Sharpness is just one of many atributes that make a good image. However, the lens is not solely responsible for achieving a nice crisp image, many other factors influence the image include those listed below:
Clean your lens
A dirty lens will affect sharpness, so clean it! Also clean any filters you may use. I prefer the q-tip with demin water method whilst others favour a lint free cloth
Use your lens hood
A lens hood will help prevent reflected indirect light affecting the image providing better contrast as well as preventing flare and it helps protect the front element.
Find the sweet spot for your lens
Most lenses are at their sharpest between about f8 and f11. It varies for each lens, so experiment to find which apertures return the sharpest images. If your lens has Vibration Reduction (VR) or Vibration Control (VC) turn it on when shooting hand held to permit slower shutter speeds in low light if desired.
Shoot at a higher f stop (smaller) aperture
This will provide greater depth of field, with more of your subject in focus. Whilst it contradicts the advice above, it’s useful in landscape photgraphy where quite often, foreground capture is desired. Whilst the MTF charts may show a decline in sharpness, having more ‘in focus’ generally over rides the negative effect.
Use a tripod
A good solid and rigid, low resonance tripod with a good ballhead like the Sirui 30x here will provide support reducing any vibration or movement. Consider using the MUP setting to lock the mirror up along with a remote release. If your lens has VR or VC then turn it off or set to minimum when using a tripod – again experiment to whats best.
Improve shutter release technique
Support your camera well, lock your arms to your body, press the shutter in a controlled manner, like pulling a rifle trigger.
Try shooting in burst mode, as after the first shot the shutter will be depressed making the camera steadier so shots from No2 onwards should be slightly sharper.
Use a higher shutter speed
If your shutter speed is too slow then expect blurred or softer images, VR or VC can help here. Using a speed of 1/(2x focal length) is a rough guide but increasing shutter speed at longer focal lengths is essential.
Please shoot RAW not JPG! JPG is a lossy and thus destructive file format, each time a .jpg is processed it degrades. Shoot raw then export to .jpg in pp maintaining your original raw.
Calibrate your lens
By applying the correct offset in camera settings for autofocus your lens will focus correctly – it does take time making it a rainy day job to calibrate your lenses. There are lots of ‘how to’s’ on line for different cameras and lenses. The Tamron G2 series and some Sigma lenses have a USB connected docks allowing focus point adjustments and new firmware to be applied saving a trip to a dealer.
Be aware large megapixel sensors have smaller pixel pitch and size. Which can make the camera slightly more prone to movement for which the D850 is fairly notorious! If you upgrade to a higher Mp camera it may require improved technique. Pixel pitches of some Nikon DSLRS below:
D300 – 12Mp – 5.51 µm pitch
D7100 – 24Mp – 3.9 µm pitch
D7500 – 21Mp – 4.2 µm pitch
D750 – 24Mp – 5.95 µm pitch
D810 – 36Mp – 4.87 µm pitch
D850 – 45Mp – 4.34 µm pitch
Making a D7100 less forgiving than a D850 with respect to pixel density. The D750 has the largest assisting its high ISO capability as the wider spacing helps cooling during long exposures.
D80 with 70-300mm @ 300mm hand held catching a slight propeller blur.
Please note: I am not sponsored or affiliated to any company mentioned in this post. The opinions and findings here are my own from first hand experience evaluating the product. Please post any questions you may have and I will be more than happy to answer below.