I only use Schmidt and Nightforce scopes (the NXS) model. After hearing negetive feedback regarding the low light gathering ability of the NXS, I deceided to set up as near scientific test as possible without using expensive light measuring equipement.
Now please realise I was completely impartial when entering into this test. All I wanted was to establish how each one compared to the other.
For the test I took 1 x NXS (3.5-15x50) and a Schmidt (3-12x50) and placed an A4 sheet of paper on the cut out of a life sized roe silhouette target made from hard board and placed this 80 yards away. Upon the A4 paper I printed out letters of varying font sizes (similar to when you go for an eye test).
I did post my findings with pictures a few years ago on another forum but am unable to find it. However, to cut a long story short, I was absolutely without doubt unable to tell the difference between the 2 scopes (they were incidenatlly set on 8 power so testing was comparable) when it came to low light gathering capability. Remember this was an impartial test. It didn't matter to me which won out but I was interested to evaluate both as accurately as possible. The one difference that was noticeable was that the field of view was significantly better on the Schmidt but as far as low light ability - no discernable difference between them.
Also please note this test was comparing the NXS against a Schmidt and not a Zeiss or Swaro and of course I could not comment if either of these other two euro manufacturers would fair any better. Would be interesting to evaluate against them both though. The reality is they are all fine quality optics and all very good in low light.
Interestingly a family member was with me at the time of testing and asked me what I was doing. They have no knoweldge of shooting or the equipement used etc and after asking them which scope they thought was better in terms of reading the letters and making out the deer silhouette, they said the Nightforce was better. I actually don't think that was the case personally but it was an interesting comment based on the fact they had no preconceived idea about either scope.
Even if one was better than the other (which as previously stated I don't think was the case), the difference with the human eye would be impossible to detect and furthermore from a practcal view point, would certainly not provide the user with any advantage when shooting game at low light.
Just my findings and thought would be a worth while post.