Idly thinking about an EF speedbooster

[kye]

I'm idly contemplating buying a Metabones Ultra 0.64x speed booster for my GH7.  This would take me into the world of EF for the first time.

I'm completely familiar with speed boosting and crop factors and all that jazz, with years of experience from my 0.71x M42 to MFT speed booster and (many) M42 lenses.

What's the deal with speed boosting to EF?  
Is the Ultra 0.64x worth it over the normal 0.71x adapter? (they seem to be similarly priced used).
Is there a different one I should consider (other than Metabones)?

Essentially I'd be getting it to shoot shallow DOF (like I do with my M42 Takumar 50mm F1.4, etc) but with more modern / cleaner results as M42 lenses are quite vintage and far dirtier than fast EF glass, especially when shooting wide open.  AF is of little importance to me, so I'd be expecting manual focus.

[stephen]

I've used Metabones Ultra 0.64x speed booster with my Blackmagic Pocket 4K. Compared to 0.71x is moves your crop factor a tad closer to FF 0.64x -> 1.28x vs 0.71 -> 1.42x  and gives you a little bit more light (1/3 stops) and a little bit more DOF. You can use it not only with Canon EF but all lenses which have flange distance > than Canon EF. Like Contax Yashica, Nikon, m42, Pentax. Biggest issues for me is the weird crop factor. x2x0.64 = x1.28. Now I want an angle of view equivalent to 35mm in FF. Which lens should I use ? 28mm as 28x1.28=35.84 And so on. That's why I moved to FF. 35mm is 35mm no matter if lens is vintage or modern, plus I can use Minolta MD, and a bunch or other brands and bayonets. No need for speed boosters. Lens is used exactly as it was intended by the manufacturer. Sensor if big and has no problem with low light. For vintage lenses and in general for lenses alone FF is the way to go for me. I was tiered to calculate crop factors and deal with speed boosters.

[eatstoomuchjam]

7 hours ago, kye said:

What's the deal with speed boosting to EF?  
Is the Ultra 0.64x worth it over the normal 0.71x adapter? (they seem to be similarly priced used).
Is there a different one I should consider (other than Metabones)?

The difference is not huge.  When wide open on very fast lenses, you're more likely to see some speed booster artifacts with the 0.64x.  Whether those artifacts are acceptable is personal taste.  If the prices weren't similar, I'd just take the cheaper one.

I was also surprised to find that the 0.64x covers the slightly small S35 sensor in my Z Cam E2-S6G.

Anyway, as far as other brands, I think that Kipon's focal reducers are well-regarded.  Otherwise, most of the third-party ones are skippable/don't seem to be too good.

7 hours ago, kye said:

Essentially I'd be getting it to shoot shallow DOF (like I do with my M42 Takumar 50mm F1.4, etc) but with more modern / cleaner results as M42 lenses are quite vintage and far dirtier than fast EF glass, especially when shooting wide open.  AF is of little importance to me, so I'd be expecting manual focus.

FWIW, you can also have your cake and eat it with a focal reducer, if you want.  Pentax K, Nikon F, Leica R, Olympus OM, and M42 lenses (including your Takumar) can all be adapted to EF mount.  I've also thought about building a recessed M39 adapter since it would be theoretically possible on any camera without a mirror assembly (M39 is 28.8mm and EF is 44mm, but I have several M39 lenses with controls near the front and that are skinny enough that they could just sit further back in the EF mount).

Anyway, for EF lenses otherwise, do you know which you're considering?