Is my Sigma 100-600 C Lens Faulty

Orias wrote in post #18463956
The problem with this is that it's very hard to see if it's front or back focusing. I don't have enough space to test it properly at 600mm (need about 30m or so), and when I do try and test it, pretty much the whole image appears as out of focus, like the original measuring stick one I posted above. Cheers

I've never tweaked the 150-600 but tweaked a few other Sigma lenses. What I did was find a sufficiently long row of fencing. I put some white tape on one of the fence posts and focused on that. Then I could judge front or back and knowing the spacing of the posts helped me to quantify the issue.

Id tesr it how you intend to actually use it...indoor shots at 600mm arent really a good test in my opinion...so after the zoo, if it still looks terrible, explore exchanging it

I've already opened up the RMA procedure just in case, as these things can take some time.

But I'll still take it along with me tomorrow to see ... as you said, that's the environment where I am going to use it the most, so it makes sense to test it there first.

Cheers

Possible candidates?

- Atmospheric haze
- Front focusing, so you need to AFMA the lens
- Lens filter
- Faulty lens

TeamSpeed wrote in post #18464069
Possible candidates?

- Atmospheric haze
- Front focusing, so you need to AFMA the lens
- Lens filter
- Faulty lens

- Could be atmospheric haze, true. It was pretty warm out here today
- From my shot in the first post (of the ruler), it did look possibly like front focusing, the bottom of the target is more in focus than the rest
- I do have a UV filter on the front (as with most of my lenses), not for any other reason other than protection from scratches etc
- I guess I'll find out about the faulty lens part tomorrow when I really put it through it's paces

I might take the filter off, just in case. Is it possible that this could actually make a difference?

Cheers

Depending on the filter, yes it can make a difference, and some lenses don't seem to behave well with any filter. The results you have could actually be a combined result of all four factors perhaps.

Orias wrote in post #18464147
I guess I'll find out about the faulty lens part tomorrow when I really put it through it's paces

Be sure to both use standard AF and Live View AF for the same shot, and then post the results at 100%.

This has a massive front element and is long FL, definitely take off the filter and re-test before sending it back.

Also test at 400mm and something not too far. It should definitely be sharp at 400mm. Atmospheric haze can definitely be a problem. Also at 100% crop and wide open at 600mm it is not razor sharp, but should be good at f8. I would test this first.

Take the filter off, use it as a coaster

It's been a long day ... 11 miles on foot + 20lb of gear, but I think I may have judged the Sigma too soon.

I ended up getting some pretty good shots with it, with a keeper-rate around 15% or so I reckon. It really doesn't deal with low-light very well, certainly not compared to my Canon 70-300L, but with some good light, it did pretty well. I removed the UV filter that I was just using to protect the lens just in case. Here are a couple of the shots without any PP at all .. so no sharpening, exposure adjustments etc. These are just the shots directly from the camera, but they should brush up quite well with some time in Lightroom:

Nice shots, but we need 100% crops to tell you whether there is something wrong.
To be honest, the tigers don’t look sharp even at web resolution.

Great images, especially that rhino [correction hippo]! I'm an engineer, not a zoologist!

If you had the filter installed when you did the dock tweaking, it probably should be redone before passing final judgment. I know it can be time consuming since it involves four focus distances for four focal lengths (150mm, 250mm, 400mm, 600mm) but the results are worth it.

Some long lenses just don't do well with a filter, any filter. My Canon 100-400 is like that. I get the same results that you do with a filter on. I haven't tried one on my 150-600 but would not be surprised if it too impacted IQ.

Mine is very sharp throughout the range on my 70D and 6D. I did MFA in camera with both. Did not screw with the dock for focus adjustments as I use it on 3 different bodies. I would not judge any AF shots on the aerial or crane. Just too much open area for the distances. I have the Sigma 100-400 also and it works well on both bodies.

CheshireCat wrote in post #18464813
Nice shots, but we need 100% crops to tell you whether there is something wrong.
To be honest, the tigers don’t look sharp even at web resolution.

I'll get some 100% crops done once I get home from work. The white tiger in that picture is in focus, the orange one isn't. It walked infront of the white one as I was taking the shot, but I quite like the way it turned out. I look at most of these on a 4K monitor where they look pretty sharp, but sometimes they look softer when I check them on my 2nd (2K) screen.

John from PA wrote in post #18464813
Great images, especially that rhino!

There's definitely something wrong with the lens if the Hippo looks like a Rhino

I also took off the filter from my EF 70-300L for this trip, just in case. That one didn't seem to make too much different from previous shots, but it was worth a try just in case. I just worry about scratching the glass or something on the more expensive lenses.

Cheers