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DxOmark: FE 100-400mm GM, compact and optically excellent
  
 
Ayoh
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p.4 #1 · p.4 #1 · DxOmark: FE 100-400mm GM, compact and optically excellent


Brandon Dube wrote:
They are assumptions, but for the lens to perform differently with AF vs MF would be a critical design flaw, and certainly noticed immediately by users.


You were implying that the lens AF control system compensates for the deviation in ideal positioning of the front focusing group with the back focusing group i.e. in AF mode the controller sends the front USM controlled group to the desired location using an open-loop LUT approach; any over/undershoot is then compensated by the more responsive closed-loop voice coil motor controlled rear focus group. So since in that lens, the front USM group is manually controllable in MF mode (i.e. has direct coupling, not focus-by-wire), then you should be able to position the front focus group in an ideal, peak sharpness position and minimize any compromised compensation by the focus-by-wire rear focus group. As such, based on your description, the lens design does have the potential to perform differently in AF vs MF mode.



Sep 07, 2017 at 06:52 AM
Brandon Dube
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p.4 #2 · p.4 #2 · DxOmark: FE 100-400mm GM, compact and optically excellent


Ayoh wrote:
You were implying that the lens AF control system compensates for the deviation in ideal positioning of the front focusing group with the back focusing group i.e. in AF mode the controller sends the front USM controlled group to the desired location using an open-loop LUT approach; any over/undershoot is then compensated by the more responsive closed-loop voice coil motor controlled rear focus group. So since in that lens, the front USM group is manually controllable in MF mode (i.e. has direct coupling, not focus-by-wire), then you should be able to position the front focus group in an ideal, peak
...Show more

No. For a 70-200mm lens, the focus group has to move quite far to change the focus distance. Linear motors lack the speed, so Sony used a USM motor. They also wanted a second focusing group for aberration correction, which uses the linear motor. That one has only small travel. The camera tells the lens "I think you're focused at x, I want you to go to y." The USM motor and linear motor move in unison to the position in the LUT that will achieve focus at y. Once near y, the USM motor is no longer used and the linear motor fine tunes the focus.

If the USM group is in the wrong position, it may generate quite massive aberrations, esp. in a lens with 3 aspheres that will have aggravated sensitivity, that are not recoverable from the linear motor.



Sep 07, 2017 at 02:02 PM
k-h.a.w
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p.4 #3 · p.4 #3 · DxOmark: FE 100-400mm GM, compact and optically excellent


Many thanks Brandon. Much appreciated.
Could you please give a reference for this detailed information. TIA

K-H.



Sep 07, 2017 at 02:37 PM
Ayoh
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p.4 #4 · p.4 #4 · DxOmark: FE 100-400mm GM, compact and optically excellent


Brandon Dube wrote:
No. For a 70-200mm lens, the focus group has to move quite far to change the focus distance. Linear motors lack the speed, so Sony used a USM motor. They also wanted a second focusing group for aberration correction, which uses the linear motor. That one has only small travel. The camera tells the lens "I think you're focused at x, I want you to go to y." The USM motor and linear motor move in unison to the position in the LUT that will achieve focus at y. Once near y, the USM motor is no longer used
...Show more

I don't think you understand this. You claimed that "In this lens, the near focus control simply changes over to the second motor. If the USM motor is in the wrong place, the image quality will suffer and this is not correctable within their control loop."
SO what you are saying is that in AF mode if the USM is not in the desired ideal position for peak focus, it is not repositioned but instead the VCM (voice coil motor) tries to compensate, but this compensated focus position may not be ideal (due to the use of aspheres, as you suggest). So what happens if the USM IS in the ideal position? well by that logic it should be at peak image quality. So given that the USM can be repositioned manually by hand in MF mode in that lens, should you not be able to reach ideal focus position by careful manual focus? Is so then the lens can behave differently in AF vs MF mode as I explained earlier. This is a consequence of the operating scenario you hypothesised for this lens.



Sep 07, 2017 at 03:06 PM
Brandon Dube
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p.4 #5 · p.4 #5 · DxOmark: FE 100-400mm GM, compact and optically excellent


Ayoh wrote:
I don't think you understand this. You claimed that "In this lens, the near focus control simply changes over to the second motor. If the USM motor is in the wrong place, the image quality will suffer and this is not correctable within their control loop."
SO what you are saying is that in AF mode if the USM is not in the desired ideal position for peak focus, it is not repositioned but instead the VCM (voice coil motor) tries to compensate, but this compensated focus position may not be ideal (due to, as you claim, the use of aspheres).
...Show more

If the zoom (internal focus groups are zoom) is misconfigured for the given object conjugate, the image quality is going to be bad. Try setting an internal focus macro lens like the 100L or Nikon's equivalent to focus at infinity, then focusing it into macro distance with extension tubes. The image quality will be very bad. This is the same scenario.

