Is it the guiding or hardware issue?

[souls33k3r]

Ok so that didn't change anything. My subs are still shifting upwards even after the meridian flip so i think it could be down to the balance but that's just me thinking it out loud.

[MarsG76]

I definitely balanced, First I'd make it slightly east heavy, than look into periodic error caused by backlash.... if all those are good the next suspect I'd look into is mirror flop... try guiding using either more FL or a OAG. 

[Davey-T]

8 hours ago, souls33k3r said:

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. 

Bear in mind that the actual focal length alters when you move the mirror to focus, plate solving may give a more accurate estimate.

Dave

[souls33k3r]

1 hour ago, Davey-T said:

Bear in mind that the actual focal length alters when you move the mirror to focus, plate solving may give a more accurate estimate.

Dave

Makes sense. It's just that i noticed the value show in SGP (Telescope tab) so thought that might help.

I still do wonder what could be causing my image to shift down (the stars were moving upwards) which is why i think i was seeing elongated stars. My hunch is still on the balance or something but i know for a fact that the balance was good.

8 hours ago, MarsG76 said:

I definitely balanced, First I'd make it slightly east heavy, than look into periodic error caused by backlash.... if all those are good the next suspect I'd look into is mirror flop... try guiding using either more FL or a OAG. 

I did make the mount east heavy but that didn't help the cause. Pardon my ignorance but how do i measure PE caused by backlash? Mirror flop is potential but from what i've read, the mirror isn't crazy heavy on the 8" version to have a significant flop or be it any flop. It's only the 9.25, 11 & the 14 version which has more of that issue. Unfortunately i've thrown enough money at this hobby already so longer FL guidescope or an OAG is a bit out of the question but if i have to go for something, i'd try an OAG but only when i have a permanent setup because i wouldn't want to waste a clear night or two trying to figure the OAG out (granted i can bring it to focus during the day time) 

[wornish]

Do the stars elongate randomly in opposite directions or is it a repeating pattern?

[souls33k3r]

24 minutes ago, wornish said:

Do the stars elongate randomly in opposite directions or is it a repeating pattern?

They're always elongating in the way the image moves. The image moved up, very rarely 12 o'clock (maybe a sub or two) but mostly moving from 7 o'clock to 1 o'clock position

[MarsG76]

2 hours ago, souls33k3r said:

Pardon my ignorance but how do i measure PE caused by backlash?

If all of you stars elongate in one direction, the RA direction than it's most likley PE. if your star elongation has an arc when you stack all of your subs without aligning the stars than its most likely mirror flop.

I had issues with using a guide scope when imaging at 1280 and 2023 mm FL, the only thing that has given me reliable long exposure subs (1800+ seconds) was a OAG... OAG will guide on the imaged light path, and correct for any mirror flop and negate and flexture.... and do it all at the same focal length being imaged.

Really the only thing that can ruin a sub with a OAG is when PA is too far off and you have radial blur due to field rotation in a long exposure sub.

[Tommohawk]

Just a thought - I had some similar problems with my HEQ5 if the clutches were overtightened. Quite likely nothing to do with it though!

[souls33k3r]

21 hours ago, MarsG76 said:

If all of you stars elongate in one direction, the RA direction than it's most likley PE. if your star elongation has an arc when you stack all of your subs without aligning the stars than its most likely mirror flop.

I had issues with using a guide scope when imaging at 1280 and 2023 mm FL, the only thing that has given me reliable long exposure subs (1800+ seconds) was a OAG... OAG will guide on the imaged light path, and correct for any mirror flop and negate and flexture.... and do it all at the same focal length being imaged.

Really the only thing that can ruin a sub with a OAG is when PA is too far off and you have radial blur due to field rotation in a long exposure sub.

I haven't stacked the subs yet so can not confirm but visually they're all elongating in one direction. Like the image is shifting up and this i noticed happens if not on every frame but every other frame. Some of the frames are fine with nice round stars but where the image shifts (like the stars are moving in 2 o'clock direction which is where i think the scope is being pulled downwards), that's where i notice the elongated stars.

