ASI1600mm cool

[iapa]

270 Mins captured ast night, half useless.

here is a single 20sec unguided exposure of Bubble nebula stretched a bit, no coma corrector, L only, 

bubble is just visible...

 

 

 

 

[iapa]

1 hour ago, brrttpaul said:

funny enough I done Andromeda the other night and fell into the over exposing trap, I done them at 1 min each 20 secs would have been ample I think. you just dont realise how sensitive the camera is

Ditto, on the Bubble couple nights ago.

tried 30s, on Sunday, still a bit much.

[brrttpaul]

my effort from the other night 60x 60 secs each of LRGB over cooked in PI and lightroom as usual. I have managed to get to grips with PI though calibrating and intergrating everything from scratch instead of BPP so I am happy in a way

[groberts]

What Gain & Offset did you use for M31?

[thomasv]

Hi,

I'm thinking of using this camera with fast camera lenses (such as samyang 135mm f2) to do narrowband imaging and have two questions.

1. I already have an EOS to CCD adapter (from 365astronomy) which is 19mm thick. If I get a filter wheel which is 20mm thick, I think I'll be just short of achieving infinity focus, please check my calculation: 44 - 19 -20 =5mm, asi1600 backfocus = 6.5mm. If that's the case, I guess I just have to get the zwo eos adapter recommended for use with the filter wheel, right?

2. I'd like to go as fast as possible, I have some fast lenses, so would people recommend buying the Baader f/2 highspeed filters or stick with the normal baader 7/8.5nm ones. I'd want to use 1.25" filters for cost reasons, I appreciate there'll be some vignetting.

Thanks.

 

[Gina]

I think the measurements sound about right - I use Pentax thread lenses so not sure with EOS but I think the ZWO T2 to EOS adapter (from FLO) is designed to give the correct back focus distance. 

I use 1.25"Astrodon 3nm filters for NB and get just a little vignetting which is easily calibrated out with flats.  This is using the ZWO EFWmini directly on the camera (no F-F ring) - I gather the larger ZWO EFW is the same thickness.

[Allinthehead]

I use the Asi with a Samyang 135mm. I bought zwo to eos adapter which comes with a little spacer that gives me perfect focus with my 5nm astrodon filter. My zwo filters are thinner so i'll find out soon if it works with those. All the filters i use are 1.25 which vignette slightly but calibrate out well. I'm also using the zwo 5 position filter wheel. Hope this helps.

[thomasv]

Thank you very much for the replies, good to know that the zwo eos to ccd adapter will work with the filter wheel. However, this makes me wonder what sort of mechanical arrangements you use. I know there is a bracket for the asi1600, but these lenses are quite heavy, so would be reluctant to hang them off the camera. Or do you fix the lens and let the filter wheel and camera hang off it. (That's why I like my existing eos to ccd adapter as it has a base, as far as I know the zwo one has not.)

BTW, how low you tend to go with the f number, apart from the slight vignetting I thought that the filter centre wavelength shifts as well for low f number.

Thank you.

 

[brrttpaul]

think you fix the lens and the camera is behind it, i would have thought anyway

[Gina]

I support both lens and camera as both are quite heavy though some vintage lenses are less heavy such as the Asahi Pentax Super Takumar 55mm f1.8.  But I still use support for these as I add remote focussing to the focus sleeve.

[IanL]

Very interesting article here by Christian Buil (who knows his stuff) comparing the performance of Atik 460EX, Atik 414EX, ASI 1600MM-C and ASI 290MM-C. Basically a shoot-out between CCD and CMOS cameras. His main focus is spectroscopy, but there are some interesting findings for more general imaging:

http://www.astrosurf.com/buil/CMOSvsCCD/index.html

Things that I have taken away from this:

- Quantum Efficiency of the 1600 is not as good as the Atiks, but the 290 it is slightly superior to them. (QE is the percentage of photons that are detected by the sensor at any given wavelength). He has had to make a fair number of assumptions in estimating QE, as absolute QE figures are rarely published by manufacturers, but it must be in the ballpark.

