SAF Front Focus and CAF/SAF Focus Comparisons with the 300mm f4 – E-M1s.

Started 3 months ago | Discussions thread
OP drj3 Forum Pro • Posts: 10,939
Re: SAF Front Focus and CAF/SAF Focus Comparisons with the 300mm f4 – E-M1s.

Stizzu68 wrote:

drj3 wrote:

Gary from Seattle wrote:

drj3 wrote:

Interceptor121 wrote:

Something is going on with the programming of the functionality here. I doubt it is a hardware problem

I am convinced it is the CDAF algorithm. It has a slight bias for the closer area within the focus points. As long as the user is aware of this issue, it is easy to avoid the problem.

It would rarely be a problem when one uses a single or limited focus area. I almost always use SAF and a single focus point with my 12-100mm f4 lens unless I am photographing a moving target or a small target at minimum focus distance.

It can be a problem when you have a very shallow DOF with very long telephoto lenses when photographing close targets or a very fast lens of any focal length photographing close targets. It is typically a difference in focus around the chosen focus point since the focus point would generally be within the DOF.

I have thought about this with S-AF and CAF. I wonder though if the chosen array/single target pattern makes a difference with CAF+Tr? I am currently using a five target cross on CAF+TR. Would I do better if I used a single small target? I haven't been doing that as I am not sure that I can consistently be that accurate in targeting; or would it make no difference in CAF+Tr because the camera essentially takes over in matching bird shapes and eyes in AI?

With CAF the camera would typically be focusing on the most distinct feature in the target area with no real focus bias. I doubt there would be much difference in the five cross and a single point with CAF+TR, since the camera will be trying to focus on specific target characteristics. Once focused, the shallow DOF will generally result in your target being more distinct than background features.

Where it would make a difference is for situations where the background is essentially at the same distance as the target and just as detailed.

For example, I always use CAF with a single point for photographing hummingbirds and hummingbird moths eating from flowers with the flower petals, leaves and stems all very close to the bird/moth where the focus can quickly jump to the background. One tenth of an inch is the difference between feather detail and a deleted image.

I also like to have the focus really nailed. With the 300F4 and the OMD1Mkii I also often use the single small point if the subject is quite enough, but I get better results with the CAF than with the SAF. Never managed instead to get anything useful from the CAF + TR with the 1MKII. Is it the Mkiii better?

I have not really checked the E-M1.3 with CAF+TR for any moving target.  It never worked well for me with the E-M1.2.  Recent posts appear to indicate it is better with the E-M1X.

The only time I use CAF+TR is for a larger stationary target where I want to focus and recompose when I might also want to change distance.  It works reasonably well, if I focus the single center point on my target and then half hold the shutter button while I recompose and move my position.

I did a little example previously with my FTs 12-60 and my cat, where I focused on the cat's eye and then moved and recomposed the image using CAF+TR.

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