Couple of shots from Monday night (M13 & M31)

Finally got a long enough clear sky to mess about with the GPUSB and autoguiding. It worked quite well this time (Thanks again to the Dave's for their advice). Had to turn the Anti-backlash settings to 10 for all four to stop the mount jumping all over the place. Once that was done everything fell into place.

The full moon was up so I tried M13 again so I could compare to the previous attempts.



10x90 seconds

I then tried my old favourite of M81 & M82 to see how a galaxy would turn out under the moonlight (to test the SAC10), but I could barely see them this night so I turned my attention to M31. Didn't notice I had framed it incorrectly until I stacked some frames but here it is anyway.




7 frames. 5 @ 2.5 minutes and 2 @ 3.5 minutes.

Both images taken with
object with the full moon up. Nearest visible naked eye star was Mirach!

Anyway it was a test of the Sac10 and the autoguiding and it turned out better than expected. Pity I didn't notice that the Galaxy was oriented the wrong way in the view to capture it in entirety until I started processing.

Sac10 on Televue Refractor @ 480mm
Guided with Neximage and PHD Guiding on 8" SCT @ 1360mm.
IR Cutoff Filter

All my doubts about ordering this camera are now gone.
Next step is to devise some kind of cannon to get that moon out of the way :lol:

Trev

Very good Trevor.

M81/82 shows some nice dust lane detail there. Shame about the framing but its a minor error that I'm sure you'll learn from.

M13 is good too - the bright star at the bottom of the images shows processing artifacts but my guess is you had to do that to bring out M13. Again, framing could be better (how's your GOTO?) but these really are minor comments.

The imager seems to be doing a great job for you. Keep it up and keeping heading up that learning curve

Cheers

Dave

Hi Dave,

Thanks for the comments. Still in the learning phase here. I meant to fix that star manually after doing the DDP :oops:

Gotos are terrible on this mount. No matter how accurately polar aligned the mount is it will always point 6 degrees away from the target, i.e. even if the two first stars are bang on, the third, which should be the most accurate is out by 6 degrees. I guess that's why I only get about 20 seconds without guiding even at 480mm & that's after an accurate polar align. The interesting thing is that it is consistantly out by the same amount each night.

The added bonus though is that I get to learn star hopping instead of relying on the gotos :lol:

Main reason I had the framing out was that I was trying to find a suitable guidestar. The NexImage only goes to 1/5 of a second. But at least it taught me something (just realign the rail that the Ranger is on - D'oh, I'll have to remember to do that the next time). Framing was actually a bit worse because both of these images were heavily cropped.

Just got Michael Covington's book "New CCD Astronomy" and there's a wealth of helpful information in there so hopefully this will help.

Trev

Trevor - that 6 degree difference is worrying. I was thinking that tube orthogonality might be the culprit, but that's not a dead cert.

Is your setup mobile? If so, levelling (or not) of the tripod could be a factor. A simple carpenter's level is all you need - and it doesn;t have to be dead nuts accurate. Just better than 'by eye' would be fine.

How about skipping the handpaddle routine and trying a drift align. I can drift align to within a few arcmins in the space of about 2 or three mins. I find that this improves GOTO operations as well as tracking.

Tube orthogonality is a bit more complex to fix but easy enough diagnose. You can diagnose it by pointing at a target, say in the South, with the OTA on West side of the mount. Then point at the same object but with the OTA on the East side of the mount. Trouble is, you need to do this with a GOTO operation, not just by manually moving the scope. The AP can do it with a meridian flip, but I dunno about your mount....

Try the levelling and basic drift aligning first though and see if that improves matters. The drift alignment can be done with the CCD imager of course so it wouldn't take you long.

Finding guidestars must be a pain with the 8" - but realigning the rail seems to be a solution at least some of the time. On the other hand, if you realign the rail, I'm wondering what effect that would have on the refractor and orthogonality...

Its never easy I guess.....

Howdy,

that 6 degree difference is worrying. I was thinking that tube orthogonality might be the culprit, but that's not a dead cert.

I think it's more a mount problem than anything & it worked well until January. My standard usual setup is:

1/ Place the scope & CG5GT in Garden facing north
2/ Level scope
3/ Align with Polar Scope
4/ Move to index marks
5/ Three Star Align
6/ Drift Align (I'd usually do about 30 minutes of a drift align here)

Sometimes I add the following before doing the drift.
- Polar Alignment via hand paddle (I usually skip this now as it causes bizarre malfunctions).
- Three star align after shutting down for 1 minute.

When I first got the mount in November last year I only needed to carry out the first two steps & that was with a much heavier Newtonian OTA.

The reason I think there is a mount problem is that if I run a session of, say, 20 shots of 60 seconds exposures I would get around 3 OK shots, followed by 5 hugely inaccurate shots, followed by 3 or so decent ones followed by 5 more terrible ones. And these aren't just the usual tracking errors, they are enormous, e.g. on M13 I would get trails about the 1/3 - 1/2 the width of the cluster. This sounds way too much for periodic error to me but I'm not sure. BTW this is only at 480mm I am imaging.

Celestron tech support are baffled by this also, but it would take ages to get fixed so I tried the autoguiding instead + it already had it's ra circuit board replaced but it made no difference.

BTW after doing a drift align the polar scope is pointing miles away from Polaris. Weird eh?

f you realign the rail, I'm wondering what effect that would have on the refractor and orthogonality...

I was worried about this too but I reckoned that if it is moved by only, say, 1/2 a degree that it would not affect things too much.

Well, you know what problems with mounts are like. Something must have happened to it at some stage but it takes a month waiting for dark skies until you know if the fix worked or not


T[/quote]

Oh trever those shots are magnificent. Particularly for first efforts at autoguiding. Isn't it so sweet standing by listening to the mount clicking away, knowing that your gonna get a well tracked photo!!

Dont worry too much about framing etc that will all come in time. One thing though, if you are serious about long exposure deep sky imaging you will need a modified webcam for autoguiding. Otherwise you'll spend all your time finding guidesatrs and lerss time actually imaging. Here's a quick step by step of what I do

1. Align scope and guide scope to be pointing in the same direction (center both on a bright star).
2. Focus both roughly for imaging camera and guide cam.
3. Center and frame target.
4. Center suitable guidestar by adjusting the position of the guidescope.
5. Check target framing (you might have knocked it off fiddling with guidescope)
6. Accurately focus imaging cam (using whatever software/focussing mechanisim you prefer)
7. check framing again (SCT focussing tends to cause image shift)
8. Lock guidestar and begin guiding.
9. Begin imaging.

Note number 4. Guiding is not materially affected by choosing a guidestar in a different position to the mainscope. This is true to a point, cleary it's no good using guidestars several degrees away but with a modified cam, any star you can see in an eyepiece will do for guiding. In my experience you will find a guidestar suitable for guiding with a webcam in 99% of eyepiece fields. I have never not found such a star within a very small distance from the target.

#'1 is only really important if you are imaging through a piggybacked scope. By aligning both you know that if you center an object in the main scope then it's also centered in an imaging piggybacked scope.

As for your goto problem. All I can say is you should never trust goto for CCD imaging anyway. Even though my goto works fine on my cg5, I still would only use if visually. I never use it for imaging. I find it best to print a starmap and use that to hop to the target. I find I can pretty much center any object this way in less than 1 minute.

ANyway I'm delighted to see such good results coming out of your stable and look forward to seeing some stunning results as your techniques develop.