TAMRON 1.4 TC converter has trouble auto focusing.

jon pafford · 05-21-2008, 06:46 PM

My camera is a pentax k100d super. I just bought a TAMRON 1.4 TC converter and it has trouble auto focusing. The lens I am using is a TAMRON AF di II 18-200mm 1:3.5-6.3 and AF Di 28-300 1:3.5-6.3. What can I do to make it auto focus.

**Canada_Rockies** · 05-21-2008, 07:15 PM

Originally posted by jon pafford

My camera is a pentax k100d super. I just bought a TAMRON 1.4 TC converter and it has trouble auto focusing. The lens I am using is a TAMRON AF di II 18-200mm 1:3.5-6.3 and AF Di 28-300 1:3.5-6.3. What can I do to make it auto focus.

You will need very bright light for this lens to autofocus with the teleconverter on it. AF is usually rated as operable at f/5.6 and faster. With the converter, your lenses hit 6.3X1.4 or almost f/9 (8.92) at the long end.

One way to help your lens focus is to use the center focus spot only (the camera doesn't have to decide among the 11 points) and lock your focus on a sharp, contrasty edge tone. A table leg with a different colored background, for example.

fwbigd · 05-21-2008, 07:31 PM

Originally posted by jon pafford

My camera is a pentax k100d super. I just bought a TAMRON 1.4 TC converter and it has trouble auto focusing. The lens I am using is a TAMRON AF di II 18-200mm 1:3.5-6.3 and AF Di 28-300 1:3.5-6.3. What can I do to make it auto focus.

Teleconverters normally are designed to work with lens with apertures f2.8 and above lens.

VR
Darryl

**Marc Langille** · 05-21-2008, 07:54 PM

Tamron TC's that I've used specify an aperture of F/4.5 or larger. The 2X units require F/4.0 to guarantee AF will work. I confirmed this - just checked my unit's pamphlet/manual - it's a Pz-AF MC4 unit, Pentax mount.

Even the Tamron 1.4x "Pro" in Canon mount doesn't work well with anything other than the Mark II or Mark III bodies (thanks Codiac for the reminder/explanation of that problem). It's practically useless with the Sigma 500/4.5 - AF constantly trying to fine tune the AF lock, so I missed some very good shots...

Back it went to Adorama...

Note that even with my FA* 300/2.8, the Tamron 1.4x TC still has issues in lower light or lower contrast images. CR has it on the money - some contrast is needed too... and your lenses have smaller apertures at the long end... that's tough on the AF to work. No TC is really a catch-all solution - something is a compromise - every time.

Regards,
Marc

Last edited by Marc Langille; 05-21-2008 at 08:09 PM. Reason: clarification

05-21-2008, 06:46 PM	#1
jon pafford Forum Member Join Date: Jul 2007 Location: houston texas Photos: Albums Posts: 80	TAMRON 1.4 TC converter has trouble auto focusing. My camera is a pentax k100d super. I just bought a TAMRON 1.4 TC converter and it has trouble auto focusing. The lens I am using is a TAMRON AF di II 18-200mm 1:3.5-6.3 and AF Di 28-300 1:3.5-6.3. What can I do to make it auto focus.

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05-21-2008, 07:15 PM	#2
Canada_Rockies Loyal Site Supporter Join Date: Nov 2007 Location: Sparwood, BC, Canada Photos: Gallery \| Albums Posts: 12,385	Originally posted by jon pafford My camera is a pentax k100d super. I just bought a TAMRON 1.4 TC converter and it has trouble auto focusing. The lens I am using is a TAMRON AF di II 18-200mm 1:3.5-6.3 and AF Di 28-300 1:3.5-6.3. What can I do to make it auto focus. You will need very bright light for this lens to autofocus with the teleconverter on it. AF is usually rated as operable at f/5.6 and faster. With the converter, your lenses hit 6.3X1.4 or almost f/9 (8.92) at the long end. One way to help your lens focus is to use the center focus spot only (the camera doesn't have to decide among the 11 points) and lock your focus on a sharp, contrasty edge tone. A table leg with a different colored background, for example.

05-21-2008, 07:31 PM	#3
fwbigd Veteran Member Join Date: Jun 2007 Location: Fort Worth TX Posts: 339	Originally posted by jon pafford My camera is a pentax k100d super. I just bought a TAMRON 1.4 TC converter and it has trouble auto focusing. The lens I am using is a TAMRON AF di II 18-200mm 1:3.5-6.3 and AF Di 28-300 1:3.5-6.3. What can I do to make it auto focus. Teleconverters normally are designed to work with lens with apertures f2.8 and above lens. VR Darryl

05-21-2008, 07:54 PM	#4
Marc Langille Site Supporter Join Date: Dec 2006 Location: NW Arkansas, USA Posts: 4,710	Tamron TC's that I've used specify an aperture of F/4.5 or larger. The 2X units require F/4.0 to guarantee AF will work. I confirmed this - just checked my unit's pamphlet/manual - it's a Pz-AF MC4 unit, Pentax mount. Even the Tamron 1.4x "Pro" in Canon mount doesn't work well with anything other than the Mark II or Mark III bodies (thanks Codiac for the reminder/explanation of that problem). It's practically useless with the Sigma 500/4.5 - AF constantly trying to fine tune the AF lock, so I missed some very good shots... Back it went to Adorama... Note that even with my FA* 300/2.8, the Tamron 1.4x TC still has issues in lower light or lower contrast images. CR has it on the money - some contrast is needed too... and your lenses have smaller apertures at the long end... that's tough on the AF to work. No TC is really a catch-all solution - something is a compromise - every time. Regards, Marc Last edited by Marc Langille; 05-21-2008 at 08:09 PM. Reason: clarification