Guiding an RC at 1500mm - best PHD settings... (Update below - thoughts?)

[Andy01]

Got a new GSO CF RC8 on Friday and gave it a test run on the weekend.

On Sat arvo, a mate collimated it for me with a TAK microscope thingy, and CCD inspector says it looks pretty good, with a minor tilt issue that will take time to resolve until the bog standard, (substandard) focusser is upgraded.

... and I discovered that urgently need to source a dew heater for the secondary!

However, despite my PA being spot on as per my usual methods - I noted that my PHD graph was up and down like a kids birthday party at Bounce!

It's normally a pretty flat line, (as in the patient's dead doctor...) I'm using a QSI 683 with a Lodestar OAG on an EQ6.

So does anyone have recommended settings for PHD at longer Focal Lengths? (I use PHD 1 - original flavour)

Cheers

Andy

UPDATE 18/10 : See thread below...

[Octane]

Were you getting round stars?

H

[glend]

That is a pretty light scope, have you got a bit of weight on to make it east heavy? NEQ6s like abit of weight. I used to add weight to the front of my RC08 to better balance the imaging gear, its a bit bum heavy orherwise.
Did you run the Guide Assistant? I would do that and accept the recommended settings and see if it gets better.
I would upgrade to PHD2.

Kendrick Astro make a very nice secondary heater for the RC08, it comes with thin copper tape that you can use instead of wire to run across the spider vanes.

[luka]

Andy, seen this post (http://www.iceinspace.com.au/forum/showthread.php?t=136730)? It may have a few useful tips.

[Andy01]

Hi H, yes except in the bottom right cnr - I've just added a LUM test pic of NGC 1365 from Sat night. :)



Thanks Glen, I'll try that, as I've not used PHD2 - also who supplies that Kendrick unit? :question:



Yes Luka, read with great interest! :thumbsup:

[glend]

Kendrik Astro supplies them. Not hard to find.

http://www.kendrickastro.com/rcoptics.html

[Andy01]

Sorry mate, should have specified in Australia - I was hoping to source one for the star party at Nhill this weekend. ;)

[gregbradley]

Longer focal lengths may show more up and downs in PHD. You've been using a very short focal length scope so the bumps up and down with the pE would be a smaller angular distance than a 1600mm focal length.

Your attached image shows round stars so there is no problem. The elongated stars at the lower part of the image are tilt issues not guiding. I have made that mistake before, trying to correct guiding when it was tilt.

Your CCD Inspector graph shows heavy tilt so I would try to pack out the offending side (probably the top of your camera looking at it from behind the scope).

Greg.

[peter_4059]

OSC index looks quite low. Perhaps try increasing RA aggressiveness.

[DJT]

Hi Andy
Bintel has them. Check under dew control under the accessories tab

[DiscoDuck]

Not sure what units PHD's RMS is in there, Andy. But if arcsec, then I'd be happy with the 0.56 you're getting!

Even if that's pixels of the Lodestar (which I suspect it might be for PHD1 - I use PHD 2), that's probably still around 0.6-0.65", which seems still OK for an EQ6.

I also have an EQ6 (and an RC8) and on a great night (very rare!) I get around 0.5" RMS for periods. Typically it's more in the 0.6 to 0.7" range for a good to medium night. And can easily push higher than that with anything more than a gentle breeze.

And when backlash rears its ugly head with a nasty gust of wind or two, it can be many arcseconds!!

[Andy01]

Ran a test at home last night, several hrs later, I finally got decent guiding. :)

Tried various amounts of RA aggression, these settings performed best on my EQ6.

Not sure if the seeing was bad as it was quite warm outside so maybe that affected it? This sub was taken at zenith.

Still some evidence of tilt though.

Gonna have to get a feathertouch and the tilt adjuster plate before getting serious with this thing! :shrug:

[glend]

Did you get the optional focuser collimation ring with your scope? The RC08 is known to need these things. Have you checked with a laser to see if your focuser is aligned to the secondary centre spot? The collimation ring allows you to setup the focuser correctly. Of course you could buy a new focuser but the ring is a much cheaper option. I think Andrews and Bintel have them.

