Astro-camera Quandry

[SteveNickolls]

Hi, I have been astro-imaging for a little over six years and now wish to purchase a cooled astro-camera to continue my interest in the hobby.

I set up my equipment each night and currently use a modified Canon 700D DSLR, clip in Astronomik 12 nm Ha filter and Samyang 135 mm lens (f/2) to capture wide field images of emission nebulae and intend to continue to do this type of DSO imaging but with the benefits that a dedicated cooled astro-camera with lower read noise and higher quantum efficiency could bring. I live in a Bortle 6 area, a typical SQM-L value being around 19.26 so light pollution is always a concern when imaging.

My budget is modest in astro-photography terms and I first considered the ASI183MM-Pro model. The intention would be to have a simple set up involving the astro-camera, ZWO filter drawer holding the clip in Ha filter in a 2” adapter sold by Astronomik connected to the Samyang lens. Out of the left field however I have recently entertained the newer and slightly cheaper ASI533MC-Pro model having a largely improved specification compared to the 183 model and has no associated ‘glow’, but this astro-camera is OSC. 

I am conscious that there would be a hit in terms of resolution between the two cameras but as I am imaging with a short lens (135 mm) the equipment is already under sampling according to the Astronomy.Tools link on our sponsors site but this may not make much real life difference in the images produced. I am also aware of the reduced light grasp with using the OSC compared to the mono astro-camera-this is something I am familiar with when imaging with my modified OSC DSLR.

Both astro-camera options will allow me to take much shorter sub-frames for stacking than with the present DSLR, and to stack more of them reducing SNR in the final image and the slightly larger pixels on the ASI533 combined with the 1.5e- read noise make the 533 model able to take even faster sub-exposures than the 183 model-so even more exposures in a given evening’s session. I’ve also thought that the higher full well capacity of the 533 model would permit me to extend exposure times if wanted without saturating stars in the image as fast as with the 183.

Before I take the plunge to order what may become my first and last astro-camera for DSO work I would be interested to learn if any other SGL member has used such a combination of OSC 533MC astro-camera, Ha filter and short but fast (f/2) optics in a light polluted sky and how successful has this been in practice?

Views would be gratefully received too on whether in the light polluted conditions that I image under the 533 model would be preferable to the monochrome 183 due to its generally better specification or that the monochrome camera wins hands down.

I look forward to member’s comments and advice.

Best Regards,
Steve

[david_taurus83]

Hi Steve. Do you image with the Ha filter to produce monochrome images? Or do you leave them as colour? If the former, then a mono camera would be a far better choice. I wouldn't rule out the ASI1600 either as its not much more expensive than the 183. Whatever you choose, ZWO usually offer sale prices in the run up to Christmas so might be worth holding out for that as well.

[newbie alert]

Look up what magnum does with his 135/533 setup in the deepsky imaging section to see what kind of results to expect 

Not really with you on the short exposure way of thinking as it's still narrowband 

[vlaiv]

Mono all the way.

You really have three choices there ASI183mm, ASI1600 and ASI294 mono.

I think the last would be the best choice for your use case - as it is largest sensor and has largest pixels.

8 hours ago, SteveNickolls said:

Both astro-camera options will allow me to take much shorter sub-frames for stacking than with the present DSLR, and to stack more of them reducing SNR in the final image and the slightly larger pixels on the ASI533 combined with the 1.5e- read noise make the 533 model able to take even faster sub-exposures than the 183 model-so even more exposures in a given evening’s session. I’ve also thought that the higher full well capacity of the 533 model would permit me to extend exposure times if wanted without saturating stars in the image as fast as with the 183.

Don't think that number of subs alone determine quality of resulting image. It is combination of factors - primary being total integration time. If that is the same (and equipment is comparable) - you'll get virtually the same result regardless if you use 50 or 500 subs in that time. In fact - larger number of subs means worse result due to read noise. You need to adjust your exposure length depending on read noise and its magnitude in comparison to other noise sources.

For NB imaging where LP impact is significantly reduced - impact of read noise becomes bigger and longer exposures are needed (fast optics does mitigate quite a bit of that so it facilitates shorter exposures).

Main difference between Mono and OSC would be in sensitivity - OSC cameras only use 1/4 of pixels to record Ha. You can think of that as being 1/4 of sensitivity of Mono camera.

I would not worry about amp glow - it calibrates out fine as long as you do proper calibration.

