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EQ8 First Light Guiding


ianaiken

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Hi All,

Managed to test some guiding on my EQ8 last night.  Not sure how to interpret the results so far.  I think my PA may be slightly out too but I need to spend a little more time on drift alignment.  This is on a side by side rig using an OAG.  Guider Focal Length is 382mm pixel scale I think 2.03.

My PHD RMS RA: 0.25 and DEC: 0.20.  My star profile is clipped, the QHY5L-2 gain was set to zero and I chose quite a dim star.  I think it's due to being in the OAG the star shape is very eggy.  I've seen the EQ8 perform better than this, but then I don't know what load goes with the stats reported.  My load is ~17KG.  All the points appear to be in the same place but not around centre.  I wonder if the mount is running too fast or slow.  The Pulseguide rate for both RA and DEC was set to 0.2x for this test (unlike the night prior where I used 0.1).

post-15076-0-88873600-1404729734_thumb.p

The previous night when I had a very unbalanced setup I had some RA run away.  I didn't see this last night (but then last night I actually tightened the AZ bolts so the mount wasn't wobbling about on the pier :-) )

post-15076-0-45228200-1404729742_thumb.p

The subs I took last night do have drift, which could suggest bad PA since there is movement in both Dx and Dy

post-15076-0-14607900-1404729662_thumb.p

My guide log is at https://dl.dropboxusercontent.com/u/1595099/SGL/PHD2_GuideLog_2014-07-06_215456.txt if anyone wants to take a look.

What are people's thoughts?

post-15076-0-68309900-1404729907_thumb.p

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Hi

I'd be inclined to upgrade to PHD2 first (Open PHD). Also make sure you use the Ascom driver with the qhy5l-ii (as recommended by qhy).

PHD2 allows you to auto-select suitable guide stars though it's not perfect. Any star you choose should not be cut-off and around 2secs exposure is usually ok (well, works for me :) ) If you have short exposures then there's a tendency to chase the seeing - guiding can only be as good as the image of the guide star that is used.

Hope that helps for a start.

Louise

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Hi Louise,

I am already using PHD 2.2.2a.  I'm goign to check which driver I am using I am sure it is the ASCOM.  Even at 1 sec the star is cut off so I think this may be to do with the shape.  I have made some adjustments and also moved the OAG closer to the FR and it is now further into the FOV so I hope in an area where the stars are not elongated/eggy.

My guiding on the NEQ6 was comparable to the guiding on the EQ8, the 8 being a little worse as PA is not as good yet.  I think the star shape may be the limiting factor here and it is the best guiding that is possible with that saturated oddly shaped star.  I think fixing that would rule it out and maybe I will end up with much better performance.

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Hi Louise,

I am already using PHD 2.2.2a.  I'm goign to check which driver I am using I am sure it is the ASCOM.  Even at 1 sec the star is cut off so I think this may be to do with the shape.  I have made some adjustments and also moved the OAG closer to the FR and it is now further into the FOV so I hope in an area where the stars are not elongated/eggy.

My guiding on the NEQ6 was comparable to the guiding on the EQ8, the 8 being a little worse as PA is not as good yet.  I think the star shape may be the limiting factor here and it is the best guiding that is possible with that saturated oddly shaped star.  I think fixing that would rule it out and maybe I will end up with much better performance.

Hi

PHD2 is a separate package from PHD.. You can download it from here:  http://openphdguiding.org/

You don't want to use a guide star that's 'cut off' - choose another. Short exposures such as 1sec are best avoided. Better to find a dimmer star and expose for 3 or 4 secs. Monitor the snr - you really want that to be in double figures but without cut-off.

Hth

Louise

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Hi Louise,

Thanks. It is phd2 I am using. I just updated from 2.2.2a to 2.3.0.

Problem I have is the guide cam is very sensitive so even at 1 second exposure the star is clipped and of course this introduces issues with chasing the seeing... potentially. The arrangements I've made should make the star a nicer shape and this will help to an extent.

I'm going to try to resolve the saturation but also I'm going to look at something called metaguide at least when it is clear next. Seems that has some good reviews.

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Hi - not clear is this OAG or a side by side guide scope? - I have an EQ8 and use ST4  guiding not pulse to good effect with PHD but have just gone over to off axis guiding and its very good although I was never aware of flexure - also the dec backlash is a n issue with this mount but something we can fix and this helps mount responsiveness - look forward to seeing other PHD and capture posts -sure you will succeed- best wishes- Tony.

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Hi Louise,

Thanks. It is phd2 I am using. I just updated from 2.2.2a to 2.3.0.

Problem I have is the guide cam is very sensitive so even at 1 second exposure the star is clipped and of course this introduces issues with chasing the seeing... potentially. The arrangements I've made should make the star a nicer shape and this will help to an extent.

I'm going to try to resolve the saturation but also I'm going to look at something called metaguide at least when it is clear next. Seems that has some good reviews.

Hi

It would seem the problem is to do with choice of guide star - try and find one that doesn't clip with a 2sec exposure!

I have the same guide cam and know how sensitive it is!

