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CCD or Sony a7s?

vertigo262

By vertigo262
in Discussions - Cameras

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ollypenrice

ollypenrice

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Posted

Here's your answer:

0b9c2b9b9b6fc7dd20ba0997164c0cc2.1824x0_

10x600s taken with 6Da through my TS 100Q and Baader 7nm Ha filter.

Split into separate colors after stacking, green and blue channel have been discarded so this is just the red channel.

Well worth having but you will get more signal if you use all the pixels...

Heart%20Ha%20Standalone-L.jpg*

This has longer, 5 hours in 10 minute subs. (One of us is flipped, Ole! I haven't looked it up to see whether it's you or me.  :grin: )

Olly

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Psychobilly

Psychobilly

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I don't think that anyone with any sense will argue that Mono is better for Narrowband...  It's just illustrating that you can grab it with a  DSLR  if thats all you have or choose to use... Modification for improved Ha response helps and you can of course if you wish Debayer the DSLR or send it off for a mono mod...

I have just had my "surplus" 7D mk 1 Full Spectrum modified  but thats more for IR pass terrestrial and the odd bit of Astro as it isn't the lowest noise DSLR of the ones I own...

Peter...

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bwana

bwana

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There are a number of reasons why cooled mono outperforms a typical modded DSLR for narrowband:

1)  For H-alpha, the DSLR Bayer matrix means that only the Red pixels pick up any signal whereas all pixels of a mono camera are responsive.  So, like for like, a mono camera picks up 4x as much data. Analogous arguments apply to the other narrowband wavelengths.

2)  Using NB filters, there is very little background sky signal.  This means that the DSLR thermal noise is the main source of image noise especially on warm summer nights. A cooled CCD does not have this constraint.

However, those arguments only really apply when you are comparing similar size sensors.  When comparing the massive full frame sensor of the A7S against the tiny ATIK 428EX sensor, the photon collecting ability of the full-frame sensor is a massive win.

Mark

I won't argue your points, both are very valid even though I do enjoy narrowband imaging with the A7S.

I'll even add a third point which derives from your last line.  In order to cover a full frame sensor and really make use of it you do require a longer scope and, normally, resulting larger focal ratio meaning longer exposures, better tracking/guiding, etc.  Although wide-field narrowband, i.e.: nebulas, is a lot of fun and can be done with a something like an AT65EDQ or 190 Mak-Newt.

bwa

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bwana

bwana

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Posted

If all you want is the H-alpha and you are using a narrowband filter then removing the red channel is exactly what you want to do.  However, I think it is generally preferable to use a DSLR for what it does best i.e. taking full colour images.

Having said that, it is certainly possible to do NB imaging with a DSLR. I have seen some good examples.    However, this works best with fairly fast optics and cool night time temperatures because of the limitations of DSLR cameras.  I certainly wouldn't describe it as pointless.

Mark

Actually it is a lot of fun...  However, if I was really (really totally) committed to narrowband imaging as my life's goal I would use a mono CCD (and I do use my ATIK 428Ex).  At least the A7S has the sensitivity to do a pretty reasonable job.  I did try narrowband with my full spectrum Canon 60D and was not at all impressed :(.

bwa

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bwana

bwana

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also, this was another thing I asked in another topic was about turning my firmware on the camera to mono, then trying ha, was told that would cause problems as well.

Not too sure what you mean by "turning my firmware...to mono"?  I simply set the picture style to B&W to get a greyscale image.

bwa

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bwana

bwana

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Without any doubt whatever I would use a monochrome CCD whether it was for natural colour, colour enhanced by Ha or possibly O111 or full narrowband.

Regarding the Atik 11000 I have lots of images using that camera. Some examples...

http://ollypenrice.smugmug.com/Other/Best-of-Les-Granges/i-SHnPvp3/0/O/M33%203SCOPE%2030HR%20HaLRGB%20ODK%20CoreV2..jpg

http://ollypenrice.smugmug.com/Other/Best-of-Les-Granges/i-3bjPNHd/0/X3/Mopdified%20Straton%20FIN%20web-X3.jpg

http://ollypenrice.smugmug.com/Other/Best-of-Les-Granges/i-ZBmVMGT/0/X3/M45%20final-X3.jpg

I must say, though, that DSLRs are getting better. It is absolutely vital, when comparing images, to note the F ratio of the instrument. In very fast scopes DSLRs do well. Down at F7, as in this example, I don't know how well they'd do.

Small   http://ollypenrice.smugmug.com/Other/Best-of-Les-Granges/i-XqpRhfL/0/X3/SAG%20TRIPLET%20TEC%20MOSAIC-X3.jpg

Full  (large file) http://ollypenrice.smugmug.com/Other/Best-of-Les-Granges/i-XqpRhfL/0/O/SAG%20TRIPLET%20TEC%20MOSAIC.jpg

Olly

Great images!  ATIK makes good cameras.  I like my little 428Ex.

I regularly use the Sony A7S on f/5-f/10 scopes with reasonable results but I wouldn't say the same about my old Canon 60D.

bwa

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Xplode

Xplode

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Well worth having but you will get more signal if you use all the pixels...

