"Messier 83 (also known as the Southern Pinwheel Galaxy, M83 or NGC 5236) is a barred spiral galaxy approximately 15 million light-years away in the constellation Hydra. It is one of the closest and brightest barred spiral galaxies in the sky,"
I was pleasantly surprised how well the Ha regions came out with the modified Canon 1100D. This is a big improvement over my previous unmodified camera.
Captured over 4 nights for a total of 5.8 hours ( I was hoping for double figures but clouds had other ideas) - 696 x 30 second subs unguided on a HEQ5 Pro, GSO 10" F4 Newtonian, full spectrum modified Canon 1100D, Baader MPCC MKIII. Filters used were a baader Semi-Apo filter for some subs (gives Ha a kick) and Baader UV / IR cut filter for other subs. Stacked in DSS in 4 groups, processed in Photoshop. Taken from the backyard observatory.
That's a very nice looking M83 Kevin and quite deep, if you could just fix those pesky stars it would be a bluudy cracker What is causing this issue you get with your stars anyway? Do you know?
Mike, is it the star elongation that you are referring to??
Cheers,
Tim
Yeah they are elongated/skewed across the frame and I think Kev has been having this as an going issues (collimation?). Perhaps he might just have to live with'em and they aren't that bad really. He just takes such great shots with his modest gear it would be icing on the cake if the wonky stars could be remedied
That's a very nice looking M83 Kevin and quite deep, if you could just fix those pesky stars it would be a bluudy cracker What is causing this issue you get with your stars anyway? Do you know?
Mike
Quote:
Originally Posted by topheart
Nice one Kevin....good signal there!
well done.
Cheers,
Tim
Thanks Tim.
Quote:
Originally Posted by strongmanmike
Yeah they are elongated/skewed across the frame and I think Kev has been having this as an going issues (collimation?). Perhaps he might just have to live with'em and they aren't that bad really. He just takes such great shots with his modest gear it would be icing on the cake if the wonky stars could be remedied
Mike
Thanks Mike. RE the stars. Yes they are a nuisance. At this stage I can't find the cause. I've recollimated several times, adjusted the spider, I just can't find it. It possibly could still be a collimation issue. I find the f4 scopes are fiddly to get perfect. I wish I got the F5 version now. And my collimation tools are a bit primitive. But it only seems to be the brighter stars. Perhaps it is vibration from mirror slap? The 1100D has no mirror lock up feature. Until I find it, it's eggs for tea every night. Just don't look as close.
Wow Kevin, that's really nice. Now I know what the M83 I'm working on 'should look like'.
You say you use a UV/IR filter. Should I be using that for galaxies with a reflector and DSLR (or other OSC) ? Is it to tighten up stars ? I hadn't used one as I thought galaxies emitted into deep red/IR ??
And could someone explain what's wrong with the stars.
Wow Kevin, that's really nice. Now I know what the M83 I'm working on 'should look like'.
You say you use a UV/IR filter. Should I be using that for galaxies with a reflector and DSLR (or other OSC) ? Is it to tighten up stars ? I hadn't used one as I thought galaxies emitted into deep red/IR ??
And could someone explain what's wrong with the stars.
Thanks Chris. An unmodified DSLR doesn't really need a UV/IR blocker, but a modified one may benefit. Though the benefits are mostly with refractors I think. I did take some frames with an IR >650nm filter, but were quite noisy so didn't use them.
The bright stars are a little bit egg shaped. It's curious that the dimmer ones are not, which is puzzling. Possible culprits are collimation, mirror slap, pinched mirror or star drift as the mount is unguided. I'll tackle them one by one and hope to get to the bottom of it eventually.
Did you notice that the elongation is in the RA axis direction?
I have a persistent problem with my HEQ5 RA that I can only resolve with careful balance and polar alignment - the result is eggy stars with subs over 5 minutes. It shows up in PHD2 as a 20 to 30 % higher RMS deviation in the RA axis tracking. I tried belt modding and rebuilding/tuning the RA axis to very little improvement. The only thing I can think of to try, short of upgrading the mount to an NEQ6 or similar is to rebuild the RA axis again with a lighter weight grease to try and remove all resistance.
Then again, I do have 11kg on the mount and that is pushing the weight limit. What weight do you have on the HEQ5 if I might ask?
Could be Tim. At high power viewing planets I can see the mount visibly drifting back and forward constantly. The mount has been adjusted and greased with new grease. Mount weight and camera come to 15kg, right on the quoted max.
I don't have the $ for a heavier duty mount yet. Not for quite a while. But I'll give guiding a go soon with a finder / guider and see if that helps. My present 68mm guidescope is too heavy.
Very good result at 15kg! I'm in the same boat - saving up for a bigger mount. At 15kg of weight you have to be just off balance east/west of RA to get the gears to mesh properly, at least I've found this at ~10kg. It's very hard to do on this mount as the RA axis can be quite stiff and is difficult to judge balance.
Just did a star test (don't know why I didn't before) and it appears the elongated stars are from collimation error. The flat mirror is not under the focuser properly. I thunk.
Kevin, I have to say this issue with star elongation is inherent with the long focal length Newts, I have the same probs with mine. I guess it's the compromise for the large light gathering capability against stars at or near the edge looking the way they do.
Correcting for collimation is the thorn in the side for each imaging session I set out for. It's never perfect but hey it's how these Newtonians behave.
Awesome M83 though, short subs x heaps of them gives us all hope.
Well done.
Thanks Anthony. Yeah I definitely miss the perfect stars of my refractor. I don't miss the lack of speed though. F4 of the reflector makes things possible that were not possible before.
What is causing this issue you get with your stars anyway? Do you know?
