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Author Topic: Mega-Pixels - Mono CCD vs DSLR  (Read 801 times)

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Offline Einari

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Re: Mega-Pixels - Mono CCD vs DSLR
« Reply #15 on: 13:42:33, 07 June, 2017 »
Don't know cmos camera users are so worried about saturated stars. The center part of a star can be pure white but does it matter ? Apart maybe the colouring, but you can take shorter exposure for that.
And even in the ccd days people used to take shorter exposures for star colours. You can burn stars with ccd too.
Tapio

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Offline midnight_lightning

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Re: Mega-Pixels - Mono CCD vs DSLR
« Reply #16 on: 20:53:00, 07 June, 2017 »
Lots of great information, thanks for that.

Chris, a couple of questions if I may,

You mention processing headaches with CMOS, is this related to processing the lights and calibration frames and/or processing the post calibration image?

I'm leaning towards a CCD but will kick it around for a couple of weeks. When I first posted about getting a CCD you suggested the ATIK 460EX, and everything I've read so far suggests this would be an excellent choice.

Whilst looking at this I came across the ATIK 490EX which is a little more expensive but in my simplistic mind has more mp and a slightly better sample rate for my set up. But you also mentioned benefits of having larger pixels. I just wondered which of the two you would recommend, for example I wasn't sure if you had recommended the 460 partially because it was slightly cheaper or because of technical features/benefits?

Apologies for so many questions and thanks for all the information, it is so helpful :)

Thanks

Mid

HEQ5 Pro, Esprit Pro 80/400, Sky Watcher 9x50 Guide Scope with Lodestar X2 (PHD2), Nikon D750 Un-modded (BYN), IDAS D1 LPS, SX814, SGPro, Star Tools.

Offline chris.bailey

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Re: Mega-Pixels - Mono CCD vs DSLR
« Reply #17 on: 22:12:14, 07 June, 2017 »
Mid

CMOS - Lots of frames, Darks don't fully match wrt hot pixels so hot pixel filter needed. Calibration frames needed for each session and lots of them too. Lack of dynamic range unless lots of frames stacked i.e. natively 14 bit devices so stacking needed to get a reasonable dynamic range.

Larger pixels - greater well depth, more sensitive (more photons fall on larger pixel area) BUT need to be a good match for scope focal length.

The 460 or 490 would both work well (I have both though the SX version of the 490 and the OSC version of the 460).

Chris
LX200|ZS70|FSQ85|FLT110|Altair DF250RC|EQ6 Pro(Rowan Belt Mod)|ParamountMX
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Offline midnight_lightning

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Re: Mega-Pixels - Mono CCD vs DSLR
« Reply #18 on: 22:15:54, 07 June, 2017 »
Thanks Chris, much appreciated.

Mid
HEQ5 Pro, Esprit Pro 80/400, Sky Watcher 9x50 Guide Scope with Lodestar X2 (PHD2), Nikon D750 Un-modded (BYN), IDAS D1 LPS, SX814, SGPro, Star Tools.

Offline midnight_lightning

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Re: Mega-Pixels - Mono CCD vs DSLR
« Reply #19 on: 21:04:15, 11 June, 2017 »
Wow, this is proving tough - OSC vs broadband vs CCD, Sensor size/Pixels/sample rate, FOV, CCD vs CMOS, Atik vs QHY, cost.

I've got a question that's been bothering me since I started looking at this and I'm not sure how to ask it. It's to do with how much of a limiting factor my Esprit 80ED will be.

Firstly, I'm looking at a CCD/CMOS because I want to improve the level of detail in my images, for example I would like to see structure and nebulosity within targets like M33/M101.
 
My DSLR takes good photos and with 24MP across a 5x3 degree FOV I can crop/enlarge smaller targets and still have enough quality for a poster print.

An image of the Soul Nebula would fill approx one seventh of the DSLR sensor and pretty much completely fill an Atik 490EX.

 if I cropped that DSLR image by a factor of 7 I would have a 3.5mp image that would take up the same area on the DSLR sensor as full sensor on an Atik 490EX (9mp).

So my simple logic is telling me that for an object like the Soul Nebula I will get much better detail using the Atik 490 at 9mp (sample rate 1.9 "/pixel) and assuming good seeing than using the DSLR and cropping to 3.5mp. Also, a large print would be better from 9mp than 3.5 mp.
Does this make sense or have I got it wrong?

The bit I'm really not understanding in the above scenario is what part does the telescope plays in getting me the detail that I am after, is the resolution of the telescope a limiting factor, is it the camera, or do I just need more lights (I typically only take around 10x300s @ISO800) ?

Thanks

Mid
HEQ5 Pro, Esprit Pro 80/400, Sky Watcher 9x50 Guide Scope with Lodestar X2 (PHD2), Nikon D750 Un-modded (BYN), IDAS D1 LPS, SX814, SGPro, Star Tools.

Offline chris.bailey

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Re: Mega-Pixels - Mono CCD vs DSLR
« Reply #20 on: 21:10:29, 11 June, 2017 »
Mid

The Espirit 80Ed (assuming its not a duff Friday afternoon one) is not the limiting factor. Sure a Tak FSQ85 will perhaps give tighter stars (though being a Petzval quad they won't be perfectly round) and may be a little flatter but the differences will be small. Scope resolution is purely down to aperture but the seeing normally is the limiting factor.

