It's not Indi or software-related, but as an owner of a QHY device (the QHY294C, from before the release of the -PRO variants - read on) and a QHY OAG I would point out that QHY has some very weird ways of attaching things together along with some embedded assumptions as to how that will happen. My OAG, the OAG-S, is oddly designed in that it defaults to a gender reversal on the threads: it has the M42f threads you'd expect on the upstream side, but then also has M42f threads on the downstream side. The default flange ring of the QHY294C was also M42f, so you have to buy a separate M42m flange ring. But that's not enough, as you now need spacers - which are attached by bolts - so the OAG doesn't strike the camera housing. They had two different pages on what adaptors you needed, and one of them was wrong. Anyway, when you assemble it all together and thread it on, the OAG just ends up at whatever random orientation it happens to end up at, including in my case at an orientation in which the pickup prism obscures a corner of the sensor. There's no built-in radial adjustment ability like on every other OAG.

The reason this happens is that they seem to have designed the system with the assumption that their filter wheel will be inserted between the OAG and the camera, and it's within the filter wheel that the radial adjustment exists. But as an OSC, there's little reason for the 294C to be employed with a filter wheel.

Which brings me to support. I've raised this issue on their forums and with their Twitter account to no avail. Someone else asked about inserting a filter between an OAG and a 294C. No response there either. Another was attempting to use a puck-style guide camera. The design of their OAGs do not allow that, but that's never explicitly stated anywhere in the documentation and again no response. They don't seem to respond to "peripheral" issues.

And it goes on: when the mono and colour -PRO versions of the 294 came out, my old 294C was discontinued. But on their website they didn't just add a new page for the new versions; no, they actually rewrote the old 294C page so you now can't get the specs and info for the old camera... the same now seems to apply to the 174 that was reissued. Not that the specs were always precise: I variously found my camera listed as having a 17.5 mm or 18 mm back focus. Well that kind of matters if you've got a flattener or coma corrector in optical path ahead.

From most accounts the cameras themselves seem to generally work all right, but there's definitely an aura of disorganization to the point of contradictory information hanging over their documentation along with some ill-thought out accessories and attachment methods. There's even a line somewhere on the website that you may need to get some "factory to custom build a connector". Umm, ya.

So if you're planning a setup that is anything more complicated than attaching the camera directly into the drawtube, be ready for some confusion and hair-pulling.

I met a friend at a star party last month, and he was using QHY294 color pro, and we compared my ASI183MM pro & ASI533MC pro vs the QHY294 color. The conclusion was:
1- Both companies use the same sensors from Panasonic and Sony
2- ASI has a little advantage of having auxiliary USB ports in the back of the camera which act as a free USB HUB and thus reduces the burden or cables a little

Other than that, both have the same features, and ASI for me works very well with INDI/KSTARS as well as QHY to my friend with KSTARS...
 I use the QHY Polemaster, and I was surprised by the quality of this small camera...

In general, IMO they are neck to neck in the race...

Yes the ASI120MM has issues with Linux. It is a hardware issue with the USB controller. ZWO is aware of the issue, but no firmware fix is possible.
It may be possible to compile a custom Linux kernel with a single edit to the USB Core module to handle the non-standard packet sizes normally.
That being said, I have one, and it works well enough with a Raspberry Pi4 for me with just the compatibility firmware.

True. however, it should be pointed out that the ASI120MM/MC are no longer sold by ZWO. Nor is the ASI130MM which is a very old camera. AFAIK it is a firmware issue and not a hardware issue. There is a so called compatible firmware that can be loaded into the ASI120MM/MC but then imaging is limited to 8 bit only if you manage to get it to work at all. I never did for example though success stories can be found on this forum. In short: these old cameras should be avoided because of the USB issues.

The ASI120MM/MC-S (USB3) work flawlessly (apart from the occasional driver issues which usually get solved very quickly).

Yes it is a firmware issue and not hardware issue. The so compatibility firmware just makes sure that the max packetsize follow the USB 2 specification and is 512 rather than 1024 bytes.
However, the issues are still remain. Switching to 8 Bit helps but there are also randomly issues (and it is for sure not the cable).
In 16 Bit mode it is like tossing a biased coin, towards not working.


