Sigma 28-70mm f/2.8 auto-focus problem

Adrian Wong · 27th May 2008, 09:37 AM

Hmm.. Noticed a weird issue with the Sigma 28-70mm f/2.8 lens. The D300's 51-point auto-focus doesn't work all the time with it. Even with high-contrast objects, it sometimes fails to focus.

When it fails to work, it just refuses to work, no matter where you point the lens at. Even if you change to a different object, it still refuses to auto-detect the focus.

Point focus works better but unlike other lenses, it has trouble with lower-contrast objects...

I wonder if it's a lens problem, or merely a characteristic of this lens. This is not the newer EX DG model .

Chai · 27th May 2008, 11:46 PM

It refuses to detect, or the lens refuses to even try to focus?

Adrian Wong · 28th May 2008, 10:07 AM

Quote:

Originally Posted by Chai

It refuses to detect, or the lens refuses to even try to focus?

Umm.. Well, when I half-press the shutter button, nothing happens. The AF light is continuously on.

Sometimes the lens attempts to focus... on other occasions, the lens does nothing.

Chai · 29th May 2008, 07:44 AM

Motor driven lens? Any other lens with similar problem?

peaz · 29th May 2008, 10:09 AM

Possibly an 'incompatible' issue with the lens focusing chip? Hmm can test on my D300 and see if it's the same.

Adrian Wong · 29th May 2008, 01:08 PM

Quote:

Originally Posted by Chai

Motor driven lens? Any other lens with similar problem?

The thing is it happens randomly, usually when I really need to take a quick shot. Hahaha...

I have another 28-70mm. I will give that a try later.

Adrian Wong · 29th May 2008, 01:09 PM

Quote:

Originally Posted by peaz

Possibly an 'incompatible' issue with the lens focusing chip? Hmm can test on my D300 and see if it's the same.

Yeah, should try on another D300. When are you free?

Chai · 29th May 2008, 01:47 PM

Yeah maybe it's a Sigma lens compatibility problem. Never get Sigma lenses...

Adrian Wong · 29th May 2008, 02:07 PM

Quote:

Originally Posted by Chai

Yeah maybe it's a Sigma lens compatibility problem. Never get Sigma lenses...

LOL!! You did!

Chai · 29th May 2008, 05:19 PM

Sorry, I meant to say old Sigma lenses...

27th May 2008, 09:37 AM	#1 (permalink)
Adrian Wong Da Boss Join Date: 10 Oct 2002 Location: In front of my BenQ Joybook 7000 notebook! Posts: 29,678 Reputation: 2878 Rep Power: 64	Sigma 28-70mm f/2.8 auto-focus problem Hmm.. Noticed a weird issue with the Sigma 28-70mm f/2.8 lens. The D300's 51-point auto-focus doesn't work all the time with it. Even with high-contrast objects, it sometimes fails to focus. When it fails to work, it just refuses to work, no matter where you point the lens at. Even if you change to a different object, it still refuses to auto-detect the focus. Point focus works better but unlike other lenses, it has trouble with lower-contrast objects... I wonder if it's a lens problem, or merely a characteristic of this lens. This is not the newer EX DG model . __________________ Dr. Adrian Wong Tech ARP \| Blog @ Tech ARP \| The Free Trade Zone DYKT : The only offshore account I have is at the sand bank? Keep Tech ARP free! Visit our sponsors! We need PROGRAMMERS and TECHNICAL WRITERS! Contact us if you are a hot shot programmer or technical writer! My items for sale : 50x SD Card \| Memory Stick PRO \| Cyclone Energy Saver \| Seiko SS watch \| Tiger/Carlsberg beer jugs \| Travel Speakers \| Motorola V600 \| Nokia N90 SOLD! \| New Lowepro Mini Trekker AW Other items for sale @ the FTZ : Zalman CNPS9500 LED @ $20 \| Zalman CNPS7700 Cu @ $20 \| Zalman CNPS7000 Cu @ $20 \| Swarovski bracelet watches \| Dell 17" LCD \| Hi-Fi speakers \| English DIVX movies \| HP LaserJet toners! \| Office chairs

27th May 2008, 11:46 PM	#2 (permalink)
Chai Administrator Join Date: 6 Oct 2002 Location: Maranello Posts: 26,272 Reputation: 3862 Rep Power: 71	It refuses to detect, or the lens refuses to even try to focus? __________________ Chai (Contributor & Forum Admin) http://www.techarp.com/

29th May 2008, 07:44 AM	#4 (permalink)
Chai Administrator Join Date: 6 Oct 2002 Location: Maranello Posts: 26,272 Reputation: 3862 Rep Power: 71	Motor driven lens? Any other lens with similar problem? __________________ Chai (Contributor & Forum Admin) http://www.techarp.com/

29th May 2008, 10:09 AM	#5 (permalink)
peaz ARP Webmaster Join Date: 13 Oct 2002 Location: http://atpeaz.placidthoughts.com/ Posts: 8,499 Reputation: 1633 Rep Power: 30	Possibly an 'incompatible' issue with the lens focusing chip? Hmm can test on my D300 and see if it's the same. __________________ Ken Ng Tech ARP Visit my web gallery - Ken's Digital Canvas Shoot and Earn Money from Stock Photography Sterling@PJ Community Forums

29th May 2008, 01:47 PM	#8 (permalink)
Chai Administrator Join Date: 6 Oct 2002 Location: Maranello Posts: 26,272 Reputation: 3862 Rep Power: 71	Yeah maybe it's a Sigma lens compatibility problem. Never get Sigma lenses... __________________ Chai (Contributor & Forum Admin) http://www.techarp.com/

29th May 2008, 05:19 PM	#10 (permalink)
Chai Administrator Join Date: 6 Oct 2002 Location: Maranello Posts: 26,272 Reputation: 3862 Rep Power: 71	Sorry, I meant to say old Sigma lenses... __________________ Chai (Contributor & Forum Admin) http://www.techarp.com/