Why do I get coma here?

[Xplode]

Just now, msacco said:

I've spent around an hour working on collimation, and I really think I got it quite good this time(still not very epxerienced with collimating)

Did you verify good collimation with your camera?

[msacco]

34 minutes ago, Xplode said:

Did you verify good collimation with your camera?

I collimated in the field before starting the sequence with everything already setup, it looked really good to me, but again, I'm still not really good at this.

Edited May 4, 2020 by msacco

[iapa]

10 hours ago, iapa said:

Here's a stack of 76 x 30s Lum images.

From C8 XLT, 6.3FR and ASI1600MM-cool - I know that there is some flexure in my spacers as I've not tightened them up fully.

 

I added  few MORE mm (16mm) between FFR and camera

brought curvature down from 103.3 as measure above to 

64.5%

a big number if probably not good as the image looks better as curvature drops.

Interesting that tilt has changed in X and Y, but over all has gone from 4% to 15%

I think I need to increase distance a bit more

 

 

 

Edited May 4, 2020 by iapa

[msacco]

4 minutes ago, iapa said:

I added  few MORE mm between FFR and camera

brought curvature down from 103.3 as measure above to 

64.5%

a big number if probably not good as the image looks better as curvature drops.

Interesting that tilt has changed in X and Y, but over all has gone from 4% to 15%

I think I need to increase distance a bit more

 

 

 

In my next imaging session I'll give this a try and see how it goes, maybe playing with the backfocus could make a difference for me.

[iapa]

it seems to be a very hit and miss

Need to see if an artificial star can be used to measure this

at least with no astronomical dark, time can be spent on the objectivists stuff

 

[msacco]

6 hours ago, iapa said:

it seems to be a very hit and miss

Need to see if an artificial star can be used to measure this

at least with no astronomical dark, time can be spent on the objectivists stuff

 

Yeah, the only issue is that I don't have an artificial star, and not sure how to make one.

[iapa]

as an FYI, I added a few more mm to the light train and the stack rowlocks like 

16 hours ago, iapa said:

I added  few MORE mm (16mm) between FFR and camera

brought curvature down from 103.3 as measure above to 

64.5%

a big number if probably not good as the image looks better as curvature drops.

Interesting that tilt has changed in X and Y, but over all has gone from 4% to 15%

I think I need to increase distance a bit more

 

 

 

I added in some spacers and the image now looks like this

curvature reduced from 65% to 42%

not that's relevant but, total tilt is lower, but that's more likely to be the reattaching of everything

[msacco]

14 hours ago, iapa said:

as an FYI, I added a few more mm to the light train and the stack rowlocks like 

I added in some spacers and the image now looks like this

curvature reduced from 65% to 42%

not that's relevant but, total tilt is lower, but that's more likely to be the reattaching of everything

That is very interesting, thanks

[ollypenrice]

On 05/05/2020 at 09:14, msacco said:

Yeah, the only issue is that I don't have an artificial star, and not sure how to make one.

Take a shiny new ballbearing and a decent sized old cardboard box. Spray the box mat black on the inside and glue the BB to the bottom. Set this up at a good distance from the scope so that the scope looks into the box at the BB. (There is a formula for how far away it should be but I can't remember it and got decent results from too close. It would google. The length of a decent driveway ought to do it.) Illuminate the BB with a torch beam, or whatever, just off axis.

The BB test is to be found in some of the best optical shops in the world. I saw it in Dany Cardoen's workshop down the road from my place and he has mirrors at Paranal. The principle is delightfully simple: only light from the part of the BB closest to the scope will be reflected towards the scope, so it approximates automatically to a point source. It isn't as fine as a star test but it's a very good start.

The problem is, with the Hyperstar, that you can only collimate with the camera and F2 is pretty darned difficult. I've commented on Starizona's claim that the Hyperstar makes imaging easy elsewhere and loudly!

Olly

[msacco]

11 minutes ago, ollypenrice said:

Take a shiny new ballbearing and a decent sized old cardboard box. Spray the box mat black on the inside and glue the BB to the bottom. Set this up at a good distance from the scope so that the scope looks into the box at the BB. (There is a formula for how far away it should be but I can't remember it and got decent results from too close. It would google. The length of a decent driveway ought to do it.) Illuminate the BB with a torch beam, or whatever, just off axis.

The BB test is to be found in some of the best optical shops in the world. I saw it in Dany Cardoen's workshop down the road from my place and he has mirrors at Paranal. The principle is delightfully simple: only light from the part of the BB closest to the scope will be reflected towards the scope, so it approximates automatically to a point source. It isn't as fine as a star test but it's a very good start.

The problem is, with the Hyperstar, that you can only collimate with the camera and F2 is pretty darned difficult. I've commented on Starizona's claim that the Hyperstar makes imaging easy elsewhere and loudly!

Olly

Thanks for the comment, I'm actually not really referring to hyperstar here, it is a completely different story, which as you said is not really as easy, but I still need to try it with my new and correct adapter.
I thought of maybe purchasing the Hubble Optics 5-Star Artificial Star(s), but idk if it's worth it...Some says it simply works, but other complains about the quality which is plastic. Don't know ^^

[ollypenrice]

55 minutes ago, msacco said:

Thanks for the comment, I'm actually not really referring to hyperstar here, it is a completely different story, which as you said is not really as easy, but I still need to try it with my new and correct adapter.
I thought of maybe purchasing the Hubble Optics 5-Star Artificial Star(s), but idk if it's worth it...Some says it simply works, but other complains about the quality which is plastic. Don't know ^^

I don't know it either. I've used the Picostar artificial star which is OK.

Olly

[msacco]

12 hours ago, ollypenrice said:

I don't know it either. I've used the Picostar artificial star which is OK.

Olly

Way too expensive though

[ollypenrice]

11 minutes ago, msacco said:

Way too expensive though

Sure, I use the BB myself.

Olly

[iapa]

Olly,

I found an old article by your good self

https://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=1&ved=2ahUKEwjY_7LRnaLpAhXzmFwKHWXgBGQQFjAAegQIBBAB&url=https%3A%2F%2Fstargazerslounge.com%2Ftopic%2F264094-artificial-star-alternative-method%2F&usg=AOvVaw0AHOGMbL6P0JmpwnjpNw62

one post mentions distances

[msacco]

On 07/05/2020 at 20:07, iapa said:

Olly,

I found an old article by your good self

https://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=1&ved=2ahUKEwjY_7LRnaLpAhXzmFwKHWXgBGQQFjAAegQIBBAB&url=https%3A%2F%2Fstargazerslounge.com%2Ftopic%2F264094-artificial-star-alternative-method%2F&usg=AOvVaw0AHOGMbL6P0JmpwnjpNw62

one post mentions distances

I guess I'll give it a short sometime, thanks!

Do you know if there is any size required?

Edited May 8, 2020 by msacco

[iapa]

Just as an update

I had the camera off to take opportunity to get some darks

stripped the image train right down, recalculated the bits I need to get the 105 from FR to sensor

and got this monstrous boil

 

[msacco]

On 21/05/2020 at 19:19, iapa said:

Just as an update

I had the camera off to take opportunity to get some darks

stripped the image train right down, recalculated the bits I need to get the 105 from FR to sensor

and got this monstrous boil

 

That's so weird..... 

Edited May 25, 2020 by msacco