Dp3 Merrill Macro Focus Issues: Am I a dingus?

Started 3 months ago | Questions thread
D Cox Forum Pro • Posts: 30,237
Re: Dp3 Merrill Macro Focus Issues: Am I a dingus?
1

jande9 wrote:

I would assume that the lens on the DP3M is a curved field lens, suitable for general photography.

Field curvature will vary with distance. It's quite likely that the DP3M lens has its flattest field at a distance such as 10 metres.

A macro lens or enlarger lens may have its flattest field at around 1/10 life size -- that is, where a 10 inch high subject comes out at one inch high on the sensor -- or conversely, a one inch high negative makes a print ten inches high. An ordinary lens will be flattest at a greater distance. For astronomy, you want a flat field at infinity, but this is too far for everyday photography.

Some macro lenses have internal floating elements which move slightly to adjust the field curvature at various distances, I don't think the DP3M lens has this.

The cure for field curvature is to stop the lens down. Then experiment with various settings of Sharpness in SPP to see if you can get the best balance between the slight blur from diffraction and the halos caused by sharpening. For instance, instead of -2.0 one might prefer -1.6.

Another thing to try is setting the focus point about half way between the centre and the corner. (Page 50 in the manual.) Don't forget to set it back to centre when you've finished doing flat field macro.

For edge to edge sharpness shooting flat surfaces you need to use a flat field lens. Apparently most true macro lenses are flat field which makes them suitable for shooting documents and art. I don't own a macro lens so I don't have any personal experience with this.

Jan

Don Cox

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