M17

[peter_4059 (Peter)]

Set up last night to try out the new focuser and see if my flexure issues had improved. What better way to find flexure than longer subs I thought so set up 4 mins with the DSI. M17 was the target this time. The initial exposures looked very promising however the flexure crept back in as M17 moved lower in the west. All up I kept imaging for 2 hours this time making this my deepest/longest DSI image from the burbs.

Comments welcome!

[AlexN]

Looks nice...

At the end of the day, are you any closer to tracking down your flexture issue? Are you certain that its flexture? or could it possibly be a balance issue? I find with bigger scopes (newts and long refractors especially) that whilst your RA and DEC might both be fairly well balanced when the RA axis is horizontal, when the RA axis is closing in on the vertical position, the balance changes quite a bit... This sounds like it could be your problem, I figure, if you can get 4min subs at the start of the night without problems, but as the target gets lower your results start to falter, either balance or perhaps poor seeing at lower altitude is the culprit.

What exposure duration were you using for guiding?? as the target sinks lower towards the horizon, I tend to bump the guide exposures up to 2~2.5 seconds.. with shorter exposures, your guiding can chase the seeing, giving the appearance of poor tracking and or flexture...

Just other things to consider I guess...

Best of luck chasing it down..

Oh, are you using adjustable guide scope rings or solid rings? If adjustables are being used, remove them, smash them up a bit with a hammer, then throw them in the bin, get some solid rings for your guider.. Those adjustable rings were designed by the devil to make people cry.. Pure Evil.

[jjjnettie (Jeanette)]

Awesome work Peter. It's a beautiful rendition of the Swan.

[allan gould]

Really nice image, Peter. Very smooth and processed just right.
That DSI II is a gem in your hands as you manage to wring the last photon out with it.

[peter_4059 (Peter)]

Thanks JJ. Alex - the guiding exposure was 1-2 secs. The reason I believe it is flexure is because I'm seeing the main image moving a few pixels each sub (in RA) however the guide star is remaining in the guide cross hairs. This is really obvious in the stacked image where a hot pixel ends up drifting because I stack on a star - see attached.

[Rastas]

Two hours total..... that's amazing Peter. Better you than me as I have the attention span of a puppy and lose the ability to guide after about 5 minutes. I had a similar issue to yours and changed scopes, guidescopes rings etc etc and found that the one thing it was NOT was a balance issue. Guide stars were perfectly round according to the guidescope but trailed in the image. It was flexture but after worrying it like a bone all it did was to drive me crazy. I went out and bought a new scope, mount and guide setup and it went away. I suggest Astrophysics and a Paramount might just handle your DSI.

[peter_4059 (Peter)]

Cheers Rastas.

I think Alex is barking up the wrong tree also with the balance theory. This problem has been hounding me for months having tried different OTA's, fixed and adjustable guide scope rings, heavier dovetails and different cameras.

The images look good near the meridian however the flexure gets worse as the scope approaches the horizon and the resulting stars become a dogs breakfast.

Peter

[AlexN]

Originally Posted by peter_4059

Cheers Rastas.

I think Alex is barking up the wrong tree also with the balance theory.

Just throwing ideas out there.. Never hurts to consider other factors, however, you do know your setup better than I do, you also know what you've already tested better than I do.. Sorry for the suggestion.

Do you get any flexture problems imaging through your ED80 using the other refractor as the guider? or is it just with the newt? is it possible that the newts tube is flexing a little bit? are your rings the type that attach to the dovetail via a single bolt? I've found those can introduce flex, even when they are done up fairly tight.. also, how long are the saddles on your side by side bar? short saddles will sometimes allow flex.. The ADM side by side that I used to have had 15cm long dovetail saddles, so when using the 7" dovetails on my refractors I had at the time, all bar 1cm of the dovetail was firmly clamped by the saddle.. I've seen many side by side bars that use small (between 7 and 10cm length) saddles, something like that coupled with a 10" F/4.7 OTA could definitely cause problems..

Sorry if im barking up the wrong tree again.. Just trying to help.

[peter_4059 (Peter)]

Thanks Alex

I think you are probably on the right track with the saddles. I'm using the Telescopes-Astronomy SBS bar. While the bar is solid as a rock the saddles are quite short and the clamp arrangement is less than ideal. I have seen similar flexure with the ED80/guidescope combo although the rate of movement is a lot less. Might have to put losmandy saddles and a new bar on my christmas list.

[multiweb (Marc)]

Yeah nice! You've got some beautiful details on the central neb. Well done.

[peter_4059 (Peter)]

Thanks Marc. It is amazing what you can capture from a light polluted location.

[Octane (Humayun)]

Peter,

That's a great effort.

Looking forward to what you can do once you've sorted out your flexure problems.

I also had the same side-by-side setup from Telescopes-Astronomy. The mini side plates are just too small. I've now gone for a stacked setup. ED127 and ZSFD80 on top. It's pretty solid now. The only thing that worries me now is that the centre of gravity is higher up. It always pays to keep the centre of gravity low and closer to the mount. Will see how I go.

Regards,
Humayun

[peter_4059 (Peter)]

Humayun,

I know what you mean about the centre of gravity and that's why I've persisted with the SBS setup. There is just too much weight in the 10" newt for me to contemplate stacking the guide scope on top. I've swapped the vixen system out for losmandy D bars and plates with the starstuff SBS bar and while the flexure is not gone it is better than it was before. I've swapped the guide scope and tried my ED80 as a guide scope and still get some movement so it's likely the remaining flexure is in the 10" newt. I need to have a look at how the primary mirror is mounted as it's possible there's some movement of the mirror in the cell.

Peter