gnomus

Do we know the RA-Dec orientation of the elongation? 

Olly

I am not entirely sure if I can answer this.  I set up my camera using that trick you have mentioned on several occasions - that is, take an image whilst slewing the mount for 5 secs and then adjust camera angle to get it squared.  In SGP's plate solve routine it states that my Angle is 0.83 degrees.  At this angle, the full image looks like this (I've only posted portions of the image before) - this is  very basic stack and levels stretch:

Does that help at all?

I've spent all morning getting my ED80 on top of my Tak using the Baader mini dovetail thing, then recabling and rebalancing - I hope this works. 

OK chaps. I'll do some serious reconfiguring tomorrow and then wait for a clear night to test. I am not sure I am quite ready for off-axis guiding - do folks like the Atik OAG? (I have an EFW2.). I would have enough spacing, even if I did eventually get the Tak reducer.

Thanks to everyone who has contributed to this thread - all very helpful.

That is interesting to see. Thanks for posting it. So, much more likley to be flexure than any optical issue then?

Edit: Poor PA wouldn't look like this would it?

I used to use an OAG with a 2.5m SCT at f10 ............. never failed to get a guide star.... although they could be a little dim!! I'm a great one for experimenting and not following published theories etc ............. Give it a go. I bet you get a guide star at f7.5 every time.

Thank you Sara. My wife has repeatedly told me that she'd like me to experiment more. Now I know what she has been on about.

What issue?

Even with a small sensor like an original Lodestar you will have a 35.33' x 27.25' FoV. I'll eat my metaphorical hat if you can't find a guidestar in that!

I'll give it a go, but, before I do, can I see a photo of the hat?

Hmm..you have the potential for mirror flop to contend with.

Rigidity is everything in guiding...and a moving mirror does not give rigidity.

<edit> I'd be tempted to try the ED80. The slightly longer focal length won't cause an issue. The ED80 is a lot heavier than the ST, but you've got the Mesu now. You'll not be running out of capacity just yet!

I could try the ED80 but what about th f/5 vs f/7.5 (from memory) issue?

I hesitate to add my 2d to the debate in view of all the expert advice offered but on the ST80 guider subject, I used one as a guidescope for a while but after the usual endless fault finding it did turn out to be the weakest link so I said goodbye to it, after that I initially used my 100mm refractor for guiding which despite the increased weight was a bIg improvement over the ST80, mainly because of the much better focuser I think.

In for a penny in for a pound Steve, more money to spend 

Dave

You enjoyed that last sentence didn't you Dave? I do still have the ED80 that I put a Moonlite focusser on, but that doesn't have the same focal ration as the ST80. I assume that trying to guide with my C8 (once I get dual mounting up and running) would be complete madness?

I honestly don't remember a tilt adjuster module on mine. I'm not at all sure that I had one, but Tak do change things around with their hardware. I certainly never used it since I didn't know about it.

Well, it looks as if nobody likes that guidescope carrier and, on single scope setups, I've never had any issues arise from approximate alignment of guidescope and imaging scope.

While I like and use (two) ST80s for guiding there are a couple of things to watch, though I doubt you've missed them. The entire rear end of the scope is held into the main tube by three screws. These need to be very tight. I wouldn't baulk at a drop of epoxy to hold the back end in firmly, either. I did have the back end cause flexure once. The drawtube is also very vague so I tighten the lockscrew rather pitilessly to keep it still. Any extensions carrying the guide camera also need careful attention.

Olly

I do super- tighten the focus lock screw. I hadn't cottoned on to the three screws holding the focuser in place. I will check these later today.

That word 'Ouch' and your subsequent paragraph has given me a terrible feeling that you may have thought I was in some way criticising you or your methods - please be absolutely assured that that was not my intent and please accept my apologies if that it how you read it! On the other hand, if the 'Ouch' was because you have spent more money but not found this to be a panacea then you have read me correctly!

Nincompoop - no, you may recall that I have sought your advice on a Mesu related issue and I wrote the flippin' manual!!

The tilt adjuster module.

Your cable management looks pretty good to me but I would rather see the loom attached to the base of the clamshell as it could pull on the Sky-Watcher adjustable guide scope mounting. I have one of these mountings and found that it was very good but I also made the following comment when I reviewed it although it should be borne in mind that I was already suffering from differential flexure before I installed this adaptor:-

You could try removing this to see if it makes any difference to your results - without doubt, the guiding system should be as rigid as possible -  did you use this guide scope mounting with your ED 80 as well?

