Switch to English Language Passer en langue française Omschakelen naar Nederlandse Taal Wechseln Sie zu deutschen Sprache Passa alla lingua italiana
Members: 68,766   Posts: 1,484,135   Online: 847
      
Page 3 of 3 FirstFirst 123
Results 21 to 28 of 28
  1. #21
    MattKing's Avatar
    Join Date
    Apr 2005
    Location
    Delta, British Columbia, Canada
    Shooter
    Multi Format
    Posts
    11,589
    Images
    59
    Quote Originally Posted by AllenBaxter View Post
    Thanks for the feedback on the pictures. I just want to get my head around understanding the exposure issue better. I have only recently taken up photography and started with digital and now am tyring film. Based on DWThomas and 2F/2F responses it makes sense that one is trying to balance the amount of visible light and IR light onto the film. Am I correct then in understanding that by adjusting the film speed from the box rating of 400 to 25 that I am reducing the visible light sensitivity of the exposure by 4 stops and that by adding the Hoya R72 filter I am again reducing the visible light sensitivity by another 5 stops which would appear to be about 9 stops of less visible light sensitivity. I tried adjusting from ISO 400 to ISO 25 and then compensating by increasing the exposure time and also using ISO 25 and compensating less. My testing involved metering without the filter and noting exposure and taking a shot. I then used this exposure as my basis for making adjustments when I added the R72 filter. Based on my understanding then it would appear that this film likes to be very under exposed for visible light. Is this correct or am I confused? Pictures are posted: http://www.flickr.com/photos/nikonfd...7627083103885/. Thanks for help in better understanding this exposure issue. Next is composition.
    Allen:

    You are making my head hurt !

    The film is sensitive to both visible light and near infra-red light. The light available in most scenes includes both types. The visible light in those scenes is much stronger than the near infra-red light, so if you shoot without a filter you need to set exposure based on how much visible light is there - otherwise the shot will be way over-exposed.

    You add the R72 filter in order to block out most of the visible light, while letting the near infra-red light pass through. Your resulting negative will show mostly the effect of the near infra-red - assuming you set the exposure correctly!.

    The question is, of course, how do you determine the correct exposure? The answer comes mostly from experience. That experience is necessary because the exposure meters we have are not sensitive to just near infra-red, but rather are sensitive (mostly) to visible light. The experience tells us that if we measure the visible light available to be at X level, then the near infra-red light available will be at Y level. This is the variable that, well, varies a lot, and it is difficult to both measure or predict. Thus the need to bracket.

    When people say that they recommend shooting a 400 ISO Rollei film at EI 3 (for example), with an R72 filter included in the equation, they are really saying that an R72 has a particular filter factor that results in 7 stops less visible light hitting the film, and that when the visible light exposure is reduced by 7 stops from "normal", there is a good chance that the remaining, near infra-red response will be suitable.

    So to put it another way, we can measure how much visible light is available, and from experience we know approximately how much near infra-red accompanies that visible light. We know how much effect the R72 has on the visible light, so when we combine that knowledge with our measurement of the visible light, we can determine what exposure to use so that the R72 eliminates almost all the visible light, and leaves the near infra-red to do it's work.
    Matt

    “Photography is a complex and fluid medium, and its many factors are not applied in simple sequence. Rather, the process may be likened to the art of the juggler in keeping many balls in the air at one time!”

    Ansel Adams, from the introduction to The Negative - The New Ansel Adams Photography Series / Book 2

  2. #22
    Sirius Glass's Avatar
    Join Date
    Jan 2007
    Location
    Southern California & Virginia
    Shooter
    Multi Format
    Posts
    12,635
    Quote Originally Posted by MattKing View Post
    Allen:

    You are making my head hurt !

    I am glad that both Matt and 2F/2F clarified this for Allen. Rather than rehash what they said in a different way, I will just add that not only do I agree with them, but I do the equivalent thing, as I posted earlier in post #7, by setting the internal light meter of my SLR to the box speed and meter with the filter on.

    Allen, since IR film gets expensive, please feel free to ask questions.

    Steve
    Warning!! Handling a Hasselblad can be harmful to your financial well being!

    Nothing beats a great piece of glass!

    I leave the digital work for the urologists and proctologists.

  3. #23
    MattKing's Avatar
    Join Date
    Apr 2005
    Location
    Delta, British Columbia, Canada
    Shooter
    Multi Format
    Posts
    11,589
    Images
    59
    Quote Originally Posted by Sirius Glass View Post

    I am glad that both Matt and 2F/2F clarified this for Allen. Rather than rehash what they said in a different way, I will just add that not only do I agree with them, but I do the equivalent thing, as I posted earlier in post #7, by setting the internal light meter of my SLR to the box speed and meter with the filter on.

    Allen, since IR film gets expensive, please feel free to ask questions.

    Steve
    Steve's approach most likely reflects the fact that he shoots IR film in an SLR, and therefore has to take the filter off to see anyways.

    Whereas I use a TLR, so the R72 filter stays on the taking lens while I compose using the separate viewing lens. I'd use the same approach with a rangefinder camera.

    One caution though - the spectral sensitivity of different meters varies. So if two photographers are metering through their filters, even if the light is the same, the meter readings may differ.

    As a result, each photographer needs to experiment with their meter and their filter, their work-flow, their experience with lighting conditions and their particular aesthetic preferences to determine what will work best for them.

    Oh, and bracket.
    Matt

    “Photography is a complex and fluid medium, and its many factors are not applied in simple sequence. Rather, the process may be likened to the art of the juggler in keeping many balls in the air at one time!”

