Testing Lenses Opinions and Tips Please

[Samir Patel]

Okay so I received a bargain late model Leica 90/2 in the mail yesterday. Loving it by the way. Upon inspection I noticed there seems to be a blemish or tiny dust spot in between lens elements. I know that it is not showing up in most shooting situations. So I ran the Scarlet with the lens on and just tested it out and I seen it mainly as a small spot in a large out of focus bokeh. Like when shooting a small LED point light.

I typically would not care about this in my own shooting situations but I was thinking:

1.) So in professional settings do people not like that? I have seen films in the past that have had dust in Bokeh but I guess it didn't seem to matter as the films did end up in theaters. Should I plan to replace the lens one day down the line? Or is something like this fixable by having a technician clean the lens? Even worth it?

2.) Can someone offer some tips on how to properly test a lens immediately upon purchasing a used lens? Aside from typically just shooting in different situations. I am more so looking for stress test tips.

 

[Samir Patel]

Anyone?

 

[Phil Holland]

I have several charts that will test things like curvature of field, resolving power, and a device to test test various lens artifacts. I do this mostly to inform myself and also to understand how to transform a lens into something else in post.

Dust and bubbles typically don't effect resolving power, however, where you do see it is direct axis and off axis out if focus highlights.

With lenses at this level you're essentialy left to copy variation. High end cinema glass rarely would pass QC with something like a bubble.

Really though, what matters is if you like how the lens looks and renders an image.

 

[Samir Patel]

Thanks Phil. I think the dust or bubble (whatever it is) only shows up in rare situations. Looks like I will keep the lens. It is a used lens after all. I like the look and rendering.

 

[Glen Powell]

I see these spots in bokeh in every TV show on the air… drives me nuts. Yet it seems to be the norm, and you got off lucky with only one spot.

 

[Samir Patel]

I see these spots in bokeh in every TV show on the air… drives me nuts. Yet it seems to be the norm, and you got off lucky with only one spot.

Haha yeah I know it drives me nuts sometime. I will have to rewatch breaking baf I think I saw it a few times in there.