Diagnosing "eggy" stars

[gnomus]

45 minutes ago, kirkster501 said:

Steve (gnomus) you sent your FSQ85 back? Did I read that correctly?

That is correct.

[Tiny Small]

18 hours ago, Thalestris24 said:

it's as though something has given it a yank! However, as DEC has continued ok, I'd say there may have been a communication loss which has affected only RA.

This is going to sound ridiculous as I'm sure this was two of the first things you've checked... but have you checked for cable snags and are you controlling the mount through its own USB port and not a hub? When I got my new mount I had very similar issues with the RA and as Louise says, it was a failure of communication to the mount going through a hub. Plugging the mount straight into the PC sorted it.

[Zakalwe]

19 hours ago, Thalestris24 said:

Hi there!

The 1600 does look quite good! It's a pity, though, that it's 12-bit - that must limit it's dynamic range? I guess you have the cooled version? I had eggy stars on my heq5 quite a while ago. I couldn't figure it at first as my PHD2 target showed a nice, tight clump of stars - but to one side of the centre. In the end it turned out that I was slightly unbalanced. My heq5 has a belt mod and it likes to be nicely balanced in all 3 axes i.e. no 'east heavy'. Dunno whether there might be similar issues with a Mesu? Your RA trace in the graph above has fallen off a cliff! I wouldn't expect that behaviour unguided - it's as though something has given it a yank! However, as DEC has continued ok, I'd say there may have been a communication loss which has affected only RA.

Anyway, hope you can sort it.

Louise

Thanks Louise

The dynamic range is restored once you stack the sub-exposures.

The Mesu is quite susceptible to any imbalance, so I have it balanced as best as I can.

I'm gradually eliminating all possibilities, though getting the tracking corrected has improved things enormously.

 

 

56 minutes ago, Tiny Small said:

This is going to sound ridiculous as I'm sure this was two of the first things you've checked... but have you checked for cable snags and are you controlling the mount through its own USB port and not a hub? When I got my new mount I had very similar issues with the RA and as Louise says, it was a failure of communication to the mount going through a hub. Plugging the mount straight into the PC sorted it.

All cables are routed through a nylon sleeve and are well tied up.

The mount is running through a hub. Over the weekend I am moving it to it's own PSU and probably will look at the hub too. 

[Tiny Small]

1 minute ago, Zakalwe said:

 

The Mesu is quite susceptible to any imbalance, so I have it balanced as best as I can.

 

Really? Given its rated payload and going from some of Olly's comments in the past, I'm surprised by this. Particularly given that your imaging rig must be about 25kg under the rated load?

[Thalestris24]

16 minutes ago, Zakalwe said:

Thanks Louise

The dynamic range is restored once you stack the sub-exposures.

 

Hi

I've stacked subs from my cooled 12-bit Minicam5s but I'd say the result is not as good as 14-bit subs from a Canon 550d and I would imagine 16-bit would be even better. But 12-bit might be good enough!

Louise

[Zakalwe]

24 minutes ago, Tiny Small said:

Really? Given its rated payload and going from some of Olly's comments in the past, I'm surprised by this. Particularly given that your imaging rig must be about 25kg under the rated load?

Its got a friction drive that can slip under an imbalance. It's actually quite difficult to balance when lightly loaded as the friction drive is permanently engaged (no clutches!) and the motor "stiction" has to be overcome.

[gnomus]

I wondered if it might be best to balance the Mesu using a hanging weight scale - like you might use in fishing (or something like a trigger pull scale).  That way you could ensure that an equal amount of force was required in both directions to overcome the stiction. I did speak to Lucas about this though and he said that one didn't need to be overly concerned about having the mount in perfect balance.  

[Zakalwe]

I guess it like many things in life. Get it in good balance but no need to get totally anal about it all.

[gnomus]

Jings.  That's borderline philosophical, Stephen.

[Zakalwe]

8 minutes ago, gnomus said:

Jings.  That's borderline philosophical, Stephen.

Ah Grasshopper......

 

[gnomus]

I bow to my Sensei.

[kirkster501]

On 12/10/2016 at 18:07, gnomus said:

That is correct.

Why did you get rid Steve?  My FSQ is superb. You weren't happy with it then?

[gnomus]

11 minutes ago, kirkster501 said:

Why did you get rid Steve?  My FSQ is superb. You weren't happy with it then?

Not happy with my version of the scope.  Not happy with the retailer.  Not happy with the European importer/distributor.  I got rid of my Takahashi, and I would never have another one.  Jings, I knew you were going to get me into trouble with this one Steve.  

If you have time, you can read the full story here - https://stargazerslounge.com/topic/255860-ovoids-with-mesu-and-tak-fsq-85/

Steve

[steppenwolf]

Quote

Steve (gnomus) you sent your FSQ85 back? Did I read that correctly?

I sent mine back too - I also sent the replacement back . Steve (Gnomus) is not alone in having the 'dream' shattered! The big difference between the two of us is that my dealer was fully supportive and deserves much credit for the support he gave, whereas Steve (Gnomus) was not so fortunate!

[kirkster501]

So the two Steve's (from another Steve) what was so wrong with them?  I got mine in October 2013.  Wonder if it was a bad batch problem with yours?  The only slight issue with mine has been focuser slip that I corrected easily enough.

