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Old 04-09-2020, 10:18 AM
RugbyRene (Rene)
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ZWO ASI2600 vs QHY268-C

Hi all,

I need some advice. I'm looking at upgrading my current OSC camera (ASI294) with either the ASI2600 or QHY268-C. The ZWO is a few hundred less than than the QHY which is the only point of difference I can see.

I've looked the specs for both and they look almost identical & both seem to take very good photos. So I am hoping the community can help me decide which is the better purchase (or doesn't it matter).

I'll be using it for deep sky photography (galaxies, nebula, etc).

Rene
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Old 04-09-2020, 11:07 AM
Startrek (Martin)
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Rene
Iíve had my 2600MC for nearly a month now and admittedly Iíve upgraded from a Canon 600D DSLR , but this camera is simply unbelievable !!
I too read the specs on this camera and the QHY 268C and again they look identical, so canít comment on the QHYís performance but the 2600MC so far has not disappointed and has exceeded my expectations

Have a look at my images in the Beginners section Iíve posted over the past 3 weeks
I just use a cheap 6Ē and 8Ē newt

All the best
Martin
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Old 04-09-2020, 07:37 PM
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With the ASI6200mm and the QHY600 ( I know not the same camera but the full frame version of the same sensor in the ASI268C and QHY268C) there are differences.

Firstly QHY users a higher grade of the same sensor. Performance is the same but its rated for a longer life.

Secondly QHY has different modes that can give a higher well depth than the ASI. I suppose you could work out the gain and offset levels to match these (I assume that is all the QHY is doing to get these "modes" but it might also be something else). QHY says their QHY26C has 75,000 electron full well depth whereas ZWO is "only" 50,000. Full well depth and read noise determines dynamic range. I am sure the deeper wells comes at a cost of higher read noise so the ultimate dynamic range is most likely similar.

Thirdly QHY has gotten on top of this faint horizontal banding the 6200 sensor can have (it apparently is not visible in most images unless they are very dim areas). They have a firmware fix for it, ZWO does not.

I have read QHY has the better build quality. The ASI6200 has 256mb DDRAM but the QHY has 2GB.

ZWO has the reputation of having solid reliable drivers. QHY in the past has not although I have read they have since sorted them (I'd double check though).

That's what I have picked up in my research into these cameras so far.

The other thing is both manufacturers seem to not have any stock and these are backordered everywhere. They are very popular cameras.

There is also a mono version of the QHY268 coming out in October for US$2095.

Its an APSc sized sensor and appears to be the same architecture as the 6200 sensor just scaled down.

Greg.
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Old 05-09-2020, 09:55 AM
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Camelopardalis (Dunk)
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I still hear folk complaining about QHY's flaky drivers, so that'd swing it for me personally. Doesn't really matter how the camera looks and feels if it lets you down in the field...

The gain settings with the QHY interface are also quite convoluted. ZWO took a straightforward approach. Each to their own.

It's quite common to see this kind of snobbery towards ZWO, but the reality is in practice there's no difference. At comparable price, it's a question of flipping a coin and taking your chances
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Old 05-09-2020, 10:12 AM
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Originally Posted by Camelopardalis View Post
I still hear folk complaining about QHY's flaky drivers, so that'd swing it for me personally. Doesn't really matter how the camera looks and feels if it lets you down in the field...

The gain settings with the QHY interface are also quite convoluted. ZWO took a straightforward approach. Each to their own.

It's quite common to see this kind of snobbery towards ZWO, but the reality is in practice there's no difference. At comparable price, it's a question of flipping a coin and taking your chances
Snobbery is it? I thought I was simply listing the features of each.

Greg.
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Old 05-09-2020, 10:43 AM
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Sounds like a case of "doth protest too much"?

Greg, presenting a list of features/extrapolations that the ZWO _doesn't_ have can be construed as one-sided/bias/whatever.

In practice, how does the extra well depth affect the images? (Is it even real? I wonder what Sony's specs say)

Is the horizontal banding relevant? Has there been any evidence that this is (also) present in the 26MP chip?

What use is the extra 1792MB memory when each image is ~52MB?

How much of an advantage does the higher grade sensor yield for astrophotography? The longer life would certainly be advantageous, but without a reference timescale, it just looks like a lot of extra money for unknown gain.

