Re: Infrared Filters for Digital Photography with D70

bino wrote:
"Neil Harrington" <not@xxxxxxxxxx> wrote in message
news:V-6dna8hjZOSLebVnZ2dnUVZ_jqdnZ2d@xxxxxxxxxxxxxx

"bino" <critic@xxxxxxxxx> wrote in message
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I've searched the archive, and it looks like the Hoya R72 is the
favorite, and oft recommended in this group. But then I found this
thread on APUG:
http://www.apug.org/forums/forum37/40361-b-w-092-vs-hoya-rm72.html

In there you'll see this list:

"Wratten # 25 (Old designation: A): 600 nm
Wratten # 29 (Old designation: F): 620 nm
B+W 091 (Schott RG630): 630 nm
B+W 092 (Schott RG695): 695 nm
Wratten # 89B: 715 nm
Hoya R72: 720 nm
Wratten # 88A: 745 nm
Wratten # 87: 795 nm
B+W 093 (Schott RG830): 830 nm
Wratten 87C: 850 nm

All Wratten data from Kodak Photographic Filters Handbook, B-3,
1992" So now I'm thinking, why not get the B+W 093, as it'll cut out
even
more of the infrared light?

You seem to be confused, unless I'm misunderstanding what you're
saying.

Yes, thanks, I'm not confused, just said it backwards.

The purpose of a 720nm cutoff in such a filter is to cut out the
*visible* light, not the infrared. That a 720nm filter does
sufficiently well and there's usually no reason to go farther. The
wavelengths of visible light are in the range of about 400 to 700 nm.


That's light visible to the human eye, what about film/digital
sensors? As the B+W 093 is also for use in infrared photography, one
must assume there's a reason for the greater cut off of "visible"
spectrum.

The visible spectrum is already almost entirely cut off by a 720nm filter.
The cutoff is not actually that sharp, i.e. it doesn't cut off everything up
to 719 nm and pass everything from 721 nm on. In other words, if you were to
graph the wavelengths transmitted the line at the cutoff wouldn't be
vertical. But it'd be pretty steep, in most filters used for this sort of
thing.

My 720nm filter looks black, but if you look at a scene through it the scene
is barely visible, in a very, very dark red. A similar IR filter with a
higher cutoff level I assume would pass no visible light at all and you'd be
able to see nothing through it.


You do understand that such a filter is used for infrared
photography, not visible light photography, don't you?


Yup.


The only reason I can think of not to, is that the shadows would be
even darker, but for all I know, the effect will be negligible.

Any thoughts?

What is it exactly that you want to do?


Talk to someone who knows the difference in practice between the two
filters I've referred to here. Thanks for responding, I do
appreciate it.

You're welcome. The next question is, Do you intend to modify your D70 for
infrared? The D70, like other digital cameras, already has a filter over the
sensor to keep the infrared *out*. So the higher cutoff filter you use, the
less likely it is you're going to get any light through to the sensor at
all. You could end up with the camera's built-in filter cutting out most of
the infrared and your add-on filter cutting out everything else.

With my D70S just now, looking out the window (a partly sunny day here) I
can barely see anything in the viewfinder with a 720nm IR filter on my 50mm
f/1.8 lens. I'm getting a shutter speed of 1/40 *wide open* -- without the
filter it's 1/2500. Remember that's at f/1.8 -- with the kit lens it'd be
about 1/10 second wide open with the IR filter. I sure wouldn't want
anything with a longer wavelength cutoff.

Your D70 might be a bit better since it's older, and generally speaking
older digital cameras have less aggressive IR filtering built in.

For $350 or so you can have your D70 converted for IR -- they take out the
IR-cutting filter and replace it with a filter that cuts off visible light
and passes IR. This has the big advantage that you can still use the
viewfinder normally, and exposure times would be reasonable since all the IR
is being passed. There are however some disadvantages, not the least of
which is that you can't use the camera normally any more -- unless of course
you have it converted back, which is also expensive.

I forget the name of the place that does the conversion, but Google would
find it for you.

As for your question about using 830nm filters instead, I can't help you
there. I have no idea why anyone would use one.

Neil


.

Relevant Pages

  • Re: Infrared Filters for Digital Photography with D70
    ... Hoya R72: 720 nm ... purpose of a 720nm cutoff in such a filter is to cut out the *visible* ... The wavelengths of visible light ... You do understand that such a filter is used for infrared photography, ...
    (rec.photo.digital.slr-systems)
  • Re: Infrared - black-and-white???
    ... Father Kodak wrote: ... Most "IR" films hit at wavelengths overlapping visible light, and with a full-visible cutoff filter, you won't get much exposure. ...
    (rec.photo.equipment.35mm)
  • Re: infrared photography questions
    ... that you'll just be shooting visible light with considerable IR ... for the camera having the low-pass filter in the first place. ... Maybe we're talking about something different, but the conversion I ... IR pictures with higher EV with a lens filter. ...
    (rec.photo.digital.slr-systems)
  • Re: Infrared Filters for Digital Photography with D70
    ... IR with a normal camera is not ... That a 720nm filter does ... wavelengths of visible light are in the range of about 400 to 700 nm. ... The cutoff is not actually that sharp, i.e. it doesn't cut off everything ...
    (rec.photo.digital.slr-systems)
  • Re: Infrared Filters for Digital Photography with D70
    ... The visible spectrum is already almost entirely cut off by a 720nm filter. ... The cutoff is not actually that sharp, i.e. it doesn't cut off everything up to 719 nm and pass everything from 721 nm on. ... A similar IR filter with a higher cutoff level I assume would pass no visible light at all and you'd be able to see nothing through it. ... The D70, like other digital cameras, already has a filter over the sensor to keep the infrared *out*. ...
    (rec.photo.digital.slr-systems)
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