[newarts]

Common wisdom (including my repeating it) is that a reversed non-macro lens is better than that lens not reversed for macros This is supposedly because when reversed, the lens' image field (which is flat) becomes the subject field which therefore should be flat. (We kind of gloss over what happens to the new image field flatness.)

I decided to demonstrate this with a real lens. I used a moderately good Pentax-A 50:2 lens reversed and not reversed for a high mag macro

Here are the results of my test:



No field curvature was observed. That doesn't mean it won't happen with other lenses but it does imply that it isn't always a problem.

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Last edited by newarts; 09-02-2011 at 01:26 PM.

[Wheatfield]

While most, if not all macros are flat field, not all pictorial lenses are curved field. It's good to know if the lens is flat field or not, especially before one dials it in with a focus chart.

[newarts]

I worried that my earlier test showing a flat focus field for the non-macro Pentax A 50:2 lens reversed and normally mounted at 2.2X might not be the same at a lower magnification so I repeated the test at a lower magnification. At 0.3X the reversed lens shows much less curvature than does the normally mounted lens.


The earlier test was at a much higher magnification which may explain the different results I suspect that there is a Chromatic Aberration and the red part of the spectrum shows a greater field curvature than the blue.