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:

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.

I didn't use jargon. I was just pointing out that what you said was wrong except in one very particular case. What you said isn't any sort of rule. I think you were patronising us by saying "too much information is likely as good as none". Misleading information and over generalisation is worse.

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.

In plain English, that's what Manny's tried to provide.

Forty years of professional photography is proof enough for me that the rough 1/3-2/3 rule for focus depth works well enough in actual and mostly critical work. Of course it is not always exactly accurate. That pesky word "rough" implies that it is, indeed, not always exactly accurate. So, if you ignore that point and claim that I said that it is exactly accurate at every aperture and focus distance, then you would be correct, although that formulation is clearly not one corresponding to what I actually said. Last, I am not being condescending at all. If you think that what you explained is something that an amateur of average experience could use as a guide to focusing, then I would like to borrow some of your smoking material.

Most people cannot pause long enough to calculate the exact distribution of the depth of focus, from "before" to "after" the point of best focus, for an image they are about to shoot when trying to a capture a fleeting moment such as the time of day that a landscape will look the way they desire to show it, and the OP seems most interested in just those kinds of photographs.

I guess it depends on whether the intricacies of optical theory and practice are more interesting to a person than is just having a rough idea of the depth of focus when creating a beautiful image of fleeting light painting a scene in order to make a good photograph.

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