AP130GT Star issue


Julien LECUYER
 

Hello,

I have recently acquired an AP130GT with 3,5'' focuser (not GTX) and performed some test on the sky with an EOS6D.
I notice some issue on the stars which have the shape of "a clover".
I used the following optical train: AP130GT (3,5" focuser) + QuadTCC + ADATCCEOS + EOS6D
I have the same result with the flattener 67PF562 + 67RLEOS+EOS6D

Have you ever had this kind of shape?
What is the origin of the problem?

Regards,

Julien.


Christopher M
 

I've seen those when using my Canon 6D as well on different optics, so I believe it is the camera, but I cannot confirm.
C


Christopher M
 

Here's a close up crop of the bright star on the RHS of the full image below.  Stack of 9 of 10m subs on my unmodified Canon 6D on my Stowaway 92 w the 92TCC.
(critics:  please don't look closely at the full image - I screwed up my flats so I know there are large dust blogs on the full image)


Chris Cook
 

As Roland explained to me last year when I began shooting with my 6D/92/TCC combo, the iron cross artifact in the corners is the result of the light rays hitting the edges/corners of the mirror box in a DSLR.  You would not see this in a mirrorless camera or with the 92FF.
 
Chris
 


 

----- Original Message -----
From: Christopher M <mirfak@...>
Reply-To: <main@ap-ug.groups.io>
To: <main@ap-ug.groups.io>
Sent: 11/13/2021 1:10:14 PM
Subject: Re: [ap-ug] AP130GT Star issue

Here's a close up crop of the bright star on the RHS of the full image below.  Stack of 9 of 10m subs on my unmodified Canon 6D on my Stowaway 92 w the 92TCC.
(critics:  please don't look closely at the full image - I screwed up my flats so I know there are large dust blogs on the full image)


Roland Christen
 

Maybe I'm confused, but your topic says "AP130GT star issue". In the statement below you say Canon 6D on the Stowaway92. So, which scope is producing the issue? Have you rotated the camera to see if the pattern stays in the same orientation? If it stays the same, the defect is on the camera.

Rolando

-----Original Message-----
From: Christopher M <mirfak@...>
To: main@ap-ug.groups.io
Sent: Sat, Nov 13, 2021 12:10 pm
Subject: Re: [ap-ug] AP130GT Star issue

Here's a close up crop of the bright star on the RHS of the full image below.  Stack of 9 of 10m subs on my unmodified Canon 6D on my Stowaway 92 w the 92TCC.
(critics:  please don't look closely at the full image - I screwed up my flats so I know there are large dust blogs on the full image)


Julien LECUYER
 

Hello Roland,

For me, its is on my AP130GT with the Canon 6D.
Christopher M seems to have the same issue on its Stowaway 92 with a Canon 6D.

I have rotated the Canon 6D but with the reducer (focuser rotation), the pattern also turned as if its orientation stays the same compared to the initial field.

When the sky will be again clear, I have to check if the issue directly exists at focus (without flattener nor reducer) and if this one also exists with my Sony a7s. 

Thanks to all for your first feedback,

Regards,

Julien.


Christopher M
 
Edited

Sorry, I'm not complaining.  I was just trying to say I thought it was the camera and then provided my own example.  
Here is another photo with the almost same optics as my previous image (Stowaway92, 92FF) but now with my STT-8300 camera.  close up of bright star in upper rh corner and no iron cross.


Chris Cook
 

It won't happen with the 8300M sensor since its not full frame in size.
Chris


----- Original Message -----
From: Christopher M <mirfak@...>
Reply-To: <main@ap-ug.groups.io>
To: <main@ap-ug.groups.io>
Sent: 11/13/2021 2:23:05 PM
Subject: Re: [ap-ug] AP130GT Star issue

[Edited Message Follows]

Sorry, I'm not complaining.  I was just trying to say I thought it was the camera and then provided my own example.  
Here is another photo with the almost same optics as my previous image (Stowaway92, 92FF) but now with my STT-8300 camera.  close up of bright star in upper rh corner and no iron cross.


