First Light with new ASI585MC Pro.: Page 2

First Light with new ASI585MC Pro.

w7ay

Kevin_A the amount of hot pixels at HGC

Hope this is not a trend. There are already zillions of hot pixels in the ZWO 2600/6200/533 series. Have you tried gains pf 20dB to 30dB with those cameras? More hot pixels than bright stars :-).

Chen

Kevin_A

w7ay I tried at 25db and that was too much. This camera is worse at HGC than my 533 and 2600 cameras. I think with this 585 camera the FWC is so small at that gain that they just light up like Christmas from current leakage…. But who knows. At unity they are easily managed.
So I prefer to use where the FWC is fairly normal maybe at 15db and I can deal with the read noise with more subs and it will allow less saturation of bright objects too. Luckily my use is on smaller dim galaxies. Narrowband with filters may prove better with higher gains or Unity.

w7ay

Kevin_A I can deal with the read noise with more subs

Yeah, no other way around that :-).

My cooled ASI585 arrived this morning, but the clouds have not departed :-).

Chen

w7ay

Kevin_A I

OK, I just did a different Frankensteining... I mixed and matched end plates of the "new ZWO 54mm filter drawer" with a "new ZWO 42mm drawer." So now I have a Franken drawer with a 54mm hole, with a T2 male on the other end for the ASI585's native 11mm T2 ring.

I would still need the PreciseParts adapter when I need to use a 54mm Filter Wheel.

No clear nights in sight, according to Wunderground.

Chen

w7ay

Kevin_A

OK, Moon uncropped (but resized) single exposure through 455mm focal length and the cooled ASI585 (0 dB gain), with ASIAIR. Through thin clouds, 1 hour before sunset, just the IDAS HEUIB. Looks clean enough with such short (10ms) exposure.

I should try the camera on the FOA60-Q (highest Strehl commercial scope :-) at 901mm focal length; should fill the frame nicely, albeit with only 60mm aperture.

Pity it is a Bayer camera, otherwise I can try it too with Solar.

Should have a clear night on Tuesday.

Chen

w7ay

Kevin_A I tried at 25db and that was too much.

One hour before we leave astronomical twilight, the ASI585MC-Pro at Unity gain, 180 second. 455mm-f/5.4. Already quite noisy, but workable. Just average more frames.

Cooling of the small camera is no sweat at all. 8ºC ambient, -10ºC with just 25% cooler power consumption.

Chen

w7ay

My cooled ASI585 arrived this morning

More ZWO cables to add to the thrash. Sigh. Their cables even looks like garbage.

Swapped in my Frankenstein M54 female to M42 female x 11mm thick spacer on the ASI585 already :-). PreciseParts says it is shipping the proper 11mm adapter ring on Apr 18.

Chen

Kevin_A

w7ay looks decent!

Kevin_A

w7ay I am going to try mine on my new Esprit when it arrives soon!

w7ay

Kevin_A

Just tried unity gain -- oh boy , really noisy.

Chen

w7ay

Kevin_A I am going to try mine on my new Esprit when it arrives soon!

The nice thing about buying a Takahashi is you don't have to constantly "upgrade" the OTA :-). Saves money on the long run. I have yet to find any new 60-90mm scope that makes me want to open up my wallet. One of them needs to produce a chromatic spot diagram close to that from the Baby-Q (Askars are about twice the spot size, although the V series looks better).

If I could take the weight, I would get the real FSQ-106; but as it is, I can barely carry that scope without camera and filters, and that is too much of a hassle. I have set everything up so I can just plop my scoe on the mount and not even do a polar alignment.

Chen

w7ay

Kevin_A I

1/2 hour before leaving astronomical twilight; same settings as above. I guess the previous image included a lot of sky backgroud. This one looks more promising (M51 vs sky). The dark vignette is one of my antenna masts. Once it clears and I leave twilight, I can try some autorun in ASIAIR after refocusing.

Chen

w7ay

Kevin_A

Just left astronomical twilight (so not completey dark quite yet). Noise appears manageable with unity gain and 180 sec exposure (around Bortle 5 for that part of the sky with some high thin clouds).

"Feels" a bit better than my cooled ASI183MM.

