Questions Setting up ZWO OAG

[gerharden]

Hi All,

Need some guidance with regard to the setup of my ZWO OAG. I have been reading lots of posts and watched a number of YouTube video's. I have it setup, but I have a couple of questions.

Firstly this is my setup as shown in the picture OAG Setup. Celestron 11" SCT + Celestron f/6.3 Focal Reducer + Celestron T adapter + M48 - M42 adapter + ZWO OAG + 11mm spacer + T2 - T2 adapter + ZWO EFW mini + ASI 1600MM cooled. I use a ASI 120MC-S as my guide camera.

I moved the prism into the light path far enough so as not to block too much of the main camera (See stretched MasterFLAT_-15C_2x2_Lum). Then I focused the the main camera and the guide camera on a piece of paper about 18m away (see picture Focus Target).

I noticed two things.

1) The image from the guide camera has about a third of the image blocked (See image ASI120MC-S). Is this normal? I do not want to move the prism deeper into the light path, or should I?

2) Also the main camera and the guide camera are pointing quite far apart of the Focus Target. Is this also normal? I suppose it does not make much difference when looking at the sky.

Your guidance (no pun intended) would be appreciated.

[michael8554]

I'm not clear what your images are showing, but from the posts and videos you'll have realised that the prism is best aligned with the long edge of the imaging camera.

Which from the Master Flat image, appears to be 20 degrees or so off ?

And you could rotate the Guidecam 90 degrees in its holder, so that the USB socket and hence imaging chip is square to the scope optical centreline ?

The setscrew that locks the periscope can tilt the periscope slightly to one side, so that the prism is not quite in line with the centre line of the imaging camera - not a big problem.

I have the Fields of View set up in my Planetarium.

So I can rotate and/or slightly offset the FOV to get a good guide star on the prism, then I GoTo the RA and Dec of that position.

Here it is pointing at Regulus. The prism appears to be well outside the FOV, but in reality is only just outside, according to the Flats.

Also the prism is picking up stars to the south of the imaging camera, but due to the optics of my scope, the prism is physically located to the north of the imaging camera.

Took a while to realise that !

Is that a Masterflat of your main imaging camera ? A lot of vignetting there !

 

 

[gerharden]

Hi Mchael,

Thanks for that.

Did not even think of rotating the periscope to be horizontal to the main camera. The one video I watch, also show the skewed shadow, so I thought that was normal

I have also rotated to guide camera to be 90deg to the main camera (USB port pointing to the main camera). Had to make some spacers to get that right.

I will have to wait for some clear skies to try this out. With the periscope being horizontal to the main camera, it might be possible to drop it a little bit further into the light path, without affecting the main camera too much.

The vignetting is not that bad. The attached image was stretched so it looks a lot worse. I have attached an un-stretched version.

Edited April 5, 2021 by gerharden

[newbie alert]

Just as a add on, do people align the long edge like this

[newbie alert]

Or like this?

[gerharden]

Hi Brown Dwarf

Not that I'm an expert at all, but from what I have seen and read, it looks like long edge to long edge, so your first image.

 

Gerhard

[gerharden]

I had a test last night (NGC 3621) and really struggled to find a guide star. The one time I got it right, it worked well. 2min exposure with no issues. I have changed to orientation of the guide camera to aligned with the main camera.

I decided to drop the prism deeper into the light path, which does give me more light on the Guide Camera, but does introduce more shadow on the main camera. Any suggestions with regard to settings in PHD for the ASI120MC-S to improve its performance?

 

Below are photos of the changed configuration:

 

Image through the ASI120MC-S

 

Image through the ASI1600MM Pro

Edited April 10, 2021 by gerharden

[knobby]

It's a fine balancing act ! But yes, long edge to long edge as you need to get the guide cam as far into the image circle as possible.

Flats will hopefully remedy a slight shadow from the stalk 🤞🏻

You can try binning the guide camera as it should improve sensitivity and possibly improve star shape to guide on.

[newbie alert]

On 06/04/2021 at 17:26, gerharden said:

Hi Brown Dwarf

Not that I'm an expert at all, but from what I have seen and read, it looks like long edge to long edge, so your first image.

 

Gerhard

If that was in reply to my question Gerhard,  thankyou..