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Star shapes... back focus distance or something else?

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26 replies to this topic

#26 unimatrix0

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Posted 08 July 2021 - 09:45 AM

Oof frown.gif Hope you didn't loosen it too much. I had a similar experience https://www.cloudyni...far-is-partial/ and it didn't have a happy ending. Crossed-fingers for you....

I checked that thread, my scope doesn't have as many screws, it has plastic screws also. Cheap design, the screws only hold the lens tight.  Can't really screw it up, it's already screwed up directly from the factory lol! I just won't care anymore, cant' really make nice images with it now, so either try to do something or keep making water drop shape star images. 



#27 bazookaman

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Posted 08 August 2021 - 12:59 PM

Update... I bought a Hotech 2" flattener to rule out the ES (45mm bf) flattener (and to make room for a fw when I get to that point. The stars have the same characteristics. Strong "X" shaped stars in the upper left corner, eccentric comet shaped bright stars across the field, and stretching inwards in the right corners, indicating I need more spacing. I also noticed that when defocused, stars are round, but are definitely not evenly illuminated. Most of the light is in the bottom left corner of each star. This is similar to the comet shape that the bright ones show when in focus.

 

Here is a 5 sec guided exposure from last night.

 

https://www.dropbox....ocus_1.fit?dl=0

 

I forgot to try one rotated 90° as I was getting frustrated trying to get plate solving to work. It's always something.

 

Anyway, I'm setting up on the same composition tonight so I'll get one rotated at 90 and 180 to compare to this one before I start my session.

 

Assuming I have a tilt issue, I'll have to read up on how to resolve it.




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