OAG might sound like a thing i might have to give it a go but at the cost of experimenting? i'm not sure. I'll check if someone has one who can lend me for a few days so that i can test and verify it works before taking the plunge.

14 hours ago, Tommohawk said:

Just a thought - I had some similar problems with my HEQ5 if the clutches were overtightened. Quite likely nothing to do with it though!

Good shout. The clutches weren't over tightened. 

[Thalestris24]

Hi

There is a useful page here which gives a reasonable way of calculating the fl of a guidescope.

Louise

[souls33k3r]

18 minutes ago, Thalestris24 said:

Hi

There is a useful page here which gives a reasonable way of calculating the fl of a guidescope.

Louise

Cheers Louise, i did go through that when i bought my guidescope. Bernard at Modern Astronomy had that linked to the guidescope page if i remember correctly. He did test this guidescope with his 11"SCT and said that he's done 10min guided exposures (maybe ambitious) but i was happy at 3 - 5 min per subs.

[MarsG76]

2 hours ago, souls33k3r said:

I haven't stacked the subs yet so can not confirm but visually they're all elongating in one direction. Like the image is shifting up and this i noticed happens if not on every frame but every other frame. Some of the frames are fine with nice round stars but where the image shifts (like the stars are moving in 2 o'clock direction which is where i think the scope is being pulled downwards), that's where i notice the elongated stars.

OAG might sound like a thing i might have to give it a go but at the cost of experimenting? i'm not sure. I'll check if someone has one who can lend me for a few days so that i can test and verify it works before taking the plunge.

It does sound like PE... I had a similar issue... every so often I had a good sub, but more bad than good, and always repetitive.

When your mount tracks, there is a certain about of time before all of the gears return to exactly the same position... my CGEM single cycle worked at around 8.5 minutes per cycle, meaning that if I did 2 minute subs, I should expect to get a repetition of a bit more than 4 subs... I say around because the CGEM has a 8:3 gear ration, so it real PE is about every 50 minutes...

This is of course unguided.. when you're autoguiding, the guider should correct for most if not all of the PE... but things are always not so simple... for example if you're imaging at 2000mm FL and guiding on 300mm guide scope, than the PE might not be picked up quickly enough, or at all... another issue is that if your polar alignment if slightly out and your guide scope is guiding on a star too far away from the object, than you could also be introducing field rotation.... this of course would not give you a good sub among bad ones, they all would be bad.

OAG doesn't seem like it'll be just an experiment here... the OAG not only fixed my guiding issue to the point that when there is no interference by clouds or environmental factors (or technical factors like computer crashes), I generally end up with 100% good subs and there are times I'll expose for 30 minutes per sub.

The OAG is a little trickier to find a guide star, especially if you're imaging at a high focal length, but when weighing up all of the factors, the OAG has been a very valuable utility to improve my Astrophotography to many levels above to what I was creating before using it.

[souls33k3r]

28 minutes ago, MarsG76 said:

It does sound like PE... I had a similar issue... every so often I had a good sub, but more bad than good, and always repetitive.

When your mount tracks, there is a certain about of time before all of the gears return to exactly the same position... my CGEM single cycle worked at around 8.5 minutes per cycle, meaning that if I did 2 minute subs, I should expect to get a repetition of a bit more than 4 subs... I say around because the CGEM has a 8:3 gear ration, so it real PE is about every 50 minutes...

This is of course unguided.. when you're autoguiding, the guider should correct for most if not all of the PE... but things are always not so simple... for example if you're imaging at 2000mm FL and guiding on 300mm guide scope, than the PE might not be picked up quickly enough, or at all... another issue is that if your polar alignment if slightly out and your guide scope is guiding on a star too far away from the object, than you could also be introducing field rotation.... this of course would not give you a good sub among bad ones, they all would be bad.

OAG doesn't seem like it'll be just an experiment here... the OAG not only fixed my guiding issue to the point that when there is no interference by clouds or environmental factors (or technical factors like computer crashes), I generally end up with 100% good subs and there are times I'll expose for 30 minutes per sub.

