Infrared Exposure Meter?

[Old-N-Feeble]

Is there such a thing as an infrared exposure meter? A narrow-field one would be optimal.

I'm interested in trying some near-IR film like SFX 200 but want to be able to meter reasonably accurately how much IR of the appropriate wavelength is reflecting off the foliage so I can more accurately expose and develop the film without having to bracket several frames on a minimum of two rolls... this allows me to adjust development on the second roll.

Hmm... now that I think about it burning extra film is probably more cost-effective than a dedicated IR meter because I won't be shooting that much. None-the-less... my curiosity is up now!!

[vinny]

Yes
Here's one:
http://www.davidromano.com/TrueIRMeter.html

Bracketing is for sissies.

[Sevo]

Is there such a thing as an infrared exposure meter?

Not that I am aware of. Given that IR film does not have a standard spectral sensitivity and the IR spectrum it sees is generally still quite close (and proportional) to the visible, a generic IR exposure meter might have disappointingly little advantages over a visible light exposure meter, and fail to pay for itself.

It should be possible to convert some common pyrometer to such a task by applying a suitable filter set and substituting a firmware that can input sensitivity and display the inverse of intensity as EV or time/aperture. But hardware hacking aside, the cost of working out the calibration for one film would probably exceed any amateurs lifetime consumption of film, even if he'd use his film's IR equivalent to sunny sixteen plus bracketing like mad...

[Sevo]

Yes
Here's one:
http://www.davidromano.com/TrueIRMeter.html


Autometer V, with blue filter removed/substituted by a Wratten IR filter. The same stunt can be pulled off with any meter without a IR blocking filter (or with the filter removed) - the real value (above the hardware components) of that kit would be in the accompanying user manual with sensitivity tables, as you'll go through insane amounts of film working out the latter.

The real issue is that the said IR filters only model the visible/IR transition, and cannot model the spectral response of the film within IR - where the currently available films are distinctly odd and difficult.

[Old-N-Feeble]

That's pricey but not as bad as I expected. Maybe I can find a used one?

I'd most likely be using #25 and #29 filters since I'm not looking for "pure" IR but rather extended red... like SFX200... because I want light but not white foliage and I don't want significant halation effects. I'm looking for subtle tonal enhancement rather than dramatic effects. The reason for the IR meter is to provide more predictability.

I guess the only concern, as mentioned above, is unpredictable exposure readings due to the meter seeing different IR wavelengths than my film and filter. Is there an affordable/predictable way around this if I stick to one film such as SFX200?

RE modifying a meter myself: Any link(s) to basic instructions?


Yes
Here's one:
http://www.davidromano.com/TrueIRMeter.html

Bracketing is for sissies.

[Sevo]

That's pricey but not as bad as I expected.

Well, if that offer still exists and the meter is new (Minolta quit making meters many years ago), that would be less than a hundred above the retail price. The same goes if he now ships the Kenko relabelled current version of the meter (KFM-1100). Not that much, if there are good tables along with it. But apart from these, any meter with a removable (or never installed) blue filter would do just as well for a DIY conversion.

[RichardSperry]

This site's bandwidth has been exceeded.

http://www.999-wed.com/pg/pg9-infrared-allenmeter.htm

But he takes a $20 lux meter and converts it to IR, and shows you how. I would try that before messing up a perfectly good Minolta.

[Sevo]

RE modifying a meter myself: Any link(s) to basic instructions?

None that I know of - the process itself probably is too trivial, and the more complex calibration issues are exactly the same as for meters without filter modification.

Given the low IR sensitivity and limited spectral range of the remaining IR films, attaching a deep red or IR filter to a unmodified meter might already be good enough. For EIR or HIE you had to remove the (IR cut-off) blue filter from meters with silicone blue cells (and ideally substitute it with a deeper IR filter), and then could meter through the same filter you'd use for exposure. Mind, these films had a wide IR response and good visible/IR relation. With all current films it never is a 1:1 process, you still have to compensate considerably to match film to meter readings, as their IR sensitivity is odd, short-range, wobbly and disproportionally lower than the visible one - hence it might even be advisable to leave the blue filter on.

