Or why it’s important to keep your kit clean…..
So, we have been unhappy with the performance of one of our lenses for a while. Especially as it was renowned for its super sharpness. We just weren’t getting that ‘on point’ razor sharp focus and resolution. We have had this particular lens for a few years and its been quite well used, but in an on/off type of way. So we weren’t sure if it was our technique, our lens or our camera that was unsatisfactory, as compared to photos taken a few years ago, sharpness had DEFINITELY suffered. It was getting us down, frsutrating the hell out of us and we were thinking of part-exchanging it, or giving up photography completely…..
Howver, luckily, we have 2 identical lenses in our kit stash so were able to perform direct comparisons lens for lens, with the same camera body and settings. It soon became apparent something was waayyy amiss. Check how soft this is, and notice the weird defraction and general ‘unsharpness’?
Here are the shots from the trouble lens before we looked into the problem more deeply.
All settings are: f4, 1/2500s, ISO500. Converted from NEF in LR (no other processing).
Click for full size.
So something was clearly wrong. First thing was to inspect front and rear elements. Under a bright torch it was apparent the front was generally dusty, not scratched but had some fingerprint smears. The rear element had a finger print, hair and lots of dust on it. A rocket blower and a lens cloth sorted those out.
Now lets see how if the images have improved…..
Marked improvement right? Well yeah, but still seemed like things could be tweaked. Now we shoot a Nikon DSLR which has inbuilt focus calibration in the body so you can compensate for front or rear focussing errors. So we broke out the calibration chart and (rather laboriously) took a series of shots until the fine focus was as good as we could get it.
Now these 100% crop photos of the calibration card show subtle changes, so pay attention…..
1st photo shows that focus is good, but note that it is slightly sharper towards the ‘-1’ than the ‘+1’ – so the camera is back-focussing slightly, which will contribute to softness.
Now the next image shows our first adjustment, to +3 on the in-camera AF adjustment. This is slightly to sharp at the ‘-1’ compared to the ‘0’ – we had adjusted too far.
Now the following image shows the setting at ‘+2’ – note that the ‘-1’ and ‘1’ mark are both about the same, and the ‘0’ is nice and sharp. This is a good setting, and focus is actually where the focus point should be.
Lets see how those adjustments have translated into the real world, look at the following images, taken with the same settings as the first image.
Much better. We don’t have to sell all our gear and close down the website. Phew.
So rather than send your lens off for expensive servicing, cleaning and calibration give it a go yourself. It’s amazing how much a bit of dust and fingerprints and sub-par focus calibration can affect an image.
So TimeChamber top tip is:
‘Clean your gear if you want to stay sharp’