[INACTIVE] Sony NEX-VG20 User Group

Why would I want a Focal Reducer?

Francis Ament (GrooveENERGY)

Francis Ament (GrooveENERGY)

Great article.

I have a question about the method of setting up the back focus of the Speed Booster as I'm not sure what a "grub screw" is for this adjustment. I think this method may help me out for an issue I'm having. On the weekend I tried taking time-exposed pictures of the night sky and found it very hard to focus (due to the image being very dark). I tried to rely on setting the Canon lens to infinity, but found it slightly off, so I experimented with guessing the focus.

Here are two samples:

This one was pretty good: fbcdn-sphotos-a-a.akamaihd.net/hphotos-ak-ash4/1053531_10201388221172192_819108876_o.jpg

This one had focus issues, as did many others. I decided not to upload them due to this issue.

fbcdn-sphotos-b-a.akamaihd.net/hphotos-ak-ash4/1049042_10201388223452249_1114395013_o.jpg

This is the album on FB. All photos were taken with the VG20.

facebook.com/francis.ament/media_set?set=a.10201388179531151.1073741826.1374143666&t

Craig Marshall

Craig Marshall

Nice shot! The 'grub screw' is a miniature Phillips head screw in the perimeter of the rear bayonet mount of the Speed Booster. You need to loosen it off so the rear glass element can be easily rotated. My 50mm lens was giving true 'infinity' at the '3 metre' setting - way out- so I rotated the rear element about two turns clockwise. If your lens is just a bit 'off', go +/- a quarter of a turn till you get it right.

Francis Ament (GrooveENERGY)

Francis Ament (GrooveENERGY)

Thanks for the advice. I tried it out and it seems that I didn't have to adjust it much. Since I live in the city, I'll have to wait 'till I get to some place dark enough for a good shot. I'll bring my screwdriver to "tweak" the lens a bit more. From my initial test in my backyard, the faintest stars seemed pretty sharp, but it was a hazy sky, so the test wasn't the best.

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