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Forum: Pentax DSLR Discussion 04-01-2017, 09:59 AM  
Pentax, autofocus and the future
Posted By photoptimist
Replies: 287
Views: 22,141
This thread is starting to be very funny.

Now it's only the inexperienced pros who may (or may not) find it harder to get good AF with Pentax cameras. If there is a difference in the AF performance of different brands, it seems like it's a difference that only occurs under obscure conditions that are corrected as the user learns their craft.

As someone who started taking pictures before any camera had AF and who has watched AF evolve over decades, I'm impressed with how good AF is on the K-1. And judging by the comments and images on this forum, it seems many others have no problems using Pentax AF to make great images.

So this whole "Pentax AF sucks" meme is just another example of internet hyperbole in which subtle differences that seldom cause real differences are amplified into bombastic statements about big winners and huge losers. Meanwhile there's enough actual differences between different brands (price, IBIS, size, WR, ergonomics, IQ, pixel shift, etc.) that reasonable people might reasonably prefer one over the other without searching for nearly indistinguishable nits.
Forum: Pentax DSLR Discussion 03-31-2017, 07:17 AM  
Pentax, autofocus and the future
Posted By photoptimist
Replies: 287
Views: 22,141
How well does that Canon sensor AF work in low light? The dedicated sensor in DSLR PDAF can have large, very sensitive pixels coupled to dedicated signal amplifiers.

Also, it will be interesting to analyze the artifacts in the RAW image created by all those PDAF-attenuated pixels. PDAF pixels lose at least 1 EV of DR. They'll be especially an issue in the bokeh parts of the image where all the left-hand PDAF pixels will be blind to the right half of the bokeh light. No doubt, the camera (or RAW developer) will just fill in the data as if it's a stuck pixel and most people won't care.

There's still innovation occurring in DSLRs such as K-1's advanced mirror mechanism and OVF overlay. And DSLR makers continue to increase the number of AF points, accelerate the processing of AF data, and extend the optical design of dedicated PDAF to handle both f/2.8 and f/8 optics.


I'm not saying SLR is superior only that both technologies have respective advantages and disadvantages.
Forum: Pentax DSLR Discussion 03-30-2017, 09:02 AM  
Pentax, autofocus and the future
Posted By photoptimist
Replies: 287
Views: 22,141
On-sensor PDAF requires compromises that affect both AF performance and image quality. Adding the little half-lenses on the main image sensor to create the phase information for AF isn't as good as having separate aperture masks used by a dedicated module. Moreover, these micro-lenses degrade image quality and mean that the micro-prism black-out effect occurs on the main sensor if the lens has a narrow aperture or has an unusual exit pupil geometry. Either the camera or the RAW developer must correct or fudge-in the values for any pixels involved in on-sensor PDAF.

The advantage of a separate PDAF module is that the module optics, PDAF sensor chip, analog electronics, and processing elements can be totally optimized for that one function (and the main sensor can be optimized for image quality). Sure, that design comes with the significant complication of all the mechanical systems of the DSLR design but camera makers have had decades to optimize those systems.
Forum: Pentax DSLR Discussion 03-29-2017, 11:25 AM  
Pentax, autofocus and the future
Posted By photoptimist
Replies: 287
Views: 22,141
On-sensor AF is not necessarily better. Disadvantages include:

- suboptimal PDAF design (constrained by the sensor's pixel pitch and semiconductor design)
- slower AF read rates (constrained by the sensor's frame rate)
- higher power requirements to run the sensor and display continuously
- higher sensor temperatures which means higher noise levels in the final image

You are right that Canon, Nikon, and other DSLR makers are selling their preferred solution, but so are the MILC makers. And mirrorless came before SLR in both film and digital worlds so perhaps MILC is the horse and SLR is the car. ;)

P.S. On-sensor AF can suffer from back/front focus if the lens has spherical aberration and the lens is not closed down during AF.
Forum: Pentax DSLR Discussion 03-24-2017, 03:08 PM  
Pentax, autofocus and the future
Posted By photoptimist
Replies: 287
Views: 22,141
Exactly!

Personally, I think Nikon and Canon are utterly failing on the image stabilization front (no stabilization for older lenses, limited selection of stabilized lenses, no stabilization of roll, no horizon leveling, etc.) yet plenty of people buy their equipment.

Could Pentax AF be better? Sure! But must it beat Nikon & Canon on AF to survive? No!
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