Help Please - OAG camera looks “cut off”

[Elp]

If you can, you've got quite a bit of room to push it down further.

[Vinnyvent84]

7 hours ago, Elp said:

I think this is your issue, all the images I've seen of that part show it assembled this way below which makes sense, most tapered flatteners also orient like this, fat end on scope, thin end camera side, you might have the OAG on the wrong way though I don't know how due to prism orientation unless it's removable and can go back in both ways looking front and back:

I believe that’s due to the fact it’s the edge SCT which utilizes a different reducer. I’m using a standard C8 with the celestron 0.63 reducer. I never actually removed the prism; only made vertical adjustments and I have the flat side of the prism facing the OTA. 

[Vinnyvent84]

8 hours ago, Elp said:

If you could take a few exploded images of the individual bits split apart with the prism and main imaging sensor in view it may help us diagnose.

 

I’ll get this for you tonight!

[Vinnyvent84]

17 minutes ago, Elp said:

If you can, you've got quite a bit of room to push it down further.

I’ll see how much more I can push it down as soon as I’m home and let you know 👍

[Vinnyvent84]

On 28/05/2024 at 14:04, david_taurus83 said:

The Celestron OAG is a great unit but the stalk is a bit short. See below pic of mine when used with the correct 0.7 Edge reducer for my C8 Edge HD. The prism looks like it would barely pick up any light through the reducer. That said, I have no problem getting guide stars across the chip of my ASI174 mini. The sensor is massive compared to other guide cameras. How does it look if you look at it like below with your reducer?

 

20 hours ago, Elp said:

If you can, you've got quite a bit of room to push it down further.

This is the furthest down I can get the prism. And here is the  best way I could get the view I believe you guys asked for. In addition, here’s a view of guiding screen last night in the ASIAir. You can see the gradient going from light to almost pitch black when you get to the left end. 

[Elp]

It may or may not be the issue but looking at that photo it looks to me the prism isn't orientated square to the telescope side, see the illustration in this post:

https://www.cloudynights.com/topic/771429-which-side-of-the-off-axis-guider-faces-the-telescope/

 

[Vinnyvent84]

4 hours ago, Elp said:

It may or may not be the issue but looking at that photo it looks to me the prism isn't orientated square to the telescope side, see the illustration in this post:

https://www.cloudynights.com/topic/771429-which-side-of-the-off-axis-guider-faces-the-telescope/

 

Now im definitely confused lol per celestrons instructions manual the flat side of the prism faces the telescope while the angled side faces the camera chip. The link attached shows a diagram saying the exact opposite of celestrons instructions?

[michael8554]

The diagram and the CN link both show flat side to telescope.

 

 

[Vinnyvent84]

18 hours ago, Elp said:

It may or may not be the issue but looking at that photo it looks to me the prism isn't orientated square to the telescope side, see the illustration in this post:

https://www.cloudynights.com/topic/771429-which-side-of-the-off-axis-guider-faces-the-telescope/

 

I took off the camera side. I do have it oriented correctly I believe. The 45 angle is facing away from the scope toward the camera 

[Hals]

That is definitely orientated correctly.

Depending on your main imaging camera sensor size you may be able to lower the prism further into the light path.

As others have said you can check by doing flats looking for the prism shadow (which calibrates out anyway).

I have a similar issue to you with a very small portion of my OAG view vignetting (Edge 8HD, Celestron OAG\0.7 reducer & 174MMMini) but it does not cause any problems guiding. 

I never have any issues with the 174 in that regard and can always do multi-star guiding.

Pete.

Edited May 30 by Hals

[Elp]

This person seems to have had a similar issue but didn't post a solution:

https://www.cloudynights.com/topic/706903-oag-prism-blocked/

[Vinnyvent84]

41 minutes ago, Hals said:

That is definitely orientated correctly.

Depending on your main imaging camera sensor size you may be able to lower the prism further into the light path.

As others have said you can check by doing flats looking for the prism shadow (which calibrates out anyway).

I have a similar issue to you with a very small portion of my OAG view vignetting (Edge 8HD, Celestron OAG\0.7 reducer & 174MMMini) but it does not cause any problems guiding. 

I never have any issues with the 174 in that regard and can always do multi-star guiding.

Pete.

Thanks Pete. So far it hasn’t caused an issue but I did notice if that the main guide star with the box around it in the ASIair encroaches too much in the vignetted area it will flicker back and forth to guide star lost and guiding. Not every time but it’s happened. 
 

I cannot lower it any further unfortunately. There’s a backstop on the prism track that lets you adjust it. If you loosen the grub screw to much you can in theory go past the backstop to get it deeper into the OAG body but you will not be able to properly tighten it back down and the prism will / can fall out. 

[Vinnyvent84]

40 minutes ago, Elp said:

This person seems to have had a similar issue but didn't post a solution:

https://www.cloudynights.com/topic/706903-oag-prism-blocked/

I’ll check it out. Thank you Elp. 

[michael8554]

An image taken looking towards the prism and imaging camera would be instructive.

Michael

[Vinnyvent84]

6 hours ago, michael8554 said:

An image taken looking towards the prism and imaging camera would be instructive.

Michael

Like this? 

 

 

[Elp]

If you measure the OAG thread size (diameter of the hole at the thread maximum), measure the one side of that tapered connecting piece (which should be the same) and then the other side which connects to the flattener you may find your issue.

Measure the approx radius of the prism furthest edge from the central axis and x2 to get the diameter.

I don't think the prism goes far enough to be clear of the smaller flattener side connection. Both my OAGs connected directly to the flattener, or via a thin adaptor piece.

Others are using it fine however like you've connected it which points to something else. Are you sure the camera is sitting square in its holder when inserted into the OAG and locked down, youre not introducing tilt to the camera?

Edited May 31 by Elp

[michael8554]

Guesstimated on comparison with the 12 x 12 prism, it could go about 6mm further down.

Michael

[Elp]

Also check if the prism stalk has some adjustment, I very much doubt it's a solid piece, the prism is attached to the stalk, and likely the stalk is a separate piece from the off axis camera holder, so there must be some sort of screws holding the stalk in place.