My first live stacks.

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nexusjeep
Posts: 105
Joined: Thu Oct 18, 2018 3:01 pm

Re: My first live stacks.

Post by nexusjeep » Sat Mar 23, 2019 10:11 am

Andy cracking images just wish the skies here would clear.

I agree with Robin that amazing images can be achieved with CMOS cameras that will compete with CCD and as Robin points out and explains exceptionally well in the talk at this years conference there are pro's and cons for both setups but one cannot be said to be outright better than the other. This is a similar discussion that would have been had 20 years ago between film camera users and digital cameras users with the debate that they would never be as good but try and find film cameras now and they are a rarity a bit like hens teeth.

I am not saying CCD will go the same way I am just stating that they are two diferent technologies that achieve a similar end result. As for the long exposures the photons are hitting randomly over the course of a period of time and if you use CMOS or CCD over that period of time the same number of photons arrive on the end of the telescope QE efficiency will determine the capture rate of these so different QE will have an effect between different sensors. However if there are a thousand photons and you do 6 x 10minutes exposures on a CCD versus 30 x 2m exposures on a CMOS then I do not see that there will be that much differnce as the read time on a CMOS is dramatically faster than CCD so the potential shutter open time (if we had one) would be very similar between each sensor so you would capture the same number of photons assuming QE was the same.

Then in the stacking stage the CMOS 30 frame stack would potentially have a lower noise level as signal to noise ratio significantly improves based on the number of images in the stack as explained by Robin in his talk.

The other thing when comparing images is you are not solely comparing the sensor as the optics will have a massive effect as well as seeing and other factors so you would never be getting a true comparison unless you had the exact same rig at the exact same time and place with exactly the same quality CCD sensor on one and CMOS sensor on the other and collected the same total exposure time regardless of sub length. With cameras you always aim to buy the most expensive glass as this will be with you the longest as camera / technology improve but the lens not so much.

Just my two cents worth not trying to start yet another CCD vs CMOS debate as I would rather spend my time imaging if the skies ever clear.

Cheers
Nick

MrAstroBen
Posts: 52
Joined: Fri Mar 16, 2018 12:19 pm

Re: My first live stacks.

Post by MrAstroBen » Sat Mar 23, 2019 11:08 am

https://www.astrobin.com/search/?q=183C&d=i&t=all

Cmos 183 sensor

https://www.astrobin.com/search/?q=694&d=i&t=all

694 CCD sensor

https://www.astrobin.com/search/?q=8300&d=i&t=all

8300 CCD sensor

https://www.astrobin.com/search/?q=Ccd& ... ras&page=2

CCD

The evidence speaks for itself.

The 1600 cmos sensor does well in mono form and a few others, 300s subs are common though.

Study the image of the day catalogue, how many are from Cmos cameras using short exposues?

We need to see the evidence please.

https://www.astrobin.com/iotd/archive/?page=2

AndyBooth
Posts: 46
Joined: Thu Mar 01, 2018 6:55 pm

Re: My first live stacks.

Post by AndyBooth » Sat Mar 23, 2019 2:56 pm

Nothing like a healthy discussion 😃

The thread summarises my position, my CCD viewpoint of old, compared to the new Viewpoint given by Robin in his talk.

I intend to do some experiements therefore, to see the results.

With the colour CMOS, using Robins equations, and my usual sky conditions, I will take 30s exposures, at gain 200, black point 24, for as long as I can In an evening (hopefully around 3hrs- my normal imaging window).

Next outing, QHY10, using Robins equations, 120s exposures, gain and offset as per my normal settings, and for same overall ‘shutter open’ time as I got with the CMOS. (Elasped will be nearer 3 3/4hr due to readout time.)

Compare noise and see what we get😀

Thanks for everyones contributions.

nexusjeep
Posts: 105
Joined: Thu Oct 18, 2018 3:01 pm

Re: My first live stacks.

Post by nexusjeep » Sat Mar 23, 2019 6:20 pm

Not wishing to start a lengthy debate suffice it to say everyone has there own opinions and are entitled to them I am just trying to say that simply stating long exposures and CCD are better is not that scientific, also thanks for the astrobin links

Cmos 183 images 8 pages worth
CCD 694 images 9 pages worth
CCD8300 images 59 pages worth
CCD on its own 43 pages worth

very nice images as and as you alluded to the ASI1600mm sensor astrobin search that you failed to include

1600mm + filter to imaging camera 56 pages worth of images including top pick + image of the day
1600mc + filter to imaging camera 13 pages worth of images including top pick awards.

CMOS is a newer technology and as such CCD has been around longer so there will be a larger user base at present for CCD but who knows what the future will bring each current technology has there own strengths and weaknesses but the whole fun of the hobby is experimenting and trying new things and approaches not simply stating that this is the way we have always done it so it must be the best method.