If the lens operated its focusing motors differently between AF and MF modes, it would be obvious to the user (different image quality) and someone would have raised an enormous stink on the internet by now.

You assume the MF ring dictates the USM motor only. That is wrong.



Sep 07, 2017 at 03:22 PM
Ayoh
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p.4 #6 · p.4 #6 · DxOmark: FE 100-400mm GM, compact and optically excellent


Brandon Dube wrote:
If the zoom (internal focus groups are zoom) is misconfigured for the given object conjugate, the image quality is going to be bad. Try setting an internal focus macro lens like the 100L or Nikon's equivalent to focus at infinity, then focusing it into macro distance with extension tubes. The image quality will be very bad. This is the same scenario.

If the lens operated its focusing motors differently between AF and MF modes, it would be obvious to the user (different image quality) and someone would have raised an enormous stink on the internet by now.

You assume the MF
...Show more

But your logic is based on the USM being in a non-ideal position due to AF control system positioning approximations. If you carefully position the USM manually in MF mode (which you can in this lens since the front focus group is mechanically linked to the focus ring) then you can remove this positioning error.
Whether the rear focus group is actuated in MF mode or not (it probably is) is secondary to the point here which was that: in AF the USM position may not be ideal and is compensated in a compromised way by the rear group, but in MF the USM position may be positioned ideally removing the compromising compensation imposed by the rear group.



Sep 07, 2017 at 03:56 PM
Brandon Dube
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p.4 #7 · p.4 #7 · DxOmark: FE 100-400mm GM, compact and optically excellent


Ayoh wrote:
But your logic is based on the USM being in a non-ideal position due to AF control system positioning approximations. If you carefully position the USM manually in MF mode (which you can in this lens since the front focus group is mechanically linked to the focus ring) then you can remove this positioning error.
Whether the rear focus group is actuated in MF mode or not (it probably is) is secondary to the point here which was that: in AF the USM position may not be ideal and is compensated in a compromised way by the rear group, but in
...Show more

The rear focus group is incapable of compensating the aberrations of the front focusing group. That is the entire premise of lens design, and is what I believe causes a lot of the inconsistency in this lens.

The rear group is an aberration generator. Its goal is to compensate the aberrations of the other 22 lenses in the system. If 2 or 3 (the front focus group) are grossly despaced, you can't compensate that. It isn't the rear group screwing up the system, it's the inaccuracy of the front group doing it.

Having 5+ zoom/focus cams doesn't help with parallelism either.



Sep 07, 2017 at 04:04 PM
Parariss
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p.4 #8 · p.4 #8 · DxOmark: FE 100-400mm GM, compact and optically excellent


Of the suspected problems, can any be improved with a software update?


Sep 09, 2017 at 11:12 PM
k-h.a.w
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p.4 #9 · p.4 #9 · DxOmark: FE 100-400mm GM, compact and optically excellent


What problems?

K-H.



Sep 10, 2017 at 12:37 AM
 

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PhilthePhrame
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p.4 #10 · p.4 #10 · DxOmark: FE 100-400mm GM, compact and optically excellent


The Sigma 150-600mm weighs about the same, is 2" longer, and a stop slower, but has more reach. The Sony is probably sharper, but at 1/3 the price, the Sigma remains attractive for some of us, and the Sony will be a hard sell.



Sep 10, 2017 at 02:27 AM
freaklikeme
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p.4 #11 · p.4 #11 · DxOmark: FE 100-400mm GM, compact and optically excellent


If the rumors are true, Sigma may launch their own e-mount superzoom, so the choices may get even tougher.

Before I sold my stock a7rII, I rented this and the comparable Canon vII to compare to my Canon 400/5.6L. The Canon zoom has the highest global contrast, but that obliterates much of the fine detail the Sony zoom and Canon prime showed. At 400, the Sony's better in the center 2/3's than the prime, but the outer 1/3 goes to the prime, which is pretty consistent across the frame (even more so on the Kolari UT mod). Where the prime really strutted its stuff was with the 1.4x vIII attached. Sony's 1.4x just can't compete, at least not the rental copy I had.



Sep 10, 2017 at 02:40 AM
virtualrain
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p.4 #12 · p.4 #12 · DxOmark: FE 100-400mm GM, compact and optically excellent


I was out testing my lens at full reach with the 1.4x TC today and I'm pretty amazed with the sharpness.

Here are a few random shots that are not only at 560mm from my a7RII but they are also cropped about 2:1 which means these are the equivalent of about 1000mm.

You should be able to click through and access the full size JPEGs if you want to have a closer look.

All three were shot handheld on a rainy day here. The first one at 1/500 (3200 ISO), the other two at 1/125 to test the image stabilization.

