Multiple AF Sensors

Hi Guys,

I am just wonderinfg why people think the announcement of multiple sensors (11 of them) on the D200 is a good thing? I got tired of guessing where and what the camera was going to focus on long ago with the 20D and use the center focus for UW work (and most land). The multiple sensors are hard to manipulate manually and don't always find what they are supposed on auto. Nikon currently has a very mangaebale 5 sensor system. I can't see where the multi-sensor approach will do anything but confuse matters. If anyone has anything to say in defense of the Canon sensors, I'm all ears.

Best,

Timbo

Totally agree. I have used Canon and Nikon systems for years and have always used the center spot for auto-focusing, just like I use the center area for manual focusing. I wonder, is this something people ask for, or is it just something the manufacturers include because they can?

I agree, I only ever use the center AF sensor. That said, the number of sensors seems to be an indicator how well the AF works in general. I dont know why but cameras with more AF points seem to be faster and more accurate even when only the center point is used. The fact that the D200 has more senosr means that more likely than not the center point will work better too.

There are instances where there's not enough time to focus and recompose.

From a lowly DRebel:

Success rate is not 100% but it's not too hard to get a few good shots.

I agree with Herb, as I also use other sensors quite a bit. For example, I used the bottom right corner sensor in this one:

I had other shots in which I used the center sensor and recomposed, but none had the sharpness on the blenny's face that this one has.

I also agree with William in that, usually the more sensors, the faster the AF system. That's probably because of differences in the in-camera AF motors, and the difference in speed in much more pronounced in non-AFS (or USM) lenses. Even though the D70, F100 and D2x all have one center cross type sensor, I can see a clear difference in speed when focusing with them. How fast is the D200 going to be? I guess we will only know after the first user reports, since Nikon (or any other camera manufacturer) doesn't give us detailed specs on AF motors.

Luiz

I can see how having multiple sensors will help. Having better sensor coverage increase the chance that one will find an area of high contrast and at least get you close for the fine tunning to kick in. It can be possible that the point you want in focus does not have the best contrast. I can see how having others that see areas of greater contrast will help the system zero in on that point. I think that's the reason the 5D has a number of "invisible" sensor, ones that you cannot select or deselect. Also, the ones that can be deselected may still aid in the autofocus even though the final focus point will not be centered on it.

Having designed a few feedback networks at my day job, it would not surprise me to find that the lens motor is more often the limiting factor in the autofocus. I've used both a Sigma 105 and a Canon 100 on the same Digital Rebel, and there is a world of difference.

Hi folks,

On new Nikon models like the D2x, and I guess the D200 will be in the same line, the sensor location can have great influence in how the camera determine the exposure.

So we now have to take an extra care when using the center sensor for focus and recomposing.

The D2x has a feature that is halfway between all manual and all automatic. It’s the sensor grouping. You can group the sensors and end up with something more manageable like Tim mentioned.

Regarding the D200 11 sensors, I just wished they were more “spread out†at the frame, like the one in the D2x.

I use all the 11 sensors manually chosen for general pictures and the grouping options for fast action.

Best regards,

Marcelo Krause.

I think that's the reason the 5D has a number of "invisible" sensor, ones that you cannot select or deselect.

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Not true, The invisable points can be turned of or off via CF 17. Even when the assist points are turned on, they are only utilized when the AF mode is AF-servo AND Automatic AF point selection is turned on.

Good post Tim and good discussion so far.

For most underwater work, the center sensor is fine - you just move it over the subject, half press, and then recompose if necessary.

But underwater with fast action, and/or big animals, sometimes you need to just make all the sensors active, set with a closest subject priority, and bang away. If you want off center compositions, you can also use groups of sensors for example, use 8/33 (for my Canon 1DmkII) up in the left-hand corner.

When I shot the airshow a few weeks ago, I used a center grouping of sensors and had really good results.

Cheers

James

Hi Guys,

I guess the big animal thing was one of my points of irritation. The multiple sensors found the critter but not the eye area necessarily and I would have a photo of a sharp body and tail and not the face, no matter how I tried to coax the sensors in that direction.

Another situation was at dusk with mating mandarinfish and a model in the background. The multiple sensors shot the fish as they rose from the coral but then switched focus at the most critical pint, when they got right in front of the mask and eyes. So I have a colorful blob in front of a sharp-eyed model.

That was the last straw. I haven't used the system since.

It may be fine for stationary critters where you have the cchance to fiddle with the housing and punch the buttons to get the right focus point. But it ain't for me.

I thought the D100 with its handy location of five sensors was the fastest and most efficient housed camera for fast and accurate focusing.

Best,

T

Luiz, Great shot and very good example for the need of AF sensor other then the center.

I only wish that my D70 will have sensors on the 1/3 points instead the cross like positions.

I am am a big AF user and I use the multiple sensors and the different groupings of sensors all the time in my shooting. I very rarely, if ever use only the centre point. But what we don't know yet is how good the AF is on the D200 - and for me that will be the most important point.

The reason I am able to make use of all these modes underwater is that my camera (D2X) has a really high spec AF system. I do not know if I would be able to shoot in the same way with the D200 - as it totally relies on AF being good.

On my D2X I most commonly use the sensors in grouped dynamic - closest focus priority. This groups the 11 sensors into sub- groups of 5, so you can set the group to the area of the frame where you expect the subject. Then the closest focus priority means that AF will pickup and focus on the front of the subject where ever it moves in that area of the frame. I use this mode for all my fish portraits. This setting is also useful for wide angle compositions. I also used this setting for this shot, which is as close an example to what Tim talks about I could find:

Here I had the AF grouped on the bottom 5 sensors in the frame. Meaning that they would track the mating fish as they moved about this area of the frame.

Using grouped multiple sensors also has the advantage that the camera is able to pick up the subject much more quickly, with several sensors to go on. This is particularly true in low contrast UW shooting. And even more so at dusk for behaviour shooting. I regularly dusk dive with Canon shooters I know I am still shooting happily without modelling lights, when theirs are already turned on. (IMO, and from what I have read, Canon 1D/1DS AF is better than the D2X/D2H AF for focus tracking, while the Nikon's are better in low light light, low contrast (i.e. underwater).

I also use single point AF a lot - particularly with off centre points. One advantage of the D2X AF over the older Nikons is the is the quality of the off centre AF points. On the D70/D100 these points have pretty poor performance - and can struggle to pick up a subject with low contrast. Where as on the D2X - these points are fantastic.

Alex

I hope really that the D200 have a better af system that the d70s

In my last trip I have, like Alex say, big problems to pick up a subject with low contrast. It was painfull. I use most off the time single point AF.

For me the new d200 must have 2 thinks. Great AF system and a 200 or 400 ISO with zero noice.

This two thinks have I miss last time.

Lambis (back from Dahab)