18 replies to this topic

[Pablo_L]

Hi, I recently installed the Celestron OAG (with ASI274mini guide camera and asi294MC main camera) into my Edge 1100 optical train. I was able to achieve decent guiding (.4-.7 arcsec total error) but the main camera images had serious vignetting all around the perimeter of the images which I assume is due to the T2 extension  tubes I used between the OAG and the Main camera but I’m not sure how to eliminate if that’s the cause. The train, which is illustrated in the pictures is simply .7 reducer -> Large OAG adapter ->OAG -> OAG to T2 M48 thread adapter, T2 M48 to T2 M42 thread spacer-> T2 M42 to M42 spacer, -> ASI294MC camera with T2 M42 thread adapter. It almost seems like the additional Back Focus space I’m using the T2 extenders to achieve should be on the OTA side of the OAG but I’m not even sure if that would eliminate it let alone if such parts even exist.

 

Thanks
 

 

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Edited by Pablo_L, 19 April 2025 - 05:36 AM.

[ayadai]

Perhaps a back focus issue. What's your reported focal length in ASTAP?

[ishorx]

if your backfocus to sensor is right,then maybe 48's needed all the way to last 42 to camera?

[Pablo_L]

Perhaps a back focus issue. What's your reported focal length in ASTAP?

The ASIAir I’m using decreased the FL by a 1 mm (set it to 1959mm) after plate solving during polar alignment. I did a quick try at processing to see if I could eliminate the circular shadow with the DBE process and to examine the stars in PixInsight and all of the stars along the edges appear quite uniform so I don’t think it’s back focus - I have 146mm per spec of the parts though I’m a bit unclear of the starting point at the FR relative to the Large OAG adapter - I assume  the way they specified the thickness of the large OAG adapter it accounts for the distance it can be threaded onto the FR since threads on the FR are still exposed when adapter is fully screwed on. It just appears the cameras FOV is encompassing the T2 extenders due to it being far away from the OAGs larger opening thus casting a shadow all around the perimeter of the M42 extension  tube.

[Pablo_L]

Perhaps a back focus issue. What's your reported focal length in ASTAP?

The ASIAir I’m using decreased the FL by a 1 mm (set it to 1959mm) after plate solving during polar alignment. I did a quick try at processing to see if I could eliminate the circular shadow with the DBE process and to examine the stars in PixInsight and all of the stars along the edges appear quite uniform so I don’t think it’s back focus - I have 146mm per spec of the parts though I’m a bit unclear of the starting point at the FR relative to the Large OAG adapter - I assume  the way they specified the thickness of the large OAG adapter it accounts for the distance it can be threaded onto the FR since threads on the FR are still exposed when adapter is fully screwed on. It just appears the cameras FOV is encompassing the T2 extenders due to it being far away from the OAGs larger opening thus casting a shadow all around the perimeter of the M42 extension  tube.

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[ayadai]

2032 * .7 =1422; If you're using a .7 reducer, I'd say that you have too much space in your imaging train. Also, the .7 reducer is for the EdgeHD C8; not the SE, which uses the .63, so there's something amiss there either with the combination or the stated specs. The image looks fine, however, so maybe don't fix what's not really broken.

Edited by ayadai, 19 April 2025 - 06:38 AM.

[Pablo_L]

if your backfocus to sensor is right,then maybe 48's needed all the way to last 42 to camera?

That’s the other thing I was considering but wanted to ensure it would work - I’d like to replace the cameras M42 thread adapter with an M48 adapter (if one exists) as well but either way I’ll need to get an M48 extender of appropriate length. I’m hoping someone has the OAG working with the Edge series SCTs / aSI294 (or equivalent) without the shadows.

[Pablo_L]

2032 * .7 =1422; If you're using a .7 reducer, I'd say that you have too much space in your imaging train. Also, the .7 reducer is for the EdgeHD C8; not the SE, which uses the .63, so there's something amiss there either with the combination or the stated specs. The image looks fine, however, so maybe don't fix what's not really broken.

Oops - I never updated my profile after getting the C11 Edge which is what I’m doing this with, FL=2800mm

[TxStars]

Can you provide an image of the the entire imaging train from the back of the scope ?

