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.
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.
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:
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...
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.
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.
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)