Having both guide telescope and imaging telescope perfectly aligned is not a pre-requisite for accurate guiding.

Ah the perils of non-verbal communication.  Please be assured Steve that I took no offence whatsoever from your comment - you are trying to help me after all.  My 'Ouch' was meant humorously - perhaps "Touché" would have been a better response.  I am however a little upset that you so lightly dismiss my credentials as a nincompoop.  I am nincompoop-and-proud.  (As this is the Internet, I should perhaps add a ).

I used the ST80 when guiding the ED80, but it was not attached with the Skywatcher thingamajig.  I had everything on the CGEM back then, and I was probably trying to keep the weight down.  The Skywatcher does add quite a bit of height to the set up.

I have this arrangement of holes on the top of my Tak clamshell:

I could try bolting the ST80 rings direct to this (although those rings will only end up an inch and a bit apart).  Alternatively I have a Baader mini dovetail that I could affix to the Tak clamshell.

I will also try moving the point where I attach the cables to lower down - between the Tak and the Dovetail plate.

OK so bin my suggestion about PA if the guide scope is on axis. I have to say that I never like adjustable guide scope holders or rings* and always prefer a bolted-down guide scope even if it isn't perfectly on-axis. With good PA this won't matter. That adjuster has to be a suspect, though it may be perfectly innocent.

I guess the orthogonality of your filters could play a role but does changing filter change the distortion? If not it's highly unlikely to be that. (You'd have done well to replicate the same tilt in every filter...)

Olly

*Except in the case of dual rigs where, on two occasions, we've found the system prefers an on-axis guide star. I can't account for this. It could be experimental error but it happend twice so I just accepted the fact.

Thanks again Olly.  I have spent some time going through various subs.  At first I had convinced myself that the Ha filters all had the same issue - worse in the top left and top right corners - and that my Lums were worse in the top right and bottom right corners.  But the more I looked at this, the less certain I was that I was seeing a consistent error.  I am increasingly coming to the view that the issue may be one of a cable dragging.  If that were the case then I might get different directions on my elongations depending on where the scope was pointing - isn't that right?.  When setting up, I was a little unsure where I should attach the cable bundle.  In the end I ran a piece of velcro around the join between the top of the Tak clamshell and the mounting plate for the guide scope bracket - I hope this image shows what I mean (ignore the velcro on the Tak lens hood: this was early on when I had temporarily attached a Telrad to the system to help set up):

 

I did think about velcroing the bundle to the join between bottom of clamshell and the dovetail bar.  I am planning to moving to a dual rig with Tak and C8 side by side over the next few days and I will try to find somewhere else to attach my cable bundle. 

I had intended to fix the guide scope in a set position with a Baader clamp until I read something on this site about how important it was that the guide scope and imaging scope be aligned!  'You say poh tah toh, and I say ......'

If the guide star were well off-axis relative to the Tak then wouldn't polar misalignment also produce this effect?

Which connector is that, Steve? Since mine departed some years ago I can't remember it in every detail but the only connector to give me gyp was the tilt-adjuster (if that's what it was meant to be) on the reducer. Steve (Gnomus), are you using the reducer here? If you are then the 'three radial screw horror' is designed to test your tilt adjusting skills! I just loosened the screws, put the flattener on the table, pressed the top part down onto the bottom and tightened them. That worked in my case.

Steve. (Just going with the flow - or should that be FLO?  )

I have one of these SkyWatcher Guidescope Mounts http://www.firstlightoptics.com/guide-cameras/skywatcher-guidescope-mount.html and I have ensured that the guidescope and the Tak are pointing at exactly the same point of the sky.

I do not have the reducer - was thinking of getting one but the stories relating to that adapter and its screws do not leave me brimming with optimism.

Can I ask again about orthogonality of my unmounted 36mm filters.  Could this be an issue or would I just be wasting my time checking this? 

I think that it's fair to say that once you start spending more money you begin to see less and less of a difference. I've often seen it quoted that you're now paying a few thousand ££'s more for a very small increase in quality.

The ED80 is a good scope and is excellent value for money. I wouldn't expect to see a huge difference in quality between that and a Tak.

