EOS 400D and InfraRed Application

tsc_tempest · July 29, 2008

Hi, I've been reading through various threads on IR and the EOS 400D, and it seems not encouraging. Be that as it

may, I'm a stubborn cuss and am trying to see what I can do with what I've got.

What I have is and EOS 400D camera; Canon 18-55mm f/3.5-5.6 IS Zoom [w/o hotspot]; Canon 55-250 f/4-5.6 Zoom;

and, an unbranded, black glass, IR filter.

What follows are some images I've captured with the above setup, ISO 1600, and long exposure noise reduction set

to Auto:

1: http://www.photo.net/photo/7616993

2: http://www.photo.net/photo/7616927

3: http://www.photo.net/photo/7616996

4: http://www.photo.net/photo/7616995

5: http://www.photo.net/photo/7616994

Now, they're not fantastic, and given the time of day, [which is almost night time] well... anyway my questions.

a) This filter is almost black, and creates pics with a dark, magenta cast. Any idea what type of filter it might be?

b) Does anyone know what exposure correction, and focus factor I need to apply for either/both of these lenses to

better predict exposure and correct image sharpness? (tabulated data would be great!)

c) If you don't have answers for the above, would you know what have to do in order to determine these for the

lenses and camera that I have?

With all sincerity, thanks to all of you who have posted various bits of info on this before. Please indulge me, I haven't

been able to find the answers to these questions in my trundling through the web. Perhaps, you are able to supply

the information I need to resolve this small dilemma.

regards,

Tsc

cabbiinc · July 30, 2008

What your running into is that there is a IR filter (to block IR) in front of the sensor on your camera. Since the filter that you have put on the end of the lens only lets IR light through and the IR cutoff filter on the camera doesnt let much IR light through your left with not a whole lot of light getting through. Thats why you have the long exposures. There is a company that will remove the IR cutoff filter, but then you'd get IR pics all the time wether you wanted them or not.

In regards to the focus factor, each make of lens is different (I beleive). The 18-55 doesnt have the IR marks to readjust focus, but you could just stop down a ways and still have an in focus picture with the added DOF.

Trial and error will probably be what you have to do to figure it all out. If you can get a lens with the IR focus adjustment setting you could open that aperture up a bit. I have a 28-135 IS that has it. And the IR adjustment at 135mm is just a tad backed up, where as the 28mm IR adjustment is pretty far backed up. My Sigma 24-70 f/2.8 has just one IR adjustment for the whole range, just a tad backed up (focus closer).

Dan

Jeff Lear · July 30, 2008

I use a 40D (not the 400D) with a Hoya R72 IR filter. The problem is that most kit lenses (you know, the ones that take a 58mm threaded filter) don't have a distance scale and thus no infrared index. In addition, IR filters appear to be priced exponentially based on their size. I paid $50 for the 58mm and the 77mm is $320.

A couple of tips that I've found to be helpful. First, shoot in black and white. Shooting in color with an IR filter creates a funky image. Second, I enable the red filter through camera software, it gives even more contrast in the IR image. And finally, without an IR index or a distance scale, you'll have to search for the optimal focus. In general, it's best to focus on infinity and then back off a tiny bit, from there it's small moves and many exposures to get it just right, or at least close.

The fact that we're shooting with different bodies is of little significance, they're both crop digitals. Most of the IR shots I have were taken using the 18-55 kit lens that came with my 20D although I've taken a few with the 50 1.4 because it doesn't hotspot as bad if you cover the viewfinder.

tsc_tempest · July 30, 2008

Hi Dan, Jeff,

thanks for your replies. I am well read on the DSLR-IR Cut Filter issue, hence I'm not into IR as a serious quest.

What does get me intimately interested in this is the fact that I do have an IR filter and a camera that has 'some'

sensitivity - what else can one do? It's there, I've just gotta play with it, it's an inner child thing. :-D

Regarding Focus Correction: you are both probably right, I may just have to resort to T&E. I was hoping that

someone might have had a table somewhere with Wavelength, Focal Length, and Focus Correction.

Regarding Filter Factor: This is a really dark filter with a magenta reflection. If you look carefully at the first image

(above) you can just make out the labeling on the 60W bulb, The filter was less than 3" from the bulb. It's unbranded,

and short of taking to some physics lab at some university and getting it tested, I've no other way of determining

what wave lengths it's likely to pass and what filter factor to use for determining a satisfactory exposure time.

As for hotspots, I seem to be lucky with these two lenses in-so-far-as there doesn't seem to be any flaring - cross

fingers. Perhaps this might become more apparent with a 'less dense' filter, I just don't know.

Thanks for the tip about covering the viewfinder, I keep forgetting little things like that. :-)

Jeff Lear · July 30, 2008

Tempest wrote: "what else can one do? It's there, I've just gotta play with it, it's an inner child thing. :-D"

Hey, I can relate to that.

Short of a lab, I don't know of any way of determining the wavelength of a given filter other than to look for any identifying marks on the filter and research it by manufacturer.

Here is a shot of a 60W bulb through my filter. I wasn't really able to read the stamp on top but I could see the filament, which was a deep magenta. Hoya filters are notorious for losing the screen printed information around the filter ring. Sorry I don't have any focus tables for you, obviously they would be different for each lens. Once you determine your filter type, I would suggest an email to Canon. I'm going to try it for my R72 IR filter and see what they have to say.<div></div>