Grain Focuser Not Focused
For some reason my grain focuser isn't giving me a totally focused image. When I foucs w/o it by eye the image is sharper than when I focus on the grain with the focuser. Any ideas as to whats going on here? I use a Peak focuser if that makes any difference. Thanks!
I think this is a can of worms! Sorry to keep mentioning Barry Thornton, but he looked into this in 'edge of darkness' finding that out of about half a dozen finders he owned, all gave different indications of focus.
I also have the same problem. When mine (paterson) is calibrated as per instructions for my eye, it is very slightly 'out' compared to what I can see on the baseboard (need a big print to be able to do this well). I then calibrated my finder so that it gave sharp grain when I could see a sharp image on the baseboard (having carefully chosen a neg that made this evaluation easy by eye). The two then continued to agree (it and my eye). However, the little hair line inside, which should be crisp to show that it is set up for your eye, was fuzzy as hell, showing that it should be miles out.
The end result? When set up to agree with what my strained eye could see or calibrated as per instructions, focus points were different. Print sharpness was identical. Weird and I never got to the bottom of it. I moved on.
Can of worms!
This reminds me of an email thread on the pure-silver list a while ago. I should look at the archives or ask Jim Brick cause he mentioned, focusers do not focus whats on the easel, but what is leaving the lens or something like that. As an example, put something a few mm on the easel and use the grain focuser. It'll be focused with or without it. As I recall, it was a heated thread about a week long. Arguments went back and forth as "thickness of paper, ect, etc. But at the end, man, I need to find the archives, I was persuaded that the focus was up top, not the bottom, hence the mirror on the grain focuser.
Okay, I will look up the thread but if anyone else on the pure-silver list, you probably remember it as well. Pure-silver list left tundraware but I"m sure the archives are somewhere.
Ouch! This is a tough one. My guess would be that something is wrong with the grain focuser, although I know Peak to be top quality (I own one myself). The distance from the lens to the mirror is very important. The angle the light hits the mirror is also important. Are you using the focuser close to the centerline of the lens, where the light rays are vertical (down).
The image seen through the eyepiece must be that of
Originally Posted by JackRosa
the image at the surface of the paper. Lifting the focuser
a bit may help. Lowering is another matter.
Good optics are required if the color of light used for focus
and the color of light used for exposure are to coincide.
I usually use the most powerfull reading glasses the
law allows. Dan
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Yes, this seems like a simple thing but can probably get hairy pretty fast. I also use a Peak model and I don't have any problems.
It's probable that you're focusing a small area of the image and then standing back and looking at the image overall and noticing that it isn't in focus. One variable you should look is the overall alignment of your 3 planes in your enlarmenent setup. It could be possible that your grain focuser is indeed focusing that small patch correctly but that your planes are out of alignment somewhat and that you can get a better overall focus by eye. As a sanity check, check out the alignment of your enlarger negative, lens and easel planes.
Are you focusing with the focuser sitting on a piece of printing paper, which will more exactly be the image position projected at the time of exposure? Some people say this makes a difference. I do it out of habit but can't prove that it makes a difference in reality.
I assume your Peak is setup and focused on the black line correctly? If any part of it that would affect the distance that the light travels to the eyepiece is out of wack, this would cause it to focus incorrectly.
Are you focusing wide open then stopping down and noticing a focus shift? Could be your lens is much sharper stopped down a few stops. I ask because it is natural to focus wide open to get a bright image and then to stop down and watch the image sharpen up. You may get a focus shift as a side-affect of stopping down or you may just be noticing a sharper image stopped down as a natural result of the lens projecting a sharper image when stopped down a few stops. If you are focusing wide-open, try focusing at the stop that you will expose at or vice versa.
Did you ever drop your focuser or anything that would move the mirror or lens elements?
Just brainstorming here. Hope some ideas help. You have a good focuser there, so it would be the last thing that I'd blame for this unless you have good reason to suspect that it's broken.
Ok this may be a stupid response but ...
are you using a glass carrier????
I have a large assortment of enlargers and grain focusers, from peaks down to those little blue devices with a hair line in the middle.
with a sheet of paper matching the desired material under the magnifyer adjusted to my eye I have not had any problems.
Without a glass carrier your negative may be heating up as you focus and drawing in the middle towards the light bulb>
then as you turn off the enlarger to get your paper and place in the easel and then find the timer and ready to expose> the negative cools down and flattens out again , this will cause you no end of problems ..
I strongly advise trying glass carrier.
Are you using a blue focusing filter? If so, don't.
Originally Posted by Silverpixels5
I did a series of experiments some years ago in which I got the probable erors of focusing with a grain focuser with three different filters and none. There was a focus shift on the average in one direction with blue, the other direction with red, and none with white or green light. The cause was the chromatic aberration of the eye. Also, the standasr error of focus was greater for both red and blue focusing filters than it was for green or no filter. You can be as scrupulous as you want about the 1/2 mm or so of paper thickness, but the random errors of focus swamped that out. These results were in Darkroom and Creative Camera Techniques, now Photo Techniques.
No matter what printing filter you use, the focusing should be done by the light that the eye sees best, which is green or white.
The effects of chromatic aberration of the eye are well know to astronomers, where they show up as apparent chromatic aberration of the telescope.
as a matter of fact, my focuser does have a blue filter. Not so sure how to use it w/o it though. The filter is part of the eyepiece, which does come off, but then where do I get a clear piece from? Do they sell those for Peak focusers? Thanks for the info though!
Originally Posted by gainer
Well it would seem that it was the blue filter that was causing my problems. I figured out that the filter was an attachment on my eyepiece and not actually part of it. So I took it off and focused....and of course the image was both sharp on the paper and in the focuser. I put the filter back on and it looked slightly out of focus. Damned blue filter! Thanks for the help!