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02-26-2010, 11:15 AM   #1
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what is "focusing helical position" and does my Sigma 105 care about it?

Found this over at photo.net:

QuoteQuote:
With a Canon or Nikon, most professionals end up using their 70-200/2.8 or 80-200/2.8 zooms as portrait lenses. These 3 lb. monsters aren't very pleasant to handhold, though, and if you know that you're only going to do portraits, you're better off with a prime lens. Prime lenses are lighter and give better image quality. Unfortunately, the prime lens in this range that a serious photographer is most likely to own is the 100 or 105 macro. These are very high quality optically but difficult to focus precisely since most of the focusing helical precision is reserved for the macro range.
What does this last (italicized) sentence mean?

Does this apply to my Sigma 105 f/2.8 macro?

Will

02-26-2010, 11:30 AM   #2
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QuoteOriginally posted by WMBP Quote
Found this over at photo.net:



What does this last (italicized) sentence mean?

Does this apply to my Sigma 105 f/2.8 macro?

Will
It does mean, that the writer does not know, what he is writing…

Ofcourse in a macro lens, the travel of the helical will be much longer or finer graduated at macro distances than at far distances. It is exactly the same as with any other prime lens, where the graduation gets finer, the nearer you focus. At portrait distances you will not see a difference a macro lens and any other lens of the same focal length, apart from the general differences between different makes and models.

Ben
02-26-2010, 11:34 AM   #3
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It refers to the mechanical components in the lens that shift the element groups when the user changes the lens focal distance. In other words, the person above is claiming the mechanical components in a true macro prime lens that make it accurate at close range can make it sloppy at long distances. It could be true. Focusing helical precision more or less refers to the built-in tolerances between the parts that allow them to move.
02-26-2010, 11:42 AM   #4
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Actually, it's possible but I think many of the folks who claim true macro primes are not very good for medium and long shots may be falling back on experiences with macro lenses from decades ago. It doesn't help that many of the decent macro primes today must also be driven by AF motors which can require more tolerance in the parts.

I do know my Nikon AF60/2.8D micro (macro) lens is a wonderful lens but it can be a trick to focus manually.

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