+Use of HD DA AF Rear Converter 1.4X AW

**Robert N** · 12-26-2018, 11:31 AM

Originally posted by stihlmania

Like honey, I have not had any focus issues using the HD 55-300 WR, the HD 1.4X and my K-3 II. Back button AF does seem to be quicker using the 1.4X [I have no idea why] . I find the converter a useful addition to the 55-300 [up to 250mm, after that the IQ in my images does get noticeably worse] and my SMC A 50 F1.7.

Stihlmania,
Many thanks for your reply. You state that the image quality deteriorates beyond 250mm with the converter - does that include using the lens at f8/f11, which is the sweet spot at 300mm - kindly advise.

**Des** · 12-26-2018, 03:04 PM

Originally posted by Robert N

You state that the image quality deteriorates beyond 250mm with the converter - does that include using the lens at f8/f11, which is the sweet spot at 300mm - kindly advise.

My experience is that the resolution on the 55-300 PLM drops from about where the widest minimum goes from f5.6 to f6.3. When you add a TC the resolution shortcomings get magnified too.

Also, using a 1.4x TC means losing one stop of light. If you stop down the lens to f8 for better resolution, with the TC your effective aperture goes to f11. Except in really bright light, your shutter speed and/or ISO will be very compromised and AF will struggle (as you have noted).

TCs are really intended for use with fast-ish high-resolution lenses. Rather than spend the money on the DA 1.4x TC just to use on the 55-300, I'd suggest putting it towards a dedicated telephoto lens to get more reach. Even a 300mm prime will give you a lot more resolution for cropping.

I know some people are happy using a TC on a consumer zoom, despite all the compromises, but with a 24mp sensor you have a lot of scope to crop. You may find that you would get better results from cropping than from using the TC on a lens like this, at least in most conditions. Even when I tried a TC on my Sigma 400mm f5.6 I felt that there was no gain as against just cropping.

**stihlmania** · 12-27-2018, 05:21 AM - **1 Like**

Originally posted by Robert N

Stihlmania,
Many thanks for your reply. You state that the image quality deteriorates beyond 250mm with the converter - does that include using the lens at f8/f11, which is the sweet spot at 300mm - kindly advise.

Yes, my experience over a 3 week period of testing this combo gave me best results at f8-f11 at all zoom ranges. Good lighting, as always, is very important at 250mm+ with or without the tc. Honesty, above 250mm all images with the tc look good enough for casual web usage. Using my heavy Bogan tripod and a gimbal , for me, improves the IQ with this combo. I did not use the shutter delay with the tripod, which I hope to test this weekend. This is my personal opinion and experience, others may get different results.

Similar Threads
Thread	Thread Starter	Forum	Replies	Last Post
For Sale - Sold: DA*300 f4, 1.4x HD PENTAX-DA AF Rear Converter AW & much more!	gsrokmix	Sold Items	8	08-10-2017 02:28 PM
K-1 and the HD PENTAX-DA AF REAR CONVERTER 1.4X AW	SteveD	Pentax K-1 & K-1 II	9	06-26-2016 06:42 PM
For Sale - Sold: Pentax 1.4x HD AX-DA AF Rear Converter AW K-Mount	charchri4	Sold Items	12	02-21-2016 10:25 PM
DA 300* with HD Pentax-DA AF Rear Converter 1.4x AW	SashasMom	Pentax SLR Lens Discussion	17	12-06-2015 01:08 AM

12-26-2018, 11:31 AM	#16
Robert N Site Supporter Join Date: Oct 2017 Location: Sale, Cheshire Posts: 247 Original Poster	Originally posted by stihlmania Like honey, I have not had any focus issues using the HD 55-300 WR, the HD 1.4X and my K-3 II. Back button AF does seem to be quicker using the 1.4X [I have no idea why] . I find the converter a useful addition to the 55-300 [up to 250mm, after that the IQ in my images does get noticeably worse] and my SMC A 50 F1.7. Stihlmania, Many thanks for your reply. You state that the image quality deteriorates beyond 250mm with the converter - does that include using the lens at f8/f11, which is the sweet spot at 300mm - kindly advise.

12-26-2018, 03:04 PM	#17
Des Loyal Site Supporter Join Date: Jan 2014 Location: Victoria Australia Photos: Albums Posts: 6,423	Originally posted by Robert N You state that the image quality deteriorates beyond 250mm with the converter - does that include using the lens at f8/f11, which is the sweet spot at 300mm - kindly advise. My experience is that the resolution on the 55-300 PLM drops from about where the widest minimum goes from f5.6 to f6.3. When you add a TC the resolution shortcomings get magnified too. Also, using a 1.4x TC means losing one stop of light. If you stop down the lens to f8 for better resolution, with the TC your effective aperture goes to f11. Except in really bright light, your shutter speed and/or ISO will be very compromised and AF will struggle (as you have noted). TCs are really intended for use with fast-ish high-resolution lenses. Rather than spend the money on the DA 1.4x TC just to use on the 55-300, I'd suggest putting it towards a dedicated telephoto lens to get more reach. Even a 300mm prime will give you a lot more resolution for cropping. I know some people are happy using a TC on a consumer zoom, despite all the compromises, but with a 24mp sensor you have a lot of scope to crop. You may find that you would get better results from cropping than from using the TC on a lens like this, at least in most conditions. Even when I tried a TC on my Sigma 400mm f5.6 I felt that there was no gain as against just cropping.

12-27-2018, 05:21 AM - 1 Like	#18
stihlmania Site Supporter Join Date: Dec 2012 Location: Spring Branch, Tx Photos: Gallery \| Albums Posts: 705	Originally posted by Robert N Stihlmania, Many thanks for your reply. You state that the image quality deteriorates beyond 250mm with the converter - does that include using the lens at f8/f11, which is the sweet spot at 300mm - kindly advise. Yes, my experience over a 3 week period of testing this combo gave me best results at f8-f11 at all zoom ranges. Good lighting, as always, is very important at 250mm+ with or without the tc. Honesty, above 250mm all images with the tc look good enough for casual web usage. Using my heavy Bogan tripod and a gimbal , for me, improves the IQ with this combo. I did not use the shutter delay with the tripod, which I hope to test this weekend. This is my personal opinion and experience, others may get different results.