Curing Focus Drift on Beseler 45 Enlargergreenspun.com : LUSENET : B&W Photo - Printing & Finishing : One Thread
I have a Beseler 45MCRX enlarger which I bought well used about 20 years ago. It has the standard condenser light source. I recently added the geared focus drive accessory that somebody is making for it (I forget the name of the company at the moment) which basically puts about a 7:1 gear train between the focus knob and the drive pinion, vastly improving the fine focus process. I use the enlarger for everything from Minox to 4x5, but mostly for 35mm film. I use a 50mm enlarging lens (APO Rodagon, at the moment) on a recessed lens board. Virtually all of my enlargements are onto 8x10 paper, and the enlargement factor is almost never more than 10x.
I am generally quite satisfied with the results this enlarger provides. HOWEVER - it has an increasing tendency to drift out of focus within a few seconds to a few minutes after I focus it critically on the easel with a Peak magnifier. (I frequently make multiple prints from the same negative, so I want the focus to hold between exposures.) It drifts out of focus both "up" and "down" - that is, the lens stage is not simply being pulled down by gravity - sometimes I have to move it up to get it back in focus, and sometimes it has to move down. Tightening up on the lock knob on the lens stage has no effect. The lens will drift out of focus - both up and down - even when the knob is tightened as much as my fingers can do. I'm mostly using HP5 film, which dries flat as a board (unlike Delta 400, which usually dries with a curl from top to bottom.) Putting the stem of my dial thermometer on top of the negative carrier and turning on the lamp only raises the temperature at the negative from about 72 to about 82 in 5 minutes, so I can't believe that in a 30 second exposure there's enough heat to cause an otherwise flat negative to bend appreciably, and besides, over a set of 5 or 6 exposures from the same negative I'll sometimes have to adjust the focus 3 times, sometimes up and sometimes down.
What's frustrating is that there's no pattern. Sometimes the focus will stay tack sharp for a whole string of 5-10 prints, then on the next one it will be completely fuzzy by the time the first exposure is over (usually 20-30 seconds, plus time to load the paper into the easel after seting the focus and to put the exposed sheet back in the paper safe for later development - maybe 60 seconds max after setting the focus.)
I've tightened up on the nylon sliders on the back of the lens stage, to the point where the focus wheel will barely move the lens stage, and that didn't help. (I've loosened them a bit now.)
Anybody have some ideas for what to try next? (Please don't suggest I chuck it and get a Saunders or some such - I have too much invested in negative carriers and lens boards to think about that big a change at the moment.)
Thanks for any advice.
-- Kip Babington (email@example.com), June 06, 2001
I have the same enlarger, however I no longer use the condenser head. What you are experiencing is most likely the negative reacting to heat when the lamp is on. The is most common with dense negatives or in humid conditions. It will rise up slightly when the lamp is on and then drop back down when the lamp is off. Do this test: with the negative in place, turn on the lamp and then focus after about 10 or 15 seconds. Turn the lamp off for about 30 seconds and then while viewing through your grain focuser turn on the lamp and watch the grain slowly come into focus. My method for getting around this was to preheat the negative by holding a card between the lens and the paper, with the lamp on for a few seconds, then turn the lamp off, pull the card away, and then immediately make the exposure. Other alternatives are glass negative carriers or another type of light source. One other item you may want to check for is to see if the heat absorbing glass is in place. It's not a cure all but it can help minimize the problem.
-- Jim (firstname.lastname@example.org), June 07, 2001.
My first thought was also your light source. I have a Zone VI cold light head on my Beseler 45 and never have the problem you describe.
-- Ed Buffaloe (email@example.com), June 07, 2001.
Current Beseler 45's have a focus lock, and I thought the older ones did, too. In fact, Beseler seems to be one of the few enlargers with this feature.
If you have a lock, and are using it, look for something other than lens movement. Negative "pop" is a possibility.
-- Charlie Strack (firstname.lastname@example.org), June 07, 2001.
