Grain Focusersgreenspun.com : LUSENET : B&W Photo - Printing & Finishing : One Thread
I have five different grain focusers and only two of them focus at the same point. I have three MicrSights of which two focus the same. The third one is way off. These are all cast metal bodies, too. The Omega grain focuser (also cast metal) and the Scopnet are both different also. What does this mean for the poor slob who shells out $50 to 100+ bucks? Is he getting a product that does its intended job? Are these things not calibrated? I'm looking for answers, Frank
-- frank Ward (email@example.com), March 31, 2000
I just got a MiniSight after many years of focusing by sight only... seems to work well, I'm able to focus the image in a second or so compared with the 'ohh too far one way, back the other way, ohh too far again method' I used to use! Don't know why someone didn't convince me to get one sooner.. like about 15 years sooner!
If you use the focusers that you think are 'off' are the prints out of foucs? If so they should be turfed (or sold!) Why have you got so many of them?
I agree that you'd think they come out of the factory being accurate but being cast, manufacturing tolerances would not be as accurate as something that was machined (usualy!)
I'm really happy with my MiniSight :)
-- Nigel Smith (firstname.lastname@example.org), March 31, 2000.
I used to have a problem with my prints being a little soft many years ago and then a friend told me about putting a thickness of the paper I was using under the grain focuser's base, walah, no more problem. Pat
-- pat j. krentz (email@example.com), April 01, 2000.
It's been a while since I used a Micro Sight. As I recall, I adjusted the eyepiece until the reticle or cross hair was in sharp focus for my eyes. I always used a sheet of the same paper I was using in the easel. It did make a difference if I forgot to put the paper in. I found the large Micro sight to work the best of what was available.
-- Tony Brent (firstname.lastname@example.org), April 01, 2000.
I've been usimg a Microsight grain focuser for about two years. I have no problem with out of focus prints. I always use a sheet of paper (same type as final print) under the unit...it does make a difference. In order to compensate for manufacturing tolerance variations and different eyesights the device has a focusing eyepiece, perhaps you need to focus the device before use?
-- Robert Orofino (email@example.com), April 01, 2000.
Thanks to Nigel, Pat, Robert and Tony for responding. I am a photo teacher and work in a gang darkroom. It was suprising for me to notice that each focusing device gave a different adjustment. For the most part, because we stop down to print, the difference is absolved with the depth of field. The situation does suggest that when buying a focusing device, you should test it out much like you would test a new enlarging lens. Even within the same brand, samples vary from piece to piece. Frank
-- Frank Ward (firstname.lastname@example.org), April 03, 2000.
OK guys, I think you have hit on a weak link in the process. I have also noticed a difference between the three magnifiers I own. The question is, now what? Is there a way to calibrate/adjust the grain magnifiers so that they are accurately and demonstrably in focus? Is one brand better than the others for focus consistancy, or is it just a matter of luck if our prints are in focus or not? I'd love some concrete answers/techniques/suggestions. Regards, ;^D)
-- Doremus Scudder (ScudderLandreth@compuserve.com), April 03, 2000.
Just to add a bit about the MiniSight adjustment aspects... I wear contact lenses but usually change to glasses when printing, but stayed with contacts the other night. I found I had to adjust the eyepiece to be able to focus correctly.. which leads me to believe, maybe everyones different and would need to adjust the focuser to themselves before using anyway.
-- Nigel Smith (email@example.com), April 03, 2000.
Are you sure you are callibrating each device properly, if applicable. I have two micro and one major focus finder. The latter cannot be adjusted but the former must be callibrated to your eyes. I also use the focus finders at the aperture at which I'm printing to aviod any focus drift.
-- Brian Thomas (Brit@bwphoto.freeserve.co.uk), April 05, 2000.
With the usual grain focuser that uses a mirror, reticle, and magnifier, there are basically three issues. First, the magnifier has to be adjusted so the reticle appears sharp to your eye. Since youre trying to match the plane of focus to the plane of the reticle, it has to be sharp. A high quality magnifier helps, thus the cost of a good focuser. Next, the distance from the center of the mirror to the base of the focuser must exactly equal the distance from the center of the mirror to the reticle. The term focuser is probably a misnomer, as the thing doesnt really focus anything. All it does is redirect the image to a more convenient location so you can look at it with the magnifier and put it in the same plane as the reticle, which is in the equivalent plane as the paper. Lastly, the angles have to be correct. There are some cheap sheet metal focusers that were poorly designed- a clue is that the bright spot doesnt appear in the center of view when the focuser is in the center of the frame. Junk!
Focusing the magnifier is easy and there is always a provision for this. Insuring that the reticle distance is correct is harder. One way to do this is to set up an SLR and macro lens, looking at a piece of crisp text about 8 away. Focus carefully, using an auxiliary magnifier if available. Now, slide the grain focuser over the text so the SLR is looking into the mirror, just as the enlarging lens would be. The reticle should appear in the viewfinder perfectly sharp. Shine a little light down the focuser eyepiece if its hard to see. If the reticle doesnt lie in the same plane as the text, the focuser is probably misadjusted. Move either the mirror or reticle, depending on how it was designed. This test works best with a fast macro lens- you want no depth of field at all so you can resolve small errors. It will normally resolve less than a millimeter of error. BTW, attaching a sheet of paper under the focuser is good practice and corrects for a known error source. It may keep the average focus you achieve closer to perfect, as opposed to always a bit high or low, but it probably isnt visible on any individual print. To get an idea whats tolerable at the paper plane, make a print with the easel tilted twenty degrees or so and focused in the center. How wide is the area of acceptable sharpness and contrast? Generally wider than corresponds to a paper thickness, unless youre making very small prints on very thick paper! Finally (whew!) I suspect that most grain focusers arent adjusted to an accuracy even close to one paper thickness.
-- Conrad Hoffman (firstname.lastname@example.org), April 07, 2000.
"To get an idea whats tolerable at the paper plane, make a print with the easel tilted twenty degrees or so and focused in the center." Another way is to make a print in the normal way then make another print with a piece of scrap paper under the sheet being exposed.
-- Tim Brown (email@example.com), April 07, 2000.
An article entitled "The Hazards of the Grain Focuser" appeared in Photo Techniques (or Darkroom Techniques, I don't know if it was before or after the name change) a few years ago. A fascinating article on the subject by an expert. Here are the key issues:
1. When focusing on an aerial image, as in a grain focuser, the focus of our eye comes into play. Our eye is not corrected for color, and our eye has significantly different focal lengths for red, blue, and green wavelengths. It is critical, therefore, to use the right color of light when focusing on the aerial image since each color will focus at a different distance.
2. The right color is green, but white light produces the same focus. Do not use blue, because the image will then be out of focus.
If you want to know why, get the back issue. It's too complicated to summarize more than I have already.
3. Don't use the blue filter that comes with the focuser.
-- Charlie Strack (firstname.lastname@example.org), April 13, 2000.
But then again, Gene Nocon uses the blue filter and his images are razor sharp. Ansel Adams didn't use anything but an old antiquated grain focuser and who can argue with his product. Get a focuser and read the directions. Most out of focus problems are enlarger misalignment problems anyway. James
-- james (email@example.com), April 14, 2000.