Aligning the base board

After my epiphania in the darkroom the other day I decided to check up everything in my new DR.
The enlarger is a Laborator 139, a 2 m high beast,with the base board on the same column as the head and adjustable every which way.

I do not have any laser tool for the alignment so I decided to use my common sense (what's left of it) and think of something cheaper. I used PS to make a black rectangle with a 10 cm side. Inside this, in the centre, I made a white rectangle with a 5 cm side.

After printing the paper I cut out the centre rectangle. The whole paper went in the negative holder. Now I had a clear, crisp shadow on the baseboard of known dimensions. I raised the head until one side of the rectangle was about 40 cm. I figured an enlargement of 8x is about the max I will ever make. 8x6 cm is just under half a meter. Good enough for me.

I then measured the rectangle side to side and top to bottom, all sides, and adjusted the baseboard until every measurement was within half a mm.

I feel very pleased with myself and now I need someone to tell me why this is a useless way of aligning a board.
Or can I consider it "good enough"?

r

Mats

Sounds good.

Now just check this at a very small enlargement, and a medium enlargement. If they are good too, then you are good to go.

Mats --

You say you cut out the center rectangle -- how did you do this? How can you be sure you cut it in such a way that both pairs of opposite sides are perfectly congruent and parallel, and that adjacent sides are perpendicular? No doubt the printed image started out this way, but my experience with cutting paper, even with a metal straight edge and a razor blade, is that it may not be able to give the kind of accuracy you're looking for.

I've tried checking enlarger alignment (at least this aspect of it) in a similar way, but I just use an empty negative carrier for my rectangle, which we hopefully assume was cut and machined to be perfectly rectangular. I set a piece of lined graph paper, whose lines are notoriously parallel and perpendicular, on the baseboard or easel and then project and focus the empty rectangle onto the graph. By registering one edge of the image with a line on the graph, any runout or discrepancies can be seen on the other edges.

While passing this test is necessary for good alignment, I don't believe that it alone is sufficient to ensure good alignment; ie, if we flunk this test we've got a problem, but just because we pass it I don't think guarantees 100% that there may not be other issues in the alignment scheme.

My understanding of the alignment process is that there are three planes which must all be parallel to each other -- the easel (paper) plane, the lens stage plane, and the negative plane. Like you, I don't have a laser tool, so I use a level, and start with my counter top, then the baseboard, then the easel, then up to the lens stage and then the negative stage, leveling all of these fore and aft, and side to side. From there, I do the graph paper test, and typically it passes and I figure at that I've given it my best shot.

Best regards,

Dave

The above processes are fine for rectilinear alignment. However, more important is having all corners of the image sharply focused. Checking for this is the final step in any alignment. I use a sheet of clear film slightly abraded with various grades of sandpaper as a test negative. The large and small scratches show up well on the baseboard.

Can you adjust the lens relative to the negative? This is much more critical than the base alignment (as far as focus is concerned).



Steve.

Interesting. Can someone tell me how to adjust focus if a corner or several are off?

r

Mats

What make/model of enlarger do you have? You'll have to somehow adjust to make sure your film stage is parallel to the lens board - which in turn has to be parallel to the baseboard.

Jim Jones said:

The above processes are fine for rectilinear alignment. However, more important is having all corners of the image sharply focused. Checking for this is the final step in any alignment. I use a sheet of clear film slightly abraded with various grades of sandpaper as a test negative. The large and small scratches show up well on the baseboard.

Click to expand...

Jim --

If you had adjusted the enlarger so that all three planes (easel, lens stage and negative stage) were parallel, and found that one corner of the enlargement was more out of focus than another, what would you adjust?

I say one corner being more out of focus than another, because it seems to me that if the center of the enlargement is in focus, that at least theoretically the corners would have to be somewhat out of focus, as the corners are farther from the negative than the center is. I would think that delivering sharp focus across the enlargement might be the real challenge in designing a good enlarger lens, which could be why enlarger lenses seem to give their best performance when closed down a few stops from wide open.

