Omega C760 alignment and focusing issues

avizzini

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I have a Super Chromega C760 enlarger and it has always been an ordeal to get the image evenly in focus. Without significant wedges, the grain closest to me will be completely out of focus if I were to focus for the grain on the image edge closest to the girder (not just a tiny amount) and vice versa if I focus the grain on the edge closest to me. If I focus in the middle I suppose it splits the difference but, it still doesn’t look great.

The only way I can get even focus on the grain is to wedge the easel nearly 2in sometimes when making a 11x14 print. So, no small amount. See this image:



Looking at the enlarger and researching online doesn’t seem to indicate much can be done about adjustments and realignments with this enlarger... any ideas why mine seems so significantly off? Anything that I can look at to possibly adjust/fix with it? Other images...



I've tried messing with the mounting screws on the enlarger head without much improvement. I’ve also tried mounting the head so it hovers above the negative carrier without touching it to remove it as a variable, still have focussing issues.

I’ve tried several lenses, in different positions (I also rotated the lens once mounted and this didn’t change anything). I’ve tried several negative carriers. The table, easel, springboard, and enlarger head all seem more or less level (my level is not super precise). Maybe it’s no single issue but a bunch of tiny ones adding up?

Wedging it this much begins to cause issues with even exposure, keystoning, and anytime I move the easel it requires more fiddling with the wedges. It just becomes frustrating and no longer enjoyable. I’m about ready to give up with this enlarger...
 

MattKing

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The lens mounting stage doesn't look to be parallel to the negative carrier stage.
Is the column mounted at the wrong angle to the baseboard?
 

btaylor

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Get or make a laser alignment tool, that will be fast to diagnose the problem and useful in the future.
 
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avizzini

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MattKing said:
The lens mounting stage doesn't look to be parallel to the negative carrier stage.
Is the column mounted at the wrong angle to the baseboard?
Click to expand...

Possibly, the photo angle exaggerated it a bit but I think the problem is on the lens mounting stage.

There’s a fair amount of downward wiggle with the lens stage, as if things aren’t flush against the focusing rails, or in the focusing knobs/housing. It rests naturally with upward pressure but you can push down on the front of it, making it more visibly level.

There’s 3 knobs at the back of the stage, two for tightening the movement on the focusing rail and a knob for tightening right/left swing. With all of those tightened I have issues BUT, if I loosen the knob for swing, I can loosen it just enough that the front of the lens mount stage will drop to the point where I can get even focus. Im guessing this is not an intended adjustment but it appears to be a way to compensate for the actual problem. I don’t use the left/right swing so this could be a valid solution.



I think either the focusing rails are bent or something within the housing that goes over the rails isn’t setting right?

The column is mounted directly to the table, the baseboard was missing when I got the enlarger. Everything looks flush against the table.
 

MattKing

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avizzini said:
The column is mounted directly to the table, the baseboard was missing when I got the enlarger. Everything looks flush against the table.
Click to expand...
You are probably right about the lens mount, but just in case, you might investigate whether the mount to the table should be shimmed in order to bring the table, the lens mount and the negative stage all into parallel.
 

ic-racer

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On the D5500 there is a knob to adjust the lensboard tilt (first picture).

After looking through your owner's manual I see that adjustment is not present. However, I do see the knob to release the lens stage for pivot. As you have discovered it may be possible to place a shim between the two pieces to get it in focus front to rear.
So, check that the knob in the second picture is tight.


 
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avizzini

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This is what I just stumbled upon a little bit ago but it's the opposite of what you are describing. If that knob is tight, the front of the stage lifts up making it out of focus. If I loosen the knob, the front drops and things will be evenly focus. It might be a valid enough solution for me as I don't use the swing/pivot so it doesn't matter if I loosen and wedge (wedge might not be needed even) this a bit.
 

ic-racer

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Yes I see, I changed my original post and I think you are on track for a solution.

