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Thread: Test strip negatives to determine ISO, is this viable?

  1. #1

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    Test strip negatives to determine ISO, is this viable?

    I puchased some 4x5 Toyo Film Holders (7) which were pretty much like new, they were all sent dark side showing of the Dark Slide so was surprised to find when I opened one up that it had film in it. The film has a shallow semi-circular notch about 8mm wide and 2mm deep, the film has a green/grey emulsion with a very dark grey back. I then took all the holders up to my newly created darkroom (just absolutely light tight not set up as a proper darkroom) and checked them all, they all are loaded with the same film stock.

    I have since done a bit of searching on the interweb and it would seem that a lot of suppliers have supplied sheet film with just a single semi-circular notch and the same manufacturers have even used the same notch for different film speeds. All I know at the moment is that it is not Shanghai 100 as even though that also has a semi-circular notch the film has a blue colour which is completely different to this film/

    So, as I do not know what the film speed is I was thinking of doing an 4 strip test (ISOs 25, 50, 100 & 400) on one of the sheets of film with each strip based on part of an overall exposure to try to determine the ISO.

    Assuming the exposure is based initially for an ISO400 film and with a constant aperture, I realise that I would have to have a number of varying exposures to build up the required exposure for the strip, assuming an aperture chosen to allow 1/200sec at ISO400 the film would be exposed, then the darkslide would be inserted about an inch (giving the strip an exposure for ISO400), for the following strip I would need another exposure of 1/200sec plus a further exposure of 1/100sec before pushing the darkslide in for the strip (giving enough exposure for a speed of ISO100), the following strip would have already had exposures giving ISO100 before a further exposure of 1/50sec which would give an exposure of the remaining uncovered film equalling a film speed of ISO50 before covering up the strip, the last strip will receive a further exposure of 1/25sec which would then give an exposure equal to that required of an ISO25 film.

    So just to make sure I have got this correct:

    ISO400..........ISO200..........ISO100..........ISO50..........ISO25

    .1/200............1/200 ............1/200...........1/200...........1/200
    .....................1/200 ............1/200...........1/200...........1/200
    ..........................................1/100...........1/100...........1/100
    ...............................................................1/50............1/50
    .................................................................................1/25

    I wouldn't bother with the ISO200 as not many films have been made at that speed. Speeds in Orange are the exposures required to complete the next strip.

    So, provided I secure the film with some double sided tape (made less sticky first) does anyone see any problems with my suggestion? If so, any better alternatives other than shooting 4 seperate sheets at the various ISOs?

  2. #2
    Kirk Gittings's Avatar
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    Re: Test strip negatives to determine ISO, is this viable?

    Sorry. I don't get it. Seems like an awful lot of work for a handful of film that may be already exposed and or seriously out of date. Why not buy some current film and spend your time testing that and establishing some usable standards for future work?

    BTW "dark side showing" means different things to different photographers. To me it means exposed. but to some friends of mine it means unexposed. There is no rigid standard practice.
    Thanks,
    Kirk

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    Re: Test strip negatives to determine ISO, is this viable?

    Thanks for your comments Kirk.

    I don't understand what you mean by a lot of effort though, 5 exposures in total, 1/200, then 1/200 & 1/100, then 1/50 and finally 1/25, with the dark slide pushed in a bit after the exposures. Not exactly onerous. I can develop the single sheet along with some others using my normal processing routine and find out which ISO works best or even if they have been exposed or not, if they are already exposed, I may just process the others to see what is on them.

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    Re: Test strip negatives to determine ISO, is this viable?

    Another option that is less complicated is to cut a piece of black foamcore to fit tightly inside the back of your camera, then cut out 1/4 of the rectangle. Insert in camera, shoot, then flip or rotate the foamcore until you have exposed all four quadrants. I use this for film testing, and carry a half rectangle when I travel so if I start running out of film I can shoot half-sheets.

    Your original idea should work as well.

  5. #5

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    Re: Test strip negatives to determine ISO, is this viable?

    Ed: Sorry but I don't get it either. If you're interested in what may be on the film in terms of images -- something I understand -- then develop one with fairly generic developer and an average time and see what you get. Adjust for subsequent sheets if your guesstimate is wrong. It may well be since you don't know what film to use in checking a chart. You do know that the dark slides have an exposed and unexposed side to them? If these show unexposed, I wouldn't bother with developing them to look for images.

    If you are brand new at this (sorry, I haven't not looked at your other 60 posts and don't mean to be insulting...) then use the film to learn with in terms of film handling, exposing, turning the slide over, etc.

    If none of the above apply, then I wouldn't spend any time trying to seriously use somebody's old mystery film. Chuck it and load them up with film you want to use. Toyo holders are fantastic quality, you did well on that.

