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Photo Forum / Film Photography / Darkroom / August 2004Reciprocity for Kodak RA-4 papers? When do long exposures matter?
Everybody says to avoid long exposures with RA-4 because of reciprocity issues. Fine but what's long? I've got some overly dense cross processed negatives and one stop from wide open they need at LEAST 20 seconds. Even that to my eye looks like they could use a little burning in. Worse I'd rather have the lens stopped down one more stop. Nick Above 25,....but I doubt you would see a real problem under a minute. > Everybody says to avoid long exposures with RA-4 because of > reciprocity issues. Fine but what's long? I've got some overly dense cross [quoted text clipped - 3 lines] > > Nick  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 >Above 25,....but I doubt you would see a real problem >under a minute. Actually I see a change between my usual 1.8 seconds to say about 4 seconds. That's right, I have a real good timer and I make lots of print with 1.8 second exposures. I will notice a color shift if I must go twice that exposure by time. Larry Under 2.5 seconds for RA paper produces color shifting. Mainly due to inconsistancies in the light source and the paper does have an ISO which means you need a threshold of exposure before the paper will show exposure. > >Above 25,....but I doubt you would see a real problem > >under a minute. [quoted text clipped - 6 lines] > > Larry 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 >Under 2.5 seconds for RA paper produces color shifting. I guess it another way of thinking about it although, most roller transport printer machines at photo outlets work way under 2.5 seconds. Larry Its about the light output of the printer as well, most mini lab printers have the bulb something like six inches over the lens staging area. Its a lot more intense. You also talking image out put thats much smaller,...I wonder if anyone here has ever looked at the printing speed of mini lab machines that produce bigger 8x10 images,....my guess is the exposures are somewhat slower. > >Under 2.5 seconds for RA paper produces color shifting. > > I guess it another way of thinking about it although, most roller transport > printer machines at photo outlets work way under 2.5 seconds. > > Larry 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 >>Under 2.5 seconds for RA paper produces color shifting. > > I guess it another way of thinking about it although, most roller transport > printer machines at photo outlets work way under 2.5 seconds. Since they always print the same way, I'd expect their base filter settings (whether physical filters or in software) to nicely compensate for whatever reciprocity departure effects come from their short exposure. Color shifts and other reciprocity departure effects are only a problem when you *change* exposure time. SignatureI may be a scwewy wabbit, but I'm not going to Alcatwaz! -- E. J. Fudd, 1954 Donald Qualls, aka The Silent Observer Lathe Building Pages http://silent1.home.netcom.com/HomebuiltLathe.htm Speedway 7x12 Lathe Pages http://silent1.home.netcom.com/my7x12.htm Opinions expressed are my own -- take them for what they're worth and don't expect them to be perfect. > Since they always print the same way, I'd expect their base filter > settings (whether physical filters or in software) to nicely compensate > for whatever reciprocity departure effects come from their short > exposure. Color shifts and other reciprocity departure effects are only > a problem when you *change* exposure time. They probably do,...however. Most mini printers have a calibration for each film type (a channel set up) The channel is typically set with a specified balance to accomodate each film the lab choose to balance for....typically the operator has the override option versus allowing the machine to make a judgement concerning exposure time. The operator can specify N+1,2,3,4 for dense negatives and -1,-2 for thin ones....otherwise the machine senses the density although in my experience can be easily fooled. Especially when the subject is taken using flash and the surrounding areas are black or are clear negative,... the subject being much more dense in exposure. 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 It's that each of the dyes has its own reciprocity curve. If you have a color reflection densitometer you wouldn't have a problem --- Jack > Everybody says to avoid long exposures with RA-4 because of > reciprocity issues. Fine but what's long? I've got some overly dense cross [quoted text clipped - 3 lines] > > Nick Why are you worried about reciprocity? If you are making a test print, you will end up adjusting the color to whatever shift occurs when you make the final print. In labs, these papers are used at exposure times varying from less than 0.5 seconds on minilab and smaller size automatic printers, to several minutes when printing large murals with horizontal enlargers. Bernie > Why are you worried about reciprocity? If you are making a test print, you will > end up adjusting the color to whatever shift occurs when you make the final > print. Now that the analyzer is working I'm not making test prints. At least for normal negatives. The only issues is the screwed up cross processed negatives. If I'd correctly exposed them then I wouldn't have any problems but these things are DENSE. If I'm okay below 25 seconds then I can live with it. Nick >If I'm okay below 25 seconds then I can live >with it. As some said before, there seems to be a shift around 2.5 seconds. So if I am at 1.8 seconds and I go to 3.6 I do seem to pick up a slight magneta shift. Larry > >If I'm okay below 25 seconds then I can live > >with it. [quoted text clipped - 3 lines] > > Larry Something is wrong then, the shift is in theory for shorter times than 2.5 seconds & you should be able to filter the light at any time between 2.5 and 25 seconds and get a consistent result without changing the filter provided the exposure time is adjusted as you change the aperture relative to the desired luminance value. In other words make a print at 4x5 size a say that the luminance value equals 1 (exposure 2.5 seconds) at f/8. b) make an 8x10 luminance value equals 2 (because of enlarger being raised to twice the image size) adjust the luminance back to 1 by opening the lens,...or making the time twice the original time in this case it should in theory be 5 seconds...Repeat no filter change is needed if you use the same paper emulsion. I believe the shift on the minus side of correct exposure would be Cyan so the magenta difference you see is normal. 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 > So if I am >> at 1.8 seconds and I go to 3.6 I do seem to pick up a slight magneta shift. [quoted text clipped - 4 lines] >2.5 seconds & you should be able to filter the light at any time between >2.5 and 25 seconds and get a consistent result Hey, I am just discribing what I get. As typical with photography, it my results and not necessary anyone elses. Larry Because some color shifts are not liner, they may only appear in certain areas of the image,......like the highlights and shadows. Read the other posts regarding short exposure,....mini printers bulbs are 6 inches from the paper (Its also an issue of out put intensity being matched to the distance from the paper). You can with enough voltage stabilization of the light source produce filtration that negates the failure that happens from long exposures,... at least thats my understanding. Why do you think those machines cost $25,000 (arbitrary figure) new? > Why are you worried about reciprocity? If you are making a test print, you > will [quoted text clipped - 6 lines] > printing large murals with horizontal enlargers. > Bernie 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 |
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