Does Olympus bodies read lenses differently?

[Luq]

Hi all,

Can't help but notice that most of the 2.8 Zuiko zooms are variable-aperture.

So I have a question on this.

For Canon and Nikon, if you have a zoom lens that is f2.8-3.5, the bodies will still read the lenses as a f3.5 lens. Thus, in some higher-end bodies, this will knock out the extra-sensitive center AF cross-sensor which will only work with 2.8 or faster lenses (as an example). Also, the VF will be darker than if you were to mount a constant-aperture 2.8 lens on it, as it reads as a f3.5 lens. This also affects the metering sensitivity, and which also means you get a slower shutterspeed for a f2.8-3.5 lens at f2.8, than you would for a constant f2.8 lens at the same f-stop.

Does it work the same way on the Olympus system?

Hope you veterans can educate me in my quest for understanding this new system.

Thanks!

[CompMac]

From my experience of using the 50-200 SWD f2.8-3.5 on a E-510, I have not come across any of the issues that you have mentioned. I believe that having a pure digital system will eliminate all the problems associated with using 35mm lenses on a digital body.

[mfahrur]

the bodies will read the lens aperture at 0.1 intervals for f2.8-3.5. i.e. f2.8, 2.9, 3.0,.. 3.5.

the 11 crosshair AF sensor for E-3 so far can register until f5.6, and are superfast. at f8, focus is hit and miss.

as for the shutterspeed, it will adjust as per aperture in 1/3 or 1/2 steps, depending on user preference, although the aperture moves at 0.1 increments.

[Luq]

Perhaps I wasn't being very clear.

I tried to dig up some reference in order to give you guys a better idea of what it was I was asking.

This site (http://www.dpreview.com/reviews/nikond300/page4.asp) states that the D300:

". . . the center fifteen (3x5 grid) being cross point sensors even with F5.6 aperture lenses" meaning cross-sensor works with lenses with an aperture of F5.6 or larger. After that, it becomes only a horizontal AF point.

This site (http://www.canon.com/camera-museum/tech/report/200509/report.html) states this about the EOS 5D:

"The center AF frame has a cross-type sensor with a highly sensitive vertical line-sensor working at f/2.8 and a horizontal line-sensitive sensor working at f/5.6 with a base length twice as long as previous models. . . .
Also six Assist AF points (two points for f/2.8 and four points for f/5.6, all invisible) (Fig. 4) are located for intensive measurement in the center area."

This means that the center AF is a cross sensor WITH EXTRA sensitivity vertically when used with f2.8 lenses. With lenses slower than f2.8, it is a normal cross-sensor. With lenses slower than f5.6, it becomes only a normal singular line sensor.

If you look at this site (http://emedia.leeward.hawaii.edu/frary/canon_eos5d_03.htm), it also states that the same is true for the EOS 1-series cameras.

All this isn't something new, and has been in play since the EOS 1n and F100 times.

I was just about to assume that somehow Olympus has made their cross sensors (of which the E420 has only 1) work regardless of the lenses' max aperture, but mfahrur's last post about the E-3's AF being off at f5.6 seems to be following the same principles.

So what exactly is the story with teh Oly AF system, as I cannot seem to find anything about it. Anyone knows?

TQ.

[Luq]

I just thought it might be informative for anyone who may be interested, so this is what I've found out so far:

Olympus cross-sensors do not feature the extra sensitive AF feature with f2.8 or faster lenses. Their cross-sensor works across all lenses (until lenses slower than f5.6, I'm assuming due to mfahrur's post).

The AF speed on the E420 and E520 are identical. Improvement in AF speed can be gotten by better lenses only or unless I upgrade to an E3. Example if I trade from pancake whose primary design concern was size and not AF speed, to something like the 11-22. The 14-54 f2..8-3.5 MAY yield a marginally improvement in AF speed.

The actual AF area for the center AF may possibly be the whole '+' boundary in the VF.

Hope this was useful.

Cheers.

[mfahrur]

with faster lenses, the AF will be slightly faster.

for the 3 AF points, the sensors are big, and actually cover the whole boundaries of the centre cross and 2 horizontals.

for the E-3, there are 2 modes, small and normal. small is for birding/wildlife/macro, etc.

all i can say thru my observe, the AF speeds are quite similar if the lenses are between f2.8 and f5.6. and highly accurate, although slow for E4/5x0.

one thing for sure, oly don't have FF/BF issues. that's oly AF logic.

also, the E-4/5x0 is lowlight 1EV sensitive, and E-3 is -2EV sensitive.

and, 11-22 AF speed is high due to deep DoF compared to 14-54 and longer lenses.

[red]

one thing for sure, oly don't have FF/BF issues. that's oly AF logic.



what is this FF/BF thing? please elaborate.


i didn't notice the viewfinder getting any darker when i'm narowing the aperture even from f3.5 down to f22. probably something to do with the fly by wire aperture control they're using.

[Luq]

what is this FF/BF thing? please elaborate.

FF/BF refers to Front focusing and Back focusing. Some DSLRs have this problem with certain lenses where you focus on 1 area, with a narrow DOF and find that the area that is in focus is slightly to the front or back of your intended area of focus.

mfahrur - I was not refering to FF/BF focusing. If the AF area is larger, it just means that it'll be harder to get what I need in focus in a shorter period of time as the camera needs to decide which in that whole area should be in focus (which invariably means the most contrasty). All in all, at least now I can contingent for this when I'm shooting and work around it.

i didn't notice the viewfinder getting any darker when i'm narowing the aperture even from f3.5 down to f22. probably something to do with the fly by wire aperture control they're using.

This isn't about stopping down the lens. If you mount a lens that is (for example) 50mm f2.8 and a 50mm f3.5, you'll find that the former will yield a brighter view through the VF, regardless of what aperture you're using.

And while we're at it, you can't mount a 50mm f1.8 and a 28mm f2 to compare as the 28mm will yield a brighter or equivalent view through the VF due to its wider focal length. ADDITIONALLY, if you take a 24-70mm f2.8L for example and compare it with a 24mm f2.8 prime, you'll also find that the prime is brighter even though the max aperture for both lenses are f2.8. This is due to the former being a zoom, hence it has more elements in the optics which will reduce the amount of light that actually reaches the imaging area.

Hope this helps to clear it.

Cheers.