What went wrong with this 20 minute X 10 subs H-alpha capture?

[vincentnm]

Hi All,

Captured this on 30th November, with a full moon around. With 20 minute X 10 subs (3 hours 20 minutes) of IC1805, I was expecting a decent result. But the signal to noise ratio is so poor. I am stumpted .

Compare, this with my bubble nebula capture, which is 10 minute X 39 subs (6+ hours).

Scope: C8 with Hyperstar3

Camera: SXVF M8C

Filter: Astronomik H alpha 12nm

Guiding: ST80 with DFK

Mount: EQ6 Pro

20 minutes X 10 subs

Calibrated and Stacked in DSS

Stretched and Sharpened in Photoshop CS3

Any ideas/theories what could have gone wrong?

Thanks,

Vincent.

IC1805:

Bubble:

[Merlin66]

Ouch!! After so much effort!!

I can only assume that the 20min subs with the 12nm filter still allowed some of the reflected sunlight ( ie moon light!!) to build up!!

[harry page]

Hi

I presume that you are using the colour camera with the filter ?

This will have a problem of being not very sensitive to Ha , have you done this before

Harry

[Whippy]

It could be the Moon. I tried imaging around the full moon with my Astronomik Ha filter when I first got it and got similar results so I don't tend to bother on those nights where the Moon is 75% illuminated or more.

Tony..

[Tim]

Assuming nothing physical, like a misted camera/objective, which is what first comes to mind, then I'd say you have just picked a dim area of the heart to image, The bubble by contrast is a much brighter emission in a darker surrounding. Possibly the moon has lit up some high cloud/mist and spoiled the contrast further?

How do the individual results look?

I think i'd go with misting on the objective as the cause, possible?

[vincentnm]

Thanks guys.

I've used the same OSC camera on other Ha targets, on moonless nights and they've come out well. No misting of the corrector plate.

I think it's most likely the moon then. 12nm bandwidth of the Ha filter would have allowed too much moonlight to come through in 20 minutes, more so because of f2 hyperstar imaging.

Thanks

Vincent.

[Aza]

I agree with TJ.

Check this thread of mine:

http://stargazerslounge.com/imaging-deep-sky/73250-heart-nebula-ha.html

I think the Bubble is as bright as the very brightest part of the Heart. So it is not fair to compare the two targets.

Same error I had

[GordonH]

Hi

I think the problem here is the camera, even with the hyperstar at what I presume is about f2, the M8C with its 3.15micron pixels is very insensitive, add into this the fact that it is OSC which is also less sensitive than monochrome you effectively have a very insensitive camera. I am using a H36 camera which has 7.5micron pixels and is monochrome and I am shooting 20 minute subframes with a f5 system. With the M8C pixels being much less than a quarter the size of the H36 pixels I would have to have an exposure in excess of 100 minutes or more (taking into account pixel size and OSC v's monochrome) if I wanted to get the same sort of S/N ratio with the M8C as the H36. With your current set up I would say it is because the exposures aren't long enough, they will need to be in excess of 20 minutes+ even with hyperstar

Best wishes

Gordon