Resolution "limit"?

[Subrosa]

Hey,
I have a 3dm file exported from Rhinoceros 5, which consists of ~2500 simple objects that are arranged on a grid.
I need a rendering of the top-view in 15.000 x 15.000 pixels for "quite" a big print / banner. The rendering is nothing special. Background is solid black, no ground shadows, the material is hard shiny plastic with a bit of a matte touch.

Technically, this problem is already solved, but that was just a workaround and I'd like to know what happened:

- When setting the resolution to 15.000 x 15.000 pixels, with the standart settings and "max 5000 samples" (so i can just end it whenever it looks good enough), I had let it run for a solid 6 hours with the image itself still being black. Only a few pixels in the center changed. 

- Setting it down to 10.000 x 10.000 showed the first image after not even 5 seconds. After 5 minutes it looked quite good already. 


So ... is this just the thing, that the difference from 10.000 to 15.000 makes the image more than twice as big and it takes so much more longer to render, probably a wrong setting somewhere or just my machine reaching its limits? (Don't know exactly since I am not home, but I got an i7 with a 3.4 ghz quadcore, quite a new geForce graphics card and 32gb ram)

I am using Keyshot 6. I managed to get my 15.000 by 15.000 image by rendering it in 4 parts of 7500 each and putting them together afterwards.


Thanks in advance!

[soren]

To save resources and improve render speed, max samples will compute the samples in small tiles when the resolution goes above 10k x 10k - this is what you were seing. The 5000 samples were being done in small tiles.

To get a good idea for how many samples you need in a render, enable the heads up display (hit H). It will show you how many samples the image in the realtime-view has received.

Søren