GH5 How much of the front lens area is used for Focal Reducer to EF lens by the m43/GH5?

A

analogs

Well-known member
I have my GH5 attached to Focal Reducer 0.71 then to a Canon 16-35 f2.8 II L Lens that has an 82mm front diameter.

Based on the widest 16mm focal length, how much of the 82mm front is used by the GH5?

I could probably solve this by just placing a paper cutout and see where the vignetting occurs, but I would like to know, if there is a general formula or concept behind this without doing actual physical tests.

The reason I am asking, is that I have a 52mm wide angle converter which I am considering using by attaching an 82-52mm step down ring to the 16-35mm lens so that I can get wider shots?

Thank you.
 
I don't know the exact answer, but you might find this link useful.

A wide angle converter will likely soften everything but the center of the frame and introduce more distortion and chromatic aberration.

You'd be better off using an ultra wide angle lens. According to this link you can use a Tokina 11-16mm @ 12mm and 0.64x SpeedBooster without vignetting.
 
You likely can answer your own question easily by just putting the step down ring in place to see how much vignetting exists - my guess is a lot.

B
 
The math I use would be 82÷(43.3÷(22÷0.71)) = 58.68mm

Also, the thickness of the converter has to be taken into effect.

I don't think it's gonna clear.
 
Don't ever just trust a formula. Stick it in front of the lens and see what it does. I don't think its going to work well. Step down is usually not a good solution. In some cases stepping down a tiny amount may be ok.

You should also check it throughout the zoom range. Wider FOV might show more issues.

You might have to consider investing in a larger wide angle converter.
 
I'd skip the wide angle mush master converters and buy a cheap wider lens. Any converter worth an image is going to cost a few hundred dollars, and for around 3 hundred you could buy an 8mm or 7.5mm in mft or a 12mm in ef.

If you already have the screw on converter, the price of the step down ring is cheap enough that you can just try it.
 
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