MikeMcK wrote:
I have and the pictures were much better. I was trying to see if I could use the Sigma, the answer may be no, I can't. There is always the weight issue.
If you are OCD about sharpness, that may be true.
For one thing, you are at infnity focus, which may not be the sharpest on a lot of lenses.
Also you are shooting through a half mile or more of sea air, which has all sorts of distorting effects. You could buy a $10,000 lens and put it on a rock solid tripod and still not get any better results, simply because you are way, way too far away from the subject.
If using a "protection filters" remove it.
An ultra-wide ranging 14X (or more) zoom such as an 18-250mm simply cannot be expected to be as sharp as a more modest 3X or 4X zoom. Ever noticed that the more "pro-oriented" , high-end, premium zooms are often only 2X, 3X, 4X... maybe 5X, at most? 16-35, 24-70, 100-400, 200-400.
There is a hell of a lot of stuff going on inside a 15X or 20X zoom, for it to be able to cover such an extreme range. It's rather silly to think it will be able to so it all perfectly. Heck, it's a modern miracle if it does some of it particularly well! There simply has to be some compromise, whenever you are trying to make optics do extreme things and still offer a reasonably priced product.
You buy an 18-250 for all-in-one convenience, certainly not for ultimate image quality!
An 24MP APS-C camera will never be as sharp as a 22MP full frame camera. The smaller sensor is more than twice as crowded with pixel sites, which are much smaller and more tightly packed.
In most cases an APS-C camera also will use a stronger anti-alias filter over the sensor, than a FF camera will. The AA filter deliberately blurs the image to reduce moiré effects. The AA filter is one of the reasons that images need to be sharpened in post-processing.
Comparing a crop sensor camera to a full frame camera, to arrive at the same size final image (say an 8x10 print), you are magnifying the smaller sensor image much more, so are therefore looking at it more critically. For example, that 8x10 is approx. an 8X enlargement when made from a FF camera... or a 13X enlargement when made with an APS-C model.
Lens calibration is another possibility. For that last little bit of focus precision, some of the higher end Canon camera models have a Micro Focus Adjustment feature, that allows the user to fine tune a particular lens on a particular camera. AFAIK, T6S doesn't have MFA, nor does any other Rebel/xxxD model. 70D, 7DII are the current APS-C models with MFA. If you can't micro adjust your own lens, you have to rely upon the factory settings, which really can only be "ballpark" calibrations... both on camera and lens. You might be able to get the lens professionally calibrated to the camera (if you really think it's worth the trouble). Lens and camera mechanisms wear and get out adjustment over time, too... so occasionally re-calibration may be needed.
"Protection" filters and dirty sensors are two more causes of "soft images".
But a lot of it just comes down to ridiculous expectations. Viewing a 24MP image at "100%" on most modern computer monitors is like making a five foot wide print and then viewing it from 18" away. Of course it looks like crap! Back off to a more realistic level of magnification... if you are making an 8x10 print, set a magnification in your software that renders approx that same 8x10 inch sixe onn your monitor, closer to the final image size you'll be using. This gives you much more realistic evaluation of image sharpness and focus accuracy. It's fine to zoom in to work on images, but some things should be done at more reasonable magnification levels.
There is massive over-emphasis on "sharpness" among photographers these days. I think it would be a good exercise for everyone to go make only soft image for a few days, to learn to appreciate that every shot doesn't need to be eye-bleeding sharp!