The image of Mars in the shadow of the secondary. Who explains it to me?

[Fedele]

I discover this thing occasionally,  both in a C8edgeHD and in a C11. Camera Asi 224MC, with 31,8 nose and  IR/UV filter,

In the dark image of the seconday mirror...you see MARS!! it is  quite clear in focus. According to the movement of the principal mirror, you can see also a sovra esposed third image. 
position (in center or not) is  ifluenced buy curvature  of the first mirror, so by the position in the field., 

[Captain Scarlet]

I can’t see a spot in your images, but what you describe might be what I have read as (and actually seen through a scope) “Poisson’s Spot”, a diffraction artifact. It can sometimes be bright red from a white point source.

Cheers Magnus

[RobertI]

Yes I can see a faint red disc in the middle if I zoom right in. Poissons spot? Sounds interesting. 

[Captain Scarlet]

From Suiter 2nd edition p23:

 

… and from my own 6” Intes Mak just now:

Elseqhere in the book I recall discussion where certain circumstances yield a vivid bright red spot, and I have observed it, but I can’t immediately recall where or how.

Magnus

PS the bright objects are a set of radar-tower warning-lights on top of a mountain about 16km from me. Extremely convenient non-moving objects for collimating!

Edited November 28, 2022 by Captain Scarlet

[RobertI]

22 minutes ago, Captain Scarlet said:

From Suiter 2nd edition p23:

 

… and from my own 6” Intes Mak just now:

 

Elseqhere in the book I recall discussion where certain circumstances yield a vivid bright red spot, and I have observed it, but I can’t immediately recall where or how.

Magnus

PS the bright objects are a set of radar-tower warning-lights on top of a mountain about 16km from me. Extremely convenient non-moving objects for collimating!

Ah very interesting, I have seen these many times with my C8, never realised what they were. Thanks! 

[Fedele]

is Marte

[Froeng]

The spot in Fedele’s images does NOT look like the Poisson spot as far as I can tell from my experience with a  SCT… maybe a reflection of something else? Filter? EdgeHD baffle lens group with reddish coatings?

Edited November 29, 2022 by Froeng

[michael8554]

Some heavy stretching:

Michael