ASI1600mm cool vs 383l

[matt-c]

An inevitable question but Im just about there for my next ccd upgrade (atik 383l) when i heard of the ASI1600, it seems to go against everything i've came to understand and actually prefers shorter exposures.

I really like the idea of shorter subs having similar quality to long ones but with an added bonus of less dependancy on guiding.

Is this the case or am i not understanding correctly?

Also what are the pros and cons to going cmos over ccd in todays world of cooled cmos.

Cheers

Matt

[Chris]

Hi Matt, yes I think you're understanding it correctly, I don't think you would need guiding at all with how these new CMOS cameras work as you can just take hundreds/thousands of short exposures, even down to 1 second subs! It's more akin to planetary imaging.

I had a little play with DSO's and an ASI120mm and it was very promising, when I say little play I was rushing to set up as the clouds were rolling in so only managed a couple of 3 second or so subs on M82. Still it looked very promising and I could imaging that if you took loads of subs and calibrated out the noise you would end up with something nice to show for it

I don't know about cooled CMOS but uncooled CMOS sensors seem to be noisier and have more amp glow if you compare a single sub to a CCD, although it's straight forward and quick to take darks and flats with such short subs.

Production wise I've heard that CCD sensors are being phased out, in which case I'm sure there is a lot of R&D going on with CMOS. Who knows what kind of cameras we'll be using in a few years time!  

[ChrisLX200]

I've seen some nice results on the brightest of objects but for the fainter ones you still need to collect enough photons, so short exposures and low read noise are only going to get you so far. I'm interested in these developments myself but I'm not sure I want to jump in just yet - this is the New Kid on the Block with a price tag to match.

ChrisH

[Gina]

I shall be jumping in with both feet when I can afford it   The ASI1600MM- Cool is about two thirds the price of the Atik 460EX that I currently use for DSO imaging, with a bigger sensor and lots more pixels.  Of course, the smaller pixels will probably make it less sensitive than the Atik, unbinned.  I'm really looking forward to trying this new technology and think it should revive my interest in astro imaging, which has flagged recently.

[ChrisLX200]

Problem for me is that the 1600 sensor needs 2" filters, my 490EX uses 1-1/4" and whilst the Moravian G4-16000 has 50mm square filters the wheel itself needs the Moravian camera to function. So - no filters I can use :-(  I really don't fancy shelling out for yet another set of filters.

ChrisH

[Chris]

22 minutes ago, ChrisLX200 said:

I've seen some nice results on the brightest of objects but for the fainter ones you still need to collect enough photons, so short exposures and low read noise are only going to get you so far. I'm interested in these developments myself but I'm not sure I want to jump in just yet - this is the New Kid on the Block with a price tag to match.

ChrisH

This is an interesting point Chris, I wonder if anyone has done the practical on this and tried them on some fainter objects? 

I know CMOS sensors are cheaper to produce, so maybe they will stay relatively cheap with a bit of luck

[Gina]

According to ZWO this camera can use 1.25" filters if sufficiently close to the camera.  The sensor diagonal is 21.9mm which is less that an inch.  I shall certainly be trying with 1.25" filters in the Atik filter wheel with camera directlty attached.  Mind you, if I get good results with this camera I might sell my Atiks and buy asi1600MM-Cools for my tripple imaging rigs instead

[Chris]

This thread has spurred me to dig out my 4 second sub with the ASI120mm, taken with an ED80 at f/7.5.

Considering it's just one sub with no calibration on a non cooled older tech CMOS camera, I'm pretty impressed! The 1600 should be very interesting.

M82_4secASI120mm.TIF

[matt-c]

Thanks for the replies Its exciting times!

Is the ASI capable of longer exposures to catch the fainter stuff without introducing issues? I must admit that would put me off if i couldnt get the faint stuff.

Other than worrying if i should buy into this new line of cameras for fear of bugs and hiccups down the line i think currently the ASI is winning 

[riklaunim]

5 minutes ago, matt-c said:

Is the ASI capable of longer exposures to catch the fainter stuff without introducing issues? I must admit that would put me off if i couldnt get the faint stuff.

1. it can do long exposures, 2. you should be able to catch faint stuff at shorter exposures too due to lower read noise. So in most cases you won't need many-minute long exposures.

[matt-c]

Is this the same with narrowband aswell? Because thats amazing if so

[Gina]

I don't see why not but maybe someone with more knowledge could confirm this.

[DaveS]

I think this is about as short a distance as you could mount a filter:

http://www.teleskop-express.de/shop/product_info.php/info/p2165_Filter-Quick-Changer-incl--1x-1-25--filter-drawer---low-profile.html

If you removed the ring from the camera you would have a very short distance and might get away with 1.25" filters.

[johnrt]

The QE graph on the ASI1600 suggests it should respond to narrowband wavelengths, the response at 656nm (Ha) is just under 80% according to this graph from the FLO, comparable to the current generation CCD chips in use in for example the 460ex.

