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  1. #11
    DWThomas's Avatar
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    Quote Originally Posted by AllenBaxter View Post
    I have tried metering through the lens with the Hoya R72 filter and the meter does not appear to pick up any light. The filter is really opaque. How does the Hoya R72 filter differ from the Red 25A filter?
    Thanks
    According to a Hoya brochure, a 25A filter passes light of wavelengths above about 600 nM which is well into the visible range. The R72 cuts off below 720 nM which is nearly out of the visible range. I have never shot IR film in a camera with a built in meter, so I have no experience to go on there. It seems possible to me that even if a light meter sensor has IR sensitivity, the maker might put some filtration over it to reduce sensitivity outside the visible range. (That's done with the sensors in d!git@l cameras.)

    Based on my limited experience, I think Ron's exposure sounds a bit short, but in spite of the anti-bracket comments, I think a bit of it isn't a bad idea until you establish some sort of base line.

    DaveT

  2. #12

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    It seems like there's some variation in the sensitivity of different meters to IR. I've had some luck metering through an R72, but for some people it's been a complete failure; I don't know if the difference is down to different built-in filtration, or different lighting conditions, or just blind luck...

    Even guidelines based on assuming a certain EI are variable, because the ratio of visible light to IR light varies. You know how sunsets look red---that's because red light propagates better than other colors through the atmosphere and haze and dust, and the same goes for infrared. As a result, at sunrise or sunset, the EI of an IR film is *higher* than it is at noon! (There's less total light, but what light there is skews to the red/infrared---thus IR film through a filter actually sees more light at those times than the amount of visible light would suggest.)

    While metering through the filter might work in a pinch, on the whole I wouldn't count on it. I tend to think it's always best to shoot IR film with a handheld meter---and then the hard part is choosing what speed (EI) to set the meter to. The speed that's worked for other people is a starting point, but for your particular conditions it may or may not be ideal. I'd say, take someone else's suggested EI as a start, shoot an experimental roll with some bracketing, and evaluate the results to figure out what works for you.

    A compensating developer is also your friend. I've become very fond of IR films in Diafine, which seems to "level out" the exposure variability quite a bit.

    -NT
    Nathan Tenny
    San Diego, CA, USA

    The lady of the house has to be a pretty swell sort of person to put up with the annoyance of a photographer.
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  3. #13
    2F/2F's Avatar
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    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."

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  4. #14
    DWThomas's Avatar
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    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.

  5. #15

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    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.

  6. #16

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    Great shots!

    Jeff

  7. #17
    DWThomas's Avatar
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    They look good. Your adjustment sounds very similar to what I found.

  8. #18

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    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.

  9. #19
    2F/2F's Avatar
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    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)

  10. #20

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    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.

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