A favourite pastime of most Canon EOS users is to experiment or play with manual focus lenses. The EF mount used on the EOS series lends itself quite good at this, but some snags remain. I'll be discussing these below...
Adapters
Obviously we need some way of coupling that non-EF lens with our Canon EOS camera and adapters are the answer. These come in basically two flavours — those without optics for lenses with a register distance longer than the EF mount; and those with optics to enable infinity focus for lenses with a register distance shorter than the EF mount.
Both types are nowadays available with and without electronic coupling chips. These chips basically provide some info to the camera and activates the focus confirm circuitry, just as if using an EF lens in manual focus mode. Although the chips are a good idea, in my opinion the current versions still have a long way to go. The main problem is that they need to be programmed correctly for the lens in terms of both f-stop and focal length, otherwise the metering and the focus confirm is not accurate. And, as outlined in the section about metering below, the chip then just shifts the exposure zero reference point from f/4·5 to wide open.
It should also be obvious that all lenses can be used as macro lenses, without optics in the adapter. The adapter then just functions as an extension tube. This opens the use of some rather spectacular macro lenses, irrespective of the original mount, on the EOS camera.
M42-to-EF Adapters
These come in two versions, namely with “aperture pin” flange and without the flange. Some M42 lenses do not have a manual/auto switch and therefor require the flanged adapters in order to close the aperture. The flangeless adapters are for some reason more difficult to find, but luckily a flanged one can quickly be deflanged with a metal file. Personally I prefer the flangeless adapters, as then the M/A switch can be used to close the aperture to the preset size.
Over the years I’ve bought several of these adapters and can’t really say that I am happy with any one of them. Probably the best, and definitely the most expensive, are the ones sold by Fotodiox. My only gripe with them are that the lens does not screw in with the markings at the top, but rather off-set somewhat to the left. I also bought some nickel-plated brass adapters from a seller on eBay, which had the same problem. I then sanded these adapters down, revealing the beautiful brass in the process.
Metering
Most, if not all, of the current EOS cameras offer three modes of metering, namely “evaluative”, “partial” and “centre-weighted average” metering. The higher-end cameras add a fourth, “spot” metering, mode. When using EF lenses, the obvious — and in my opinion only — mode is centre-weighted average metering. The question, however, is which metering mode works best with manual focus lenses. The following tables show the result of tests conducted in an extremely unscientific manner, i.e. field conditions.
| 1·4 | 2 | 2·8 | 3·5 | 4 | 4·5 | 5·6 | 6·7 | 8 | 9·5 | 11 | 13 | 16 | 19 | 22 | 27 | 32 | ||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Macro-Takumar 1:4/50 | 0 | 0 | ½ | ½ | ½ | ½ | ½ | ½ | 0 | 0 | -½ | |||||||
| Super-Macro-Takumar 1:4/50 | 0 | ½ | ½ | ½ | ½ | ½ | 0 | 0 | -1 | |||||||||
| Super-Multi-Coated MACRO-TAKUMAR 1:4/50 | 0 | 0 | ½ | ½ | ½ | ½ | ½ | ½ | 0 | -½ | ||||||||
| Super-Takumar 1:1.4/50 (Mark II) | ½ | -½ | -½ | -½ | ½ | ½ | 1 | 1½ | 1½ | 2 | 2½ | |||||||
| Auto-Takumar 1:1.8/55 | -½ | -1 | -1 | -½ | 0 | 0 | ½ | 1 | 1 | 1 | 1 | |||||||
| Auto-Takumar 1:2/55 | -½ | -1 | -1 | -½ | 0 | 0 | ½ | 1 | 1 | 1 | 1 | 1½ | ||||||
| Super-Takumar 1:1.8/55 (Mark II) | 2342973 | -½ | -1 | -½ | -½ | 0 | ½ | 1 | 1½ | 1½ | 1½ | 2½ | ||||||
| Super-Takumar 1:1.8/55 (Mark II) | 3006009 | -½ | -1 | -½ | -½ | ½ | ½ | 1½ | 1½ | 2 | 2 | 2 | ||||||
| Super-Takumar 1:1.8/55 (Mark II) | 3679232 | -½ | -1 | -1 | -½ | 0 | ½ | 1½ | 1½ | 1½ | 2 | 2 | ||||||
| Super-Takumar 1:1.8/55 (Mark II) | 3680071 | -½ | -1 | -1 | -½ | 0 | ½ | 1 | 1½ | 1½ | 2 | 2 | ||||||
| Super-Multi-Coated TAKUMAR 1:1.8/55 | -½ | -1 | -1 | -½ | 0 | 0 | ½ | 1 | 1 | 1½ | 2 | |||||||
| SMC TAKUMAR 1:2/55 | -½ | -1 | -½ | -½ | 0 | ½ | 1 | 1½ | 1½ | 2 | 2 | |||||||
| smc PENTAX-M 1:1.7 50mm | 2901270 | -½ | -1 | -1 | 1 | -½ | 0 | 0 | ½ | ½ | 1 | 1 | 1½ | |||||
| smc PENTAX-M 1:1.7 50mm | 7287148 | -½ | -1 | -½ | -½ | 0 | ½ | 1 | 1 | 1½ | 2 | 2 | 2 | |||||
| smc PENTAX-M 1:1.7 50mm | 8384769 | -½ | -1 | -1 | -½ | 0 | ½ | 1 | 1 | 1½ | 1½ | 2 | 2 | |||||
| smc PENTAX-A 1:1.7 50mm | -½ | -1 | -½ | -½ | 0 | ½ | 1 | 1½ | 1½ | 2 | 2 | 2 | ||||||
| smc PENTAX-A 1:2 50mm | -½ | -1 | -½ | 0 | 0 | ½ | 1 | 1 | 1½ | 2 | 2 | 1½ | ||||||