- In terms of Read Out Noise, the 1600 is the clear winner (at -20C cooling and 20dB gain, i.e. set the gain to 200 in the driver).  Of course one then needs to limit individual exposure lengths on bright targets to avoid saturation.

- Dark current accumulation rate for the 1600MM at -30C (0.0029 e/s/pixel) is the same as for the 460EX at -10C. The 460EX has larger pixels though, so accumulation for the same pixel area is still better, but the 1600MM's performance in this respect is good in real world use. The practical upshot is to try to push the 1600MM cooling to the max for ambient conditions. It's specified at -45C below ambient; in practice I am seeing about -39C below ambient for my 1600MM. I have been using -15C as my target value in summer months when night time temperatures are about +20C. I am now going to try to go much lower in the winter as dark current will be halved by going from -15C and -30C (with consequent reduction in dark current noise).

- Unlike CCDs, CMOS sensors suffer from Burst (Telegraph) noise, which is random in nature and results in those white speckles that look like hot pixels that move from frame to frame (and so can't be calibrated out like real hot pixels). Upshot is that, for a given total exposure time, the 1600MM will do better with more shorter exposures vs the 460EX so that burst noise can be more easily rejected / averaged out during stacking.

The only bit I wasn't quite clear about was where he says:

"The thermal noise of the ASI290MM detector reach the value of the electronic read-out noise for an integration time of 20 seconds  (at -22°C operating temperature). So, the thermal noise dominates for individual exposure  greater then 20 seconds, which affect the excellent readout noise performance for long exposure."

Now my understanding is that dark current noise is the square root of dark current signal, so if we want dark current noise to be the same as read out noise (1.1e RMS) at 20dB gain, then we need a dark current signal of 1.21e (square root of 1.21 is 1.1), which requires an exposure time of 24.2 seconds to reach, which is a bit higher than the 20 seconds quoted.

Assuming I haven't got that wrong (experts chip in here please??), translating that to the 1600MM, dark current at -20C is 0.0037 e/s/pixel and read out noise is 1.4e RMS at 20dB gain. So using the same maths to get 1.4e dark current noise, we need 1.96e of dark current signal, which requires an exposure time of 529.8 seconds.  He does say the 1600MM is ten times better in terms of dark current, but this would suggest more than twenty time better so I probably have this wrong?

Still further, if we can reach -30C sensor temperature, then any exposure up to 675.9 seconds would mean dark current noise does not exceed read out noise. Of course this may only matter for very dark skies, otherwise shot noise from the background sky will dominate regardless.

Anyhow, it was a fun read.

[sharkmelley]

3 hours ago, IanL said:

Very interesting article here by Christian Buil (who knows his stuff) comparing the performance of Atik 460EX, Atik 414EX, ASI 1600MM-C and ASI 290MM-C. Basically a shoot-out between CCD and CMOS cameras. His main focus is spectroscopy, but there are some interesting findings for more general imaging:

http://www.astrosurf.com/buil/CMOSvsCCD/index.html

 

Thanks for posting this - it was an informative read.

By the way, I agree with your dark current and noise calculations.

Mark

[thomasv]

Thanks Gina for the picture. At the end (for now) I kept my EOS-to-CCD adapter and went with a filter drawer solution for 36mm filters, the filter changer is 10mm wide. I know it's larger filters than necessary, but already had an Ha in that size. Also, a more hands-on filter change method than the filter wheel, but will do for now for experimentation.

Just had to mill the female threaded adapter that came with the camera to about 7mm, and managed to confirm last night that I can focus.

Mechanically seems ok with the shown 85mm lens, I'll figure out something for the larger lenses.

[thomasv]

In case it helps other people: I had a lot of issues yesterday on my Windows 10 laptop using APT. I had the well reported 'BUSY' or freeze after the first exposure issue. That was with the latest ASCOM driver (V1.0.3.6). Rolling back to Beta v1.0.3.3 solved the problem. 

 

[SyedT]

The more I work with this camera the more impressed I get! This image has only been calibrated with bias and darks, no flats. No post-processing performed, all I've done is perform an autostretch in Pixinsight to make the image non-linear. 

