Don't you love this imaging lark!!!

[Carole]

After all the hassles of replacing my dew heaters and not being able to find the right springs for the cigarette lighter plugs, I decided to try out one of the plugs with a less than satisfactory spring last night, and luckily it worked OK.

Started imaging narrowband and all was going reasonably well, except some of the subs had slightly elongated stars probably due to the occasional thin cloud passing through a 15 minute sub.

I then changed to Oiii but I kept looking at the subs and they did not seem to be in good focus, which I thought was strange as the filters are parfocal. So I went back to the obsy and slewed to a bright star to check and tweak the focus only to find the camera and FR had slipped slightly in the drawtube and one of the screws was loose. I know I screwed them up tight and this is the first time this has happened to me in 5 years of imaging. That could have been an expensive accident, but luckily I found it in time. No idea how it worked loose. Anyway in these short nights that was 45 minutes subs wasted.

Re-focussed and then went back to the target which I had synced, but I guess with the adjusting of the drawtube the target was shifted. So I had to spend time getting it back in position.

I then realised that I would have to open the dome onto the PZT otherwise the target would have passed behind the dome.
Could I get the first Quick release bracket to release - no I couldn't? Ended up having to remove the bolts, but luckily the rest of them came off OK.

Then after all that effort I only got one more sub before the clouds rolled in.

Don't you love this hobby?

Feel free to add your own frustrating experiences to this thread. 

Carole

[JohnP]

In my experience filters are never parfocal & even if they were inaccuracies in the mechanical tolerances of filter wheel etc. mean that when you move wheel focus shifts. Not that I have done it much recently but I would never change filters without refocusing. Anyway, sorry about probs you have - its nights like that when you feel like kicking all the kit into touch...

John

[Kenny]

I've absolutely no idea what any of that means but it sounds infuriating.

[MarkH]

The screw probably came loose due to a change in temperature.

[Carole]

The screw probably came loose due to a change in temperature.

Seems odd to suddenly happen when I've been doing this for about 5 years and it's never happened before.  I am always pedantic about tightening the screws for fear of the camera falling out.  Well I guess I will never know for sure, but I am going to make some sort of safety strap now as a precaution.

Carole

[RobertM]

I'm sorry to hear that Carole, I've had many's a problem over the last year so I can fully sympathise.  We should congratulate ourselves when something goes right - it happens infrequently enough !

Well this is in a similar vein so I hope it makes you feel better.  Out imaging with new tube rings, perfect focus and perfect guiding but... each of the subs had drift.  Differential flexure I thought, only to check everything and find all was tight and locked down but had to give up as it was very late and still not found the issue.  The following morning I went up to investigate and what I found was that the felt in the tube rings had slipped out of the rings by about a quarter of an inch !   I guess with all the heat and crappy glue the felt just couldn't hang on.  As a fix, what I intend to do now is to use two thin strips of styrene epoxied together (to take up and space since the rings aren't a good fit) then epoxy that onto the tube rings. Hopefully that wont slip and neither will the telescope, as with everything in this hobby we waste a lot of time trying so I just hope that's not time down the drain.

...and yes I love this imaging lark, especially when things work !

Robert

[Fay]

Oh I know it all soooo well!!! sometimes i think the only way to go involves a big hammer!!

[Carole]

Yes, you can be imaging for years and still have something unexpected come and bite you on the backside, even things that you have done hundreds of times, (like screwing my camera on securely). 

As you say Robert, it's great when it all works fine. 

In my experience filters are never parfocal

I've checked my filters John to make sure they are parfocal and provided nothing slips like it did last night, I never need to re-focus when I change them.

Carole

[MarkS]

Let me tell you about my C11 problems.  At Kelling and ever since, all my C11 imaging sessions have been ruined by out of focus stars.  Each time I carefully focused the scope using the Bahtinov mask but the focus subsequently drifted.

Eventually I traced the cause to the Dow Corning Vacuum Grease that had been used to lubricate the mirror's travel on the baffle tube.  It is so viscous that it made the movement of the mirror really stiff and once the focusing knob was turned the mirror would continue to ease upwards against gravity for the next 5-10 minutes.  It was only a movement of 0.1-0.2mm but enough to defocus the image.  I demonstrated the effect to Duncan on the last imaging night at my house - using Bahtinov Grabber you could adjust the focus exactly and then watch as BG showed it drifting out of focus.

