Should I be getting a higher frame rate?

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covington
Posts: 9
Joined: Mon May 28, 2018 3:33 pm

Should I be getting a higher frame rate?

Post by covington » Sat Jun 02, 2018 3:24 am

Camera: ASI120MC with Linux-compatible firmware installed.

Hardware and software: 3 combinations:
ASUS UX32A laptop, USB 3 port, Linux Mint, FireCapture under Linux.
ASUS UX32A laptop, USB 3 port, Windows 10, FireCapture 2.6 and SharpCap under Windows.
Lenovo Ideapad 320, USB 3 port, Windows 10, FireCapture 2.6.

(I understand this is a USB 2 camera; it is connected to USB 3 ports; maybe the problem is that they are not emulating USB 2 perfectly.)

In all cases I get a frame rate of about 9 fps at 1280x960x16 bits.
It doubles to about 18 at 8 bits.
It also increases proportionally when I use a smaller ROI, so can easily get 40-70 fps for a small field.

I have tried two USB 2.0 cables with the same results. A cable not rated for USB 2.0 was much worse.

Adjusting the FireCapture USB traffic settings, RAM buffer, and heap size made only a small difference (raising it from about 7.5 to 9 fps).

If I choose "High speed" in either FireCapture or SharpCap, the camera freezes (stops sending frames at all).

I should emphasize that this is not a serious problem because I am getting excellent pictures, and I would rather have reliability than high speed. But if there is something simple I've overlooked, I'd like to know. Thanks!

s3igell
Posts: 37
Joined: Mon Apr 10, 2017 12:04 pm

Re: Should I be getting a higher frame rate?

Post by s3igell » Sat Jun 02, 2018 6:09 am

Do the Math...
You are getting every bit of USB2 throughput - and then some...

1280*960*3*8*18= ~506Mbit
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covington
Posts: 9
Joined: Mon May 28, 2018 3:33 pm

Re: Should I be getting a higher frame rate?

Post by covington » Sat Jun 02, 2018 9:44 pm

s3igell wrote:Do the Math...
You are getting every bit of USB2 throughput - and then some...

1280*960*3*8*18= ~506Mbit
Remember, the deBayering is in the computer, not the camera. So in 8-bit mode I am getting

1280 * 960 * 8 * 18 = 178 Mbit/second

which is not the full capacity of USB 2. Right?

covington
Posts: 9
Joined: Mon May 28, 2018 3:33 pm

Re: Should I be getting a higher frame rate?

Post by covington » Sat Jun 02, 2018 9:50 pm

I should add that my exposure time was 1 millisecond and I was not deBayering at all.

covington
Posts: 9
Joined: Mon May 28, 2018 3:33 pm

Re: Should I be getting a higher frame rate?

Post by covington » Sun Jun 03, 2018 2:46 am

Interesting observation: I experimented with disabling USB 3.0 in BIOS by making two settings, Legacy USB Support Disabled and XHCI Pre-Boot Mode Disabled.

I ran FireCapture and noticed that, on one particular run,
- Initializing the camera took longer than normal;
- USB Traffic setting made an appreciable difference in frame rate (normally it doesn't);
- High Speed mode gave me high speed rather than freezing the camera.

I achieved 32 fps at full frame (1280 x 960 x 16 bits).

But then I couldn't reproduce it. Behavior went back to what it had previously been. Maybe Windows detected the absence of USB 3.0 support and corrected it.

So I assume my frame rate limit comes from a limitation of USB 2.0 emulation on USB 3.0 hardware. I am content with that; the camera works reliably, and I'm planning to move to the USB 3 version of this camera soon.

But I wanted to make sure I wasn't doing anything wrong or missing something obvious.

covington
Posts: 9
Joined: Mon May 28, 2018 3:33 pm

Re: Should I be getting a higher frame rate?

Post by covington » Sun Jun 03, 2018 9:38 pm

Actually I just did the right thing and ordered an ASI120MC-S (USB 3.0) at the sale price.

I'll probably autoguide with the ASI120MC (non-S). I know autoguiding is better with a monochrome camera; that's coming in the future.

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Support@ZWO
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Re: Should I be getting a higher frame rate?

Post by Support@ZWO » Mon Jun 04, 2018 1:25 am

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