It may just be a GAS attack but I am considering changing from my Nikon d7100 to a mirrorless in the near future. My two main reasons are that I hope to lighten and shrink my equipment even a small amount as it's getting harder to lug my d7100 and Tamron 18-400 lens around. I realize there will be some change in how I view my photography with a mirrorless and also that some lenses will be as big as what I have but between lugging the gear in the tank bag of my bike and jumping in and out of safari vehicles and walking through the brush I'm ready for a little relief. Second, I also find myself pushing the ISO in the d7100 for a lot of shots in very low light conditions and a lot of my pictures are very difficult to bring back from the snow factor when using high ISOs even with subscription Lightroom/Photoshop. My 50mm makes pushing possible but not enough for acceptable pictures.

Right now many reviewers are saying that the mirrorless Nikon Z6 is the best buy now but there are as many still sticking the the Sony a7III (both are at about the same price point). The Nikon attracts me because I'm used to Nikons. If I get the Z6 I'll also get the 24-70mm f4 lens for my general lens.

First Question: My two main lenses on my d7100 are the Tamron 18-400 and a Nikon 50mm 1.4 lens. Both are, I believe, for the crop sensor. So if I get the adapter for the Z6 will these work for me on the full frame Z6? I know they will increase the bulk when I need to use them but I will no longer need to use the 18-400 as a walk-around lens.

Second Question: Will I see low light improvement in the quality of my pictures with a mirrorless? (I understand that I am responsible for the content and getting the exposure factors right and I will always be working on that.) Low light performance is one of the things advertised about these full frame mirrorless cameras.

Last Question: Nikon vs. Sony--Will I have to do anything special with the FTZ cards, are they expensive and does anyone have experience with them?

If anyone has any other cameras in this range I'm open to suggestions. I'm not a pro and won't be but I do like trying to get good images that I can use in picture stories and other things but probably no huge prints.

Thanks for any thoughts. I will go to the local camera store tomorrow to see how each of these cameras feels to me and see what they say about my issues but I've been somewhat disappointed in their advice in the past which is why I'm posing this question.

I rented the Z6 with the 24-70 f/4 S lens for one week recently. I used my D500 side-by-side with the Z6 for comparison purposes. I can say that the Z6 autofocus is not as good as the autofocus in the D500. The Z6 would often hunt in even slightly dim light. My D500 would acquire focus right away. The Z6 does have a low-light autofocus mode. It improves things a little. It's still very good autofocus but for low light or action photos I would trust my D500 AF a little more. One thing that's good is that no AF fine tuning is needed. It nails the best focus every time since it's finding the highest contrast at the sensor.

I took photos with the Z6 at up to ISO10000. The photos still looked good but colors were becoming a little wonky and the resolution was dropping.

It's actually XQD cards not FTZ. I use them in my D500. They're more robust than SD cards and have higher transfer rates. They have the same type of contacts inside as SD cards which I think is good. I'm glad Nikon went with those instead of CF or CFast cards. The CF cards have pins that have been known to bend or break.

I agree with imagemeister above about the quality of the images with lenses that are designed for the Z cameras. I was very impressed with the 24-70 f/4 S lens. The image quality is stellar I always thought that Nikon's AF-S (ultrasonic silent wave motor) lenses were very smooth and quiet. The stepping motor in the 24-70 f/4 S lens seems to be even quieter. It's so quiet and smooth that the only way to know it's focusing is when you see the subject come into focus in the viewfinder.

I also want to purchase a Z6 but want to wait a little to see what the D750 replacement is going to be like.

I did comparison shots with the Z6 and my D500. I made diptychs with them for comparison purposes. I'll post them below. Some of the differences can be attributed to the different lenses also.

I have the Z7 with 24-70 F4.0 and love it. The weight is definitely a factor and will continue with many of the new Z series lenses in part because there is no longer a need for VR lenses because stabilization is built into the body. My former D810 with 24-120 F4.0 weighed in at 5+ lbs and the Z7 and 24-70 clocks in at 2.7lbs (Z6 weighs the same). As for IQ and low light capability I 'll let you be the judge. See attached photo finished last week-the moon was layered in Photoshop. Shot the moon with and older Micro Nikkor 105 F2.8 that lacked VR and is manual focus that I picked up used for $225. The skyline was tripod mounted at 24mm, ISO 200 for 3 seconds at F8.0. I have done daylight shoots of this image at F4.0 showing same corner sharpness and resolution. Pat

If you want to lighten the load, I would suggest sticking with a crop frame sensor in the mirrorless camera of choice. Here's why. My main camera is a D500 with a large number of lenses. This is too heavy/bulky to take on plane trips (IMO). I opted for the Sony a6000 and 18-105 lens with a 35/1.8 for low light. I loved this kit. Alas, I wanted a full-frame camera and went with the Sony a7Riii with a 24-70/4 lens. Although I LOVE this camera, it is quite a bit bulkier than the previous Sony kit and I feel like I don't have enough reach with the lens I chose. I have 2 other lenses for it, but may need to get either the 70-200 or the 100-400 for that reach I want. But, that adds to the weight and size of the kit.

