Which Camera for H-alpha Imaging

[Mandy D]

I've just bought a Daystar Solar Scout 60mm DS for H-alpha imaging of the Sun. I am now looking for a suitable camera to use with it. I know I could use my DSLR, but for H-alpha that is not going to give best results, so am looking for a dedicated monochrome imaging camera. I have identified the ZWO ASI178MM as a possibility that fits my budget and has a large enough (I think) sensor to image the entire Solar disc if I use a 0.5 focal reducer which will give me a total focal length of 465 mm.

Does anyone have any experience of this camera in this application, or know if it will be suitable? I know it does not have an IR blocking filter, which I understand is an advantage for H-alpha. The spec is available here:

https://www.rothervalleyoptics.co.uk/zwo-asi178mm-usb-30-monochrome-cmos-camera.html

Thanks

Mandy

 

[johninderby]

3 hours ago, Mandy D said:

I've just bought a Daystar Solar Scout 60mm DS for H-alpha imaging of the Sun. I am now looking for a suitable camera to use with it. I know I could use my DSLR, but for H-alpha that is not going to give best results, so am looking for a dedicated monochrome imaging camera. I have identified the ZWO ASI178MM as a possibility that fits my budget and has a large enough (I think) sensor to image the entire Solar disc if I use a 0.5 focal reducer which will give me a total focal length of 465 mm.

Does anyone have any experience of this camera in this application, or know if it will be suitable? I know it does not have an IR blocking filter, which I understand is an advantage for H-alpha. The spec is available here:

https://www.rothervalleyoptics.co.uk/zwo-asi178mm-usb-30-monochrome-cmos-camera.html

Thanks

Mandy

 

I’ve just bought a ZWO AS1290MM for use with my Daystar Scout. Considered the 178 but after some research found the 290 would be more suitable as the Scout is effectively an f15.5. The 178 is good with shorter focal lengths but the 290 is a better match with long focal lengths. 

Waiting for my SolarQuest mount to come back from FLO so I can try it out. Looks like a bad power switch.

 

Edited August 1, 2019 by johninderby

[Mandy D]

I'm confused. Why do you suggest that the 290 is better suited to longer focal lengths? From my research it has a smaller sensor than the 178 (1/2.8 against 1/1.8). I'm also not sure what the effective focal ratio of f/15.5 has to do with it. Surely what matters is the effective focal length or am I somehow getting confused?

It looks like you have an interesting setup, there. I guess that is a geared stepper motor you are using for focussing with an inside-out timing belt around the barrel to act as a matching gear. I need something to focus my 800 mm mirror lens, so I might look at doing the same.

Thanks for your reply. Cloud Bringer makes me smile. I've seen no blue sky since I got my new scope.

[johninderby]

Lot of usefull info on the Cloudy Nights forum on the subject but basicly the longer the focal length the bigger the pixel size so the 290 pixel size is closer to the ideal than the 178. The 290 is more sensitive and has less read noise, and the smaller sensor is going to see less of the aberrations caused by focal reducers  Also the 178 doesn’t do binning. The 178 is ideal in a short focal length refractor though and would be a good choice if you are going to use it in other scopes.

I will also be using the 290 in a long focal length mak so that was another reason for choosing it.

Anyway  will have the SolarQuest mount back tomorrow. Turned out to be simplya wire that had come loose inside.

 

 

Edited August 2, 2019 by johninderby

[michael.h.f.wilkinson]

I have the ASI178MM and use it a lot at 480 mm focal length for full disk imaging in white light and Ca-K. If your reducer doesn't add a lot of aberration your combo should work.

[Mandy D]

Thanks for the explanation, johninderby. That makes sense. I'll be using mine in the H-alpha and a Skywatcher 250PX with 1200 mm focal length, so it could be an OK match. I take on board your comments about the focal reducer and the bigger pixels of the 290, but what I really need is the larger sensor in the 178 to fit the entire Solar disc on with 0.5X reducer.

