I have this scene, and here is how it looks like rendered in cycles with 1200 passes
Now, question is, is that 600 extra passes difference proportional with the quality increase, and therefore i should just continue and render it on higher ammount of passes(was thinking something around 4000?)
or
the increase in quality is very little and i should take some meassurments and reaproach materials and settings to avoid insanely long rendering time.
The general rule of thumb for progressive ray-based engines is that the more passes you allow to render, the more samples you get on the image and the higher quality you get.
In this case, I think 4000 samples is not too far off from what would be required to clean up the image completely, alternatively, you can download a trunk build off of graphicall or the build bot, set the samples to the max allowed, and tick ‘progressive refine’. That method will mean you will see the whole image rather quickly, but it will be very noisy, in this case you can simply let it render until the noise is low enough to call it done.
Unless you are in a terrible hurry just leave your PC render it over night/day?
I think that with still images it doesn’t matter so much even if your render takes long because of the material/lighting settings. If it was an animation I would consider to do some compromises so that the thing gets rendered in my life time.
Also even real photos have a small amount of noise 
5000 passes
yes, improvement is visible. I’ll try rendering it overnight with 15000 passes and hopefully it will be ok.
Could you share your lighting setup? A Screenshot or so. Such a scene should not require that many samples…
Thanks,
basically, you can remove the walls of the room, they add quite some render overhead. Keep only the floor plane.
And, thats the biggest fish, in the “Light Paths” panel, check the option “No Caustics”. It will clear much faster then.
With both tricks you should only need 300-400 Samples.
Try to render 2 separate images with 250 samples but different Seed value and then mix them 50-50 in compositor or photoshop. Usually it gives better result than single image on 500 samples.
I like more the first one, you have better reflections and overal ambient light.
Combining 2 renderings with different Seed works, but usually this gives inferior results. Can you show an example where it gives better results?
You can try using the Clamp setting and decrease the light bounces to 4.
, did what you said, result in 500 passes