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I know this isn't the ideal setup but I have access to a good selection of Minolta glass so I can try it without any expense.

I've got a Canon 600D, a "Minolta Sony Alpha AF Mount Lens to Canon EOS EF mount adapter" and some Minolta lenses, including the 70-210mm f/4.

With the recent blood moon I mounted the 70-210 on my 600D to try and get some half decent shots. The movement of the moon was one thing but mainly my focus at infinity was useless. I thought it was maybe at infinity slightly back from the stop, but that produced worse results. I then tested at a building ~70-100m away from me in the day time, but it was still very soft.

This was all with a tripod and remote trigger so I don't believe it to be a stability issue. Similarly, my manual focusing skill are poor but I can get it pretty sharp when I'm focusing on near field objects so this does seem to be an infinity focus issue.

Can anyone confirm if this is a register distance issue?

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It's definitely worth reading Can I use lens brand X on interchangeable lens camera brand Y? and the answers to Why I can't find an A-mount to Canon EF Adapter?, but the issue here is that the registration distances for the Canon EF mount (44.0 mm) and Minolta A mount (44.5 mm) are very close - just 0.5 mm apart. This means that for an adapter to allow infinity focus, it would need to be just 0.5 mm thick and that's not enough to contain all the physical bits needed to get the lens mounted - therefore you do lose infinity focus when trying to mount an A mount lens onto an EF mount, unless the adapter has a glass element in it.

  • Ahh, I read a bit more after posting and thought that may be the case, but wasn't sure. Thanks. Is it the case that down to the minimal focal length is ok or are both ends of the focal range affected? – Linef4ult Oct 8 '15 at 11:14
  • My adapter claims to have an optic to adjust for infinite focus, but clearly thats not working. How likely is it that another brand might do a better job or is just not worth it? – Linef4ult Oct 8 '15 at 14:52

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