| Average Deviation: | -½ | -1 | -½ | -½ | 0 | ½ | 1 | 1½ | 1½ | 2 | 2 | 1½ | ||||||
| 2·8 | 3·5 | 4 | 4·5 | 5·6 | 6·7 | 8 | 9·5 | 11 | 13 | 16 | 19 | 22 | ||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Super-Takumar 1:2.8/105 | 678219 | -½ | -½ | 0 | ½ | 1 | 1 | 1½ | 2 | 2 | 2 | 2 | 1½ | 2 |
| Super-Multi-Coated TAKUMAR 1:2.8/105 | 7849195 | 0 | 0 | ½ | 1 | 1½ | 1½ | 2 | 2 | 2 | 1½ | 1½ | ||
| Takumar 1:3.5/135 | 784135 | -½ | -½ | 0 | ½ | 1 | 1½ | 1½ | 1½ | 1½ | 1½ | 1 | ||
| Super-Multi-Coated TAKUMAR 1:3.5/135 | 5253420 | 0 | 0 | 0 | ½ | ½ | 1 | 1 | 1½ | 1 | 1 | |||
| Super-Multi-Coated TAKUMAR 1:3.5/135 | 7187816 | 0 | ½ | 0 | ½ | 1 | 1 | 1½ | 1½ | 1½ | 1 | |||
| Vivitar VMC 135MM 1:3.5 AUTO | 0 | ½ | 1½ | 2 | 2 | 1½ | ||||||||
| Takumar 1:3.5/200 | 1104822 | ½ | ½ | 1 | 1 | 1½ | 1½ | 1½ | 1½ | |||||
| HANIMEX AUTOMATIC 1:3.5 f=200mm | 0 | 0 | 0 | ½ | ½ | 1 | 1 | 1½ | 1½ | 1 | 1 | ½ | ||
| Soligor C/D ZOOM+MACRO 80-200mm 1:4.5 MC | 38119644 | ½ | ½ | ½ | 1 | 1½ | 1½ | 1½ | 1½ | 1½ | ||||
| Average Deviation | 0 | 0 | ½ | ½ | ½ | 1 | 1½ | 1½ | 1½ | 1½ | 1½ | |||
Some things are apparent from the tables:
- Metering mode does not effect accuracy;
- Accurate metering seems to be centred at f/4~4·5;
- Metering inaccuracy seems to be somewhat consistent;
- Focal length does not affect the tendency to over-expose with apertures smaller than f/4·5, but;
- Focal length does affect the tendency to under-expose with apertures larger than f/4.
Some investigation revealed that the reason for f/4~4·5 being accurate is that Canon designs the focus screen so that any larger aperture will provide the same degree of illumination. Check it for yourself with an f/1·4 lens... the screen does not brighten/darken significantly until f/4·5.
Now, from the above data I came up with the following formula:
-E = P + F
Where:
- E is the exposure error, in stops;
- P is the difference, in stops, between the meter reading for f/4·5 and the current reading; and
- F is the difference, in stops, between f/4·5 and the current aperture.
Unfortunately this is as helpful as the metering system itself, for you need to know the correct exposure at f/4·5 in order to calculate the exposure error. If you already know the correct exposure at f/4·5, then it’s rather easier to make the adjustment mentally, like with the Sunny-16 rule — which is now the Canon-4-point-5™ rule!
Interesting is that when using “Live View” the camera meters correctly, which is great for macro-photography and if your camera has this dubious feature.
The other solution, advocated by nearly everybody on whatever forum, is to shoot RAW and then adjust the exposure — since RAW “gives” you a two-stop latitude. Let’s test this.
The first image is a JPEG exposed using evaluative metering and as suggested by the camera; the second image is a JPEG shot with exposure determined by the sensor (i.e. LiveView) and checked with an external lightmeter; the third image is the RAW file processed to correct exposure; the fourth image is the first JPEG processed to correct exposure; and the last image is a composite of the second, third and fourth images. All images shot at f/8 with a Super-Multi-Coated TAKUMAR 1:1.8/55 lens, using RAW+JPEG on an EOS 1000D camera; external lightmeter used is a Sekonic L-VI.
Camera determined an exposure of 1/180 using evaluative metering.
© Robert I. Sadler, 2011
Camera determined an exposure of 1/500 using the sensor.
© Robert I. Sadler, 2011
RAW image corrected by -1½ stops in DPP.
© Robert I. Sadler, 2011
JPEG image corrected by -1½ stops in PSP.
© Robert I. Sadler, 2011
Combined image of corrected RAW and correctly exposed JPEG images.
© Robert I. Sadler, 2011
It is clear that getting the exposure right right there in the camera at the time of taking the picture produces the best result. RAW can save the photo, and lazy photographers can thus use RAW to just shoot now and fix exposure later. But then what’s the point of using a manual focus lens?
So, although the Canon EOS range of cameras have the ideal mount for using most manual focus lenses, both the lightmeter and the focussing screen are inadequate. The focussing screen is optimised for f/4·5, which severely affects the depth of field view. The lightmeter also does not actually just read the light, but obviously applies some formula to it — in all metering modes, even spot — which is linked to the f-stop of the focussing screen. The question is whether this can by modified or not.
The only real solution, at this stage, is to forget the lightmeter and learn to read the light.
HOLD THE PRESSES!!! I’ve had the opportunity to test the programmable EMF chips and although the AF portion is nice, the big breakthrough is accurate metering. It actually works!