Happy holidays, everybody! I wasn’t able to update the blog last weekend since I was busy and I had to work last Saturday. This coming Christmas is no different for me because I am going to have to work as well. This is Japan and Christmas is nothing more than a Western idea celebrating capitalist ideals. Speaking about Christmas, I have an assignment for you guys this season if you have ever bought an old lens or have inherited one. Read along!
Damaged Lens Artifacts:
Today, I will show you how to check wether a damaged lens element will affect an image or not by using light sources like Christmas lights! Some people claim that damage on a lens’ optic will not show up in the final image, while it is true for minor problems like a patch of fungus it is not true for something more serious like a scratch or chip. Sellers and people on the internet make this claim and I will show you how to test their statement by doing these simple tests.
Some damages that are too feint to see with the naked eye without using the help of a light source such as a torch can fool you into thinking that nothing is wrong with a lens but this simple bokeh test can help you determine wether the lens is still OK or not. This test only works in darkness so I do this at night or inside a dark room.
First, focus your lens to it’s minimum focusing distance and stand 1.5-2m away from some Christmas lights or any bright sources of light. This also works on light sources that are far away like some street lamps 60m meters away from you. So long as you can produce clean and clear bokeh balls you are on the right track.
Second, set your lens to it’s maximum aperture and set your exposure settings so that you will get a nice picture with bokeh balls, ISO400 at 1/250s usually works for me. The key to this is to underexpose the bokeh balls a bit so that things will show up.
Examine your picture and zoom into your bokeh balls and look for artifacts. The following images show a few examples of bad bokeh from some of the lenses that I encountered.
Dirt or a bad scratch can cause this artifact to appear. Depending on the cause, it can easily be fixed by cleaning the lens elements in case of dirt or having a professional re-polish the problem element for you and re-coat it after. This particular lens looks immaculately clean but as you can see from the picture above, the lens produces bad bokeh. I am yet to open it again to find the cause but I suspect that a minor scratch in the coating is the cause. More