Canon 1DX vs Nikon D800 in Low Light?

I am the house photographer for the entertainment department at the Chumash Casino Resort in Santa Ynez, California. I have been their contract photographer for ten years. I have shot over 500 concerts and other events there. All of my equipment has been acquired with that venue in mind. I have two 1DXs and lenses include a 70-200mm f/2.8L IS USM II ... see my gear list (via my .sig) for all the other stuff I have, which is substantial.

Over the years I have needed an assistant/replacement shooter for when I have been indisposed. I have had Brooks Institute students who have been uniformly awful. I have had two military guys from Vandenberg AFB who have been superb. Sadly, one got deployed and the other fell in love and moved away (I will be his best man in October.) So, I now have found a local Pro who shot for NFL and then a local newspaper for 25 years, recently parted ways with them and is teaching and working with the fire department, etc. I have several events over the next several months when I am going to be out of town and need a stand in. This guy is an excellent shooter in the newspaper photographer sense. But he is a Nikon guy!

I am having him shoot two or three events with me so I can get his RAW images and verify my workflow. He shot Gladys Knight with me last night. He shoots with a D800 and 70-200mm f/2.8 lens at ISO 6400. Compared to my 1DX with 70-200mm his images are stunningly soft and I don't know why. Shooting side by side of the same subject at the same time covering the width of the stage from the light board Gladys' face is so soft that you cannot tell it is her. My images are uniformly crisp. The only difference in settings is that I am shooting at ISO 3200. I am shooting f/4.5 and he f/4.0. Shutter speeds are close. I am at 110mm and he is at 85mm.

It does not look like a focus issue or a subject or camera movement issue. It looks like a noise or soft lens issue to me. But all the reviews I read suggest that his equipment should deliver results almost identical to mine. He seems a little resistant to accepting that his images are marginal so I've asked him to come by my studio and look at them with me.

Anybody have any insight? Is the D800 bad in low light/high ISO? Is the Nikon 70-200mm f/2.8 poor wide open? I'm not sure where to go with this.

The Nikon D800 and Nikon 70-200mm should be excellent. Especially if it's the II version. The first version is still good and at 85mm f/4 should be very good really. The Canon might be better in some ways (especially focus breathing).
The D800 has twice as many pixels, but you're at 110mm vs. 85mm, which is approx 30% more, so the D800 still gives slightly hgiher resolution (ignoring focus breathing which affects pixels on target). Depends on your distance too.

The D800 is good at high ISO and the 1DX is better. However you're at ISO 3200 vs. the D800 at ISO 6400. The 1DX is a little better at high ISO and significantly better when it is a stop lower. In addition, although the D800 gives more pixels (just slightly and also depends on focus breathing, distance... who knows), the noise is per frame, so it is more significant for the target (face). In this case the noise can have a very significant effect.

As far as shutter speed, who knows. Maybe he took the photos when at least double the shutter speed was necessary, while you didn't. Depends on luck+experience+choice​.

Of course I'm assuming you are comparing RAW files. If you are comparing camera JPG then it's impossible to really say anything since the cameras' JPG edits can be significantly different.

If you can post examples that might be best to try to see what the problem is.

Thanks, Clarnibass. I expect that I will just ask him to shoot at ISO 3200 at the next event as I am now very suspicious of ISO. Yes, RAW files in Lightroom 5. And since this isn't a controlled test but a review of images in a real world situation the parameters are not identical.

I realize that images are what it is about. If the ISO change doesn't improve things I will post again with images.

Again, thanks.

I assume you have a free moment next time you meet, so before you start you can do one test photo of a person at lower ISO with both cameras, same frame from the same distance and same parameters (especially aperture and ISO).

Could it just be that you are better at getting the shot?
Anyway, that's not your question, so I won;t go on with hypethesis, other than to say, I can;t imagine any modern camera, especially a well respected one like the D800, making such a large visible difference with one stop bump of ISO. ie: If he'd shot at ISO 3200 I don;t imagine that would have fixed things.

Nothing scientific, I know,.

Clarn, it's way complicated as there are lots of variables beyond our control ... can't just stop and say, let's shoot a test shot. Really, I have a LOT of experience.

Jake, yes, it is entirely possible that a lot of the difference is experience but I don't know what? Yes, I agree 100% that one stop shouldn't be so much difference. If the ISO doesn't make a difference then I will come back with example images but I don't think any will be EXACT matches for every parameter. If the issue continues I will attach images ... the test images I generated to demo the problem to him are too big for POTN attachments as I didn't want file size to be a distraction.

I regularly find that when I am in a venue that I shoot often at that I get better photos than those who only occasionally shoot there. Like one's equipment, you instinctively know when to be and when to press that shutter. That's a hard thing to duplicate.

I also wonder if you are overthinking this, Dwight. We are usually our own worst critics and this guy's photos might be more than adequate for the client. If that is the case, I wouldn't worry about it.

Ski, I think you are right on all counts but I do think I'm going ask him to reduce his ISO from 6400 to 3200 just to see. He doesn't need quite so much shutter speed.

Dwight, if you haven't already done so, I think I'd put that lens/body on a tripod to see where the problem lies.

I got some ISO 3200 frames from it tonight so I'll be looking at them in the next couple of days.