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> Ilford Reciprocity Calculation |
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#11
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I noted Ilford's attempt to explain the reason for the increased contrast resulting from reciprocity corrections, which I thought could be stated more clearly (or is it just me?). Allow me to say it my way:
The illumination level at the film plane in the shadows is subject to the reciprocity issue and thus requires the recommended increase in exposure time. However, the higher illumination level of the highlight(s) at the film plane does not require the reciprocity correction, so the additional exposure to the highlights produces a density increase that is disproportional to the shadow density that is being maintained. This causes an increased slope of the characteristic curve (greater contrast) that necessitates a shorter development time to correct the slope. My planned reciprocity testing of my favorite films to about 4 minutes+ will allow me to determine when a specific reduction in development time is needed for contrast control. I have no feel for how long the illumination level of a scene can be expected to remain unchanged. Last edited by Jerry Bodine; 1st September 2017 at 06:49 PM. |
#12
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I use a simple formula I can do in my head. It works for me.
T = 0.1*t^2 + 2t Where T is the compensated exposure time and t is the metered time. That formula is is close to the old Ilford curve for t greater than about 2sec. With these long exposures being off by a second or two makes hardly any difference. |
#13
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Well done Ilford!
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#14
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I note the given factor for FP4+ is the same as Kentmere 100, and For HP5+ it's very close to the factor for Kentmere 400...... nudge nudge wink wink say no more.
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#15
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Quote:
I've always done my own practical tests for reciprocity, the last was with Fomapan 100 and 200 which are supposed to have poor reciprocity failure but I fond reslts close to FP4+ as idicated in Jerry's chart using the Ilford factor, it may well help that I shoot both at half box speed anyway. Ian |
#16
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Yep I realise that, the Kentmere versions supposed to be lower in silver too (hence cheaper). But still, the chart does seem to confirm their inherent similarities that everyone suspects. |
#17
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Can you imagine being in a business planning meeting " hey guys, I've got a great idea whey don't we sell HP5 and FP4 as Kentmere films and sell them for less money ! ". What would the reaction be in the room ? - stoney silence , rolling of the eyes or something a bit more fruity ??? Ilford have always struck me as quite business savvy - after all until quite recently it was actually their own money they were talking about. Martin |
#18
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The other Ilford films (Pan 400, etc), don't produce negatives that match the overall quality of HP5+, or FP4+.
Alex Sent from my iPhone using Tapatalk Pro |
#19
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I have the Ilford chart but I would like reciprocity factors for other films. Can anyone provide factors for: Adox, Fuji, Foma and Kodak films. Thank you in advance.
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#20
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I use an app called reciprocity on my android phone. It's free, very simple/basic and no ad's.
It's probably the next best thing to buying the film and doing all of the tests and the calculations yourself.
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MartyNL “Reaching a creative state of mind thru positive action is considered preferable to waiting for inspiration.” - Minor White, 1950 |
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