..... Just my opinion

Thanks Sara. I quite understand the law of diminishing returns, it is the direction of travel (quite literally in this case) that concerns me.

I downloaded your two frames (frames 3 & 6). In both frames, the stars have an overall elongation top-left to bottom-right slope, just as you said. Now blink the two frames - you'll see all the stars move in that very same direction between frames 3 and 6. Coincidence?

I strongly suspect your have some kind of flexure somewhere, so the image is slowly drifting relative to the guide camera's view.

Mark

Thanks for looking and confirmng my suspicions Mark. The elongation is all in the same direction - it is worse in some corners but it is present in the centre. I am dithering, so it is just possible that the 'blink' test is coincidental.

I will recheck cabling and balance. With the Mesu, one cannot 'declutch' and It is not always clear where the precise point of balance is.

I hate to say this but ...

What better gear should do is put the onus on the operator to get the best out of it and not blame the equipment if the results aren't great ...........

Ouch.  However, I have not found this to be the case with astronomical or indeed any other type of gear, and I too have suffered from the 'hifi sickness'.      

What I am trying to do with my question is ascertain whether or not I do have a significant issue and, if I do, seek advice as to how to fix it (thereby getting the best out of my equipment).  I may well be a nincompoop, but I was getting rounder stars with my ED80.  

Indeed, this will confirm whether or not there is sensor tilt - be aware though that there are other potential causes for the sensor to be tilted to the light cone including focuser slop, that awful adjustable connector that you get with the FSQ 85.

I would agree that the diffraction spikes on the bright stars are indeed the micro-lenses on the KAF 8300 sensor as this is a well known issue with this chip (note that the spikes are exactly N/S and E/W in the field of view).

Ollie makes a very valid point about the 'pixel peeping' though (and many of us including me are guilty of doing it) - your image is far removed from a disaster and with our limited imaging opportunities, you could just get on and enjoy yourself!

Thanks Steve

You are probably right.  I was quite pleased with the images last night as they downloaded from the camera.  I don't mind the mini-spikes, I just was not expecting them.  I understand that my image is not a disaster, but, at this price point, I was hoping for a significant step up.  I think I got rounder stars with my ED80 (and on a lesser mount).

Hi Gnomus

Post drobox links and I'll check with ccd inspector.

Steve

Thanks Steve (Is everyone on this site called Steve?)

Links:

https://www.dropbox.com/s/fbkvlc0rkdrykpe/Pelican_1200sec_1x1_HA_frame3.fit?dl=0

https://www.dropbox.com/s/6dl0o1d0mediw1e/Pelican_1200sec_1x1_HA_frame6.fit?dl=0

Frames 3 & 6 - the last ones taken before an autofocus run.  

I'm very grateful to you for this.

Steve

I would agree with that...the bottom corners look OK to me too. the top right looks marginally worse than the top left.

It could be sensor tilt, a bit of slop in the focuser, flex in the filterwheel front or rear plates. it could be a right old so-and-so to track down.

Steve, are you using a fully threaded connection from the focuser to the camera? Do you have CCD Inspector to run some subs through?

I am using a fully threaded connection and all connectors are Tak parts.  I do not have CCD Inspector (and am not sure I'd know what to do even if I did).  I can post Dropbox links to a couple of subs if that would help. 

I think you're pixel peeping, which has its virtures but should be kept in its place. If you look at Tak FSQ images you see a lot of excellent ones. You also see plenty of stellar artefacts. I get the odd PM or email asking if I've noticed this or that that is wrong with my stars and do I mind? I have noticed and I don't mind. Here's an example. Have a look at the bright young blue stars on the left. They have classic Tak 'inverse light house beams' coming from either side. Greg Parker tells me that they arise from pinching. He knows more about optics than I do so I'll settle for that. https://ollypenrice.smugmug.com/Other/Best-of-Les-Granges/i-Vtk6nfM/0/O/VDB152%20HaOIIILRGB27Hrs.jpg

But what interests me in this image is that the Tak has allowed me to catch more of the red SN remnant than I have ever seen before on the net. That doesn't mean nobody has gone deeper, it just means that I haven't seen it (and, yes, the processing is exaggerated but that was my intention - to drag it into view via colour.) So my advice - and my own policy - is not to let the details blind me to the big picture.

Anyway I'm still backing PA... but it could be tilt. The standard test for tilt is to rotate the camera.

