First light through a new GSO 8" f/5 reflector. Not overly impressed.
Think the Helix is the toughest target I've yet attempted. Took me 10 mins just to find the rotten thing, didn't realise it's so dim!
GSO 8" f/5 Newt
NEQ6 unguided
Nikon D3300 45-second subs @ ISO 3200
Best 70% of 45 subs stacked & edited in DSS (no darks, flats or bias)
Further editing in Lightroom
The poor little Nikon 3300 struggles at ISO 3200; I think 1600 is its ideal upper limit, with best results at 800. The seeing didn't seem great tonight either. No clouds but the stars weren't as crisp as they often are. Will have to revisit this one when I finally get guiding hooked up in a few weeks. I'll also apply darks & flats next time.
Mate, those stars are pretty darn tight! but guiding will definitely help. this is one of those targets that really needs some deeper images. a couple of mins would really help make it pop. a really good start though.
Hi Chris, I don't understand why you struggled to get much detail or colour.
I have attached one of my early efforts produced with the SW 8"Newt that
you now have. Also no darks, flats, etc, and 50 x 30 sec subs @ISO 1600 with my Canon 1100D, stacked and processed in DSS, and sharpened and downsized in PS. Maybe the answer lies in the processing rather than the acquisition.
raymo
Yeah see that's the sort of result I was expecting!! And those are the camera settings I expected to use too. Hmmmmm.
Dunno why it came out so dim. Maybe the CC or secondary got fogged over...? I noticed even when drift aligning that everything seemed very dark, even darker than my ED80. Tried a full frame DSLR and got the same result, so just plugged on so I could have a result of some kind.
But yeah there was definitely something odd going on during acquisition. I'll investigate tonight, will maybe put the old Skywatcher back together for some A/B comparison (I've taken it apart for painting).
You could very well be right about the fogging up. The pic I attached
somehow got ruined in the downsizing last night. Here is another, albeit
very small [73kb] copy showing what you should expect.
raymo
Yeah, that's in line with other planetaries I've images in the past few months. There's something odd going on.
I've compared it to my ED80 with flattener and taken note of the shutter speeds required for correct exposure for both scopes. With identical settings, the same target is slightly BRIGHTER through the ED80. Focal ratios for both, allowing for CC and flattener, should be f/6.375 for the ED80 and f/5.5 for the Newt. I'm missing about half a stop.
How should the two compare in the real world? Can the light blocked by the secondary take as much as half a stop?
GSO talk about mirror reflectivity of 93% on their site. That means you're losing 13.5% of the light before it gets to the coma corrector on top of the few percent lost to the secondary shadow.
It,s impossible for an image taken through an ED80 at f/6.375 using the same camera settings to be brighter than an image taken through a 200mm f/5.5
Newt. The Newt has 6.25 x the light gathering power of the ED80, and is
also somewhat faster. I suspect that fogging is probably on the mark.
raymo
I tried removing it and there's about a quarter of a stop difference.
So combining the light blocked by the secondary, the vignetting and the 30mm spacer, I can see how that would all add up to about a half a stop.
Conclusion:
I should've spent the extra for the Baader MPCC, which doesn't require as much spacing (and would have saved a lot of effort getting the damn thing into the Skywatcher's focuser), instead of going with the cheaper GSO. Sigh. Lesson learned.
I tried removing it and there's about a quarter of a stop difference.
So combining the light blocked by the secondary, the vignetting and the 30mm spacer, I can see how that would all add up to about a half a stop.
Conclusion:
I should've spent the extra for the Baader MPCC, which doesn't require as much spacing (and would have saved a lot of effort getting the damn thing into the Skywatcher's focuser), instead of going with the cheaper GSO. Sigh. Lesson learned.
Thanks mate - I think just getting guiding happening will solve most problems, but would be interested to compare the Baader to the GSO.
Tried Helix again tonight and couldn't even find the wretched thing! Its magnitude is 7.6 and it was simply invisible with any eyepiece, whereas the mildly brighter Omega Nebula (mag 6) was easily visible even through the camera viewfinder. Dunno what it is about the Helix, but it simply doesn't want me to see it...!!
I'll come back to it in a month or so. I ain't giving up.
The difference between mag 6 and 7.6 is actually huge Chris. If two nebulae
are of very similar apparent size the mag 6 will be 3.5 to 4 times as bright
as the 7.6.
raymo
Lol I had the same problem with my first go at the Helix last year (this year I'll have another go) A 30 sec sub at iso 3200 and I could only just see it against the background. This nebula is large but has a low overall surface brightness, any sky glow makes it near impossible to see.
