Re: Ilford - new reciprocity failure compensation factors
Quote:
Originally Posted by
devb
Could the other variables include environmental factors like the spectral qualities of the light being captured?
Yes, of course, as film spectral sensitivity is not flat. SPD (spectral power distribution) of light that our silver crystalls receive depends on the illumination SPD and on the spectral reflectiveness our subject has, and our filters. So at the end we have light with particular SPD reaching our silver crystals. Is SPD peak hits a valley in the film spectral sensitivity curve then we need longer exposure, with greater LIRF correction (Low intensity reciprocity failure).
I may be like the way exposure correction for a particular color filter depends on the light source, see here different corrections for same filter (for TMX) depending on if daylight or tungsten, page 20 : http://www.kodak.com/global/en/profe...JGWRQHIO3JXWJI
Also a great variation (Alaska -30ºC vs Death Valley +45ºC) of temperature will substantially change LIRF, it is lower with cold, as astronomers saw in 1930s, they were using "dry ice" cold backs.
Re: Ilford - new reciprocity failure compensation factors
Quote:
Originally Posted by
tgtaylor
I'd take the new reciprocity factors with a heavy grain of salt. I have had excellent results using Ilford's published reciprocity graph for Delta 100. For example the negative for this salt print
http://spiritsofsilver.com/yahoo_sit...5649_large.jpg was metered at 30 seconds which translated to 160 seconds on the graph. Important exposure considerations were the light on the water, the clock, and the office lights. Plugging 30 seconds into the new equation gives an exposure of 73 seconds - almost half that of the old. If I had cut the exposure by 1/2 I would not have gotten the print that I ended up with which is exactly as I visualized it when I took it.
Thomas
I'd add that beyond any LIRF calculation it is a suitable practice giving an extra stop and then making a N-1 compression, because LIRF works different in the shadows than in the lights, as Ilford document says, thus increasing contrast, so it is easy to get too much contrast in night photography.
Best LIRF calculation is Acros calculation: no calculation, just an easy rule, and good negatives.
Sadly Fuji nasty managers have destroyed LF Acros market and we'll attend a funeral, R.I.P.
Re: Ilford - new reciprocity failure compensation factors
Quote:
Originally Posted by
Pere Casals
I'd add that beyond any LIRF calculation it is a suitable practice giving an extra stop and then making a N-1 compression, because LIRF works different in the shadows than in the lights, as Ilford document says, thus increasing contrast, so it is easy to get too much contrast in night photography.
Best LIRF calculation is Acros calculation: no calculation, just an easy rule, and good negatives.
Sadly Fuji nasty managers have destroyed LF Acros market and we'll attend a funeral, R.I.P.
While overexposing by 1-stop and developing N-1 might work for night photography with Delta, I needed all the density the film could deliver for printing as a salt print. That meant over developing the negative to the max. Acros, of course, would have required a 30 second exposure but I wonder if the water would have appeared as smooth as it does in the Delta. At the time the Bay had a strong current running and I was looking for the silver light reflecting off the black bay water under a black sky. No fog was present but ripples or waves would have resulted in a different look.
Thomas
Re: Ilford - new reciprocity failure compensation factors
Quote:
Originally Posted by
tgtaylor
While overexposing by 1-stop and developing N-1 might work for night photography with Delta, I needed all the density the film could deliver for printing as a salt print. That meant over developing the negative to the max. Acros, of course, would have required a 30 second exposure but I wonder if the water would have appeared as smooth as it does in the Delta. At the time the Bay had a strong current running and I was looking for the silver light reflecting off the black bay water under a black sky. No fog was present but ripples or waves would have resulted in a different look.
Thomas
Hello Thomas,
Of course I've no doubt Delta is a superb film that will work perfect with the right process, and I ignore the intrinsics of the amazing Salt Printing, one day I'll try it !!! Now I'm very busy with dry plates...
Anyway, if you want 2min exposure with Acros it is also possible, by stopping diafragm or ND filter... IMHO the advantage Acros (still) has is that it not increases contrast much with long exposures. A film with LIRF has more LIRF for the shadows, as the the Ilford doc points. So in reality one has to make a LIRF correction calculation for the shadows and another one for the lights, and then one knows in what zones of the negative each zone of the scene will end, and if resulting contrast will we printable without troubles.
The disadvantage Acros has is that infame Fuji managers are to discontinue it for LF... and this is a major disadvantage !
