NikonGear'23

Gear Talk => Lens Talk => Topic started by: stenrasmussen on July 08, 2015, 20:20:40

Title: Nikkors and their field of curvature
Post by: stenrasmussen on July 08, 2015, 20:20:40

In my nerdy world I like to understand how the lenses I use behave across their optical field. I know my method is that of an amateur but I still like to believe I achieve enough information.
The setup is quite simple. I plot out a large (1.2x0.8m) sheet of paper with lots of black dots on. I take a shot at a very low angle at the largest aperture and make sure I level the camera as best I can.
The resulting image looks like the upper one. Then I bring it into Photoshop where I run a high pass filter with a large radius (3-4) and make a duplicate of this layer. I then blend the upper layer using the darken color option. I can now see how the optical flatness of the focused area behaves.
The 35/1.4 Ai-S has a little backward field of focus from the center and 2/3 towards the edges and a forward field of focus from here on.

Title: Re: Nikkors and their field of curvature
Post by: Jan Anne on July 08, 2015, 21:35:57

Really missed you Sten, really dig stuff like this  :)

Title: Re: Nikkors and their field of curvature
Post by: elsa hoffmann on July 09, 2015, 06:50:59

interesting!

Title: Re: Nikkors and their field of curvature
Post by: Andrew on July 09, 2015, 09:17:14

What is conclusion??
Great? Bad?

Title: Re: Nikkors and their field of curvature
Post by: Erik Lund on July 15, 2015, 00:26:59

Great Sten!

But do also teat along the diagonal!

Lensrentals has this as well

Title: Re: Nikkors and their field of curvature
Post by: Roland Vink on July 15, 2015, 02:47:52

Great demonstration of field curvature. It also shows traces of LoCA. I guess the lens was focused at around 1m? Field curvature changes with distance so it might be better or worse near infinity or at extreme close range. It would be interesting to see a series showing how it changes with distance.

Title: Re: Nikkors and their field of curvature
Post by: pluton on July 15, 2015, 05:54:09

I think I can see it better in the unprocessed shot.  Good choice of test pattern.

Title: Re: Nikkors and their field of curvature
Post by: stenrasmussen on July 15, 2015, 20:19:59

I've tried to improve the illustrative aspect.
Added 1/3 grid plus a diagonal line for reference. Also corrected the high pass colors so that magenta and green are at their right side of the point of focus.
This is the behavior of the 50/1.4 Non-Ai @ f/1.4 (note that my alignment is not perfect so that this is not an absolutely true diagonal test).