[Old-N-Feeble]

Thank you... I'll keep trying that website until I get through.


This site's bandwidth has been exceeded.

http://www.999-wed.com/pg/pg9-infrared-allenmeter.htm

But he takes a $20 lux meter and converts it to IR, and shows you how. I would try that before messing up a perfectly good Minolta.

[Old-N-Feeble]

Basically, what you're conveying is, particularly with films with spectral response similar to SFX200, I'm just as well off metering through a #29 filter with a non-SBC meter? There's not much I can do to more accurately read the IR reflected from foliage? If that's true then I'm back to bracketing and shooting a roll of film as a back-up to development time.


None that I know of - the process itself probably is too trivial, and the more complex calibration issues are exactly the same as for meters without filter modification.

Given the low IR sensitivity and limited spectral range of the remaining IR films, attaching a deep red or IR filter to a unmodified meter might already be good enough. For EIR or HIE you had to remove the (IR cut-off) blue filter from meters with silicone blue cells (and ideally substitute it with a deeper IR filter), and then could meter through the same filter you'd use for exposure. Mind, these films had a wide IR response and good visible/IR relation. With all current films it never is a 1:1 process, you still have to compensate considerably to match film to meter readings, as their IR sensitivity is odd, short-range, wobbly and disproportionally lower than the visible one - hence it might even be advisable to leave the blue filter on.

[Sevo]

Basically, what you're conveying is, particularly with films like SFX200, I'm just as well off metering through my non-SBC through a #29 filter? There's not much I can do to more accurately meter the IR from foliage?

Yep - there is not much to be done about SFX (and other similar speed trap films) that can't be done with a regular meter, they don't reach far enough into IR that you need to bother. And EFKE on the other hand has such a bizarre low-sensitivity IR response that a corresponding metering filter would be quite a expensive research subject. Hacked meters were more helpful in EIR/HIE days.

[Lynn Jones]

I've converted several, all of the meter sensors are tremendously more sensitive to long wave lengths the the shorter ones. Virtually all meters have IR cutting filters built in. I would suggest that you use the meters I have used for this such as the Luna Pro, you can buy them used pretty inexpensively. Open the meter up, you'll find a small glass filter that has a greenish/blue cast. First clean it! Next get an 87 or 88 gel filter, cut it the same size as the glass filter and insert it, now close the case. Now you will know what the approximate exposure in a daylight situation, so set up the ASA/ISO so that the indicated exposure is the same as the expected exposure. Now it is just a matter of fine tuning the meter according to the IR exposure. This will work for daylight, flash (yes there is a great deal of IR in electronic flash), tungsten, or whatever. If you convert a DSLR to IR it will work for that as well.

Lynn

[Old-N-Feeble]

I suppose that works with a Luna Pro-F as well?

[Jeff Dexheimer]

I simply use my pentax digital spotmeter. I set the film speed to asa 12. If there is blue sky I meter that with my IR filter over the front of my light meter. That is usually my darkest shadow. I check other shadows just to make sure. I place my lowest reading right between zone 3 and 4 and fire away. Hasn't failed me yet.

ETA: I am using Efke IR820 and a Hoya R72 filter.

[Sevo]

I suppose that works with a Luna Pro-F as well?

That (or rather, its non-flash predecessor) is the converted one I still have around. Easy to do, just disassemble the case and replace the blue filter with the IR one you are after (I put a yellow filter in mine, for EIR, but that would be pointless now). Oh, and if you have the same meter with and without conversion, paint the converted one bright red (or do something else that makes it immediately identifiable) or you'll be in for some ugly surprise sooner or later...

[Old-N-Feeble]

I want to try SFX200 for pictorial landscapes and want a subtle effect so I'll probably be using a #29 Wratten filter.

Will the meter behave differently if I hold the filter in front of the meter rather than install a cut piece of filter at the sensor?

[Brian C. Miller]

... because I want light but not white foliage and I don't want significant halation effects. I'm looking for subtle tonal enhancement rather than dramatic effects. ...

