M44 - 19th Jan

[jgs001]

I had to go to a meeting early on, but the sky was still clear when I got back. I got out and setup. Went for M44 tonight, as M35 was too high. Anyway, got some more data tonight, although I think I've badly framed it, it's much better than my first attempt at this last year with the Z2.

Still some tracking errors, but dramatically improved. They look mainly like trailing rather than drive train errors. Nought I can do about that in Alt Az, and I think the 600mm instead of 400mm is showing it a little more.

[661-pete]

Well you've got a nice lot of stars there, your focus is spot-on and I don't see much if any of a trailing problem. As for the framing - well you could crop the image to portrait-style to deal with that - since the Beehive is an 'upright'-aligned cluster it would look well I think. Many's the time I haven't centred something properly (usually due to my impatience) and cropped to conceal the fact...

It would be nice to see if you can get longer subs, with your setup (given a reasonably clear night... ). Say 1 or even 2 minutes, if your alt-az will allow that?

[jgs001]

Thanks Pete. I threw the trailed subs in the bin they didn't end up in the stack. I threw away about half my total subs. M44 was too high by the time I started to get up to 2 minutes. 2 minutes has been possible with the ST80 clone, I'm still working out the niggles with the C80ED and I suspect that the longer FL is highlighting trailing a little more. I plan, if the weather allows, going back to have another go at M44 (if it doesn't get to high or far south in the meantime) and having another go. I'll go portrait for that. I'd been attempting to get M67 as well, but the clouds put paid to that.

[Psychobilly]

Just a thought... seeing as we resize the imgaes for web use anyway .. you can shoot at a shorter focal length and crop instead in which case the trailing will be less evident...

Billy...

[jgs001]

So use a focal reducer (which I don't have) ? or use the Vista ? doesn't that defeat the point of the decent lens cell though ?

[661-pete]

Just a thought... seeing as we resize the imgaes for web use anyway .. you can shoot at a shorter focal length and crop instead in which case the trailing will be less evident...

Billy...

Sorry, I don't quite follow that, Billy .... trailing is a function of mount errors (usually) which are expressed in angles, and as such will extend for a specific number of arc-seconds. It won't make any difference at what magnification you capture the image and how much you re-size it afterwards ... with the same mount performance the trails will still be the same length in arcseconds on the final image... so if the final image scale is the same in pixels per arcsecond, the trail lengths will still be the same number of pixels...

If the trailing were due to optical effects in the OTA (e.g. coma) it would be a different story of course.

John, it would be great if you did get in a shot of M67 for comparison. It's quite a nice little cluster, fairly similar to M44 but fainter. I had a go about 2 years ago... I'm sure you can improve on mine!

[Psychobilly]

Pete I'm having one of those days....

SO much so that I am tempted to say.... :withstupid: :withstupid: :withstupid: :withstupid: :withstupid:

Time for a Holiday.... :)

[jgs001]

Pete, I was using a 400mm ST80 and suffering from noticeable star trailing on 50% of frames after 2 minutes. So hitting 60 seconds was easy. However, with the C80ED which is 600mm, I'm getting trailing happening earlier. I'm thinking this is down to the longer focal length of the scope. This isn't PEC errors in the drive train (seagulls), I've had plenty of them over the last couple of sessions, changing attachments and fittings messed up the balance *sigh*... I was able to get a couple of framing shots of M67 before the clouds moved in, and it looked quite small but defo there (30s @ISo1600). I think I'm gonna have to push the ISO up to 1600 again...

[thing]

Looks fine to me, I don't see any trailing in it. Mind you, I'm blind as a bat.

[jgs001]

thanks Dave. I threw the trailed ones away. Only the good subs went into it.

[661-pete]

Pete, I was using a 400mm ST80 and suffering from noticeable star trailing on 50% of frames after 2 minutes. So hitting 60 seconds was easy. However, with the C80ED which is 600mm, I'm getting trailing happening earlier. I'm thinking this is down to the longer focal length of the scope.

Ah: maybe if the C80 is a longer OTA and heavier than the ST80 (is it?), it's possibly putting more strain on the mount and hence more PE. But if it's just that you're noticing the trailing earlier, bear in mind that your images - and the trails - are now magnified 50% more. Apologies if this is stating the obvious... :oops:

[jgs001]

I think I've pretty much eliminated the PE, getting the balance right has helped. The OTS is about 0.5Kg heavier than the ST80 clone. I think it's just I'm noticing the trailing earlier. I'm going to review the alignment process as I think getting this as accurate as possible will help.