 

[riklaunim]

12 minutes ago, johnrt said:

The QE graph on the ASI1600 suggests it should respond to narrowband wavelengths, the response at 656nm (Ha) is just under 80% according to this graph from the FLO, comparable to the current generation CCD chips in use in for example the 460ex.

Note that it's a relative chart, not absolute and can't be compared against other if you can't scale it to absolute QE values.

[riklaunim]

4 hours ago, matt-c said:

Is this the same with narrowband aswell? Because thats amazing if so

Yes. Narrowband is limited by signal/noise ratio you get from the camera and skyglow - from Moon, light pollution and what not.

[ChrisLX200]

Remember the ADC in this camera is only 12-bit though (at best - it also does 10-bit), quite different to the 16-bit CCD cameras we are used to. This means the fainter signals we might be interested in lying just above the noise level are not as well resolved in terms of dynamic range.

ChrisH

[rwg]

9 minutes ago, ChrisLX200 said:

Remember the ADC in this camera is only 12-bit though (at best - it also does 10-bit), quite different to the 16-bit CCD cameras we are used to. This means the fainter signals we might be interested in lying just above the noise level are not as well resolved in terms of dynamic range.

ChrisH

I'm not sure that the ADC bit depth on its own is a valid comparison measure - the real measure of interest is the dynamic range between the brightest signal that is not quite saturated and the noise floor. In that respect a 12 bit sensor (4096 levels) with +/- 1 noise would have exactly the same range as a 16 bit sensor (65536 levels) with +/- 16 noise - in both cases a factor of 4096. (Not that I'm claiming those particular noise levels apply to the sensors being compared - just making an example).

The extra fine division levels on the 16 bit sensor in the example above doesn't gain you any extra data since all those fine levels are doing is recording the noise.

Robin

 

[ChrisLX200]

I'm looking for excuses not to buy one and you're not helping Robin... !

:-)

 

ChrisH

[rwg]

2 minutes ago, ChrisLX200 said:

I'm looking for excuses not to buy one and you're not helping Robin... !

:-)

 

ChrisH

I'm pleased with mine, although I've only had it outside maybe twice so far due to a combination of bad weather, summer and other commitments.

My take is that the non-cooled colour version would be difficult to justify if you already have a DSLR. From what I've seen of how the dark noise dies away with cooling, I'd probably not be tempted by the non-cooled mono either.

Just to put cat amongst pigeons, QHY have posted a teaser on their facebook page today for what looks like an equivalent camera

cheers,

Robin

[Andyb90]

3 hours ago, ChrisLX200 said:

I'm looking for excuses not to buy one

Probably best to avoid Cloudy Nights at the moment then  There are some nice images being posted 

Edit: Well at least any threads with 'ASI1600' in the title. 

Andy.

[derrickf]

17 hours ago, ChrisLX200 said:

Problem for me is that the 1600 sensor needs 2" filters, my 490EX uses 1-1/4" and whilst the Moravian G4-16000 has 50mm square filters the wheel itself needs the Moravian camera to function. So - no filters I can use :-(  I really don't fancy shelling out for yet another set of filters.

 

2 hours ago, ChrisLX200 said:

I'm looking for excuses not to buy one and you're not helping Robin... !

The sensor of the 1600 is much closer to the front of the camera body than in the Atik 383L so you may be able to get away with 1.25" filters.

You can calculate the minimum filter clear aperture required for full illumination using the formula:

minimum filter size = CCDdiag*(FL-DC)/FL + (DC/f), where FL is focal length, CCDdiag is the size of the chip diagonal, DC is the distance between the chip and the filter, and f is the focal ratio of your scope

 

 

HTH

Derrick

[Gina]

Right then, let's see how it does with my SW Esprit 80ED Pro with 400mm FL and f5 plus Atik EFW2 filter wheel.  I'll have to check further but it looks like the filter to camera reference plane is about 10mm.  Camera back focus = 6.5mm so filter to sensor = 16.5mm (approx).

Now to apply the formula...  minimum filter size = CCDdiag*(FL-DC)/FL + (DC/f) = 21.9x(400-16.5)/400 + 16.5/5

1. Chip diagonal = 21.9mm
2. (FL-DC)/FL = (400-16.6)/400 = 0.95875
3. x 21.9 = 20.996625
4. DC/f = 16.5/5 = 3.3
5. Adding these gives 24.296625 or 24.3.  This is less than an inch.

Q.E.D.

[MattJenko]

Hi Gina,

That conclusion is what I came up with as well for my setups. I have a TS60 with reducer at a FL of 260 and Fratio of 4.3 : 25mm. 10" Newt at FL1200 and Fratio of 4.9 : 26mm. I went for a longer chip distance of 21, using a rounded up half thickness of my SX Filter wheel. No new filters for me . I do expect a bit of flattable vignetting though, but the theory points to a win.

Matt