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10-04-2009, 07:59 AM   #1
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Problem with non Pentax lenses

The only lens I use that is not a Pentax is my Sigma EX 105/f2.8 Macro. This is a great lens and the only one of the lenses I kept when I switched from 35mm film to APS-C digital.

I have my K-7 USER setting configured to use on a tripod - now I do not have the lens correction features activated for hand held use, as this is mostly at event photography etc., where the long delay in the image processing is a problem. Not so on the more deliberate type of photography when using a tripod, however, the lens correction feature does not work with non-Pentax lenses. Not that there is much to correct with this lens ...but another reason to shoot with Pentax glass. I will wait to see what Pentax will produce with macro lenses dedicated to the APS-C format, already have the 35mm limited macro ...need something around 70mm now.

10-04-2009, 08:44 AM   #2
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If the lens doesn't need correcting, which you mention, then why wait for Pentax to make a lens that does? I have lenses of several brands, 4 of them Pentax. A good sharp lens is just that, a sharp lens. You seem to expect that a lens will be a little "off". When I buy a new lens I expect it to be right and if it isn't it goes back. The lens correction feature might be a bigger consideration when buying used glass that you may be stuck with.
10-04-2009, 09:39 AM   #3
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QuoteOriginally posted by reeftool Quote
If the lens doesn't need correcting, which you mention, then why wait for Pentax to make a lens that does? I have lenses of several brands, 4 of them Pentax. A good sharp lens is just that, a sharp lens. You seem to expect that a lens will be a little "off". When I buy a new lens I expect it to be right and if it isn't it goes back. The lens correction feature might be a bigger consideration when buying used glass that you may be stuck with.
Well you are right ...not a big deal with this lens, but all lenses under certain situations are subject to CA and I have made a decision to stick with Pentax glass. Given todays technology, and the way lenses and bodies communicate with each other, I just feel better avoiding 3rd party lenses that may not be 100% compatible in this regard.

Anyway, the 105 seems to be between focal lengths with the APS-C for macro/close up work; I think 35, 70 and 135 would duplicate what we had in the 35mm days and what most of us are accustomed to.
10-05-2009, 08:07 AM   #4
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I only have one Sigma, the fairly cheap 70-300 and I am quite satisfied with the lens. I am seriously considering the 17-70 right now. It's a size that worked very well for me on my Nikon Pronea (aps film SLR) and the 55-70 range is the only size range I now lack. The Sigma has a lot of good reviews and is also a macro along with being a hundred dollars less than the Pentax. I'm really not sure if the capability to fine adjust the lens to the camera will make that much difference. I certainly can't complain about any Pentax lens I own, all are great performers. As I compare the Pentax and Sigma 17-70 lenses, the Sigma is faster on the short end (f2.8) and has macro which makes it a little more versatile as a walk around. Going back to your first post, do I go without a lens I think would work very well for the way I shoot right now because Pentax doesn't make it? I am not knocking Pentax or the quality of their glass in any way, just that the aftermarket lens makers also make some quality products that may meet someones uses better than Pentax's lineup.

10-05-2009, 08:16 AM   #5
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And that's the point

QuoteOriginally posted by MikePerham Quote
but all lenses under certain situations are subject to CA and I have made a decision to stick with Pentax glass. Given todays technology, and the way lenses and bodies communicate with each other, I just feel better avoiding 3rd party lenses that may not be 100% compatible in this regard.
That's the point of this feature. I'm willing to bet money that Hoya sent a little note to the Pentax designers and said "lets have a feature or 2 that only works with DA lenses. We are the most backward compatable brand and it's killing the bottom line. Canikon changed the mounts and they get to sell their own lenses all day long while these cheap Ba****d's buying Pentax are taking great shots with 40 year old Taks."

I would be willing to bet that in a few years there will be a few other features that are Pentax glass only. This little thing already has you thinking Pentax only. So that's the point now isn't it?
10-05-2009, 05:44 PM   #6
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QuoteOriginally posted by Peter Zack Quote
I would be willing to bet that in a few years there will be a few other features that are Pentax glass only. This little thing already has you thinking Pentax only. So that's the point now isn't it?
No doubt you have a point here ...however, it doesn't bother me much. Of many of my lenses, there are no choices outside of Pentax. The 50-135 and 35 macro limited, FA 77 and many other Pentax lenses are unique. As I mentioned in my orginal post, the only non Pentax lens I use now is the Sigma EX 105/f2.8 macro ...a good lens and one I will keep till something better comes along.

