Switch to English Language Passer en langue française Omschakelen naar Nederlandse Taal Wechseln Sie zu deutschen Sprache Passa alla lingua italiana
Members: 74,638   Posts: 1,648,395   Online: 1172
      
Page 2 of 3 FirstFirst 123 LastLast
Results 11 to 20 of 23
  1. #11

    Join Date
    Apr 2008
    Location
    Los Angeles, CA
    Shooter
    Multi Format
    Posts
    8,006
    Images
    4
    Using a visibly-transparent red filter on this film will not make it work all that much differently than most b/w films. When you use anything but an opaque filter, the amount of visible light exposing the film by far overwhelms the amount of IR, and you get a barely-noticeable IR effect most of the the time. It is a great and sharp general purpose film, if that is the intent, but think about the price before you shoot it with anything other than an opaque filter for IR results.

    And when using opaque filters, you should shift focus if you want sharp shots. It is not necessary with filters you can readily see through, as visible light is doing almost all of the exposing in those cases.

    Shooting IR film is sort of like shooting with flash. In both cases, you are making two exposures at once, and you need to decide how to balance the two to get the results you want. With flash, you have an ambient exposure and a flash exposure. You set your diaphragm to expose for the flash, and your shutter to expose for the ambient light. You can choose to effectively remove the ambient exposure from the equation if you'd like, by speeding up the shutter. Similarly, with IR film, you have a visible-light exposure, and you have an IR exposure, both going on at once in every shot. Filtration affects the ambient exposure, but the IR exposure is constant as long as the filtration cuts off below about 750 nM. You can balance the two with each other in varying ways, or you can effectively eliminate one or the other from the equation. The heavier the filter you use, the less ambient is picked up, thus the longer exposures get, thus the more the IR is seen. Filters do not increase the IR exposure; they simply decrease the ambient exposure, so increase the relative IR exposure. Use no filter, and by the time the right exposure has been reached on the visible-light-sensitive part, the IR-sensitive part has barely been tickled; it has been effectively eliminated from the picture, and the film looks like any other b/w film. Go to yellow, orange, and red see-through filters, and the proportion of IR making it into the exposure increases, but the film still doesn't look all that different than a regular b/w film. But when you start getting to the heavier red filters, you are blocking out a lot of visible light, and the IR and the visible light even out. Move to the opaque filters, and IR takes over as visible light is completely blocked from hitting the film.

    FWIW, the R72 is not truly opaque to visible light. You can still see through it, actually. But it does allow a noticeable IR effect while allowing some barely-visible light to tickle the film.

    In regards to exposure, I usually start with an incident reading, just to get a general sense of the lighting conditions, but with the understanding that I am not actually metering IR; I am metering for a lighting condition that experience has shown will work with a certain procedure. I will meter at EI 3, and then add about 3 stops on a sunny and clear day (or EI 400 and add about 10 stops). This is using a Hoya R72, which lets in some visible light. If you can get a filter that cuts off right around 750 nM, it would be ideal for getting the best IR effect from this film, as it would cut out all visible light, even the very deep reds, and the entire exposure would come from the IR.

    With cloudy days or other untested weather, all bets are off using that formula. I add large amounts of exposure on top of the above formula and see what happens. 3, 4, 5, 6 stops extra. I usually get something usable. Hey, it's negative film. It's good for some slop!
    Last edited by 2F/2F; 07-12-2011 at 02:15 AM. Click to view previous post history.
    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)

  2. #12
    DWThomas's Avatar
    Join Date
    Jun 2006
    Location
    SE Pennsylvania
    Shooter
    Multi Format
    Posts
    2,453
    Images
    72
    2F/2F has provided a very good explanation of the considerations. One potential difficulty using the Rollei material is that it doesn't really extend much into the infrared range. Last summer I came up with incident metering at 400 and increasing exposures 6 or 7 stops with a 720 filter or about 12 or 13 stops(!) with a 760 filter. The latter gives more IR effect, but you are really working down the cutoff slope of the film. With the EFKE IR820, there was only a stop or two difference between the filters.

    At least one discussion last year came up with a problem that suggested a guy had a miss-marked filter also. You might be able to tell a K-1 from a K-2 by looking at it, but 750 versus 850 nM IR, not likely.

    I still think a lot of normally intuitive stuff goes out the window because we don't see the spectrum the film sees. Where I might normally bump up a half stop or a stop to "improve shadow detail" in a visible light shot, I have no idea that oak tree looks like a giant cotton candy in IR, for example.

  3. #13

    Join Date
    Mar 2011
    Shooter
    35mm
    Posts
    15
    Thanks to all the responses. I have posted several of my pictures with exposure information on my flickr photostream: http://www.flickr.com/photos/nikonfdslr/

    I developed in Kodak D76 stock solution for 6 minutes.

  4. #14

    Join Date
    Sep 2007
    Location
    Richmond VA.
    Shooter
    Multi Format
    Posts
    6,932
    Great shots!

    Jeff

  5. #15
    DWThomas's Avatar
    Join Date
    Jun 2006
    Location
    SE Pennsylvania
    Shooter
    Multi Format
    Posts
    2,453
    Images
    72
    They look good. Your adjustment sounds very similar to what I found.

  6. #16

    Join Date
    Mar 2011
    Shooter
    35mm
    Posts
    15
    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.

  7. #17

    Join Date
    Apr 2008
    Location
    Los Angeles, CA
    Shooter
    Multi Format
    Posts
    8,006
    Images
    4
    Hi,

    Downrating the film affects exposure, not sensitivity ("speed").

    Downrating without a filter only overexposes the film. It does not change the ratio of visible-to-IR light that is making the exposure.

    Changing that ratio is what makes the film look more or less "IR-like." You change that ratio by selecting a filter.
    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)

  8. #18

    Join Date
    Mar 2011
    Shooter
    35mm
    Posts
    15
    2F/2F:
    OK. That makes sense. I was incorrectly thinking that reducing the ISO # decreased the exposure by allowing less light and therefore required compensation. I was thinking that this was a negative adjustmen, i.e. 400 to 25 was a negative 4 stops when it sounds like it should be a plus 4 stops. This will make me rethink my overall adjustment logic. Thanks for setting me straight. I really appreciate the feedback.

  9. #19
    MattKing's Avatar
    Join Date
    Apr 2005
    Location
    Delta, British Columbia, Canada
    Shooter
    Multi Format
    Posts
    13,711
    Images
    60
    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

  10. #20
    MattKing's Avatar
    Join Date
    Apr 2005
    Location
    Delta, British Columbia, Canada
    Shooter
    Multi Format
    Posts
    13,711
    Images
    60
    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

Page 2 of 3 FirstFirst 123 LastLast


 

APUG PARTNERS EQUALLY FUNDING OUR COMMUNITY:



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