Showcase Canon 24mm EF-S STM


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Aug 31, 2013
The weird, long lost (and inexpensive if you don't count the Speedbooster) and possibly exotic cousin of the Olympus 17mm f/1.8 as a 17(.04!)mm f/2 lens. Size wise, they're actually ridiculously close given that the Canon has to mount on the massive throat diameter of EF mount. Must be debaffled to be used on Speedboosters, the baffle is the plastic piece that has a little rubber ring around it. You can pull the rubber ring off to get to the edge of the plastic piece and just yank with some force. There's some mild adhesives on the tab edges from what I can tell.

Do not use the white mark to mount it on the Speedbooster Ultra. That's for EF-S bodies. You align the bottom of the area where the AF/MF selection switch bulges out of the side of the barrel to mount it instead.
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Quick testing showed that it rapidly improves at the corners immediately at f/2.8. At f/4 the edges and corners hit peak and f/5.6 starts to soften the image a tiny bit. The center I think it has better contrast than the Olympus at f/2-2.8. The Olympus works up to f/4.0-5.6 pretty well for improvement but it doesn't have a rapid jump at f/1.8 -> f/2.8.

I believe this lens might be a smidgen better than the Olympus 17mm f/1.8 in certain cases but I will need to use it more to confirm this and do a MTF test out of curiosity. I know it is a pretty good performer on Canon but the Speedbooster Ultra should provide something like a 150-200% boost around wide open (my own testing with a 50mm f/1.2 vs plain adapter), which explains the behavior of this lens.

Autofocus is a bit slower for S-AF. C-AF doesn't appear to be reliable as of the current firmware on the date of this post when used in conjunction with the E-M1II but it does work with tracking - it'll just lose lock time to time (but maintains focus with the red box) and/or lose focus time to time. Also it makes a little bit of noise. Christopher Frost on Youtube has a review of this lens and you can probably find a good audio example of it.

It'll protrude in and out during focusing like the Panasonic 20mm f/1.7. If you disable reset lens, it'll stay in the extended state when you power the camera down. If you keep it enabled, it'll retract every time.

It also focuses closer than the Olympus 17mm f/1.8 (I know, Olympus lenses typically focus pretty close) at 0.16m/0.52ft versus 0.25m/0.82ft.

Absolutely an insane bargain at a dirt cheap $105 or so from the Canon refurb store if you buy at promotional periods. Taxes will probably apply but shipping is free for $100+ stuff and Canon has some yearly sale that I've noticed they do (Missed the 35mm EF-S Macro... Interesting lens with the lights. More interesting in that it becomes a 24.85~25mm f/2 with a built in macro ring light...)

If you have a Speedbooster already, I think this might be a worthwhile alternative consideration because it is a "flatter" Olympus 17mm f/1.8 with slower AF and lack of good C-AF on the E-M1II. The price is insane if you plunked the money down on the Speedbooster.
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I'll see if I can make a stl for a "short" baffle that covers up all the visible wiring later.
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