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    Re: Test strip negatives to determine ISO, is this viable?

    Thanks Tim, That is a good idea. How about if I use your idea and cut a quarter out of a sheet of flexiplas card and stick it with double sided tape to the film-holder. I realise this will move the film plane back by about 0.25mm or so then this could be moved simply for each additional exposure.

    I was concerned that my suggestion may lead to issues with the value of the exposures.

    It's pretty well known that when doing a test strip of paper under an enlarger you get different results if you do individual timed exposured than if you do one exposure for the full time and move the cover during the exposures. I think it's commonly thought to be the light of the enlarger coming up to full brightness for each of the individual steps that cause the problem. I was just curious that my idea would cause something like that.

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    Re: Test strip negatives to determine ISO, is this viable?

    Quote Originally Posted by Kevin Crisp View Post
    Ed: Sorry but I don't get it either. If you're interested in what may be on the film in terms of images -- something I understand -- then develop one with fairly generic developer and an average time and see what you get. Adjust for subsequent sheets if your guesstimate is wrong. It may well be since you don't know what film to use in checking a chart. You do know that the dark slides have an exposed and unexposed side to them? If these show unexposed, I wouldn't bother with developing them to look for images.

    If you are brand new at this (sorry, I haven't not looked at your other 60 posts and don't mean to be insulting...) then use the film to learn with in terms of film handling, exposing, turning the slide over, etc.

    If none of the above apply, then I wouldn't spend any time trying to seriously use somebody's old mystery film. Chuck it and load them up with film you want to use. Toyo holders are fantastic quality, you did well on that.
    Hi Kevin, thanks for your comments. I have only been involved with Large Format for a short time, but have been involved with photography in one way or another since 1979. I tend to develop everything these days semi-stand in Caffenol CL which has the advantage of allowing different films and ISOs to be processed together for the same time whilst still giving a very useable result.

    On reflection it does seem a bit stingy to use someone else's old film (especially as I have 7 boxes of assorted 4x5 B&W film in my fridge), I was just interested in seeing what could be done with it and if it was something I had not tried before (that is certainly the case) that I might have liked.

    As for the Toyo film holders, that was a fantastic bit of luck, they were advertised as mint- condition with 6 for 49 by Peter Walnes, which I thought was a great price (everything over here is dearer than the US) and as I have done a lot of business with Peter over the years he included a 7th Film Holder in the same condition for free. So Toyo film holders for 7 a pop (approx 10$ each, bargain)!

    I think I will make a 4x5 mask with a quarter cut out just to try it though!

  8. #8
    Maris Rusis's Avatar
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    Re: Test strip negatives to determine ISO, is this viable?

    Doing test-strip exposures on sheet film by moving the darkslide between "clicks" and adjusting shutter speeds and apertures to deliver an exposure doubling sequence is quick and easy. I use a standard sunlit subject, the view across the road from my house, shoot the film, develop it immediately, and look at the "best" part of the test strip. That tells me the "best" exposure. A minute later (the light hasn't changed) I'm back in front of the scene with my spotmeter adjusting the ISO dial so the meter tells me the aperture/shutter speed numbers I know are right. Job finished!

    For normal kinds of film and reasonable exposures there is no discernable intermittency effect with this method. There are plently of potential sources of minor errors doing dark-slide test strips (wrong shutter speeds, wrong apertures, reciprocity failure, etc) but the technique gets you a ballpark Exposure Index, alias E.I. (technically not ISO), very quickly.
    Photography:first utterance. Sir John Herschel, 14 March 1839 at the Royal Society. "...Photography or the application of the Chemical rays of light to the purpose of pictorial representation,..".

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    Jonathan K. jcoldslabs's Avatar
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    Re: Test strip negatives to determine ISO, is this viable?

    Having recently opened a film holder that I thought was empty but wasn't (d'oh!), your description of your film matches my Efke PL100 sheet film perfectly: small rounded notch, grey/green emulsion with a dark grey backing. It may be that ALL Efke films have this appearance, I don't know. Good luck.

    Jonathan

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    Re: Test strip negatives to determine ISO, is this viable?

    @Maris, Thank you for your coments, I vaguely remember doing a similar test strip on 4x5 lith film when at college in the late 70s, but I seem to think we just used an additive exposure measured in seconds rather than fractions of a second.

    @Jonathon, Thanks for your post, as far as I'm aware (from googling) almost all the Eastern European and Asian film manufacturers use the notch purely to identify the emulsion side of the film unlike Fuji, Kodak and Ilford who's films can be identified by the notch codes.

    Looking at the Fuji notch codes, it could be that the film is actually Velvia RVP. If so and they are not exposed, that would be interesting as I have never shot 4x5 transparency film.

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