I have a similar enlarger with the old fan cooled Dichro head. I suffer from the same problem. I am going to try some heat absorbing glass to see if it makes any difference. Printing small format on my old Durst M301 NEVER gave any problems even with long exposure times. I have never been happy with the Beseler 4X5 with more struts than a 1930 biplane & too many adjustments that move when you least expect them to. If you come up with a better suggestion than the glass please post your findings on this site. If I find a good answer to the problem I will do the same.
-- Melvin Bramley (email@example.com), June 07, 2001.
I just replaced my 45MX condensor head with an Aristo VCL 4500 cold light head. I love it. I wish I had done it a lot sooner.
-- Jim (firstname.lastname@example.org), June 07, 2001.
Thanks to all for these suggestions. I dug out my 4x5 glass negative carrier and, lo and behold, absolutely stable negative focus for hours (I actually went away for a few hours leaving a negative in place, and it was still in focus when I turned the enlarger on upon returning.)
So - with a glassless carrier the focus shift is due to negative movement, not mechanical enlarger movement. But keeping a glass carrier clean and dust free is not what I want to spend time doing in the darkroom, whch leaves the question of an alternative solution.
Heat absorbing glass sounds like a place to start. As far as I can tell, this enlarger only has the two condensers in place. Where would a heat absorbing glass go? Above the condensers in the lamp housing? Or below, between the condensers and the lens? And is a heat absorbing glass a Beseler part or accessory, or is it something you go out and get for yourself somewhere else?
As for cold light, I tried an Aristo cold light head a long time ago and it gave terribly uneven illumination with 35mm negatives (not that the stock Beseler is anywhere near perfect in this regard, but the Aristo was much worse.) Also, I gather that cold light heads don't work with variable contrast papers, which is all I've used for the last 20 years or so. Am I misinformed in this regard, or is there something out there that will run cool and handle VC papers too?
Thanks again for the help. This is a terrific resource.
-- Kip Babington (email@example.com), June 08, 2001.
Kip, Glad to hear you are making progress. To see where the heat absorbing glass goes, go to this link at the Beseler website http://www.beseler-photo.com/Technical_Info/45mxt/45mxt.html There you will see an exploded view along with the heat absorbing glass (part number 6).
I use the Aristo VCL 4500 head, which is designed specificaly for variable contrast papers. The illumination is even. No problems there. It is a very nice piece of equipment. You can check out it out by going to http://www.aristogrid.com/vcl.html.
-- Jim Billups (firstname.lastname@example.org), June 08, 2001.
There are 3 kinds of Aristo Cold Light tubes:
1. A variable contrast head which uses 2 different cold light tubes to create the proper light color for variable contrast paper. They are expensive, but probably the ultimate light source for B&W. This is the Aristo VCL 4500 refered to in the post above. 2. The original cold light head which uses a tube that is a significantly different color than condenser light sources and is therefore not compatible with variable contrast filter sets that are commercially available. 3. A new single tube cold light head (using the V54 tube) that is compatible with existing variable contrast filter sets.
If you have the original cold light head, you can get a replacement V54 tube from Aristo.
If you experienced uneven illumination with a cold light head, you might have set it up incorrectly. Most people find these to have extremely even illumination. My Aristo cold light head came with a piece of frosted diffusion plastic that sits right below the tube, giving even illumination.
-- Michael Feldman (email@example.com), June 08, 2001.
Darkroom equipment is so common on the market right now it may be reasonable to buy a decent used dichro head or perhaps even an entire enlarger just to get the dichro head. The dichros give even illumination, relatively low heat and can handle VC paper just fine.
-- John Hicks (firstname.lastname@example.org), June 08, 2001.
Beseler make a 4X5 carrier that (if I am correct) stretches! the negative rather than just hold it in place. I wonder if such a carrier is available for smaller formats?
-- Melvin Bramley (email@example.com), June 08, 2001.