Not at all second guessing you, but did you not want to get one with sun through the window?
I mean I assume you did and it didn’t look as good…
The sun blew out the pic when seen through the window.
I quite like how it is in the pic above. 
It’s a great photo, was just wondering.
i’m assuming this is a photography nerd type thread
are the budget brand lenses (tamron etc) worth the bother?
i’ve been getting back into sport photography and have some ok gear, but my lenses max out at 250mm so miss a lot of the further away action. i want to invest in a longer lens (200-400mm), but don’t want to drop a couple of grand without getting some practice in first.
so i was thinking of picking up a second hand el cheapo to get some reps in. the old bunnings principle of if you use a cheap tool long enough for it to wear out/break, then you’re obviously using it enough to make buying a better one worth it.
or are they just so sht that it’s not worth even doing that
Tamron and Sigma are both excellent.
Back when I was covering our VFL side quite a bit, I was using Pentax bodies with a Sigma telephoto . Not exactly a “pro” setup but it worked. And Sigma are better now than they were then.
First up, which brand / body are you using ?
i’ve got a couple of canon bodies. 200d and 750d
Ok, so in my experience the biggest limitation of those bodies are the less than great noise performance as the iso starts to rise. And if you’re going to shoot field sports in winter , it’s going to rise.
So it then becomes a question of aperture. If you’re looking at a 100-400 I presume it’s the Canon USM L . On those bodies it’s going to become a 640mm field of view, which will give you pretty good zooming ability . At maximum zoom, it’s running an aperture of F/5.6 . Which isn’t terrible, but will need iso raising to get usable shutter speeds. A quick Google suggests that you can find a series 1 100-400 L for a bit under $1000 . Cheaper than I thought.
Sigma has made a stack of different telephotos in EF mount over the decades. I used a 150- 500 on my Pentax and it was really very decent. They also made a 50-500 ( known lovingly as the “Bigma” ) but the general feeling was that the 150-500 was slightly better optically , and I found that for sports use the extra zoom range was at best irrelevant and at worst slower to rack from minimum zoom to maximum zoom. They later released ( and still make iirc) the 150-600mm. On your canons, this takes you out to 960mm and is seriously impressive zoom range, you can cover most of a footy field here, especially with the 24mp of your 750D allowing further cropping. The downside? Well, it’s a slower lens at the long end, down to F/6.3. So you’ll need to crank up the ISO another stop. But, it’s a very nice lens.
Now, just to further confuse things, Sigma make two different versions. The Contemporary, and the Sports. Optically, the consensus is that they’re identical. The Sports is heavier, more rugged, and maybe, technically, more weather sealed. But the Contemporary is also weather sealed. So unless you’re going to beat up the lens, the Sport seems to involve carrying more weight for no real reason. Buy the contemporary.
Some of the early Tamron lenses ran old style focusing motors rather than the newer ultrasonic linear motors. They could be more accurate, but could also take more time to lock on. For this reason, I tended to lean towards Sigma and I can’t offer a real world opinion on their long lenses. ( If you want a short prime, though, their 45/1.8 is fantastic) .
Tldr? A cheap 150-500 Sigma will do you well as a teeth cutting exercise for field sports. The newer 150-600 gives incredible zoom ability and ( off topic) can give surprisingly versatile creative options. It’s possible to custom match it with the Canon AF system if it needs a little adjustment. The Canon 100-400L is an old warrior that will serve you well and theoretically should have perfect AF from the get go. All of them will be demanding on your sensors if the sun isn’t shining. If the sun is out, then almost anything will give nice results.
Example - this was shot on the even older Pentax K10 ( 10mp ccd sensor that was utterly deplorable above ISO320 but gave lovely colours and tones if the sun was out) and a kit 75-300 ( shot at f/7.1 which was probably wide open for that lens).
PS - Yes, I loved Tyson Slattery as a player. Tough as nails.
Oh, and I will add, even for footy there’s a place for a 70-200/2.8 The big aperture to run lower ISO’s is useful. Once again, don’t be scared to get a Sigma EX 70-200/2.8 variant. Good value.
And a (very low res , couldn’t find the original) example with the Pentax K5 ( 15mp cmos sensor that imo was miles ahead of the contemporary canon sensors and in some aspects is as good anything made today) and Sigma 150-500.
What an excellent reply 
After saladin’s exposition on camera bodies, lenses, iso settings, f stops etc etc, here is one from the other end of the photographer’s spectrum: a quick photo I just took with my iphone out our front window:
Of course it would have been better if I had that fancy-schmancy camera gear and knew what to do with it…
Thanks. Always happy to talk cameras for people 
thanks heaps for this. a month of google searches wouldn’t turn up insights like this. really appreciate it