Win a Pentax Limited Lens: Raffle Now Live!

**tduell** · 12-30-2020, 10:30 PM

I have a Sigma 18-300 F3.5-6.3 DC Macro HSM, and the Pentax HD DA AF Rear Converter 1.4x AW.
The TC appears to have all the contacts which I assume provide all pass-through communication needed by lenses.
This combination doesn't work too well (AF is almost non existent), and I'm wondering if anyone has an explanation as to why it is so.

Cheers,
Terry

Unregistered User 8 · 12-30-2020, 10:52 PM

Hi Terry, the rear converter was designed for lenses F4, or faster. At F6.3 + the extra stop, your combo is really pushing past reliable auto-focus.
I've linked the excellent forums review of the rear converter below, and I think many of your concerns will be answered. Good luck.

Pentax-DA 1.4x AW AF Rear Converter Review - Introduction | PentaxForums.com Reviews

**UncleVanya** · 12-30-2020, 11:03 PM

I sometimes use mine on my f4.5 FA* 300 (results in an F6.3 420mm lens and that focuses well but your lens pushes the limits. F3.5-6.3 becomes f4.9-8.8.

Realistically the best use of a fine teleconverter is on an especially sharp fast lens.

Fogel70 · 12-30-2020, 11:50 PM

Does the TC work with your other Sigma HSM lenses?

kypfer · 12-31-2020, 02:07 AM

I use a tele-converter with my Sigma lenses regularly.
For a lens with a maximum aperture of f/6.3, as mentioned above, you really are at the limits of the a/f system's capability.
AF-S in "central-spot" a/f mode, with a contrasty static subject in good light, is usually not a problem. Just give the camera a second or so to establish "lock", with the shutter button half depressed, and the results can often be very acceptable. In poorer light, manual focus is often more reliable.
Good luck

**Crooski** · 12-31-2020, 11:00 AM

I think it doesn't always have to do with aperture
My 55-300 PLM lens works well with the HD DA AF Rear Converter 1.4x AW.
But my Sigma 70 200mm HSM doesn't work with the Pentax rear converter

Camera KP

**tduell** · 12-31-2020, 02:18 PM

Originally posted by Fogel70

Does the TC work with your other Sigma HSM lenses?

I've heard it said that it doesn't work with HSM lenses, which was really the point of my question.
The advice from others that it is an aperture problem is a bit of a furphy...I use it regularly and successfully with my DFA 150-450 which is f/6.7 at best with the TC, and normally at f/8.

late edit: Sorry misread your post, missed the 'your'...no the TC doesn't work with any of my HSM lenses, but works well with all my other lenses.

Cheers,
Terry

Last edited by tduell; 12-31-2020 at 03:04 PM.

12-30-2020, 10:30 PM	#1
tduell Loyal Site Supporter Join Date: May 2015 Location: Melbourne Posts: 1,517	Sigma HSM lens not focussing when teleconverter attached I have a Sigma 18-300 F3.5-6.3 DC Macro HSM, and the Pentax HD DA AF Rear Converter 1.4x AW. The TC appears to have all the contacts which I assume provide all pass-through communication needed by lenses. This combination doesn't work too well (AF is almost non existent), and I'm wondering if anyone has an explanation as to why it is so. Cheers, Terry

Similar Threads
Thread	Thread Starter	Forum	Replies	Last Post
New model sigma 18-250 lens not focussing correctly on k3	David&karen	Pentax SLR Lens Discussion	2	05-16-2014 08:02 AM
Focussing problem Sigma EX 70-200mm 1:2.8 II MACRO HSM	Bruce Clark	Pentax SLR Lens Discussion	4	08-29-2013 01:19 AM
Focussing problem Sigma EX 70-200mm 1:2.8 II MACRO HSM	Bruce Clark	Troubleshooting and Beginner Help	2	06-18-2013 06:22 AM
How can I check if my Tamron 17-50 is front-focussing/back-focussing and needs repair	photoleet	Pentax SLR Lens Discussion	6	03-31-2013 03:58 PM
Wanted - Acquired: Sigma 150-500mm HSM, 150mm MACRO HSM, Sigma 18-250 HSM, Sigma 10-20mm HSM	mackloon	Sold Items	7	05-01-2011 02:25 AM

12-30-2020, 10:52 PM	#2
Unregistered User 8 Closed Account Join Date: Mar 2015 Photos: Gallery Posts: 8,694	Hi Terry, the rear converter was designed for lenses F4, or faster. At F6.3 + the extra stop, your combo is really pushing past reliable auto-focus. I've linked the excellent forums review of the rear converter below, and I think many of your concerns will be answered. Good luck. Pentax-DA 1.4x AW AF Rear Converter Review - Introduction \| PentaxForums.com Reviews

12-30-2020, 11:03 PM	#3
UncleVanya Loyal Site Supporter Join Date: Jul 2014 Photos: Gallery \| Albums Posts: 28,472	I sometimes use mine on my f4.5 FA* 300 (results in an F6.3 420mm lens and that focuses well but your lens pushes the limits. F3.5-6.3 becomes f4.9-8.8. Realistically the best use of a fine teleconverter is on an especially sharp fast lens.

12-30-2020, 11:50 PM	#4
Fogel70 Pentaxian Join Date: Sep 2009 Location: Stockholm, Sweden Photos: Albums Posts: 3,062	Does the TC work with your other Sigma HSM lenses?

12-31-2020, 02:07 AM	#5
kypfer Pentaxian Join Date: Jan 2018 Location: Jersey C.I. Posts: 3,600	I use a tele-converter with my Sigma lenses regularly. For a lens with a maximum aperture of f/6.3, as mentioned above, you really are at the limits of the a/f system's capability. AF-S in "central-spot" a/f mode, with a contrasty static subject in good light, is usually not a problem. Just give the camera a second or so to establish "lock", with the shutter button half depressed, and the results can often be very acceptable. In poorer light, manual focus is often more reliable. Good luck

12-31-2020, 11:00 AM	#6
Crooski Loyal Site Supporter Join Date: Feb 2013 Location: Rozenburg , Zuid-Holland Photos: Gallery Posts: 3,683	I think it doesn't always have to do with aperture My 55-300 PLM lens works well with the HD DA AF Rear Converter 1.4x AW. But my Sigma 70 200mm HSM doesn't work with the Pentax rear converter Camera KP

12-31-2020, 02:18 PM	#7
tduell Loyal Site Supporter Join Date: May 2015 Location: Melbourne Posts: 1,517 Original Poster	Originally posted by Fogel70 Does the TC work with your other Sigma HSM lenses? I've heard it said that it doesn't work with HSM lenses, which was really the point of my question. The advice from others that it is an aperture problem is a bit of a furphy...I use it regularly and successfully with my DFA 150-450 which is f/6.7 at best with the TC, and normally at f/8. late edit: Sorry misread your post, missed the 'your'...no the TC doesn't work with any of my HSM lenses, but works well with all my other lenses. Cheers, Terry Last edited by tduell; 12-31-2020 at 03:04 PM.

Sigma HSM lens not focussing when teleconverter attached

Win a Pentax Limited Lens: Raffle Now Live!