[Andy01]

Already did the laser focusser check with a Cheshire as best we could at the same time as we collimated the scope with the TAK Microscope, but will do it again after the following upgrades are aquired next month...

Looks like I'll have to order the following...

- Tilt adjustment ring (from Andrew's)
- Secondary dew heater from (Kendrick: Canada - Bintel is out of stock)
- Feathertouch Focusser & adapter (from the USA)
- Losmandy weights (no idea where from as yet)

I'm used to imaging with refractors straight out of the box, so this is a new challenge - all good fun! Will sort it out eventually and those galaxies arn't going anywhere soon ;)

[xelasnave]

Congratulations on your new scope Andy and good luck with setting it all up.
alex

[xelasnave]

Are you aware these scopes may need time to reach thermal equilibrium?
I dont know what it may be here but coming from refractors this may be an aspect to consider..I can imagine you wanting to get out there for some results so just maybe???
alex

[Andy01]

Yes thanks Alex, I was out there until Midnight and I think during that time the focus did move a tad, although it's a CF tube. All the more reason for a decent focusser as my QSI 683 camera is VERY heavy. ;)

[Camelopardalis]

Certainly looks promising Andy :thumbsup: great test subs.

[DJT]

Agreed, getting closer.

[Moon]

Andy
I've used a similar combo (EQ6 + PHD + GSO RC8) and the guiding can be tricky! Some nights just a small amount of wind can cause huge problems. Also depending on where you are in the sky as well - some areas of the sky seem to guide better than others. And some nights guiding is terrible for no apparent reason - cable snags, balance, poor gear mesh etc etc.
There are some images on my site with this combo you can view here: https://deepspaceplace.com/images.php?sort=&filter=GSO8RC

Most are on the EQ6 but some are on the PME - it's noted on each image. All with the stock focuser. A flattener might be a good investment for you.

My advice for PHP and collimation is to keep doing what you are doing - stick at it. Make small adjustments, make notes, check, measure etc and you will dial in the best results possible within the limits of your gear and all the other factors. I think this focal length is pushing the EQ6 to the max IMHO.

Also this might help https://deepspaceplace.com/gso8rccollimate.php

Cheers
James

[Andy01]

Thanks James, appreciate your thoughts and input here - and I'll surely try that collimating method you've documented so well!:thumbsup:
Hopefully it will work with my QSI as well as it did with your Canon.
Seems though that a better focuser is mandatory with the QSI - it's a heavy beast! :)

PS: I've since managed to throw together a rough colour "First Light" as is LRGB test image from data gathered before VicSouth.
Clearly shows up the limitations of the std focusser & my first attempts at collimation!

[Trekrider]

I'm watching this thread with great interest Andy as I too have just got a GSO CF RC8 which I'm running on an EQ6-R mount with PHD2. I think your comment about the focusser being 'substandard' is very generous - I wouldn't rate mine that highly but I do have a Feathertouch Lightweight focusser on order for it.

Did you have any luck sourcing a Dew heater for the secondary?

[Andy01]

Hi BArry, I called Bintel - they're out of stock - We'll have to get one from here - http://www.kendrickastro.com/rcoptics.html

Cheers

AC

[Trekrider]

Thanks Andy, I was thinking I would have to go to them as well.

[Moon]

Andy
That's an interesting image. The star at the top right looks okay, but on the others it looks like mis-registration of the colors - can you process again or just do a stack without registration to see what is going on over time. I can't really see any 'bumps' in the stars that would indicate poor tracking, but it does look like your collimation is out and maybe some field curvature too.

Remember - a new focuser won't fix tracking or poor collimation - so it's best to get those sorted first. Is the focuers slipping or just wobbly? Mine is holding up a STL 11k - which is a very heavy camera btw.

James

Edit - btw I can see potential here!

[PRejto]

Andy,

If you are not doing so already I would recommend binning your guide camera 2x2 at this longer focal length. You will see a big improvement. At 1x1 the resolution is too high and you will chase seeing all over the place.

Peter