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Photo Forum / Film Photography / Darkroom / November 2004going from 8x10 to 11x14
Hi. When one has made the perfect print in 8x10 and then decides to go larger to 11x14 how much should the f stop be opened to comensate for the higher magnifacation? Michelle > Hi. > > When one has made the perfect print in 8x10 and then decides to go larger > to > 11x14 how much should the f stop be opened to comensate for the higher > magnifacation? It seems highly unlikely that one who cannot answer that question has made The Perfect Print. > > Hi. > > [quoted text clipped - 5 lines] > It seems highly unlikely that one who cannot answer that question has made > The Perfect Print. Well, let's see _your_ prints... > Hi. > [quoted text clipped - 3 lines] > > Michelle Approximately half an f/stop.  SignatureLF Website @ http://members.verizon.net/~gregoryblank "To announce that there must be no criticism of the President, or that we are to stand by the President, right or wrong, is not only unpatriotic and servile, but is morally treasonable to the American public."--Theodore Roosevelt, May 7, 1918 close enough since it's unlikely the first print @8x10 was made on the 11x14 paper. For around $30 you can get an Ilford EM-10 exposure meter and eliminate all the guess work. That's less than the price of a 100 sheet box of 8x10 paper. Signaturedarkroommike ---------- > > > Hi. [quoted text clipped - 6 lines] > > Approximately half an f/stop. > close enough since it's unlikely the first print @8x10 was made on the 11x14 > paper. [quoted text clipped - 5 lines] > -- > darkroommike (1+M)^2 / (1+m)^2) = exposure factor. M or m is the magnification ratio, which is 8.4x for 35mm and 2x for 4x5 negatives enlarged to 8x10.1+M is the desired enlargement and 1+m is the print size being enlarged from. Square and divide. Or, for 35mm multiply the exposure time by 1.8, or from 4x5 by 1.6. This equals somewhere between 1/2 and 3/4 stop increase. > ---------- > > [quoted text clipped - 15 lines] > > is not only unpatriotic and servile, but is morally treasonable > > to the American public."--Theodore Roosevelt, May 7, 1918 ---------- > (1+M)^2 / (1+m)^2) = exposure factor. > [quoted text clipped - 6 lines] > from 4x5 by 1.6. This equals somewhere between 1/2 > and 3/4 stop increase. 1. Make a good 8x10 2. Pull the negative carrier, null the meter, using the dial, using the "raw light" at the center of easel. 3. Insert carrier, elevate head, compose and focus 11x14 4. Pull the carrier and, null the meter, using the aperture ring on the enlarging lens, using the "raw light" at the center of easel. 5. Make a perfect first print. Note that neither my method or Tom's will account for different paper emulsion batches, speed shifts from age in different packages of paper or fog levels (yes, you could get more--or less--fog when changing magnification). Note 2: Magnification factors can be more accurately determined by measuring the projected IMAGE at the easel and then a second computation for actual magnification is required. But my method doesn't require ANY math!! And rather than approximate it is rather exact. Signaturedarkroommike > ---------- > > [quoted text clipped - 21 lines] > fog levels (yes, you could get more--or less--fog when changing > magnification). Should also note these methods calculate only the base exposure change. Fine tuning is usually necessary but you don't have to waste paper starting all over. Enlarging also reduces overall contrast, so higher contrast filter/paper may be desirable or greater buringing/dodging. > Note 2: Magnification factors can be more accurately determined by > measuring the projected IMAGE at the easel and then a second computation > for actual magnification is required. yes always measure the projected image to projected image size. The magnification ratio, to be clear, is the linear enlargement from the original negative to m or M. A 4x5 negative to 8x10 print is 2x because 10 / 5 = 2x (5 inch negative x 2 = a 10 inch print size.) 4x5 to 11x14 is 2.8x (14 / 5 - 2.8) > But my method doesn't require ANY math!! And rather than approximate it is > rather exact. True but the math doesn't require any $$$. Which is easier likely depends on the mindset :-) > But my method doesn't require ANY math!! And rather than > approximate it is rather exact. I'd say EXACT. That is because the level of light is adjusted at the aperture to the exact same level. Exposure time remains the same which is my problem with the EM-10. Any calculation done for exact same exposure must include the change in lens speed. The ratio of areas method will make for a ballpark exposure but not be exact. Dan > For around $30 you can get an Ilford EM-10 exposure meter and > eliminate all the guess work. That's less than the price of a > 100 sheet box of 8x10 paper. I'm thinking of a step up from the EM-10. Do you know of an enlarging meter that will read out a time correction? An EM-10 is good for f stop corrections only. Dan I usually use a difference in exposure time rather than changing the stop. Assuming the print is not actually the full size of the paper, the general rule is: square root of (length of the larger image divided by the length of the smaller image) multiplied by the #of seconds of exposure. In reality, I have found that the image I get is usually too intense by this method, so I often have to adjust to approximately 85%-90% of this calculated time. Although this sounds a bit goofy (and maybe is), to me there seems to be a difference in the visual impact of the "same" image when it is blown up. Perhaps it is that a larger mass of certain values has a more overpowering impact on the eye. Ultimately, I'd like to see the same sense of values in the two prints. Maybe this is why when I have seen certain photographers' works at a gallery if the works are available in different size prints, I am drawn to one print size of a certain inage contrasted with another? The image seems to work better when it is smaller or larger. Sam > Michelle > I usually use a difference in exposure time rather than > changing the stop. ... the general rule is: square root [quoted text clipped - 5 lines] > too intense by this method, so I often have to adjust to > approximately 85%-90% of this calculated time. The reason for the needed adjustment is the change in focus for the larger print. Just as for a camera lens an enlarging lens is most fast at it's focal length and that is when it is focused at infinity. The lens becomes faster as it draws nearer the negative. Dan Michelle, Why not just trust your eye, and start with another test strip. The larger print might have a different look and feel anyway, so why not start fresh. You can keep the 8x10 print nearby for reference, and who knows, you may actually improve upon the "perfect print" ;-) Curt Blood > Hi. > [quoted text clipped - 3 lines] > > Michelle Divide the area of the larger by the smaller and use the result to multiply the time of the exposure. Don't change the f/stop. 11x14 = 154 8x10 = 80 154/80 = 1.925 Increase the time by a factor of 2. |
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