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Some Red at last (the good kind)

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Started taking astro-photos again after a long hiatus. I now have two new toys in the box - a Canon 50mm F1.8 lens and the astronomik cls clip filter.

I had been wondering whether to brave removing the IR filter on my camera, but after this test shot I have decided it can wait.

Single 4 minute exposure at F3.2, ISO 800. I used a custom white balance, otherwise the sky is bright blue! Before I got the filter, the longest I could have gone is about 1.5min, with a completely saturated sky (East Kent area). Although I have picked up NGC 7000 before, it was always a pale and watery incarnation. This filter is pretty nifty!

One thing I noticed is some red fringing to the stars, which I never had before when I tested this lens. Could this be due to the filter interfering with the focus point of the lens maybe? I desaturated the stars in this one to make it less annoying.

Anyway, I hope someone finds this interesting/useful. ;)


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Update: I have found a work-around to the red fringing - if I focus slightly short of spot on, the fringes disappear. As I suspected, must be the extra layer of glass causing the different wavelengths to focus slightly differently. Testing on Arcturus (obviously very bright and plenty of red I couls actually see the red fringe in live view...

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Psychobilly: It's the CLS-CCD clip in, ie the one that includes an IR filter. I thought it was worth the extra £20 as I may mod the camera. I was going to do it myself, but now it doesn't seem too urgent, and I may wait until I can afford to get it done professionally.

Themos: It's money well spent!

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I have been looking at these myself. Could you do me a favour plesae, can you take two photos of the same thing, one with and one without the filter so I can see a side by side comparison?

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Will sort something out for you.

Trust me, there's no comparison. Without the filter an exposure half as long is almost white in the background from overexposure (your site may of course be better than mine). I can process most of it out, but it makes what's left look much more artificial and it removes the red I want to capture.

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Just to back up the point, and the review mentioned above, here are two images of (roughly) the same area of sky. They were taken on different nights about a week apart, but similar conditions. Both are at F3.2 and ISO800, same camera and lens.

The first is 112 seconds without the cls, the other is 240 seconds with it. The only other difference is the white balance used, daylight for first, custom for second. No processing of either except converting to jpg.



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