I have some old A and M series lenses that I never use because of the minor annoyance of having to manually enter the lens data into the camera. I just don't see any logic to paying the price of a K-7 and then going cheap on old lenses that are not able to offer all the advantages of todays technology. But ...each to their own and Pentax have a big following of legacy lens users ...that may well be phased out as you suggest over time.
10-05-2009, 07:24 PM   #7
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QuoteOriginally posted by reeftool Quote
The Sigma has a lot of good reviews and is also a macro along with being a hundred dollars less than the Pentax. I'm really not sure if the capability to fine adjust the lens to the camera will make that much difference.
The Sigma is not a true macro lens, it's only 1:2.3. The Pentax does have close focus ability, but not as much at 1:3.2. Neither lens is exemplary for CA, vignetting and especially distortion, so the K-7 corrections should make quite a difference.

QuoteOriginally posted by reeftool Quote
As I compare the Pentax and Sigma 17-70 lenses, the Sigma is faster on the short end (f2.8) and has macro which makes it a little more versatile as a walk around.
You seem to only be giving the plus side of the Sigma 17-70. It's also not as sharp as the Pentax and not as good at colour rendition and contrast. The Pentax is silent when focussing, which could be a major advantage in some situations, although reliabililty of SDM has been questioned lately.

The Sigma is a very good lens, but nothing I've seen would make me choose it over the Pentax, even given the difference in price.
10-05-2009, 07:35 PM   #8
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QuoteOriginally posted by reeftool Quote
If the lens doesn't need correcting, which you mention, then why wait for Pentax to make a lens that does? I have lenses of several brands, 4 of them Pentax. A good sharp lens is just that, a sharp lens. You seem to expect that a lens will be a little "off". When I buy a new lens I expect it to be right and if it isn't it goes back. The lens correction feature might be a bigger consideration when buying used glass that you may be stuck with.
As I understand it. that's not how lens correction works. All lenses have some CA, distortion and vignetting. The correction program applies a standard correction according to the known lens specs (i.e. at a certain aperture and focal length, a given lens will have x% distortion, y blur units of CA and z stops of vignetting). A lens will only be corrected according to the known standards. Corrections will not turn a defective lens into a good lens.

10-05-2009, 07:44 PM   #9
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QuoteOriginally posted by Peter Zack Quote
I would be willing to bet that in a few years there will be a few other features that are Pentax glass only. This little thing already has you thinking Pentax only. So that's the point now isn't it?
Also note that it's Pentax digital glass (DA and D FA) that are corrected. FA and FA Limited are not included, nor are any of the older film lenses. Still, I think this is a great feature. It's understandable that they have confined it to new Pentax glass. It is a business, after all.
10-05-2009, 08:06 PM   #10
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Dan, I think that's what I said. DA lenses.
10-05-2009, 08:17 PM   #11
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QuoteOriginally posted by Peter Zack Quote
Dan, I think that's what I said. DA lenses.
Oops, so you did.
10-06-2009, 08:26 AM   #12
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QuoteOriginally posted by audiobomber Quote
The Sigma is not a true macro lens, it's only 1:2.3. The Pentax does have close focus ability, but not as much at 1:3.2. Neither lens is exemplary for CA, vignetting and especially distortion, so the K-7 corrections should make quite a difference.



You seem to only be giving the plus side of the Sigma 17-70. It's also not as sharp as the Pentax and not as good at colour rendition and contrast. The Pentax is silent when focussing, which could be a major advantage in some situations, although reliabililty of SDM has been questioned lately.

The Sigma is a very good lens, but nothing I've seen would make me choose it over the Pentax, even given the difference in price.
At this point I haven't made the decision on which lens I will get. On paper anyhow the Sigma looks good and also based on some of the shots and comments I have seen here in the forum with that lens I would consider it a very good buy. Thanks for the input though. I always try to get as much info as possible before making a major purchase. The SDM is a concern. I don't own one yet and have been seeing a steady stream of complaints about failed SDM motors. Like most, I consider a lens purchase a long term use purchase outlasting a few cameras so that is a big reason why I am considering the Sigma over the Pentax.
10-06-2009, 11:55 AM   #13
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It's worth mentioning that PC software like PTLens should be able to correct lens distortion and aberration just as well as the K-7 onboard correction. And it will do it for third-party lenses.

I perused the web site, and it doesn't appear the Sigma 105mm is in their database at their moment, but the author promises to add lenses upon receiving some specific test shots.

The only real downsides are (a) it's an extra step, (b) it takes place off-camera, and (c) it's a little extra money.

Of course, macro primes are usually pretty well optically corrected already, so there might not be much benefit in that particular case. But for things like the Sigma 17-70, this is an option.
10-06-2009, 01:09 PM   #14
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Am I understanding correctly that the focus adjustment/storing lens for the K20d and K7 is limited to Pentax glass only?
10-06-2009, 01:49 PM   #15
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No, we're talking about a new K-7 feature, which corrects chromatic aberration and distortion in the picture after it has been taken. THAT only works with certain (DA, DA*, D FA) Pentax lenses.

Focus correction should work with third-party lenses also.
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