Why are guiding errors only showing with Esprit80?

[Sp@ce_d]

Not sure if it's a case of "wood for the trees" here.. Can someone help me understand whats going on and confirm I am on the right track looking at guiding errors causing this.. or is this flexure ?? 

I've been at this for a couple of weeks now.. well since I got the Esprit 80. I normally image with a 2 or 3 scope setup & use a finder guider. ( I have also been testing out an OAG but had same results as set out below)

I've been trying to introduce the Esprit into the setup but no matter where I place it in the side by side ( + 1 in centre) setup, it always shows eggy stars. Whereas the other scopes do not? If I run it on its own it seems ok. I'm probably pushing the mount I admit but why don't any of the other scopes show this as well? I've had the rigg apart several times & rechecked tightness, balance & signs of flexure. (I must have spent 7 or 8 hours rebuilding it all again today)

Here's a run from tonight.. all at the same time.. well, staggered by a few seconds so as not to saturate the bus at download times.

Tonight's test configuration is: 80ED -- Esprit 80 -- ZS71 (ie. Esprit in center of bar)

15 Mins - Ha subs. A quick DDP stretch in Neb.

------------- ED80 ---------------

------------- Esprit 80 ---------------

------------- ZS71 ---------------

[swag72]

Do you have an original fit that we can look at? The jpeg is tricky to get much from to be honest.

I would be checking flexure and spacing as a starting point.

[Sp@ce_d]

Do you have an original fit that we can look at? The jpeg is tricky to get much from to be honest.

I would be checking flexure and spacing as a starting point.

I dont have access to last nights .fits right now, I'll stick them on Dropbox when I get home tonight. I do have one from Sat night though. I've had everything apart since then but it shows similar drift.

900s OIII. Scope position was on the outside of the bar with finder/guider attached to Esprit as opposed to the 80ED on last nights examples.

https://dl.dropboxusercontent.com/u/32747771/Rosette_ES80_23-11-13_314L_033_OIII.fit

[Gina]

I agree with Sara, I can't see anything wrong from these JPEGs.  Just downloaded that FITS and had a good look at the image by zooming right in in Ps and I can't see anything wrong with the stars

[Sp@ce_d]

I agree with Sara, I can't see anything wrong from these JPEGs.  Just downloaded that FITS and had a good look at the image by zooming right in in Ps and I can't see anything wrong with the stars

  I wouldn't be surprised if I was seeing things Gina, wouldn't be the first time...  but to my tired 'ol eyes that .fits has elongated stars from bottom left to right top.

I normally use Nebulosity's preview feature to check though my subs first.. come to think of it I haven't checked these in anything else yet though.

[Gina]

  I wouldn't be surprised if I was seeing things Gina, wouldn't be the first time...  but to my tired 'ol eyes that .fits has elongated stars from bottom left to right top.

I normally use Nebulosity's preview feature to check though my subs first.. come to think of it I haven't checked these in anything else yet though.

Ah - that's different.  I can see slight elongation in the corners - that's not guiding problems, it's field curvature.  Assuming you're using the flattener (or it would be lots worse) your camera sensor is slightly too far from the flattener.  I haven't got enough experience to say how much but I suspect it might be only a fraction of a millimetre - it's very critical with these shorter focal length scopes.  I read a very useful post/link that pointed out that radial elongation means too close and circular means too far away (as I recall).

[Sp@ce_d]

Ah - that's different.  I can see slight elongation in the corners - that's not guiding problems, it's field curvature.  Assuming you're using the flattener (or it would be lots worse) your camera sensor is slightly too far from the flattener.  I haven't got enough experience to say how much but I suspect it might be only a fraction of a millimetre - it's very critical with these shorter focal length scopes.  I read a very useful post/link that pointed out that radial elongation means too close and circular means too far away (as I recall).

Hmm.. I have been checking the spacing with the digital callipers but I wouldn't expect it to show right across the sensor like this. Incidentally, both my WO scopes are faster & a lot more tolerant with the 314L+'s. I haven't had a problem. I saw that thread, here.. 

http://stargazerslounge.com/topic/199452-flattener-reducer/?p=2107104

if i recall elongation is too close but this appears worse at the edges and to my eyes this is even right across only bottom left to top right? I guess I can pull the flattener off and test this without anyway to eliminate.

[swag72]

I quickly stretched this one sub and had a look, and there does seem to be an elongation to my eye across the whole image, going from the bottom left to top right. Can you try it on the mount by itself?

[Sp@ce_d]

I quickly stretched this one sub and had a look, and there does seem to be an elongation to my eye across the whole image, going from the bottom left to top right. Can you try it on the mount by itself?

Thanks for taking the time to look Sara. Here's the links to the .fits from last night.

I've picked the same ones from each scope/camera combo so they were exposed at the same time & also had plenty of time for the guiding to settle down.

Esprit 80

https://dl.dropboxusercontent.com/u/32747771/NGC2175_ES80_24-11-13_002_Ha.fit

ZS71

https://dl.dropboxusercontent.com/u/32747771/NGC2175_ZS71_24-11-13_Ha_002.fit

80ED

https://dl.dropboxusercontent.com/u/32747771/NGC2175_ED80_24-11-13_Ha_002.fit

Not looking very good at the moment for getting a solo test run with the Esprit tonight.

The thing with last nights run is that the ED80 & ZS71 subs look ok to me, yet the Esprit (ES80) sub looks like trailing rather than anything else, which I would expect to show up on all the scopes on the mount if that were the case?

