Remember the Seagull 50mm F1.8 MC Minolta MD-mount lens I had for my infrared-modded Fujifilm Digital Q1 camera? It now has a prime companion, the Vivitar 24mm F2.0 Olympus OM-mount lens.
Assuming ISO400 sensitivity:
Compared to a 50mm F1.4, it has the same darkness performance, giving steady shots at absolute EV4.66. How so? The F2.0 would be one stop darker than the F1.4… but because it is one stop wider (to be exact, 25mm is one stop wider) it can use one shutter speed stop slower. Bokeh is two stops smaller, but it’s a practical walkaround lens. The Nikkor 28mm F1.4D is the most expensive wide prime, which can shoot in EV4, merely 2/3rds of a stop darker than this 24mm F2.0. (A Canon 50mm F1.2L lies halfway between, in terms of dark performance at EV4.33.)
Top, from left to right: Fujinon 50mm F1.4 EBC lens (Fujica mount but without lens body), Seagull 50mm F1.8 MC Minolta MD-mount lens, Vivitar 24mm F2.0 Olympus OM-mount lens, Cosina 19-35mm F3.5-4.5 MC Pentax K-mount lens, 35mm-equivalent manual focus webcam lens.
Below: The Seagull (left) is joined by the Vivitar.
This time around, I made an effort to document approximately where I should set the manual focus to camwhore at arm’s length.
The Olympus OM mount is unique – the depth-of-field (DOF) preview button is on the lens, not the body; the lens release button is on the lens as well. However, the lens I bought had a problem – the DOF preview button did not work. So I’d be stuck at F2.0 all the time. And so, I opened the lens, taking care to separate screws of different layers, by putting them on different filters (top row).
The underside of the rear-most piece; on top is the DOF preview button, which pushes the lever; below is the lens release button.
I then removed the aperture ring (on left) and a tiny ball bearing dropped out onto the lens. Arrow denotes where it came from; the ball runs along the notches on the lens, to make the clicks you feel on your aperture ring.
Finally, the root of the problem! It took me a while to figure out what controlled the aperture, since a DOF preview system is complicated and has a few springs. The problem was that the spring on the left was supposed to pull a lever (in the middle, nearer to the lens) that closed the aperture blades. The spring did not have enough tension to pull the lever!
Note the loose spring in the bottom-left corner; the hook was loose. This lens had 6 circular aperture blades.
After toiling about, I decided to superglue the spring solidly to the mechanism! I removed the other spring that returned the lever to open the aperture blades. The downside was that once I had pressed and released the DOF preview button, the aperture would stay closed. Fortunately, I could open the aperture by turning the aperture ring.
I suppose the spring weakened because the previous owner tried to forcefully press the DOF preview button while the lens was at F2.0. The DOF preview button, I found, was supposed to provide resistance; it should only travel all the way down if the aperture was at F16. You should only be able to half-press it at F2.0, at which point the springs would stop you.
I also suppose that the previous owner (or someone unfamiliar with the camera) tried to press the DOF preview button while at F2.0, thinking it was the lens release button. Since it didn’t dislodge he/she would’ve pressed harder, breaking the spring. Ouch! I wonder if any other Olympus OM system users have this problem. I hope Google leads all you broken-DOF-button-Olympus-users here!
I prefer the rear diaphragm lever method used by every other non-digital lens.
And now, a group photo from left to right: infrared-modded Fujifilm Digital Q1, and them lenses in order of brightest to darkest, coincidentally going wider, too.
The infrared-modded Fujifilm Digital Q1 puts on the 24mm F2.0 after the fixing. Note the screw in the rear lens cap; it locks the lens in place. The button with grooves is the lens release button. I don’t know why, but with this lens-to-sensor distance I can focus closer than the lens says, and yet focus beyond infinity.
I had to reopen the lens when I pressed the DOF preview button and weakened the spring. More superglue!
I had to reopen the lens again when it seemed to be focusing close; the lens was too far out despite being screwed all the way back in. The giant screw thread that connects the lens to its housing has a few entry points! Enter the wrong one, and the lens will have the wrong distance and thus lack the correct focusing range.
Alright, enough of the tech talk. I’m stoked to have opened and fixed my own lens mechanism!
24mm with a crop factor of 6x gives a 144mm equivalent focal length.
Okay, so the depth of field is nothing to shout about.
However, reversing the 24mm in front of my Canon Powershot A520 at 140mm equivalent, closest manual focus, gave the image on the left. The right-side image is from the reverse Fujinon 50mm F1.4.
This might put a scale to things; text was typed on my phone; focus was not changed with lenses.
So how’d I choose the lens to use?
The Seagull 50mm F1.8 is great for performances and shooting candid shots from a distance. The Vivitar 24mm F2.0 is usable, twice as wide, but not a stalker lens. The Cosina at 19mm is the widest I have… but F3.5 seems rather dark, and it seems sharper at the 35mm F4.5 end!
I say it’s dark because the Fujifilm Digital Q1 is very basic, lacking ISO sensitivity control. It will only go to ISO200 if it is at 1/15th of a second and can’t budge (the slowest it will go.)
Perhaps when I’m free, and it’s bright, I’ll compare the Cosina at 24mm at F8 versus the Vivitar at 24mm F8.
You could also say that I don’t have an allegiance to any camera/accessories brand; I have:
Cameras: Canon, Fujifilm, Nikon Coolpix 2200 (in repair)
Filters and rings: Hollywood, Hoya, Pixel, Raydawn, Toshiba, Vanguard
Lens mounts: Fujica, Minolta MD, Olympus OM, Pentax, 52mm screw thread
Lenses: Cosina, Fujinon, Seagull, Vivitar
Memory cards: Fujifilm, Kingston, Nokia, Olympus, Transcend
Oh, and GP batteries. Yeah.