Meopta Meochrom Color 3: Extremely Short Exposure Times

cliquenoir · Sep 2, 2017

First, thanks in advance for any insight.

I'm working through some of my first test prints with an Opemus 6 outfitted with a Meochrom Color 3 head, and I'm finding the exposure times to be incredibly short: with filtration at 30M and ND dialed all the way up to 60, I'm getting an exposure time of roughly 1 stop (2 sec.).

Here's the info I have on hand and some of the things that I've checked:

- Lens is an 80mm Nikkor @ f8
- Paper is Arista EDU Ultra FB 8x10
- Printing 6x6 negs at approximately 7.5" x 7.5"
- Bulb is properly rated at 85W
- Mixing chamber is in good condition and correctly matched for 6x6 negs
- Using my Darkroom Automation Enlarging Meter I checked the light reading with the enlarger plugged directly into the outlet as well as into my enlarging timer and found them to be the same
- Safelight paper test was all clear

Does anyone have any other things I might want to check? My results seem pretty extreme, so hoping that I've missed something (not so) obvious.

Cheers!

Svenedin · Sep 2, 2017

Is the ND working? Is the light reading different at ND 0 as opposed to ND 60? Are the negatives very "thin"? (even if they were, this is a very short exposure time).

cliquenoir · Sep 2, 2017

Hi Svendin,

Thanks for the reply. Yes, the ND filter is working and engaged (you can swing a lever to engage/disengage the filtration--for both the color filters and the ND). And, no, the negatives are not overly thin.

Svenedin · Sep 2, 2017

I'm at a loss then but I'm sure somebody more familiar with your set up can help!

pentaxuser · Sep 2, 2017

Checking that the ND is working correctly as Svenedin has suggested sounds worthwhile. It is difficult to believe that it is working OK, given a time of 2 seconds at f8 with the correctly rated bulb of 85W. I don't have a ND filtration available to me but with a 6x6 neg at a 7x5 enlargement and a Rodenstock 80mm @ f8 I get nearer 8 secs. My bulb is only 10W less at 75W.

I take it you are sure that the aperture is working OK and stopping down to f8?

pentaxuser

Svenedin · Sep 2, 2017

pentaxuser said:
Checking that the ND is working correctly as Svenedin has suggested sounds worthwhile. It is difficult to believe that it is working OK, given a time of 2 seconds at f8 with the correctly rated bulb of 85W. I don't have a ND filtration available to me but with a 6x6 neg at a 7x5 enlargement and a Rodenstock 80mm @ f8 I get nearer 8 secs. My bulb is only 10W less at 75W.

I take it you are sure that the aperture is working OK and stopping down to f8?

pentaxuser

Exactly. I don't have the same enlarger but I do have ND control. When I dial it in I can see the projected image become dimmer. Taking a light reading at ND 0 and ND 60 would soon show whether it is working properly. That the lever works does not necessarily mean the ND is working. Also as Pentaxuser suggests, worth checking the lens is stopping down as it should (again this is obvious when looking at the projected image).

AgX · Sep 3, 2017

Looking at the projected image means it getting darker at each step? I ask as a diaphragm may close perfectly at the start but not reach the desired aperture as it stops closing down before.

Svenedin · Sep 3, 2017

AgX said:
Looking at the projected image means it getting darker at each step? I ask as a diaphragm my close perfectly at the start but not reach the desired aperture as it stops closing down before.

Yes, as you close the aperture of the lens the projected image becomes darker at each stop. if you think there is a problem with the lens you can take it off the enlarger and look through the lens. You can see the aperture become smaller as you close it down. Some enlarging lenses have a preset facility. This allows you to close the lens only as far as a preset aperture. This is useful so that you can compose the print with the aperture fully open (bright image) and then quickly stop the lens down to the preset aperture. You can adjust the preset aperture stop or disable the feature -how this works depends on the enlarging lens. With some lenses you pull the aperture ring and rotate it to adjust the preset stop. Some lenses have a slider that disables the click stop so that the aperture is continuously variable. If you are unsure tell us which lens it is and someone will be able to help you.

Cloudy 8 · Sep 4, 2017

Hi cliquenoir,

I have the same setup as you do, and recently printed a 645 negative to 24x18cm paper (9.5"x7") at f11, M30 and ND60 with an exposure time of 12s. Definitely a short exposure, but not quite 1 second.

You say you're using the COLOR 3 head with an 85W bulb. However, as far as I know that head expects a 100W/12V bulb (and mine does have one).
A 85W halogen reflector lamp is used by the COLOR 4-ES head, which has a built-in stabilizing unit. But that device powers the lamp at 82V (!).
Are you sure you have the correct lamp? A mismatch still wouldn't explain the problem, as the 85W/82V lamp should be too dim at 12V, not brighter.

Also, what kind of transformer are you using? Could this be a 120V vs. 240V issue?

AgX · Sep 5, 2017

A doubling of voltage would blow any bulb immediately, instead of yielding extreme short exposure times.

Berri · Sep 5, 2017

I have the meochron Color 3 head. For black and white I get reasonable exposure times between 6-8 seconds up to 20 with normal filtration. My bulb is 12v 100w as it is recommended. The density dial should dim the projected image. If you remove the bulb from its housing and look inside you should be able to see the filters moving as you dial in more density. Are you sure you mixed the chemicals properly?

Meopta Meochrom Color 3: Extremely Short Exposure Times

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