Page 1 of 2 12 LastLast
Results 1 to 10 of 20

Thread: IR 760 filter - rating film speed

  1. #1

    Join Date
    Oct 2010
    Location
    Brookfield, Vic., Aust.
    Posts
    460

    IR 760 filter - rating film speed

    I recently bought an IR 760 filter and notice it's almost black, allowing little or no visible wavelengths to pass. Compared to the IR 720 filter I have of the same brand, the comparison is quite stark. I have had excellent results with the 720, rating Rollei 400 IR rollfilm at ASA 6 and developing in D76 for 6 min, but am looking for suggestions for a starting point with the 760. Just as a rough guess I'd say ASA 3 for 400 ASA film as a starting point; it all depends I guess on how much visible is transmitted.

    Just as an aside, I found these filters, Green.L from China on eBay and decided to give them a try. They seem to have a narrow product range and make filters for photography and scientific applications, apparently. They claim to use optical glass and high grade aluminium. I now have several of their products, IR and ND, and am impressed with the quality. https://translate.google.com/transla...m/&prev=search The eBay shop is called Galacticos.

    Thanks for any ideas.

  2. #2

    Re: IR 760 filter - rating film speed

    I’d say your rough guess is a good starting point. All you can do from there is test. I have some IR filters from China as well and they do seem to be quality.
    --- Steve from Missouri ---

  3. #3

    Join Date
    Jul 2016
    Posts
    4,313

    Re: IR 760 filter - rating film speed

    Quote Originally Posted by Barry Kirsten View Post
    I have had excellent results with the 720, rating Rollei 400 IR rollfilm at ASA 6 and developing in D76 for 6 min, but am looking for suggestions for a starting point with the 760. Just as a rough guess I'd say ASA 3 for 400 ASA film as a starting point; it all depends I guess on how much visible is transmitted.
    Click image for larger version. 

Name:	ir.jpg 
Views:	21 
Size:	137.7 KB 
ID:	197582


    See the graph in the datasheet...

    The vertical scale is logarithmic... this film is around 40 times less sensitive for 760nm photons than for 720 photons, if your filter blocks well shorter than 760nm it would be hard to expose an image because the film has a very low sensitivity by 760.

    Going that deep in the IR would require a film like the defunct Efke IR820.

    You may also hack your film by a pre-exposure bath in a deeper infrared sensitizing dye dilution, but this may be difficult because it not always work with any film (Cryptocyanine, 3,3'-diethylthiatricarbocyanine etc... Several recipes around)

    https://www.largeformatphotography.i...ed-Photography

  4. #4
    Les
    Join Date
    Dec 2011
    Location
    Seattle, WA
    Posts
    1,077

    Re: IR 760 filter - rating film speed

    I looked up 850nm filter and it's described as 200X limiting factor (7.6 f-stops). Not really clear on linearity here, but in my silly brain that would have been 1.52 f-stop difference (1/5th). Someone might suggest that I'm ingesting the 5th on this, but that would be too much proof for me.

    Hmmm, however close or far away it is, I'd explore it with digital camera before I'd use a sheet of film. Just looked up 760 filter on B&H and the store indicate 1000X limiting factor. Ouch!!!! They call it 10-stopper. So there is that.

    Les

  5. #5

    Join Date
    Jul 2016
    Posts
    4,313

    Re: IR 760 filter - rating film speed

    Quote Originally Posted by Leszek Vogt View Post
    I'd explore it with digital camera before I'd use a sheet of film.
    A (converted) digital sensor has a lot of sensitivity by 760nm, compared to Rollei 400 IR

  6. #6
    おせわに なります! Andrew O'Neill's Avatar
    Join Date
    Sep 2003
    Location
    Coquitlam, BC, Canada, eh!
    Posts
    4,601

    Re: IR 760 filter - rating film speed

    I think Leszek just gave you a good starting point with this filter. That would result in a very long exposure... but then you also have to slap on reciprocity correction. You could be looking at a half hour or longer exposure. Is it really worth it? I'd stick with the 720... but hey, go for it! Let us know how it went, and if you got anything, post them here!

  7. #7
    Les
    Join Date
    Dec 2011
    Location
    Seattle, WA
    Posts
    1,077

    Re: IR 760 filter - rating film speed

    Quote Originally Posted by Pere Casals View Post
    A (converted) digital sensor has a lot of sensitivity by 760nm, compared to Rollei 400 IR
    Pere, perhaps you were thinking about a 'converted' rig....I did not or I'd have mentioned it.

    Les

  8. #8

    Join Date
    May 2009
    Location
    Vermont
    Posts
    177

    Re: IR 760 filter - rating film speed

    Rather than getting a converted camera, I have a Leica M8, it does not have an infrared cut filter. In fact to get good color you need an infrared cut on the lens. With a 720nm filter it is giving me, in sun light, an exposure of f5.6 at 1/30 set at 320 ISO. Have never used the Rollei film, but may try.
    With Kodak HIE I would meter and ISO 6 or 12 with a Kodak 87C. I also had interesting result putting an 87C on a flash, using a Speed Graphic.

  9. #9

    Join Date
    Jul 2016
    Posts
    4,313

    Re: IR 760 filter - rating film speed

    Quote Originally Posted by Leszek Vogt View Post
    Pere, perhaps you were thinking about a 'converted' rig....
    In theory a DSLR sensor cannot see infrared because a NIR blocking filter is installed, the right exposure with a DSLR and a 760 filter won't give a clue about what exposure is required with Rollei 400 IR film because different practical factors are involved, with DSLR exposure depends on how good/bad is the NIR blocking, with Rollei 400 IR it depends on remaining sensitivity at +760nm.

  10. #10

    Join Date
    Sep 1998
    Location
    GA
    Posts
    12,664

    Re: IR 760 filter - rating film speed

    Quote Originally Posted by Pere Casals View Post
    In theory a DSLR sensor cannot see infrared because a NIR blocking filter is installed, the right exposure with a DSLR and a 760 filter won't give a clue about what exposure is required with Rollei 400 IR film because different practical factors are involved, with DSLR exposure depends on how good/bad is the NIR blocking, with Rollei 400 IR it depends on remaining sensitivity at +760nm.
    And how much IR is present under the shooting conditions.

Similar Threads

  1. Fuji X-ray film: development and EI rating?
    By Ari in forum Darkroom: Film, Processing & Printing
    Replies: 4
    Last Post: 7-Dec-2012, 14:48
  2. Rating Tri-x 320
    By dazedgonebye in forum Darkroom: Film, Processing & Printing
    Replies: 29
    Last Post: 11-Apr-2009, 00:56
  3. Rating FP4
    By Wayne Crider in forum Darkroom: Film, Processing & Printing
    Replies: 9
    Last Post: 30-Jul-2000, 19:57

Bookmarks

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •