Is it the guiding or hardware issue?

[souls33k3r]

Hi All,

I hope you're all well. 

Am imaging at the moment using my E6 mount with EdgeHD 8 scope and spent the last 2hrs tweaking PHD2 with a friend to get the numbers reasonably acceptable (1.10" is the best i could achieve) but what's really troubling me is the star shapes are elongated in one frame and are fine in the next. So basically one good frame and then 2 bad frames with elongation. Some times the elongation occurs in up/down direction, some times it's in sideways director and some times it's in 11 o'clock/4 o'clock.

Scope is properly balanced.

Would appreciate any input and help with this. 

Thanks in advance

[Davey-T]

Backlash ?

Dave

[souls33k3r]

Good shout mate.

I did run guiding assistant at the beginning of the session which calculated the backlash compensation but because i'm using "Resist Switch" in DEC and "Hysteresis" in RA, that value only got applied to DEC.

Can i use resist switch in both DEC and RA? what's your suggestion?

[Thalestris24]

Hi

If you monitor your guide graph with corrections showing that should give you an idea as to how much your guide scope is 'wandering' around. But you're imaging at a long focal length so that effect will be amplified. What RA Osc figure did PHD report? You want that tending towards 0.5 for round stars. What did the guide assistant say re RA and DEC movements? I'd have thought you might need an oag with the EdgeHD? I've no experience with them I'm afraid!

Louise

[souls33k3r]

Hi Louise, thank you for your input. I agree, longer focal length is an issue but my frustration is that stars are fine in one frame and then the next 2 frames they're elongated. I know i have collimation issues as well but that does not explain why i'm seeing what i'm seeing.

The RA OSC at the moment is showing 54 to 0.57. The Guiding Assistant just s0.uggested some MinMo values which i applied and then also added some numbers to backlash but in DEC only because i'm using Resist Switch in Dec.

[Davey-T]

Is your EQ6 belt drive ? if not a bit of imbalance won't go amiss.

Likewise perfect PA may not be a good thing, if you imagine stars rising in the east and travelling up to the meridian in a curve which the scope is trying to follow if the stars go below the mount track and then above the mount tracking due to mechanical errors it will keep switching north / south in dec, you can fiddle with it so it only needs guiding north to eliminate dec backlash.

Ra elongation is more likely to be PHD settings as AKAIK PHD doesn't drive the mount back in an easterly direction but just pauses the drive until the stars catch up so eliminating backlash but this may have altered in PHD2.

I guess using the Edge it's more critical, I run my 10"SCT with PHD1 but it's wedge / fork mounted so a bit different mechanically guidewise.

Dave

 

 

[Thalestris24]

Hi

I think the backlash setting only applies to DEC. You usually compensate RA backlash by unbalancing slightly - ie east heavy. Unless you have a belt mod? In which case backlash isn't an issue in either DEC or RA but you need perfect balance instead. Also seeing conditions may be putting a limit on your guiding though it sounds like your guiding error is very small.

Good luck

Louise

ps what is your phd2 target like? Can you snip the screen and post it?

[souls33k3r]

Yes it is an EQ6 and no it's not belt modded but i agree being at this FL it is indeed a big task getting round stars.

I'll go out and make the mount a bit east heavy and see if that improves it a bit.

[souls33k3r]

Here's a snippet of my guide graph

[Davey-T]

Looks like it's sending a big pulse in dec that doesn't have a big effect so may be backlash.

You can turn off guiding and see on the PHD screen which way the mount drifts on it's own, it helps to have the guide camera lined up so north is straight up on the screen.

If your sky is anything like mine ATM you may as well use it to sort the guiding for a good night, Moons rising as well now

Dave

[Thalestris24]

Hi

That looks pretty good to me! But the target could be better, probably, though it might be the seeing that's causing the scatter, else flex with the guidescope. Has the east heavy adjustment helped? TBH if it were my setup, I'd probably go for a longer focal length guidescope and make sure it's bolted down rigid. Perhaps an oag would be best though they can have their own problems. I have a Celestron Travelscope 70 mounted on my 800mm APO. I probably don't need that focal length (400mm) but I decided to try it (with a qhyl-ii) and it seems to work quite well for me. The Travelscope is quite light  The guiding assistant will give you info about how the seeing or other external factor e.g. wind might be affecting the performance of the setup.

Louise

[Thalestris24]

Yeah, those DEC correction spikes look a little odd... If they were actual corrections I'd have thought you'd see a corresponding deflection in the DEC trace but there's nothing there! If there was something that needed correction then the corrections would repeat until stability was achieved. Hmm.. I'm wondering if they might be some sort of artefact or electrical noise or something mysterious? Maybe somebody else will know. Would certainly be worth looking in the logs later.

Louise

[souls33k3r]

4 minutes ago, Davey-T said:

Looks like it's sending a big pulse in dec that doesn't have a big effect so may be backlash.

You can turn off guiding and see on the PHD screen which way the mount drifts on it's own, it helps to have the guide camera lined up so north is straight up on the screen.

If your sky is anything like mine ATM you may as well use it to sort the guiding for a good night, Moons rising as well now

Dave

Funnily enough, it's the RA that drifts and DEC behaves.

I might be wrong but it's south that is straight up on the screen as the image is inverted. 

I'm just trying to finish this on going project so can't really tinker with not imaging so i'll try to adjust anything on the fly.

6 minutes ago, Thalestris24 said:

Hi

That looks pretty good to me! But the target could be better, probably, though it might be the seeing that's causing the scatter, else flex with the guidescope. Has the east heavy adjustment helped? TBH if it were my setup, I'd probably go for a longer focal length guidescope and make sure it's bolted down rigid. Perhaps an oag would be best though they can have their own problems. I have a Celestron Travelscope 70 mounted on my 800mm APO. I probably don't need that focal length (400mm) but I decided to try it (with a qhyl-ii) and it seems to work quite well for me. The Travelscope is quite light  The guiding assistant will give you info about how the seeing or other external factor e.g. wind might be affecting the performance of the setup.

Louise

There's certainly no flex in the guidescope, believe me i've checked and the very first thing that i did tonight.

I haven't done the mount east heavy yet as the target is due to pass the meridian at 1am so once done i will do just that.

I know i'm asking for a slap on my wrists here but i have a Qhy Mini guidescope  with QHY5L-ii (mono).

 

[souls33k3r]

2 minutes ago, Thalestris24 said:

Yeah, those DEC correction spikes look a little odd... If they were actual corrections I'd have thought you'd see a corresponding deflection in the DEC trace but there's nothing there! If there was something that needed correction then the corrections would repeat until stability was achieved. Hmm.. I'm wondering if they might be some sort of artefact or electrical noise or something mysterious? Maybe somebody else will know. Would certainly be worth looking in the logs later.

Louise

I've just lowered the DEC aggressions and will see how this behaves.

Oh meridian flip is happening so going to head out and make the mount east heavy

[Davey-T]

1 minute ago, souls33k3r said:

I might be wrong but it's south that is straight up on the screen as the image is inverted. 

Just rotate the guide camera, saves confusion of the brain 

I've used all sorts to guide mine f/l 2500mm from the finder converted, 100mm f/6, 80mm f/9 and OAG it doesn't affect it greatly in PHD.

Dave

 

[souls33k3r]

1 minute ago, Davey-T said:

Just rotate the guide camera, saves confusion of the brain 

I've used all sorts to guide mine f/l 2500mm from the finder converted, 100mm f/6, 80mm f/9 and OAG it doesn't affect it greatly in PHD.

Dave

 

Hahahaha can't see jack at night so will do that during the day time

I'm contemplating converting my  9 x 50 finderscope to a guidescope for this scope and see if that helps.

Oh and i've just made the scope east heavy so let's see

[Davey-T]

Just now, souls33k3r said:

I'm contemplating converting my  9 x 50 finderscope to a guidescope for this scope and see if that helps.

Converted the Meade finder had to saw a bit off the end.

