Infrared photography Question

[Ebag17]

I got my IR filter and took a few shots in my backyard. I'm trying to figure out what all these spots are. Are they hot spots? They were taken with a Canon 40D and Sigma 10-20mm

Here are the photos...

Flickr: Ebag17's Photostream

Thanks for your time and help.

-G

 

[Josh66]

That's not hot spots. A hot spot will be a large spot in the center of the frame, the more you stop down the bigger it will get. Not all lenses will produce them.

Were you shooting into the sun? Looks like lens flare, or maybe water droplets on your lens...?

 

[Ebag17]

Hmmmm. Thats what i thought at first. In those photos the sun was behind me and a lens hood. I made sure the filter and lens was clean. I went to a camera shop and they did'nt really have an explanation either, except that light could be gettng in between the filter and lens?

 

[Josh66]

except that light could be gettng in between the filter and lens?

Not really sure how that could happen, and if it did - it wouldn't be red (since it would be unfiltered).

I really have no clue what that is... I've never seen it in any of my IR pictures, and it's definitely not a hot spot.

I would bet that it's some kind of flare though.

Just had an idea-

Did you cover the viewfinder?

Since this was likely a long exposure (5-10 sec?), I assume that you didn't have your eye to the viewfinder the whole time. If left uncovered (your camera probably came with a cover for it), light could enter through the viewfinder. Maybe that's what's causing this?

edit
But that light would be unfiltered too, so it still shouldn't be red...

 

[Dwig]

...
Since this was likely a long exposure (5-10 sec?), I assume that you didn't have your eye to the viewfinder the whole time. If left uncovered (your camera probably came with a cover for it), light could enter through the viewfinder. Maybe that's what's causing this?

edit
But that light would be unfiltered too, so it still shouldn't be red...

Not light through the VF because during the exposure the mirror is up sealing the mirror box. Light entering through the eyepiece can't get to the sensor during the exposure. Eyepiece covers and blinds are to prevent light getting into the VF through the eyepiece and influencing the meter prior to exposure.

The spots are obiously bright, very out of focus, and in front of the IR filter as evidenced by their having a noticable hexagonal shape and the same color as the rest of the image. Given that no bright light sources are in the primary distant portion of the image they are most likely something very near the lens that is either emitting or reflecting substantial amounts of light (more than the rest of the scene). These could be water droplets or dust near the lens lit by some source (flash??) or possibly smoke particles (was the photographer smoking at the time??).

 

[Josh66]

Eyepiece covers and blinds are to prevent light getting into the VF through the eyepiece and influencing the meter prior to exposure.

Ah- Gotcha.

 

[Ebag17]

Nope. Don't smoke. Neither was there a flash. I have a UV filter between the lens and IR filter? I don't know if that could have any effect. Playing around with the white balance seems to help a little but, there's still obvious spots everywhere.

Also when you said exposure time of 5-10 sec is that how long IR is suppost to be? those images where taken for 60sec?

As pertaining to it being dust. The spots seem to be random. Would there not be a somewhat pattern to them if they where fixed spots of dust on the lens.

The filter I'm using is a 77mm Tiffen 87 filter. Have you ever heard of any problems with these filters?

 

[Josh66]

I have a UV filter between the lens and IR filter

That could be the problem. If not, it sure isn't helping.

I would remove it when you have the IR filter on.

If you're using it to block UV light, the IR filter is doing that.
If you're using it for protection, the (much more expensive) IR filter is doing that now too since it's on top.

I wouldn't move it to the top of the IR filter either. Just remove it, then put it back on when you're done if you like using it.

 

[Garbz]

What IR filter is it? Is it a screw on filter or a plate type sitting in a Cokin holder.

I say this because it looks like there may be light leeking into the side of the filter lighting up the dust specs on the lens. Now due to the long exposures these dust spots suddenly really matter.

Remove the UV filter, Place the IR filter flush against the lens and maybe surround it in electrical tape. See if it still happens. If not maybe there's some problem in the filter.

 

[Josh66]

Also when you said exposure time of 5-10 sec is that how long IR is suppost to be? those images where taken for 60sec?

That's how long my exposures typically are, but that doesn't necessarily mean your's will be the same. There are too many variables for your settings and mine to match up.

 

[benhasajeep]

I think your getting reflection between your filters. The spots have moved and are a different size when you went from one scene to another. The light is bouncing around and creating the spots, they are octagnal shapes becasue of your aperture blades (reflections).

I would take off the UV and use just the IR filter.

 

[Ebag17]

Alright I think I've got it figured out! Thanks all for your help

-G

 

[Garbz]

Care to share so we all know what the problem was?

 

[Ebag17]

I think it had to do with using the UV filter. It helped a lot after it was removed.

Could using a really low aperture cause lens flare in IR photos? I read this in an article I found.

-G

 

[Garbz]

Low as in large aperture? Yes. The the wider area of the glass used means that any problems that are located towards the outside of the lens elements would becomes more apparent. This is also why CA is more of a problem at large apertures since there's more deformity on the edges of each element.

If whatever was wrong with the IR filter was away from the centre of the filter a smaller aperture may have fixed the problem.