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Archive 2008 · Crummy ND filters seem to be a crummy IR filter...

  
 
Sorensiim
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p.1 #1 · p.1 #1 · Crummy ND filters seem to be a crummy IR filter...


I had a thread some time ago about my Cokin filters, specifically the ND 0.6 and 0.9 that produced what was dubbed "Barbara Cartland Vision" by a fellow FM'er.

The filters produced a red cast when stacked:
http://farm3.static.flickr.com/2260/2342103407_b1a5c31575.jpg

and it sure wasn't a WB problem - corrected WB version here:
http://farm3.static.flickr.com/2023/2342110041_fa26d57c31.jpg
Using the clouds as white point.

I then shot the same scene without any filters:
http://farm4.static.flickr.com/3176/2342944632_a4cee13bec.jpg

My conclusion: Cokin filters are crap and should be replaced. So I did just that, and got myself some nice HiTech filters after advice in the original thread. I even went completely overboard and ordered an ND 3.0 filter - thats 10 stops of ND. I tested their regular ND's (0.6 , 0.9 and 1.2) without any problems. Then came the ND 3.0 and BAM - back to Barbara Cartland vision.

Hitech ND 1.2, 2 second exposure:
http://farm3.static.flickr.com/2058/2466827735_2ae2b73b7b.jpg

Hitech ND 3.0, 90 second exposure:
http://farm3.static.flickr.com/2392/2466827739_d063e16872.jpg

My conclusion: HiTech filters are crap and should be replaced. So I sent in the ND 3.0 for it to be replaced. A few days later, an e-mail from Formatt (the makers of HiTech filters) informed me that my filters were absolutely fine but it seemed that the IR filter on my camera might be defective. Hrm... needed to find a way to test it out.

So last night my buddy Thomas showed up, bringing among the rest of his kit, my old Cokin NDs. A filter holder was mounted on his Tamron 17-50 and the Cokins (ND 0.6 and 0.9) were mounted along with my HiTech ND 1.2. Filters, holder and lens were then mounted on his 30D and clicked onto my tripod. Just to be sure we had the color cast to begin with, he took a test shot:

http://farm3.static.flickr.com/2355/2513623710_0543f8f8e4.jpg

What the deuce?!? No color cast, 3 stacked (and apparently rather dirty) NDs.

The lens+holder+filters combo was then mounted on my 40D, with the same settings, WB etc:

http://farm4.static.flickr.com/3184/2513623704_f2f29b0701.jpg

So today I called my local Canon service center and spoke to a tech. He said that the CMOS might need some adjustments or perhaps the WB was off. I told him about the identical settings on the cameras, shooting RAW and Formatt saying that the IR filter was malfunctioning, but he wasn't convinced. They'll take my camera in next thursday and do some diagnostics etc.

Then I thought of a simple test: Shooting a remote control transmitting IR should show up as a black remote doing nothing...

http://farm3.static.flickr.com/2202/2513640762_6d743961a7.jpg

My judgment may be clouded, but I do believe that the diode lights up in the exact same color as the casts that have been ruining my long exposures.

Sorry for the long rant - Just thought I'd share my experiences with various filters and Canon sensors.

Edited on May 22, 2008 at 05:25 AM



May 22, 2008 at 05:20 AM
ohenry
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p.1 #2 · p.1 #2 · Crummy ND filters seem to be a crummy IR filter...


Quite an interesting event going on here. Will be interesting to find out what Canon finds.


May 22, 2008 at 08:32 AM
HerbChong
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p.1 #3 · p.1 #3 · Crummy ND filters seem to be a crummy IR filter...


i've mentioned that HiTech ND filters act as a weak IR filter here before. that's why i can't recommend them except for cameras with a very effective IR filter. i use B+W solid NDs for a reason. i tried most of the rest.

Herb...



May 22, 2008 at 10:26 AM
jbaduini
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p.1 #4 · p.1 #4 · Crummy ND filters seem to be a crummy IR filter...


I have experienced this issue too, using two HiTech 4-stop ND filters stacked with my 5D. It seems that Herb is right, these filters allow enough IR to pass that with the long exposures times we're trying to achieve, there is a much higher percentage of IR light reaching the sensor relative to the amount visible light.

One thing that comes to mind: I am frequently using the 17-40L with these filters, does anyone make an IR-cut gel type filter that could be put in the rear slot of this lens? Perhaps that would be a solution, as it seems nobody is making strong square ND filters except HiTech.



May 23, 2008 at 03:58 PM
bpark42
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p.1 #5 · p.1 #5 · Crummy ND filters seem to be a crummy IR filter...


This matches my experience. I recently bought (and used extensively) a few HiTech split grads, which worked great, but the HiTech solid ND 3 stop always added a reddish cast to the photos from my 40D (no examples on hand)

Never occurred to me that it might be IR....



Jun 09, 2008 at 04:02 PM





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