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12-28-2013, 07:28 PM   #16
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Yes the Sigma 30 is soft in the corners. In the center, it is sharper than all get out. It's not a general purpose lens, but when it's good, it's very good. If you are using it wide open to isolate a subject, the soft corners aren't a problem. If I want across-the-frame sharpness at moderate apertures, I use my DA40.

12-28-2013, 07:55 PM   #17
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QuoteOriginally posted by rx7ong Quote
i would love to try out Sigma 120-300mm f/2.8 DG OS HSM Sport if ever made in K Mount..

(:
That's a lens I'm drooling over. Outdoor sports at night (soccer and Football) would make that a great lens to have.
12-29-2013, 01:28 PM   #18
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Im hoping for a 50mm Art. Ive been really lookin hard at the 35mm Art.
I can wait if they introduce a usb dock
12-30-2013, 10:16 AM   #19
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Why would I need a USB dock? Am I missing something?

Charles.

03-06-2014, 08:20 AM   #20
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Sent a query to Sigma this morning. Here is their reply:

"Good morning,



I confirmed with our parent company last night that we have them on order, but they told me there is no updated word on when they will start production. So as of now, we are expecting them in early May.



Please let me know if you have any questions. Have a great day!



Best regards,



Michael Sinnott

Sales Operations Supervisor

Sigma Corp of America"

Cheers,
Lou
03-06-2014, 08:25 AM   #21
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QuoteOriginally posted by ChopperCharles Quote
Why would I need a USB dock? Am I missing something?

Charles.
The USB dock provides the ability to do AF microadjustments (for front/back-focus) on the lens. While it's not necessary on prime lenses since Pentax cameras provide AF microadjustment in the body, it is pretty useful for the 18-35 zoom, 17-70 zoom, and all future Sigma AF zooms as well - because the Sigma Dock allows you to do AF microadjustments at certain focal lengths.

So for example, in the 17-70, I believe it gives you ability to adjust the AF at 17mm, 24mm, 35mm, 50mm, and 70mm. While it's true that a zoom lens shouldn't have AF shift depending on the focal length - manufacturing tolerances sometimes allow for that shift and it's great that Sigma gives us an option to fix it.
03-06-2014, 08:44 AM   #22
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I have just been told over the phone that the new Sigma Art 30mm F/1.4 for Pentax (A30DCHP) is in stock at Sigma Canada's (aka Gentec's) warehouse!

Last edited by Doundounba; 03-06-2014 at 08:45 AM. Reason: add model number
03-06-2014, 09:44 AM   #23
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QuoteOriginally posted by JinDesu Quote
The USB dock provides the ability to do AF microadjustments (for front/back-focus) on the lens. While it's not necessary on prime lenses since Pentax cameras provide AF microadjustment in the body, it is pretty useful for the 18-35 zoom, 17-70 zoom, and all future Sigma AF zooms as well - because the Sigma Dock allows you to do AF microadjustments at certain focal lengths.

So for example, in the 17-70, I believe it gives you ability to adjust the AF at 17mm, 24mm, 35mm, 50mm, and 70mm. While it's true that a zoom lens shouldn't have AF shift depending on the focal length - manufacturing tolerances sometimes allow for that shift and it's great that Sigma gives us an option to fix it.
Can you explain to me how this works because I don't get it. The camera is providing power to a small motor in the lens and do this until the camera thinks the subject is in focus. How can some values stored in the lens change that? Because I have heard from a Pentax service centre that AF adjustments are not stored in Pentax lenses, they are stored in the camera and I don't think Pentax has made support for reading adjustment values out of Sigma lenses.

03-06-2014, 09:55 AM   #24
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QuoteOriginally posted by StigVidar Quote
Can you explain to me how this works because I don't get it. The camera is providing power to a small motor in the lens and do this until the camera thinks the subject is in focus. How can some values stored in the lens change that? Because I have heard from a Pentax service centre that AF adjustments are not stored in Pentax lenses, they are stored in the camera and I don't think Pentax has made support for reading adjustment values out of Sigma lenses.
I do not know how it works, unfortunately. I'll try to find the link where Sigma gave a demonstration showing it working on their camera - but I would think that surely they wouldn't be advertising this feature if it didn't work for other manufacturers.

If I were to guess, I assume that the in-lens motor receives instructions from the camera body and the programming within the lens will tell the motor to travel that little bit further or closer.
03-06-2014, 10:02 AM   #25
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QuoteOriginally posted by JinDesu Quote
I do not know how it works, unfortunately. I'll try to find the link where Sigma gave a demonstration showing it working on their camera - but I would think that surely they wouldn't be advertising this feature if it didn't work for other manufacturers.

