Cross type focusing point

[ketan]

Hi,

Sorry to ask a basic question.

On my 6D, I have only one cross type focusing point and 11 normal ones, compared to many many more cross type and normal on other cameras like 5D and 70D etc.

I normally focus any composition with center cross type and with half way pressing the shutter quickly recompose the frame.

What am I missing having so less focusing points?

Regards,

 

[KmH]

The other 1/2 of crosses?
How about - you're missing autofocus robustness and flexibility.

Understanding Camera Autofocus

 

[ketan]

Hi,

Thanks, read the article on the link. It's an extremely informative article, though it does not answer the question that I have above.

 

[robbins.photo]

Hi,

Thanks, read the article on the link. It's an extremely informative article, though it does not answer the question that I have above.

Ketan,

A cross type focusing point is more accurate because it looks at the contrast differences in two dimensions, both vertically and horizontally. A single type focusing point only looks at contrast differences vertically.

The end result is that a cross type focusing point is generally more accurate and produces more reliable results. However it should be noted that a lot of people shot cameras for years before the cross type AF point was invented, and managed to produce good results without them.

So how vital are they? Well I like having more than one on my D7100 - but I guess you'd have to look through your pictures, see how many shots were missed because the AF system didn't produce the desired results, see if you can find a workaround that suffices (such as the one you listed above) and then decide if the cost of upgrading to a body with better AF would be worth it to you personally.

 

[JacaRanda]

You would be able to compose and choose a more accurate off center focus point as opposed to focus and recomposing; which sometimes causes misfocus when the focus/sensor plane changes.

 

[KmH]

What am I missing having so less focusing points?

Once again.
You're missing AF robustness and flexibility by having fewer focus points.
Particularly by having only 1 cross-type focus point at the center of the frame.

My Nikon D300s has 15 cross-type focus points out of 51 total focus points.

 

[TCampbell]

All focus points are advantageous (whether single axis or double axis (aka "cross type" and in some focusing systems they rotate the axes so it's shaped like an "X" instead of a "+").

But the difference is that a single axis focus system might either struggle to focus or might miss focus IF the subject has contrast in the same direction as the focus axis.

Suppose you are photographing something with a vertical orientation (it could be a flagpole, a picket fence, etc.) And suppose also that you have a single axis focus point which is also oriented vertically. That focus point is trying to detect a difference in focus by comparing how the left and right side of the focus point compare. The phase will shift vertically but a vertically oriented AF point is really more sensitive to phase changes which are horizontal (not vertical). This means the camera might struggle to focus that subject using that particular focus point. But a different single-axis point might work (and would work if it's oriented horizontally instead of vertically).

Focus point are sensitive to phase changes in focus in the direction which is perpendicular to the axis of that point. In other words, use a "vertical" point when trying to focus on an object with a horizontal pattern. Use a "horizontal" point when trying to focus on an object with a vertical pattern.

On your 6D

• the center point is a "cross type" point.
• the points directly above and below the center point are oriented horizontally (sensitive to vertical patterns)
• all other points (the four left and four right of the center column of points) are oriented vertically (and sensitive to horizontal patterns.)

Few objects in nature have contrast patterns that are so perfectly horizontal or perfectly vertical as to be able to fool a single axis focus point -- but it does happen just occasionally. But a "cross type" point is able to detect differences in vertical and/or horizontal patterns AT THE SAME TIME meaning it's almost impossible to fool a cross-type point (assuming the object has ANY contrast at all.)

 

[Derrel]

I have read on many occasions that if one is using a camera with only a single cross-type focusing point, if the camera is turned on an angle, it may help the AF system get a focus lock on difficult targets or under poor conditions. I do not have a camera that can test this out. I do know however that with a 35mm rangefinder camera that has a central split-image rangefinder, that I have used this angling of the camera trick many times in past decades.

 

[Dave442]

I do a lot of focus and recompose. I find this much easier using back-button focus. I will usually grab focus on the main subject, then compose the shot, then go back and grab focus again if I have moved around some while composing, repeat as necessary and then take the shot.

I would just make what you have work for you. You may not be missing out on all that much.

I usually call the cross-type focus point(s) the "normal" one.