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Martin Meredith

Table of mono cameras for EAA

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On 07/03/2019 at 06:12, Martin Meredith said:

I've been looking into the state of mono cameras for EAA under 2.5 megapixels and thought it might be useful to share what I've found. Let me know if you have any of the missing info, anything needs correcting, or if I've not included cameras that I should have, and I'll update the table. 

[updated 8th March 2019]

48116417_ScreenShot2019-03-08at21_33_03.thumb.png.54f51521ad6b8e8a9579a920b0f68c4a.png
 

Notes

(1) These are all uncooled except for Atik 414EX

(2) All except the two Atik models have a 1.25" profile so can slide into a 1.25" eyepiece barrel to reach focus.

(3) The two FOV and resolution (res) columns are meant to be illustrative for two types of scopes often used in EAA (that I happen to have at hand). "Quat" is an 8" f/4 Quattro Newtonian reflector. "Borg" is a 77mm f4.3 refractor.

(4) QE is given along with peak wavelength

(5) Prices as of 7th March 2019

(6) mp = megapixels

(7) read noise in e- is a 'typical' value as obtained from manufacturers specs in the main; check the specs to see how it varies with gain etc. Likewise FWC = full well capacity varies with gain. 

Courtesy of astronomy.tools, here are indications of the FOV for most of these sensor/scope combinations (note that the same sensor is used in the Ultrastar and the two Atiks so only the Ultrastar is shown)

8" f/4 Quattro:

1551862511_ScreenShot2019-03-07at14_57_46.png.03b93df75723f9ea4f09403f7b7ece88.png 

77mm f/4.3 Borg:

1059171937_ScreenShot2019-03-07at15_06_37.png.87e853c4e01a1adb5f3ff301da21768d.png

 

[Edit] I should probably add that much of this info is pulled off FLO's website!

Hi Martin,

SX also has the SX825 Trius that is the cooled version of the Ultrastar.  I imagine specs are the same as the Ultrastar similar to the Atik 414 v Infinity.

Don

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5 hours ago, Martin Meredith said:

A quick look suggests it is certainly possible that my formulation is wrong. The main effect of this change in terms of the numbers above will be to boost SNRs across the board in the N=30 subs case (with more boosting as N gets larger), which will favour the high read noise sensors (so the numbers for the Costar will be increased the most, and the ASA 290 the least). Does this agree with your findings?

I'll look in more detail tonight and update the tables.

cheers

Martin

If the read noise of stack scales as sqrt(n)*read noise, I get - which indeed agrees with the statement above 

image.png.ea08b17c9e87750e31239a83e1edb6ec.png

As I say, I don't know if one is right (and which one is right). I am using the calculations for a different purpose - namely to optimise (determine the minimum) exposure for an acceptable increase in noise for a stack.

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Having dug out my 'bible' for this kind of thing (Berry and Burnell's Handbook of Astronomical Image Processing; excellent but expensive unless you can find a 2nd hand copy like I did) and done a few more simulations, I think you are right that I should be using root(N) here. I've been looking at keeping the total exposure constant (say 1000 s) and changing the number of subs. My formula doesn't behave as it should for large N (that is, the SNRs get unreasonably low), whereas using root(N) the SNRs don't vary that much, within the expected range for the 'mere' effect of read noise. So I'm going to update the code and the tables.

⚠️ For anyone reading down this far into the thread take note: the code has changed slightly!

Thanks for spotting this, and good luck with your project.

Martin

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Thanks Don for the Trius suggestion. When I get round to adding all the other cameras that have been suggested I will certainly add it in. A quick calculation suggests it will score 3.18 in the SNR stakes for the 10 x 30s subs, and 3.16 for 30 x 10s subs. Once we are sure there are no more bugs I will produce some charts too.

Martin

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I find myself wondering if this can be used to justify the often repeated assertion that with a CMOS camera it's better to take more shorter exposures rather than fewer longer ones.  I'm not sure what the definition of "better" is, but I'd assume it means a maximised SNR.  I must read the linked paper and get my head around the maths.

James

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I am not sure we will ever get a definition of "better" for various reasons.   Maybe the assertion that a CMOS is better for shorter exposures vs longer exposures for a CCD is true but I have not seen any large datasets with statistics to back this up.  I think this can only be done using various CMOS and CCD cameras on the same scope at the same time on the same ROI,  multiple times over various nights under various sky conditions.  I doubt this will ever happen.  Instead, what we mostly read and hear are the theoretical  physics as to why this has to be true.  Nothing wrong with that and, in fact, that is extremely important.  However, like I have said in the past, if I had a dime every time  we (me and my research colleagues) theorized on an outcome of an experiment we planned doing our neuroscience research and theorized "A" but got "B", I could have retired years ago.  Nature has a way of fooling us even if we think we have all of the theoretical information to predict the outcome.  Besides, in the end, each of us decide "better" for ourselves. 

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Hi Bruce

I see this kind of model as just a starting point for generating and maybe one day testing hypotheses. It would be great to set up a dual rig but not something I can easily do here. However, a sequential test on a run of similar nights would be possible if seeing is measured adequately. Hmmm. Maybe it is time to invest in an ASI 290mm. 

Incidentally, as someone who occasionally works with cognitive neuroscientists myself, I'd say neuroscience is orders of magnitude more complex than the CMOS/CCD debate! At least we think we know the laws that photons and the associated capture electronics obey...

Martin

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Hi Martin

Agree- studying neural networks are a tad more complicated than a stream of photons being converted into a digital value.

If you figure out and decide to setup a dual rig, I am sure that Don and I will come over and help you test things out! :)  

Bruce

 

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Although on reflection, the Watec cameras are perhaps not as commonly used as the other cameras in your list. Their output is composite video which requires an analogue to digital convertor to be able to link it up to a laptop. 

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2 hours ago, London_David said:

@JamesF @umasscrew39 a good explanation about short and long exposures and some other things around this is here:

 

Not seen that one before.  Thanks for the link.

James

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Posted (edited)
23 hours ago, Phil Fargaze said:

Although on reflection, the Watec cameras are perhaps not as commonly used as the other cameras in your list. Their output is composite video which requires an analogue to digital convertor to be able to link it up to a laptop. 

True Dat! Aside: Have just "exhumed" my Watec 910HX and now putting it through
its paces again. Indeed, with addition of an ADC, a possibility of RT stacking exists... 
Sharpcap identifies (the typical!) USB *Capture* Dongles as "USB 2861 Video" now. ?

I'm *still* using a Watec 120N+ as an "All Sky" (Meteor!) Camera with a 6mm Lens.
Have an Watec 902H2 Ultimate too. With 9x50 finder scope now... "Electro Finder"! ?

? 8-bits (only)... large pixels. The  result is a bit "blobby" and requires... "twiddling":

crop.jpg.5caa1680b85585b044b3e2bbe50e4d24.jpg


The "integrating" Watec cameras I NOW think of as "summing" rather than stacking 
(as in averaging) cameras? But I'm pleased there may be LIFE in the "old dogs" yet! ?

Edited by Macavity

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