When the lens and negative are farther away, the paper needs to be closer; but on the opposite side (due to the reversal). I made that mistake in my original post.
 

ic-racer

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Don't feel bad if you have to place a shim there. The service manual for the D5500 indicates shims need to be fitted under the column to correct any baseboard sag, so not everything on these enlargers is adjustable with screws.

So, the lens stage should be made parallel to the negative (this is the most important adjustment). Then those two can be made parallel to the baseboard by shimming the column (but this can be omitted in many cases unless it is very bad. )

 

MattKing

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avizzini said:
If I loosen the knob, the front drops and things will be evenly focus. It might be a valid enough solution for me as I don't use the swing/pivot so it doesn't matter if I loosen and wedge this a bit.
Click to expand...
If the problem is with the lens stage, this may solve your problem.
However, if the problem is elsewhere, this will result in a focused but out of square image. So check that.
I would still make a point to check whether the enlarger post is at the correct angle to the table.
 
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avizzini

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ic-racer said:
Don't feel bad if you have to place a shim there. The service manual for the D5500 indicates shims need to be fitted under the column to correct any baseboard sag, so not everything on these enlargers is adjustable with screws.
Click to expand...

A couple sheets of paper to adjust the lens mount stage is far better than the 1-2 inches of cardboard and styrofoam under the easel that I have been using...
 
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avizzini

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I'm going to give that a try later as well, I'll need to enlarge the drilled holes to have more "play".

At least at a glance it looks squared.
 

MattKing

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avizzini said:
I'm going to give that a try later as well, I'll need to enlarge the drilled holes to have more "play".

At least at a glance it looks squared.
Click to expand...
The possibility exists that the standard baseboard has a mount area that requires a non-square attachment.
 
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avizzini

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MattKing

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Looking at that page in the manual, and in light of your post, the girder is probably at the right angle.
Assuming you didn't drill the holes at an angle!
 

Arvee

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I suspect you have the same problem that I had when I first got mine. Take apart the rod/handles that focus the lens stage. Inside the box you will find two rotted plastic parts that ride on the two vertical round bars.

I bought some rubber hose at the auto parts and repaired the focus adjust. The 'wiggling' in the above photo is exactly what was causing my problem. I just checked mine and once those rollers are fixed alignment is a snap and it is very easy to adjust all stages to parallel the baseboard.
 
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avizzini

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That sounds very plausible, how easy was it to take apart and fit the hose? For now I'm happy enough to just shim it but, that sounds like a solution later on to look into.
 

Arvee

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avizzini said:
That sounds very plausible, how easy was it to take apart and fit the hose? For now I'm happy enough to just shim it but, that sounds like a solution later on to look into.
Click to expand...
Pretty easy to fix as I remember. The handles just pull off, no set screws. With one handle removed I recall pulling out the rod from the other side. I would have to look but I think there were a couple of screws securing the lid on the enclosure. Just removed the bad parts and took the rod to the auto parts and selected a black rubber hose that slid tightly over the rod with approximately 1/4" wall thickness or equal to the thickness of the rotted part. I think .25 inch is pretty close. Then slide the bar w/hose back inside the box and close the enclosure and push the second plastic handle back on the bar. Your done! Think it took me about half an hour to disassemble and reassemble not counting the shopping for hose at the auto parts. If you have any other questions I'd be happy to look into them.

Once it's fixed, there should be zero wiggle on the lens focus assembly.
 
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ic-racer

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That is a good point on replacing rubber on the focus drive. The D5500 has metal-to-metal focus drive, but had its own problems with deteriorating rubber that needs to be replaced on the lift mechanism and on the wheels that drive the filters.
 

Arvee

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Yep, same type of material in the 760. Mine had pretty much crumbled into bits like yours!
 

Ian C

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The starting point in analyzing non-uniform focus should be to restrain the negative flat within a glass carrier. Otherwise, the warming of the negative can temporarily belly the negative making uniform focus impossible. The lens-stage-pivot lock knob should be snug to prevent looseness in the lens stage.
 
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