[SteveNickolls]

Thank you vlaiv for your summary and explanations I really do appreciate it. 🙂

Thanks,

Steve

[Adam J]

No question in my mind that if Ha is your thing and you want something that's going to last then mono is the way to go. On a tight budget the 183mm will serve you well. 

[wimvb]

Mono with nb filters seems a straightforward choice, but don’t disregard osc with a dual band filter without at least looking into it. Osc cameras are sensitive enough to allow thinking outside the box, I’ve seen good images that were taken with osc and dual band (Ha and Oiii) filters. Direct comparison is always difficult because of local lp conditions .

[SteveNickolls]

Thanks vlaiv, Adam J and wimvb for your helpful comments, I had expected the mono-camera to be preferable but there seemed something about the 533MC model that caused me to ponder a left field alternative. I did wonder if the technology had reached a point where it had least met the limiting physics part-way to give a decent image. I've not seen too many images of nebulae using the 533MC under such light polluted conditions as I encounter here. I think had my sky been somewhat darker, say Bortle 5, the 533MC would have been ok especially when the camera can make use of the dual and tri-band filters for OSC cameras now on the market.

Cheers,
Steve

[wimvb]

I think that it very much depends on what you wish to achieve. With the European weather being the way it is, you really have to plan photo sessions. That extra night where you had thought to also collect Oiii for an object, may never materialise during one season. Osc with dual band may just be simpler than mono and a filter wheel. Only you can make that decision. I find that the development we have seen in astro cameras forces us to reevaluate old truths. What was an obvious choice yesteryear is no longer so.

just a few years ago, coming from dslr, a mono camera seemed the obvious way to go for me. But my next camera will be an osc.

[Lee_P]

OSC plus a dual-band filter can work very well even from a city centre. I've made a whole website about just that; you may find this article in particular useful: http://urbanastrophotography.com/index.php/2021/06/12/osc-vs-mono-from-a-city/

 

13 minutes ago, wimvb said:

I find that the development we have seen in astro cameras forces us to reevaluate old truths. What was an obvious choice yesteryear is no longer so.

100% agree, and that's very well phrased too 😁

[geeklee]

On 15/09/2021 at 21:56, SteveNickolls said:

My budget is modest in astro-photography terms and I first considered the ASI183MM-Pro model.

I find the 183MM with the Samyang 135 an excellent combination.  The small pixels with fast speed produce some surprising detail for the focal length.  Even resampling later still produces good output with modest integration.

I've also used the ASI533 with the Samyang.  On one occasion I remember using a dedicated Ha filter in front of the camera and wasn't impressed - as mentioned above, that inefficiency with the OSC (compared to mono).  In general though, the ASI533+Samyang was a very easy relationship.

My Astrobin page has images from both these combos - the 183MM images (the latest ones) were done during summer (so no astro dark)

Edited September 17, 2021 by geeklee

[wimvb]

59 minutes ago, geeklee said:

've also used the ASI533 with the Samyang.  On one occasion I remember using a dedicated Ha filter in front of the camera and wasn't impressed - as mentioned above, that inefficiency with the OSC (compared to mono).

With a ”classical” narrow band filter on an osc camera, you only use a quarter of the pixels during Ha capture, and the other 3/4 during Oiii capture. With a dual band filter you always use all the pixels. If you image 1 hr with Ha and 1 hr Oiii with an osc camera, you need 2 hrs imaging time for 1 hr of data. With a dual band filter, you get 2 hrs of data during those 2 hours.

Edited September 17, 2021 by wimvb

[geeklee]

37 minutes ago, wimvb said:

With a ”classical” narrow band filter on an osc camera, you only use a quarter of the pixels during Ha capture, and the other 3/4 during Oiii capture. With a dual band filter you always use all the pixels. If you image 1 hr with Ha and 1 hr Oiii with an osc camera, you need 2 hrs imaging time for 1 hr of data. With a dual band filter, you get 2 hrs of data during those 2 hours.

Yep, I realise this 👍 I was just offering my experience up as that was a scenario spoken about by the OP.

Edited September 17, 2021 by geeklee

[The Admiral]

2 hours ago, geeklee said:

On one occasion I remember using a dedicated Ha filter in front of the camera and wasn't impressed - as mentioned above, that inefficiency with the OSC (compared to mono). 