I've faffed about a bit with the configs over the last couple of weeks so I'm trying to remember exactly which configurations I've tried now. Whilst I'm waiting for clear skies I'll see if I can find some subs I did that looked ok & recheck them. I've a feeling I might not have done long enough subs with it solo for it to show up perhaps.

[lensman57]

Hi,

I guess the fast scope is showing itself up here.

Regards,

A.G

[Sp@ce_d]

Ok.. Here's one when the spacing wasn't correct. It shows the classic "warp speed" but the stars in the center are round to my eyes. Now this one was done with the Esprit & 80ED on the mount. It's also just a 300s L

https://dl.dropboxusercontent.com/u/32747771/M81-82_ES80_314L_09-11-13_006_L.fit

[Sp@ce_d]

Hi,

I guess the fast scope is showing itself up here.

Regards,

A.G

Hi

Yeah but the ZS71 is running at f4.7 even faster than the f5 of the Esprit. I've been running the 80ED (f6.3) ,ZS71 (f4.7) & ZS66 (f4.7) at the same time for ages with no problems... ??

Could it be spacing... on such a small chip as the 285?  It doesn't have the characteristic warp speed look now?

I'll admit I'm pushing the mount. To be honest I'm surprised I got away running the previous triple shooter setup. If it is the case I don't understand why the other two subs look so good?

[lensman57]

Hi

Yeah but the ZS71 is running at f4.7 even faster than the f5 of the Esprit. I've been running the 80ED (f6.3) ,ZS71 (f4.7) & ZS66 (f4.7) at the same time for ages with no problems... ??

Could it be spacing... on such a small chip as the 285?  It doesn't have the characteristic warp speed look now?

I'll admit I'm pushing the mount. To be honest I'm surprised I got away running the previous triple shooter setup. If it is the case I don't understand why the other two subs look so good?

If you have the spacing correct and the orthogonality is good then you might be over stretching the mount with 3 scopes hanging around. As an unrelated point, a few weeks back I  started having egg shaped stars even with a light ZS71, after having eliminated all probable causes I traced it to a loose RA axis on the mount HEQ5 that is only 3 months old, I had to take the cover off  tighten up all possible screws untill it got back to normal, now it is a lot better. Just a thought.

Regards,

A. G

[Sp@ce_d]

If you have the spacing correct and the orthogonality is good then you might be over stretching the mount with 3 scopes hanging around. As an unrelated point, a few weeks back I started having egg shaped stars even with a light ZS71, after having eliminated all probable causes I traced it to a loose RA axis on the mount HEQ5 that is only 3 months old, I had to take the cover off tighten up all possible screws untill it got back to normal, now it is a lot better. Just a thought.

Regards,

A. G

Yes, I spent yesterday pulling apart, going through checking for play & tightening, apart from stripping the mount internals down. The thing I don't get is if it is the mounting then it has to be local to the one scope otherwise surely all of them would show the errors?

Anyway, next step will be running the Esprit solo & checking that on long subs first.

Sent from my iPhone using Tapatalk

[lensman57]

Yes, I spent yesterday pulling apart, going through checking for play & tightening, apart from stripping the mount internals down. The thing I don't get is if it is the mounting then it has to be local to the one scope otherwise surely all of them would show the errors?

Anyway, next step will be running the Esprit solo & checking that on long subs first.

Sent from my iPhone using Tapatalk

Is this the only time that is happened with the Esprit?

A.G

[Sp@ce_d]

Is this the only time that is happened with the Esprit?

A.G

Not exactly. At first I tested with short subs & it looked ok, apart from needing to tweak the spacing. It seems to show up on longer subs (which is why I thought it was guiding related) & it doesn't matter whether it's in any of the 3 saddles I have on the side by side mount. (The fixings are all ADM)

The M81/82 sub a few posts above was done in a dual side by side config with the 80ED. Ok it shows spacing issues at the edges but center stars look ok. In fact there's a very quick & rough process at the end of this thread.. & stars look round in the center.. http://stargazerslounge.com/topic/199076-spce-d-s-esprit-80/?p=2100593

Now that's only 300s subs so not so taxing on guiding.

The Rosette sub (link up above) was it mounted in the right end position & the Monkey head from last night was in the center position, that ones a fixed saddle the outer 2 have the adjustable saddles.

So, it seems to be the same no matter where it's mounted but only on longer subs. Now if it's slippage then surely it should differ between subs & the focus should change?... it doesn't. Also, if it is movement of some sort it has to be on the scope itself as surely the other 2 scopes I now have mounted at the sides would show trailing stars too!!

The next chance I get, I'll fire off some short & long subs to have a closer look at before I touch anything. If it is the focal plane or flattener distance, sub length should make no difference.  I'll then need to check if it differs pointing at the horizon & overhead I think.

[Sp@ce_d]

Right, got some time on it last night. I removed the other 2 scopes, didn't touch the Esprit apart from balancing & ran 5 mins & 15mins on the same target. They look fine!

So, think I'll put it back together & see if it's consistent and trails again. Maybe cone error is playing a part in this?

[ollypenrice]

You mention a multi scope rig. These can be very difficult. All sorts of tricky geometric effects come into play and I don't pretend to understand them all but I do have some experience of them. Using a long focal length parallel rig with a colleague we had one scope giving good results and one trailing. We didn't suspect flexure. We felt that the effect was geometric in origin.

The first thing I'd do would be to make sure that the guide scope was centred on the active imaging scope. I'd expect that to be a great help but then I'd try to reduce any cone error because if that is variable between imaging and guide scopes I'd expect difficulties.

Olly