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  #1  
Old 25th July 2020, 11:38 PM
maxwellmakosk maxwellmakosk is offline
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Default What is CL? / Creating XTOL Temp Converter

I am in the process of writing a program to reliably convert XTOL times/dilutions/speeds to different temperatures. I have no clue what to expect so to start I am just assembling all the data available to me and generating exponential functions for each time/dilution/speed set I can find. When Going over Kodak J-109 I noticed to the right of the speed column there is one labelled "CL" with values ranging from roughly 0.5-0.9. What in the world is this? Never come across it before then again Ive never looked this closely at any Kodak documentation.

In addition would any experts have any suggestions on what to expect from this endeavour in terms of temp conversion in general? I've made a program for HC110 before which used an arbitrary formula and just converted values you threw at it but for this XTOL program I want to be more precise. I am aware that its bad practice to use any "universal temp conversion" charts such as the infamous one from ilford but how nuanced is it really? I remember reading a discussion with PE from photo trio on the subject a while ago (which I cannot find anymore) and the general consensus there was that conversion rates differ per film AND per developer, so I may have a ton of work ahead. I am curious how much these rates differ. In any case these are questions I hope to answer myself in due time but any input is much appreciated

Edit: Just realised it CI not CL whoops! Should have noticed with "Exposure Index" right next door but the I,L switch up will always confuse me.
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  #2  
Old 26th July 2020, 12:27 AM
alexmuir alexmuir is offline
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It looks like CI which would be Contrast Index
Alex


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  #3  
Old 26th July 2020, 09:09 AM
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MartyNL MartyNL is offline
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Firstly, I think it's admirable what you're attempting to do and secondly, I'm not am expert. However, I have used Kodak Xtol and Tmax film developers for decades with primarily Kodak Tmax and Ilford Delta films. And these are wonderful combinations for the kind of look and feel that I'm after in my photography.

In my view, sticking to Kodak's own data, which I believe we can safely assume has been derived from real film laboratory testing under controlled conditions, I don't think you can go too far wrong.

However, IMO, the further afield you may stray from the official publications, therein lies the problem. Alternatively, you may need to conduct a lot of testing yourself, not without considerable time and expense, in order to arrive at statistically relevant data, for your program to be meaningful.

Best of luck with your endeavour!
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Old 26th July 2020, 09:20 AM
maxwellmakosk maxwellmakosk is offline
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Ahh Thanks Alex! Clear as day. And Thank you Marty, I sort of figured I would have to generate some of my own data as well, id like to support at least the major film manufacturers emulsions. I have most of the equipment to make it happen but definitely not the time! Its always like that. Anyway thanks again!
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Old 26th July 2020, 11:18 AM
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Talking of CI, are you planning on incorporating data for both diffuser enlargers and condenser enlargers?
Not to mention the ever growing 'other way' of printing?

And just out of curiosity, why Xtol?

Come to think of it, which dilutions will be covered and some use replenished developer?
Which formats?
Which agitation methods, rotary, tray, hand-tank, (semi-) stand?

No doubt, all questions you're asking yourself at this moment?
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Old 26th July 2020, 12:54 PM
maxwellmakosk maxwellmakosk is offline
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Haha yes questions I am asking myself indeed! I always find it hard to limit the scope of my ambitions to make them actually attainable sometimes and this is no different. Who knows what this will turn into but at the moment I don't plan on incorporating any data for enlargement.

This idea for this was born out of a desire to have more control over black and white hand tank processing without spending money on temperature controlling devices like jobo, fishtank heater, ice etc...


I chose XTOL just because I use it the most. People often say its a good general purpose developer and I tend to agree. Supporting multiple developers would be impossible because of the massive amount of data I would have to generate so I think XTOL hits most bases.

I plan on just supporting stock and 1+1, 35mm and 120 and standard hand tank agitation.

I'm writing it in TI Basic because I use a ti83 in the darkroom and it doesn't give off light. Of course no one has these anymore so its probably the worst system to support due to inaccessibility. I eventually plan to port it over to python and maybe start supporting more features but I am really just making it for my own workflow for now so TI Basic is where ill start.
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Old 26th July 2020, 07:44 PM
Mike O'Pray Mike O'Pray is offline
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maxwellmakosk, I had thought that you were simply trying to work out what the development times would be when you depart from the standard 20 degrees C and I was going to say that most of the times for any variations upwards are already in the Kodak sheet.

I was then going to add that if it is an Ilford developer then it provides a conversion chart.

It now sounds that I may have not fully understood what it is you are trying to go based on the replies you have got i.e. what you are trying to do is more complicated that a simple time/temp conversion

Can you just summarise what it is you are trying to do just for my education?

Thanks

Mike
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Old 26th July 2020, 10:35 PM
Stocky Stocky is offline
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You will notice that the Ilford chart is on semi-log scale. All you need is two points at reasonably widely spaced temperatures to calculate an exponential coefficient for that developer. The Ilford chart assumes that all developers need the same correction which is probably near enough. I did a spreadsheet years ago which I could send to you if you would like it.
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Old 26th July 2020, 11:59 PM
Mike O'Pray Mike O'Pray is offline
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Quote:
Originally Posted by Stocky View Post
The Ilford chart assumes that all developers need the same correction which is probably near enough.
Yes that was always my assumption. None of the charts or tables I have seen mention that it is developer specific. If it was and to anything other than a very marginal degree, you'd expect that the likes of Ilford and Kodak would say so, given how long they both have had to carry our their research.

Interestingly enough and I have been there for 15 years now, I cannot recall a Photrio thread on the subject which given the number of people who seem to want to have an ambition to "check on things " would seem to speak volumes on the subject

Mike
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Old 27th July 2020, 11:57 AM
Stocky Stocky is offline
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If I remember correctly, I did the spreadsheet because I had started using PMK and the corrections were different to the standard Ilford graph. I used times for two widely spaced temperatures from The Book of Pyro, then calculated the times for intermediate temps from that.
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