Discussion in 'This or That?' started by pcake, Jun 6, 2012.
leaving out the omd, which micro four thirds camera would you say has the most accurate focusing?
They are all accurate. Micro 4/3 cameras don't suffer from back- and front-focusing.
Accuracy has never been an issue on focussing Mu43 when using AFS (not so clever on AFC for sports etc), however speed was at first but not now.
I started with the wonderful GF1 and always found the focus to be spot on for what I shoot but it did struggle in low light and on some scenes with minimum contrast but that is the nature of the system.
I now have the GX1 and find it is still 100% accurate on AFS and also a great deal faster to lock on in all lighting conditions and even locks quickly on low contrast subjects.
The only issue if it really is one is around continuous focus and focus tracking and it appears to be an issue across the whole Mu43 range including the OMD (from what I have read) - as I do not use my GX1 for shooting fast moving objects I do not need AFC so it is not an issue but for those who buy the Mu43 for sports use, I suspect thay may be a little dissapointed especially, if they are coming from a DSLR.
Definately a case of "Horses for courses"
No, but there is the problem of having an AF 'box' vs. an AF 'point'. Especially with the default AF box size on Olympus bodies, it's easy to focus on things you didn't intend to.
Frankly speaking, the problem is not new. PDAF sensors in DSLRs also cover more than the markings in the viewfinder indicate.
That is as much operator error as camera issue IMHO. There is no way for the camera to know what you want to focus on - you have to tell it. The pinpoint mode on the new generation cameras allows this to be communicated better than even a DSLR.
The larger focus box on the E-P1 and E-P2 could make it hard to focus on a thin foreground object compared to a Panasonic or the later Pens.
Agreed - That is my biggest complaint with my E-PL1 regardless of what lens I have on it.
I know that on DSLRs, focus can be an issue. They can have front or back focus or even focus shifts... This is more noticeable with large aperture primes when shooting wide open.
Sometimes you can use the AF Micro Adjust on some camera bodies to go around the issue or you have to send the lens and camera body for calibration together for optimal results.
I know this was a big issue with Sigma Lenses, but all other lenses are more or less prone to this...
Then I read that m43 cameras are imune to the issue because they use Contrast Detect AF instead of the Phase Detect AF used on DSLRs...
Can someone with more knowledge please clear this out?
What's the difference in focus systems and why DSLRs are prone to focus problems and m43 cameras aren't?
Cheers and thanks!
Contrast detect AF determines the optimum focusing distance directly from the imaging sensor. It tells the lens focus motor to stop at the exact point that it measured the maximum amount of contrast.
Phase detect AF is a separate system from the imaging sensor which makes it prone to calibration errors which can be from a number of causes. PDAF communicates to the lens to stop where it thinks the image should be in focus.
Technically that's true, but even the 'small' AF box on my E-PM1 is significantly larger than the actual AF sensor points on any of my DSLRs.
Phase detection (what's used in SLRs) uses a sensor that essentially automates the rangefinder focusing method. By comparing the phase of the light through two different paths (created by a prism) it can detect the distance to the subject. It then tells the lens to move the elements to the setting for that distance, and bam, you're in focus. Due to manufacturing variation in the lens, these settings can be ever so slightly different, resulting in a lens that focuses in front or in back of the specified distance.
Contrast detection is much easier to understand IMHO, and its very obvious on the old bodies or most compact cameras. It moves the lens elements back and forth until it determines when the highest contrast is obtained. Since highest contrast = in focus by definition, there is no front/back error. There are some pretty sophisticated algorithms that must be going on to get it close beforehand so the lens doesn't have to rack the full length of the travel each time.
Considering the head start PDAF has, it shows how much better CDAF is as a concept that it has caught up so quickly. Things like face detection are not possible with PDAF, but are easily accomplished with CDAF. IMHO, the next "generation" of CDAF with better tracking of subjects towards/away from the camera will spell the death of PDAF. CDAF already matches or beats PDAF in tracking side to side (obviously, that is rarely of use in real life as subjects are usually moving not directly perpendicular to the viewing path!)
Well, the smallest AF box on both my Panasonic GH2 and GF2 is really small. I've never experienced a problem with my cameras focusing not where I want them to focus. I guess it's just another thing which Panasonic does better than Olympus.
I find the smaller focus box on the current Olympus bodies to be small enough to pick out small and/or thin objects against a background. What IS annoying is that choosing the smaller focus point essentially puts the camera into a separate display and control mode.
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