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      12-10-2017, 10:37 PM   #1
dcstep
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Sony 1.4x and 2.0x Teleconverter Comparison

My current rig includes the Sony a7R III, the FE 100-400mm f/4.5-5.6 GM OSS and the FE 1.4x and 2.0x teleconverters. I've had the bare lens and the 1.4x since September and I've been pleased with both image quality and autofocus performance, with no noticeable slowdown in AF.

I received the FE 2.0x teleconverter last week and was very happy to report that it autofocuses on both the a7R III and a9 bodies, with very little, if any flow down. I thought, holy cow, if I can shoot this thing in good light, I've got 800mm of reach in a very small package.

In early testing, I was very happy to run across a kestrel, in great light, at a reasonably close range, but I was very disappointed that none of my shots were as sharp as I'd come to expect with my bare 100-400m and even with my 1.4x teleconverter attached. (My Canon equipment was also sharper). See example, notice lack of feather detail and this is the best out of 50:
Untitled by David Stephens, on Flickr

I decided to test, in good light, using a static subject. I took shots with the bare lens, all from the same distance, and then cropped the bare lens shot and the 1.4x teleconverter shot to match the 2.0x shot. So, the 2.0x is uncropped, the 1.4x is cropped a bit and the bare lens shot is cropped 50%. Here are the results:

Bare Lens
Bare Lens - 3892x2596p to approximate 2.0x teleconverter by David Stephens, on Flickr

1.4x Teleconverter
1.4x teleconverter - 5481x3656p Crop by David Stephens, on Flickr

2.0x Teleconverter
2.0x Teleconverter - Uncropped 7952x5304p by David Stephens, on Flickr
I cropped further so that you can study detail. Keep in mind that I took these all at the same distance, so the DOF shrinks as the focal length goes up. To get the DOF equal, I would have needed to back up from the bare lens to get the perspective and magnification the same. So compare in-focus to in-focus. I want to use real, in the wild, elements, to see realistic detail. BTW, resolution on the camera is 42.4mp. Magnified results:

Bare Lens
Bare Lens - Cropped to 1955x1304p by David Stephens, on Flickr

1.4x Teleconverter
1.4x teleconverter - 2737x1825p Crop by David Stephens, on Flickr

2.0x Teleconverter
2.0x Teleconverter - Cropped 3912x2610p by David Stephens, on Flickr

Sorry for the flaw in my methodology. My focus was on the front of the bunch on top.

As expected, the bare lens is best, even with the severe cropping needed to get the subject the same size. The 1.4x is close and acceptable. I can't accept the 2.0x's performance and will send it back. IQ trumps focal length.
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      12-11-2017, 10:50 AM   #2
dcstep
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Now that I've seen the DOF issue caused by my methodology, I'll take my tape measure along today and redo the comparison. I really like my target, so I'll set up something similar.
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      12-11-2017, 09:48 PM   #3
dcstep
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As promised, I tried again today, using a slightly different approach. Rather than taking all the images at the same distances and then cropping the shorter focal lengths to equal the subject size of the 2.0x teleconverter image, I equalized the distance in relation to focal length. Specifically, I took the bare 400mm lens image at 4', the 1.4x teleconverter image at 5' 7" and the 2.0x teleconverter image at 8", using a construction tape measure. The subject sizes in the images were still a bit different, but, at least, the depth of field was more comparable shot to shot vs. keeping the distance constant. I used the 42.4mp Sony a7R III for all three shots. These are handheld, so I took several safety shots of each and made sure to use the sharpest of the groups. Of course, stabilization was engaged. All are at ISO 100, f/11, 1/200-sec.

Bare Lens
Bare Lens by David Stephens, on Flickr

1.4x Teleconverter
1.4x Teleconverter by David Stephens, on Flickr

2x Teleconverter
2.0x Teleconverter by David Stephens, on Flickr

I'm very happy with the bare lens and find the 1.4x teleconverter not far behind. I have no reservations about using the 1.4x for critical subjects like birds and furry mammals.

The 2.0x teleconverter has serious problems in my testing. First, I think that the varying images sizes has to do with the focal lengths being "nominal" readings. For instance, I've read that actual focal lengths for some 100-400mm lens may actually be closer to 105-385mm. I've never read the same things about teleconverters, but wouldn't be tremendously surprised if the Sony isn't actually closer to 2.1x. That said, there are sharpness issues with the 2.0x. Contrast and color are acceptable. The lens seemed to be back-focusing, being in focus behind the plane where the focus was taken. Despite taking the 800mm image from twice the distance of the 400mm image, the depth of field seems quite shortened. Look at the very fine bristles at the top of the bloom to see sharpness that makes me think that the lens is back focusing.
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      12-12-2017, 10:40 PM   #4
dcstep
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My pro shooting buddy, Chris Dodds teles me that his sample is stunning. I'm going to return this and request another. He IS getting great results.
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