M 3 - one more glob image

[decay]

Hi all,

so here comes my version of M 3 ... no fancy LLRGB processing, no sophisticated cooled camera
Taken two weeks ago. That evening guiding worked pretty well (for my skills), but after 45 mins I realized that my camera was out of focus So only 25 x 90s lights (~ 37 mins).
For post processing I tried to apply the hints that have been discussed in the latest threads concerning globs here in the forum.

Best regards, Dietmar.

m3-astap-2.jpg (331.63 KiB) Viewed 2418 times

[Mike in Rancho]

Well done, all things considered. Yes I thought maybe there was a bit of coma or something going on, until I saw you mention a slight focus problem. But I like the color balance and you got some blue stars deep into the core.

Nothing too fancy about LLRGB, especially since ST so readily sets all this stuff up for us.

In fact, I bet you did a fancy (synth)LRGB yourself and maybe didn't even know it.

[Stefan B]

It's glob time

Really nice image, Dietmar! Good resolution well into the core

Regards
Stefan

[decay]

Hi Mike,

In fact, I bet you did a fancy (synth)LRGB yourself and maybe didn't even know it.

Yes, I know that ST does exactly this behind the scenes. I was just kidding a bit about LRGB because I was quite fascinated by your explanations.

Yes I thought maybe there was a bit of coma or something going on

Maybe you are right. You already presumed that in our discussion in Stefan's thread about M81/82. Most of it is visible at the left side and maybe this is due to a collimation problem. I did a complete collimation with a laser collimator and an eyepiece with a small hole (I don't know the right English word for it?!), but the stars show visible coma (visual with eyepiece) if they are slightly defocused (even in the centre of the FOV, coma to one direction). I tried to do a "star test", but atmosphere is always boiling here and so I defocused a bit more and tried to put the visible inner disc (projection of the mirror) into the centre. But I have the impression that this was not the best idea and maybe it is better to trust the laser collimator?! But what about the visual problems using the eyepiece in that case?!

Best regards, Dietmar.

[Mike in Rancho]

Hi Dietmar,

Sight tube? If it is just a little hole to look through.

And if it is a sight tube with cross hairs, then I think that is a Cheshire.

At least that's what I guess.

I am no master of collimation myself, and unfortunately my tools are rather imperfect. A cheap 1.25" laser, cheap 1.25" Cheshire, and I made my own sight tube (also 1.25") out of an old 35mm film cannister.

I really need to get better quality and 2" tools, since that's what I use. In fact it is probably what we all use, as I don't think there are really any 1.25" coma correctors out there.

I have the collimation book by Vic Menard (and have even asked him some questions on CN), but collimation is still a bit of a mystery to me. I try. And I even bought a webcam that I can place on my sight tube to look down (potential parallax, of course, but that's true of eyeballs also) and view a live video while adjusting, over which I can lay re-sizable concentric circles on the computer screen. That said, I rarely use that anymore and do just kind of trust my eyes and the laser to get it close. So, sight tube for location placement of the secondary; laser dot for angle of the secondary, so that it hits the center of the primary mark; then laser to ballpark the primary; and then Cheshire to actually confirm/adjust the primary for real.

Initially I also tried the star defocus in the field, however, I am not sure that is very accurate. I have read that it takes a pretty high mag eyepiece to actually do it correctly, and that using the big defocused circle (also shows the shadow and vanes) is not actually correct. Again, I don't quite understand it. Anyway now I just trust that I did it right inside before taking the scope out. Once I get some quality 2" tools, hopefully things will be better (though it seems not too bad now).

I have a few foggy nights in the forecast, so last night I actually took apart my Newt entirely, and am going to add some flocking paper to everything.

[decay]

Thanks, Mike,

Sight tube?

Yes, that's it!

I really need to get better quality and 2" tools

Good point. The first problem is the 1.25" adaptor, which is needed for the laser and of course adds inaccuracy.

I have the collimation book by Vic Menard

I wouldn't have thought that such books do exist. 80 pages! Unfortunately there's no way to buy it here in Europe

So, sight tube for location placement of the secondary; laser dot for angle of the secondary, so that it hits the center of the primary mark; then laser to ballpark the primary; and then Cheshire to actually confirm/adjust the primary for real.

That's my procedure as well, except from the last step as I do not have a Cheshire. I think, the main problem is the location placement of the secondary. Interesting idea to use a webcam

Initially I also tried the star defocus in the field, however, I am not sure that is very accurate.

I'm sure by now, that this was indeed not a good idea. I will try again to do the collimation as you described and take more time to get the location placement of the secondary mirror a bit more accurate. And as you said, that seems all in all not to be too bad.

I have a few foggy nights in the forecast, so last night I actually took apart my Newt entirely, and am going to add some flocking paper to everything.

And soon you will be out taking shots while the full moon is standing high above

Best regards, Dietmar.