Chen

Kevin_A

w7ay Idid my first light at unity gain and may drop down to gain 150 but I do not like dropping too much below Unity… here is just slightly less than 3 hours of 180s subs at Unity… better than my 183 for sure. This scope has a bit of lateral CA and Unity did oversaturate bright stars.

w7ay

Kevin_A Idid my first light at unity gain and may drop down to gain 150 but I do not like dropping too much below Unity… here is just slightly less than 3 hours of 180s subs at Unity… better than my 183 for sure.

Clouds came in just a few minutes after I started an autorun. 1 hour later, my all-sky camera shows this :-)

(Hey, night time sky is also blue. Just so dark that you think it is black :-). You can see the dipper on the bottom left. North is to the left.) Daytime is about -11.7 EV on this system (ASI294MC with a Samyang fisheye), the above image is at +8.5 EV. 20 f-stops difference.

Chen

w7ay

Kevin_A

Hoo boy, this camera is sure noisy at unity gain (180 sec at 457mm-f/4.3). (Doesn't help with the Antlia RGB robbing me of the photons.)

Stable seeing tonight. This is what I got a little earlier in the ASIAIR autofocus routine:

Notice you can actually see a pretty clean Airy disc in the 3 second exposure. ASIAIR Auto focus actually works with this kind of plate scale (and very fast too, with such a small sensor). Temperature is also not changing too much; 0.7ºC in 90 minutes. But I will soon need to refocus the FSQ.

Autoguiding is pretty clean too.

Chen

Kevin_A

w7ay I am going to test out gain 150 as I think it will be a bit better than Unity and I need to bring up the FWC to a point where stars are not saturating at 180s. My skies are bad again so no testing for now. Gain 150 has a good balance of noise and fwc and it is not so bad that photons start being dismissed due to rounding off in the electronics.

w7ay

Kevin_A My skies are bad again so no testing for now.

I have not even created dark frames yet. That could take a while :-). Just trying to get some initial feel for this camera.

I am going to test out gain 150 as I think it will be a bit better than Unity

Perhaps a factor of 3 difference in full well vs unity gain, while losing not quite 50% of the quantization steps. Hate to have to make decisions like that.

You said HCG (read noise of around 1e- from 4e-) made the total noise worse? I might take a look myself tonight if I get clear skies.

A -20ºC (probably doable for the small camera) should be able to bring dark current noise by almost two. I should look at that too.

Chen

Kevin_A

w7ay using HGC increased the hot pixels substantially only so I do not find that would be good overall. I did not find that dropping the temperature to -20c from -10c did much in reducing dark current either. I think gain 150 may be the best overall comprise.

w7ay

Kevin_A using HGC increased the hot pixels substantially only so I do not find that would be good overall.

Back of the envelope... Dark current noise at -10ºC is about .002e-/sec, or 0.36e- with 180 sec exposure. At Unity gain, this (0.36e-) should be the actual (unity) contribution of random sensor noise, while the read noise is at a whopping 3.8e-.

With HCG, the RMS random noise is increased by a factor of 2 (HCG kicks in at a gain of about 5.4 dB above Unity Gain), so the 0.36e- dark current noise becomes 0.72e-, while read noise falls to about 1e- : the total noise (RMS) is now about 1.25e-. This should be better than the 3.8e- at Unity gain.

Perhaps I am missing something. If not, are we seeing mostly read noise at Unity Gain and 180 second exposure at -10ºC?

Also, if dark current is the problem, then -20ºC should help. But if read noise is the problem, that extra 10ºC cooling will do nothing.

Chen

Kevin_A

w7ay I just tested the darks and from my visual observations which were very non scientific… I could not see much improvement in visual noise at the lower temperatures. My rationale would be also… how do hot pixels get treated in stacking? Would they have zero data and just get averaged out to a close regular pixel data? So is that just lost data that is fudged when replacing hot pixel data?
My goal with this camera is broadband targets like galaxies so I am ok with a 4-7k FWC but 2.5k may be too small to handle bright stars when adding all that Christmas tree light data.
Maybe you can test out 150, Unity and HCG and see what your thoughts are.
I may be wrong about dark current as I would have thought -20c would give a difference but I could not see much difference in darks but the hot pixels at HCG scared the crap out of me.

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