ZWO ASI 120MC versus Philips SPC900NC

[michael8554]

ICX098BQ Sony HAD Colour CCD sensor, 640x480, 5.6um x 5.6um, 8bit  (Philips SPC900NC)

AR0130CS CMOS Colour sensor, 1280x960, 3.75um x 3.75um, 12bit  (ZWO ASI120MC etc)

Which of these sensors is the more "sensitive" in 2 to 4 second exposures at full resolution, so will be better at seeing dim guide stars?

Michael

[Cornelius Varley]

No contest. The ASI120 is a better camera. 

[michael.h.f.wilkinson]

Agreed. I have had both, and the ASI120MC is a hands-down winner in terms of sensitivity (and most other things, really).

SPC 900NC:

ASI120MC

 

Same scope used

[michael8554]

Nice images Michael.h.f. but to me neither demonstrates better sensitivity ??

Michael

[Cornelius Varley]

58 minutes ago, michael8554 said:

Nice images Michael.h.f. but to me neither demonstrates better sensitivity ??

Michael

The ASI 120 is a better and more sensitive camera.

[michael8554]

Thanks Peter, the Saturn images were presumably stacked high speed avi's, I was after info on 2 to 4 second long exposures.

Michael

[Zakalwe]

Given that the SPC is now 13 year old technology I'd be amazed if it was anyway near as sensitive as a modern camera. I would think that that would be self evident.

[RichLD]

It's also probably worth mentioning the superior noise floor and superior DR of the 12 bit ZWO, which has to be a plus whatever the application.

[michael8554]

Well folks, without some figures to back up the statements, I'm not convinced.

As Zakale says, after 13 years the ZWO should be better - but I don't yet find it self evident.

For instance, the Sony pixel area is over twice that of the AR - so which sensor is more sensitive now.......??

Better Sig/Noise and Dynamic Range most likely, but I find the 2x2 Noise Reduction in PHD2 makes a big difference.

Remember I'm interested in Guiding, not sharp high speed imaging on bright planets.

Michael

[Zakalwe]

55 minutes ago, michael8554 said:

Well folks, without some figures to back up the statements, I'm not convinced.

As Zakale says, after 13 years the ZWO should be better - but I don't yet find it self evident.

 

 

Really?

You don't think that over 13 years of development in a fast moving field such as digital imaging that the advances in both sensors and control electronics will not produce a better dedicated astro cam compared to a re-purposed consumer webcam?

 

55 minutes ago, michael8554 said:

Remember I'm interested in Guiding, not sharp high speed imaging on bright planets.

I can't understand why you are considering a colour camera then? The mono will be more sensitive as it does not have a RGB Bayer matrix.

 

[michael8554]

3 minutes ago, Zakalwe said:

Really?

You don't think that over 13 years of development in a fast moving field such as digital imaging that the advances in both sensors and control electronics will not produce a better dedicated astro cam compared to a re-purposed consumer webcam?

Like I said - probably, but not proven.

I can't understand why you are considering a colour camera then? The mono will be more sensitive as it does not have a RGB Bayer matrix.

Agreed, but a colour one would be more versatile for me - and if it's as sensitive as you suggest, it shouldn't be a problem ?

 

 

[Zakalwe]

I can't find a QE chart for the ICX098QB that the SPC camera uses. I stand by my feeling that over a decades worth of development in sensor and electronics will leave the SPC in the dust though. Sensor technology is moving at an enormous rate. To give an example, the old DMk21au04 camera used the ICX098QB sensor and it was comprehensively beaten by the latter DMK21au618 which used the 618 sensor.

Secondly, the ZWO camera has a physically larger sensor, giving a better opportunity of having a guide star on-chip. Guiding with a tiny sensor can be a frustrating experience.

Lastly, if getting dim stars is your goal, then a mono camera is the only option. The Bayer matrix on a colour camera cuts the sensitivity down, and there's no need for colour on a guide camera.

What exactly are you trying to achieve? What guiding arrangements are you using (OAG/guidescope?) and what focal length are you imaging at? It's a strange comparison to be considering, IMHO,- a decade old modified webcam compared to a relatively modern astro cam. Why this comparison?

 

[Gina]

My thinking too.  Only if you have the SP900NC and nothing else should you consider using it for the dark stuff and save a little cash.  It may work but you're giving yourself much more difficulty in an already difficult job.  A sensitive guide camera will make it so much easier to find a star to guide on.  Believe me I've been there.

[michael8554]

"the ZWO camera has a physically larger sensor,  giving a better opportunity of having a guide star on-chip"  -  Good point Zakalwe, hadn't spotted that.

" What exactly are you trying to achieve? "  -  my LX modded SPC900 has never failed to find a guide star at the 2 to 3 second exposures I guide at, but I feel the guiding would be better at the arcsec/pixel the GPCAM/ZWO cameras  would provide.

