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NGC891, TEC140.

ollypenrice

By ollypenrice
in Imaging - Deep Sky

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ollypenrice

ollypenrice

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1015mm is not a long focal length for galaxy imaging so there's a nice challenge in seeing what we can squeeze out of the TEC140 with the small-pixel Atik 460. This had an hour per colour under a slightly iffy sky and then 3.5 hours of luminance on a second night, all 10 minute subs. Unfortunately, recent cold winds have messed up the seeing so, although transperency wasn't too bad (SQM21.3), the FWHM values were poor, around 2.3. We sometimes see 1.3 in this outfit. Enough excuses! Mount was our recent second Mesu, working like a good'un.

This is a heavy crop.

Imaged with guest Marcel Vonk from the Netherlands. 

NGC%20891%20TEC%20CROP-XL.jpg

EDIT: Please scroll down for corrected star colour.

Olly/Marcel

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swag72

swag72

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12 minutes ago, tomato said:

And here is me thinking I need a 12" TT RC to go after subjects like these...

Goodness no...... a nice longish refractor and a small chipped camera should work a treat...... Olly shows that his combo works well.??

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ollypenrice

ollypenrice

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1 hour ago, swag72 said:

Great detail....... that combo is looking good. The stars look a little off though..... too blue I think..... not like your usual starfields

Yes, you're right. I think this was due to a questionable red layer which we shot rather low down so that it was affected by the poorish sky. In fact we re-shot it on night two so I have a new red layer to try. I'll see what it gives. (I was too idle to reprocess the RGB to be honest!) I'd meant to check some key stars against the published colour index, which is what I usually do, but I forgot.

Back soon, and thanks for the heads up...

Olly

 

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ollypenrice

ollypenrice

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2 hours ago, tomato said:

Very nice, one of my favourite galaxies as you have probably guessed!

And here is me thinking I need a 12" TT RC to go after subjects like these...

It wouldn't do any harm (other than to the wallet) to add a large reflector to the arsenal and I have a 10 inch ACF waiting in the wings to try. However, if you use small pixels in a large-ish refractor you seem to be able to engage with the galaxies - and the challenge is enjoyable. All being equal (which it rarely is) larger apertures will give you smaller stars and I'm finding that quite a lot of processing effort needs to go into star control with this setup. The poor seeing didn't help any this time, either.

Olly

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ollypenrice

ollypenrice

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1 hour ago, pietervdv said:

Very nice Olly! On the first version the blue stars don't look right, but I see you corrected it already. What resolution do you get with this combo? Below 1arc sec?

 

Pieter

Hi Pieter, the rig works at 0.91 arcsecs per pixel. The true FL of the TEC140 with flattener is 1015mm/F7.3. It's a shame we didn't have better seeing but that's how it is at higher resolutions. Nothing you can do other than shoot colour in the bad bits!

Olly

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ollypenrice

ollypenrice

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2 hours ago, steppenwolf said:

Zero change to the galaxy (good thing!) but I much prefer these stars although they're not as tight as usual for this rig so the conditions must have been hard.

...and the stars have had a lot of processing effort, here. They were quite 'Bloaty McBloatface' as they came down the spout! Still, I doubt that a larger reflector would have fared any better. Worse, maybe? Who knows?

Olly

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tomato

tomato

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I was hoping that a big aperture RC would still be the weapon of choice for small galaxies, they are definitely my favourite DSO and I am a sucker for carbon fibre, anodised machined parts, and a never ending cc bill:icon_biggrin:

Mind you, a large aperture, good quality refractor doesn't come cheap either.

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wimvb

wimvb

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4 hours ago, ollypenrice said:

...and the stars have had a lot of processing effort, here. They were quite 'Bloaty McBloatface' as they came down the spout! Still, I doubt that a larger reflector would have fared any better. Worse, maybe? Who knows?

Olly

Probably worse, unless it's floating in space and has a 2.5 m mirror. Land based reflectors have all kinds of diffractions. I would think that for tight stars, a (large) refractor wins anytime.

Great image by the way. Now I just wonder if the 'new' red data would make a difference in the galaxy.

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ollypenrice

ollypenrice

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2 hours ago, tomato said:

 

Mind you, a large aperture, good quality refractor doesn't come cheap either.

LZOS list their 10 inch F8.8 at 77,800 euros but a TEC 180, for the more parsimonious astronomer, is listed at a trifling 18,000 dollars...

What's the problem?

:eek:lly

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ollypenrice

ollypenrice

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1 hour ago, DaveS said:

TEC do a 250mm Fluorite triplet too.

http://astrograph.net/epages/www_astrograph_net.sf/en_GB/?ObjectPath=/Shops/www_astrograph_net/Products/AGTEC250-35

A steal at £50k

http://astrograph.net/epages/www_astrograph_net.sf/en_GB/?ObjectPath=/Shops/www_astrograph_net/Products/AGTEC250-35

Two hands, please! (Is the scope's owner just out of shot on the left and in a state of some anxiety?

:icon_mrgreen:lly

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tomato

tomato

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Sorry I hi-jacked your post Olly with discussions on scopes instead of your image of NGC 891. 

To bring it back  to the topic in hand, it's interesting to compare your image with the superb examplehttps://stargazerslounge.com/topic/205083-ngc-891first-light-with-the-fully-functioning-12-inch-rc/?tab=comments#comment-2173416 taken by Rob Hodgkinson with I believe, a very well engineered GSO 12" RC, and 2 nights of data. I know I'm not comparing like with like except for the scopes but certainly  the refractor (in your capable hands) is certainly capable of delivering comparable results on this type of subject. I love 'em both!

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ollypenrice

ollypenrice

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2 hours ago, tomato said:

Sorry I hi-jacked your post Olly with discussions on scopes instead of your image of NGC 891. 

To bring it back  to the topic in hand, it's interesting to compare your image with the superb examplehttps://stargazerslounge.com/topic/205083-ngc-891first-light-with-the-fully-functioning-12-inch-rc/?tab=comments#comment-2173416 taken by Rob Hodgkinson with I believe, a very well engineered GSO 12" RC, and 2 nights of data. I know I'm not comparing like with like except for the scopes but certainly  the refractor (in your capable hands) is certainly capable of delivering comparable results on this type of subject. I love 'em both!

No Hijack. I was always a great admirer of Rob's images and am sorry that he's 'retired' from AP. There is no question but that Rob's image has it on resolution - and quite comfortably. How much we really lost to the seeing on our shoot is hard to say, though our FWHM values were about twice what we see on the best nights.

I still have time to come back to this one should we get some very stable nights fairly soon. Tonight, after a windless day, the seeing is significantly better already but Marcel is onto a new project.

Olly

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