C300: Canon Speedbooster questions for C70

R

rweissman

New member
Two questions:

1) How important is it to use the mounting rails on the Canon .71x speed booster to secure normal weight EOS lenses? After 1.5 hours of trying, I have not managed to attach either of the rails. Not sure what the magic formula is, but I've experienced 1.5 hours of frustration. If they are not needed for normal weight lenses should I bother? And if. should bother, what's the secret in attaching the rails? While the wrench and mounting screws appear to be above the correct holes, the screws fail to attach to them.

2) I've tried several lenses--Sigma 35mm 1.4, Canon 100 L Macro, Canon 16-35 f4, and all work well. However, Iris control (auto/manual) is greyed out. Does the adapter not support auto iris?

Thanks for any help you can provide.
 
The regular RF to EF mounts don't need additional lens support so I fail to see why the Canon .71x would. That said, I don't have it yet so can't say anything from experience with it.

I believe I'd read that you can either mount it to the RF mount, or remove the RF mount and mount it naively. If that's true, I don't see the advantage of the latter. My plan would be to use it some of time so it would be ideal to be able to quickly switch it out with either the normal RF to EF mount when I'm using lenses that only cover Super35 or want a longer reach, or using the RF the PL mount.
 
I literally just threw on the canon 71 to my c70. It should be very simple so something may be defective with the camera. I unscrewed the 4 mount allen wrench screws/bolts surrounding the bolts. fit the speedbooster in and twisted until it clicked, then put the rails on each side. I did have to apply minimal pressure pushing the rail toward the lens but it lined up pretty easy. found this video below in case you havent seen it.

https://www.youtube.com/watch?v=p2FjNWahJ_8
 
Can any .71x owners tell us how EF-S lenses work on it if the C70 is set to super16 crop? How much of the S35 FOV do you get back?
 
Wouldn't third party EF-S glass mount? I can put a Sigma 18-35 on my 6D. And I can get a 17-55 2.8 to mount on full frame if I remove the rubber gasket.
 
drummondb said:
Wouldn't third party EF-S glass mount? I can put a Sigma 18-35 on my 6D. And I can get a 17-55 2.8 to mount on full frame if I remove the rubber gasket.
Click to expand...

I shouldn't have generalized. It's entirely possible that other Efs lenses will mount. I only tried it with my 17-55mm. The bulbous rear element collides with the bulbous front element of the focal reducer.
 
EF-S only applies to Canon. That is their creation and only they make EF-S lenses.

3rd parties who develop lenses for APS-C/S35 sensors have a standard EF mount.
 
SO can anyone do the math for me? Super 35 lens on the .71x speedbooster, and the camera set to super 16mode? Still a big crop right?
 
It's tough to visualize how much for sure based on different image circles, but I'd say definitely on the wider lenses, and only darker corners - unnoticeable to many - on the normal, tighter FOVs.

___

Kind of relevant...check out this test of the 18-35mm on a full-frame camera.

The 35mm end could be passable for many so think about how a 50mm+ would look...after the focal reduction and then the S16 cropping, lol.

https://www.youtube.com/watch?v=r0A0pkq5zWU
 
I guess I should I ask first: does the C70 let you enter Super16 crop mode if the speedbooster is attached?
 
drummondb said:
SO can anyone do the math for me? Super 35 lens on the .71x speedbooster, and the camera set to super 16mode? Still a big crop right?
Click to expand...

About 2 x crop.

Calculated Results
Crop Factor
1.98
Effective Focal Length
69.33
Effective Aperture (DoF)
2.77
Crop Factor with Speed Booster
1.41
Focal Length with Speed Booster
49.22
Aperture (DoF) with Speed Booster
1.97

Chris Young

More here:
https://danielscottfilms.com/crop-factor-calculator/

C70 calculated crop.jpg
 
Awesome site, Chris. Thanks! Looks like it's 2x with no speedbooster, right? But 1.41 with the speedbooster?

So a Sigma 18-35mm f/1.8 would be a 25-50 f/1.2 (with the DoF of about f/2.5)?
 
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