From my research, it appears that the 178 does do binning. Here is the relevent section from the manual:

"6.6Binning  The ASI178 camera supports hardware bin2 and bin4 mode. The ASI178 camera supports software bin2, bin3 and bin4 mode. Hardware binning is supported by sensor but is done in digital domain like software binning and use 10bit ADC. The only advantage of hardware binning is faster fps. We recommend customer to use software binning if you don’t care speed. "

Thanks again.

Mandy

Edited August 2, 2019 by Mandy D

[Mandy D]

14 minutes ago, michael.h.f.wilkinson said:

I have the ASI178MM and use it a lot at 480 mm focal length for full disk imaging in white light and Ca-K. If your reducer doesn't add a lot of aberration your combo should work.

Hi Michael

Thank you. That is what I want to know. Is it likely to be OK for H-alpha with my Solar scope? My reducer is this one:

https://www.rothervalleyoptics.co.uk/antares-05x-focal-reducer-125.html

Obviously, I can adjust it's position with extension tubes to minimise aberration and tweak the focal length a bit.

Mandy

[Thalestris24]

Hi all

Are these Daystar SS60 bundles actually ok for solar imaging? What are their limitations? I think I'm being tempted . I've not been too enamoured with previous white light imaging - I'd like to image in Ha but without breaking the bank!

Louise

[Thalestris24]

47 minutes ago, Thalestris24 said:

Hi all

Are these Daystar SS60 bundles actually ok for solar imaging? What are their limitations? I think I'm being tempted . I've not been too enamoured with previous white light imaging - I'd like to image in Ha but without breaking the bank!

Louise

ps do they really have 'doublestack' performance or is that meaningless marketing blurb?

[Merlin66]

Louise,

Basically yes.

The mica etalon design in the "Quark" module is supposed to give a much narrower bandwidth than a conventional single stack etalon.

 

[vlaiv]

12 hours ago, Mandy D said:

Thanks for the explanation, johninderby. That makes sense. I'll be using mine in the H-alpha and a Skywatcher 250PX with 1200 mm focal length, so it could be an OK match. I take on board your comments about the focal reducer and the bigger pixels of the 290, but what I really need is the larger sensor in the 178 to fit the entire Solar disc on with 0.5X reducer.

From my research, it appears that the 178 does do binning. Here is the relevent section from the manual:

"6.6Binning  The ASI178 camera supports hardware bin2 and bin4 mode. The ASI178 camera supports software bin2, bin3 and bin4 mode. Hardware binning is supported by sensor but is done in digital domain like software binning and use 10bit ADC. The only advantage of hardware binning is faster fps. We recommend customer to use software binning if you don’t care speed. "

Thanks again.

Mandy

It "supports binning" pretty much in the way every camera supports binning - it is in fact software binning. Rather hardware bin in CMOS sensors is not true hardware binning it is software binning done in sensor that has some disadvantages over regular binning (reduced "dynamic range"). Pretty much all CMOS sensors don't support true hardware binning because of the way they are built and the way true hardware binning works.

But manual is right - if you need to bin for any other reason than faster transfer speeds (that you can get also by using ROI) - do it in software with this camera.

On pixel size vs F/ratio - there is well know relationship (although many don't know how to calculate it properly) between pixel size and maximum F/ratio that will produce critical sampling - optimal sampling to get max possible detail that telescope can provide (or rather aperture of that telescope). Larger the pixel size - slower the F/ratio needs to be, regardless of focal length or aperture of telescope on their own - it is combination of the two that counts.

ASI178 has 2.4um pixels and optimum F/ratio for sampling image with such pixel size is around F/9 (depending on wavelength, usually green light is given). For Ha this value is F/7.2.

If you plan on using slower scope - you need to use larger pixel camera (or do some tricks with binning or sparse sampling). ASI290 has 2.9um pixels and has critical sampling for Ha of ~F/8.7 so it is a good match at F/15.5 if you do sparse sampling for example or binning x2 in software (it's better to do sparse sampling than regular binning due to pixel blur).