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  #1  
Old 11th November 2012, 07:53 AM
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Default Leitz Focomat V35 Focus Drift.

OK, so I got a V35 enlarger and have set it up in my darkroom, the autofocus is set up to give sharp grain at 16x enlargment and is sharp at 3x, the helicoid is in the notch, everything working perfectly, on returning to the enlarger a few hours later focusing is well off helicoid still in the notch, column not moved, same masking frame, reset everything, two hours later focusing has drifted again

Any advice much appreciated.
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Old 11th November 2012, 08:00 AM
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can only think the electrics need time to warm up stupid as that may seem. Maybe one of the elctricians here will have a view on this.

Last edited by Argentum; 11th November 2012 at 08:25 AM.
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Old 11th November 2012, 08:34 AM
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can only think the electrics need time to warm up stupid as that may seem. Maybe one of the elctricians here will have a view on this.
Thanks, darkroom is very cold at the moment so was wondering about expansion/contraction, I also have the glassless neg carrier and I believe that the standard carrier has anti newton ring glass which of course would keep the neg flatter, I can't see popping to be a problem as virtually no heat is generated at the neg stage
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Old 11th November 2012, 08:35 AM
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I was thinking more of the transformers and other electrical components rather than neg flatness.
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Old 11th November 2012, 10:02 AM
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Some of the contributors here know that I am an electrical engineer and will expect me to say something on this, but I am really unfamiliar with your enlarger or others to that matter.

I use an LPL C7700 fitted with the fine focus accessory and have both heads for it. The colour head with the filters, I use very little and this is the one with the transformer in the supply cord which is quite distant to the enlarger. It does not seem to get unduly hot and doubt this would cause any problems.

I prefer to use the black and white head, with condenser lenses and a 75 watt bulb. This does get quite hot though.

I do feel the need to check the focus with each print exposure and make a fine adjustment frequently. I use a glassless neg carrier, though I do have a glass type with anti Newton Ring glass.
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Old 11th November 2012, 11:09 AM
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I have one Durst auto-focus enlarger and sometimes it feels the need to re-focus itself!

Perhaps some points to consider even though it's a different make;
1.Is there anyway to clear or reset the old auto focus reference points and start from scratch with new reference point data?
2. My durst manual states, "IMPORTANT: To eliminate mechanical deviations in programming always approach final position of sharpness from below."
3.The durst manual also states, "NOTE: If a corrected enlarger head position is less than 5mm from a reference position stored during calibration, then that reference point is overwritten. Otherwise the unit establishes a new reference position.
To correct a calibration point this must be set again exactly within 5mm. Preferably use the positions recommended."

Finally, due to the age and use of these machines isn't some drift to be expected? Personally, I don't trust any of my machines and always do a final check just before exposing the final print.
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Old 11th November 2012, 08:08 PM
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Could it be that the brake is slipping a little, even if the clamping knob is tight?
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Old 11th November 2012, 10:14 PM
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Could it be that the brake is slipping a little, even if the clamping knob is tight?
Hi
Thanks for your response, not sure what you mean by this, even if the arm moves surely the enlarger should stay in focus? I have tested a couple more times and find that after returning to the enlarger after 2 or 3 hours the focused neg which has been left in the enlarger is a little unsharp however if I move the head up and down a couple of times and turn the helical focusing mount off the indent and then back again sharp focus returns
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Old 11th November 2012, 11:21 PM
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Is your darkroom constantly cold, or do you have a heater on when working? I am guessing that changes in ambient temperature and humidity could cause movement in the neg similar to 'popping'. I use a V35 and have the standard glass carrier. I don't use autofocus at present because it doesn't work well with my RRB easel. I do notice, however, that I can set focus at the start of a session, but need to reset soon after. My darkroom is in a wooden shed. I put heating on 30mins before I go out. The focus 'settles' after 10 mins or so and stays fairly stable thereafter. The irregular heating pattern causes other problems with condensation, but I have learnt to accept this as part of the job! The other thing I do is switch the enlarger lamp on for a short period at the start of a session to heat it up. This seems to reduce focus shift for me, but I don't know why it works. Alex
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Old 12th November 2012, 09:00 AM
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Quote:
Originally Posted by alexmuir View Post
Is your darkroom constantly cold, or do you have a heater on when working? I am guessing that changes in ambient temperature and humidity could cause movement in the neg similar to 'popping'. I use a V35 and have the standard glass carrier. I don't use autofocus at present because it doesn't work well with my RRB easel. I do notice, however, that I can set focus at the start of a session, but need to reset soon after. My darkroom is in a wooden shed. I put heating on 30mins before I go out. The focus 'settles' after 10 mins or so and stays fairly stable thereafter. The irregular heating pattern causes other problems with condensation, but I have learnt to accept this as part of the job! The other thing I do is switch the enlarger lamp on for a short period at the start of a session to heat it up. This seems to reduce focus shift for me, but I don't know why it works. Alex
Thanks Alex
I suspect the problem is with the glassless neg carrier and negative movement/pop, I have cut a piece of sheet film to 35mm width and focused up and left it in the enlarger to see what will happen with this thicker flatter material
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