121*300s subs = 10h5mins of total integration time over 3 nights. Single 300s exposure from the most recent run also attached. WO GT81 with 0.8x FF/FR, 2-inch Ha filter.

The first two nights were with my old guiding setup (60mm guidescope in adjustable rings). I've since switched to a SW ST80 in tube rings with my ASI 120MC-S, and it was guiding like a dream; I was getting sub 1-arcsecond performance consistently. It may also be the fact that I stripped down and re-greased the mount! Makes such a difference, not having to glance every 10 mins to make sure it's not guiding and there's no flexure (I was previously getting flexure despite guiding, probably to do with the suboptimal guiding setup).

I also have to say that using 2-inch filters was definitely the right call for me, as I can't stand doing flats after every imaging session (even though I have a flats panel). There's some star elongation in a couple of the corners, but I'm sure I can address that in post-processing.

[brrttpaul]

I have been reading up about gain and offset ( doing my head in on the quiet lol) and decided to try it out the other night.  Gain at 75 and offset 15 I went for the heart nebula, for some strange reason i couldnt get it at all, I had andromeda i had the soul nebula but in the end I give up ( even copied the coordinates in CDC and put them in sgpro. Anyway I just said sod it and decided to run a sequence in narrow band . Ha Sii and Oii and done them @ 60 secs long x 400, they came out ok so went and tried BPP everything worked untill it came to stacking as it couldnt find any stars, tried manually (image calibration image intergration same thing. I will just put it down to experiance that my subs were way too short for narrowband

[Allinthehead]

4 minutes ago, brrttpaul said:

I have been reading up about gain and offset ( doing my head in on the quiet lol) and decided to try it out the other night.  Gain at 75 and offset 15 I went for the heart nebula, for some strange reason i couldnt get it at all, I had andromeda i had the soul nebula but in the end I give up ( even copied the coordinates in CDC and put them in sgpro. Anyway I just said sod it and decided to run a sequence in narrow band . Ha Sii and Oii and done them @ 60 secs long x 400, they came out ok so went and tried BPP everything worked untill it came to stacking as it couldnt find any stars, tried manually (image calibration image intergration same thing. I will just put it down to experiance that my subs were way too short for narrowband

Hi Paul. I use a minimum of gain 300 offset 50 at 60 seconds. Why don't you upload a single sub here and i'll have a look.

[Filroden]

8 minutes ago, brrttpaul said:

untill it came to stacking as it couldnt find any stars

60 seconds at 75 gain in narrowband should give you more than enough to stack. I was stacking 45 second Ha images at unity gain. Maybe you need to relax the star finding parameters?

[Filroden]

57 minutes ago, SyedT said:

121*300s subs = 10h5mins of total integration time over 3 nights. Single 300s exposure from the most recent run also attached. WO GT81 with 0.8x FF/FR, 2-inch Ha filter.

That’s a lovely Heart. Shows the power of the camera well.

[brrttpaul]

It was just a thing i was reading up on with all the cloudy nights lately about gain etc, I was trying to get my head arounsd it comparing it to ISO etc (and failing lol). what I did read was the more gain the more noise and everything seemed to point towards gain @75 so thought I would give it a go

[SyedT]

10 minutes ago, Filroden said:

That’s a lovely Heart. Shows the power of the camera well.

Thank you, it really is a fantastic piece of kit. With the limited imaging time we get in the UK, the main reason I bought this was for brighter targets which you can stack very short subs with and still come out with a decent image, but I thought I'd go for something a bit fainter. Currently working on a heart and soul nebula mosaic, and 5min subs seem to do the trick very well.

[brrttpaul]

going to have another look see if im missing something

[brrttpaul]

just very quickly took two snips of the computer screen first one unstretched 2nd one stretched, this is uncalibrated no bias no flats nothing

[Allinthehead]

Looks to me like it's under exposed. Here's a screengrab of a 60 second sub gain 399 offset 60

[brrttpaul]

probably right plus the fact that I was off the heart didnt help, just couldnt do anymore with getting up at 5 in the mornings