What causes unsteady FPS rate?

[Prasad]

I mainly do spectroheliograph work. The FPS rate plays a critical role to obtain good quality images from the scans. The required FPS is adjusted by setting the Turbo USB slider. For example, my camera is an ASI178MM, and I do captures (scans) with an ROI Capture Area set to 2280x96. The mount is run to scan the solar disk at a speed of 20X solar rate. For this, I need an FPS rate of about 256 fps. I often experience the FPS rate fluctuating randomly. This does not always happen. Steady FPS gives me excellent results, but when it is unsteady, the images show distortion.

I run a Dell laptop with an Intel Core Ultra 9 at 3.30 GHz, 32 GB RAM, and a 1 TB SSD drive. My SharpCap Memory settings are 10368 MB for both HighSpeed frame Cache and Live Stacking & Display.

Can you suggest a cure for this fluctuation?

Thanks
-Prasad

[archer1960]

Switch to Linux? Windows is not known for having consistent realtime response rates.

[Prasad]

I want to add that the ideal frame rate at 20X is 256 fps, but the variation I notice is that the FPS rate drops to a figure like 180 and then jumps back to 256, etc. This is a major fluctuation that is bothering me. It doesn't happen all the time. I have tried switching to a brand-new USB cable, etc. I am confident that it is not the USB cable.

Thank you
-Prasad

[admin]

Hi,

the SharpCap frame rate shown is averaged over a few seconds, so there must be some significant variations for things to change that much.

Things to be aware of:

* If the fluctuations are only while capturing and the frame rate is steady when just viewing the images, focus on the speed of writing images to capture files

* If the fluctuations also happen just when viewing and no capturing then the USB transfer is the likely cause.

* Initially test with short USB cables (1.8m, no extensions or hubs). Adjust Turbo USB down to 80 or below to maximise stability, a single cable from the camera straight back to the PC

* If you can get stable running on short cables, no extensions/hubs then gradually build back to your normal configuration one change at a time, testing each step to see what re-introduces the instability.

* Don't try to use 'frame rate limit' to set a particular frame rate - that will not give evenly spaced frames. Adjust exposure instead

cheers,

Robin