[gnomus]

15 hours ago, kirkster501 said:

So the two Steve's (from another Steve) what was so wrong with them?  I got mine in October 2013.  Wonder if it was a bad batch problem with yours?  The only slight issue with mine has been focuser slip that I corrected easily enough.

We are hijacking Stephen's thread somewhat.  I don't know if it was a 'bad batch' or not - a quick search reveals that Steppenwolf got his FSQ85 around 2013 - I got mine in 2015.  That would be a pretty big batch.  Now that I have been 'bitten', I keep noticing the odd post here and elsewhere about people having similar problems with their FSQ 85s (and one or two with their 106s).   I am severely hampered by a lack of knowledge - bet hey - this is the Internet   I do wonder about these multi-lens 'astrographs', though.  The issues with the WO Star 71 Mk I are well known and this scope was eventually discontinued.  Were there not also problems with the 5-element Skywatcher Esprit 100?      

[ollypenrice]

Re Mesu balance, all we've ever done with ours is push it both ways against the friction of the drives (which can't be released) and guesstimate it. It's had an assortment of heavy rigs on it (14 inch, Twin Tak, 10 inch SCT) and this has always been adequate.  It may be possible within the SiTech config to measure the current draw, which is the usual way of balancing non-releasable mounts. Failing that, could it be measured using some kind of inline metre? I know nothing about electricity!

I think that power supply or hub are likely to be cause of the jumps, though a bad connection anywhere in the power supply, including within the mount, might lie behind this. Best of luck.

Olly

[gnomus]

Olly

Are you using PHD these days?  Like Stephen, I have noticed that, whilst I get good guiding, in the 'TARGET' window the blue dots centre around a spot slightly right of the bullseye.  I get round stars, but I wonder if I need to change my Tick settings too.

Steve

[swag72]

8 minutes ago, gnomus said:

Olly

Are you using PHD these days?  Like Stephen, I have noticed that, whilst I get good guiding, in the 'TARGET' window the blue dots centre around a spot slightly right of the bullseye.  I get round stars, but I wonder if I need to change my Tick settings too.

Steve

Your stars are round Steve .......... Isn't that enough?

I too get guiding in different parts of the bullseye depending on where the target is ..... it can start off to the right and by the end of the night it can be bang in the middle...... I used to let this bother me.... Now I couldn't care two hoots  

[gnomus]

16 minutes ago, swag72 said:

Your stars are round Steve .......... Isn't that enough?

I too get guiding in different parts of the bullseye depending on where the target is ..... it can start off to the right and by the end of the night it can be bang in the middle...... I used to let this bother me.... Now I couldn't care two hoots  

You are no doubt quite right.  How much do I owe you for this counselling session?  

[Zakalwe]

On 16/10/2016 at 08:43, swag72 said:

Your stars are round Steve .......... Isn't that enough?

I too get guiding in different parts of the bullseye depending on where the target is ..... it can start off to the right and by the end of the night it can be bang in the middle...... I used to let this bother me.... Now I couldn't care two hoots  

^^This^^

I couldn't care less about the guide graph as long as the stars are round and sharp (within the limits of my crummy atmospherics). I've seen people chasing the flattest possible graph, but I'm not bothered about that as long as the product of that graph is good. In my case, it wasn't and to be honest, it knocked my enjoyment, especially after spending the thick end of £5K on a mount that performed worse than my EQ8. Altering the tick setting has improved it a lot* and I now need to test it for longer to see if the "jumping" has been cured. Over the weekend I installed another PSU just for the mount and I'll see how that goes. The next step will be to run the mount directly back to the PC rather than through the USB hub.

 

 

*Using PHD2's Guiding Assistant made it pretty easy to calculate out the problem, once I worked out the maths behind it. I've now got a simple spreadsheet that calculates the necessary change.

[Zakalwe]

On 12/10/2016 at 20:46, Thalestris24 said:

Hi

I've stacked subs from my cooled 12-bit Minicam5s but I'd say the result is not as good as 14-bit subs from a Canon 550d and I would imagine 16-bit would be even better. But 12-bit might be good enough!

Louise

Have a read of this thread:

http://www.cloudynights.com/topic/553142-zwo-asi1600mm-cool-performance-stats/#entry7479621

Quote

I have always been one that criticized this camera's 12 bit ADC but today I decided to (hopefully) put my worries to rest so I did some analysis comparing the high dynamic range mode and the unity gain mode. I can confidently say I am not worried anymore. I measured a dynamic range of 5700:1 dynamic range in HDR mode and much lower (expectedly) in unity gain mode. These data can be seen attached from Pixinsight. To compare, my KAF-1301E measured a dynamic range of 6999:1 dynamic range using the exact same method and my KAF-8300 measured a disappointingly low 2800:1 dynamic range. The full well of 20ke- noted in their literature was pretty spot on. I still dislike the ADC chosen but from their point of view I can see why. Of course the dynamic range of 5700:1 calls into the fact that it's a 12 bit ADC and is limited to 4095:1 which is a bummer to me.. but still much higher than the KAF-8300. Even the perfect electronics of the QSI 683 quote a 3160:1 dynamic range (my chip had 12e- of read noise rather than the 8e- in the documents from QSI).