But these cameras have CMOS sensors versus CCD  (but yes, I think it is safe to say the technologies are now similar in sensitivity, they weren't 13 years ago).

And pixels half the size.

So before I shell out £160, I'd simply like to know are they as sensitive, and nobody has come back with a clear statement such as  "I get more guide stars with the ZWO".

Yes Gina, a sensitive guide camera makes it easier - but is it more sensitive, with all your Sky Cam work surely you know the answer to that?

Michael

[riklaunim]

Well, I never guided on 2 seconds, always 1 sec, or sometimes 0,5sec. I've started with DMK21 then went to DMK21AU618, QHY5, ASI120MM and now I can guide with ASI178MM Cooled but that would be an overkill as it's intended to be the imaging camera in my rig. QHY5R-II will guide it.

If you use a finder-guidescope or alike small refractor than nearly any guide camera will work. I would pick a ST4 guide camera (AS034 or QHY5R-C at minimum, ASI120/QHY5L-II at optimum) just for the sake of easy ST4 (had to many random crashes wit RS232-USB and Windows). SPC900 and modern Windows versions will a problem too. In general ASI120/QHY5L-II are Windows 10 supported, don't compress the image, have USB 2.0 speed (not 1.1), and as for sensors - lower read noise and around 2x the QE (plus it's mono not color).

If you use an OAG then you need a really good guide camera. Things like Atik Titan, SX Lodestars and alike come to play as they seems to benefit most from X seconds exposures when looking for guide stars. Newer CMOS based planetary cameras - 174, 178, 290 would do it too due to way lower read noise but if you want to guide only - better to pick dedicated guider for more challenging setup.

 

[Gina]

I gave up using the SPC900 several years ago as not having sufficient sensitivity.  I use OAG for guiding and ended up with the Lodestar X2.  I haven't tried using the new ZWO cameras for guiding but having great success with using the ASI178MM for all sky and the ASI1600MM-Cool for imaging though I've only had an hour or so of clear night sky for the latter.

[Guest]

I use the ASI120MC for guiding and never fail to find a guide star with an AltAir 60 mm finder guider

As it's an MC I can use it for planetary too which is a perfect combo :-)

I don't have any numbers to back up my decision to use this camera but it works perfectly so hopefully that might help you make a decision :-)

David

 

[Stub Mandrel]

The ZWO is 12 bit, the SPC is 8 bit.

This suggests that the ZWO is able to detect a 16 times smaller signal difference.

[michael.h.f.wilkinson]

In my Saturn shots, I could use shorter exposure times, and lower gain in the ASI120MC than in the SPC900. On the SPC900 I needed to drop to 5 FPS on Saturn to get decent S/N in each frame, whereas I could rattle along at 20 FPS on the 120MC. That suggests the ASI120MC is a lot more sensitive. I recall the SPC900NC had the same sensor as the old DBK21, which in the DMK counterpart sported a QE of about 32%, versus 68% for the later 618 version. That means more than double the sensitivity, assuming no improvements in read noise control. I seem to recall the ASI120MM had about a 75% QE, but I might be wrong.

[michael8554]

Thankyou all, some comparisons at last, and there doesn't seem to be much doubt!

Now trending towards a mono version.

Choice seems to be between:

ZWO ASI 120 MM

Touptek GCMOSO1200KMA

OpticStar PL-131M

Altair GPCAM

But seems that only the ZWO has T-2 thread, all the rest are C/CS mount.

Michael

[riklaunim]

Skip OpticStar, Touptek rather too. Altair is a Touptek related camera but the vendor seems to care and support it (and is in UK). ZWO/QHY are the most well tested and supported.

There is no problem in going from C/CS thread to 1,25" nosepiece.

[michael8554]

Thanks riklaunim

I believe the C/CS cameras all come with a C/CS to 1.25mm nosepiece, the ZWO has T-2 M42x0.75 threads plus a screw-in 2" nosepiece.

Flex is the perennial problem with guiding, so I have always used rigid T-2 adapters for guiding.

With the SPC900 I use pulse guiding - a long USB to the PC, a long RS232 back to the mount.

The ZWO offers ST4 - a long USB to the PC, a short ST4 to the mount.

Pulse guiding with one less cable between the OTA+Guidescope and the mount seems the better option?

Michael

 

[Gina]

Having used both QHY and ZWO cameras I would definitely go for the newer ZWO cameras - a lot more sensitive.  I'm very impressed with ZWO cameras even compared with CCD astro cameras like Atik.

[michael8554]

Well took the plunge and FLO are now minus a ZWO ASI120MM.

Drivers installed and camera working on a W7 netbook and a XP PC without any hassles.

When some T2 spacers arrive I'll try it guiding, but with the supplied wide angle lens it appears to be much more sensitive, and has less noise, than the modded SPC900.

Michael