First, yes, I did do a "search" on this topic before posting this. However, the few threads I found were 7-10 years old, and were either from people who take photos of fire trucks or campfires.

I do "fire photography". By that, I mean going to the scenes of brush fires, structure fires, "rescue" calls and other assorted situations where firefighters are involved. The purpose is to obtain good photos for possible publication in local newspapers and fire- and EMS-related publications. I'm primarily interested in photographing aerial firefighting helicopters and fixed-wing aircraft ("air tankers") dropping either water or Phos-Chek retardant. So, now to the "photography" question I have.

I shoot with a Nikon D7100 and D7200, with a Sigma 17-50mm f2.8 on one, and Nikon 70-300mm f4.5-5.6 ED-IF on the other. However, especially when it comes to aircraft, which are often some distance away, sometimes 300mm is not quite enough. Yes, I can crop in and "simulate" the effect of a longer lens that way, but I'm looking at adding a new lens to "reach out" further. I'd like some advice and comments as to which might be the better way to go.

My first choice would be the Nikon 200-500mm f5.6. I would expect most of my use of this lens would be at the 500mm end of its range. The extra 200mm I would get over the lens I already have is significant.

My next option would be either the Sigma or Tamron 150-600mm f5-6.3. A little more on the "wide" end, and another 100mm on the "long" end. I don't care so much about the 150mm and the difference in field of view from 500mm to 600mm is also insignificant and could be simulated by cropping.

I would be interested in which lens is the "best bang for the buck". From what I've read, the Nikon gets points for being the sharpest of the three, the constant aperture across the zoom range and for having the fastest and most accurate AF. However, I've read comments about the Sigma and Tamron claiming that those users are also getting sharp photos and feel that the AF response is excellent.

All three are heavy lenses, heavier than anything I've used before. But, I'm not at the point, yet, where the weight of the lens would be an issue.

I'd rather have a 500mm prime, but even the Nikon 500mm f4 PF is a $3500 lens and not exactly within my budget. So, looking for opinions and recommendations between the three mentioned above.

Thank you.