Honestly, the biggest issue with the 1.4TC that I can see, is that in less than ideal light, the ISO required to get decent shutter speeds to stop action and compensate for hand holding are getting up there. If you shoot at 1/500 and f/8 you're looking at anywhere from 3200 to 20000 ISO which is going to kill image quality more than any perceived reduction in optical quality. The first image is a good example of how the ISO is affecting it more than the lens.


DSC07859 1 by VirtualRain (Junk Photos), on Flickr


DSC07897 by VirtualRain (Junk Photos), on Flickr


DSC07884 by VirtualRain (Junk Photos), on Flickr





Sep 10, 2017 at 06:36 AM
virtualrain
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p.4 #13 · p.4 #13 · DxOmark: FE 100-400mm GM, compact and optically excellent


Here's a couple of different looks at that last sail boat image...

The first is the uncropped image at 560mm. The second is a 200% zoom so you can read the label on the Propane Tank


DSC07884 1 by VirtualRain (Junk Photos), on Flickr


Crop 200-Percent by VirtualRain (Junk Photos), on Flickr



Sep 10, 2017 at 06:56 AM
virtualrain
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p.4 #14 · p.4 #14 · DxOmark: FE 100-400mm GM, compact and optically excellent


Here's another 560mm shot, this one at 1/125 and 640ISO so a bit cleaner. Very sharp as you can see from the 100% crop.


DSC07882 by VirtualRain (Junk Photos), on Flickr


100 Percent Crop by VirtualRain (Junk Photos), on Flickr



Sep 10, 2017 at 07:17 AM
Parariss
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p.4 #15 · p.4 #15 · DxOmark: FE 100-400mm GM, compact and optically excellent




k-h.a.w wrote:
What problems?

K-H.


Sorry,I wasn't clear:
I was referring to the discussion about the 70-200GM's issues.



Sep 11, 2017 at 07:01 AM
freaklikeme
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p.4 #16 · p.4 #16 · DxOmark: FE 100-400mm GM, compact and optically excellent


virtualrain wrote:
I was out testing my lens at full reach with the 1.4x TC today and I'm pretty amazed with the sharpness.

Here are a few random shots that are not only at 560mm from my a7RII but they are also cropped about 2:1 which means these are the equivalent of about 1000mm.

You should be able to click through and access the full size JPEGs if you want to have a closer look.

All three were shot handheld on a rainy day here. The first one at 1/500 (3200 ISO), the other two at 1/125 to test the image stabilization.

Honestly, the biggest
...Show more

Hmm, your copy with the 1.4x looks better than my rental at 400 without the extender. Did you do anything to these in post?



Sep 11, 2017 at 07:15 PM
virtualrain
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p.4 #17 · p.4 #17 · DxOmark: FE 100-400mm GM, compact and optically excellent


freaklikeme wrote:
Hmm, your copy with the 1.4x looks better than my rental at 400 without the extender. Did you do anything to these in post?


Hi sorry for the delayed response, but yes, there is some minor sharpening applied in post. I can post some RAW files on Dropbox for anyone interested.

The more I examine the difference with and without the TC on this lens, the more it comes down to subtle differences in sharpness really only seen at 100% before applying any post sharpening. Some people say they see no difference between shots with the TC and without. I'm certain those folks are not pixel peepers.

The TC definitely does slightly reduce sharpness and contrast vs shooting without it, but it still captures all the detail, if not a bit more, so when you apply a bit of added sharpening and levels you get images with the TC that are just as good as without, but obviously magnified.

This makes sense if you think about what the TC is doing optically, which is magnifying the image circle to be 1.4 times bigger... all the same detail the lens resolves is still there but it's magnified or projected larger on the sensor. The edges are slightly less refined. Sharpening things a bit or adding some clarity or structure snaps the image back to non-TC like sharpness and contrast without artifacts.

Personally, I would have no trouble sharing a 100% crop of an image shot at 560mm with the TC after a bit of sharpening and levels like the samples above, and the same obviously goes for a 100% crop of a shot at 400mm without the TC. But what is ugly, of course, is comparing the 400mm cropped to 140% vs the 560mm at 100%... so if you need that added reach, the TC is better than cropping, or buys you even more reach, as both can be cropped about the same amount before they get ugly.

Now one other thing I've looked at, is should I be taking the TC off when shooting a FoV between 100-400mm? The answer is, it doesn't really matter. Shots between 100-400 without the TC will be sharper out of the camera than the same composition with the TC on there, but as I say above, you can get the TC images looking just as good as the non-TC ones just by adding a bit of sharpening and contrast in post. Where the TC kills you is not in optical sharpness, but in doubling noise from a stop higher ISO.

Hope that makes sense. If anyone disagrees, I'm open to a discussion as I'm really just still wrapping my head around this combo and can guarantee I haven't got it all figured out just yet. I need to spend some more time with it.



Sep 13, 2017 at 07:22 AM
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