Without wishing to derail the topic, if you are just imaging Ha with a OSC camera, with the blue and green pixels essentially redundant, does just selecting the red channel to process improve the noise levels? I'm thinking that if you only use the red pixels you only have their read noise, or am I being too simplistic in respect of de-Bayering OSC data?

Ian

Edited September 17, 2021 by The Admiral

[SteveNickolls]

Thanks everyone for your contributions. 

4 hours ago, wimvb said:

I find that the development we have seen in astro cameras forces us to reevaluate old truths. What was an obvious choice yesteryear is no longer so.

just a few years ago, coming from dslr, a mono camera seemed the obvious way to go for me. But my next camera will be an osc.

Yes it was that development that made me consider the 533MC against what I would have instinctively chosen as the set from a DSLR. Can I ask what Bortle scale you image from especially you saying your next astro-camera would be a OSC?

4 hours ago, Lee_P said:

OSC plus a dual-band filter can work very well even from a city centre. I've made a whole website about just that; you may find this article in particular useful: http://urbanastrophotography.com/index.php/2021/06/12/osc-vs-mono-from-a-city/

What a great site, thanks for pointing me in its direction. It has some extra considerations for me to ponder and I like the approach taken on the topic. 👍

3 hours ago, geeklee said:

I've also used the ASI533 with the Samyang.  On one occasion I remember using a dedicated Ha filter in front of the camera and wasn't impressed - as mentioned above, that inefficiency with the OSC (compared to mono).  In general though, the ASI533+Samyang was a very easy relationship.

My Astrobin page has images from both these combos - the 183MM images (the latest ones) were done during summer (so no astro dark)

Thanks for your view of the 533MC and Ha filter I appreciate real world experiences most helpful in choosing. It's sounding like the 533MC and a dual band filter may be the way to travel and take advantage of the better specification of the newer OSC option. Can I ask what Bortle zone the images were taken in?

Thanks,
Steve

[geeklee]

18 minutes ago, SteveNickolls said:

Can I ask what Bortle zone the images were taken in?

No problem - 5/6 with the usual street lights helping out too 🙂

[wimvb]

59 minutes ago, SteveNickolls said:

Can I ask what Bortle scale you image from especially you saying your next astro-camera would be a OSC?

I honestly have no clue about Bortle, but my darkest nights are at 20.7 mag, rural Sweden with Stockholms light dome more than 20 - 25 miles to the south. Osc is certainly doable here, even if a magnitude darker wouldn’t hurt. Osc means just one less device to worry about, and I seldom do narrow band imaging.

[wimvb]

2 hours ago, The Admiral said:

or am I being too simplistic in respect of de-Bayering OSC data?

Not at all. Normal debayering ”fills in” the missing data by interpolation. But if you use superpixel debayering, the colour from 4 (2x2 ) pixels is simply combined into one colour pixel. Extracting the red channel from this would give the clean Ha signal without any deBayering artefacts.

[The Admiral]

4 hours ago, wimvb said:

Extracting the red channel from this would give the clean Ha signal without any deBayering artefacts.

Do you mean that it won't include the readout noise for the redundant blue and green pixels?

Ian

[wimvb]

1 hour ago, The Admiral said:

Do you mean that it won't include the readout noise for the redundant blue and green pixels?

Ian

No, it shouldn't. The green pixels data goes into the green channel, blue pixel data into the blue channel, and red data into the red channel. Green and blue end up empty with the use of an Ha filter, apart from the camera's dark signal. During super pixel deBayering, there is no interpolation, so no green or blue is mixed with the red.

[The Admiral]

I guess the problem with superpixel debayer is that it is best for over-sampled imaging, I believe, which is likely not what the thread starter will be achieving with his short focal length set-up. I'm not sure how important that would be though.

Ian

[wimvb]

Most of the time, atmospheric conditions determine star shapes and best sampling rate. But if undersampled, there's always the option to drizzle.

https://www.stsci.edu/~fruchter/dither/drizzle.html

[happy-kat]

Saw this thread and saw a relevance to your thread.

https://stargazerslounge.com/topic/383202-osc-nb-filter/

[SteveNickolls]

Thanks happy-kat for the link. 👍

Cheers,

Steve

[Jp114]

I recently tried using a Canon 70-200 f/4 at 200mm, with and Atik 314L+ (6.4 micron pixels), so I was severely over sampling. 
 

I think this was 7 x 300s through a Ha filter, I was planning to grab some Oiii but the clouds rolled in. I’m happy with it though.