GH2 Speedbooster Focus Shift on Sigma 18 - 35

[jimmiesner]

I was testing out my new speedbooster adapter on my Sigma 18 - 35 and I noticed when I zoomed in and out the focus changes quite a bit. Is this normal using a zoom lens on a speedbooster adapter?

Jim

 

[Bjorf]

Hi,

I doubt that the Siggy 18-35 lens is a parfocal lens. Most DSLR lenses aren't. As a result, focus will change when you zoom, with or without the Speedbooster. Some lenses are worse than others.

Cheers

 

[mcbob]

Do a web search for "speed booster adjust" or similar... The SpeedBooster allows adjustment so lenses can be properly collimated. I noticed my Sigma to be parfocal on a Nikon body but varifocal on m43 adapters (including my SB). After adjustment, my Sigma became parfocal with the SpeedBooster. It's still varifocal with both of the cheaper non-SB adapters I own.