Ian Grant
Allowing Ads
The response will probably be something like "that's what I meant all along". Yeah sure. Among the other statements made earlier: The real speeds of the TMax films are lower than their ISO ratings (as opposed to other films), etc.
On the subject of ZS EIs differing from ISO speeds by predictable amounts, I'd have to ask why you think that would/should not be the case. If one compares the speed measurement criteria of the two methods, it makes sense there should be a relatively constant difference between the ISO speed and ZS EI.
On more than one occasion I've pointed out to you that there's no predictable differences between Zone system EI's and box ISO speeds, in theory you might expect a correlation between the two but it doesn't exist.
The answer is very simple, despite there being a current ISO standard not all films have been tested the same way by the manufacturers to determine box ISO.. Agfa always used the DIN methodology which was also part of the ISO standard when their films were released. EFKE probably used the DIN method as well but put the Tungsten ISO on the boxes rather than the higher Daylight ISO. Kodak use the ASA standard which was changed to allow the manufacturers to choose what developer they used for their tests. That in itself introduces a significant variable factor.
Nobody has presented any evidence supporting the assertion the TMax films in particular perform better when rated lower than ISO speed, in comparison to other films with the same ISO speeds. When I plot curves for the TMax films relative to Tri-X, FP4 Plus, Delta 100 and Acros, I see no sensitometric evidence of the TMax films being slower.
...but what drops when development is reduced is an EI, not speed. When an EI is determined using a fixed density criterion (Zone System for example), it will always vary directly with development. Develop to lower contrast, and EI declines. This is not necessarily the case when it comes to "speed". Speed has to do with the 'shadow' gradient in relation to the overall gradient...
Stephen, the ISO tests allowed manufacturers to use either the ASA, BS or DIN tests, and has done since 1974. Where the confusion arises is the DIN methods are not valid the US or the UK which have to use the ASA/BS component of the ISO standard for testing film speed.
Just checking and my films are all marked with the ISO speed as you say but that is marked as ISO 400 / 27º, ISO 200 / 24º, ISO100 / 21º etc
EFKE improved their films slightly, I've not used the PL100 although I have some I bought last year, they may have improved the red sensitivity . This is the datasheet from the first EFKE films I used back around 1975, before they changed the names to the ASA equivalents:
the 1974 ISO standard encompasses both ASA and DIN standards, so technically both ASA and DIN speeds disappeared but in practice films are labelled still with both and either methodology can be used.
Speed has to do with the 'shadow' gradient in relation to the overall gradient.
I highly doubt that. It's much more likely that the ISO standard hadn't been universally adopted and that ASA and DIN were still being used. The only way to prove it one way or the other is to have a copy of the 1974 ISO standard. It is still available and I have found it in the New Zealand Standards website. It's around $60 US. I'm debating.
Did a search as well. You can indeed buy the standard, for example http://www.iso.org/iso/iso_catalogue/catalogue_tc/catalogue_detail.htm?csnumber=7690I highly doubt that. It's much more likely that the ISO standard hadn't been universally adopted and that ASA and DIN were still being used. The only way to prove it one way or the other is to have a copy of the 1974 ISO standard. It is still available and I have found it in the New Zealand Standards website. It's around $60 US. I'm debating.
Did a search as well. You can indeed buy the standard, for example http://www.iso.org/iso/iso_catalogue/catalogue_tc/catalogue_detail.htm?csnumber=7690
Could only find the first page for free:
My bad. Thought it would be covered in this standardWhat you have is for exposure meters. We are discussing film speed determination.
This looks excellent for a film that is underexposed by two stops
This looks excellent for a film that is underexposed by two stops
pentaxuser
First of all;the color stain easily disappears with HCA and added washing.2nd learn to love the film grain; It's great and digital folks add it in PS to fake the real film look.I'm surprised this hasn't been stickied yet.
But can we put together a guide for getting beautiful black and white negatives with no hassle?
So far, I know enough to use a fast film. I like fp4 , but tmax 100, apx 100, and delta 100 are all great. Though I dislike tmax because the color stain is hard to get out.
But what developer and what actual ISO?
Also, what other tips can you give? Use fresh film. Keep the film cool.
Does temperature control during development really matter?
What about agitation?
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