Which lens for D850

Hey guys, I'm hoping you guys can help me make my mind up. I have narrowed my choice of lens to the Sigma 150-600mm F5-6.3 DG HSM OS SPORT possibly with the 1.4 teleconverter (cheaper as kit) or the the
Nikon AF-S Nikkor 200-500mm F5.6E ED VR. Both are good from the reviews. I've swapped numerous times which I like. Whilst the Sigma would be brand new £1250 I can get the Nikon for £900 as new second hand from a reputable company. I'm hesitant getting the Nikon as I'd like to use it on the beach taking photographs of surfers and other bits along there like wildlife or military helicopters that practice.
What lens would you buy and why? Should I be worried using the Nikon at the beach on windy days ?
Nikon AF-S Nikkor 200-500mm F5.6E ED VR. Both are good from the reviews. I've swapped numerous times which I like. Whilst the Sigma would be brand new £1250 I can get the Nikon for £900 as new second hand from a reputable company. I'm hesitant getting the Nikon as I'd like to use it on the beach taking photographs of surfers and other bits along there like wildlife or military helicopters that practice.
What lens would you buy and why? Should I be worried using the Nikon at the beach on windy days ?

The 1.4 TC will lose you light and probably AF, you'lll be better off cropping as required.
Don't worry tooooo much about using either lens on a beach, I've done loads of beach photography with no issues with any lens, as long as you don't drop them into the sand / water
you could always go for a lens cover, personally I'd go for the Nikon with its constant aperture.
Don't worry tooooo much about using either lens on a beach, I've done loads of beach photography with no issues with any lens, as long as you don't drop them into the sand / water


i have the sigma with a d850, works very well on it, I too had that choice a while ago and went for the sigma because of the extra 100mm, I don't find the change of aperture that much of a problem. also I use a x1.4 teleconverter with it, loses a stop and softens a little but still reasonable, you would possibly get the same result from the nikon lens

The Nikon D850 being an f8 combination with a TC 14E or Kenko 1.4x has "reasonable" AF ability.
The D850 can rarely AF at all with a TC on an f6.3 combination.
My hands-on experience with the 2 Nikon items is that image resolution is a little higher than cropping by an equivalent amount.
A Nikon D850 has enough resolution for a 19 inch wide print at 300 dpi that ideally needs viewing at more than 25 inches to see detail in the corners of a print without swivelling your eyes to see the frame corners.
By 25 inches distance the human eye cannot resolve 300 dpi detail.
This leaves reasonable scope for increasing ISO (which tends to cost resolution), some small loss of resolution compared to (if one existed) a 700mm lens and some cropping while still retaining more detail than the human eye can detect in a 19 inch wide print at a comfortable viewing distance.
Photographers can buy a copy of Vogue magazine to study the fashion photography images - or they can use a magnifier to examine the dot spacing of the printing process on a Vogue magazine cover.
Which lens you buy is up to you.
As the 200-500 is £1,199 new; £900 second hand I consider on the high side.
The D850 can rarely AF at all with a TC on an f6.3 combination.
My hands-on experience with the 2 Nikon items is that image resolution is a little higher than cropping by an equivalent amount.
A Nikon D850 has enough resolution for a 19 inch wide print at 300 dpi that ideally needs viewing at more than 25 inches to see detail in the corners of a print without swivelling your eyes to see the frame corners.
By 25 inches distance the human eye cannot resolve 300 dpi detail.
This leaves reasonable scope for increasing ISO (which tends to cost resolution), some small loss of resolution compared to (if one existed) a 700mm lens and some cropping while still retaining more detail than the human eye can detect in a 19 inch wide print at a comfortable viewing distance.
Photographers can buy a copy of Vogue magazine to study the fashion photography images - or they can use a magnifier to examine the dot spacing of the printing process on a Vogue magazine cover.
Which lens you buy is up to you.
As the 200-500 is £1,199 new; £900 second hand I consider on the high side.