Ok. I'll give my impressions, and then Cyres may want to comment and give his, as it was he who was with me to do a comparison. I think though that we were in broad agreement on the evening.
For me, it was useful gathering the kit together and doing the assessment as it's not often we all get the chance to do something like this with such a cross section of optics.
Binoculars: Not a lot to separate them. If anything, I found the Steiners fractionally brighter and they retained a very slight edge as darkness started to creep in, but there was just a cigarette paper in it! The Leicas had better edge sharpness though.
Scopes:
First, resolution:
My rankings:
At dusk, I thought that all of them were pretty good really.
I did think (looking at distant objects and trying to pick out texture and detail) that the Nightforce just had the edge over the others. The Zeiss, Delta and Bushnell all exhibited similar resolution with the Optima just missing out...not quite up there with the others but it was close.
So for resolution at dusk:
1st place: The Nightforce, closely (very closely) followed by
2nd place: Zeiss,
3rd place: Joint 3rd Delta Titanuim and Elite DMR scope;
4th place to the Optima.
If pushed hard, I'd say that the Bushnell DMR just bettered the Delta for resolution at Dusk.
Resolution when almost dark: This shook things up a bit, as expected. The Bushnell started to struggle a little here as it didn't retain enough brightness to make the most of its pretty decent resolution. The optima fell short by quite a margin here for similar reasons.
1st place again, and this really surprised me, had to my eyes anyway, go to the Nightforce. I was just able to resolve detail, albeit, once again not quite as bright (that not being the operative word by now!) as the others. I could still make out the top wire on the fencepost and even leaves in the background when the others started to lose the sharpness a little even though their image seemed a bit brighter. Whilst it took longer to fix on the target than the Zeiss or the Delta, once locked on and steady, there just seemed to be a slight edge in definition. I really wasn't expecting this. Now whilst I have said that the Delta and Zeiss were able to hang onto the image a little longer than the Nightforce, the reality is that I wouldn't take the shot in such dark conditions. So where the light just started to fade to the extend that you couldn't make out, say, the eyes, nose and antlers of a Roe buck against woodland, that was the limit and this limit was pretty similar for the top three scopes. It's just that when looking through the scope a little longer at this point, whilst the image was a little darker, oddly, the Nightforce seemed to retain a fraction more detail and resolution than the Zeiss...just enough to make the minute advantage in contrast and shape allow better rendition of detail.
2nd: Joint 2nd went to the Zeiss & Delta but it really was close. Someone with different eyesight may have ranked the Zeiss and Delta equal joint first
3rd: Optima. I didn't think it could live with the others for resolution but it was still good and more than capable of shooting at dusk with sufficient precision.
4th: DMR: It didn't retain quite as much brightness as the Nightforce so you couldn't use its excellent resolution to any great effect and it would not cut it for shooting in this low light, especially as it had no illuminated ret and was FFP. Think again if you consider FFP a good choice for stalking without some sort of central dot illumination.
Next, Brightness/clarity
Again, some unexpected results but still easy enough to judge on merit for brightness and edge to edge clarity:
Dusk:
1st: For me, it was close, but the shear "pop" of the image and the stunning brightness available had to go to the Delta Titanium. Pretty remarkable really. It also had a better field of view at 15x magnification than anything else on test and by a reasonable margin.
2nd: Very close indeed, but the Zeiss was also clearly brighter than the other scopes and had slightly better edge picture definition than the Delta but I felt didn't quite match it for overall brightness. Another thing of note was as the dusk started turning to darkness, the Zeiss lost its finer crosshair before the Delta (which uses a very slightly thicker central crosshair...but still finer than most 4s type rets). The central dot illumination on the Delta I felt was also nicer and could be adjusted so that you could take a crow's eye out at 200 yds!
3rd: Joint 3rd to the Nightforce, optima and Bushnell DMR. The Bushnell may have even just edged it a little over the other two. The Nightforce and DMR, as with the Zeiss, both retained really impressive edge to edge sharpness, and the Nightforce in particular slightly better resolution. Edge sharpness was easily on a par with the Zeiss and better than the Delta.
As darkness fell:
This started to separate things more. Whilst the Nightforce makes a truly superb dusk scope and with its resolution advantage would make I think the better longer range dusk scope, that resolution advantage started to slip with the light almost fading to darkness. I liked its illuminated Np-1 ret a lot. Not too bright. However, two scopes stood head and shoulders above the rest:
Joint 1st place: Zeiss and Delta. There was nothing, and I mean nothing, to choose between them. Both picked out that fence wire, albeit with loss of definition, right up until it became simply too dark to use anything other than dedicated NV gear. The reality is that they both out-performed our eyes as we would both probably not have shot in that level of darkness.
2nd place: Nightforce. It was usable right out to within 5 or 10 minutes minutes of the top two, but eventually, that cracking resolution wasn't usable by the time 7:30pm had been and gone whilst the other two held on for about another 5 to 10 minute longer.
3rd: Optima. Just but only just hung in there! It faded a fair few minutes before the others though and wouldn't realistically have been usable when you were still able to take the shot with the Zeiss, Nightforce or Delta.
4th place: Bushnell Elite Tactical DMR: Just started to fade within about a few minutes ahead of the others so not usable when darkness descended, as much due to the ret as anything but the glass itself was good to dusk.
Overall Ranking:
The biggest surprise for me, at any rate:
Based on a sensible balance of brightness, clarity and resolution, optically at any rate, this is how I would rank them:
First: Delta Titanium. The shear brightness and field of view meant that in realistic (not near darkness) shooting scenarios I genuinely would have the Delta Titanium for stalking over anything else here on test. Married to that, the superb ret with fine adjustable central dot and it's the winner for me anyway;
Second: It would have to be the scope that I thought would walk it. The Zeiss. It's really good edge to edge sharpness and clarity and overall brightness simply kept it ahead of the others;
Third: Whilst arguably it retained for me anyway the best resolution of all the scopes on test, the Nightforce couldn't quite live with the Delta or Zeiss for brightness or field of view and for that reason, as a stalking scope, I ranked it third.
Fourth: Had to be the Optima. It really did fare better than I thought it might and was a decent scope more than capable of shooting to just gone dusk.
Last: The DMR. To be fair, it was never intended as a staking scope. For one thing, at close to a kilo in weight, it's far too heavy. For another, the non illuminated first focal plane ret is definitely NOT suited to stalking imho. It's a superb long distance target scope which is where it excels.
So there we have it. As Jeremy Clarkson might say, on that bombshell, the Delta Titanium HD is the winner for me...but ONLY just! It provides simply stunning performance per £.
On matters of build, it has to be noted that I have dropped the 12lb outfit containing the Delta and guess where it landed....yep, on the scope. It not only survived unmarked, but even held zero! Of all the scopes, the Nightforce is built like a tank and you just know will be going on forever. It had the best turrets of the lot too, but more tactikewel than stalking. The delta's lower profile turrets (with re-settable zero) under caps was more suited to stalking as were the excellent turrets of the Zeiss which did retain better build than the Delta but at two or three times the price, you'd expect that. The DMR was also, like the Nightforce, built like a tank. If you do use one for stalking, you'd be able to club the deer to death using it rather than relying on its optical brightness!
Now before anyone shouts "Swarovski!" I have actually tried a Swaro Z6 in similar conditions and felt that it performed pretty close to the Zeiss on test here. It had better edge to edge than the Delta but it would not have matched it for field of view, nor did it have such generous eye relief, nor bettered it much, if at all for brightness at dusk. Just calling it how I experienced it, but it would be interesting to do a side by side with the Delta nonetheless. Happy to accommodate that test!