Home made large format 10x8 enlarger

After having made several x-ray photographs on 10x8 inch sheets of photographic paper, and contact printing them as positives, I thought they would look very well enlarged onto 20x16 or bigger. However, when I looked into prices for even 35mm enlargers, I nearly fell off my chair! 7x5`s are even more expensive, and to enlarge 10x8`s I would have to take out some kind of pact with the bank!

I decided to set about designing one out of fairly inexpensive components, the most expensive being the lens.
The quality of the enlarged prints will ultimately be determined by the lens, so this was chosen first, and everything else, was built around it.

The first consideration for the lens is focal length. For your negative you need a focal length that is at least equal to, and preferably greater than, the length of the longest side of the negative, in this case 10 inches or 254mm. I found a large format camera lens on eBay, for £ 60, it is a Linhof Rodenstock-Rotelar lens with a focal length of 270mm and aperture of F5.6, ideal for this application. The second consideration is aperture of the lens. In the above bargain the largest aperture was F5.6, and really you dont want it much smaller than that, since a smaller aperture requires more light, and thus more heat to get rid of (unless you go solid state, more about this later), and more energy wasted.

When the lens arrived, I took it to the darkroom, to determine the physical size of the enlarger, this was done by mounting the lens in a holder on the bench, with a light bulb where the negative plane is going to be, and a screen, where the paper is going to be. After experimenting with this setup for a while, it became apparent that I could enlarge an 8x10 to 32x40 inches, in the space I have, IF I made the enlarger large enough (~6ft)!
The height of the ceiling in the dark room is a little over 6ft, but that doesnt leave a lot of room to play with, and the enlarger head will be somewhat unwieldy at 2 ½ feet long, and probably quite heavy! So I decided to build it horizonatally.

I also managed to aquire, quite cheaply (£ 32) a set of tapered bellows 8x10 to 5x7, measuring 10x10 at one end and 7x7 at the other, which look much tidier than the originally proposed bag bellows.

Front view of the enlarger. The mounting plate for the lens is simply bolted onto a small board, attached to the front of the bellows.
The lens assembly, is also bolted onto a sled, that mates with a large aluminium rail below, for focusing.

Side view, showing the bellows fully extended.

The light source is in the rear box, and is just a 200W bulb.There is no condenser lens or ground glass plate in here,
though the inside is painted flat white.
I can get away with this, as I`m using paper negatives,which do a surprisingly good job, of eveny diffusing the light!

The negative carrier is simply a 10x8 picture frame with two glass sheets to hold the paper. To access the negative carrier, the little brass hooks are flipped up, and the bellows pushed out of the way.

Home made large format 10x8 enlarger.

By Leslie Wright

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