./zwo_FWTool_USB2 -i ../../../firmware/USB2.0/ASI130MM.iic -t li2c
[36233.666737] usb 1-1.2: new high-speed USB device number 8 using ehci-pci
[36233.919714] usb 1-1.2: config 1 interface 0 altsetting 0 bulk endpoint 0x82 has invalid maxpacket 1024
[36233.921050] usb 1-1.2: New USB device found, idVendor=03c3, idProduct=130a, bcdDevice= 0.00
[36233.921054] usb 1-1.2: New USB device strings: Mfr=1, Product=2, SerialNumber=3
[36233.921056] usb 1-1.2: Product: ASI130MM
[36233.921058] usb 1-1.2: Manufacturer: ZWOptical company
[36233.921060] usb 1-1.2: SerialNumber: 00000

./zwo_FWTool_USB2 -i ../../../firmware/USB2.0/ASI130MM-compatible.iic -t li2c
[36214.974532] usb 1-1.2: new high-speed USB device number 6 using ehci-pci
[36215.188389] usb 1-1.2: New USB device found, idVendor=03c3, idProduct=130a, bcdDevice= 0.00
[36215.188393] usb 1-1.2: New USB device strings: Mfr=1, Product=2, SerialNumber=3
[36215.188395] usb 1-1.2: Product: ASI130MM
[36215.188397] usb 1-1.2: Manufacturer: ZWOptical company
[36215.188398] usb 1-1.2: SerialNumber: 00000

The binary diff between the two firmwares is:

$ cmp -l ASI130MM-compatible.iic ASI130MM.iic | awk '{printf "%08X %02X %02X\n", $1, strtonum(0$2), strtonum(0$3)}'
000001FA 02 04
000002A6 02 04
0000031A 02 04
0000038C 02 04
00000958 02 04
00000B48 02 04

One can for fun, change the "02" to "01", then the USB kernel layer complains:
config 1 interface 0 altsetting 0 bulk endpoint 0x82 has invalid maxpacket 256

Anyhow, it is still a shame, that ZWO is not able to fix the firmware. At least they could release the code and somebody would for
sure fix it for them. Just search on github.com for ASI120mm, you will find some projects reverse engineered the SDK library.

I am wondering how many INDI users had to sell (stop using) there 120/130mm cameras.
I bought a used Starlight Xpress guider and did not regret it. 130mm was my only and last ZWO product.

Interesting replies there, thanks all for sharing your experiences with Zwo - QHY products, I see that like on CloudyNight it's a toss up between the two brands. 
Some have great experience with one and bad ones with the other, and vice versa. The thing is as usual on the Internet we're always quick to complain about something broken but slow to praise something good.
 

I have been very happy with the 2nd-hand QHY183C I use with my Z61. I have encountered zero INDI/Ekos issues. The image scale would be a nice match to the Redcat, but you might be looking for a larger sensor even if it means larger pixels.

The compatibility firmware helps but it is not a true solution to the fundamental issue. Which is that the USB controller hardware sends non-standard packet sizes.
Those packets work ok on Windows because they are not handled as a security vulnerability the way the Linux kernel does.
Link rot is an issue, but I managed to dig up the old discussions I found on the issue.
bbs.astronomy-imaging-camera.com/d/6901
bbs.astronomy-imaging-camera.com/d/7132
I never managed to compile and install a custom kernel for myself. But it would be nice to know if someone can try and report back.

But the bottom line in regards to the main topic. I believe they would've fixed it if they could, so I would not hold it against them.

I did do this several years ago when I still had an ASI120MC (USB2). You need to install the kernel source package of Ubuntu, make the change to one of the C files (basically disable an error when the package size is invalid) and recompile. Then the camera worked for me. There were instructions somewhere (sorry, it's been a long time since I did this) and I am not sure if those instructions still work since the kernel source has evolved a lot since.

Just found this old thread from 2018 where I added a link to the kernel instructions but the link seems to be broken now:

indilib.org/forum/ccds-dslrs/2131-asi-12...ailes-to-expose.html

Hi all, my experience has been this. A few years ago i purchased a QHY163C. Initially everything was fine with using it with indi, but then QHY did a driver update and i was never able to get the thing to work. Even the cooling oscillated.

I rebuilt my computer(s) RPi4, tinkerboard, even my laptop, nothing helped.

After talking to QHY, their first response was does it work with Windows 10. I dont use windows so was never able to test it. It basically got to the point where i had to sell the camera because i just could not acquire or download photos.

I eventually bought a ZWO ASI 071 and have never had an issue with it using the same computer(s).

ZWO are on top of their game when it comes to drivers, but i suppose they have an interest in making sure things work under linux because they sell the ASI-AIR. QHY on the other hand, do not really seem to care about those who use anything linux.

Just my experience.

Thanks everyone for your inputs I decided to get the ZWO 183MM. Was going for the QHY model, but I will need that little hub at the back of ZWO camera.