Heart%20Ha%20Standalone-L.jpg*

This has longer, 5 hours in 10 minute subs. (One of us is flipped, Ole! I haven't looked it up to see whether it's you or me.  :grin: )

Olly

I'm the one that is flipped :p

With a mono 6D i would be able to use all pixels for Ha :tongue:

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bwana

bwana

Posted
Posted

Well worth having but you will get more signal if you use all the pixels...

Heart%20Ha%20Standalone-L.jpg*

This has longer, 5 hours in 10 minute subs. (One of us is flipped, Ole! I haven't looked it up to see whether it's you or me.  :grin: )

Olly

And a Heart and Soul mosaic in color off the Sony A7S: (Imaging details)

Soul%2B%26%2BHeart%2BNebula%2BMosiac%2B%

Two imaging sessions of 30x60 sec @ ISO 5000

bwa

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bwana

bwana

Posted
Posted

Or a Baader BCF Modified 1000D and 2" 35nm HA Filter...

used to replace the Red Channel  in this HaGB image...

...

Veil-6HaRGB-QS-8b.jpg

Apologies to the OP for answering the HA with a DSLR question in thread...

Peter....

While I was testing the A7S prior to modding it I shot: (image details)

NGC%2B6960%2BEast%2BVeil%2BNebula%2B-%2B

Astro-Tech 8" RC (1600mm fl, f/8), unmodded Sony A7S, 31x30sec @ ISO12800

This is one of the images that gave me some initial confidence in the A7S's capabilities.  Some background noise but still reasonable.

bwa

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bwana

bwana

Posted
Posted

bwa,

Pardon the silly question, is the red around the edges amp glow?

I'm not sure if I shot this in full frame or crop mode?  But based on the star stretch in the corners I suspect it was full frame.  At ISO 12800 and higher you will see some amp glow on the bottom and left edge of an image..  In crop mode you won't see any amp glow; it is outside the frame.

bwa

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vertigo262

vertigo262

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Not too sure what you mean by "turning my firmware...to mono"?  I simply set the picture style to B&W to get a greyscale image.

bwa

That is what I meant, the picture style. seems smarter to do, then removing the red channel. I will give it another try, now that I know it isn't pointless.

and as for a7s or ccd, or mono. Can you guys just send me ya cameras?  :rolleyes:

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bwana

bwana

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That is what I meant, the picture style. seems smarter to do, then removing the red channel. I will give it another try, now that I know it isn't pointless.

and as for a7s or ccd, or mono. Can you guys just send me ya cameras?  :rolleyes:

It is not a good idea to shoot Ha (or any narrowband) in B&W mode on the camera.  Greyscale averages/blends all the color channels together to get B&W, i.e.: it blends the red, green & blue channels.  If you're shooting Ha subs it is far better to shoot color subs then split the color into its red, green and blue channels, and only use the red channel.  Discard the green and blue channels because they very likely contain nothing except noise.

bwa

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ollypenrice

ollypenrice

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Posted

It is not a good idea to shoot Ha (or any narrowband) in B&W mode on the camera.  Greyscale averages/blends all the color channels together to get B&W, i.e.: it blends the red, green & blue channels.  If you're shooting Ha subs it is far better to shoot color subs then split the color into its red, green and blue channels, and only use the red channel.  Discard the green and blue channels because they very likely contain nothing except noise.

bwa

Indeed. Since the blue and green filters pass only blue and green light, and since they didn't get any blue and green light to pass because that was blocked by the Ha filter, they are best discarded. What they may contain, though I don't know for sure and it depends on how the camera software works, is an interpolation of what lies on the missing pixels derived from what is seen on the red ones. If this is so then 3/4 of the image is guesswork, which doesn't sound good to me.

Olly

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Mick J

Mick J

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Posted

so did anyone ever figure out who is flipped, and who is not? :)

Post #58 Ole (Xplode) flipped,  Interesting thread you've started here, thanks - interesting to follow.   :smiley:  :smiley:

Stunning seeing the exposure time on these shots, Brian's (bwana) Sony A7S numbers are something, half hours work and he's done.

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vertigo262

vertigo262

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I was doing a lil research :)

You can use the sony software to capture sequences tethered, and you can use capture pro 8.1  for sony to use it's live view tethered. 

not as nice as something like APT, but it would get the job done tethered to a laptop.

All I need is bwana to give me his a7s : O)

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ollypenrice

ollypenrice

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Post #58 Ole (Xplode) flipped,  Interesting thread you've started here, thanks - interesting to follow.   :smiley:  :smiley:

Stunning seeing the exposure time on these shots, Brian's (bwana) Sony A7S numbers are something, half hours work and he's done.

They are indeed good for the exposure times and do make me wonder about the future of chip technology.

Olly

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ollypenrice

ollypenrice

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Posted

Flips just occur in software and can be instantly unflipped in most astro software along with Photoshop etc. When we export captues from Nebulosity on a Mac we get a flipped image, though on the capture screen it's normal. This doesn't happen when we capture in Artemis on a PC. It isn't a problem though.

Olly

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