Cheers
Nick

nexusjeep
Posts: 105
Joined: Thu Oct 18, 2018 3:01 pm

Re: My first live stacks.

Post by nexusjeep » Sat Mar 23, 2019 10:28 pm

I know its not good practice to reply to my own post but thought it better as a reply rather than an edit in case anyone had already read the previous one as to the question of short exposure the image of the day from 03/08/2019 is from a 1600mm cool 50 second exposures at unity gain so not massively long and the image is very impressive of M106 and a very large number in the stack.

https://www.astrobin.com/393292/?page=3&nc=iotd

Cheers
Nick

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oopfan
Posts: 456
Joined: Sat Jul 08, 2017 2:37 pm
Location: New York
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Re: My first live stacks.

Post by oopfan » Sat Mar 23, 2019 11:44 pm

Nick,

If I am reading this correctly, his scope is a Rowe-Ackermann Schmidt Astrograph having an aperture of 280mm and focal length of 620mm. His f/ratio is f/2.2. With luminance filter he took 30-second exposures. To make a fair comparison I need to calculate the equivalent exposure with my f/5.9 scope.

From this article:
https://en.wikipedia.org/wiki/F-number
after algebraic rearrangement of terms:

d = (log(n2) - log(n1)) / log(2^0.5)
E2 = E1 * 2^d

where:
n1 is the f/number of the scope you are coming from.
n2 is the f/number of the scope you are going to.
E1 is the exposure in the n1 scope.
E2 is the exposure in the n2 scope.

Given:
n1 = 2.2
n2 = 5.9
E1 = 30
d = (log(5.9) - log(2.2)) / log(2^0.5) = 2.85
E2 = 30 * 2^2.85 = 216

So, his 30-second exposure at f/2.2 is equivalent to my 216-second exposure at f/5.9

Thankfully the brightest star in the field of view is magnitude 10.6. My rule of thumb with my equipment is to limit exposures to 50 seconds if the FOV contains a 9th magnitude star that I can't or won't crop out. I do that in order to prevent stars from saturating. With a magnitude 10.6 star I could increase my exposure 4 times. So 4 times 50 seconds is 200 seconds. That is awfully close to his 216-second equivalent exposure.

30-seconds sounds short but that's at f/2.2

Brian

MrAstroBen
Posts: 52
Joined: Fri Mar 16, 2018 12:19 pm

Re: My first live stacks.

Post by MrAstroBen » Sat Mar 23, 2019 11:54 pm

An F2 RASA x 17.5 hrs.

Each f stop is a factor of 2 increase.

F2, f2.8, f4, f5.6

F2 x 50s is equal to a long exposure at f5.6

The noted data for Ha is 150s.

This example is demonstrating the benefits of equivalent long exposures.

MrAstroBen
Posts: 52
Joined: Fri Mar 16, 2018 12:19 pm

Re: My first live stacks.

Post by MrAstroBen » Sun Mar 24, 2019 12:28 am

nexusjeep wrote:
Sat Mar 23, 2019 6:20 pm
Not wishing to start a lengthy debate suffice it to say everyone has there own opinions and are entitled to them I am just trying to say that simply stating long exposures and CCD are better is not that scientific, also thanks for the astrobin links

Cmos 183 images 8 pages worth
CCD 694 images 9 pages worth
CCD8300 images 59 pages worth
CCD on its own 43 pages worth

very nice images as and as you alluded to the ASI1600mm sensor astrobin search that you failed to include

1600mm + filter to imaging camera 56 pages worth of images including top pick + image of the day
1600mc + filter to imaging camera 13 pages worth of images including top pick awards.

CMOS is a newer technology and as such CCD has been around longer so there will be a larger user base at present for CCD but who knows what the future will bring each current technology has there own strengths and weaknesses but the whole fun of the hobby is experimenting and trying new things and approaches not simply stating that this is the way we have always done it so it must be the best method.

Cheers
Nick
Nick,

Image of the day is current data. So the age of the camera technology becomes irrelevant.

Yes, i highlighted the 1600 sensor as an example of a cmos camera that performs well. As you note 56 pages so a lot of posted images indicating a lot of submissions. More than many of the CCD examples.

I have no doubt Cmos out sells CCD by a considerable margin.

I dont see a lot of very short exposures though so not sure of the relevance facts being submitted?

I own 4 cmos cameras.

My guidecam is cmos, my Allsky camera is cmos and I use cmos for solar imaging.

Cmos has benefits for various applications and the cost can be low.

What I wish to see are the examples of images taken using a cmos camera and short exposures which match or better the best examples @ equivalent f ratios?

I have no vested interest in any technology or brand.

I am just interested in the evidence.

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