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FPS limitations

PostPosted: Tue Jun 25, 2019 12:11 pm
by Clark
Hi there. I recently hired an IQ3 100MP + XF for a commercial shoot, and was struck by the slow rate at which it was possible to shoot images.

I was tethered with USB3.

What's the bottleneck? Is it the data transfer via the cable, or the image capture in the back?

Is it any faster using card?

Do any of the other backs do a higher FPS?

Re: FPS limitations

PostPosted: Fri Jul 05, 2019 5:14 pm
by Jon
Speed will depend on the file type chosen. IIQL-16bit will be the slowest, but the standard IIQ-L or IIQ-S will be about 1FPS.

Re: FPS limitations

PostPosted: Sat Jul 06, 2019 8:52 am
by Clark
HI Jon, thanks for the reply.

Sure, I was aware of the speed I was getting, and it was about 1 frame per second. For me this feels incredibly slow, as I am much more often using a Canon or Nikon that can shoot sometimes more than 10 times faster.

Now I'm not saying that to criticise Phase One in some immature fashion. The images being produced are much bigger of course, and on this occasion I needed that quality, and the camera delivered that beautifully.

I just wondered why it is so slow? Obviously there's a significantly bigger file size is at the root, but is it the data transfer to the storage media? Or the on-board processing of the images? I guess this is actually a pretty obvious question for anyone with a little technical knowledge.

Just wondering if new tech like CFExpress / USB-C might give us a jump in speeds in the near future with the next gen IQ backs, or if it's more likely to be a slower progression (if it's depending on computing power in the back)

Thanks, Clark

Re: FPS limitations

PostPosted: Tue Jul 09, 2019 4:45 pm
by Jon
Hi Clark,

The two main limitations to capture rate are Sensor readout speed and camera recycle speed. In the case of the IQ3100, it is the sensor readout times that limit it rather than how fast the shutter can move. Digital backs will be slower than 35mm size sensors because they are pushing so much more data. After that, the power of the back and storage options are actually really well matched for performance. For instance, when shooting on USB 3 or to a UDMA 7 CF card, you will see little to no buffering even in fast continuous shooting. Tethering performance is often faster than DSLR because of the way we structure it.

IQ4 150mp can do up to 3 frames a second due to new technology in the sensor - in that case it is helped out by the XQD card as we can write the files almost instantly... thus it becomes possible to shoot continuously at 2-3 frames a second and never hit the buffer. It would be possible to have an even faster FPS rate with the 150mp sensor, but we would have to run at a lower bit depth (12 or 10 bit), but that negates the reason to use a high end camera.

Re: FPS limitations

PostPosted: Thu Jul 11, 2019 6:47 am
by Clark
Thanks again Jon for the very informative reply.

In the future I will definitely opt for the IQ4 then if possible!

Re: FPS limitations

PostPosted: Wed Feb 10, 2021 6:37 pm
by Rsicak
Hi Jon,
I kindly would ask you to explain how IQ4 150mp can reach 3FPS? As I know, raw file size is about 300MB so it is 900MB/s. So can an XQD card support this speed? I see only CFexpress B cards which has such speed.
Robert

Re: FPS limitations

PostPosted: Thu Feb 11, 2021 6:41 pm
by Jon
For 3FPS, you need to be in 14bit mode as this affects the sensor readout speeds. File size then can range from under 100mb to about 150mb. -Even in 16-bit mode raw file size is about 200mb - we have better lossless compression than our competitors ;-)

However, you also have a rather large buffer which means that you do not have to write files to the card at a rate of 450-600mb/s. Both XQD and CF Express perform well in this regard. You would only need such speeds if there was a reason to shoot at that high of rate for an unlimited amount of time.