    Ansel Adams, from the introduction to The Negative - The New Ansel Adams Photography Series / Book 2

  4. #24
    Sirius Glass's Avatar
    Join Date
    Jan 2007
    Location
    Southern California & Virginia
    Shooter
    Multi Format
    Posts
    12,635
    Quote Originally Posted by MattKing View Post
    Steve's approach most likely reflects the fact that he shoots IR film in an SLR, and therefore has to take the filter off to see anyways.
    No, I leave the red 25A filter on because I can see through it.

    Now a R72 ... I do not know and I do not have one. Since HIE is no longer available, I am not all that interested in shooting IR again.

    Steve
    Warning!! Handling a Hasselblad can be harmful to your financial well being!

    Nothing beats a great piece of glass!

    I leave the digital work for the urologists and proctologists.

  5. #25
    2F/2F's Avatar
    Join Date
    Apr 2008
    Location
    Los Angeles, CA
    Shooter
    Multi Format
    Posts
    8,008
    Images
    4
    Steve, Rollei IR400 with a 25A filter doesn't look much different than any other panchromatic film with a 25A filter. It is an expensive film (10 bucks a roll last I shot it). I wouldn't bother using it unless it is with heavier filters than a 25A. It is not unique unless you use it with an opaque filter, or a near-opaque one like the R72. Without a heavy filter, it might as well be T-Max in the camera, IMO.

    HIE, on the other hand, definitely looked like an IR film when used with a 25 or 29 see-through filter. That was HIE's greatest strong point IMO: it could be used hand held with IR-looking results, and without having to shift focus.
    2F/2F

    "Truth and love are my law and worship. Form and conscience are my manifestation and guide. Nature and peace are my shelter and companions. Order is my attitude. Beauty and perfection are my attack."

    - Rob Tyner (1944 - 1991)

  6. #26
    Sirius Glass's Avatar
    Join Date
    Jan 2007
    Location
    Southern California & Virginia
    Shooter
    Multi Format
    Posts
    12,635
    Quote Originally Posted by 2F/2F View Post
    Steve, Rollei IR400 with a 25A filter doesn't look much different than any other panchromatic film with a 25A filter. It is an expensive film (10 bucks a roll last I shot it). I wouldn't bother using it unless it is with heavier filters than a 25A. It is not unique unless you use it with an opaque filter, or a near-opaque one like the R72. Without a heavy filter, it might as well be T-Max in the camera, IMO.

    HIE, on the other hand, definitely looked like an IR film when used with a 25 or 29 see-through filter. That was HIE's greatest strong point IMO: it could be used hand held with IR-looking results, and without having to shift focus.
    I agree. I would have to get a stronger filter and the cost of the film ... excuses ... but I would rather work with my 4x5s and learn large format in more depth, use the Hasselblads for my serious [sirius] work, and 35mm for traveling light when I what I am doing is not centered around photography than shoot IR. There are too many other interesting things to do.

    Steve
    Warning!! Handling a Hasselblad can be harmful to your financial well being!

    Nothing beats a great piece of glass!

    I leave the digital work for the urologists and proctologists.

  7. #27
    DWThomas's Avatar
    Join Date
    Jun 2006
    Location
    SE Pennsylvania
    Shooter
    Multi Format
    Posts
    2,147
    Images
    62
    Quote Originally Posted by 2F/2F View Post
    Steve, Rollei IR400 with a 25A filter doesn't look much different than any other panchromatic film with a 25A filter. It is an expensive film (10 bucks a roll last I shot it). I wouldn't bother using it unless it is with heavier filters than a 25A. It is not unique unless you use it with an opaque filter, or a near-opaque one like the R72. Without a heavy filter, it might as well be T-Max in the camera, IMO.

    HIE, on the other hand, definitely looked like an IR film when used with a 25 or 29 see-through filter. That was HIE's greatest strong point IMO: it could be used hand held with IR-looking results, and without having to shift focus.
    This jibes with my experience with the Rollei material. Somewhere I saw a graph of the HIE spectral sensitivity that showed it not only sensitive way farther into the IR spectrum, but also what looked to be a bit of a notch in the yellow green range. Thinking area-under-the-curve stuff I'd guess almost any red filter would skew HIE pretty well towards IR. The Rollei barely makes it into the IR range; I somewhat preferred the effect with a 760 filter over a 720, but that involves working so far down the spectral cut-off it takes a lot of extra exposure and seems a bit touchy for latitude.

    Enh, experiment, experiment. And as pointed out, though the Rollei 400 is a nice pan film, the price of a roll would buy about three of Acros 100!

  8. #28

    Join Date
    Jul 2011
    Location
    Long Beach, Ca
    Shooter
    Multi Format
    Posts
    8
    In my experience with infrared films using a Hoya R72 filter, I always meter the visible light and focus, apply the filter, adjust to IR focusing marked on the lens and adjust / bracket +4 to 6 stops. Never had a problem with any infrared film and the results are amazing! As far as ASA/ISO goes, I either follow the retailer's suggestion or set it at 200. I heard with these new IR films in the market today, a Red 25 filter is impracticable but I have never tried it for myself. I am a big fan of EFKE IR820 Aura because it's the closet film to Kodak HIE (R.I.P.).

Page 3 of 3 FirstFirst 123


 

APUG PARTNERS EQUALLY FUNDING OUR COMMUNITY:



Contact Us  |  Support Us!  |  Advertise  |  Site Terms  |  Archive  —   Search  |  Mobile Device Access  |  RSS  |  Facebook  |  Linkedin