Switch to English Language Passer en langue française Omschakelen naar Nederlandse Taal Wechseln Sie zu deutschen Sprache Passa alla lingua italiana
Members: 70,290   Posts: 1,535,398   Online: 774
      
Page 3 of 3 FirstFirst 123
Results 21 to 25 of 25
  1. #21

    Join Date
    Mar 2008
    Location
    San Diego, CA, USA
    Shooter
    Multi Format
    Posts
    2,251
    Images
    21
    Quote Originally Posted by Christopher Walrath View Post
    Well, i plan on bracketing to start until I get used to what whichever film I choose will do with filtration, light quality and subject matter. As mentioned by Bruce, I do not intend to waste EXPENSIVE IR film on trial and error beyond the true 'I have no idea what I am going to get' phase.
    I don't disagree with you philosophically, but I think you'll find it's unexpectedly difficult to get a handle on the relationship between visible light and IR under a wide variety of circumstances. In particular, the three-way relationship between IR level, visible-light level, and time of day is maddeningly counterintuitive. (There's actually more IR at midday than at morning and evening, but there's even *more* more *visible* light, so you end up having to downrate your film when the amount of light goes up!)

    Basically, your filter factor needs to vary inversely with the ratio of IR to visible light, which is not the easiest thing in the world to develop a good instinct for. I certainly haven't managed it yet.

    -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.
    -The Little Technical Library, _Developing, Printing, And Enlarging_

  2. #22
    keithwms's Avatar
    Join Date
    Oct 2006
    Location
    Charlottesville, Virginia
    Shooter
    Multi Format
    Posts
    6,079
    Blog Entries
    20
    Images
    129
    Quote Originally Posted by Bruce Osgood View Post
    http://www.digitaltruth.com/store/ca...er-p-1322.html

    I have no idea if this even works but I thought I'd pass along the info
    In principle it could work well but you'd need to meter through two filters: one to simulate the cutoff of the film, and the IR filter itself. Otherwise the meter will have too broad a range of sensitivity. Now, obviously metering through the IR filter is easy enough, but the other filter is a specialty item; I had to special order one and it also will never match the film cutoff exactly... and technically, we'd need a different cutoff filter for each different IR film, i.e. one for sfx, one for efke, one for rollei, one for HIE....

    For example, just suppose the film's sensitivity cuts out at 800nm, and the filter becomes transmissive at 750nm. So then you really need to meter between 750 and 800. But the meter is probably sensitive over a much wider range of IR light, say 700-1200 nm, and perhaps further down into the visible also. So you'd need to narrow that broad range down or else the metering info will be way off.

    Anyway even without the low end cutoff filter, it might be good enough to narrow down the bracket range a bit. Which could save $$$ in the long run.
    Last edited by keithwms; 07-30-2009 at 06:39 PM. Click to view previous post history.
    "Only dead fish follow the stream"

    [APUG Portfolio] [APUG Blog] [Website]

  3. #23

    Join Date
    Dec 2008
    Shooter
    Medium Format
    Posts
    175
    Quote Originally Posted by jasonhall View Post
    I rate Efke IR820 which is 100 ISO at ISO 3. So that is 5 stops. I often bracket a stop above and somtimes below. So as stated above, 6 to 1.5 ISO.

    BTW, this was my first roll shot on 120 and I developed it Diafine. I rarely use Diafine, but in my opinion it is really nice with Efke IR820.

    Jason

  4. #24
    2F/2F's Avatar
    Join Date
    Apr 2008
    Location
    Los Angeles, CA
    Shooter
    Multi Format
    Posts
    8,008
    Images
    4
    The starting point filter factor is 32x, requiring 5 extra stops. At first, shoot some to test, and bracket around using that filter factor. IMO, you should go ahead and start at 6 or 7 stops instead of five your first time, since Efke is tremendously contrasty, and only reaches its rated speed of 100 if developed in a speed-enhancing developer. The amount of IR present in each scene will actually determine the "proper" exposure. Try to do it in sunny 16 conditions for a roll, and also try some other conditions on another roll to see if you get anything. Also, try different hours on that "sunny 16" day. (Hint: in scenes low in IR, expect to have to give much more extra exposure.)

    With the films available today: 1. You do not get a notable amount of IR exposure unless using an opaque filter, 2. you generally have to be on a tripod to get a sharp shot (assuming the f stops most often used on tripods), and 3. you almost certainly have to experiment to determine the reciprocity maintenance (or rather, the lack thereof) of your film during long exposures (again, assuming the f stops most commonly used on tripods).

    Don't forget to refocus your shots after composing. This may not be as necessary with IR820 as it was with HIE, but I always use the red line and the shots look OK.

    R72 (the 72 = 720 nM cutoff) is opaque only on films that do not respond to radiation (light) of 720 nM or more. Most films do not. SFX does, and IR films do.
    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)

  5. #25
    2F/2F's Avatar
    Join Date
    Apr 2008
    Location
    Los Angeles, CA
    Shooter
    Multi Format
    Posts
    8,008
    Images
    4
    Quote Originally Posted by accuteoptical View Post
    Our IPG-720 filter is avaiable for you.
    Three posts, all advertising yourself. You can't seriously think this is ok, can you?
    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)

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