If all three planes are indeed parallel, and one corner of the image is not focusing the same as the others, I would suspect an issue with the lens itself being off-axis (ie, not perpendicular) to the lens board.

Best regards,

Dave

tkamiya said:

What make/model of enlarger do you have? You'll have to somehow adjust to make sure your film stage is parallel to the lens board - which in turn has to be parallel to the baseboard.

Click to expand...

It's a Laborator 139. A big beast. I thought that if I had a "perfect" rectangle on the baseboard then all three planes would have to be parallel. Is this not so?
This is getting confusing. I will make a scratched neg and check the focus.

r

Mats

Mats,

There are conditions where image could be perfectly rectangular and more critical alignment between film stage and lens plane could be off. Way off, in fact. When I rebuilt my D-2, I made this mistake myself. If it isn't rectangular, then it's NOT aligned correctly - that's all it says. Converse isn't true.

Try this.... take a film leader or something that is opaque and put it into your carrier. Scratch a big X from corner to corner. Project the image. Does the scratch show up crisply (is that a word??) in entirety? Another trick I've been told.... take a picture of a news paper after making very sure paper and your lens are parallel. Use that negative and see if you can see all letters crisply.

Keep in mind, not all lens will show corner-to-corner sharpness especially at large magnifications. But it should be reasonably good....

Mats_A said:

It's a Laborator 139. A big beast. I thought that if I had a "perfect" rectangle on the baseboard then all three planes would have to be parallel. Is this not so?
This is getting confusing. I will make a scratched neg and check the focus.

r

Mats

Click to expand...

Mats

If the lens isn't parallel to the other two planes, it is the same effect as the one you get with a view camera when you are swinging the lens to vary the plane of focus.

If the rectangle isn't a rectangle, it is the same effect as the one you get with a view camera when you are swinging the film plan to vary the shape of the image (e.g. when you want to correct converging parallel lines).

Mats_A said:

Or can I consider it "good enough"?

r

Mats

Click to expand...

Ok, but now you have to align the focus!

Think view camera. You have eliminated converging verticals and horizontals, but now you need to adjust the lensboard tilt to get it in focus.

Just to give you an example... I had "aligned" my D-2 to a point image projected was exactly rectangular. I ignored all other parameters. I moved "stuff" to achieve rectangular image. It was PERFECT!

A surprise came in when I actually put a negative in... I could never get all 4 corners (and the center) to come to focus at the same time. It wasn't just little off... it was WAAAAY off!

Your case may be different - but having a rectangular image is not a confirmation of anything. If it isn't rectangular, you know it's off. If it is rectangular... it may be? or may be NOT!

I ended up borrowing an alignment tool and do it right. My suggestion to you is.... if you are even bothering to do this, do it right.....

Square One

Dave Martiny said:

Mats --e

I've tried checking enlarger alignment (at least this aspect of it)
in a similar way, but I just use an empty negative carrier for my
rectangle, Best regards, Dave

Click to expand...

Same here. A 21/4 square if I recall correctly. If its projected
image is square the enlarger is aligned. To test for square,
a square. No more than one corner need be tested. All
four corners will be equally sharp.

Of itself all four corners being sharp does NOT mean
a correct alignment has been achieved. Dan

I have a Beseler 23CIII and last weekend, after previously having aligned the three stages on my enlarger (negative, lens and easel) with a bubble level, I decided do buy a carpenter's square and follow the alignment instructions on the manual. Scroll down to page 7 and see figure 8.

http://backglass.org/duncan/darkroom/beseler_23ciiixl_manual.pdf

My enlarger was misaligned by the bubble level method, but my 11x14 enlargements from 6x7 negs look pretty sharp corner to corner. I always work at f 8.0-11. Now the enlarger seems to be correctly aligned. Please someone correct me if I am wrong, but my guess is that perfect alignment becomes critical when making very large prints. Just wanted to share my experience.

Axel