SYS wrote in post #18632708
Frankly, I had some difficulties, and quite disappointed with, using this lens during the air show. This event was when I missed having my old Canon 100-400L. With the Sigma, I was experiencing atmospheric distortion the same way I had with the photo above of elk chasing a duck. The only difference between the elk photos and the Thunderbirds is that the latter was lot more amenable to PP, sharpening and noise reduction in particular. PP allowed the air show photos to come out pretty decent but not the elk photos. Both were affected by atmospheric distortions, in my best evaluative analysis. My findings about the Sigma lens is that it's excellent when the subject is close enough that there's no atmospheric effect. When the subject is far enough away and particularly when the sun is pretty bright enough to produce heat off the surface, then that's when the Sigma gets into difficulties. While both the elk and the air show shootings posed difficulties, I'm still pretty happy with the air show photos results.
IMAGE LINK: https://flic.kr/p/27HpQPG Supermarine Spitfire Mk Ia
I think I just replied to something similar to one of your posts in another thread about this lens. Having been a competitive rifle shooter, and coach for many years I've a lot of experience with dealing with the atmospheric distortions we usually refer to as mirage. In general the better the quality of the optics the more mirage you will see. Get some seriously good glass, top end Zeiss spotting scopes spring to mind, and you will see mirage on a cold day even, when most other optics show no movement at all. Also increasing the the magnification/focal length will increase the observed mirage too, so you would really need to make the comparisons between two lenses side by side, and at the same magnification. I'm certain you would notice the effects getting worse in the same conditions were you to move to say a 600 L. The distance as you noted also has an effect, but with enough magnification you can see lots of mirage at even 25 yards. Puts on broad Scottish accent and says "You cannae change the laws of physics"!
The conditions will also affect how much mirage you will see. In general once wind speeds get over about 12 mph the mixing effect it has will generally remove the visible effects of mirage. You need layers/areas of different density, caused by temperature differences to create the refraction you see. The wind tends to mix this out. Shooting over sunlit water will always be worst, since the water vapour adds to the differences of RI in the different bits you are looking though. Any area, such as grass land, that will hold moisture during the night will also be more prone to mirage, especially early in the morning. Mirage effects are also always much greater closer to the ground. This is because the air is less likely to get mixed, to the density variations will form more easily. So yes the effect when shooting subjects in the sky will be much less noticeable. Wind speed usually increase with altitude, so of course you reach speeds that will not allow mirage to form.
Your Blue Angel shots look great BTW, I'd be very happy with them. I actually came to this thread to post a few pics from the Duxford Air Festival, which was on the last weekend of May.
This was cropped to vertical.
by Alan Evans
, on FlickrIMAGE LINK: https://flic.kr/p/26u9xS4 Dassault Rafale C
by Alan Evans
, on FlickrIMAGE LINK: https://flic.kr/p/27Mft27 Dassault / Dornier Alpha Jet E
by Alan Evans
, on FlickrIMAGE LINK: https://flic.kr/p/27Hqafu Boeing CH47D Chinook (Chinook HC Mk 1)
by Alan Evans
, on Flickr
Yes that last one was taken at 1/30s, but as well as utilising mode 2 OS I also use a shoulder stock rig for stability. I was never able to manage a tripod at an airshow, even when I was an agile teenager. Now I'm a wheelchair user a tripod would be a complete hindrance for an airshow.