Anyone try Metabones Speed Booster on a Nikon Mirrorless body?

[Kim Pilegaard]

I have a cheap PIXCO Speedbooster with a focal length extension of 0.7x. It is originally for Nikon G to Sony E. With a Sony E to Nikon Z adapter, I can make it useful on my Z7 II. However, the specs says that it has a max. f-stop pass through of 1.4, so I do not gain anything using it with the 50/1.4.

[BruceSD]

I have a cheap PIXCO Speedbooster with a focal length extension of 0.7x. It is originally for Nikon G to Sony E. With a Sony E to Nikon Z adapter, I can make it useful on my Z7 II. However, the specs says that it has a max. f-stop pass through of 1.4, so I do not gain anything using it with the 50/1.4.

That's strange.   1.4???   A genuine Metabones .71x Speed Booster has a max speed ceiling of .9 ! 

[Bill De Jager]

Very nice results, Bruce.

I want to see if I understand focal length reducers correctly.  Based on my readings, depth of field varies proportionately to aperture and by the inverse square of focal length.  So if focal length is multiplied by 0.71 (inverse square root of 2) while aperture is made one stop wider (factor of 0.71, also the inverse square root of 2), then depth of field should be the same. 

This is assuming that distance to the subject plane in focus doesn't change to compensate for the changed field of view.  If the camera is moved closer to compensate for the changed field of view, then I think depth of field is reduced by the inverse square of distance.

Do I have this right or am I missing something?

[BruceSD]

.
Forget the math.

Everything you need to answer your question can be found in the second link in my first post.   Check it out.