Render times get slower in animation

Hey peeps,

Have a problem with inconsistent render times, I have a camera just pulling back, its a very simple animation. The first two or three frames will render in maybe a minute or two and it will get progressively slower after that i.e the fifth frame is taking nearly 20 minutes. Nothing new comes into the shot its literally moving a tiny but since its only 5 frames and increases a stupid amount.

I also have inconsistency in normal renders, one second it will fly by and then the next time the exact same shot will take 5 times longer, sometimes switching in and out of rendered view fixes this

Any idea?

CPU: 5800x
GPU: Rtx 3070
RAM: 32gb 3200mhz

Do you have motion blur or depth of field enabled?

I do indeed have DOF on but I think I might have found the problem, I’ve been keeping an eye on my GPU power draw while rendering and it’s weirdly low for some reason. When it runs slowly it’s at 100% but drawing only 80w and when it’s fast it draws 160w both of these are quite a bit below the 200-220 it should be running at

Your CPU will bottleneck how much power your GPU uses:

To be fair, your MOBO and PSU can also bottleneck your GPU, but it’s not that surprising that your GPU isn’t using the maximum amount of power it says it can on the box. To do so, you also need a maximum-strength CPU, MOBO, and PSU.

On a more related note, have you tried changing your DOF settings? Reducing the strength of that effect (increasing the f-stop of your camera) will greatly speed up your render

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If you start the render on the fifth frame, does it start slow? Or does it become increasingly slower based on the number of frames you have rendered in a row?

Also, does it happen only with your GPU?

Is the scene really heavy? What is the memory use during render?

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Well my CPU, Motherboard and psu are all towards the top end so I cant see a bottleneck there

Its not that its slow thats the problem really its that it gets slower over time but ill try taking off DOF

No it always starts strong and then slows down, this also seems to be mostly a problem with blender as when I play games the power draw sits above 200w which is pretty much where it should be.

The scene is quite heavy but again if that was the problem then it would fail every time but its every now and then.

Memory use is high 7 out 8gb so still not abnormal

Read the link and thank you for finding that, seems like people with similar systems are having the same problem. Theyre all fairly decent systems though so seems like a bug