homemade Alignotron

[frank_scheitrowsky]

I read with interest the post about the Alignotron and it got me

wondering if such a device couldn't be made simply with a lazer

pointer. One would have to mount it on it's own base so that it is

perfectly perpendicular to it, and put a circular paper or plastic

disc around its top so one can see where the reflection of the beam

comes down again. This is such a perfectly simple idea, or am I

missing something and this is just a simple idea from a simple mind?

 

Frank

[lwg]

Yes you can do it this simply. I built one from a Crossman laser scope for an air gun. I think it was $25 from Wal Mart, but it is much better than a laser pointer since it will stand upright on its own, and it has small screws to adjust the aim of the beam. Adjusting the beam was by far the hardest part. Since I was lacking two perfectly parallel surfaces I had to just rotate the pointer until the reflected spot stopped moving. Then I could adjust the lensboard. You also need a mirror to reflect off of.

[ed b.]

A simple alignment device can be made from two mirrors, but you have to drill a hole in one of them, and it has to be the same size as your negative carrier. Place the mirror with the hole in the enlarger where the negative carrier goes, mirrored surface pointed down, and place the other mirror face up on the baseboard. Adjust the enlarger until you see only a single circle of light in the bottom mirror when you turn on the enlarger lamp.

[andy_eads]

Very flat front surface mirrors are available from surplus stores. Also, rather than drilling a hole in one of the mirrors, you need only remove the silvering from the desired spot. A razor blade and some TLC will do the trick.

[mark_gulbrandsen1]

One thing all of you have missed is that the commercially available laser alignment devices are precision calibrated devices... your home made devices are not. Commercial devices are calibrated to point exactly straight out from their base within a certain calibration distance. Merely setting any laser on your enlarger base is not really good enough... its got to be calibrated otherwise your final calibration of your enlarger will be the same (or more) than the error of your homemade laser. Probably the best of the enlarger alignment tools is made by Versalab and called the Parallel, it is calibrated to the piece of reflective glass that it comes with!! Mine has a calibration sticker on the bottom and the laser has its own aperature so you end up with a round spot.... laser diodes as used in these items generally project an oblong spot. Another thing that you will also need is a precision ground piece of glass so the laser beam is reflected exactly straight back down..... Any error at any stage... laser, glass(or mirror) will contribute to you still having an enlarger that is not properly aligned. Alignment with this presision gauge is not only touchy but takes quite a while.... its high accuracy causes it to be touchy, just like a machinists level!!

 

Here is a link to information about the Versalab Parallel...

http://www.versalab.com/server/photo/products/parallel.htm

 

Mark

[conrad_hoffman]

Mark, from a standards and certification perspective (i.e., paperwork), you are completely correct. From a practical standpoint it's pure nonsense. Many optical alignments rely on first principles, and the parallel mirror technique is one of them. You will not better it with a laser based device (unless you start viewing interference fringes, gross overkill for the application), and it's basically the initial step in aligning plano interferometers to sub-wavelength precision. The technique is far more precise than the degree to which any commercially manufacturered enlarger can be aligned. Perhaps you own stock in the company, or perhaps you need to justify a large expense, but there is no technical justification for discouraging use of that method. As far as making your own laser based device, that is also well within the capabilities of most amateurs, and again, can be done to more than sufficient precision for the task at hand. We suffer from way too much "you have to buy it or it isn't any good" mentality.