By far the biggest performance per buck will come from the better tracking and guiding that comes from a better mount, but even then it will be marginal. Getting spot on focus is also a factor not to be ignored!

Chris

My advice (for what it is worth) is to dive in
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Offline midnight_lightning

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Re: Mega-Pixels - Mono CCD vs DSLR
« Reply #21 on: 22:23:19, 11 June, 2017 »
Thanks Chris, that really helps.

I'm going to get a camera, still not sure which yet, probably something like the Atik490Ex, Trius-SX814 or QHY23. All look similar but the QHY/Trius claims stronger cooling and QHY is £250 cheaper, the Trius also has a triple USB hub which might be useful. I don't know anything about the various brands so not an easy choice.

I also want to consider CMOS and OSC but I think I'm heading for CCD, if we had better weather mono (BB or NB) would be a no brainer but I only get perhaps 8-10 sessions per year and the extra time for mono is a consideration.

Kind Regards

Mid

PS. I did the Belt mod yesterday so hopefully this will help with guiding, I don't know how people do it in the 1 hour claimed on YouTube, it took me all afternoon to get the belts 100% aligned on the pulleys!
HEQ5 Pro, Esprit Pro 80/400, Sky Watcher 9x50 Guide Scope with Lodestar X2 (PHD2), Nikon D750 Un-modded (BYN), IDAS D1 LPS, SX814, SGPro, Star Tools.

Offline midnight_lightning

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Re: Mega-Pixels - Mono CCD vs DSLR
« Reply #22 on: 13:09:41, 15 June, 2017 »
I notice some of the Filter Wheels bundled with cameras have an OAG included - do I want one?

I currently use a Lodestar on the Finder scope that came with my Esprit ED80, would OAG provide any benefits?

Thanks

Mid
HEQ5 Pro, Esprit Pro 80/400, Sky Watcher 9x50 Guide Scope with Lodestar X2 (PHD2), Nikon D750 Un-modded (BYN), IDAS D1 LPS, SX814, SGPro, Star Tools.

Offline chris.bailey

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Re: Mega-Pixels - Mono CCD vs DSLR
« Reply #23 on: 08:51:17, 16 June, 2017 »
OAG vs Guide Scope

A couple of years ago I noticed some slight trailing in long Ha subs. I did a series of tests and concluded that differential flexure between guide scope and main scope was the culprit. If you stack a series of subs with no rejection and no dithering during acquisition hot pixels should all be in one place, the guider keeps things in one place after all.  If you get a trail of dots, that trail is the degree of differential flexure and the length of the trail gives you a measure of the amount of differential flexure over time. Now you can reduce the impact through improving the mechanical stiffness of connections between the two but you can't get rid of it entirely. As OAG's share the same optical and mechanical system, differential flexure is all but eliminated (other than the slight flex of the two camera mounts ).

My conclusion was that for long subs in particular, an OAG was the way to go.

Chris
LX200|ZS70|FSQ85|FLT110|Altair DF250RC|EQ6 Pro(Rowan Belt Mod)|ParamountMX
ATIK383L+/EFW2/OAG|Lodestar|Baader 36mm LRGBHaSIIOIII
Starlight Express SXVRH16/ONAG/FW|Lodestar X2|Baader 2" Filters
Starlight Express SXVRH814/ONAG/FW|LodestarX2|Baader 2" Filters
Lunt LS60PTBF1200|DMK41|Quark Chromo

Offline psjshep

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Re: Mega-Pixels - Mono CCD vs DSLR
« Reply #24 on: 20:51:43, 16 June, 2017 »
I use a finder/guider + Lodestar X2 with the 70mm & 102mm.... for me, I have a stable setup capable of 10 - 20 minute guiding (That's as high as I have gone so far)...

As Chris has said, adding a telecsope as piggyback can have flexure issues due to the many parts around & on the mounting system (rings/focuser main & or guide scope/etc) - with the finder/guider there is no slop in focuser (it's just a threaded screw) & the mounting bracket is secure & solid and the whole thing is much lighter.

Some people still get flexure with a finder/guider... the most accurate is OAG (or ONAG - ask Chris) but it's not the only way.

- just my opinion...

Phil

EDIT:
For an SCT without a mirror lock.... OAG every time...
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Offline midnight_lightning

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Re: Mega-Pixels - Mono CCD vs DSLR
« Reply #25 on: 13:47:54, 17 June, 2017 »
Thanks , I think I will stick with my guide scope for now, I can always add OAG later if I hit problems. My guiding seems pretty good up to about 15 mins, haven't really tried above that so probably won't be an issue with lrgb, the short fl helps. Maybe more of an issue with NB , we'll see.

I'm hoping to do an hour tonight to test my belt mod, and a new web cam which I have attached to the polar scope for PA, it will be so good not to be on my knees trying to look through polar scope 😁. I have also hopefully fixed my scope balance problem by screwing a mounting bar to the scope shoe. Whether I'll feel like it after going out for a curry first remains to be seen but it's going to be too hot to sleep tonight anyway😜

Mid
HEQ5 Pro, Esprit Pro 80/400, Sky Watcher 9x50 Guide Scope with Lodestar X2 (PHD2), Nikon D750 Un-modded (BYN), IDAS D1 LPS, SX814, SGPro, Star Tools.

 

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