Questions about IR?

kelox · May 6, 2005

Hello all, I have a few questions about IR photography. I have never done it,it, but I've seen some very nice photos done using it and it has piqued my curiosity. When using a DSLR, do you need to buy a special lens, or is it as simple as buying an IR filter? Does the amount of available light matter, that is to say, would it be better to shoot on a bright sunny day, or on a cloudy overcast day OR can it even be done at night? Do the shutter times need to be increased, decreased or do you just shoot normally?

DIRT · May 6, 2005

I have a 10D and have done some IR. you will need an IR filter I recoment the Hoya r72, it is basically black. you need to shoot RAW and set the white balance in PS. the skills come into play in photoshop and i fall short a bit there but just look at some posts by Digital Matt, he is insane and he has helped me a ton. your exposure times with r72 filter on bright sun will be around 20 seconds. also IR focuses at a different plane than visible light. IR should be done in bright daylight, Night IR might be impossible, never tried it. Good luck to ya.

kelox · May 6, 2005

Thanks DIRT, that has helped me alot.

ksmattfish · May 6, 2005

kelox said:
Does the amount of available light matter, that is to say, would it be better to shoot on a bright sunny day, or on a cloudy overcast day OR can it even be done at night? Do the shutter times need to be increased, decreased or do you just shoot normally?

Infra red covers a wide area of the spectrum. While there are devices that can image from heat, IR photography takes place just on the other side of the visible spectrum. You need an IR light source. The most popular one is the sun, but you can shoot IR at night if you have an IR lamp. Many regular light sources give out IR, but you'd need to filter out the visible light to get a pronounced IR effect. I have experimented with using a filter on a flash that blocks most of the visible light, but allows the IR to go through.

IR doesn't bounce around. This means there is usually very little IR in the shade. On the other hand it tends to penetrate through haze, etc... So slightly overcast days may be as good as bright, sunny days. Also there will be lots of IR when the sun is low in the sky, while it may seem quite dim in visible light.

Shutter speed and aperture are the same with IR film/digital as when shooting normally. However IR wave lengths are longer than visible light wave lengths, and the focusing is different. If you have a prime lens it should have a red mark on the focus ring. You focus as normal, say at 10', then you manually adjust the focus so that 10' lines up on the red mark instead of the normal focus mark. If you can use a small aperture, and get lots of DOF, then this isn't so important.

DIRT · May 7, 2005

Oh yes, I forgot. if you want to make an IR filter for your flash just buy a roll for color print film (120 size) then pay for it, then hand it back to the clerk and say process this please. the resulting unexposed and processed film will be dark and it passes IR when used over your flash.

ksmattfish · May 7, 2005

If you process unexposed print film (C-41) you will get a transparent orange strip of film back. You want to process unexposed slide film (E-6). Then you'll get the dark strip you are looking for. I use 2 layers of this in a mini softbox on my flash to do IR flash photography.

kelox · May 8, 2005

Matt, let me see if I have this right. I can make the softbox and don't need to get the IR filter? What would be the difference in using an IR filter and not the softbox. Not sure if I have the skills needed to make the softbox.

ksmattfish · May 8, 2005

I put the filter in a softbox because I have been advised that applying a filter directly to the flash can cause the flash to possibly overheat if used a lot.

If you are using the sun you want to use a filter on the lens (#25 red or something stronger). If you are shooting in low light, and want to turn your flash into the IR source, you only need the filter on the flash. A filter on the lens would be redundant.

kelox · May 8, 2005

Matt, I've seen several different IR filters on different websites. i understand the number has to do with how dark the lens filter is, but why are there different colors? Do they block out different parts of the visible spectrum? I thought IR lenses blocked out all of the visible. Let me know if I am completely wrong on this.

Digital Matt · May 8, 2005

ksmattfish said:
Shutter speed and aperture are the same with IR film/digital as when shooting normally.

This is not the case with digital. DSLRs have a filter over the sensor to reduce the transmission of IR light. In a normal exposure of the visible spectrum, IR light is undesirable, and can add unwanted noise. Most sensors are very sensitive to it.

Exposures for digital IR typically range from 6-30 seconds, or (depending on the strength of your filter) 5-10 minutes. Bright sunny days, are your best bet. The more light you can get, the better off you'll be. Just don't shoot into the sun. I normally shoot at f/8 to take care of the focusing problem, and a good shutter speed to start with would be 10 seconds. See what you get, and work from there.

As for lenses, not all lenses work well, because some have a coating that will cause a large hot spot during long IR exposures. A lens flare basically. Here's a link to my DA journal, with a list of Canon mount lenses that will work for dig IR, and the ones that wont, that I know of.
http://mperko.deviantart.com/journal/4289193/

A good filter to get, as mentioned is the Hoya R72 because, being that it only blocks the visible spectrum below 720nm, it's letting some visible light in, which gives your sensor a bit more data to work with. A 50mm f/1.8 and an R72 should be a good combo to start out.

Last but not least, the post processing can be tricky. Let us know when you get there, and I'll explain the different photoshop techniques.

Here's a small gallery of my dig IR stuff: http://www.anti-rejection.com/photography/infrared/

Good luck! ?

ksmattfish · May 8, 2005

Digital Matt said:
This is not the case with digital. DSLRs have a filter over the sensor to reduce the transmission of IR light. In a normal exposure of the visible spectrum, IR light is undesirable, and can add unwanted noise. Most sensors are very sensitive to it.

I just assumed that all filters and general IR sensitivity would be taken into consideration when calculating exposure.

DIRT · May 9, 2005

OOPS! sorry, I said neg, I meant slide.

Daniel · May 9, 2005

Can someone please explain the technical background of the focussing problem?

Thanks!

kelox · May 9, 2005

Matt, I thought you were a nice guy, come on. You are killing me. I went to your two links and it just makes me want to try IR even more. Your pictures there are striking, I'd like to tell you my favorite one, but to be honest they are all great! The one titled Frozen city looks as though it was taken during the winter time(hence the name), I'd never even thought of trying IR during the cold season.

I keep tellling myself I need more time behind the lens, but seeing your pictures makes me want to get out there and just dive right in. I have made a deal with myself though, I won't buy the IR lens until I get home on R&R(waiting till the end of my deployment would be an exercise in futility).

Matt, thanks again for answering my questions, I'm sure as I read more I'll have more.