Pacman, single sub, C9.25 full frame with vignetting ref

[Tim]

To answer some of the questions in a concurrent thread, here is a single frame, albeit 3600 seconds, from my C9.25 with 0.63 reducer spaced to be around f4.7 I think.

Full frame picture, stars to bottom right and extreme corners show optical distortion, possibly worse in the one corner due to the extension tube fitting, cant use my centring adapter with this config. Also included is a picture to show the kind of vignetting I am getting, think it was MartinB who asked.

1 x 3600 secs, qhy8 with astronomik 6nm Ha filter, DBE in Pixinsight and levels stretch. Binned 2x2, not sure how or if that affects the way a RGGB OSC result comes through.

Fairly pleased with this one, as it was already starting to lighten in the east when the sub was started at 02.25, and positively light when it finished at 03.25, Ha filters really do lengthen these short nights!

Cheers

Tim

[jgs001]

Very nice image Tim, that is a lot of vignetting.

[Tim]

You think John? It didn't seem too bad to me, the qhy8 has a big chip. Flats would help, but Pixinsight just laughs at stuff like this

Here's a single sub of M16 also binned 2x2 that I took last night as well, haven't DBE'd this one. M16 is so low that a proportion of the objective is actually viewing my obsy wall, and I woke just in time for this to see it finally dip below the wall and lose its guide star. To avoid losing the sub, which was about 50 minutes into an hour exposure I put the end cap on for ten minutes, seems to have done the trick!

[jgs001]

I'm not an expert on this stuff Tim. Comparing the vignetting on my st80 compared to my 80ed, the st80 looked about the same as that and I thought it was quite bad

I can't see the new one on my iPod,

[Tim]

I'd be concerned if it looked like that with my little H9 camera!

[MartinB]

I think the reducer has worked very well with that spacing. I might try something similar with my AP 0.67 and LX200R.

I'm not sold on the idea of hour long exposures though, 10 hours to get a decent sigma reject stack and 60 mins down the pan when a cloud passes by for a couple of minutes.

[Tim]

I throw surprisingly few away Martin as it goes. If there is patchy cloud then I do shorter subs anyway. The longer subs seem to help bring out the darker elements within the Ha emission clouds.

[fatwoul]

3600 seconds. Crikey. You're intimidating this newbie.

The crop is nice, too. Pacman deserves more space, like this.

[mike_777]

nice!

[swag72]

I'm impressed at what you have caught in 1 sub, albeit it for a long time!! Especially with the QHY8 and Ha filter - The QHY8 is a OSC right?

[ollypenrice]

It's an interesting post, Tim, but when you say PI laughs at the vignetting you are dealing with a discrete nebula in the middle of the image. What happens with an extended nebula out at the edges where you are struggling to distinguish signal from artefact?

Olly

[mark7331]

3600 seconds between subs? How many cups of tea is that? I'm still in the 1 cup of tea = 2/3/4 subs league.

Seriously though, nice image.

[Tim]

It's an interesting post, Tim, but when you say PI laughs at the vignetting you are dealing with a discrete nebula in the middle of the image. What happens with an extended nebula out at the edges where you are struggling to distinguish signal from artefact?

Olly

Then you do flats

Even so, I have been surprised at what PI can do with a custom DBE routine