Let me clarify for the Schnozz. The problem with large and small
apertures only has to do with metering. The cone of light that the
meter sees from a fast lens is affected by the size of the mirror.
Stopping down a bit returns the situation to normal. Actual picture
taking is unaffected since the mirror is no longer in the light path.
If you want to take a shot at f/2 for very narrow DOF then meter it at,
say, f/5.6 and set the shutter speed 3 stops faster as you open the lens
back up to f/2. Alternatively, build your adjustment table for each
lens as suggested below.
Moose has a test page he posted recently (for the second or third time)
that perfectly illustrates the problem as seen on his C*n*n 300D. The
E-1 will be a little different as will each lens but the same phenomenon
is at work.
Chuck Norcutt
AG Schnozz wrote:
>> Now that I'm seriously considering going digital, I'm
>>starting to pay close attention to these digital camera posts.
>>What do you mean by "crank in two stops"?
>
>
> F2.8 - F4.5 tends to overexpose the pictures slightly (depends a
> bit on lens focal length and focus distance) and F11 and above
> tend to underexpose the pictures. (do I have this right?)
>
> So, just focus with the lens, stop it down a click or two to get
> it beyond that F4.5 point and shoot away.
>
> The reason for this has to do with the tiny mirror. Effectively,
> the viewfinder is getting an F4.5 image regardless of the
> brightness of the lens (provided that it's larger than F4.5).
> Even on the C*nons this is an issue with the 20D wheras it
> wasn't near the problem with the 10D.
>
> I recommend that you do controlled tests of your lenses. It only
> takes a few minutes. Set the camera on a tripod aimed at an
> evenly lit colorchart, picture or something with gradients and a
> known mid-tone. Put a post-it note with the lens identification
> in the picture (ie 50/1.8). Mount the lens in question, put the
> camera on Auto, and start at the widest aperture and fire away.
> One shot per click. Change lenses, repeat. Use a low-res, high
> compression image format for this so you can quickly go through
> the images for comparison. It'll take you about two minutes per
> sequence. It didn't take me long, but some of you with dozens of
> lenses might need to get an extra cup of coffee.
>
> AG
>
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