Do you always refocus?

[NedL]

Get a decent glass carrier and you don't have to worry about this nonsense. If your negs are popping or curling en route, it just shows you have no guarantee of ever being consistently in focus.

Drew, so with your glass carrier you don't re-focus after changing negatives?

 

[youngrichard]

I REFOCUS ONCE EVERY 6 MONTHS

I seem to be out on a limb and out of line, but bear with me.

I acquired a Focoblitz several years ago. I think I paid GBP100 or so for it; it is a precision laboratory instrument, and they come up on eBay about once every other year. It was made by a company called CIR somewhere in Europe. It is mains powered . The sensor you can see has a lens which sits on your baseboard and focusses the grain on some sort of photo-electric cell and reproduces the grain, greatly enlarged, on the B/W cathode ray tube display. You can judge its size against my RH Designs Analyser 500 in top left of picture. Not sure for what purpose they were originally made.

I have 3 enlargers (well, more, but three I use) - Focomat 11c, Leica V35, and Durst DA900. Each one is autofocus. Now, the joy is that you don't have to keep bending over and squinting into a grain focusser, reaching above your head and trying to make precision adjustments whilst straining in discomfort.

Lots of experimentation showed that negative pop doesn't usually occur suddenly, it happens progressively over time; so you can't say "Ah the negative has popped, I just need to refocus", it will carry on bending after you have refocussed, especially with 120 film. The only solution is a double glass carrier, except in the case of the V35 which has a single upper glass and that seems to solve the problem for 35 mm film.

So, how good is autofocus? Armed with the Focoblitz you can easily and effortlessly see that focus is as near as dammit perfect throughout the autofocus range of all these devices, once they have been accurately set up. You can relax and watch the television! No bending and squinting. The V35 is best and most easily adjusted; the other two need tuning - up to the top, adjust focus; down to the bottom, fine tune, repeat till right. DA900 needs tweaking but that is quite complicated and involves tuning the grub screws in the lens holder, unless your DA900 came with matched lenses and lens carriers; the Focomat 11c is easy, again provided you have the original Leitz lenses.

The reason I don't re-focus with the Focoblitz every time is firstly, that I don't need to; and secondly, being a cathode ray tube there is persistent glow after switching off; whether that would be a problem, I don't know because I haven't tested it.

So far as focus creep goes, it may be because the lens stage is creeping - solved with autofocus because the focus creeps with the lens stage. Or it may be negative slowly buckling - as noted, my experiments suggest that negatives don't 'pop', they slowly buckle.

So, bottom line is, I check focus once every 6 months, or even less.

Richard

 

[Alan Gales]

I haven't used an enlarger in a long time (I used to print Cibachrome prints of Kodachrome slides). I owned a Beseler 67 with color head and the single mast. I always checked focus with my grain analyzer. Cibachrome was expensive so rechecking focus gave me peace of mind.

 

[DREW WILEY]

All my enlargers, with the exception of an old 4x5 Omega machine, are very precise. So I could leave a neg in place for six months if I wanted, and it will still be in exact focus within the glass carriers, as viewed thru a critical focus magnifier (the expensive one). Normally a fresh neg dictates some tweak to the composition, so if there is a change in the ht of either the head or baseboard, of course re-focus is necessary, but not for any mechanical reason. And once in awhile I'll use a cheap 75mm f4 EL Nikkor for 35mm black and white film because I don't want to pull my better 105 Apo Rodagon off the color enlarger. It's a really wretched lens for medium format compared to the 5.6 EL Nikkor equivalent, but does a decent job with 35mm cause only the center of the lens is used - but does have focus shift from wide open, so has to be re-focused. Otherwise, here in eathquake country my enlargers are all rock solid. I can even stand on the vacuum easel of my
8x10 color enlarger without deflecting it. But it weighs a couple hundred pounds itself. And the enlarger column was made to hold dimensional stability for months on end... but that's a long story. The more common problem with lesser machines is simply that the film is
not held flat to begin with. I cut all my roll film negs apart and mount them individually in high-quality carriers with optical glass on both sides.
I don't want to get into a debate on glass versus glassless carriers here at the moment, but in my case, the question was definitively answered a long time ago. I'll never, ever go back to glassless.

 

[eclarke]

No, never.

 

[cliveh]

I always check with a focus magnifier, but find I often don't need to refocus, but sometimes I do. Odd that.

 

[WayneStevenson]

I always check focus. Mainly because I split grade using a dichro head. So I'm dialing those wheels regularly several times for the print. No guarantee I'm not moving the stage.