GH4 Speedbooster question - optimal fstop

Samir Patel

Samir Patel

Active member
This may be a dumb question but here it goes. So I know that each lens has an optimal f-stop when it comes to sharpness before diffraction occurs and I know that when using a speed booster that it will report a 1 stop increase through the camera. So lets say my 50mm Nikkor's optimal sharpness is at f/8 traditionally. Should I no be concerned when shooting at 5.6 when I have using the speed booster? (As going up to f/8 in a speed booster enabled camera - I would think is really shooting at f/11). What do you think?
 
The Speed Booster doesn't actually change anything to a lens, except using more of the outer edges of the lens its frame due to the 0.71x magnification.
You get an extra F-stop because the focal length changes. As you know, the f-stop is the ratio between focal length and lens opening. The lens opening stays the same, but the focal length becomes shorter (wider) and thus you get an extra f-stop.
This doesn't change anything to the optics of the lens and how they function. So if F8 on the aperture ring on your lens gives the optimal performance, then this will still give the optimal performance with the Speed Booster attached. You've just gained extra light and a wider focal length.

Hope this helps.
 
mr bill said:
Just to be pedantic, using a speed booster means using less of the outer area of the lens.
Click to expand...

Don't you mean it uses more? With Speed Booster the entire lens image area is condensed down to a smaller size which means you see the entire lens area. Not using a Speed Booster means you are only seeing the middle portion of the FF lens and therefore cut out the softer edges of the lens.
 
Maybe not relevant, but I bought a Sigma 30mm f1.4 lens that was absolutely unusable at 1.4 on a speedbooster, like someone smeared vaseline on the lens, so I returned it.
 
Batutta said:
Maybe not relevant, but I bought a Sigma 30mm f1.4 lens that was absolutely unusable at 1.4 on a speedbooster, like someone smeared vaseline on the lens, so I returned it.
Click to expand...

FWIW, the Speed Booster will increase the sharpness/contrast (i.e., MTF) of nearly any f/1.4 lens except for a handful such as the Zeiss Otus that are already so sharp at f/1.4 that there's not much headroom for further improvement. I've tested the 30/1.4 Sigma Art lens, and found that it works really well with a Speed Booster. In fact, the resulting 21mm f/1.0 lens is significantly sharper than the Voigtlander 25mm f/0.95:

Comparison Matrix.jpg
 
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