Accuracy of Autofocus Systems with High-Speed Primes?

[christopher_engeler]

I often wonder what the technical limitation of the autofocus sensor

array is with high-speed lenses. How does this compare with a

rangefinder camera? Specifically, has anybody had experience with the

new AF-S VR Nikkor 200mm F/2G IF-ED? There is not a lot of room for

focus error with such shallow depth of field.

[erik_loza]

What are you really asking, since this seems more speculative than practical? Are you interested in knowing about AF detection systems, which are a function of the camera body in use, or about lenses, since you mention the new 200mm? How would a rangefinder factor into this equation and lenses like the fast 85's and the fast DC never have seem to had a problem with focusing ability? What's your question, is I guess what I'm getting at.

[christopher_engeler]

Erik: To generalize, yes, I am interested in a comparison of autofocus with traditional rangfinders (Leica, etc.). Most modern AF SLR's no longer give you the choice of using the split-image screen for focus confirmation, so you have to trust the AF completely.

[david_h._hartman]

Ive found the AF system in the F5 extremely accurate

compared to visual focus with the DW-31, high magnification 6x

finder and this with 300/4.5 and 400/5.6 Nikkors on extension

tubes at about 1/2 life size. I would expect that the Nikon D2H

will focus as well or better than the F5.<br>

<br>

B&H Photo doesnt show this lens even as "Accepting

orders" so there is little reason if any to think anyone

here can do more than speculate.<br>

<br>

I think it depends on the camera you use. Id only bet on

the F5, F100 and D2H.

[erik_loza]

Do you want an autofoucus camera or do you want a rangefinder? I drive both a stick-shift and and car with an automatic transmission. I like them both but comparing the two is a matter of apples and oranges. Maybe I'm reading you wrong but it sounds to me like you're finding reasons to dislike AF and stick with a rangefinder. If you don't trust a fast prime that nobody has really tried yet and worry that current AF technology won't meet your needs, then I would definitely stick with split-image rangefinder for your picture taking needs.

[richard_cochran]

There are two issues to consider: SLR vs. rangefinder, and AF vs. MF.

<p>

Traditional rangefinders aren't so good with fast telephotos.

For a fast 200mm and above, any SLR (AF or MF) is going to have an

inherent advantage over a rangefinder. The nice thing about an

SLR is that, as the DoF gets narrower with a long fast lens,

the focusing precision naturally increases, because you're

using that narrow DoF to focus. In contrast, a rangefinder

has the same precision regardless of the lens in use, so

it has a relative advantage with slow wideangles, and

a relative disadvantage with fast telephotos.

<p>

As to AF versus MF SLRs, that's an issue that's been discussed

repeatedly, without solid conclusions. I think MF is quite

a bit faster and easier to precisely control, but it requires

practice. AF doesn't require as much thinking, can be

quite fast, and AF certainly has its fans.

[david_h._hartman]

<em>"Most modern AF SLR's no longer give you the choice

of using the split-image screen for focus confirmation, so you

have to trust the AF completely." --Christopher Engeler<br>

</em><br>

Not true: the F5 has an excellent finder for focus on the matte

screen surface as does the F4. There are focus screens available

for both that feature split image rangefinders and micro prisms.

Focus on the matte surface is more accurate anyway. The F100 does

not have a condenser in its finders optical path so

the image is not as crisp. There are after market focus screens

for the F100 with split image rangefinders also.<br>

<br>

If using a AF-S 200/2.0G ED-IF VR on the side lines of a football

game a plastic camera like the N80 may make sense, otherwise

Id use an F5 or D2H.<br>

<br>

Regards,<br>

<br>

Dave Hartman.

[mag_miksch]

<p><i> ..For a fast 200mm and above, any SLR (AF or MF) is going to have an inherent advantage over a rangefinder..</i></p>

 

not that difficult as there are no 35mm rangefinder lenses over 135mm focallenght

[ilkka_nissila]

Yes, and even that 135 mm isn't fast nor easy to compose or focus.