RodS57 wrote in post #17426028
The other day I posted focus issues to the "discuss and post photos" thread when it should have been posted here so a quick recap: oncoming train shot in ai servo at 1/2000 and F7.1; case 2 first and second shot set to focus. All were out of focus. It was suggested that I send the camera in to either fix the problem or confirm there is nothing wrong.
Today I ran another set of tests and viewed the shots at 63% zoom. Had the camera on center focus point; 'M' mode; F7.1; 1/1250 sec; case 2
Took shots with and without a tripod of cars and trucks coming toward and going away from me. Took sets of shots with the tamron set to 300mm and the 70-300L at 300. Being rather generous with the scoring considering the zoom level I ended up with 75 usable shots and 8 unusable shots. (Remember I said generous with the scoring). Nothing razor sharp.
I obtained close to perfect results with shots of a car passing the end of my driveway. Sort of like shooting between buildings. The snow banks are higher than the passing traffic. The tamron worked very well. The canon not quite as good but the truck was white in a world of snow and I haven't spent the time with this lens that I have with the tamron.
Lots of shots of static objects which came out good. Had reasonable results with a flying raven even though I was only using center point and didn't manage to keep it on target.
Yesterday it definitely looked like this camera needed to be sent to canon. Today I am not sure. What will tomorrow bring.
As you live in a climate close to my own is it possible my focus issues are temperature related. -19C at lunchtime today and the camera worked better than any other time. Soft shots on Saturday and Sunday when ambient temp was around -30C. A few weeks ago I tried the cereal box focus test outside at about -30 or below and even with a tripod the shots were a disaster. Anyone else with experience in these conditions feel free to comment. In particular anyone using the tamron 150-600
Gone from I don't think I have a problem to looks like I have a problem to maybe it's all ok
I can't seem to find your pics, but the first thing that comes to mind reading your description of the shooting situation is heat shimmer. Super cold with heat coming off the train would be a recipe for disaster. I have experienced this shooting ducks on the edge of a lake at close and far ranges with both my 7d2 and 1Dx. Images get made but nothing is in focus - like there is a haze. A tripod will not help in this case.
Your tests today sound more logical, though heat shimmer could still come into play with the exhaust once the vehicle has passed, even as it is approaching with engine heat. I did a similar test with similar results when I first tried the camera. I chalked the results up to shutter speeds too low to stop cars traveling city road speeds. Your driveway test would kinda confirm that, assuming you live in a neighborhood with a lower speed limit.
Find a way to try something moving but not putting off heat. A bike rider, someone running towards you. You need to do it head on and side to side. Some lenses can't handle head on very well (Sigma 50-150 OS that comes to mind from personal experience) so the Tamron may struggle with keeping up on something like that. If it nails the side to side, but not the head on, you'll have a pretty good answer. You're 70-300 should handle that easily.
Just a couple thoughts.