The critical focusers all have front-surface silvered mirrors, right? If someone had replaced original mirror with an ordinary glass mirror your focus would be quite far off.
The grain focusers all appear to have the original mirrors. They have that extra shiny look of a first surface mirror to me. Like I said, though - this equipment is second hand. That's the nature of the darkroom these days!
The conclusion we came to after getting replies from a couple of grain focuser manufacturers was that it makes no difference. No harm using a piece of paper but no need either (apart from your point about protecting the easel surface).
Originally Posted by Newt_on_Swings
Gene Nocon - "There is a popular belief that focussing on a sheet of photographic paper placed on the baseboard will give you a more accurate result because it compensates for the thickness of the print. This is nonsense. Save your paper".
And the last page of the thread we had a while ago: http://www.apug.org/forums/forum41/7...rpness-12.html
Last edited by Steve Smith; 10-23-2012 at 12:07 PM. Click to view previous post history.
Thanks for the more detailed workflow information. I agree that nothing stands out there as a likely culprit. I have a Durst 138 also, and it does hold focus very well. What format were you testing? Your enlarger is set up with the condenser head? I don't understand the focus lever on the lens. Is that to open the aperture?
I thought you must be focusing with the lens open since you are able to focus by eye. That doesn't explain the problem, but is certainly not the normal way to use a grain focuser. I wouldn't expect that much focus shift, and that still wouldn't explain the situation, but it is certainly a variable I would eliminate. Another variable to eliminate is the test negative. I can think of no reason that would be an issue, but I would focus using a real negative, focusing on the grain at working aperture since that is what you will do when making photographs.
I have used a lot of grain focusers over the years and never seen a single issue like you describe, so have trouble imagining 3 (or is it 2 - not entirely clear) that don't work. I see very slight differences between my Critical Focuser and my Microsights, but I mean barely detectable. This could easily be down to adjustment, or just tolerances.
Ctein's book (linked above, I think) describes a way to test focus accuracy while eliminating many of the variables here.
Steve - you have no idea of how accurately I work. On one of my enlarger I actually have a custom
focus telescope for magnifying the grain too, simply because the registered neg holder is about ten
feet above the vac easel, which is solid enough to stand on without deflecting it! Otherwise there are all kinds of potential issues, and they simply have to be isolated one at a time. Yes Bill, I have
seen grain magnifiers w/o front surface mirrors - they shouldn't exist, but do. And certain enlgr lenses are certainly capable of focus shift - one more thing to double-check. And to get a good idea
of the reprentative quality-control of a particular model magnifier, you'd have to compare dozens if
not hundreds of them. Just like buying a try square at the hardware store: bring along a true machinist's square and you'll discover just how very few conventional squares are really square!
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To back up to that sheet of paper "nonsense" as you call it, Steve - there's more than one reason
for using a very accurate grain magnifier. For one thing, I print some very big polyester prints, and
nobody is going to confuse them with a damn fuzzy inkjet or even Lightjet. Sometimes I need to
enlarge a 4X5 or smaller original onto an 8x10 dupe chrome or interneg. There is a very precise vac
filmholder involved, carefully selected apo graphics lenses, and meticulous alignment of everything.
When that gets enlarged to a 30x40 print, not only would the hypothetical thickness of paper matter, but rather, I focus upon a sheet of film exactly the same thickness. Otherwise a lot of time
and money would go down the drain! This illustrates the principle involved. Just because typical fiber
based papers can't always reproduce that level of detail does not mean thickness is not an actual
It's not really me saying it's nonsense, it's the manufacturers.
The thread I linked to started off with me suggesting that the paper was not required because I assumed that the designer of the grain focuser would have built this in to the total height making it un-necessary (which is how I would design it). Ralph Lambrecht disagreed but claimed that the paper was not needed.
As no one could find any instructions stating if paper should or should not be used, I decided to ask some of the manufaturers.
Based on the replies we received, it was obvious that I was wrong about them designing in the thickness compensation but that Ralph was right (as far as the manufacturers were concerned) in that it was not necessary to use paper under them.
I don't doubt that you work very accurately considering the size of prints you are making but it would be interesting to see the difference if you focused both with and without a piece of paper printing just an 8x10 section of a 30x40 print.
I don't think that you will see a difference but real life results trump theory every time!
Last edited by Steve Smith; 10-23-2012 at 02:53 PM. Click to view previous post history.
Steve, I thought you had some shop skills. And do you think that I go around believing everything manufacturers say, and don't test myself??? I make quite a bit of my living talking to engineers and
telling them how to do things better! I love working with German companies because they listen and
want to do things right. I hate working with large US mfgs because the engineers can improve an
idea, but the CEO doesn't give a damn and will just outsource it to China anyway. Japan is another
story, which involves a lot of "lost in translation" attempting to cut thru all the intense hierarchy until you reach the right people or right division (often worth it). But I never take a manufacturers
word at face value. That's why so many folks do business with me.
Well after 5 pages we seem to be no nearer solving the issue. Before you did the test you describe in your original post, how did you focus your negs? It sounds as if eyeballing focus was only done and discovered to be the best when you did the test. Previously I presume you used one of your focusers at random. That is you simply picked one up and focused a normal neg then printed it. Did you stick with the same focuser for all of a particular printing session or stick with the same focuser each time you print and ignore the other focusers?
In examining your previous normal neg prints I presume you weren't aware of a lack of focus when examining the prints and your decision to conduct the experiment was simply curiosity that arose as a result of deciding to try two focusers on the same neg quite by chance? If you had not done this then I assume you would have been quite satisfied with the prints you had previously produced.
If eyeballing is better and for some reason in your case it is, then I presume that until you did the experiment all your previous prints were judged to be OK with focusers until out of curiosity you tried two focusers one after the other and discovered a difference which led you to try eyeballing as well which was then the best method.
If you examine previous prints that I presume you thought to be OK before your experiment and do them again with eyeballing then can you make them visibly sharper in every case?
As you will have noted one of my thoughts was that the neg in question was in fact out of focus. I had this happen to me and produced a print that was fuzzy despite being able to focus the grain sharply. I had to examine the neg under a big magnifier to see that it was out of focus. It wasn't easy to see this even with a 6x6 neg and a big magnifier.
I then tried to improve things with eyeballing and was able to make a slightly better print but I think I was able to do this because the grain focuser was so sharp compared to my eye that in effect the grain focuser was simply sharpening the "out of focus" neg and making the out of focus clearer
Tip: to really isolate the variable of the paper plane itself, you'd have to expose a sheet of film (not
paper) on a precise vacuum easel. Ordinary paper doesn't lie all that flat on an ordinary easel, and can't pick up enough detail for critical work. You're only as good as your weakest link.