IR Questions

Discussion in 'Digital Discussion & Q&A' started by magicmonkey, Apr 24, 2006.

  1. magicmonkey

    magicmonkey TPF Noob!

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    I'm thinking about trying out IR photography as the filters are quite cheap (well, for photographic equipment anyway!) but I have a couple of questions before I go off and spend any actual money. Firstly, will an IR filter work with a Canon 350D? Secondly, if I can't see through the lens how on earth do I focus?
     
  2. doenoe

    doenoe TPF Noob!

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    I got an Hoya R72 filter and a 350D. The 2 together work just fine. You just need some longer exposures then other camera's. I went out today, with alot of sun, and i needed shutter speeds between 2 and 4 seconds. So i tripod is a must.
    The focus: you first take of your filter and focus automaticly. Then your put on your filter again and set your camera on manual focus. You do have to turn the focus ring a bit after that though, since IR is weird and the focus is different then normal light. Just a small turn (few mm) works fine. Its just a trial and error thing.
    Also, you have to set your camera on custom whitebalance. The whitebalance image you need, can be created by taking a picture of grass with the filter on. Just grass, nothing else in the frame.
    Thats about it, when it comes to my knowlegde of IR. Just have to try alot and learn.
    Good luck with it, if you decide to go IR.
     
  3. Digital Matt

    Digital Matt alter ego: Analog Matt

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    Yes, an IR filter will work with the 350D.

    You should look for a Hoya R72.

    The tricky part is, what lens to use it with. Some lenses have coatings that will create an undesirable hotspot on the center of your photo. The Canon 50mm f/1.8 MKII works great.

    You compose and focus your shot with the filter off, and then carefully screw it on, and go for it. Focusing IR light can be tricky, because it's not the same wavelength as visible light. The 50mm f/1.8 does not have a focus scale to show you how to focus in IR. I find it best to shoot at f/5.6 or f/8 to ensure enough DOF to take care of it.

    Be prepared for very long exposures, even in broad daylight. Even though your camera is sensitive to IR light, it has a filter over the sensor to reduce this sensitivity. IR light in a normal photograph will only add to the noise.

    Now imagine you have a filter over the lens that blocks the majority of the visible light, and then there is a filter built in over the sensor that blocks some of the IR light. You have a problem.

    I just took a few IR shots yesterday, and my exposures were ISO 200, f/8, 30 seconds. I have a 20D which seems to have a stronger IR filter over the sensor than the 300D. I don't know about the 350D. You'll have to just experiment and bracket, and wait. You'll need a tripod, and a remote switch is preferrable.

    As for white balance, I prefer to shoot raw, and worry about it in post. I use the eyedropper to set my white balance by clicking on anything green, (or what should be green, ie grass, leaves, etc..) I normally then invert the colors in Photoshop by duplicating the background layer, inverting it (ctrl+i) and setting it's blend mode to "color".
     
  4. magicmonkey

    magicmonkey TPF Noob!

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    Well I've been looking at the R72, found one for about £20 + P&P on ebay (must remember to wash my mouth out now!) so I think I'll be getting that at the end of the month...
     
  5. doenoe

    doenoe TPF Noob!

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    i totally forgot about the hotspot. I shoot with the kitlens now and it depends on what focal lenght you shoot. The shutterspeed is a factor too, as is the place of the sun. But you will find out when you get out and experiment alot.
    The Canon 50mm f/1.8 MKII works great eh? Good stuff, just ordered one of those. Only need a stepup ring now.
     

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