Infrared Exposure Meter

greenspun.com : LUSENET : Advanced Photography : One Thread

HAs anyone ever seen an exposure meter for IR? I've been shooting more IR film recently and, like everyone else, having problems getting the exposure right without bracketing the hell out of every shot (expensive).

Seems to me an IR expsoure meter should be pretty simple. All you need is a response curve from about 650nm to 950nm, which is in the range of a silicon photo cell. Calibration is another matter, but one roll of test film should be enough for that.

I was considering building one. My day job involves measuring light from UV to IR, so I have the background), but I'm just wondering if anyone else has done this, or if a commercial lightmeter is available, and how well it worked.

-- Bob Atkins (bobatkins@hotmail.com), August 03, 1999

Answers

Looking into my crystal ball, I predict that you are about start a new business with a built-in market. You will make lots of money and get calls at odd times of the day from exotic corners of the world. I see you investing some of your profits in the IPO for a new digital company called Ars Digita which will make you richer than you ever thought you might be and then semi- retiring to spend your time making only the photographs you like and consulting Kodak and Konica in the odd spare hour. You will begin an astonishing world famous collection of photography and eventually have a name of a museum named after you. And in the end you will look back and say "to think I owe it all to photo.net!"

-- Ellis Vener (evphoto@insync.net), August 03, 1999.

Well, this guy seems to have done some fairly sophisticated IR work:

http://www.a1.nl/phomepag/markerink/mainpage.htm

He's had success using some oddball gear. 87C filters inside of cameras, military goggles to preview IR effects. I don't remember if he ever got meters modified.

If you can find out the details of Zone VI's "calibration" of Pentax Digital Spotmeters that might give you a start. They've adjusted that meter to match the response of most panchromatics, and the design allows you to mount filters on it. That would be where I'd start if I had the money to burn on one.

If it makes you feel better about bracketing, I'll be in the darkroom tonight developing 4x5 macro shots on IR, bracketed for focus correction and exposure. Expensive and probably futile.

Hope this relatively useless answer doesn't violate the forum.

-- John O'Connell (oconnell@siam.org), August 03, 1999.


The IR link is a good one, but I don't think there's anything about IR exposure meters there (unless something has been added in the last few days!).

I suppose that given the miniscule market for IR "goodies", it's not too surprising there aren't any IR meters. On the other hand, all you would need (in principle) would be a modified silicon based meter. Germanium photodiodes go out further into the IR, but since HIE cuts off around 950nm and Si diodes go out to 1000nm (with reduced sensitivity), Si should be all you need.

I guess I should stop whining about the cost of a +/- 2stop bracket on 35mm HIE ($1.40 per sequence!). Must get expensive in 4x5.

Now if only I could figure out a way to get the focus right without having to stop down to f16...

-- Bob Atkins (bobatkins@hotmail.com), August 03, 1999.


There is a consistent relationship between visual light and infrared in hard sunlight that allows using a normal light meter. Once you've figured your eposure index (developement time etc.) you can depend on consistency under these conditions.

I never bracket more than one up/down and I only shoot one over on rare instances (two over has been consistently bullet proof). The ratio of visible to infrared does change with the amount of atmosphere at sundown and rise. Infrared stays constant as visible goes down. I then bracket to the under-side only (using the "visible" light reading meter). I never shoot infrared under overcast conditions, it's just too flat for me...t

-- tom meyer (jparady@mindspring.com), August 15, 1999.


There is a fellow who teaches in Chicago at Columbia College. Can't recall the name but he had worked out an exposure scale for infrared based on the ambient temperature. I know it was published in View Camera a looooooong time ago. Want more info lemme know.

-- Sean yates (yatescats@yahoo.com), August 30, 1999.


Sounds wierd to me! IR film isn't recording anything related to ambient temperature, it's recording reflected IR. To record emitted IR from objects at ambient temperature you'd need a film with an IR response at MUCH longer wavelengths than anything currently available.

I'd guess the "correct" IR exposure for an object illuminated by the same light would be the same at the North Pole at -50C as in the middle of Death Valley at +50C.

-- Bob Atkins (bobatkins@hotmail.com), September 01, 1999.


Just a thought and not really an answer, but how about a conventional digital readout type silcon meter (e.g. Pentax digital spotmeter) with an appropriate IR filter in place? I imagine viewing would be a little difficult, but one could rig up a viewfinder of sorts if needed. Would this work, or am I missing something? Regards ;^D)

-- Doremus Scudder (ScudderLandreth@compuserve.com), September 02, 1999.

It could work - even an IR filter on an SLR could work - IF the meter doesn't have an IR blocking filter of some sort in place. The intrinsic sensitivity of a silicon detector peaks at around 900nm, so if I were desiging a metering system for visible light, I'd make sure I blocked IR from the detector cell to avoid spurious readings or oversensitivity when used indoors under tungsten light. If they do that then IR response would be WAY down and would make it difficult to use the meter for IR with an IR transmitting filter in place.

-- Bob Atkins (bobatkins@hotmail.com), September 02, 1999.

Moderation questions? read the FAQ