70-200 F4 Help

Started 4 weeks ago | Discussions thread
briantilley Veteran Member • Posts: 4,711
Re: 70-200 F4 Help

Matt_24 wrote:

briantilley wrote:

Matt_24 wrote:

Leonard Shepherd wrote:

Several responded to your previous thread.

Based on the images you posted in one thread I and several others instantly concluded there was no evidence of field curvature.

Can you post some more pictures - they will either show field curvature or show your lens does not have field curvature.

What do you want me to photograph? I don't know how you came to the conclusion that it isn't field curvature. You still haven't given me a reason the center of the hill is affected significantly different than the corners by atmospheric effects. I can add more samples?

Let me ask you a question (you'll probably tell me off for "de-railing" another thread, but anyway...) - in the second of the two railroad images in your original post, how far from the camera was the locomotive, and how much further away was the distant hillside?

Your fence images do seem to indicate a slight degree of field curvature at close distances, but I'm not sure you understand how little effect that - if it were replicated at distance - would actually have on the sort of images you say you'll be shooting. Other factors such as depth of field, atmospheric haze and the natural corner softness of most lenses are (whatever you may think) far more likely causes - and would affect any other similar lenses just about as much.

One more question - why are you so concerned about this? Whatever is causing the far distant corners to be softer, it in no way detracts from the actual image.

Look at the new samples, there's no special atmospheric distortion in the corners, things at the same distance of the corners or further or closer are sharper. My home tests indicate the lens can be sharper in the corners. At least to me it appears the field curvature is not really a problem except in the corners and the far edges of the sides.

I'm going to concentrate on the second image again (which is also the second image that you have re-posted above).  I disagree with your assessment - to me, the upper left and right corners are no softer than the top centre area.

Why am I concerned? I have a full frame camera and I want to use the entire frame (or close to it, leveling in post occasionally crops it a bit but you would have to crop way more to hide the problem I describe).

I simply don't believe you'll find any lens of around 200mm that will render this type of scene pin-sharp corner-to-corner and front-to-back.  There's just too great a range of distances.

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