Julien LECUYER
 
Edited

Hello all,

I have performed this night some tests on my AP130GT in order to understand the issue on a bright star.
I found the same results with the flattener or with the reducer or without them. There is also no difference on the results between my Canon 6D and my Sony a7s (mirrorless).
I only perform a rotation of the camera, the pattern stays fixed compared to the other stars and I have noted a position than this last one disappear (see pictures below: no pattern on the third).  

What is the origin of this pattern?

Thanks for your feedback,

Julien


Julien LECUYER
 

Hello all,

I have performed this night some tests on my AP130GT in order to understand the issue on a bright star.
I found the same results with the flattener or with the reducer or without them. There is also no difference on the results between my Canon 6D and my Sony a7s (mirrorless).
I only perform a rotation of the camera, the pattern stays fixed compared to the other stars and I have noted a position than this last one disappear (see pictures below: no pattern on the third).  

What is the origin of this pattern?

Thanks for your feedback,

Julien


Roland Christen
 

It is possible that you have some small obstruction at the edge of the front objective lens. The way to check that is to remove the camera, point the scope to a bright star and place your eye at the focus so that the starlight illuminates the front lens aperture. It takes only a very small obstruction at the very edge to create this diffraction. Only 1 - 2 mm on the edge of the lens will do it. A dirt spot, or tiny insect, or something baked on the front surface. You cannot see it looking at the lens. You must look thru the lens at a bright star with just your eye looking at the lens from the rear.

Roland Christen
Astro-Physics Inc.

-----Original Message-----
From: Julien LECUYER <lecuyerj@...>
To: main@ap-ug.groups.io
Sent: Thu, Nov 18, 2021 3:17 pm
Subject: Re: [ap-ug] AP130GT Star issue

Hello all,

I have performed this night some tests on my AP130GT in order to understand the issue on a bright star.
I found the same results with the flattener or with the reducer or without them. There is also no difference on the results between my Canon 6D and my Sony a7s (mirrorless).
I only perform a rotation of the camera, the pattern stays fixed compared to the other stars and I have noted a position than this last one disappear (see pictures below: no pattern on the third).  

What is the origin of this pattern?

Thanks for your feedback,

Julien


Roland Christen
 

Another way to see what might be in the optical path is to defocus the star by a large amount so that it is about 2 to 4 mm diameter on your 35mm chip. You can do it inside focus and outside focus, and then look for any dark obstruction at the edge of the defocused star circle in your image.

Roland

-----Original Message-----
From: chris1011@...
To: main@ap-ug.groups.io <main@ap-ug.groups.io>
Sent: Thu, Nov 18, 2021 3:36 pm
Subject: Re: [ap-ug] AP130GT Star issue

It is possible that you have some small obstruction at the edge of the front objective lens. The way to check that is to remove the camera, point the scope to a bright star and place your eye at the focus so that the starlight illuminates the front lens aperture. It takes only a very small obstruction at the very edge to create this diffraction. Only 1 - 2 mm on the edge of the lens will do it. A dirt spot, or tiny insect, or something baked on the front surface. You cannot see it looking at the lens. You must look thru the lens at a bright star with just your eye looking at the lens from the rear.

Roland Christen
Astro-Physics Inc.

-----Original Message-----
From: Julien LECUYER <lecuyerj@...>
To: main@ap-ug.groups.io
Sent: Thu, Nov 18, 2021 3:17 pm
Subject: Re: [ap-ug] AP130GT Star issue

Hello all,

I have performed this night some tests on my AP130GT in order to understand the issue on a bright star.
I found the same results with the flattener or with the reducer or without them. There is also no difference on the results between my Canon 6D and my Sony a7s (mirrorless).
I only perform a rotation of the camera, the pattern stays fixed compared to the other stars and I have noted a position than this last one disappear (see pictures below: no pattern on the third).  

