I'm finding it difficult to believe there is THAT much difference between different focusers. It's quite a significant difference to be able to see on print and have an agreement between two people.
Going 35mm (I am assuming) neg to 12x16 isn't all that unusual.
I wonder if there is another factor involved. Say you focus carefully with a grain focuser. The focusing stage could drift a bit and the image goes out of focus. Something like that? Can you carefully focus the image with one focuser. Let it sit there for 30 seconds or so then look again. Is it still in focus?
It is true the DOF at base board is quite big. But the focuser is used to adjust the distance between film stage and the lens stage. This adjustment is quite critical.
I'm amazed you can actually do better with your naked eyes. I cannot. Not even close.
Develop, stop, fix.... wait.... where's my film?
I forgot about that, you're right.
Originally Posted by tkamiya
But as you focus, the distance from lens to baseboard also changes, this complicates things a bit.
Marco, I presume you're using VC paper? If so, does a UV filter, say a 2B or stronger, improve the focus situation substantially? (If no UV filters around, perhaps adjust for the softest grade possible.)
One other thing that tkamiya's post has reminded me of. Check the movement in the enlarger bellows.There should be a screw that allows you to tighten the bellows so after focusing they don't move. Movement can be a problem if the print size means that the bellows are tightly compressed. I have had this problem with my Durst 605 and need to tighten the screw so that focusing knob is stiff to move.
It is possible that you correctly focus with each focuser then the bellows move slightly before you expose. In the case of the eye-balled print, was this the last print to be made? If it was and you focused by eye then instantly hit the expose button the bellows might not have had a chance of moving so that one was the best.
Just a thought
There is a book of which I have a copy (now out of print) by the late Canadian Photographer, Gene Nocon. He goes into this focussing lark in some depth and recommends the use of a blue filter over the focussing magnifyer eyepiece lens because the light from the enlarger bulb tends towards the red end of the spectrum and the paper is at the blue end. Using a blue filter over the lens allows the light rays to focus on the actual paper which is blue sensitive as well.
He is using a Peak focus finer in the book illustrations and this has a blue clip on filter for the eyepiece. I do find that it does make a very slight difference so I use the same technique, but calibrate my diachronic filtration in the LPL enlarger head to give me a blue light for focussing. I suppose if you are well off enough to afford an APO lens this does not matter.
Last edited by BMbikerider; 10-22-2012 at 11:06 AM. Click to view previous post history.
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Well, I looked at things with a fresh set of eyes today. I roped in some of my colleagues in the darkroom as well. My conclusions were the same; the prints focused by eye were sharper. You really can't miss it on the test negatives, because of the series of fine lines, swirls, etc... I should scan these so people can see what I'm talking about. But it's quite apparent. The test negs are rather brilliant for that; errors in focus stick out like a sore thumb.
I then focused the test neg by eye, noting the column height. The grain focusers were focusing roughly 2mm closer to the neg than I feel was correct. The durst column has these markings, so it's not too hard to see. Another thing I did was re-focus by eye, then go through the whole range of adjustments (from lowest setting to highest - it's helical focus) of the grain focuser eyepiece. Never did it look visually sharp. Not that critical sharpness I see when I move the lens 2mm closer to the neg.
So, what Bob-D659 says is relevant. Maybe all these grain focusers have been dropped, or had glass replaced, etc... Who knows. It's all old equipment. None of it was bought new, I don't think. I doubt it, personally, but it is possible.
I did a quick and dirty test to see where the base of the grain focuser had to be in order for it to jive with my focusing by eye. It looked like it needed to be 5mm to 10mm higher off the baseboard. I loathe the idea of shimming a grain focuser.
Perhaps the more mathematically sound members can determine weather this approximate 2mm difference will be apparent visually when making a print, stopped down to a working aperture.
My feelings are why go to the trouble of using a glass carrier, aligning my enlarger, etc... if my grain focuser is slightly off?
Sometime this week I reckon I'll get my eyes checked to see if I've got astigmatism or whatever it's called. Maybe I'll post a follow up with those results!
Oh, and tkamiya: I'm sure that the focus column is not slipping. The Durst 138s is a beautiful machine. I routinely leave a negative in the enlarger for a weekend, and come back to make more prints a few days later and the grain is still as sharp as when I left it. I believe I can almost 100% rule that out of the equation.
Thanks for all your thoughts on the matter.
Not sure about that. However, when it is properly in focus, a 2mm difference in paper height will not be noticeable.
Originally Posted by Marco Buonocore
In his book, Edge of Darkness, Barry Thornton did an experiment. He put his easel on a 1/2" thick piece of board then focussed normally and made a print. He then made a print without the 1/2" board and another print with two boards. He says that he could see no difference in the sharpness of the prints 1/2" either side of optimal focus - and he was a sharpness fanatic!
So basically, a 2mm difference will not be discernable - however, you do need to be focussed first, and this is where you are having problems.
Steve: The difference of 2mm is between the lens and the negative, *not* the lens and the paper.
That will make a lot of difference - ignore previous answer!!
I still have the same questions - I am heading somewhere with this. The idea is basically that your VC paper may be sensitized well into the UV range. The enlarging lens probably isn't well-corrected for UV, so the result could be a significant focus error (you can't see the UV light). Ctein explored these ideas in detail in his book.
Originally Posted by Mr Bill