Bultaco wrote:
The Sport model has better IQ, they also have a 60-150mm both are weather sealed. Check Best of the Tetons Mike Jackson uses the 60-150.
I'm sure you mean the Sigma 60-600mm Sport.
The only problem with that is it's pretty hefty. And more than twice the price of the 150-600mm "C". The Sigma "sport" lenses are more robustly built than their "contemporary" lenses... but it's at a cost.
Sigma 150-600mm "C".... 4 lb., 95mm filters, 10.25" long (+hood)... $899 (on sale right now).
Sigma 60-600mm "Sport"... 6 lb., 105mm filters, 10.5" long (+hood)... $1999
Sigma 150-600mm "Sport"... 6+ lb., 105mm, 11.5" long (+hood)... $1849
Tamron 150-600mm G2... 4.5 lb., 95mm filter, 10" long (+hood)... $1199
Nikkor 200-500mm f/5.6... 5 lb., 95mm filter, 10.5" long (+hood)... $1397
So it really comes down to how much weight do you want to carry around and how much do you want to spend?
On a full frame 24MP camera, in terms of image quality you won't see a great deal of difference between these lenses. See for yourself
https://www.the-digital-picture.com/Reviews/ISO-12233-Sample-Crops.aspx?Lens=990&Camera=453&Sample=0&FLI=6&API=0&LensComp=1035&CameraComp=614&SampleComp=0&FLIComp=3&APIComp=0. Note: You can change the focal length, aperture and even switch lenses to do side-by-side image quality comparisons. Keep in mind that what you see there are magnified portions of test target (see here for more info:
https://www.the-digital-picture.com/Help/ISO-12233.aspxThis site is primarily about Canon gear so most of the tests are shot with Canon cameras. Where possible, I'd recommend looking at tests done with the 1Ds Mark III, which is full frame 21MP and fairly similar to D750. Of course, direct comparison is not possible with the Nikkor lens. There I selected the D3X, which is full frame 24MP same as D750. At this site there are also lens flare, vignetting and distortion comparison tools. You also can view detailed specs. Many lenses are also extensively reviewed... But not so much with Nikkors or native Sony lenses, etc. Most reviews there are Canon gear, including both native lenses and third party lenses in Canon mount.
Another possible consideration... The Sigma lenses have a 1 year warranty plus a 3 year extension in the USA at no add'l cost. They offer the extension here because Tamron offers a 6 year warranty. The Nikkor lens has a 1 year warranty (there may be option to purchase extended warranty).
Another small thing... The Tamron 150-600mm has an Arca-Swiss compatible dovetail built right into it's tripod mounting foot. This is great, for example, if planning to use with a gimbal (popular with large telephotos), almost all of those require Arca quick release compatibility. Besides gimbals, the Arca system is by far the most universal QR system used by many manufacturers. Unless they've changed them recently, the Sigma lenses don't have this feature built in. So if you want to use the Sigma with an Arca-compatible quick release system you will need to buy a lens plate (approx. $25 to $40). The Nikkor also doesn't come with built-in Arca compatibility and only certain lens plates work with it. Hejnar Photo offers one ($38). Many users of that lens choose instead to replace either the tripod mounting foot ($100-$120) or the entire tripod collar ($210-$260) with improved, Arca-compatible versions. The replacement feet and collars are offered by Kirk Photo, Really Right Stuff, Wimberley and a few others.