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Photo Forum / Film Photography / Darkroom / July 2004Enlarger Scale
My enlarger has a vertical scale marked in increments of one inch. To me the obvious use is to record enlarger setting while making a print. Does this scale have other function/uses that I can take advantage of? Is there a way to use this scale to estimate the enlargment factor? Alan Tippett > My enlarger has a vertical scale marked in increments of one inch. > [quoted text clipped - 5 lines] > > Alan Tippett You can calculate magnification and exposure correction (effective stop) from the ratio of the lens to film and lens to subject distances but the scale on the enlarger probably does not indicate either directly. Once you calibrate it you could use it to preset for both. I find it easier to use a simple exposure matching meter than to try to calculate the exposure and generally set the magnification visually. I use the Ilford EM-10, which is cheap and works well. Once you have established a good exposure you can reset it using the meter. The sensitivity dial can be calibrated in stops and time so that it can be used to change time as well as adjust the stop. Which enlarger do you have. I remember old Kodak commercial enlargers having distance scales on the support.  Signature--- Richard Knoppow Los Angeles, CA, USA dickburk@ix.netcom.com > You can calculate magnification and exposure correction >(effective stop) from the ratio of the lens to film and lens [quoted text clipped - 10 lines] > Which enlarger do you have. I remember old Kodak >commercial enlargers having distance scales on the support. My enlarger is a Beseler 23C. This problems is further complicated by the fact that it has the extention on it which raises the enlarger about 6 inches above the board. You can make a magnification guide good with any enlarger by making a ruler marked off in units equal to one side of your film holder opening. Then lay it across the projected image and read the magnification directly. >> You can calculate magnification and exposure correction >>(effective stop) from the ratio of the lens to film and lens [quoted text clipped - 14 lines] >that it has the extention on it which raises the enlarger about 6 inches above >the board. >You can make a magnification guide good with any enlarger by making a >ruler marked off in units equal to one side of your film holder >opening. Then lay it across the projected image and read the >magnification directly. Sounds like a really good approach. I am going to try it. But shouldn't the units be 1.4 times (sqrt of 2) the negative dimension? For example a 4X5 would go to 8X10 which is 4 times not double. Alan TIppett You may want to try marking the enlarging column rule in paper size and stop adjustments: Size Linear Stop dim. adjust. scale 4x5 1:1 0 5x7 1:1.4 1 8x10 1:2 2 11x14 1:2.8 3 16x20 1:4 4 20x24 1:4.7 5 24x30 1:5.6 6 Numbers above are approximate, and the aspect ratio changes for 5x7 and 11x14. Such a scale needs to be made from real exposure tests so it is accurate for your enlarger, light source and lens and different scales will be needed for negative sizes. Things are a lot messier than what the freshman physics book shows. With a stops scale, when going from 5x7 -> 16x20 the adjustment is "4 stops - 1 stop = 3 stops". Which may or may not be easier than (4 / 1.4) = 3 It is also an interesting table to contemplate. The top chart shows how little changes in enlargement ratio at large print sizes cause large swings in exposure. 4x5 -> 5x7 is a one stop exposure adjustment and it doubles the print size. That same 1 stop change only gets you from 20x24 to 24x30 - a measly 20% change as the eye sees it. Power rules get really obscene when it comes to pricing sailboats and the price is proportional to the cube of the length. Changing your mind and 'supersizing' your boat from 40 to 42 feet can add $20,000 - $40,0000 to the price: $40,000 for an extra 2 feet of boat! And all because the wife wants a different bathroom layout. If an 'area' scale is used then the ruler would read: 4x5 => 20 5x7 => 35 8x10 => 80 11x14 => 154 16x20 => 320 Going from 5x7 to 16x20 with an area scale would involve calculating sqrt(320/35) ~= 3 stops. -- Nicholas O. Lindan, Cleveland, Ohio Consulting Engineer: Electronics; Informatics; Photonics. Remove spaces etc. to reply: n o lindan at net com dot com psst.. want to buy an f-stop timer? nolindan.com/da/fstop/ > >You can make a magnification guide good with any enlarger by making a > >ruler marked off in units equal to one side of your film holder [quoted text clipped - 6 lines] > > Alan TIppett |
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