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Infra Red Filters :?:
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I recently got an ifra-red filter for my camera I’m just a bit worried as the exposure times seem a bit long even with the aperature wide open. So I was wondering could anyone point in the right direction as too either finding out if my filter is too dark or am I heading in the right direction with the long exposure times.
Thanks
from what im told ( im not an expert on this btw) you must use long exposures to capture your image up tio 30sec or more
Presume your talking digital, it its film i’ll let Peter (thefizz) answer that one as he’s the IR Film expert around here.
On a digital camera your talking long exposures up to 30 seconds, this is because the manufacturers have put IR blocking filters over the sensors (prevents white/red casts on your pictures). To bring down the exposure times on digital you have to get the camera converted ie get the IR blocking filter removed.
M
I was talking about Digital. I have a Canon 40D. Don’t really want to void the warranty just yet. I also have a film camera so I guess I could work away with that and scan the film.
You should not have any problems i have an IR filter for my 400D and i can get results with 25/45 sec exposures but you have to make sure there is plenty of natural light.
Yes, 30 seconds in broad daylight with an open aperture is just about right for current DSLRs. You mentioned 15 minutes in a post though – if that is the case, there’s definitely something going on. Sure you don’t have the lens cap on instead of the filter? =)
Cheers,
PeterThat’s your problem, then. The 87 filter is pushing the camera significantly into the infrared. Most people can’t see colour past 700nm. The Hoya R72 blocks (most) light shorter than 720nm or so, which means a small amount of visible light does leak through. Your filter will block light shorter than 870nm, so no visible light gets through at all.
The IR blocking filter on modern DSLRs is very efficient, and very little IR actually gets through. As you go deeper into the infrared two things happen – the IR filter becomes more efficient, and the sensor itself is getting less sensitive to the frequencies that are being let through.
The company (MaxMax.com) that did my camera conversion say that their 830nm conversion (which is less restrictive than the filter you’re using) causes a two-stop drop in light hitting the sensor. So put an IR blocking filter on top of that and small wonder you’re getting such long exposure times.
My advice is to buy an R72 filter and try it out. If you like it, then consider getting your camera converted with an R72-like filter. Keep the Tiffen 87, as you can use it on top of your converted camera to take photos in the slightly deeper (but still near) infrared.
From MaxMax’s page at http://www.maxmax.com/IRCameraConversions.htm
With the IR-Only SLR cameras, you can see through the lens like normal, but the picture taken will be in infrared. The 715nm glass is similar to the Hoya R72 glass. A 715nm camera conversion will see almost the same amount of light as a stock camera. This means that if you can hand-hold the camera for a stock picture, under outdoor sunlight, you can do the same for a 715nm conversion.
With an 830nm conversion, you will lose about 2 F-Stops or have a slower shutter speed. Notice on the examples below, holding F-Stop constant at F8.0, shutter speed went from 1/500 to 1/125 when we went from 715nm to 830nm. The advantage of a 830nm filter is that the red, green and blue channels are more evenly exposed than at 715nm. The red channel more open on a 715nm than on a 830nm conversion. When you more evenly expose the RGB channels, the camera can resolve better. Also, the infrared effect is more dramatic at 830nm versus 715nm – skies are darker and clouds whiter. The most popular conversion is the 715nm, but the 830nm conversions are increasing in popularity
Hope that helps.
Peter
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