Last weekend I discovered that my enlarger wasn't as square to the baseboard as I hoped. Today I decided I would try and rectify this.
I have discovered that I needed to shim the column by around 3mm on the front of the column to get that square to the baseboard. I also checked the alignment between the bottom of the housing (just below the negative holder) and the lens board and have found that there is a bit of difference, around half a mm from front to back (side to side is adjustable, so I have got that reasonably spot on). I can see it is due to the slop between the rails and the lens board housing. I have to admit, this annoys me a little.
Am I being pedantic? Should I really be chasing better precision or am I wasting time?
Nothing wrong with wanting it as correct as you can get it. With an enlarger, the most important parts to have correctly parallel are the negative holder and the lens mount. You can get away with a fair amount of error at the base board but a tiny error in the negative position will translate to a lot of focusing error.
The degree of precision to which you align the negative and lens is dependent on your magnification. The greater the magnification, the more closely you need to have the lens and negative aligned.
If you work backward through the 'diffraction/defocus' equation for enlarging you can calculate how far off you can be and still have a good print at a reasonable viewing distance.
If we say 10x enlargement of 35mm negative at f8 and a 50mm lens:
Focal spread at the baseboard level will be 20mm at f8 based on the diffraction/defocus equation ( f8 = 20/(10+1) * square root of 20)
With this number and the simple lens equation (1/f = 1/p + 1/q) we can calculate the side to side displacement of a negative where each side focuses 10mm higher or lower on the baseboard from the center of the negative.
1/50 = 1/600 + 1/54
1/50 = 1/800 + 1/53
So one side of the negative will be 54mm from the lens and the other side of the negative will be 53mm from the lens. So the approximate the maximum allowable negative stage displacement for an 10x enlargement of 35mm frame is about 1mm.
It is too common for the weight of the enlarging head to gradually tilt the column forward, requiring shimming as Hoffy did. This is especially true of enlargers with fiberboard bases. Replacing these base with heavy plywood (with the surface plys running from back to front) may be worth while.
Thanks for the replies. By the sounds of things, I am borderline pedantic at the moment, but I would like to get the alignment between the lens and the negative holder spot on. If you are saying 1mm maximum at 58mm, I would probably be OK. I know my prints are good enough, but I have hardly done decent corner to corner checks.
One thing I would like to do is possibly build a steel frame, for which I could mount the enlarger to. I am not 100% sure whether I will go ahead with this, but it certainly will help to enable a good base point to start with.
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Speaking from experience....
Aligning an enlarger precisely is pain in a butt and without correct instruments, it's pretty much impossible. After struggling with various methods and many makeshift tools, I ended up sourcing a ready-made tool for the job to finish it up. Carpenter's level isn't even close to sensitive enough.
You hear lots of stories like if your image is perfectly square on the baseboard, it's good to go. NOT SO! It is possible to have a square image and have one corner perfectly in focus but the opposing corner perfectly OFF focus. Try to bring that in focus and the image now isn't square.... Then do the other corner and the opposing corner. It's quite maddening! Oh, let's not forget baseboard warping, vertical support sagging, and side to side play.... Raise the head and lower, it's off again.
Unless you have the correct tool and have the wills to spend hours on end to get it right, if it's close enough, I wouldn't mess with it. I was forced to do one because I had to rebuild my second enlarger. It taught me a lesson NOT to try to better my primary enlarger.
Develop, stop, fix.... wait.... where's my film?
Originally Posted by tkamiya
Your reference to "the correct tool" is intriguing. What tool do you suggest?
Will something like the LASER Alignment Tool from Freestyle meet your requirements?
Ralph Javins, Latte Land, Washington
When they ask you; "How many Mega Pixels you got in your camera?"
just tell them; "I use activated silver bromide crystals tor my image storage media."
I used a Bessler's alignment tool that I could borrow. (my enlargers are Omega) This device has two bubble levels mounted at a right angle to each other. Very nice... Laser kind would be nice but I really didn't want to buy one.
Develop, stop, fix.... wait.... where's my film?
The critical alignment for big enlargements is between lens and negative. The exact analogy is taking a picture of a billboard at infinity. It doesn't matter if the billboard is perpendicular to the film plane.
Originally Posted by hoffy
I like simple solutions. To check alignment, I use a piece of black (developed) film with a grid of lines scratched on the emulsion side with the point of a sharp knife. At full aperture and at the enlarger height required, I slip narrow card shims under one side of the negative carrier until I have it spot on. For a 12" x 16" I need 3 thicknesses of postcard. I then expose the paper with the lens stopped down to f5.6 or f8. It is worth the effort.
In this way I also discovered that my enlarger column (I would guess most enlarger columns) droops when the enlarger is up towards the top. My solution was to do away with the baseboard, fixing the enlarger column directly to the bench, and bracing it against the wall behind using a length of threaded bar and some nuts inside the column. These measures must also help to prevent that other source of unsharpness, vibration.
Last edited by Jonathan R; 06-07-2011 at 11:32 AM. Click to view previous post history.