M16 A comparison

[bert]

Hi all,

Just a quick comparison, I thought it was kinda interesting.

Taken with st4000xcm with ao8, eq6 mount, internally guided. Same 10 minute sub exposure length. The difference is the wide field is taken with an Vixen ed103 refractor and the narrow(er, thats for you fred) field is taken with a vc200l.

One thing that I noticed form the comparison is star color. The refractor at f7.7 is slightly faster and is burning the star colour out to white, the vc200 at f9 is a little slower and I think 10 minutes is about the sweet spot for this type of brighter nebulosity, without blowing star colour. So in future the subs exposure length for this refractor will be dropping to around 8 minutes. Moot point anyway now that I have my new vixen Fl102.:shrug:

Comments welcomed

Brett

[CoolhandJo]

Both are very nice images indeed!

[Screwdriverone]

As Dr Paul said, both are very nice Brett....

I would say I would agree with the observation on the VC200L, it seems to be in the "zone" for the 10 min exposure, but there is more light gathering area over the refractor, so its pretty much on the money for the sub length.

The Refractor's wider field reminds me of my F5 Reflector's field of view and overall composition feel as I looked at it and thought it's colours and stars reminded me of the few short pics I have taken (stacked of course).

I think if the refractor had a few 10 min subs stacked up, the result would probably knock the VC off for wow factor, but as you said, its interesting to see the same object identically captured in two very different scopes to see the difference.

If I was to pick which one of those two I preferred, the narrow field wins in a direct shoot out.

Thanks for posting, quite interesting to ponder these.

Cheers

Chris

[TrevorW]

Both fine images, now you can combine the data from both

[leinad]

Interesting; yes the VC200L seems to really like those 10min exposure lengths, and the mono(RGB) really pops!

I have an image on my drive here somewhere Brett, of M16 in LRGB(VC200L), with Ha from a FLT132, both using QHY9. If you're interested I'll send it over; if I havnt already :P

[Hagar]

Great images Brett. I always liked the VC200L and would have kept it had I been able to get a aftermarket focuser for it. I notice FT now make one.

[leinad]

.. they have for the past year. Finally they have included it on their product pages. :)

[bert]

Hey Chris,

There is from memory over 30 subs in each image.



I think it would be interesting to see the difference. The qhy9 has a small well depth but is mono so may still get star colour. I have found that it is far better to go 15 to 20 minute subs on fainter targets like the helix, but it doesn't do the star colour any favours being an osc cam.



I use an fli df2 absolute encoding focuser, with autofocusing via focusmax. I went down that route as vixen has a standard drawtube, so all my vixen scopes can use the same imaging train with the same adapters.

I wish you had kept you vc200 too, I would love to see how it goes with a kaf11002.


I dont have the right stacking programs for differing image scales. Suggestions?

[leinad]

What software do you use Brett?

MaximDL can do a scale align, then do a star match align.
Using the same CCD this worked quite nicely using data from FLT132 and VC200L.

I'll email the result so you can have a gander :)

When I used the QHY8, the star colours were quite nice and true to colour; it was just the processing that was needed to try and keep the colours true.

[multiweb]

Both great shots. I like the close up best. :thumbsup:

[bmitchell82]

I think you already covered what the difference is though bert with the star colours. Your refractor is a faster scope and the photons are landing on less pixels this doesn't diminish the amount of photons landing, and with the vixen those photons are spread out over more of the sensor due to the focal length hence you get the benefit of seeing the lovely colours and rainbow diffraction spikes.

Also the well depth is a major component on star colour that i have noticed too.

Oh by the way :D lovely images

[bert]

I think you just hit the nail on the head Brendan. I didnt think that the f-ratio couldnt be responsible for all the colour loss. The kaf 4020 has a pretty good well depth, around 34000e from memory.

[bert]

Maxim 5.

I'll give it a crack.

[Bassnut]

Well, duh ;).

Tight one Brett, good work, but a tad ummm, ....... red ? :thumbsup:

[multiweb]

You reckon it was free? :P

[spearo]

yep both fine images
I always like good comparisons like that
very informative
frank

[gregbradley]

Great images. The VC200L I prefer, but its a bit too red. Apart from that its a high class image.

Greg.

[Bassnut]

Enough of that, im in all sorts of grief already with the notion of actually paying for the good stuff :P.

[bert]

My wife always said I look through rose coloured glasses....