I have no experience with Nikon's mirrorless camera; but if I were considering it, I would wait a year or two for a better model. Seriously consider the Sony crop sensor, maybe an upgrade to the a6000. I think the newest is a6500.

Good luck. You will like having a lighter kit!

As you are considering the D500, please look at it with a battery grip. Rather than change formats, I have installed battery grips (I strongly recommend only factory grips) and find that the drastically improved ergonomics provide benefits that are much better for me than trying to hold an even smaller camera and lens, even if they are lighter. And...this approach may not work for you, but it is at least worth a look.

And if it works, the grip, even at $300 or $400 is about 10-20% the cost of a new camera, before buying any lenses.

I have been a Nikon user for many years. I currently have a Nikon D500, which I use for bird photography, and absolutely love it! But, I am getting older, and the size of the mirroless cameras attracted me, as well as the simple, illogical fun factor of a new toy! First, I purchased an Olympus mirrorless camera, complete with several lenses. It's a great camera! I loved the smaller size! But, my old mind, which was used to the Nikon menus, didn't do well with the Olympus menus. It was totally the user, and not the camera! After going to the camera store with the same "dumb" questions, I sold it in frustration, and not wanting to wait for the Nikon Z6, I purchased the Sony a7IIIr. It's in between the Olympus and D500, in size. I love this camera! My old mind has adapted to the menu and I get fantastic low light photos! At times, I do the same thing with the D500, so the comparison could very well be the user and not the camera. Though I am dealing with a 42mp Sony, compared to a 24mp Nikon. So, perhaps that can make a difference.
My son-in-law has purchased the Z6 camera. He let me play with it, and I think it is very high quality! My only concern is the lack of lenses for the Z6, right now. Like you have said, an adapter can be used, but you do sacrifice some quality, in doing so. As an amature, in it for fun, this is not a big concern to me, but, it could be for you, if you want a more accurate photo.
Back to the Sony. I recently took action shots of Canada Geese, lifting off from a river. Those photos absolutely pop!
All these stories being said, I think you will be happy with the Sony a7IIIr, if you choose to go that route. The down side is that you will pay a bunch of bucks for all the lenses you need. The Nikon Z6 is also a fantastic camera, and if you don't mind the slightly softer photo quality, when using an adapter, you will have a great camera set up. You mentioned that you want less weight, though. You will still have quite a heavy outfit, when you put the old lenses on that camera. So, that may be something to consider.

You are having an attack. A FF mirrorless body will be lighter without the mirror and pentaprizm but the lenses will be the same size and weight. The only way to save wt is to move to the Panasonic/Olympus crop sensor where they are making the lenses fit the sensor. In the Sony which has been making both crop sensor and a FF, you can buy crop frame lenses that are smaller but for the most part the lenses are the same size. So is the weight savings of the body enough to switch systems? Low light should be about the same among a DSLR and a mirrorless, Sony does seem to be the leader in low light with their FF.

It may just be a GAS attack but I am considering changing from my Nikon d7100 to a mirrorless in the near future. My two main reasons are that I hope to lighten and shrink my equipment even a small amount as it's getting harder to lug my d7100 and Tamron 18-400 lens around. I realize there will be some change in how I view my photography with a mirrorless and also that some lenses will be as big as what I have but between lugging the gear in the tank bag of my bike and jumping in and out of safari vehicles and walking through the brush I'm ready for a little relief. Second, I also find myself pushing the ISO in the d7100 for a lot of shots in very low light conditions and a lot of my pictures are very difficult to bring back from the snow factor when using high ISOs even with subscription Lightroom/Photoshop. My 50mm makes pushing possible but not enough for acceptable pictures.

Right now many reviewers are saying that the mirrorless Nikon Z6 is the best buy now but there are as many still sticking the the Sony a7III (both are at about the same price point). The Nikon attracts me because I'm used to Nikons. If I get the Z6 I'll also get the 24-70mm f4 lens for my general lens.

First Question: My two main lenses on my d7100 are the Tamron 18-400 and a Nikon 50mm 1.4 lens. Both are, I believe, for the crop sensor. So if I get the adapter for the Z6 will these work for me on the full frame Z6? I know they will increase the bulk when I need to use them but I will no longer need to use the 18-400 as a walk-around lens.

Second Question: Will I see low light improvement in the quality of my pictures with a mirrorless? (I understand that I am responsible for the content and getting the exposure factors right and I will always be working on that.) Low light performance is one of the things advertised about these full frame mirrorless cameras.

Last Question: Nikon vs. Sony--Will I have to do anything special with the FTZ cards, are they expensive and does anyone have experience with them?

If anyone has any other cameras in this range I'm open to suggestions. I'm not a pro and won't be but I do like trying to get good images that I can use in picture stories and other things but probably no huge prints.

Thanks for any thoughts. I will go to the local camera store tomorrow to see how each of these cameras feels to me and see what they say about my issues but I've been somewhat disappointed in their advice in the past which is why I'm posing this question.