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Seeing and guiding terrible tonight...

kirkster501

By kirkster501
in Imaging - Discussion

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JohnSadlerAstro

JohnSadlerAstro

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Any time now, apparently. I can see the front running diagonally across the sky, the north west is clear but got to wait for the south to clear so I can start PA. My plan is NGC 7331 and Stephan's Quintet for tonight, I want to get some 4 min subs in if the skies allow for the main quintet and Lick Groups, then I'll probably need a lot of shorter ones for the middle of 7331.

John

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JohnSadlerAstro

JohnSadlerAstro

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Almost turned into a failure--but not through the seeing, I've been having setup issues on and off for the last 6 months and I was determined to hit them head on. 2 1/2 hours of messing about got me centred (I kept accidentaly leaving the mount handset in 16x, then the guiding would crash and throw it off again, etc). Theres some quite nasty coma, unfortunately the galaxies aren't quite centred so they are affected by it a little, I will crop the image though so most will go.

I got 8 x 4 min at ISO 800, doesn't sound like much but that was the result of a 4 1/2 hour imaging session. :D They should provide a good base set of data, next time it's clear I want to collect another hour or two.

But the setup overall seems to work again now, I was getting maximum total errors of 1.8", which for me is very good. :) As im running a 5.75 micron px DSLR and then the 650mm f 130PDS, that's not really too much to worry about imo.

John

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Shibby

Shibby

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Well, it's good to get those troubles addressed on the nights with worse conditions!

I could tell as soon as the clouds cleared, the stars were twinkling lots. I noticed it while focusing, but thankfully the guiding has been fine so have somehow gathered nearly 4 hours of data! ?

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ollypenrice

ollypenrice

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We've had a six night clear run here which ended tonight (ie Thursday) with cloud. However, on the first of those nights I think we had your jetstreams because, though clear, the seeing was abominable. The TEC/Atik 460 was giving an FWHM in the fives. It can get down to 1.3 but about 2 is typical. It will still guide, though, using 4 second subs. We decided to reshoot the first night's data with better seeing.

Because my sleep's all over the place I'm up early and have just seen Orion high and mighty in a clearing sky.

Olly

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kirkster501

kirkster501

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It was all over the place jumping to between 1.5-2s error then was fine for a bit then went again.  I am confident enough not to "tinker" because not a thing has changed on the rig and the graph was pancake flat last week.  Takes confidence not to tinker sometimes (he says)....!

That said, this was imaging with my FSQ85 with reducer and with big chip 8300.  I would have thought the guiding would be easier at that scale......  It al calibrated though fine and guiding assistant did not give any warnings.

My polar alignment is 13arc minutes.  Seem to recall it was that before too so that seems OK to you guys?????

A good opportunity wasted, I wanted to get the RGB on North American Neb last night :(

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Shibby

Shibby

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Well, I'd been waiting 12 days for a clear night (also to gather further data on NGC7000) so was determined to get some data whatever the conditions! My guiding was averaging ~0.7" RMS, so I hope the data will be good enough. I think the altitude of the nebula helped somewhat. I've just checked FWHMs and they're only 0.5 higher than the previous session.

1 hour ago, kirkster501 said:

A good opportunity wasted

It is frustrating when you miss an opportunity, knowing how infrequent they can be in our country. But you have to remind yourself there will eventually be others!

5 hours ago, ollypenrice said:

Because my sleep's all over the place I'm up early and have just seen Orion high and mighty in a clearing sky.

Work is already a struggle this morning! The comforting prominence of Orion isn't a bad reward for powering through :)

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ollypenrice

ollypenrice

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Steve, I would always take a test exposure in the main camera whether the guiding is good or not. If the FWHM is terrible then you're wasting your itme imaging at all, though if you're going to shoot luminance then soft RGB wouldn't matter much.

I'd always take a test of the FWHM because, if it's not bad, then you do have an issue to track down in the guiding. Basically a test of FWHM is independent of the guider and may signal a guiding problem.

Seeing alone does not have a huge effect on our Mesus. Of course guiding's best in stable seeing but even with an FWHM of over 5 last week the guiding remained quite good. Bad transparency is another matter though. If you lose the guide star then it's curtains.

I have to say that things working-not working without being touched in between is not unknown in this mad game. Cable connection, USB... they're all out to get us.

Olly

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kirkster501

kirkster501

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Thanks Olly,

Well, as it happens, I'm too much of an engineer not to tinker. It got to this afternoon, it's quiet at work (work from home most Friday's) so I just could not resist a check of balance, cables, updated my drivers etc.  I'm just not sure if my guide stars on this rig are tight enough.  I know they don't have to be that tight, but just feel they should be a bit tighter still.  I am not 100% convinced that my Lodestar x2 guider on my G2-8300 OAG is focused sufficiently.  But for 100% sure, I never touched anything before last night's session from the previous session that was perfect.  I find this Lodestar x2 on the Moravian OAG's helical focuser a swine to focus.

I never seem to have a problem with my TEC140/FF/Atik460 rig (both TEC and FSQ scopes permanently mounted side-by-side on MESU in the obs).  It just works.  And that should be the harder one to guide because of the smaller image scale.  The wide field of the FSQ85 should be easier.  That said at F3.9 the focus is even more critical.

So I am not convinced that everything is hunky-dory.