The OAG is a little trickier to find a guide star, especially if you're imaging at a high focal length, but when weighing up all of the factors, the OAG has been a very valuable utility to improve my Astrophotography to many levels above to what I was creating before using it.

Cheers @MarsG76, i'm getting the feeling that i might have to go down the OAG route but i'm saving up for an autofocuser at the moment so OAG will have to take a back seat. Plus it's not my main scope this EdgeHD 8" so should i suck it up and live with these eggy stars or actually do something about it, even though it's annoying the hell out of me. 

I'm checking if i can borrow one for a few days to test it out to figure that my issue is completely gone with using one then i'll go for it. It's a bit of money to be experimenting with at the moment.

[Thalestris24]

2 hours ago, souls33k3r said:

Cheers Louise, i did go through that when i bought my guidescope. Bernard at Modern Astronomy had that linked to the guidescope page if i remember correctly. He did test this guidescope with his 11"SCT and said that he's done 10min guided exposures (maybe ambitious) but i was happy at 3 - 5 min per subs.

Hi

It obviously all depends on the figures you plug in when calculating, plus how good your mount is. The imaging scope at 1422mm will give you a theoretical arc secs/pixel of 0.55 but you're never going to get that, I don't think. If you aim for 1" (I wouldn't get that here in Glasgow, lol, but your mileage may vary) and assume a centroid accuracy of 0.2 then you'd need a 156mm focal length guidescope. But at 0.1 centroid accuracy that halves to a mere 78mm. I think you probably have to throw the theory out and experiment and do your best to eliminate any sources of flexure. I know the qhy mini guidescope comes equipped with a finder foot but using a finder shoe for a guidescope is generally not recommended. If you are using the finder shoe then I think I'd try securing the miniguider by some other means and see if things improve (I think it has a thread in the base which could be used to bolt it in place and that might be better if it can be held tight - maybe you're actually already doing that?)

Good luck!

Louise

[souls33k3r]

1 hour ago, Thalestris24 said:

Hi

It obviously all depends on the figures you plug in when calculating, plus how good your mount is. The imaging scope at 1422mm will give you a theoretical arc secs/pixel of 0.55 but you're never going to get that, I don't think. If you aim for 1" (I wouldn't get that here in Glasgow, lol, but your mileage may vary) and assume a centroid accuracy of 0.2 then you'd need a 156mm focal length guidescope. But at 0.1 centroid accuracy that halves to a mere 78mm. I think you probably have to throw the theory out and experiment and do your best to eliminate any sources of flexure. I know the qhy mini guidescope comes equipped with a finder foot but using a finder shoe for a guidescope is generally not recommended. If you are using the finder shoe then I think I'd try securing the miniguider by some other means and see if things improve (I think it has a thread in the base which could be used to bolt it in place and that might be better if it can be held tight - maybe you're actually already doing that?)

Good luck!

Louise

Hi Louise, you're absolutely right. I might be fighting a losing battle here with the miniguidescope but given the link, it does seem that going by the old wisdom of 1/3rd of the FL should be your guidescope was an old school of thought and that this little thing would perform. Maybe it's a combination of a few things like you mentioned which i'm really struggling to figure it out.
Yes the guidescope as you rightly mentioned does have the thread in the base and that's exactly how i'm bolting it down so no flexture is present.
I checked with a few friends and one of them who i'm meeting tomorrow for drinks after work anyway has a Orion thin OAG which he's happy for me to borrow and test this OAG theory out. I'm hoping this works and if it does, i'm buying one straight away. Let's see how this goes.
Now going to have to figure out the spacing.