What is the origin of this pattern?

Thanks for your feedback,

Julien


Julien LECUYER
 

Thanks Roland for you feedback.
I performed the test and I saw some small dark zone at the edge of the star.
Then, I decided to disassemble the AP130GT in its three parts.
On the objective part (the three lenses), I note that some rectangular hold of the internal last lens slightly exceeded and are in therefore in the optical path (see cercle in the picture below).

Regards,

Julien


Roland Christen
 

Your picture doesn't show the pad, but yes, if the pad is slightly inside the optical path, then you can get this pattern on a bright star. Perhaps you can move it out of the optical path with a thin plastic tool. Don't use any metal or you might scratch the coating on the lens.

Roland

-----Original Message-----
From: Julien LECUYER <lecuyerj@...>
To: main@ap-ug.groups.io
Sent: Thu, Nov 18, 2021 6:01 pm
Subject: Re: [ap-ug] AP130GT Star issue

Thanks Roland for you feedback.
I performed the test and I saw some small dark zone at the edge of the star.
Then, I decided to disassemble the AP130GT in its three parts.
On the objective part (the three lenses), I note that some rectangular hold of the internal last lens slightly exceeded and are in therefore in the optical path (see cercle in the picture below).

Regards,

Julien


Peter Nagy
 

My old TEC 140ED had a small black pad that was sticking out and barely obstructing the lens and was causing funny looking star spikes. I removed the pad and problem solved. Eventually I returned the scope to TEC for service and they replace all pads.

Peter


Peter Nagy
 

Here is what my small pad looked like from TEC 140ED. That was enough to cause weird looking star spikes in my images until I removed it.

Peter


Julien LECUYER
 

Thanks for your feedback.

I really do not feel able, personally, to disassemble the lenses for move the accused pads. I do not have the correct device to do that.
In addition, I notice that an internal lens is very durty, undoubtedly an incorrect stockage of the refractor by the previous owners (see pictures below).

Is it possible to send the objective part to Astro-physics for pad correction and cleaning?

Regards,

Julien.


R Botero
 

Julien

You do not need to disassemble the lens, the whole lens cell will come out from the OTA and the pads sit at the back of the lens (not inside it).  Just make sure you put the lens cell in the same position as it came out.

Roberto


Roland Christen
 

You don't have to disassemble the lens to fix the pads and clean the back. The lens is one piece and does not come apart. It can be easily slid out of the cell for both operations and put back in without losing collimation. Instead of ending it here, you could ask our dealer, Gilles at Ovision in France to do this repair and clean it. Gilles is a master optician and can do this much quicker than if you send it here and back. It also avoids a lot of customs and shipping problems. You can contact him here:  http://www.ovision.com/

Rolando

-----Original Message-----
From: Julien LECUYER <lecuyerj@...>
To: main@ap-ug.groups.io
Sent: Fri, Nov 19, 2021 5:04 am
Subject: Re: [ap-ug] AP130GT Star issue

Thanks for your feedback.

I really do not feel able, personally, to disassemble the lenses for move the accused pads. I do not have the correct device to do that.
In addition, I notice that an internal lens is very durty, undoubtedly an incorrect stockage of the refractor by the previous owners (see pictures below).

Is it possible to send the objective part to Astro-physics for pad correction and cleaning?

Regards,

Julien.


ROBERT WYNNE
 

That dew appears to be very dirty. -Best, Robert

On 11/19/2021 3:04 AM Julien LECUYER <lecuyerj@...> wrote:


Thanks for your feedback.

I really do not feel able, personally, to disassemble the lenses for move the accused pads. I do not have the correct device to do that.
In addition, I notice that an internal lens is very durty, undoubtedly an incorrect stockage of the refractor by the previous owners (see pictures below).

Is it possible to send the objective part to Astro-physics for pad correction and cleaning?

Regards,

Julien.