Need input on mono camera for Ha

this is the main message area for anything solar :)
Post Reply
Bruce Girrell

Need input on mono camera for Ha

Post by Bruce Girrell »

I was speaking with a sales rep regarding mono cameras. He made a statement that surprised me and i hope you folks can help me clear it up. I was comparing two cameras, the QHY 163M and the ZWO ASI174mm. I was pretty much set on the QHY, but the sales rep said that those who are imaging the Sun in Ha usually choose a camera with a global shutter (the ZWO) as opposed to a rolling shutter (the QHY) due to banding issues in the image.

I understand how rolling shutters work and why they produce distorted images of moving objects and why they have banding issues with LED lighting, fluorescents, etc. But the Sun is not flickering in the manner of those light sources, so why would the rolling shutter be a problem? It appears that another source of banding with a rolling shutter is due to low data transfer rates out of the camera. The QHY 163M has an internal buffer to handle at least some degree of traffic jams. So I find myself confused. Is banding indeed a problem with a rolling shutters? Why would that be?

Cost aside (the ZWO is much less expensive), the image sensor of the QHY is much larger and it has smaller pixels. While I can see a drawback to smaller pixels in DSO imaging, it would seem that in a solar application, the efficiency difference between small and large pixels would not be a significant concern. Is there something I'm missing?

I would appreciate your input to help me in my decision

Bruce G


User avatar
marktownley
Librarian
Librarian
Posts: 42272
Joined: Tue Oct 18, 2011 5:27 pm
Location: Brierley Hills, UK
Has thanked: 20435 times
Been thanked: 10243 times
Contact:

Re: Need input on mono camera for Ha

Post by marktownley »

Your sales rep is right. Rolling shutters are the work of the devil, global all the time.

Get the 174


Image
http://brierleyhillsolar.blogspot.co.uk/
Solar images, a collection of all the most up to date live solar data on the web, imaging & processing tutorials - please take a look!
Bruce Girrell

Re: Need input on mono camera for Ha

Post by Bruce Girrell »

Mark,

Thanks for the recommendation. But why? This makes no sense to me. I have looked through the archives and I see recommendations for global shutter, but i have not yet found an explanation for the banding. Why does it occur, when the Sun doesn't flicker? And if it's traffic problems on the computer doesn't USB3 plus the local buffer of the QHY deal with that? Clearly this has been a problem at some time. Does the problem still exist?


User avatar
pedro
Way More Fun to Share It!!
Way More Fun to Share It!!
Posts: 12256
Joined: Sun May 01, 2016 8:26 pm
Location: Portugal
Has thanked: 14 times
Been thanked: 6576 times
Contact:

Re: Need input on mono camera for Ha

Post by pedro »

I agree with Mark, go for a global shutter


User avatar
Montana
Librarian
Librarian
Posts: 34560
Joined: Mon Oct 17, 2011 5:25 pm
Location: Cheshire, UK
Has thanked: 17667 times
Been thanked: 8789 times

Re: Need input on mono camera for Ha

Post by Montana »

The proof is in the pudding, rolling shutters produces terrible artifacts on solar work, that is why nobody uses them or wastes their money on them. I don't think anyone has done a study on why. Small pixels are good for small focal length refractors, large pixels are good for long focal lengths. There is a good summary here from Mark Townley viewtopic.php?f=4&t=21118&p=194834&hilit

Alexandra


LauraMS
Ohhhhhh My!
Ohhhhhh My!
Posts: 143
Joined: Thu Jul 13, 2017 11:10 pm
Location: Germany
Has thanked: 55 times
Been thanked: 81 times

Re: Need input on mono camera for Ha

Post by LauraMS »

Bruce, I think the reason for global shutter is that although the sun itself is not flickering, the atmosphere introduces severe and rapidly varying image distortions even at the 1ms exposure time one likes to use at solar. I would expect (but have not tested it myself) that a rolling shutter camera would produce severe small-scale image artifacts because of the well-known rolling shutter artefact stemming from these rapid atmospheric image variations.

Moreover, at this price class the IMX174 chip is one of those chips with fastest readout: >155fps at full resolution (1932x1236). The QHY 163m may be more interesting with regard to the large number of pixels (16MPx), but if you look at its speed (57fps at 1920x1080 according to the QHY webpage) it is much slower than the IMX174. Having many images to select only the few best for stacking is not absolutely required (Mark Townley demonstrates that nicely with his IMX249 chip, which is the slower variant of the otherwise identical IMX174), but in my opinion it helps a lot in imaging the sun.


christian viladrich
Way More Fun to Share It!!
Way More Fun to Share It!!
Posts: 2150
Joined: Sun Jun 14, 2015 4:46 pm
Location: France
Has thanked: 1 time
Been thanked: 2713 times
Contact:

Re: Need input on mono camera for Ha

Post by christian viladrich »

This is an interesting question ;-)

This is the rolling shutter effect ... I like that one :-)
Image

As for the sun, there is no moving part, but as pointed by Laura, the turbulence is the source of fast frequence distorsion (in the range of a few hundreds of Hertz).

What about rolling shutter in solar imaging ? Fred Jabet did some tests 2 to 3 years ago. There were some artefacts on the images. Still, there has been some improvements in rolling shutter modes on more recent sensors. It is difficult to say whether there are still some artefects with the current sensors.

What is the use of rolling shutter ? This is to reduce read noise. Still, read noise is not of concern for solar imaging. So there is no use of having very low read noise. The IMX174 has 6 to 7 e- read noise. This is already very low.

With a global shutter, you sure not to have any issue. Indeed, the question is more about the size an number of pixels and the S/N you need.

The IMX 174 is one of the best (if not the best) current sensors for solar imaging.


Christian Viladrich
Co-author of "Planetary Astronomy"
http://planetary-astronomy.com/
Editor of "Solar Astronomy"
http://www.astronomiesolaire.com/
Ewan
Almost There...
Almost There...
Posts: 678
Joined: Wed Apr 01, 2015 6:41 am
Has thanked: 13 times
Been thanked: 41 times

Re: Need input on mono camera for Ha

Post by Ewan »

Yep I have a Point Grey IMC174, 1920 x 1200 res, at full res, Mode 7 on in 16 Bit it does around 87Fps, 8Bit will over double that rate.
Very low noise as Christian explained.

1280 res is a good setting for me as 3ms - 5ms 20 second captures give a lot of frames with a high chance of good images.
A SSD drive is a very good option to go hand in hand with the 174 as it will gobble up frames like nothing ;-)


User avatar
Merlin66
Librarian
Librarian
Posts: 3970
Joined: Tue Dec 13, 2011 1:23 pm
Location: Junortoun, Australia
Has thanked: 173 times
Been thanked: 615 times
Contact:

Re: Need input on mono camera for Ha

Post by Merlin66 »

+1 for the ASI 174MM
It does everything it says on the lid, and more!
To get very high frame rates you'll need a fast computer, good USB3, SSD drive and probably a T2 tilter.


"Astronomical Spectroscopy - The Final Frontier" - to boldly go where few amateurs have gone before
https://groups.io/g/astronomicalspectroscopy  
http://astronomicalspectroscopy.com
"Astronomical Spectroscopy for Amateurs" and
"Imaging Sunlight - using a digital spectroheliograph" - Springer
Post Reply