In your second image the reducer looks a bit far from the back of the scope.

[ayadai]

Oops - I never updated my profile after getting the C11 Edge which is what I’m doing this with, FL=2800mm

No worries, I missed the bit about the "Edge 1100 optical train" in your first post. I wonder if what you're seeing is vignetting. I'm also imaging M63 at the moment with the ASI294MC and Celestron OAG, albeit with an 8SE and no reducer, and I'm seeing something similar, but not quite so pronounced, in my images. The images yesterday night did not have this "glow" around the object and nothing's changed in the imaging train.

 

N.I.N.A screenshot:

 

Edited by ayadai, 19 April 2025 - 07:01 AM.

[Pablo_L]

Can you provide an image of the the entire imaging train from the back of the scope ?

In your second image the reducer looks a bit far from the back of the scope.

Yup - I was wondering why the Large SCT adapter doesn’t thread all the way onto the reducer - the reducer certainly goes all the way onto the OTA as far as I can see. Also, I did use it with the 8SE OTA and there was also a shadow present around the perimeter of the center - the camera end of train was basically identical diameter wise but I used the SCT adapter that came with oag which supports the smaller opening on the OTA

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Edited by Pablo_L, 19 April 2025 - 07:24 AM.

[Pablo_L]

No worries, I missed the bit about the "Edge 1100 optical train" in your first post. I wonder if what you're seeing is vignetting. I'm also imaging M63 at the moment with the ASI294MC and Celestron OAG, albeit with an 8SE and no reducer, and I'm seeing something similar, but not quite so pronounced, in my images. The images yesterday night did not have this "glow" around the object and nothing's changed in the imaging train.

 

N.I.N.A screenshot:

 

m63nina.jpg

I also used it with the 8SE and had the same shadow as with the C11

[ayadai]

I also used it with the 8SE and had the same shadow as with the C11

Just for reference, here's an image of my current imaging train; I'm not seeing any vignetting other than a tiny bit from the OAG prism ATM:

 

[Pablo_L]

Just for reference, here's an image of my current imaging train; I'm not seeing any vignetting other than a tiny bit from the OAG prism ATM:

 

c8imgtrain.jpg

Same setup I had with the  8” - I was easily able to retract the prism to eliminate its shadow while keeping good FOV for the 174 guider

[Pablo_L]

Same setup I had with the  8” - I was easily able to retract the prism to eliminate its shadow while keeping good FOV for the 174 guider

Oh not quite - I was using the .63 reducer with the 8se tube but everything else was the same spacer wise

[ayadai]

Same setup I had with the  8” - I was easily able to retract the prism to eliminate its shadow while keeping good FOV for the 174 guider

I'm lazy, so will probably get around to that after this session; it's easily dealt with in post for now, as it's a very minor effect. I'm using the Touptek G3M2210M for guiding, which has a smaller sensor than the 174, but at $160 appealed to my cheapness.

Edited by ayadai, 19 April 2025 - 07:52 AM.

[TxStars]

Are you at the 146mm distance with the imaging camera

 

I would start with the offaxis guider as close to the imaging camera as it can be and still have both at the same focal point.

Then I would use the largest I.D. connectors I could find or have made..

Edited by TxStars, 19 April 2025 - 09:24 PM.

[cosmic07]

Tracking this thread! I’ve got a Celestron OAG too, and I’m stuck struggling to nail the right backfocus with the adapters I have—whether it’s the native C11 or the 0.7x reducer. If you crack this puzzle, could you share your image train setup and where you snagged the parts? 

[Pablo_L]

Tracking this thread! I’ve got a Celestron OAG too, and I’m stuck struggling to nail the right backfocus with the adapters I have—whether it’s the native C11 or the 0.7x reducer. If you crack this puzzle, could you share your image train setup and where you snagged the parts? 

It seemed straight forward - Need 146mm

 

OAG to OtA adapter = 38mm

OAG = 29mm

OAG to M48 optical train adapter = 12.5mm

 

the above leaves 66.5 mm for camera and M48 tubes

 

My 294 consumes 17.5 mm so I have 49mm in M48 tubes (7, 12, and 30)