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Push and pull

Discussion in 'B&W: Film, Paper, Chemistry' started by Graham.b, Feb 17, 2009.

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  1. Feb 17, 2009 #1
    Graham.b

    Graham.b Member

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    Morning all.

    Has any one ever put a list together of the times needed to do this,

    1 Start with say a 400, and give the times they used with good results to push and pull.

    E.g 400 @200 @100
    " 800 @1000

    I think you can get the picture, (no pun there).

    There is a lot of notes on this subject from the forum, i just used a 100 @50.
    Many of us use different times and chemicals. Just wondering is there a happy medium.
    When there is a new member, this is one of the post that come up, maybe some kind sole would put up a list as a sticky.

    What do you think.

    Graham
     
  2. Feb 17, 2009 #2
    Ian Grant

    Ian Grant Subscriber

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    Yes, there are many sources for times, but the best place to look is on the film manufacturers own websites, so check out Ilford.

    Ian
     
  3. Feb 17, 2009 #3
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    Graham.b

    Graham.b Member

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    Hello Ian.
    I do think a lot of know this, (don't take it the wrong way) all i was trying to get across was for the new to this film D/P. Some of the film manufactures sites can be a bit miss leading.
    From the new comers point of view. We can go there and know this is a guide line to the people in the know, i do very often adjust the times to suit, but a new-be may get a little lost with 10% here 2stops there add 25 secs.

    Graham
     
  4. Feb 17, 2009 #4
    Steve Smith

    Steve Smith Member

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    My general rule is for every stop I over-expose (i.e. use ISO 400 film at EI 200) I subtract 25% of the development time.

    e.g. If I use HP5+ at EI 400 and it requires 10 minutes development, then at EI 200 it would get 7.5 minutes and at EI 100 it would get 5.6 minutes.

    Going in the other direction at EI 800 I would add 25% so it would get 12.5 minutes development.

    This is just a general rule which works for me with HP5+ and should be close for most other films. Obviously you will need to test to see what suits you.



    Steve.
     
  5. Feb 17, 2009 #5
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    Graham.b

    Graham.b Member

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    Thank you for your input, this is the sort of thing i was trying to get across, to a new-be this would all sound a little bit of, how do they come up with these No's. 400 EI @200 - 25%.
    For us it is a simple matter of take here take there. I was only talking to some one at work on this and no matter how i explained it, there lights did not shine. May be me. This is why i thought a sticky would be a good starting place for the new-be, then to work from there and get to the understanding of what they want, and where these No's come from.

    Graham
     
  6. Feb 17, 2009 #6
    Steve Smith

    Steve Smith Member

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    The terminology can be confusing. No matter how we treat a film, its speed rating, or ISO remains constant. We can however use it at a different EI which stands for Exposure Index.

    Therefore an ISO 400 film can be exposed at an EI of 200. It's still a 400 speed film but we are treating it as a 200.

    Basically if you give it extra exposure, it needs less development and conversely, if it receives less exposure it needs more development.

    There is some technical stuff from Kodak here: http://www.kodak.com/global/en/professional/support/techPubs/cis185/cis185.pdf

    And another article here: http://www.nelsontan.com/articles/pushpull.html



    Steve.
     
  7. Feb 17, 2009 #7
    ic-racer

    ic-racer Member

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    Depends on how one defines "good results." As pointed out, most B&W negative films produce proportionally inferior negatives with underexposure.
     
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