I'm not taking sides here. While I have a ZWO camera, QHY have been putting out some pretty appealing offerings of late, at aggressive price points. Competition is good.
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Old 05-09-2020, 12:09 PM
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A look at the graphs on the QHY page suggests that the full well of the sensor might be around 75Ke, but you have to interpolate a bit from graphs which dont have very clear scales, what is clear though is the gain would have to be below unity to use it. From my experience of the ASI294 there was no great benefit and some downsides to going below unity so I have no idea if the extra full well would really be an advantage or not, at least when 50KE is on offer to begin with. I have not found an explicit Sony spec so far which states unequivocally what the pixel well capacity is.

I am inclined to wonder if extra memory on board is any advantage, my understanding is that it is used to optimise the readout speed off the sensor without any USB speed issues to contend with, if that is all it is used for it is hard to see what more achieves?

All I can say so far is that with the every limited use the weather has given me, the ASI2600 is promising to be a very nice camera and a solid step up from the ASI294, and it is simple in operation, set 0 gain, 50 offset, cool it down, enjoy. Comparisons to the QHY I will have to leave to others as I can't compare real world use with a camera I don't have and real world is what matters after all.
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Old 05-09-2020, 12:15 PM
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Quote:
Originally Posted by gregbradley View Post
Snobbery is it? I thought I was simply listing the features of each.
Reading it back, looks like I was projecting some CN angst unintentionally, so I apologise Greg

This subject comes up so often over there...the end results are inconclusive. I guess at roughly the same price point, it almost doesnít matter
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Old 05-09-2020, 12:24 PM
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A look at the graphs on the QHY page suggests that the full well of the sensor might be around 75Ke...I have not found an explicit Sony spec so far which states unequivocally what the pixel well capacity is.
Nah me neither...just 75ke sounds out of kilter with the specs from the 6200 with the same pixel size, and the two sensors seem to employ much of the same technologies. Pure speculation of course.
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Old 05-09-2020, 02:07 PM
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Quote:
Originally Posted by Camelopardalis View Post
Reading it back, looks like I was projecting some CN angst unintentionally, so I apologise Greg

This subject comes up so often over there...the end results are inconclusive. I guess at roughly the same price point, it almost doesnít matter
No worries Dunk.
Greg
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Old 06-09-2020, 07:28 AM
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Its true these specs may not have much real world difference. That is also what I have read on CN from users of these cameras.

The extra memory on the QHY I read was to allow the fibre optic to work on the Professional version (I am not interested in that model).

If there are still driver issues that would be a deal breaker for me as there is nothing worse than getting a new camera and trying to get it to connect up.

I have an ASI183 and it was no trouble to get up and running which was impressive as not all cameras I have gotten in the past.

The handling of the horizontal fixed pattern noise in the QHY is impressive even if a minor problem noone wants to contend with that sort of noise in a dim image.

I am studying up on these cameras because I intend to get one or the other in the near future. What makes it harder is on Astrobin the bulk of the really good images are QHY600mm images but then it has been out for longer.

ASI is US$600 cheaper which is close to AUD$1000 so the QHY would have to be fairly clearly better for that.

Are these different modes in the QHY merely some combo of gain and offset values? Does anyone know?

Greg.
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Old 06-09-2020, 07:43 AM
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I found this:

https://www.qhyccd.com/index.php?m=c...94&id=55&cut=1

Scroll down about half way under "QHY linearity test".

So the different modes have to do with the speed of driver timing. I thought it might be the same as FLI cameras where you have a choice of digitization rates with the slower ones taking longer to download but have lower read noise (but as far as I know this does not affect full well depth).

To be practical though, you'd have to settle on one mode for all use or at most one for LRGB and one for Narrowband otherwise it will become a complicated mess trying to manage the files with different sets of calibration files needed.
Its bad enough with exposure length, gain and offset plus different temperatures as variables compared to CCD where its only exposure length temperature. Plus in the case of FLI digitization speed.
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Old 09-09-2020, 09:27 AM
RugbyRene (Rene)
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Thanks for the advice everyone. I've decided to go with the ZWO 2600 as the brand is a known quantity given I already own two ZWO cameras.

Rene
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