 

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ollypenrice

ollypenrice

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7 minutes ago, kirkster501 said:

Thanks Olly,

Well, as it happens, I'm too much of an engineer not to tinker. It got to this afternoon, it's quiet at work (work from home most Friday's) so I just could not resist a check of balance, cables, updated my drivers etc.  I'm just not sure if my guide stars on this rig are tight enough.  I know they don't have to be that tight, but just feel they should be a bit tighter still.  I am not 100% convinced that my Lodestar x2 guider on my G2-8300 OAG is focused sufficiently.  But for 100% sure, I never touched anything before last night's session from the previous session that was perfect.  I find this Lodestar x2 on the Moravian OAG's helical focuser a swine to focus.

I never seem to have a problem with my TEC140/FF/Atik460 rig (both TEC and FSQ scopes permanently mounted side-by-side on MESU in the obs).  It just works.  And that should be the harder one to guide because of the smaller image scale.  The wide field of the FSQ85 should be easier.  That said at F3.9 the focus is even more critical.

So I am not convinced that everything is hunky-dory.

 

Sorry, I'm not dead clear on your setup.  Do you have an OAG on both scopes or does the one on the Tak do the job whichever is your imaging scope? If the guiding issues are associated mostly with the Tak guider then that would suggest it isn't happy. Why not use the TEC OAG, assuming you have one, to guide the Tak? I know the idea is to use the same light cone but this is solving a problem that won't exist with a small refractor.)

In my experience a clear sky, however bad the seeing, will let both our Mesus track quite accurately.

Olly

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kirkster501

kirkster501

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Hi Olly,

No, both scopes have an OAG.  If I'm imaging with the FSQ85 I use the OAG on the FSQ.  If I'm using the TEC then I'll use the OAG on the TEC.  The camera on the unused scope switched off and cover over the objective .  Yes dual rig setup in the pipeline :) )

Two scopes on the same MESU and they are both permanently mounted and are never moved.  This is my imaging setup and it never changes.  1.  FSQ85<>Reducer<>OAG<>camera (Moravian G2-8300)   2.  TEC140 <>FF <>OAG <> Atik 460

I *have* thought of using the TEC to guide the FSQ though.  I thought the different imaging scale could cause issues and that's why I hadn't pursued this further????

Following your suggestion of looking at the FWHM.  Actually I have used the HFR because I hav'nt got software that can measure FWHM ( have I?) I can only look at completed subs though and I guess that the HFR checks should be on a short 5 second exposure to look at the seeing?

Anyway, for completed subs, the HFR of my "bad" pictures last night which have some trailing is no worse than my "good" subs from previous nights.  Implying that the seeing is OK and that the issue is with guiding....

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ollypenrice

ollypenrice

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1 hour ago, kirkster501 said:

Hi Olly,

No, both scopes have an OAG.  If I'm imaging with the FSQ85 I use the OAG on the FSQ.  If I'm using the TEC then I'll use the OAG on the TEC.  The camera on the unused scope switched off and cover over the objective .  Yes dual rig setup in the pipeline :) )

Two scopes on the same MESU and they are both permanently mounted and are never moved.  This is my imaging setup and it never changes.  1.  FSQ85<>Reducer<>OAG<>camera (Moravian G2-8300)   2.  TEC140 <>FF <>OAG <> Atik 460

I *have* thought of using the TEC to guide the FSQ though.  I thought the different imaging scale could cause issues and that's why I hadn't pursued this further????

Following your suggestion of looking at the FWHM.  Actually I have used the HFR because I hav'nt got software that can measure FWHM ( have I?) I can only look at completed subs though and I guess that the HFR checks should be on a short 5 second exposure to look at the seeing?

Anyway, for completed subs, the HFR of my "bad" pictures last night which have some trailing is no worse than my "good" subs from previous nights.  Implying that the seeing is OK and that the issue is with guiding....

I *have* thought of using the TEC to guide the FSQ though.  I thought the different imaging scale could cause issues and that's why I hadn't pursued this further????

Setting aside differential flexure (but your scopes are going to be rock solid on the mount, I don't doubt) you'd get better guiding from the TEC, almost certainly. It has a higher resolution and a considerably bigger fully illuminated field so it will have better guide stars.

Following your suggestion of looking at the FWHM.  Actually I have used the HFR because I hav'nt got software that can measure FWHM ( have I?)

FWHM/HFR: To be honest I don't know what the difference is but I think they are essentially the same. Homework time!

Anyway, for completed subs, the HFR of my "bad" pictures last night which have some trailing is no worse than my "good" subs from previous nights.  Implying that the seeing is OK and that the issue is with guiding....

For sure. You suspect the optics (focus) and you might well be right. It might be OAG focus. Is the OAG really solid? I wasted a lot of time with a rocking turret on an SX OAG at one time but they redesigned that. My first port of call is always cable connections but you have proper connections, in principle, with the LodestarX2. I have the old ones with abominable cable connections.

Olly

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ollypenrice

ollypenrice

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1 hour ago, kirkster501 said:

Thanks Olly.

Ain't no differential flexure on these bad boys...... You could winch a LandRover off of these scopes and they won't move a fraction ;)

The side-by-side plate from Astro-Mekanik Stefan alone weighs about 12kg.

IMG_2366.thumb.jpeg.2e51336f330b76bc3cfd123408cf4b3d.jpeg

I'd have thought as much, so why not guide with the TEC by default? I would.

Olly

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