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Struggling with new SCT Setup Image?

astrophotography collimation equipment Meade optics SCT
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4 replies to this topic

#1 adamchicago

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Posted 19 September 2020 - 12:03 AM

Please help me resolve these SCT imaging issues that I'm not sure how to tackle:

 

I've completed a new SCT with crayford focuser setup and was able to achieve focus, HOWEVER I have a dark left corner that I'm not sure about what it maybe but back focus distance is a prime a suspect (an outlier maybe a filter wheel issue).  I'm also wondering if possibly the SCT (a brand new Meade 10" F10 SCT) has a collimation problem, but I'm new to SCTs so really don't know, what I don't know about this.

 

Additionally I'm also having trouble with the OAG which seems to also potentially suffer from a back focus distance issue but I'm totally confused about this, being new to SCTs.

 

Attached are the two suspect photos (SCT main camera and OAG camera...both focused independently, haven't yet achieved simultaneous focus).  The main camera image shows a dark shadow in the bottom left with a red outline drawn around it.  And the OAG camera image is the one where the image is shrunk into a circle in the middle of the full image.

 

Order of setup:

1. Meade 10" F10 LX200 SCT

2. Feather Touch SCT adapter

3. Feather Touch crayford focuser

4. ZWO EAF electronic focuser (can use with APT's Auto Focus to achieve perfect focus)

5. Optec 0.62 reducer (no flattener because Meade is already coma corrected)

6. Optec 50mm spacer (to achieve recommended 100mm from reducer to camera sensor)

7. Another 15mm spacer (came up short with only using the 50mm spacer above)

8. ZWO OAG

9. ZWO 174mm Mini camera for OAG

10. ZWO 7 place 2" filter wheel

11. ZWO 1600mm camera

Attached Thumbnails

  • APT Lower Left Darkness SML.jpg
  • OAG Camera Image Circle SML.jpg

Edited by adamchicago, 19 September 2020 - 12:16 AM.


#2 james7ca

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Posted 19 September 2020 - 02:15 AM

The shadow in the corner MAY be from the OAG's pick-off prism. Thus, you may need to adjust the position of the prism (there should be an adjustment that will move the prism either toward or away from the optical axis of the scope).



#3 michael8554

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Posted 19 September 2020 - 03:49 AM

The prism is usually positioned adjacent to the main imaging camera's FOV long side.

 

That's where the prism can be positioned the furthest into the light cone without intruding onto the images.

 

Adjust the periscope protusion  to remove the shadow from top or bottom of your image.

 

Regarding the guidecam focus, with the main camera in focus, your starting point is:

 

Roughly measure the distance from the main camera sensor to the prism with a ruler.

 

Set the distance of the guidecam sensor the same distance from the prism.

 

Don't alter the main camera focus, fine-tune the guidecam focus on a star by moving the guidecam up or down the locked-off periscope.

 

Then lock that off.

 

From then on only adjust focus with the SCT focuser. 



#4 adamchicago

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Posted 19 September 2020 - 02:50 PM

Hmmmm, could swear I responded to this already...oh well, will try again;

 

I am so relieved that both of you guys believe this to be an OAG prism issue which is something that should be easy to tackle.  I was afraid it was going to be a much harder issue to chase down such as potentially collimating the mirrors/lenses etc (I am new SCTs).

 

Thank you!!



#5 adamchicago

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Posted 20 September 2020 - 09:29 AM

Confirmed it was the prism last night...adjusted it up a bit and rotated the camera and all is good now.

 

Thank you!




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