Lurking under the term "contrast detect autofocus" is the reason for its
existence. DSLRs normally focus using "phase detection" while digital
P&S cameras use "contrast detection". It's the contrast detect
autofocus that allows live view in the E420 to offer continuous focusing
with the mirror up. Without it the mirror has to be lowered to focus
and then raised again to see the live view image. For an overview of
autofocus methods see: <http://en.wikipedia.org/wiki/Autofocus>
I don't understand why there's a firmware dependency in Olympus lenses
to operate with contrast detect autofocus but there is. Maybe the
autofocus is normally disabled with the mirror up? Anyhow, apparently
any lens can be updated to use contrast detection but so far only three
have been. Now that the E30 is out which, unlike the E3, also supports
contrast detection perhaps there will be some more urgency in updating
other lenses.
Incidentally, finding the lens compatibility info is difficult. One
would expect a little table covering specs on all the lenses including a
column for contrast detection compatibility. If it exists I didn't find
it. Even those lenses which are compatible don't say so in their specs
pages. Very frustrating when the user's manuals for the E420 and E30
simply refer you to the Olympus web site for lens compatibility info.
From the FAQs on the E420 at OlympusAmerica.com
--------------------------------------------------------------------
At the time of the E-420’s release in May 2008, the compatible lenses
were the 14-42mm f3.5-5.6, the 40-150mm f4.0-5.6, and the 25mm f2.8
“pancake” lens. Depending on the date of purchase, a compatible model
may require a firmware update in order to support IMAGER AF. In the
future, Olympus may add IMAGER AF support to other Zuiko Digital lenses
via firmware updates.
--------------------------------------------------------------------
Chuck Norcutt
Moose wrote:
> AS wrote:
>> ....
>>
>> What is major difference between the 410 and 420? I didnt see any difference
>> while checking specs.
>
> New features (compared to the E-410)
>
> * Larger, 2.7" LCD display (versus 2.5" on the E-410)
> * Contrast detect autofocus (with select lenses)
> * Face detection in live view mode
> * Auto Gradation (Dynamic Range enhancement)
> * Faster continuous shooting speeds (3.5 vs 3.0 fps)
> * Improved right hand grip
> * Perfect Shot Preview
> * Wireless flash control
>
>
> Moose
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