I am playing with basics on pyro and smoke effects and I noticed that I always get a more blurried rendered version of my smoke than the viewport's, why is that?

you probably need to decrease Volume Step Size Parameter on Mantra/Properties/Sampling Tab

you may also increase the density in the shader to match the viewport. The gl display is quite opaque, and the shadows strong.

If I increase the density it gets whitter not shapper, the step size also it's not making any difference.

This is a great problem, I can never show the result in the Viewport to the client because I can't get the same result, in this case the the viewport visualization gives me the sense that I have more sharpness and detail than the final result.

What would be the right way to deal with that?

By default, the volume filter size is quite high: 1.5. This blurs the renders.
Try to lower the filtering values, and/or change the filter type.
Parameters to add to you object are:
- Volume Filter (vm_volumefilter)
- Volume Filter Width (vm_volumefilterwidth)

Cool, it seems that this was what I was missing, I'll try that and tell later what I got.

Thank you very much for this info.

That´s it, that´s what I was really missing, this filter makes a difference, I just change the filter to sinc and now the render is much sharper and closer to the viewport.

Thank you very much for the help.