Low fps with QHY5L-II C in Firecapture

[ofranzen]

Hello,

I can't get decent fps with my QHY5L-II C in Firecapture. Max/actual is 100/7.5 with current settings and lower resolution at 640x400. If I do a test recording it is indeed 7 fps captured. Where is a good place to start looking for the error? If I try max resolution I get <4 fps.

Tried on two different computers. Windows 10 and 11. Two different cables. Exactly the same result. Latest drivers from qhy and latest version of Firecapture.

Thanks in advance

/Ola

[Stargazer33]

Have you enabled 'HighSpeed' transfer and what is your 'USB Traffic' setting?

[ofranzen]

I read elsewhere about the "high speed transfer" setting but I don't know where it is. I thought it was perhaps an older setting as it was an old post. USB settings are default.

[CraigT82]

If you click the 'more settings' button that is highlighted in your screenshot, what is in there? There should be a usb traffic setting you can play with.

[symmetal]

According to the specs it is a USB2 interface camera so the quoted frame rate of 640x480 @ 106fps is rather optomistic and may be quoted for the max theoretical usb2 transfer speeds which are usually never reached in real life. Is it sharing a hub with other equipment connected which will split the USB2 bandwidth available between the devices connected to the hub.

Also what's the length of the cable being used and is there a repeater in the cable if it's a long extension cable. These will significantly reduce the maximum data transfer speed. Use a separate USB port on the PC to connect the camera only and the shortest, good quality cable you can use is your best option.

The USB Traffic options usually refer to USB3 interfaces so may not be available or do much for USB2. High speed mode uses a lower bit depth for A to D conversion. The camera spec just specifies only 12 bit so this mode may not be available. As others have said these will be listed in the options if you click the 'More' button.  

Edit: 640x 480 @ 106fps is 32MB/s data rate just for the image data. There will be extra bandwidth required for all the other traffic needed to achieve the transfer. USB2 max theoretical data speed is 480 Mb/s which equates to 60MB/s. This is for the USB2 controller chip in the host PC and may be shared between 2 ports or more on the PC. Not all of the 480MB/s are available for data transfer as some will be used in managing the USB protocol data blocks and handshaking etc. The general concensus seems to be is that the maximum sustained data transfer you can achieve in practical terms on one port in ideal conditions is 40 to 45MB/s.

Alan

Edited August 24, 2021 by symmetal

[ofranzen]

Wow, that's some of the strangest settings I've seen. A program pretty much meant for high speed video capture and you have a not obvious setting "high speed" and a very non descript "usb traffic". Checking "high speed" and setting usb traffic to "1" (whatever that means) gives ~65 fps from the previous 7.5, both at 640x400. The "usb traffic" setting easily did half of that increase. No idea why.

Thanks for pointing these out to me!

Can anyone say if there is a noticable image degration with "high speed" mode?

Maybe I can find a shorter or better cable but pretty much a 9x increase is good enough for me to be honest

Thanks again

/Ola

[symmetal]

I mentioned above that high speed uses a lower bit resolution depth so is quicker to convert each pixel. Your camera is 12 bit as specified so high speed would probably be 10 bit. As you record at 8 bits, sampling at 10 bit has no effect on image quality. As you're stacking many 'noisy' frames you will recover up to 4 bits more sampling resolution anyway so your final stacked image will have effectively 12 bit resolution. Your camera spec didn't specify dual sampling rates so wasn't sure if it had a high speed mode but it seems to. 🙂

USB Traffic is setting the speed at which the capture program will send the data over USB. If set too high a bottleneck in the imaging recording process somewhere may cause data to be lost so the capture program can throttle the data speed with the USB Traffic setting. Setting it to 100% or 1 in your instance means no throttling. If your capture program doesn't flag any errors you should be OK at 1. Again I wasn't sure if it had any effect over USB2 but it seems to. 🙂

A shorter cable was a last resort so probably won't affect things if your speed has increased a lot without problems. Not sending the camera data via a USB hub should still benefit you though as far as speed is concerned.

Alan

[ofranzen]

Again many thanks. I will do some tests with and without the USB hub in place and see if it makes a difference. That hub has been playing nice so far so I am actually not expecting any decrease in fps, but one never knows of course. The camera is only USB2 so it may very well be maxing out already.