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Old 23-11-2007, 06:25 AM
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iceman (Mike)
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H-Alpha filter for an unmodded DSLR?

With the recent H-a narrowband images posted by Lee, and the O-III ones posted by Bill, and the ones that Scott has done in the past, got me thinking about narrowband imaging to help cutdown light pollution, reveal some fainter stuff, and be able to image while the moon is up.

Will a H-alpha filter work on my unmodded 350D? What will it reveal?
How much of the filtered light will be blocked by the IR filter in the camera?

Is it worth getting a h-alpha filter, or would a modded 350D be better? What would the difference be?

Could I make H-a/RGB images by using a H-a filter for some exposures and then RGB images without the filter, and use the H-a as the luminance?

How much are the H-a filters? Are they typical 2" filters? Would it just screw into the WO 0.8x reducer?

Thanks
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Old 23-11-2007, 10:04 AM
gbeal
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I'll get the ball rolling Mike.
I tried one a while back, on the 20D (un-modified as well). It worked OK, but it does soak up the light as you will find. Brighter Ha rich areas really stand out though, and it is a great distraction for when the moon is bright, or in the middle of town perhaps.
I also have an OIII and am looking to try that.
In my case the OIII is a 2" and fits on the front of the image train. I already had the 2" one as I used it for visual as well. I would imagine it would simply screw onto the front of the W/O reducer yes, that is if it has a 2" thread on the front.
Experimentation is the key, give it a go.
Gary
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Old 23-11-2007, 02:44 PM
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I had a Canon 30D and tried it with a 2" 7 nm Halpha filter both before and after the mod (clear internal filter).

The difference was that the mod increased the sensitivity by about 5 times at the Ha wavelength. I suppose what this really means is that with a modded camera with a Ha, you not only collect the same number of photons in a shorter time, but for the same number of photons, the amount of noise that you get is much less.

By the way, I wrote "I had" a modded 30D, as now someone else has it, along with some of my other camera gear, first aid kit and daughter's toys... (Strange combination of things to pinck, don't you think?)

The camera may turn up on eBay or at Cash Converters or in the Trading Post, but so far, I haven't seen it.... And probably whoever ended up with it is wondering why all the images, particularly on the full auto settings, have a rather strange pink tint.
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Old 26-11-2007, 10:58 AM
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Omaroo (Chris Malikoff)
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Excellent thread Mike. I have a 2" O-III filter which I'll give a go on the front of the T-adapter tube. A H-alpha would be interesting too. With my Tak Sky Patrol coming I'm very keen to set it up outside on my suburban back lawn and have the ability to ignore the moon and ambient light pollution.
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Old 26-11-2007, 11:48 AM
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iceman (Mike)
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yeh I'd love to try it. But by the sounds of it, a modified camera in combination with a h-a filter would give the best results.

But I'd really need to get a NEW modified 350D, as I still use my current one for non-astro purposes as well. No bduget for that in the near future.
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Old 26-11-2007, 02:47 PM
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Quote:
Originally Posted by iceman View Post
But I'd really need to get a NEW modified 350D, as I still use my current one for non-astro purposes as well. No bduget for that in the near future.
You can use a modded 350D (or whatever) for normal photography as well. What you need is a UV/IR blocking filter over the lens. Suitable filters are the B+W 486 or 489 (available from www.filtershop.com.au or do a websearch) or the CC1 or CC2 at www.maxmax.com or similar.

Another possibility is an under-the-lens filter such as the EOS Insert Filters from http://www.telescope-service.com/fil...OS_Klemmhalter However with this type of filter, you can only use EF 35mm lenses - not the EF-S lenses like the EF-S 17 - 85 mm.

With these filters, you then need to do a manual white-balance on the 'creative-modes' - the normal full auto modes on the Canon D's can't cope. You may also need to do a bit of fine tuning afterwards on the computer.

Have a look at http://www.iceinspace.com.au/forum/s...&highlight=486
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