Wobble with OAG

mcgillca

Hi - I already have a 1600mc-cooled for imaging, and today bought a 120mm-s and OAG for guiding.

I'm having problems with getting the X2 driver to work (lots of timeouts), but am also having problems with the OAG.

The connection to the guide camera is very secure perpendicular to the direction of the telescope , but there are noticeable movements (~1mm) parallel to the telescope. I haven't tried guiding with this yet, but previous experience would say that this level of movement would not yield a good result.

Not sure if I'm doing something wrong? I tightened the screws to set the focus and prism depth as tightly as possible.

Any suggestions greatly appreciated.

Thank you,

Colin

moonprince

Hi,mcgillca.Thanks for feedback.

"getting the X2 driver to work" , I don't understand what are you talking about, could you explain?

movement of oag, Is the screw loose?

mcgillca

Hi - there are two separate issues.

One is related to getting the X2 driver (software that allows your cameras to work with The Sky X from Software Bisque) to work properly on the Raspberry Pi - currently there are timeouts every few minutes - see this thread.

http://zwoug.org/viewtopic.php?f=17&t=6862&start=10

The second is more fundamental - as I described in my post, the connection from the OAG to the guide camera is on a stalk, fixed to the main body of the OAG via two thumbscrews.

Unfortunately, with this design, it allows movement perpendicular to the thumbscrews (~ 1mm). I haven't had the chance to use this yet, but I would anticipate that this will cause differential flexure between the guidecamera and the main camera, which will mean that the guider will not do a good job keeping the mount pointing to the right position - I might be wrong, but I've had previous experience of this even when the connection appeared to be absolutely rock solid.

If the weather ever improves here in the UK, I'll gather some data to investigate.

It is possible I've missed someway to remove this movement - I'm sure you have tested this out too - if so, it would be great to know.

Thank you,

Colin

moonprince

Thank you for explaining. I will ask our engineer for help :)

mcgillca

: Well, I might have to eat my words here...

I tested this on Wednesday night. I measured the differential flexure between the camera and guidecamera, and this is essentiallly zero, and this despite having a USB cable and a guide cable.

I found that stacking 20 x1 minute images (without aligning the subs) only increased the size of the stars (FWHM) from 2.2 to 2.4 pixels (about 4.6 to 5") - my scope has focal length of 350mm, so relatively large pixel scale.

So looks like although there is movement of the camera, there is sufficient restraint to stop any serious issues, at least for a small guide camera - I suspect that this would not be true if anyone e.g. used a cooled camera.

I think though, that if your engineer could design out the wobble, it would still be a good thing - though I do like the very compact size of the OAG - it allows me to keep the OAG on the scope in its case.

I may try out with a longer focal length scope and see if this conclusion still holds with more demanding guiding.

Colin

elken2004

Sam I bought one from ZWO a few weeks ago.

I drilled a hole on guider carrier and the body of the OAG, and added two grub srews to take out the wobble, if you added this to your production it would make a big difference to how stable the unit would be.

cheers

Clive.

tgmorris99

I was thinking that if the existing thumbscrew and grub screw were moved slightly off the center-line of the post then they would apply not only force to lock it in place but they would force the post against one side of the supporting structure.

Sam@ZWO

elken2004 wrote:
Sam I bought one from ZWO a few weeks ago.

I drilled a hole on guider carrier and the body of the OAG, and added two grub srews to take out the wobble, if you added this to your production it would make a big difference to how stable the unit would be.

cheers

Clive.

we will add one screw to one side of the OAG to avoid wobble problem

elken2004

I actually added one screw to the part that is guider holder and one screw the part that is on main OAG body to stop post from woobling both ends :)

cheers

Clive

moonprince

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arie

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xsnrg

Greetings Sam,

Has this been fixed in the OAGs now? That is, if I were to order one today, would it arrive with the extra screws and no wobble when fully assembled?

Thanks

Jim

anofeles

Hi everybody.

I wanted to give it to myself for Christmas too. Is that wobble corrected yet?

ebenezer

I want to purchase OAG. Has the wobble been fixed on later units?

Support@ZWO

Yes, Already improved.

sgreiner

How do I know if I have the OAG with this new, improved design? I received mine a couple of weeks ago and I have flexure in mine. I have made sure to tighten the thumb screw and there is still too much movement.

chrismoses

I'm having the same issue. How do a get a replacement part? Between the wobble side to side and front to back, It is almost impossible to focus.

Thanks

Support@ZWO

ChrisMoses wrote:
I'm having the same issue. How do a get a replacement part? Between the wobble side to side and front to back, It is almost impossible to focus.

Thanks

Please contact with info(at)zwoptical.com