G3 and Red filter experiment

[ryuwulf]

Hello,

I had recently taken some pictures using a red filter. For those who dont already know what a red filter does, it helps to increase contrast in B&W film. It also will darken blue skies and lighten red objects.


I noticed that all of my pics were a little out of focus with the red filter on. On my manual SLR(AE-1) i dont have this problem

Here are my results. By the way the bucket is red. Notice how light the bucket gets with the filter on.
ISO 50 Av 1/400 F8
http://www.ryuwulf.net/pics/test/without.jpg
ISO 50 Av 1/100 F8 with red filter
http://www.ryuwulf.net/pics/test/with.jpg
this is the original without the filter and it looks crisp
http://www.ryuwulf.net/pics/test/normal.jpg
this has the red filter and it is not entirely crisp
http://www.ryuwulf.net/pics/test/red.jpg

[hypokondriak]

Interesting... I'm guessing the red filter is throwing the CCD off (which would explain why the SLR is ok).

It would be interesting to see if these results were similar across all non-SLR lines, just Canon, or even G3 specific...

*edit: Did you use autofocus or manual? If autofocus, can you try some manual shots?

[Andy_T]

I remember reading on the forum that the Canon cameras use horizontal lines in the GREEN CCD pixels for focusing.

Naturally, that should not work too well with a red filter...

Regards,
Andy

[gandini]

Interesting! Since the red filter lies in the visible range just short of the InfraRed range the "softening" of the image (I prefer to think of the image as soft, without reference to whether it is focussed, or not) appears as a common factor. My IR images appear quite soft, but respond quite well to sharpening, although not as well as regular full range images. Other posters have talked about the soft focus of the G3 with IR filters as if the camera does not actually focuss correctly (for example, it focusses at 30m rather than infinity for a landscape.)
I would guess that the built-in IR filter (so-called hot mirror) in the G3 has quite a slow "roll-off" and affects the visible red spectrum to some degree. And you see the results in your examples, confirming that anyone wanting a strong IR performing camera should not choose the G3!

cheers,

[ryuwulf]

Thanks for the responses!!!!
I will actually do more tests this coming week, with a deep yellow filter. i did two test runs one with auto focus and the other with manual. The both still looked the same, but i just posted the autofocus pics.


gandini : i pretty decent with IR photography, but only with my trusty AE-1. A red filter with a polarizer does wonders, and portraits looks really eerrie. This whole digital photography has me rethinking my shots and trying to re-experiment with filters.With my SLR i can just shoot away and know my shots will come out decent with a filter.

oh well, live and learn for me :)

thanks for the info

[gandini]

Actually, I now remember another post (perhaps on dpreview) that showed some interesting images made with the G3 just after its release. These photos showed a full spectrum of colors and I remember the center of attention was the soft focus on the red lettering. This now makes more sense, and fits in with my IR, red-filter story. Of course, I might just be imagining all of this, and creating a wonderful world of internal consistencies...

[stopbath]

What brand of filter were you using in your red filter shots?

Was it made of optical glass (B and W, Nikon,...) or regular glass (cheaper glass filters), plastic, or gel?

With anything but optical glass filters I would expect some light dispersion. More with some than others, so even a cheapo may perform well. But hands down your best performance would be with optical glass.

Also, I notice your red filter shot is 1/100 second, while your non-filter shot is 1/400 second. Camera shake could be the trouble here.

B&W is great fun.

[ryuwulf]

I used a tiffen 58mm red filter.

Anything over 1/60 shouldnt produce a shake effect. Ive been taking quite a bit of pics, so i know how to stable myself. I also noticed it was 1/100 but the camera was compensating(roughly) for the 3 stop difference with the filter on.

1/125 is deal to prevent shake, but i see your point. iam going to reconfirm all this but with a tripod to eliminate some doubts and try using the manual focus.

Iam in the works of composing a filter faq for the g3, ill be using focusing on the red 25, yellow 15 , and polarizer. The polarizer will be a Sunpak, while the other 2 are tiffen.

Thanks, for the input :)

[hypokondriak]

Camera shake shouldn't be a problem, but if you redo can you try with a tripod just to eliminate any variables?

Can anyone confirm or deny that the G3 uses the green ccd pixels for autofocus?

[ryuwulf]

hypokondriak wrote:


Can anyone confirm or deny that the G3 uses the green ccd pixels for autofocus?

Now thats a good question :)

ill post my beginner/newbie silencer faq for filters soon.

[kb244]

Hrm speaking of red filters. I shot a couple filter tests ( Red, 80B and diffuser ) on my G3 shown here.

http://www.kb244.com/images/filters/

I'm hoping to add R72 ( infrared ) , soon as I can get a NIR light source, and a couple other filters.

[ryuwulf]

Hello,

Good job in showing some examples of filters. Your focusing seems a bit off. Did you use manual or autofocus. Practice makes perfect. Thanks for contributing! :)


cheers

[kb244]

ryuwulf wrote:
Hello,

Good job in showing some examples of filters. Your focusing seems a bit off. Did you use manual or autofocus. Practice makes perfect. Thanks for contributing! :)


cheers

It was auto-focused, I assume the filters may have contributed some to the throwing off of the focusing. Possible. Speaking of the R72 filter I mentioned, I got it this morning.

Some shots here

http://www.kb244.com/gallery/?gallery=ir

Today was pretty crappy conditions for IR but I managed.

[gandini]

Karl: Your IR improves daily! Can you tell me what process steps you used to turn the "houses on the other side of the duck pond" image into color with the strong blue sky? Much appreciated.

thanks

[kb244]

Basically I opened it up in Photoshop, kept the image in it's original color cast captured by the camera (Magenta).

Took the magic wand ( kind of hard to do, so I figured out the polygon cut tool instead and practiced on other pictures ) , and just went around , first I captured parts of the water, holding shift to add on selections, unless it pretty much covered the portion of the water not reflected. Then went into changing levels just for that selection til I Got the desired color, did the same with the trees, only instead I desaturated the trees to some extent while leaving a little bit of a copper color tone to them. Then on the sky I did the same thing, but changing the levels more intensly.

The houses and the lake bed, and gard rails, etc I left alone.

Oh almost forgot to mention, after using wand on alot of portions, I right click the image, choose feather, and put in anywhere from 8 to 16 pixels, to smooth the edges of the selection which causes fades outside of the selectoin, before I changed any levels, otherwise its way too sharp.