How will a coating defect affect my images

Question

I have rented an RB 67 and the 90mm lens it came with seems to have a very visible defect on the coating of the front element. How is this likely to affect my images? And what sort of scenes/lighting should I avoid in order to minimize any issues?

As this is an experiment I am not too concerned about overall quality, but I want to be forewarned so I can choose my scenes more carefully. My main subject material is going to be landscapes, but also some portraits and other up close subject material. Note that I also have a 180mm lens that appears to have no serious issues, and I will probably be swapping between the 2.

Answer 1

Don't even give it a second thought! You will not see any (zero) effects.

Answer 2

The most immediate impact will be a 'spot' (I use that term broadly) on the raw capture. It's hard to predict the exact shape and intensity but the good news is that front lens marks are far less visible than spots on the sensor or back of the lens. Apart from blocking a partial amount of it, I don't think it will affect the light path in any other way.

I'd be very surprised if you couldn't remove any and all spots on the image with a raw converter. They have become so good nowadays (layers, cloning, healing) that one can often avoid photoshop or gimp.

If I was in your position, assuming there isn't any more serious damage with any of the optical elements, I'd literally ignore the defect, take the shots you want to get and make any necessary adjustments in post-processing.

Hey, who knows, you may be able to get some funky lens flare if you shoot towards the sun although I'm not advising to do so :)