With Robert's help we dismantled the scope and replaced the grease - this time with White Lithium.  The difference was dramatic.  The focus knob now works in a silky smooth manner and focus is retained.

The remaining problem with the C11 is that focus changes as the scope slews around the sky - this is due to the shifting weight of the moveable primary.  It is slight but noticeable.  Both my C11 scopes are identical in this respect (I've tested them).  It's the problem of having a moveable primary.  Eventually I think something like a Ritchey Chretien is called for.

So that's my tale of woe.  This, in addition to the storm damage to my observatory roof (which I can now hold in place with heavy duty ratchet webbing straps).  This year has not been a good vintage, thus far.

Mark

[Carole]

Robert, and Mark, I feel your pain, and so often it's not something easy to diagnose, often it is sheer luck you find out what the problem is.  

For a long time I had lovely round stars with the finder guider, but sometimes I get egg shaped stars with the same set up, and as stated above even in the same imaging run, some were fine and then latterly all were egg shaped if I dared go over 300secs.  
So this afternoon I dismantled the rig and set about finding my old guiding set up (ST80 and guide rings), removed the QHY5 from the finder guider and started to set up the Guide rings.  I thought I'd try to rule out focal length and flexure in the first instance.  What I found as I was trying to screw the guide rings on, that there was a miniscule amount of movement in the RA axis of the mount.  I tightened the RA lock but although marginally better there is still a very very small amount of movement if I wiggle the scope.  

Now not being technical or into engineering, I am wondering whether this might be the cause and if so what do I do about it?  I tried tightening up a few hex keys (no idea what I am doing), but they all seemed tight.  If it requires something more technical than this I might need some assistance.

Any thoughts on how to adjust this guys?

Carole

[MarkS]

Now not being technical or into engineering, I am wondering whether this might be the cause and if so what do I do about it?  I tried tightening up a few hex keys (no idea what I am doing), but they all seemed tight.  If it requires something more technical than this I might need some assistance.

Very difficult to explain how to do it but it's something that could be easily adjusted at DSC.  However, it shouldn't be causing egg shaped stars if you weight the axis more on the East.  What direction is the elongation - RA or DEC?  My guess is that it will be DEC because that is far more difficult to control.

If you use PHD2 (and you really should!), any egg shape guiding issues are immediately made very obvious on the "Target" graphic.

Mark

[Carole]

Not sure how to tell if the elongation is RA or Dec, plus the images tend to come out upside down and back to front, so I've orientated the object so it appears more or less as it appears in Stellarium, i.e. tail upwards and larger end downwards, and the elongation is roughly horizontal, so I guess this means RA.

Always reluctant to update software Mark, nearly always find features that I love disappear to be replaced by something I don't like and the graph wouldn't mean anything to me, though I guess it would do to you.

Carole

[Carole]

it's something that could be easily adjusted at DSC

It's not that mount that I take to camp Mark.  I have the offending mount permanently mounted and alignmaster polar aligned.  I'll have to see if some kind person would pop over and do it for me, but if you think that's not causing my guide problems it's not so urgent, and I do weight to the East, though perhaps I am not doing it sufficiently, I normally move the counterweight about an 1" or so downwards once I am balanced if imaging East or South East. 


Carole

[Carole]

Following on from the above conversation and my guiding problems, I did some imaging last night using the ED120 and piggy backed ST80 and QHY5 (my old set up) and did 20 minute subs with lovely round stars, so it has to be something to do with the finderguider set up.  Either the focal length of the finderguider is wrong (but others use it OK) or some flexure. 

On the WO I have it mounted on a SW findershoe which is welded onto a ring around the WO scope, so I think there could be a flexure problem there.  Trouble is there is no way of mounting a guidescope or finder onto the WO scope except using some sort of adaptation, and I don't like using side by side due to clash with the pier plate.  I am thinking of adding a 2nd ring to the WO scope and mounting a plate accross the two (like I did with the Megrez), and I'd like to use small guide rings for the guidescope rather than use the finderguider bracket which I think could possibly be a cause for the flexure, but hardly any-one makes them that small unless they are really expensive with extra hardware attached I don't need. 

So using the WO scope is still to be resolved, but at least I have narrowed down the problem.

Carole

[JohnP]

check for dangling cables