pissed just I find this DOF issue with enlarging lenses and some of the statments made go against the grain and I humbly have to disagree .
    I have been taught to focus wide open when printing and then close down to two stops . I have been told by my instructors as well as the lens manufactures that this is the proper way of focusing for critical sharpness.
    I have found out that by practical experience that the grain is the same at both f stops. I rarely focus down 3-4 stops but when I do I use the above method and I always find my images grain sharp.

    I should state what I find most frustrating is the issue that if you close down the lens you will get the same effect as DEPTH OF FIELD when one takes a photograph.

    When enlarging we are focusing on an emulsion that is lying flat much like the easal we are projecting onto. If I find that the grain is sharp at different apetures at a given magnification with out refocusing , I believe it is not attributed to DEPTH OF FIELD but to a perfectly aligned enlarger in conjunction with using glass carrier to hold the negative flat and also using a Apo rodogan lens that is a nice piece of glass.

    I am not arguing that DEPTH OF FOCUS is not present in this scenerio.

    If I am wrong and as you suggest that the grain is less sharp at different apetures, with all of the above in place(glass carrier, exact same magnification, aligned enlarger) and as you say it is hard to focus at the lower apetures, how on earth would you suggest to focus the enlarger ???

    In your senerio I would have to work at a wide open apeture as as I close down the focus shifts, as I would not be able to go to a lower apeture to focus because lack of light.

    I am now going to have a coke and wait for you to insert your coins into the machine and join me on this discussion

    best regards
    bob
     
  24. Ed Sukach

    Ed Sukach Member

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    There is a lot of confusion here in definitions. Resolution is related to, but not the same as "depth of field / focus". Image quality is related to, but not the same as depth of field / focus. Diffraction is something else entirely.

    It is true that *every* lens - not exclusively enlarging lenses - has an "Optimum" f/stop. However, optimum does NOT mean that all others are useless. If this were true, all lens manufacturers, of both camera and enlarging lenses would not equip them with iris diaphragms.

    I'm tying to think of a way to define depth of focus/ field concisely, without first going into an extensive "course" in basic optics. I'll try...

    Depth of focus is the distance separating of two planes perpendicular to the optical axis, deviating in either direction from an ideal focus, where acceptable resolution is maintained. Not "the best possible resolution", but acceptable. An example: A given lens is perfectly focused at 10cm. Using a finite f/stop, and lessening the focusing distance to 9cm, the resolution (~ squinting, approximately - call it "sharpness") is still "acceptable", that is, it does not exceed an arbitrarily chosen value for resolution. Moving in the other direction, it is still "acceptably sharp" at 12cm.

    The depth of focus here is 3cm - between 9cm and 12cm.

    I hope this conveys the idea. For better, more polished information, I can only suggest reading a book on Basic Optics.
     
  25. Bob Carnie

    Bob Carnie Subscriber

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    Hi Ed

    would this acceptable area on both sides as you suggest be called the *circle of confusion*.
    being the small area of depth of focus that the human eye will accept as sharp.
    I suggest we are both talking about the same thing here, My only concern is too not confuse the issue by considering * depth of field * as an applicable method of setting up an enlarger because the 1/3-2/3 idea is unrealistic when focusing on a flat playing field.
    I am going back quite a few years from when I studied optics at college so maybe my memory is rusty, but from focusing thousand's of negatives my practical knowlege tells me that when focused at f4 you will get the same level of sharpness as if you stop down to f11 and adjust your printing time accordingly. (using a glass carrier and a aligned enlarger)
     
  26. Ed Sukach

    Ed Sukach Member

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    We are not talking about the same thing.

    A circle of confusion has been defined as: "When we try to focus all the rays of light from a lens into one point, we cannot. The best we can do is to form a circle of light. That circle's deviation from an infinite point - is the "Circle of Confusion". It can be reduced by eliminating some of the rays toward the outside extremities of the lens - restricting the image to the central rays... in other words, using a smaller f/stop."

    Formula for determining Depth of Focus / Field:

    First calculate the "Hyperfocal Distance - the distance where the lens, when focused at infinity, will produce an acceptably sharp image of the nearest object.

    Hyperfocal Distance = ((FxF)/f) x (1/C)
    Where:
    F= Focal length of the lens
    C= Circle of confusion
    f = f/stop = diameter of aperture / Focal length of lens

    An example = A 50mm lens at f/8, with a Circle of Confusion of 1/100mm:

    H= ((50 x 50) / 8) x (1 / (1/100))
    H= 312.5 x 100
    H= 31250mm; 31.25 meters

    Everything from 31.25 meters to infinity will lie within a Circle of Confusion (acceptably sharp) of 1/100 mm.

    It is obvious that reducing the f/stop (increasing numerically) will decrease the Hyperfocal distance.

    Now, Depth of Field:

    For the nearest sharp plane:
    (H x D) / (H + ( D - F))

    Where:
    D = Distance focused upon
    H = Hyperfocal distance
    F= Focal length of lens

    and the farthest sharp plane:

    (H x D) / (H - ( D - F))

    Working the same lens, same aperture and and the same circle of confusion; focused at 25 meters:

    Np = (31.25 x 25.0) / ((31.25 - (25 - .05))
    Np = 12.4 meters

    The Farthest plane:

    Fp = (31.25 x 25.0) / ((31.25 - (25.0 - .05))
    Fp = 124.0 meters.

    Someone check my math!!!

    I haven't cracked those books for one hell of a long time!!! I just realized HOW long!!