If it isn't Kodak HIE/HIR, then it's always questionable about what you will get. Here's the reason: different plants reflect IR in different ways. The cell structure reliably reflects IR at the wavelengths that made HIE so great as an aerial surveillance film. But without that spectral sensitivity, you don't know what you'll get if it isn't deciduous foliage. Up where I live most of the trees are conifers. These reflect IR in different spectra, and not all reflect IR in the same spectral sensitivity as is needed for the film. Some are black, some are grey, some are white, and that's with a very dark B+W 092 filter. (B+W 091 = Wrattan 29)

If you use a 25, then you may not get anything. If you use a 29, you might see a bit with deciduous foliage. One time I was out with Konica IR (similar to SFX 200 and Efke), in the deep shade under pines or similar. I thought that there wasn't hardly any IR around. Boy, was I absolutely wrong. The first exposure and +/- brackets were good, and the rest just turned the film oh-so-overexposed.

With IR, you just take your chances.

Oh, yeah, halation: you won't see it. Kodak film did not have an antihalation layer. The only film you'll get with this is the Adox (Efke) "Aura" IR film.

[Old-N-Feeble]

Does anyone make a narrow band IR pass filter... something like 600-700 nanometers? Or maybe I can combine a Wratten #70 filter with an IR cut-off filter at 700 nano or so? If so then maybe I could take separate spot readings of visible and IR light so I can combine the two for more predictable results with SFX.

[Sevo]

Does anyone make a narrow band IR pass filter...

Edmunds, Surplus Shack and the like might have suitable dichroic bandpass glass filters. But be warned, these are quite hard to cut down.

And as I said, you need not worry that much about exposure as long as you stick to SFX. The IR band provided by SFX can be treated as a simple matter of object colour (which you generally don't explicitly adjust your exposure for when using panchromatic film) - in that near-visible range the IR intensity of daylight and incandescent lighting will be in a fairly constant proportion to the visible band.

[tgtaylor]

Believe it or not but my Pentax 67II meters Rollie 400 IR film with Cokin 007 IR filter attached perfectly.

Thomas

[Helen Bach]

There were instructions about how to modify a Pentax spotmeter in an old issue of Photo Technique. The idea was to set the long end of the meter's sensitivity to the long end of HIE, using a Melles Griot interference filter, then add whichever visibly opaque filter that you were going to use over the camera lens - all this happens right in front of the meter cell so you can still see through the meter. I modified a Pentax and a Sinar Booster that way. All my old copies of Photo Technique are in storage, so I can't look the article up. I still have some of the Melles Griot filter somewhere in a drawer - but it isn't correct for the IR films available now, of course. It was quite easy to cut down - just like very thin glass, protected with tissue paper when snapping along the scratch.

[Old-N-Feeble]

(filter at the sensor) "...so you can still see through the (spot) meter."

Ahh... why didn't I think of that? These days I miss the obvious all the time!

[nolindan]

I find just setting a plain-ole Sekonic 398 - the type with a selenium cell - to ASA 6 [well, ASA 12 and doubling] gives very good results with the near-IR films and a #72 filter.

If you want to you can meter through a #72 filter to get some idea of relative IR intensity. The 'blue' filter on a silicon photodiode isn't very good at blocking IR, enough gets through for the meter to register.

[Kodachrome25]

I have a David Romano meter conversion, works great. I had it made when I cleaned out Samy's of HIE and bought 50 rolls of Romano 70mm Aerographic re-spool from a private seller some years back. If IR is important to you like it is to me, the meters are worth it...

[dave]

I find just setting a plain-ole Sekonic 398 - the type with a selenium cell - to ASA 6 [well, ASA 12 and doubling] gives very good results with the near-IR films and a #72 filter.

If you want to you can meter through a #72 filter to get some idea of relative IR intensity. The 'blue' filter on a silicon photodiode isn't very good at blocking IR, enough gets through for the meter to register.

I also just use an ordinary meter set at ISO 12 and open up a stop. Converting a meter seems to me to be an expensive way around a simple problem.