Dave

[Thalestris24]

Just now, souls33k3r said:

Hahahaha can't see jack at night so will do that during the day time

I'm contemplating converting my  9 x 50 finderscope to a guidescope for this scope and see if that helps.

Oh and i've just made the scope east heavy so let's see

Yeah, the qhy miniguider is only 130mm so you might be asking a lot of it to guide a 2032mm scope! However, it seems to be doing surprisingly well!

[souls33k3r]

4 minutes ago, Davey-T said:

Converted the Meade finder had to saw a bit off the end.

Dave

Thank GOD i don't have to do anything like that to mine, the end bit simply screws off. I'll just need to find the correct attachment for it to house the QHY5LL-ii camera.

2 minutes ago, Thalestris24 said:

Yeah, the qhy miniguider is only 130mm so you might be asking a lot of it to guide a 2032mm scope! However, it seems to be doing surprisingly well!

Yeah it's a tiny little thing but has done well for me so far. It's perfect for my Star 71 but i guess not so much for my 1422 FL scope. I'm wondering if my pixel scale in SGP has got anything to do with it?

[souls33k3r]

Made no difference making the mount easy heavy. Maybe i didn't do much. Guide graph still showing those spikes in DEC but this time the DEC line does wander off but comes back

Also i just checked the EdgeHD whitepaper and it shows that the FL of this scope at native F/10 is 2125 and not 2032 that we've all come to know ? so by introducing the 0.7x reducer, the FL of the scope becomes 1487.5 and not 1422. 

[Thalestris24]

14 minutes ago, souls33k3r said:

Thank GOD i don't have to do anything like that to mine, the end bit simply screws off. I'll just need to find the correct attachment for it to house the QHY5LL-ii camera.

Yeah it's a tiny little thing but has done well for me so far. It's perfect for my Star 71 but i guess not so much for my 1422 FL scope. I'm wondering if my pixel scale in SGP has got anything to do with it?

Hi

I don't know SGP... Less than an arc sec/pixel is probably not going to be achieved here in the uk. I think that just means your images wouldn't be super sharp. Using a reducer will help a lot. I think the ASI has quite small pixels? You could plug all the scope/camera data into 12DString to calculate your pixel scale.

Off to bed now. Night night, astro world!

Louise

[souls33k3r]

Also one thing i just noticed. My image keeps on shifting up and up from frame to frame. I wonder it's the balance that's causing the elongated stars? It's like the scope moved up during the exposure causing elongated stars and then in between when it settles for a frame, i get nice round stars (not perfect but not elongated of course)

[souls33k3r]

1 minute ago, Thalestris24 said:

Hi

I don't know SGP... Less than an arc sec/pixel is probably not going to be achieved here in the uk. I think that just means your images wouldn't be super sharp. Using a reducer will help a lot. I think the ASI has quite small pixels? You could plug all the scope/camera data into 12DString to calculate your pixel scale.

Off to bed now. Night night, astro world!

Louise

Yeah i found the pixel scale from astronomy.tools.

Thank you for all your help Louise. 

Good night and sleep well

[Thalestris24]

3 minutes ago, souls33k3r said:

Also one thing i just noticed. My image keeps on shifting up and up from frame to frame. I wonder it's the balance that's causing the elongated stars? It's like the scope moved up during the exposure causing elongated stars and then in between when it settles for a frame, i get nice round stars (not perfect but not elongated of course)

I did see you have dithering on but it doesn't seem to be causing a noticeable shift in the dec trace? However, it's PHD that's dithering the guide scope so that will be amplified by your long focal length and small imaging pixels. Try turning it off and see how that affects things.

Going now!

Louise

 

[souls33k3r]

2 minutes ago, Thalestris24 said:

I did see you have dithering on but it doesn't seem to be causing a noticeable shift in the dec trace? However, it's PHD that's dithering the guide scope so that will be amplified by your long focal length and small imaging pixels. Try turning it off and see how that affects things.

Going now!

Louise

 

Yes i do have dither on but it's small dither and every 4 frames. I have turned that option off now so will monitor.

Go go go go go!