Olly

I am quite certain I am pixel peeping!  At 100% I am a little suspicious of those stars, but I really need to go to 200% (or 2:1 in PixInsight) to see the ovoids clearly.  

I will check polar alignment again if I get the chance (recent weather here has been beyond a joke).  Could this be cause by a little bit of cable drag on an insufficiently tightened scope (see my previous post)?  I can also rotate the camera - I presume that if I rotate it 90 degrees I would expect the direction of ovoid-osity to change by the same amount.

Firstly (call me sloppy)

.....

Olly

If you insist: You're sloppy.

Thanks for your response.  I went ahead and processed the 8 x 20 min subs I took last night.  I still think I'm getting ovoids in the centre (highlighted in red).  The other thing I have noticed on all the images I have taken with the Tak are small diffraction spikes (best one highlighted in yellow).  I must say I was not expecting to get these with a refractor.  Again, you'll probably need to click on the image to get the 100% crop.  Am I expecting too much from the equipment?

I thought I had reasonably good polar alignment.  Certainly the PHD assistant tool reported excellent PA (but I don't know how reliable this is).  Following your comments, I went out and checked the tightness of everything.  I was able to tighten up the Tak rings and connections by a very small amount (a 'wee thochty' as they say back home).  I am not sure if this could have been responsible.  Something interesting did happen when I was doing this though - the whole scope rotated slightly in the clamshell.  It is possible that I hadn't tightened this up sufficiently (trying not to crush the tube).  Could this make a difference I wonder?

The final thing I have been thinking about are the 36mm unmounted filters that I have in my EFW2.  Fitting these filters into the wheel was a fiddly job to say the least.  Is it possible that one or more of these are not exactly square?  Would that make a difference?  If so, how do you get these things in square?????

I had hoped I'd be imaging by now - not still troubleshooting, but there you are. 

Thanks Steve. If it is sensor tilt, what am I supposed to do about that?

I am someone who is still trying to figure out when I should ‘soldier on’ rather than admit defeat.  Last night may have been a case in point.  The moon was pretty huge - mid-90% size.  Nevertheless, (and despite advice from people who know what they are doing) I decided that I would press on and try to get some Ha of the Pelican Nebula.  I went out at around 8pm, I rolled the roof off, and I fired everything up.  Then I took a peek over the observatory wall.  In the half hour or so since going out, it had completely fogged up - dense fog.  So, I shut everything down and rolled the roof shut again.  About an hour later, things seemed to have improved considerably, though ‘Clear Outside was still showing ‘Red’ for dew point and relative humidity.

 I went back out and tried again.   

Most of the time I got really good guiding – flat graphs with <0.2 pixel RMS error.  Every now and again the graph would throw a slight wobbly with Dec moving between +1 and -1 arcseconds for a few seconds, but overall it didn’t seem too bad – My Tak 85 and Atik 383L give me a resolution of 2.47” x 2.47”.  I was taking 20 minute subs and, on my warm room screen, SG Pro seemed to be showing me reasonably good images.  However …… Once I got indoors and looked at my subs on a decent screen I saw that I had some star trailing.  I attach some 100% crops taken from the middle and the four corners of my image - you may need to click on the image to make it the 100% size.:

It seems to me that all of these crops show stars with a top-left to bottom-right slope.

When I finished for the night (some 3 hours later) it was quite one of the wettest evenings I had encountered.  The equipment was all soaked and there was water streaming down the observatory walls.  The dehumidifier seemed to have dried everything up by morning.

Is this then simply a problem of 'seeing' or have the conditions pointed up a more fundamental problem with my set up?  I use an un-reduced Tak 85 (at least for the moment).  

I've managed to reach focus this evening.

This is HD 231061 (the bright one)

unguided, 300 sec exposure.

http://nova.astrometry.net/user_images/756460#annotated

Thank goodness.  Does that mean that you won't now have to take the scope back to the UK with you, and that you are now "up and running"? 

Thanks for all the nice comments, appreciated.

...

I will be taking the scope back home, but will leave the mount as it's aligned now.

Can't you get some extension tubes from http://www.teleskop-express.de/shop/index.php/language/en ?

It looks like you are well out of focus. What looks like stars are hot pixels. The "smudge" is a massively de-focused star.

I agree with Zakalwe's analysis.

Magnificent.  Congratulations on the new set up.  Looking forward to seeing some images from it..