Using non-Global Vision (preferred) Sigma lenses - on SD Quattro Mirrorless cameras.

Started 2 months ago | Discussions thread
Scottelly
Scottelly Forum Pro • Posts: 12,662
Re: Using non-Global Vision (preferred) Sigma lenses - on SD Quattro Mirrorless cameras.
1

danski0224 wrote:

xpatUSA wrote:

Or carry all that extra weight.

I can understand that the technology might preclude the use of some GV lenses but I can't understand that the sd cameras don't offer some easy option, such as pure CDAF for non-GV lenses allowing their use without all this messing around.

Let the new mirror-less camera roll ... apart from the 1:1:1 thing, it would be SO nice if it would take ANY previous Sigma lens (of course with an SA-L adapter), EX or not, and just work without prejudice!

As I understand it, the problem (or rather, difference) is how focus is achieved and the very fine steps that the lens motor is driven to get there. This was not required for DSLR AF sensor focusing.

Really? Why not? It doesn't make sense to me that focusing would be so different, but what do I know? I'm no auto-focus engineer.

Sigma would probably have to release something like this adapter from Sony to get full functionality of ALL non-Global Vision Sigma lenses:

https://www.sony.com/electronics/converters-mount-adapters/la-ea4

This also means that Sigma would have to make significant improvements in their phase detection AF sensor and calibration, so it works better than the SD1M and earlier cameras.

Canon doesn't seem to have the same issues driving their EF lenses to focus on Canon mirrorless cameras, and I'd bet that this is a benefit of the Canon DPAF (dual pixel auto focus) sensor design.

This explains the basic differences between contrast detect (most mirrorless) and phase detect (DSLR with AF not on the image sensor):

http://media.digitalcameraworld.com/wp-content/uploads/sites/123/2013/12/Contrast_AF_vs_Phase_detection_AF_cheat_sheet.jpg

Sigma's SD Quattro and SD Quattro H cameras have on-chip PDAF, so I don't see why they can't make their cameras work just as well as Canon can make their cameras auto-focus with old lenses. Wasn't on-chip PDAF supposed to cure the "problems" of CDAF? Well, with Sigma cameras it hasn't, which just doesn't make sense to me. It almost seems to my conspiracy spidey sense that it's all just a scam to sell more Global Vision lenses.

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Scott Barton Kennelly
http://www.bigprintphotos.com

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