IR with or without autofocus

winger · Jul 17, 2005

I know the infrared assist in some cameras can mess up IR film. Does this only happen if you use the autofocus? Or is the IR assist "on" at all times? I have a Pentax PZ1P and am pretty sure it has some type of assist 'cause I could see a red beam when shooting in a cave this spring. So, would it be safe to try HIE in it as long as I don't use the AF ('cause I rarely use AF anyway)?

David A. Goldfarb · Jul 17, 2005

You probably should use manual focus anyway, unless your autofocus camera can compensate for the IR focus shift.

winger · Jul 17, 2005

So the "IR assist" will only interfere if use autofocus?

David A. Goldfarb · Jul 17, 2005

Isn't the IR assist for AF in low light? I don't believe it is related to shooting IR film.

With most lenses, IR light will focus at a different point than visible light.

On a manual focus lens for a 35mm camera, there is usually a red dot on the focus scale for IR focus. To focus with IR film, the normal practice would be to focus conventionally, look at the focus scale on the lens, and then move the focus ring from the regular focus index mark to the red dot. The image will look slightly out of focus in the viewfinder, but it will be in focus for IR film.

Unless the AF program on your camera can make this adjustment automatically for IR, you shouldn't use AF for IR film.

winger · Jul 17, 2005

The IR assist is for low light for AF. I ask mostly 'cause I don't normally use AF, but wonder if it would prohibit my using this camera for IR film whether I'm using Af or not. I've seen it recommended to not use cameras that have the IR assist with IR film, but if the camera only uses it when autofocusing, then I wonder if it really isn't a problem.

bjorke · Jul 18, 2005

I think you're confusing IR focus assist with IR sensing of sprockets for the motor drive in cameras like some EOS's and Contaxes. I bit the bullet and ran some HIE through my G2, it didn't seem to make much difference.

David is right though, standard AF will focus in the wrong place for IR. Your lenses probably have a red dot to mark the correct offset.

winger · Jul 18, 2005

I don't use autofocus and wouldn't with IR film anyway (I've used HIE before and know how to focus). I don't know if my Pentax PZ1P will mess up the HIE. That's what I'm trying to find out (preferably without shooting a roll as an experiment).
Since it has the IR assist with AF, does it also use IR for anything else that would then mess up HIE?

kaiyen · Jul 18, 2005

For what it's worth, I've found that, when using a red 25, enough visible light gets through that the subject still looks in focus, even with AF. I see no significant loss in sharpness.

allan

colrehogan · Jul 18, 2005

winger said:
I don't use autofocus and wouldn't with IR film anyway (I've used HIE before and know how to focus). I don't know if my Pentax PZ1P will mess up the HIE. That's what I'm trying to find out (preferably without shooting a roll as an experiment).
Since it has the IR assist with AF, does it also use IR for anything else that would then mess up HIE?

How does your camera count the film? When you open up your camera back, is there a little opaque looking window inside? If so, this is the IR sensor used for counting the sprockets on the film (and is what has the possibility of fogging the Kodak HIE IR film).

winger · Jul 18, 2005

colrehogan said:
How does your camera count the film? When you open up your camera back, is there a little opaque looking window inside? If so, this is the IR sensor used for counting the sprockets on the film (and is what has the possibility of fogging the Kodak HIE IR film).

Thank you - I'll check. You're the only one who 'got' what I was asking.

Dave Parker · Jul 18, 2005

I have to say, I was a bit confused as well, your orginal question delt with the IR focus beam and not the IR counter in the camera, which is what everyone answered you about, if you were asking about the frame counter IR beam, it sure would have clearer if that is what you had said.

Dave

winger · Jul 18, 2005

Sorry, but I had been lead to understand that the 2 were the same. That if your camera had the IR to assist with AF, then it also used it in a way that would interfere with HIE.

Bob F. · Jul 18, 2005

IR focussing assist and IR counting of sprocket holes are not the same thing. IR counting of sprocket holes will cause problems because it shines the IR on to the film edge: only a little in some cameras, a lot in others. From what I have read, the amount of fogging varies even between individual cameras of the same make and model. IR focus assist does not shine IR light on the film, it shines it on the subject, so will not be a problem.

Happy shooting, Bob.

TheFlyingCamera · Jul 18, 2005

I have not heard anything about the Pentax AF line and fogging of film - I think the best thing to do would be to put a roll through the camera and find out. The IR Focus Assist beam turns OFF when you make the exposure, so it will never fog the film. I would be suspicious of your Pentax PZ1P because it is an older camera, and if it uses IR for frame counting, the beam may be stronger (it seems that most manufacturers have cottoned on to the idea that people want to shoot IR with their cameras, so they've reduced the intensity of the IR frame counting beam). I have a 1st generation XPAN, and despite concerns about the IR frame counter, I have had no fogging that ever intruded into the image area on the film, just a little fog between the sprocket holes. The older Canon AF SLRs had this problem in spades, but I believe it has improved.

IR with or without autofocus

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IR with or without autofocus

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