Tips please

[Jemapela]

Hi all IR-lovers,

I hope I'm posting this correctly.

I did a IR test shoot with my Canon kit lens (yes I know it's said to be crap for IR). I tried different focal lengths at 1 aperture to see when the hot-spot starts to disappear. I hope this test can be useful to others, or can be verified with others who have used the kit lens.

All images were processed in the same way in Photoshop.









From the experienced and seasoned IR lovers, I hope you can answer a question.

On some old or better lenses, I noticed that the focusing scale has a distance index (red mark) for IR photography. If I'm correct, whatever you focus with normal photography has to be offset to the red mark when doing IR photography. If not, IR images are out-of-focus.

Problem is, when your lens doesn't have this red mark, how do you offset the focus?

[TrailsofLife]

Hi J,

Most of us here uses the auto-focus function on the camera, none have short focussed or out-of-focus image. So I presumed the filter in front of the lens, and focussing is thru-the-lens, the focussing distance is already corrected.

Lately, I even put the filter behind my camera's mirror(Yes, I'm crazy ), so that I can see thru the lens to compose my pix, the image still turns out to be pretty focus and sharp.

So my conclusion is digital IR shooting is different from film ones.

Did I answer your question? he he

[Jemapela]

Originally Posted by Max 2.8 Hi J, Most of us here uses the auto-focus function on the camera, none have short focussed or out-of-focus image. So I presumed the filter in front of the lens, and focussing is thru-the-lens, the focussing distance is already corrected. So my conclusion is digital IR shooting is different from film ones. Did I answer your question? he he

Since the R72 filter is so dark, I don't know what my camera might be focussing on. I don't even know if it can focus (although the AF confirmation beeps). Hence, I focus without the filter, then set in on MF, screw on the filter, then take the shot.

What you were saying is that you focus with the R72 on?

I believe that IR shooting with film or digital would be the same. The red mark on the lens barrel to offset focus is on some lenses. I believe it's got something to do with the IR wavelength and hence the offset is needed. On cheaper or consumer grade lenses, the red mark is absent (obviously if there is no distance scale at all).

I have red marks on my Canon 28-105 and 100-300. I can't remember if my 70-200 has them (because it's "sleeping" in S'pore and not with me.)

[PandaOng]

Hi, it seems to me from the focal length, that the longer focal length seems to enlarge the hotspot. as though you are actually zooming into the hotspot.

You were saying that you actually zoom till the hotspot disappear. but i still find hotspot on all the focal length.

Another test that you might be interested to do is to actually try on different aperture...i guess this could be done on a rather sunny day. guess it is winter down under

[TrailsofLife]

Originally Posted by Jemapela Since the R72 filter is so dark, I don't know what my camera might be focussing on. I don't even know if it can focus (although the AF confirmation beeps). Hence, I focus without the filter, then set in on MF, screw on the filter, then take the shot. What you were saying is that you focus with the R72 on? I believe that IR shooting with film or digital would be the same. The red mark on the lens barrel to offset focus is on some lenses. I believe it's got something to do with the IR wavelength and hence the offset is needed. On cheaper or consumer grade lenses, the red mark is absent (obviously if there is no distance scale at all). I have red marks on my Canon 28-105 and 100-300. I can't remember if my 70-200 has them (because it's "sleeping" in S'pore and not with me.)

Dun need to be so troublesome. When I use 300D, I just compose, make sure my focussing point is at my subject, put on the filter, press focus, shoot. So far, no problem.

None of my lens have distance mark, even if have, i never use them at all. So its ok to shoot without compensating.

[Jemapela]

Originally Posted by PandaOng Hi, it seems to me from the focal length, that the longer focal length seems to enlarge the hotspot. as though you are actually zooming into the hotspot. You were saying that you actually zoom till the hotspot disappear. but i still find hotspot on all the focal length. Another test that you might be interested to do is to actually try on different aperture...i guess this could be done on a rather sunny day. guess it is winter down under

Now that you mention it, I think you are correct to say that the hotspot seems to be enlarged. I couldn't quite figure out what happened to it but felt upset at the blurry center.

Yes, I tried different apertures but I read that smaller apertures make the hotspot more visible. The images are going to be posted soon.

Yep, there is not much sun here in Melbourne during winter.

[Jemapela]

Maybe, for the benefit of others who may want to learn or observe, here are 2 more images using the Canon EF-S kit lens at different apertures.

Generally, the smaller the aperture, the more obvious the hotspot becomes. (I tried f/6.7 but didn't see the need to show the image here, just f/5.6 and f/8 will do.)





I recently bought the Tamron 17-35mm f/2.8-4 IF LD ASPHERICAL to (sort of) replace the kit lens. However, because it has a 77mm filter diameter, I was unwilling to buy the R72 yet. (It would cost about A$200+.) I tried holding the 58mm R72 over the Tamron lens, saw that the FOV was completely covered by the R72 but my shots came out completely blue with a slight concentric pattern radiating from the center.

Any idea why?

[PandaOng]

that is most likely the light leak....

No, you dun have to invest in the fun 77mm filter....because of the crop factor in DSLR, you could just get a smaller ring size....I have previously used the 58mm + 77->58mm step-down ring....that could help you save a lot of money....

You could even use your existing filter...get a step-down ring adaptor.

[Jemapela]

Originally Posted by PandaOng that is most likely the light leak.... No, you dun have to invest in the fun 77mm filter....because of the crop factor in DSLR, you could just get a smaller ring size....I have previously used the 58mm + 77->58mm step-down ring....that could help you save a lot of money.... You could even use your existing filter...get a step-down ring adaptor.

I didn't think such a step-down ring would exist. I mean, it's a drastic step-down!

[PandaOng]

haha....you bet....i got mine...ask and you will get it....



http://cgi.ebay.com/STEP-DOWN-RING-7...QQcmdZViewItem

[OlivierC]

A red "R" (or a Red Mark) is used to indicate the infrared red focusing index.
I got this on allmost all my old lenses kits.

[KCLow]

Because I use a Minolta 7Hi (which is certainly not recommended for IR), I also get quite serious hotspots. Being stuck with built-in lens, I did some PP with 2 adjustment layers+masking and brightness controls to remove the hotspot, and the results were still quite OK.