Askar 180, strange star shapes, how do I fix this?

[Quetzalcoatl72]

I bought the askar 180 triplet ed super from flo because it had good reviews I've seen what people have captured for this. Thought I'd try it out on m32 which is my main reason why i got it. Obviously the worst time of the year to do so, but desperate times! If you look at the image I captured 2 180 stacked(broadband cables constantly blocking it) you will see that it has terrible star shapes going on. I'm guessing coma? this was taken at f5.5 220mm with my asi533

[david_taurus83]

Did you have it set at the correct backfocus of 55mm?

[Clarkey]

I think you need to use the reducer / flattener and use it at 180mm FL. That was how I understood it. (I'd be interested to know as I am considering the FMA180 as a widefield scope)

[Quetzalcoatl72]

2 hours ago, david_taurus83 said:

Did you have it set at the correct backfocus of 55mm?

not sure, I used the 2 smallest extension tubes. Just checked the manual and for "photographic mode" you use the reducer connection tube and reducer for f4.5 and extention 2 and reducer tube for f5.5. I could try that next time. Still don't fully understand backfocus. Extention 1(the one i used) is shown to observation mode

Edited June 23, 2021 by Quetzalcoatl72

[Quetzalcoatl72]

50 minutes ago, Clarkey said:

I think you need to use the reducer / flattener and use it at 180mm FL. That was how I understood it. (I'd be interested to know as I am considering the FMA180 as a widefield scope)

one thing I can tell you is that it's extremely high quality. I just can't wait for darker nights so I can spend more than an hour testing it out.

[david_taurus83]

I believe @Adam J has one of these so can probably offer better advice.

[Adam J]

13 hours ago, Quetzalcoatl72 said:

I bought the askar 180 triplet ed super from flo because it had good reviews I've seen what people have captured for this. Thought I'd try it out on m32 which is my main reason why i got it. Obviously the worst time of the year to do so, but desperate times! If you look at the image I captured 2 180 stacked(broadband cables constantly blocking it) you will see that it has terrible star shapes going on. I'm guessing coma? this was taken at f5.5 220mm with my asi533

 

It certainly looks like you either dont have the corrector reducer fitted or you have fitted it incorrectly. The corrector should be fitted directly after the focusing ring. You then add the shortest of the three extension tubes after the corrector and the sensor should be 55mm from the end of that tube not the end of the corrector. 

Adam

[Quetzalcoatl72]

3 hours ago, Adam J said:

It certainly looks like you either dont have the corrector reducer fitted or you have fitted it incorrectly. The corrector should be fitted directly after the focusing ring. You then add the shortest of the three extension tubes after the corrector and the sensor should be 55mm from the end of that tube not the end of the corrector. 

Adam

so i can only use this scope with the reducer at f4.5 when it's advertised as both 4.5 and 5.5 otherwise i get terrible commas?

[Quetzalcoatl72]

also looking for a focus mask for this? any available to buy in the uk? can i just make my own easy enough, any special shapes?

[Adam J]

3 hours ago, Quetzalcoatl72 said:

so i can only use this scope with the reducer at f4.5 when it's advertised as both 4.5 and 5.5 otherwise i get terrible commas?

You can use it visually or as a guide scope at f5.5, I never expected it to work for imaging without a corrector, nothing would. 

[Adam J]

47 minutes ago, Quetzalcoatl72 said:

also looking for a focus mask for this? any available to buy in the uk? can i just make my own easy enough, any special shapes?

Can't help with that I use an autofocuser. 

[carastro]

Starsharp sell them, as do a number of astro traders.  You can make your own especially if you have a 3D printer.

A Y mask which is easier to make apparently works well too.

What about this one on Ebay, by Morris Engraving, I have a feeling this might be Starsharp but I definitely am familiar with the name of Morris engraving. 

https://www.ebay.co.uk/itm/293064134499?hash=item443bfbcf63:g:wvsAAMXQobdQ9KNV  

Carole 

[andyonroad1969]

There is a 3D printed one for the FMA180 here that i use.

https://www.thingiverse.com/thing:4796364