[Thalestris24]

1 hour ago, souls33k3r said:

Hi Louise, you're absolutely right. I might be fighting a losing battle here with the miniguidescope but given the link, it does seem that going by the old wisdom of 1/3rd of the FL should be your guidescope was an old school of thought and that this little thing would perform. Maybe it's a combination of a few things like you mentioned which i'm really struggling to figure it out.
Yes the guidescope as you rightly mentioned does have the thread in the base and that's exactly how i'm bolting it down so no flexture is present.
I checked with a few friends and one of them who i'm meeting tomorrow for drinks after work anyway has a Orion thin OAG which he's happy for me to borrow and test this OAG theory out. I'm hoping this works and if it does, i'm buying one straight away. Let's see how this goes.
Now going to have to figure out the spacing.

Good good! As I say, I've no experience of imaging with an sct and my general imaging experience is limited. I've just been using simple logic with a wee bit of wisdom . Maybe there's somebody else, on here or elsewhere who is using your combo of mount/scope/camera/guider, or something similar. I'm sure there must be! So it would be good to hear from someone else who has successfully guided an EdgeHD with reducer and short focal length guider.

Louise

[souls33k3r]

54 minutes ago, Thalestris24 said:

Good good! As I say, I've no experience of imaging with an sct and my general imaging experience is limited. I've just been using simple logic with a wee bit of wisdom . Maybe there's somebody else, on here or elsewhere who is using your combo of mount/scope/camera/guider, or something similar. I'm sure there must be! So it would be good to hear from someone else who has successfully guided an EdgeHD with reducer and short focal length guider.

Louise

Any help is much appreciated and your Louise have helped me loads here as did others so I can't thank you enough

I'd most certainly love to hear other people's views as you said but it can be any SCT with small guidescope. 

[Davey-T]

My 10"SCT guided fine with converted finder, did 10 minutes easily, could do 30 minutes with OAG if the skies were up to it.

Mind I'm not obsessed with perfectly round stars like some people ( no names no pack drill ) 

Dave 

[RayD]

5 hours ago, souls33k3r said:

Cheers @MarsG76, i'm getting the feeling that i might have to go down the OAG route but i'm saving up for an autofocuser at the moment so OAG will have to take a back seat. Plus it's not my main scope this EdgeHD 8" so should i suck it up and live with these eggy stars or actually do something about it, even though it's annoying the hell out of me. 

I'm checking if i can borrow one for a few days to test it out to figure that my issue is completely gone with using one then i'll go for it. It's a bit of money to be experimenting with at the moment.

I've got a SX filter wheel with OAG and GP Cam you can borrow to test, mate.

[souls33k3r]

3 hours ago, Davey-T said:

My 10"SCT guided fine with converted finder, did 10 minutes easily, could do 30 minutes with OAG if the skies were up to it.

Mind I'm not obsessed with perfectly round stars like some people ( no names no pack drill ) 

Dave 

Well I'm not super obsessed either but round'ish is all what I need.

The finder guider you mentioned, which one was it? I have the El Cheapo Celestron one that comes as part of the EdgeHD kit. 

Got a sub to show mate? 

3 hours ago, RayD said:

I've got a SX filter wheel with OAG and GP Cam you can borrow to test, mate.

Ah cheers mate, you're top man you are. Appreciate the offer and you know you've already helped me loads mate ? (I've lost the count the number of times you have plucked me out of tricky situations for which I'll forever be grateful) but I've already sourced the OAG from someone else who I'm meeting tomorrow for some social drinks after work. 

[Davey-T]

16 minutes ago, souls33k3r said:

The finder guider you mentioned, which one was it? I have the El Cheapo Celestron one that comes as part of the EdgeHD kit. 

Got a sub to show mate? 

Well I'm not super obsessed either but round'ish is all what I need. What right into the corners ?

The Meade finder that came with it butchered a bit 

Subs are on the obs'y laptop, I'll dig some out tomorrow.

Dave

Your problem sounds more mechanical to me, I thought the Edge had 2 clutches to eliminate mirror flop ?

[souls33k3r]

1 minute ago, Davey-T said:

Well I'm not super obsessed either but round'ish is all what I need. What right into the corners ?

The Meade finder that came with it butchered a bit 

Subs are on the obs'y laptop, I'll dig some out tomorrow.

Dave

Got an EdgeHD so I do expect round stars in corners too

No worries mate, whenever it's easy for you ?