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  #11  
Old 1st September 2017, 06:39 PM
Jerry Bodine Jerry Bodine is offline
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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.
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  #12  
Old 1st September 2017, 08:27 PM
Adrian Adrian is offline
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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.
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  #13  
Old 2nd September 2017, 01:14 AM
JulioF JulioF is offline
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Well done Ilford!
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  #14  
Old 2nd September 2017, 03:52 PM
DaveP DaveP is offline
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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  
Old 3rd September 2017, 11:36 AM
Lostlabours Lostlabours is offline
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Quote:
Originally Posted by DaveP View Post
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.
They are related emulsions but not the same, both the plain Ilford 100 & 400 as well as the Kentmere 100 & 400 lack some of the refinements of FP4+ and HP5+. Adjuncts are added to the emulsions to improve their latitude, increase the sharpness and reduce grain size.

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
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  #16  
Old 3rd September 2017, 02:48 PM
DaveP DaveP is offline
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Quote:
Originally Posted by Lostlabours View Post
They are related emulsions but not the same, both the plain Ilford 100 & 400 as well as the Kentmere 100 & 400 lack some of the refinements of FP4+ and HP5+. Adjuncts are added to the emulsions to improve their latitude, increase the sharpness and reduce grain size.


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.
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  #17  
Old 4th September 2017, 02:08 PM
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Martin Aislabie Martin Aislabie is offline
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Quote:
Originally Posted by DaveP View Post
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.
I'm sure they are similar but they are not the same - after all the same team created them all.

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
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  #18  
Old 4th September 2017, 03:26 PM
alexmuir alexmuir is offline
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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


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  #19  
Old 15th October 2021, 08:50 AM
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GoodOldNorm GoodOldNorm is offline
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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  
Old 15th October 2021, 10:25 AM
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MartyNL MartyNL is offline
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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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