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09-15-2011, 11:53 AM   #1
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PENTAX DA 70mm F2.4 Limited vs Sigma 17-70mm

Has anyone compared the image quality of the Pentax 70mm to the Sigma 17-70mm @ 70mm focal length?
Any opinions about these lenses?

For certain photography I shoot 70mm 95% of the time, and I was wondering if it is worth investing in a dedicated lens. It would not make sense if the image quality is about the same.

Thanks

09-15-2011, 12:06 PM   #2
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I don't think it's even fair to compare the two. For starters, the prime is much faster (f2.4 vs Sigma's f4.5 at 70mm). Second, it's a limited lens, which means it has a certain ineffable IQ factor... Third, the difference in weight/size is significant. Third, the DA 70mm is a limited--have I mentioned this? Which doesn't mean you can't take superb shots with either.
Check out these links to compare them:
Full-size sample photos from Sigma 17-70mm F/2.8-4.5
Full-size sample photos from Pentax 70mm F/2.4

Be sure to make pics full-sized, otherwise they might look the same.

For an independent review of the two lenses,
http://www.photozone.de/pentax

Last edited by causey; 09-15-2011 at 12:25 PM.
09-15-2011, 12:22 PM   #3
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why not just go for the 70mm? that way, you'd have the best lens for 95% of shooting situations
09-15-2011, 12:48 PM   #4
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The Sigma is a big/heavy lens....

09-15-2011, 12:50 PM   #5
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I forgot to mention that I currently have the Sigma 17-70mm....
09-15-2011, 12:58 PM   #6
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The DA70 is a magnificent lens; when I acquired it, I wasn't ready for how well it resolved. It has splendid contrast for crops. It pointed out to me how many things I needed to work on in my photography.
09-15-2011, 01:09 PM   #7
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Well, if you have the Sigma...

1) Has it ever been a hindrance in shooting, both in weight and size? the 70mm range feels like far portrait to short telephoto to me, so I would be using it more indoors than outdoors, or in a private outing.
2) Do you shoot wide open often, or is it always stopped down? I'm not sure if the DA 70 is that much more amazing when compared to the Sigma stopped down to F8. Could be though, if someone more knowledgeable could correct me.
3) Would you miss landscape shots?
4) Is it a problem to actually have both lenses, and alternate times you need to take them with you?
09-15-2011, 03:47 PM   #8
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If you don't have any prime so far, then getting the DA70 is definately a good idea if you like that FL. I believe you will soon realize what difference it makes and buy more prime lenses... As I did before.

09-15-2011, 04:55 PM   #9
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The Sigma will excel over the Pentax DA70 in one area... minimum focusing distance. In every other respects, the Pentax wins, but then again, the Sigma can go a lot wider...
09-16-2011, 11:08 AM   #10
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Thanks for your responses so far. The reason I am deciding this is because my Sigma seems to be acting up a little lately. So I can decide to buy the Pentax 15-21-40-70mm series, or simply buy another Sigma. When I use the Sigma at 70mm, I stop it down to f/6.3 - f/8. At four times the price with the Pentax primes (plus new filters), there would have to be a significant improvement in the image quality (e.g. flare resistance, bokeh, resolution, contrast, etc.). I might just have to rent the lenses and play with them to get a feel for image quality myself. Also potentially having to change lenses all the time might be a disadvantage when using primes...
09-16-2011, 12:59 PM   #11
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QuoteOriginally posted by causey Quote
Second, it's a limited lens, which means it has a certain ineffable IQ factor
I believe the OP tries to measure just that. Saying it's good BECAUSE it's a limited doesn't say much, and could even be false for all we know

QuoteOriginally posted by JinDesu Quote
4) Is it a problem to actually have both lenses, and alternate times you need to take them with you?
That's what I do with my primes/zooms lineups.

QuoteOriginally posted by Eric Seavey Quote
So I can decide to buy the Pentax 15-21-40-70mm series
I own the Sigma (and love it, it's an excellent lens really) but my primes lineup is not a duplicate of the Sigma's range : 21-50-100 (macro). I find that more comfortable.

to anwwer your question, I'd say if you have no other prime and don't particularly like shooting with them, a high-quality zoom like the Sigma is a great tool. For me that Sigma is my main go-to lens. However it's not my favourite lens, that would be the DA21 or 100 macro WR, probably.
09-17-2011, 06:18 AM   #12
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I use to have the 17-70 and I think it was a great lens, If I was in you situation I would maybe look at the FA77mm or maybe an 85mm lens. That way you get a diffrent lenght added to your lineup.
My 17-70mm started acting up also, one of my reasons for looking at new lenses. I handed it down to my father, he still uses it and it works fine ( 2 years later ).
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