OAG Guider Focus

[cardconvict]

Hello,

Can anyone help me, I went out for the first time in a very long time last night and managed to get the scope and camera and mount all set up. But I had a nightmare trying to achieve focus with the guider. The scope is a ED80 with a midi starlight express filter wheel and OAG QHY5II camera on a CDDT67 focal reducer and SX Trius 694. I can get focus with the main camera but I have not look with the OAG, It seems the focus is towards the filter wheel and I have no travel left inwards. I also noticed the star where long streaks instead of donuts. Has anyone else got a similar set up or have had issues like this before that could help.

 

Ian

[michael8554]

It's not clear from your description what order the components are in.

The FR needs 85mm Back Focus, you have that set ?

Can you rearrange the order to place the Trius further away from the OAG prism ?

Which will allow more distance from the prism to the QHY5II.

Michael

[cardconvict]

Hello Michael

Thank you for replying the order is CDDT67(16mm)+5mm spacer+9mm spacer+midi filter wheel (38mm)+SX 694 (16mm). I'm not sure I have any adapter to move the camera back. The image below is taken from the website of SX  as is how mine is set up.

 

[Anne S]

I've the same setup except for the guidecam. I was advised by Starlight Xpress a while ago that you need 7mm difference between main and guidecam. In my case my SXVR H694 is 17.5 ish and my guidehead is 12.5 ish. The guidecam is as far down its stalk as it can get.

Whats the backfocus of your guidecam?

[cardconvict]

16 minutes ago, Anne S said:

I've the same setup except for the guidecam. I was advised by Starlight Xpress a while ago that you need 7mm difference between main and guidecam. In my case my SXVR H694 is 17.5 ish and my guidehead is 12.5 ish. The guidecam is as far down its stalk as it can get.

Whats the backfocus of your guidecam?

Hello Anne, thank you for replying and looking at the website for QHY511 mono camera it is saying it is "The CS/C standard backfocus is 12.5/17.5mm."

Are you also using a CDDT67 ? After looking over the web seems a lot of people are using at a 0.72 reduction which increases the image circle.

Edited Sunday at 12:35 by cardconvict

[Anne S]

No, I've used it at 1370 on my Ritchey Chretien without anything else, using the midi fw. Also both with a flattener and a reducer with a 80 mm refractor but that was with the original fw. I did have blobby stars with the flattener, focus was better with the reducer. But guiding was fine with all three.

is the Qhy camera sensitive enough? I had issues with a SX superstar, I replaced it with a secondhand lodestar for my travelling setup.

I did roughly focus in daytime first.

 

[cardconvict]

17 minutes ago, Anne S said:

No, I've used it at 1370 on my Ritchey Chretien without anything else, using the midi fw. Also both with a flattener and a reducer with a 80 mm refractor but that was with the original fw. I did have blobby stars with the flattener, focus was better with the reducer. But guiding was fine with all three.

is the Qhy camera sensitive enough? I had issues with a SX superstar, I replaced it with a secondhand lodestar for my travelling setup.

I did roughly focus in daytime first.

 

I think possibly the QHY5II is not really cutting the mustard, I think I will start looking for a second hand lodestar. I'm sure the QHY5II was picking up the stars but not being able to get it into focus inwards was driving me nuts. May give SX a call tomorrow but I think getting the lodestar is the way to go.

[cardconvict]

1 hour ago, Anne S said:

No, I've used it at 1370 on my Ritchey Chretien without anything else, using the midi fw. Also both with a flattener and a reducer with a 80 mm refractor but that was with the original fw. I did have blobby stars with the flattener, focus was better with the reducer. But guiding was fine with all three.

is the Qhy camera sensitive enough? I had issues with a SX superstar, I replaced it with a secondhand lodestar for my travelling setup.

I did roughly focus in daytime first.

 

Anne, was wondering which side you have spacers for the 85mm gap camera to FW or FR to FW ?

[Anne S]

I've just re-read your first post. You said you had long streaks. I've had those too but it guided fine. It s because it's getting the distortions from the edge of the refractor lenses. Have you adjusted the prism height? It can go lower which will improve the guider skies. Just make sure it's not causing a shadow in the main camera light path.

[cardconvict]

15 minutes ago, Anne S said:

I've just re-read your first post. You said you had long streaks. I've had those too but it guided fine. It s because it's getting the distortions from the edge of the refractor lenses. Have you adjusted the prism height? It can go lower which will improve the guider skies. Just make sure it's not causing a shadow in the main camera light path.

Yeah the streaks where long and out of focus for sure very blobby and long.  I did try with the prism fully down without such luck.

[Anne S]

I suggest the spacer should be between camera and filterwheel. That'll have the maximum effect. I assume your camera end of the filterwheel is m42. You've much more space to do it than I have. I had to change my reducer and flattener adapters to fit in the OAG. I have an original filterwheel with external OAG.

[cardconvict]

Thanks Ann, I think it is M42 I will need to see if a can get extensions rings camera side. Glad it's payday tomorrow

[michael8554]

The StarlightXpress site says the threads are "Male T-thread (42x.75mm) for output side"

Roughly measure how far the QHY sensor is from the prism centre with the guidecam focus not quite all the way in.

That's the figure you need from the prism to the Trius.

Which will tell you what standard size of spacer you need, there will be some wiggle-room using the guidecam focuser.

Additionally the prism height (not focus) needs to be as low as possible.

Lower until you see a shadow of the prism on the Trius Flats, then backoff until clear.

If the QHY worked "a very long time" ago,  then no need to change ?

Michael

[cardconvict]

Hello Michael 

Thank you for the advise, I plugged the QHY5 into the a finder guider scope and manged to get it to focus in the little scope ruling out any issues with the camera. I hope I have a set of m42 spacers arriving today or tomorrow to move the trius away from the FW. Will report back once I have them and testes. Fingers crossed.

[cardconvict]

Thank you to everyone who commented and gave advise, I'm pleased to report the M42 spacers arrived from FLO in double time and tested theis evening and now main camera and guider camera are in focus together. 

Stars are no longer streaks and pin point on the guider camera. For the ED80 the QHY5II is not having any issue finding stars but this might be a different storey when switching to the GSO RC8 scope.