Another aproach I'm considering for night photography is minimal agitation with Pyrocat HD as Steve Sherman teaches it
Regards
Re: Ilford - new reciprocity failure compensation factors
Quote:
Originally Posted by
tgtaylor
I'd take the new reciprocity factors with a heavy grain of salt. I have had excellent results using Ilford's published reciprocity graph for Delta 100. For example the negative for this salt print
http://spiritsofsilver.com/yahoo_sit...5649_large.jpg was metered at 30 seconds which translated to 160 seconds on the graph. Important exposure considerations were the light on the water, the clock, and the office lights. Plugging 30 seconds into the new equation gives an exposure of 73 seconds - almost half that of the old. If I had cut the exposure by 1/2 I would not have gotten the print that I ended up with which is exactly as I visualized it when I took it.
Thomas
That is an exquisite salt print, Thomas. :-)
Re: Ilford - new reciprocity failure compensation factors
Has anyone put the new Ilford reciprocity correction factors to the test in the field? I would be interested to hear your experiences.
Re: Ilford - new reciprocity failure compensation factors
Quote:
Originally Posted by
David Karp
Has anyone put the new Ilford reciprocity correction factors to the test in the field? I would be interested to hear your experiences.
Yes... I shot at night with HP5
David, the newly Ilford published correction factors are accurate, but only useful for very careful spot metering en each zone. The former graph in datasheets contains a safety factor of aprox 2/3 stop (for 15s base at least), and it is a good advice for an starting point.
The right correction factors are very sensitive to the way we meter, and to the other factors, so IMHO the old good graph recommends a good starting point.
For example, the graph says that 15s base has to be corrected to 50s, while the new factors say 35s for HP5 and 30s for FP4.
Principal problem with correction factors is that the shadows have more failure than mids and highlights, so one thing is correcting for the scene average illumination and another one is correcting for the shadows.
IMHO if we have a low contrast dull scene the new factors can be used, but with a contrasty scene (urban night) we should apply an additional correction if we want some shadow detail, and in this case the old graph included a lot of wisdom to get our starting point.
Lower correction factors were published by Howard Bond 5 years ago: http://phototechmag.com/kodak-ilford...te-films-2013/
One has to be careful when comparing LIRF features of different film manufacturers, because ilford used a generous safety margin for good practical results.
Anyway, if one want to do the thng perfect one should calibrate LIRF, this is making contact prints of the Stouffer wedge with known lux, and using also long exposures (15, 30, 60s , 120 for example) and different N+/-. With that information one can guess very well what density he will obtain in the negative for each scene metered spot. I made some informal tests in this way, enough to see that full calibration it's interesting for night shots.
Let me repeat, IMHO new factors are useful for accurate metering, if one wants to use spot metering in the shadows to know in what density it will end a "zone" in the negative, but better make calibrations with the Stouffer. If it's not the case, better to start with the old graph, because that safety margin is benefical to conserve shadows.
Re: Ilford - new reciprocity failure compensation factors
Math challenges me. I looked up factors and looked at Ilford's explanation, including the mention of the x-superscript-y button on calculators. I get different results if I multiply a given time by 1.31 (HP5+ factor) or use that time, then press the x-super-y button on Windows calculator, and then 1.3. Which is correct, and why?
Thank you.
Re: Ilford - new reciprocity failure compensation factors
Quote:
Originally Posted by
Ulophot
Math challenges me. I looked up factors and looked at Ilford's explanation, including the mention of the x-superscript-y button on calculators. I get different results if I multiply a given time by 1.31 (HP5+ factor) or use that time, then press the x-super-y button on Windows calculator, and then 1.3. Which is correct, and why?
Thank you.
Since we are both lousy at math I tried the same thing you did. I plugged in 10 sec and 100 sec for meter times. Then did it the WRONG WAY by simply multiplying the P factor times my 10, of 100 seconds.
Then I did what Ilford clearly says to do. When we use the P factor with the special key Xy we get far different numbers that in no way are direct multiples of our wrong way attempts.
Just follow the instructions, splaining won't get us anywhere. It's calculus factorial. Never any fun.
Re: Ilford - new reciprocity failure compensation factors
Do they state what their specific light source was (K)? Even if threshold exposures are matched, significantly different colors of filtration cannot just be corrected with a filter factor, because the contrast gamma also significantly diverges at long exposures, and is inconsistent from one film to another, and even with the same film at different lengths of exposure. You're back to square one, realistically needing to test in advance with analogous parameters.