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10-24-2009, 08:42 AM   #31
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The DA70 vs FA77 discussion is rather academic. I recently opted to buy the FA77 over the DA70 simply because it is faster. I expect to use this focal length for (but not exclusively for) available light/informal portraits and the faster lens is more apealing for that purpose.

Mark makes the point about shallow DOF but even if I crank up the ISO a bit and shoot at f2.8 or f4.0, of which the DA70 is capable, I still have the brighter viewfinder to make composing easier. All my other lenses are f2.8 or slower and I just wanted something faster and MTF numbers notwithstanding, the IQ and bokeh on the FA77 is superb. Perhaps there is a measurable difference in auto-focus speed, but in practical terms, the FA77 snaps into focus quickly and I have no complaints, plus I like the built in lens hood.


Last edited by MikePerham; 10-24-2009 at 09:06 AM.
10-24-2009, 10:01 AM   #32
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QuoteOriginally posted by creampuff Quote
And yes the DA 70mm does focus a little faster, but I attribute it to the fact that the lens elements are smaller. Being smaller and lighter in weight less effort is needed for the motor to initiate AF. Practically speaking yes there is a difference, but to me it is small and not significant.
For the record, I'm in total agreement with you on all counts here. As someone who is as likely as not to focus manually, AF speed wasn't a huge consideration in my own decision-making. In my case, quick shift, lighter weight, and lower price that did.

Had I perceived a *need* for the larger aperture at this particular focal length, or if had been disappointed with the IQ of the images from the DA70 I had seen, I I'm sure I'd have ponied up the extra $$$ for the 77, and accepted the lack of quick shift. Actually, I might have simply bought an M85/2. But I know that for my purposes, f/2.4 at 70mm is enough, and I'm perfectly pleased with the IQ.

Point being, everyone has their own set of criteria for making these decisions. While sometimes I might get involved with telling people why they should or shouldn't care about a given feature or aspect of performance, those generally end up being losing arguments.

QuoteQuote:
Please let us know how a lens' sharpness wide open has any correlation to greater AF speed? I think it is you that needs to show the evidence, not me. Please don't call it common knowledge when it isn't.
Hmm, well it's something I've read many times over and just sort of assumed to be true because no one had ever questioned it before. But now you've got me curious, so I looked it up. Found a few interesting references to various aspects of focus performance; nothing particularly conclusive. This one in particular from the almighty Wikipedia I found especially thought-provoking:

"The speed of the AF system is highly dependent on the maximum aperture offered by the lens. F-stops of around f/2 to f/2.8 are generally considered optimal in terms of focusing speed and accuracy. Faster lenses than this typically have very low depth of field, meaning that it takes longer to achieve correct focus, despite the increased amount of light."

But overall, I'd say I failed in finding anything worth posting as "evidence", so since it doesn't seem to actually matter to the discussion, I'll simply withdraw that claim.
10-24-2009, 01:53 PM   #33
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The best way to choose yourself one of the awesome 70's is to simply look at photos in PPG or pbase and determine which lens renders images the way you like. I went for the fantastic sigma 70 which is of course slower than the other two and weighs a ton. Mind you I got my lenses before the da 35 and da 15 were released so my 3 prime setup (14, 43, sig70) is a little more bulky than what you can get now (15,35,70)
If only i had the money to own all three 70's I would!
Cheers
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