Original EOS 750 post at http://exit272.com/?p=1626

With a couple of exceptions, a camera with almost no control isn’t usually one I’d shoot with again. A fellow Youtuber asked if the 750 might gain aperture control using a speed booster. A Speed Booster™ (trademark of Metabones) isn’t available for a full frame camera and not for EOS to EOS. It would mess up the flange focal distance, losing infinity focus. That plus the anti-teleconverter aspect of the Speed Booster™ is more math than I want to tackle to figure out what it would do to the image.

I don’t have a speed booster but I do have lens adapters and old lenses. What will the 750 body do if it doesn’t find an EOS lens? Most modern DSLRs have a setting that allows the shutter to work without a lens being detected for macro tubes, bellows, etc., that break the lens-body communication link. This is a much older camera with no menus but it’s worth a shot.

First up, an M42 screw mount adapter. Nothing is passed through to the camera, it just puts the lens at the right distance from the film (or sensor) plane. A fresh battery, pop on the adapter, turn it on and…

No errors. Promising. In goes a dead roll of film (great for testing transport without wasting film) and the film pre-winds like it’s supposed to. The camera body lets me “take pictures”. The 750 is from 1988 and the EOS system had only been out about a year and a half so I guess it’s not that surprising that the firmware doesn’t have a routine for failing without a lens. ROM space used to be expensive.

I have some craptastic Photoworks film (a 24 exposure roll of “Use by 11/2004” ISO 200) so I’m good to go — just gambling some developer.

I used a Helios 44-2, a beautiful Soviet-era lens. It can be tedious but one of its quirks is what I want for this experiment. It doesn’t stop down automatically. You set the aperture and a separate ring swings between wide open (f/2 in this case) and your setting. This lets you focus on a nice bright image and then rotate the ring to stop down without having to look at the lens.

The 750 does full aperture metering. There is a separate, 6 zone light meter that reads the light with the lens wide open to get the exposure value (EV) so the camera can calculate the shutter/aperture combination.

It could be implemented as a lookup table in the camera. The bottom line is the red one.

How it works with an EOS lens. Anthropomorphizing and probably not completely accurate:

EOS body: Hey lens, what are you?
Lens: I’m a 50mm and I go from f/1.4 to f/22.
EB: Open up to 1.4 so the nice human can see what they’re doing.
L: Done.
[ Human 1/2 presses the shutter ]
EB: We’ve got focus lock. EV is just about zero. At 1/125 second I’m reading 2 stops over.
[ Human presses the shutter button the rest of the way ]
EB: Stop down to f/2.8.
[ f/2.8 is 2 stops dimmer (smaller) than f/1.4 ]
L: Done.
EB: Mirror up. Shutter fired. Mirror down. Advancing film. Open up to 1.4 so the nice human can see what they’re doing.
[ The 750 actually sucks the film back into the can rather than advancing but you get the idea ]

If the camera defaults to aperture priority, I’m golden. It’ll meter the scene and pick a shutter speed. If it does some shutter and aperture auto-exposure (AE) voodoo or shutter priority (Tv in Canon-speak), the experiment is toast. AE is bad because it can’t control the manual lens to match an aperture to its chosen shutter speed. Tv is bad because there is no feedback to tell me what shutter is chosen so I can pick an aperture.

Either I got lucky with a lot of exposure combinations or it does aperture priority. This also makes sense. When EOS was introduced, people who’d spent a fortune on the mechanical FD lenses screamed bloody murder. Canon even made FD to EOS converters with corrective lenses in them. With no way to communicate between the lens and the body, the only solution is to do aperture priority or manual (if the body lets you select the shutter speed).

Here’s my process. Turn the lens ring to wide open so the scene is bright and focus. Turn the ring to the f/stop I want and 1/2 press to turn on the meter.

Slow blinking ‘P’ = open up, use a tripod, or flash. Fast = figure out over or under & adjust.

Helios 44-2 at f/16. Metering at f/2, the ‘P’ in the viewfinder blinks indicating exposure out of range.

Some macro shots. I’ve had the broken balsa plane and cicada wing forever. Add feathers and a seed and I have a theme. To get some depth of field, I had to stop way down. F/16 was too dark. Not bad exposure dark, just not an attractive image.

F/16 with flash was too bright.

F/16 with some LED lights was just right.

F/16. I used flash but I was so close it was partially blocked by the lens.

Next I tried a Nikon adapter. It has a “Dandelion” chip for focus confirmation but the 750 ignored it completely. It works with a Canon 60D DSLR so it’s probably the age of the 750’s firmware.

Nikon 50mm at f/1.4.

Same scene at f/16 with flash.

I’m not sure what’s up with the flower images (ignore the dust and cat hair — that’s a different issue entirely). It might be the film — the Photoworks stuff has lost a lot of speed from age and tends to make really crummy, thin negatives. It’s also possible my notes are wrong. According to my notes, the first one is at f/2.8 but it’s so thin the scanner had to boost the gain and made it ugly and grainy just to get something.

Nikon at f/2.8.

My notes say f/11 and this looks OK.

F/16 with flash. Exposure is all right but the colors are way off. The wall isn’t blue.

While writing this, it dawned on me that the bad images are under artificial light. Everything else is outside or on the sun porch. It fits the symptoms if the old film lost sensitivity to specific wavelengths.

The short answer (too late) is: The EOS 750 works well as an aperture priority camera with manual lenses.

Thanks to Salvador for asking a good question leading me to this fascinating journey.