Cheers

Louise

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Yeah that would be good but it's virtually impossible in phd2 to find one and when I do the snr is too low so guiding suffers that way. I have a very narrow field in the oag.

I'm going to try metaguide next it has some good features plus the latest version has support for the qhy5l-ii just need some clear skies.

I think there are some other settings too which need adjusting and these have been tweaked. Balance in ra is a bit of a pain too since the eq8 motors are on the west side. It's a nuisance to go East heavy on a remote controlled obs.

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Yeah that would be good but it's virtually impossible in phd2 to find one and when I do the snr is too low so guiding suffers that way. I have a very narrow field in the oag.

I'm going to try metaguide next it has some good features plus the latest version has support for the qhy5l-ii just need some clear skies.

I think there are some other settings too which need adjusting and these have been tweaked. Balance in ra is a bit of a pain too since the eq8 motors are on the west side. It's a nuisance to go East heavy on a remote controlled obs.

Hmm... I'm afraid I've no experience of using an OAG, or an eq8 for that matter (I wish!). I had a look at Metaguide - it might indeed help. Do post your experience here! Of course, there are also issues surrounding balance which might relate to your initial problem. I always balance according to Dion's very comprehensive set-up video on YouTube (Astronomyshed).

Anyway, hope you can sort it all.

Cheers

Louise

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Hi Ian,

before tweaking your mount settings and all that,  off course balance is important,  i would be considering getting a better guide camera, you spent a lot on kit, telescope and mount, and i don't think the QH5L is the best option. i just got the ZWO ASI120mc and tried that for my guiding, and it was all over the place.  I then went back to my trusty Lodestar, and behold my guiding was back to good results.  Im not saying the QH%L is no good, but it seems you got to make a lot a adjustments, this clipping bothers me,

With the Lodestar its really plug and play.  I normally do 5 seconds,  think short exposures tend to chase the seeing, especially in the North East England. 

cheers

Paul

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Hi Paul the saturation and over sensitivity wss certainly a problem but I since switched to metaguide and guided brilliantly with bad pa. I was using 0.3s video but it is clever and you can set it to average seeing. It's also capable of making smaller adjustments but not so small it creates oscillation. Of course I'm testing all this through poor skies but I can say sorting out the over saturation and star shape (by moving the oag closer to the FR and also having it more towards the centre instead of right on the outer edge where the bad shape occurred.

I own both the qhy5l-ii and an asi120mm and they are great and very sensitive just maybe a bit too sensitive on a fast scope but all this means is to change settings. With the older qhy5 I couldn't find any bright stars and now with the qhy5l-ii I couldn't find any stars dim enough!

All sorted now though.

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I'm in two minds about longer exposures. Too long and you can suffer by your mount but too short and you could suffer by bad seeing. I've suffered bad subs by both exposure settings on previous mounts.

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I find my QHY5L-IIM is great in PHD2, using a travelmate 70 as guide scope - no problem finding a suitable guide star on anything I've tried thus far, though the more limited fov of the oag will limit the choice a little.   Perhaps if the minimum gain is too sensitive you could add an ND or red filter to the guidecam nosepiece?  

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I could add a filter I did speak to Bern about that but the spacing was a bit tight and filter width may have been a problem that's when he pointed me to metaguide which solves that by taking more smaller exposures and averaging the centroid. Support for the qhy5l-ii has just been added recently.

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I've just upgraded from the old QHY5 to the slimline QHY5L II - and it works great!!

I use an on-axis guide system for spectroscopy and AstroArtV5 (or PHD 2.3) for guiding...

The C11 is still fitted with the Lodestar but I'll swap over for extended trials.

Certainly no complaints with the QHY5L II so far....

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Well I had positive results with metaguide and I got some good guiding with my test sub.  I could really fine tune the settings and exposure to let the software accurately calculate the centroid.  I will be doing some PEC correction too once I figure out how to use that with EQMOD.  I don't think it is permanent so I am not entirely sure how to apply the correction so it matches up with the right point on the worm cycle.

Metaguide was also useful to help with Polar Alignment (although PHD2 Drift tool is better).

Here is a 30 min sub.  If it is possible to zoom in you will notice some eggy stars which I believe is down to focuser sag on the WO GT81.  I have saw a thread on this and will be adjusting it which should mean round stars for most of the frame.  The sag is related to wobbly focuser (its rotatable) and also proper adjustment of the R&P tension screws.

Quite happy with this image considering it is a simple stretch with no calibration.

post-15076-0-96176000-1405603793_thumb.j

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I've made the adjustments on the WO GT81 focuser so now I need to get a clear sky to test it.  I slackened off the retaining screws that stop the focuser from rotating and then evenly tightened them up.  This should get the focuser on nicely.  I then used my flat panel and then adjusted the R&P retaining screws (the two large ones on top) so that the light from the flat panel, which appears as a circle, was centred correctly.  It was quite off before adjusting all of the above.

Come on clear skies!!!

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  • 2 weeks later...

Hi Olly good catch. I wonder if that's from rotation. I'll need to check closely DSS would give me the stats on that. Failing that not sure if it could be tilt and it can be guiding affecting just one side.

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