EOS Documentation Project

Elan 7E Metering manual lenses

by Gerard Maas and Julian Loke

Contents

• Introduction
• The Problem
• The Fix
• Revision History
• Comments

Introduction

So, you want to use a non-electronic all-manual lens on your Elan 7E. Perhaps you need the 4 frames per second motor drive; or the sophisticated flash system on the camera. Or maybe you have a special lens without any equivalent in the EF lens mount. Or you have a special lens, such as a fisheye or a perspective control or tilt-shift lens that is significantly cheaper than the Canon professional quality lens.

If you have correct adapter, it ought to be possible to mount such manual lens physically on any EOS camera. Although Canon does not manufacture them, separate custom non-electronic adapters are available that allow Elan 7E users to mount M42 or Leica-R or even Nikon-F lenses. Users of other EOS cameras who are prepared to forego automatic focus, and automatic metering can successfully use such manual lenses.

However, Elan 7E users are in for an particularly unpleasant surprise. Unlike other previous EOS cameras, the Elan 7E the first EOS camera that is unable to meter correctly through manual focus lenses! The release of the Elan 7E also corresponded with an advertising campaign in the USA that only Canon lenses were compatible with Canon cameras. Coincidence?

The Problem

Can it be done? Yes, of course! So what's the trick?

Firsly, we had to learn more about the problem. To measure the error, we needed to meter through the SAME lens first in AUTOMATIC mode, then in MANUAL mode, on the same EOS body with the same target. The difference between the two readings has to be the metering bias inherent in the camera body.

For consistency, I suggest putting the lens right up to a lightbox (or LCD monitor screen) to fill the entire frame. Use centre-weighted metering at ISO 100. Do not use an "intelligent" metering mode, such as evaluative or matrix metering. Spot metering is also susceptible to hotspots or reflections, and might also not give an unbiased result.

First meter the scene in Av mode with the lens wide open. Record the reading. (e.g. f/2.8 1") Use the meter reading to calculate the EV setting.

The difference between the two meter readings (e.g. f/00 1/8") is the metering bias for THAT PARTICULAR CAMERA BODY.

To check that the metering bias is linear, we also needed to meter with the lens STOPPED DOWN. The EV readings at the stopped-down apertures should be the same. For example, f/4 1/500 = f/5.6 1/250 = f/8 1/125.

How do you turn an EF lens into an f/8 manual Aperture lens? Easy: first set the desired aperture and activate DOF preview. Then uncouple the lens, but do not remove it from the camera body. When you do this, the aperture blades remain stopped down, and you can fake a manual lens with any selectable aperture (e.g. from f/1.8 down to f/32).

So, what if your camera does not have DOF preview? Set M mode with your desired aperture and a shutter speed of 2 seconds. Release the shutter, and while the shutter is open (and the lens is stopped down), uncouple the lens before the shutter closes. Of course, this is cheaper if your camera does not have film loaded :-)

The Fix

By performing the metering experiment with our Elan 7E and EOS 30 cameras, using a variety of lenses set to different apertures, we determined that the metering bias was 3 stops, and that it was consistent across the entire metering range of the camera.

3 stops of underexposure would produce unusable, dark pictures, even on wide-lattitude film.

Test shots with narrow-latitude slide film confirm the 3 EV error with ambient light as well as with E-TTL flash.

So, when you want to use a manual focus lens, simply apply 3 EV exposure compensation. The best way to do this is by adjusting the camera ISO setting, which will correct the exposure for ambient metering and for flash metering simultaneously.

Unfortunately, if you use film slower than ASA 50, you reach the limit of ISO indexing on the camera. No problem: just dial in extra exposure compensation on the camera, and also on the flash if you are using flash. Confused? Consult the following table:

Film Speed (ASA)		Adjusted ISO		Extra Compensation
25		6		+1
32		8		+1
40		10		+1
50		6
64		8
100		12
160		20
200		25
320		40
400		50
800		100
1600		200
3200		400

The numbers in the table might be hard to remember. Remember to adjust the ISO setting so that it is one eighth of the film ASA rating. E.g. for film rated at ASA 800, set ISO 100.

The Elan 7E also offers an easier method. When adjusting the ISO value, each click is worth one third of a stop. Nine clicks are required to change the ISO setting from 800 to 100.

Of course, when you are remounting your EF lens, don't forget to change the ISO back to the correct value for your film.

Finally, just in case your meter is slightly different to ours, be sure to check your results before an important shoot.

Note: The E-TTL modeling flash function does not work if the EOS 30 has a manual lens mounted. This feature appears linked to the DOF preview Since a manual lens does not have automatic aperture control, the modeling flash is also disabled.

Revision History

v0.7 2004May27 jul: grammar
v0.6 2002Sep04 jul: minor reformat, added note about linearity; grammar
v0.5 2002Jul08 jul: EV calculator, fixed missing header
v0.4 2002Apr30 jul: method note, neater table
v0.3 2002Mar27 gm: modeling flash note
v0.2 2002Feb16 Redraft - jul & gm
v0.1 2002Feb08 Original by Gerard Maas and Julian Loke

Comments

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