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Old 14-07-2016, 12:23 AM
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luka
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M8 Lagoon nebula in Ha (on the cheap with DSLR)

Finally a clear night for the first test of my IR modded, cold-finger cooled 450D. It was not really a cooling test as as the ambient temperature dropped down to 1C and the cooler hardly did anything.

The moon was high in the sky so I decided to try out my H alpha filter for the first time. This filter is not an astronomical filter. I am guessing that the transmission is about 50% and the bandwidth may be as narrow as 1nm FWHM. Not sure. The focusing was a real pain as live view was not registering anything. I had to take 30s exposures of a bright star and look for change in star size while adjusting the focus.

The filter was held by sticky tape on the top of my field flattener

DSLR was not debayered and only every 4th pixel on the sensor was used. I used dcraw to convert the RAW files to TIF and then octave to extract the red channel only.

- 29 x 3min lights (1h 27min total)
- bias used instead of darks
- no flats (got too excited and forgot to do them)
- Stacked with DSS, processed with StarTools
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Old 14-07-2016, 02:58 AM
glend (Glen)
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Luka, not too bad for a OSC camera, but it is a lot of work as you state. A longer sub length would help, at least 300". Even sensitive mono cameras like the ASI1600 need 300" subs in narrowband. Keep at it.
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Old 14-07-2016, 08:50 AM
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Atmos (Colin)
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It has turned out quite well, especially with all that work that went into it
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Old 14-07-2016, 10:17 AM
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ZeroID (Brent)
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Agreed, not bad at all. Well done.

I know you said that the cooler did not do much work at all but if it hadn't been operating the sensor temp would have crept up during the exposures. Probably not make much difference down at that level but maintaining a set temp at the sensor the objective to get best results.

Good to see results from all the work eh ?
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Old 14-07-2016, 10:43 AM
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Thanks for your replies.

I will try longer exposure times. 3min is my usual exposure time, limited by the light pollution here. But Ha is a different game of course. May have to fix the DEC backlash before trying longer exposures.

It was my first attempt with the Ha filter. I had it for a while but could not find a way to mount it until the brilliant moment to just sticky tape it

Nothing is perfect about the setup, 1/4 efficiency of the DSLR and <1/2 efficiency of the filter. However, it is a cheap starting point and the best thing is that the moon is not the limitation any more. Now if only clouds would go away...
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