Laowa RF Mount 14mm F4 RL ZERO-D - a bit of struggle either MF issue or resolution

Started 4 months ago | Discussions thread
David Franklin Senior Member • Posts: 1,542
Re: Laowa RF Mount 14mm F4 RL ZERO-D - a bit of struggle either MF issue or resolution

Sittatunga wrote:

David Franklin wrote:

<snip>

Finally, one needs to practice setting the lens for the best focus point, by keeping in mind the optical properties of focusing; a rough rule of thumb is the when you set a particular focus point of the lens, approximately one third of the visible space of the image before that point will be in rough focus, and two thirds of the space after your focus point will be in that same rough focus, with the total distance amount of rough focus determined by the aperture and distance from the focal plane to the exact focus point.

That's a widely quoted factoid that's only true if you focus at exactly half the hyperfocal distance. In that case the depth of field will extend from a third of the hyperfocal distance to the hyperfocal distance. If you focus at a tenth of the hyperfocal distance, the depth of field will extend from an eleventh to a ninth the hyperfocal distance and the point of best focus will only be 10% off halfway between the extremes. The point of best focus changes within the depth of field, depending on what's its proportion of the hyperfocal distance.

I've never found focus peaking satisfactory for critical focus, as the depth of field of a 14mm lens is huge. It could well be that the lens isn't sharp enough for you if you can't achieve critical focus using magnification. You could try using a 'find edges' Photoshop filter on an image from that lens of a flat grass field, as recommended by Roger Cicala.

Basically, your are just repeating what I said with more specific technical information and jargon. That's why, for instance, I said that the 1/3-2/3 rule was a "rough rule of thumb" because to someone like the OP, too much information is likely as good as none, when it comes to a subject about which hundred page articles could be written.

As to the actual "sharpness" of his lens, more very specific and better samples would be necessary to determine whether it is defective or the performance typical of its optical design is not ideal for his uses.

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