If I were to guess, I assume that the in-lens motor receives instructions from the camera body and the programming within the lens will tell the motor to travel that little bit further or closer.
It works for other manufacturers, but perhaps Canon or Nikon found out they should store adjustment values in their lenses instead of the camera.
03-06-2014, 02:30 PM   #26
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QuoteOriginally posted by BATMON Quote
Im hoping for a 50mm Art. Ive been really lookin hard at the 35mm Art.
It hasn't been announced for Pentax and I suspect that it won't. If there's one thing Pentax has done well, it's fast 50mm lenses. The ubiquity of used FA and F f/1.4 and f/1.7 lenses and their price makes for stiff competition for the Sigma. While it will likely be better at f/1.4 than the F/FA are, that makes its market limited only to those who need 1.4. Otherwise, everyone who shoots at f/2 and above will opt for a Pentax F/FA or DA 50mm, all of which can be had for 25-35% of the price of the Art lens.

Not saying it won't happen, but given that Sigma's Pentax sales are likely small to begin with, I'd expect them to declare Pentax's fast 50mm lenses the winner.

Pentax doesn't make a fast 35mm; only the FA35, which is not so good at f/2 and maybe discontinued anyway, is competition there. The 30 f/1.4 Art obviously takes a swing at the FA31, which is 2.5X the price of the Art lens.

Last edited by MadMathMind; 03-07-2014 at 09:17 AM.
03-06-2014, 05:37 PM   #27
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QuoteOriginally posted by StigVidar Quote
Can you explain to me how this works because I don't get it.
To my understanding, basically when the subject is in focus, the camera tells the lens to stop moving (or stop it's own motor for SD), but at the speed the motor (or shaft) is turning, once the stop command is received, the lens already overshot the target by a minute amount. Also, no electric motor will stop exactly on the spot, too much braking and the motor will bounce back a little. Too little braking and the motor will coast past the target. Add to that some delay in the processing speed of the camera. It's all very small "errors" but it adds up and sometimes the errors might cancel each other. Out of the factory, the lens is configured with preset compensation for this behaviour, like "move back 0.05% after you get the stop command"

On a screwdrive lens, the same behaviour is true but since the lens is not hosting the focus motor, adjustments will need to be in camera. (this is why the lens adjustment thingy will only ever be available for HSM lenses)

I don't believe the SDM contact are Power ON / Power OFF or Forward / Reverse. More than likely it is a data connection sending command like forward, reverse, or stop to the lens, the lens controlling it's own motor, always receiving power.
03-07-2014, 05:19 AM   #28
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QuoteOriginally posted by StigVidar Quote
Can you explain to me how this works because I don't get it. The camera is providing power to a small motor in the lens and do this until the camera thinks the subject is in focus. How can some values stored in the lens change that? Because I have heard from a Pentax service centre that AF adjustments are not stored in Pentax lenses, they are stored in the camera and I don't think Pentax has made support for reading adjustment values out of Sigma lenses.
The AF correction values for lenses are stored in the lenses themselves (in the Lens-ROM, to be more specific). You can of course store additional corrections in the body for each lens ("micro AF adjustment"), but this is something else. The correction values in the Lens-ROM can also specify different AF correction offsets for different focal lengths or even for different f-stops.
03-14-2014, 03:40 PM   #29
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QuoteOriginally posted by StigVidar Quote
Can you explain to me how this works because I don't get it. The camera is providing power to a small motor in the lens and do this until the camera thinks the subject is in focus. How can some values stored in the lens change that? Because I have heard from a Pentax service centre that AF adjustments are not stored in Pentax lenses, they are stored in the camera and I don't think Pentax has made support for reading adjustment values out of Sigma lenses.
The USB dock allows fine tuning of how the lens communicates with the camera . With zoom lenses, it is often problematic to adjust front vs back focus at all focal lengths. For example, some zooms tend to front focus at short focal lengths, and back focus at long (or visa - versa). The usb dock would allow selective focus adjustment at each focal length range. Occasionally a prime will require greater than + or - 10 for the fine focus adjustment, and the dock would also allow one to solve this problem without having to send the lens plus camera in for warranty repair. The dock allows adjustment at each of three focal ranges with the zooms . Also, 3rd party lens sometimes do not work as intended with subsequent camera body releases from the mount specific camera manufacturer. The USB dock would allow for the lens firmware to be upgraded if you want to use it with a future pentax camera that does not work with the original release lens firmware. This is an attractive feature to me.
05-02-2014, 06:19 AM   #30
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The USB dock is now available in the US directly from Sigma (Sigma USB Dock | Sigma Corporation of America--$59 + $5 standard shipping.

It has not shown up yet on B&H or Adorama.

Cheers,
Lou
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