Off axis guider .v. QHY5

[cloudbuster]

Good day all

I have an equinox 80, TRF 2008 ff reducer, manual filter wheel and Atik 314L.

Basically I'm getting flexure. My guide scope 9x50 is tightened into the corner of its mount to help avoid this. I've checked all the cables...but alas!

I am tempted to go over to off axis guiding...my mate sings it's praises.

Any thoughts peops?

Cheers

Bob

[cloudbuster]

I should add that like for many imaGers...this flexure issue has caused me soooo much pain. I am however leaning towards oag.

Bob

[Zakalwe]

The 56mm backfocus that the TRF requires makes it tricky getting everything in. This was my setup when I was using the Xagyl filterwheel which is one of the thinnest going:

It works very well though

I've recently upgraded the FW to a Starlight Xpress and that took a lot of fettling* to get it all parfocal and fitted in. The best that I could get it to was 58mm to the sensor chip, which is inside the +-4mm that Televue specify.

*By fettling I mean having to attack the SX T-Thread adapter with a sander to get it flush. And having to pay £30 for a continuous T-thread tube from TS

https://www.teleskop-express.de/shop/product_info.php/info/p561_Baader-Adapter--Continuous-male-T2-thread.html

[Thalestris24]

I should add that like for many imaGers...this flexure issue has caused me soooo much pain. I am however leaning towards oag.

Bob

Hi

I have to ask what makes you think you have a flexure problem? TBH I can't imagine you have a serious flexure problem with an 80mm frac. It only has a short focal length - 500mm. OAG's are usually only recommended for much longer focal lengths. I have an HEQ5 Syntrek as well and it's a pretty beefy mount.

I obviously can't say for sure but I suspect whatever problem you have lies elsewhere... Are you by any chance using Astrotortilla? There is a possible problem with it that I've suffered from - hopefully cured now!

Louise

[Thalestris24]

Ahh seeing the previous post now puts a different light on it!

[ollypenrice]

OAGs are a necessary evil when you get to image at long FLs with reflectors. Really there is no need to get involved with them with an 80mm refractor. You can do so if you wish but, personally, I wouldn't entertain the idea. A nice ST80, bolted down hard. Lots of guide stars, easy focus, no negatives...

Olly

[IanL]

How have you got the finder mounted?  If you're using three point rings or a single stalk finder bracket, that could be the culprit.  Try for some solid rings with a more solid attachment to the main scope. Also check your cables aren't dragging on the finder or imager.  You need to bundle up the cables and run them back to the first tube ring or centre point of the main OTA and fix there with something like velcro or ties.  The cable needs to be loose enough so there is no pull on the connectors, but no more than that - no big loops of cable hanging down from the cameras. Put the loops in for mount rotation after the first fixing point.

An ST80 gives you more opportunities to make the system rigid.  Mine is on a long dovetail which is screwed in to the top camera brackets of the main tube rings, and the cone error holes at each end have small screws that bear on the front cell and the focuser body - rock solid.

[cloudbuster]

thankyou, Ian, Olly, Louise, and Zakalwe for your superb input, and sorry i didnt reply sooner, as have been unwell.....too much red wine over the weekend!

i was rather hoping that the prospect of an Off axis guider would draw messages of approval....but many of you, quite rightly, have said that i should perhaps look elsewhere for a sollution.

My cable management could be a possible culprit....Ian has kindly messaged a few pointers....and i shall take note!

this really has caused sooo much pain....your input, far from drawing a blank, has given me food for thought.

many thanx for your help peops....round stars to you all!

bob

[cloudbuster]

also Ian....in answer to your question, i only have the single stem guidescope backet that comes with most skywatcher 9x50 finderscopes. i was wondering though....if maybe this is the source of the problem, would and OAG eliminate this?

 

cheers

 

bob

[Thalestris24]

also Ian....in answer to your question, i only have the single stem guidescope backet that comes with most skywatcher 9x50 finderscopes. i was wondering though....if maybe this is the source of the problem, would and OAG eliminate this?

 

cheers

 

bob

Hi Bob

I have a 9 x 50 finder which I used to use as a guider. They are pretty solid if the attachment base isn't a spring-loaded one and the screw is tight. Assuming the finder isn't rattling around in it's holder, of course! A gentle hand-tug will tell you straightaway if it's loose or unstable.

I wonder if you could elaborate what your symptoms are? I sound like an expert - I'm not! But plenty of people here are very knowledgeable and experienced with these things.

Cheers

Louise

[cloudbuster]

Hi Bob

I have a 9 x 50 finder which I used to use as a guider. They are pretty solid if the attachment base isn't a spring-loaded one and the screw is tight. Assuming the finder isn't rattling around in it's holder, of course! A gentle hand-tug will tell you straightaway if it's loose or unstable.

I wonder if you could elaborate what your symptoms are? I sound like an expert - I'm not! But plenty of people here are very knowledgeable and experienced with these things.

Cheers

Louise

hi Louise

yes it is a spring loaded finder bracket....but on the sides i can tighten it, its locked down tight.

cheers

bob

[IanL]

Just to follow up on a PM between me and Bob for anyone else who finds this post, here is a diagram of how I cable my cameras (the picture is an older set-up, so I have shown the current set-up with some artistic annotations).

The key point is that between 1 and 2 there should be no slack, just enough cable to avoid pulling on the connectors but nothing more to avoid weight on the cameras and focuser.

Between 2 and 3 and 3 and 4 you need to experiment to ensure there is enough slack for the mount to rotate 180 degrees in both directions from the home position.  The benefit is that the two loops here are independent; if you have enough cable to allow 180 degrees rotation in Dec, the RA Axis has no effect on loop 2 -> 3, and similarly the Dec Axis has no effect on Loop 3 -> 4.

Hope this helps someone.

(Oh and you can see that I have drilled small indentations in the concrete for the tripod legs and marked them with a lot of white paint - a lot since one dink in the concrete looks much like another.  Saves time setting up and polar aligning since I am almost spot on just by dropping the tripod legs in the little holes).

[dmahon]

I use an OAG with my equinox, TRF 2008, SX filterwheel and SXVRH694, with lodestar. It's excellent.

[ollypenrice]

I love that signature line, 'Round stars to you all.' Brilliant. It should replace 'clear kies!!'

Olly