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focus accuracy vs precision SLR vs mirrorless
Klaus said:
Too simplistic - DSLR PD AF can't help with RSAs for instance. In mirrorless systems, it can be handled if stopped down AF metering is used (some do (e.g.Sony), others don't).
Accuracy is also heavily depending on the AF motor in the lens. Some stepping motors are really coarse, others are extremely fine-grained.
DSLR PD AF is heavily relying on the calibration of the AF system and lenses - which is just not necessary in mirrorless cameras.

Sorry, I don't understand the bulletin board method to quote so I just copied and pasted to quote you, Klaus.

The RSA thing is way over my head. I would have thought that again, it is the lens design that determines RSA. Of course stopping down will lessen the problem. If the Sony is running a sort of editing on the fly its pretty awesome, but is that the same as AF? You might just as easily say that a DSLR PD could do focus stacking and call that better focusing. Seems like multiple images/ multiple settings are being merge, or composited. Don't get me wrong. I don't deny they greatness of the mirrorless system. I feel totally obsolete now, but I don't mind because I do just very basic shooting and it relaxes me. I do just use the center point for AF. Where is the art in that? Well, it gets worse, I use single shot mode most of the time. But it does work to focus on what I am pointing at. I live in terror of that AF that tracks where my eye in the viewfinder is looking. I mean, could that be used in court? How could I explain to my girlfriend the things that end up in sharp focus?

Sorry! So here is something sort of cool. I downloaded this free tool GUI for Exiftool. I originally was hoping to find a tool that would edit my EXIF so that the stuff I care about is on top and I don't have to scroll down to see what focal length and what lens were used. I soon lost interest. But what I found, I hope I'm not repeating myself, was an estimation of focus distance from object to image plane. How far away something was! Am I the only one excited about this? Maybe the only one who hasn't known this already? But I also saw something that probably answers the next question. There was the "increment number". And actually it was not a huge number. For an owl 80 feet away, around 24 meters for most of the world, the value was 31 increments. The lens was the better than expected for the price Olympus 75-300mm and it is at 300mm. I assume it would be focusing wide open at F/6.7. So does that mean there are 31 steps from close focus to 24 meters away? You'd think there would be more maybe? And yet some things are hard to see when dealing with mirrorless cameras. The manual focus is by wire. So there would be no way for me to tell how much my manual adjustment has. Is it discrete and not continuous.

Go back to a DSLR lens. Here manual focus means in some case very fine control. But I digress, this was my question.

What does "Linear Focus Motors" mean. I'm going to try to look it up. It's good right? Fast? If the elements actually move in a linear way...well that would not be all good. But by counting increments you would have a built in distance, which is nice. I have to warn you that if you edit the file first before looking at GUI for Exiftool you will probably find that the image editing program also decided what items to display, and the distance and increments will be gone.

I really do have enthusiasm for this new technology. And I'd love to not worry about MFA. I guess I am lucky I have only two fast lenses!


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RE: focus accuracy vs precision SLR vs mirrorless - by Arthur Macmillan - 08-17-2021, 12:06 PM

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