As others have noted, there are a lot of variables that affect the outcome in terms of sharpness here.
When shooting from a car as a blind, I minimize the impact of air temperature variations by turning the whole ventilation system OFF and opening windows on both sides of the car so that the outside air flows through the car. If the temperature of the lens is very different from the temperature of the (outside) air, use of a lens hood can create a warm air pocket inside the hood (the lens warms the air and hood prevents it from escaping) which also can create problems. So, I would turn off active ventilation and air conditioning, open all windows in the car, and take off the hood (and certainly take off any in front of the lens, unless you're shooting in a sandy / dusty environment which could be harmful for the front element. The lens might be big enough to take advantage of a car window mount, which could help with stability especially if you have to wait for the subject.
Stopping down can improve sharpness because it reduces lens aberrations and this can also help with the focusing system if it will focus at the aperture selected for taking the picture. A zoom lens can vary in sharpness across the frame and across focal length in a way that depends on the lens sample but whether this is something a tech can fix is uncertain. It may be a result of variability in the material parameters as much as positioning although obviously manufacturers will try to minimize this. When photographing a subject like yours where the eye is a small part of the body separated by the neck and the focusing system may be dancing around the eye, face, and the body which would result in quite different results. Thus this is a challenging problem from the focusing point of view and some inconsistency can result. Increasing the depth of field can obviously increase the odds of a sharp image. And yes, shutter speed, aperture, air quality, distance, temperature variations, stability of the lens, possible confounding background features etc. all can affect the result so it is probably best to think of parameters that increase your probability of success and work to optimize those, and for sanity it's best to accept that sometimes the result is not perfect when the conditions were not favorable, and/or luck was not with you. Sometimes it can also be good to take a step back and forget about the pixels, and look at the picture as a whole and as a part of a set of pictures illustrating something about the subject, does that evoke emotions and/or communicate information? Those things can happen without the image being pixel-sharp when viewed at high magnification, and in that case it may be the best on focus on the big picture rather than the details, in my opinion.
duncangr wrote:
Can you drop the RAW files in that folder ? The f9 seems to be better exposed than the f8 version - or the light changed outside - but there is no metadata to see what the settings are.
I concede the car does add another variable, but I did have all 4 windows down and it's a hybrid in EV mode. I wouldn't have expected that to cause many issues. That being said I will continue to test., but I'm having the same issues when on foot as well.
One thing I've learned after using a lot of different lenses of 800mm (or equivalent) focal length is that 95% of sharpness issues are due to atmospheric distortion, even for close-range shots. The rest are usually due to the shutter speed used.
They are both a little ordinary aren't they. I wouldn't be happy with either but I would want to eliminate atmospheric distortion by doing some other tests as they both have that smeared/painted look typical of atmospheric distortion.
So I have a test lens in to try. Unfortunately by the time I got the aftermarket foot swapped to the new lens the sun had gone down behind the trees so the tripod results aren't really worth sharing. I will do some test shots tomorrow. The handheld ones I did real quick look sharper when zoomed in. Interestingly, when I compare the focus distance, my lens is repeatedly focusing 0.5m further than the test copy. So I'm beginning to think that I might be correct that it's a focus problem, not necessarily an IQ problem.
Hopefully weather and time permitting I'll get some tripod tests done manually focused and with autofocus to try and put this to rest. I dropped a crop of the side by side comparison in the folder with the other shots. The caveat being that of course it is handheld so not a smoking gun. Was shot at 1/2000 800mm f/8 braced against a railing.
For anyone who cares. Got them both on a tripod and tried as best I could in the limited time a dad with twins has. I no longer think my lens is necessarily back focusing, it's just the 2 lenses repeatedly show a .5m difference. No idea why. Now to image quality, they're both disappointing at 800 f8 on the tripod. Both sharpen up nicely at f9. Manual focusing them didn't seem to alter the results much at all. So I guess I'll just shoot this at f9 in the meantime. Images added to the link shared above.
I looked at your images (fence shots), I see what you mean but this isn't the best way to test focus, you may want to shoot something like a ruler at a 45 degree angle (or you can buy an AF test kit like this https://www.bhphotovideo.com/c/product/1439588-REG/vello_lens_2020_af_lens_calibration_tool.html online) to verify if the lens is really consistently front or back focus. This would be very unusual in a mirrorless camera, it was a thing back in the day when with DSLR's that did not have any contrast detect AF. Also the shutter speed seems to be slow, it's best to use a fast shutter speed to rule out any slight motion induced blur even when using a tripod.
I have not noticed any systematic focus inconsistency with my 400-800, but the lens is definitely not tack sharp as I would like at 800mm and not comparable to Nikon PF lenses in that regard.
