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11/11/2005 06:56:47 PM · #1 |
| I'm looking for a teleconverter for my G6 but I really don't know too much about lenses. What do you think of this deal |
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11/11/2005 07:04:28 PM · #2 |
7 elements, with 4 of those split off into 2 groups, so like 2 1 2 1 1 from front to back or something. Meaning that some of the lenses are set up in doublets.
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11/12/2005 07:08:04 PM · #3 |
| I'm even more confused now. :) |
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11/12/2005 07:12:43 PM · #4 |
| 7 elements means 7 pieces of glass. 5 groups mean 5 separate groups of pieces of glass together (most of which consist of just 1 piece of glass, by the sound of it) separated by gaps, possibly variable in distance, for focusing and/or zooming, or just spacing out the lens. |
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11/12/2005 07:17:12 PM · #5 |
A group of two elements (a doublet) is sometimes used to correct chromatic aberration.
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11/12/2005 09:15:42 PM · #6 |
| Thank you. So the more elements and groups the better? |
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11/12/2005 09:19:14 PM · #7 |
Originally posted by A4wheelin:
Thank you. So the more elements and groups the better? |
Well, sorta. Depends on the type of glass you're using. I guess if you're using crappy glass and have a good design, you can minimize the effects brought on by using bad glass, but nothing is a substitue for a finely made lens.
I've not used on myself, but some of the pictures I've seen have made me uneasy enough to skip it and save my money for a dSLR...
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11/13/2005 12:24:25 PM · #8 |
Originally posted by A4wheelin:
Thank you. So the more elements and groups the better? |
It depends entirely on the type of lens. Fewer elements is advantageous in some circumstances, as there's less room for flaws and imperfections in the glass, and less glass means more light getting through. Longer lenses usually tend to need more elements, especially zoom lenses, to correct aberrations at all focal lengths. Here's a good example - the 100-400L IS USM:
This has 17 elements in 14 groups, but the groups themselves are in only 6 clusters which will move relative to each other both in zooming and focusing. In theory there's no reason why you couldn't build the same lens with just one element in place of each of those clusters, with the same functionality - except of course it would have appalling chromatic aberration and inconsistent focus.
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