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Longitudinal Chromatic Aberration 1X Macro Lens Test
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Doppelgänger



Joined: 11 Feb 2018
Posts: 15

PostPosted: Thu Feb 15, 2018 7:59 am    Post subject: Reply with quote

Lou Jost wrote:
Doppelganger, you've stated several times that CA can be corrected in post, while lack of sharpness cannot. However, the type of CA that Robert's tests were designed to reveal, LoCA, is not readily correctable in post. That's why Robert's tests here, which are aimed just at that aspect of the image, are especially useful.

Also, sharpness can indeed be increased in post to a certain extent.

I surely agree that this is just one aspect of an image, and that other aspects also need to be taken into account when choosing a lens for a particular job. I am sure Robert was not implying that LoCA is the only criterion for lens choice.



Respectfully, I disagree. It is not possible to do a stack wide-open, with a soft lens, with average rendering, and come out with a razor-sharp outcome with beautiful rendering. It's simply not possible.

The CA that this test showed was in 'worst possible scenario' conditions, and even here the difference in sharpness between the two lenses was unmistakable.

The difference in quality in real world stack of a flower (or other natural subject), in nice light, at f/4 would be quite noticeable. No amount of post processing could transform a stack from the Sigma at f/4 to what the CV 125 could produce at f/4 IMHO.
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ChrisR
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PostPosted: Thu Feb 15, 2018 8:21 am    Post subject: Reply with quote

Quote:
Yet in even this test, the difference in sharpness wide open between these lenses is literally night and day.
That's not apparent from what I see on the quoted photos, because the focus point is clearly not the same. The Sigma's may even be on the paper between the printing, I can't tell. It's obviously further back because the next row is sharper.
That has no bearing for the intended purpose.

The internet is awash with people posting images trying to justify their statements about some fave lens. All too frequently the accompanying images have something different and relevant about them, which was not considered.

DG You clearly enjoy your Apo-Lanthar. I'd like to see some objectively taken comparison photos which demonstate its qualities, in a separate thread.
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Doppelgänger



Joined: 11 Feb 2018
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PostPosted: Thu Feb 15, 2018 8:23 am    Post subject: Reply with quote

RobertOToole wrote:
billjanes1 wrote:


Robert did indicate that LoCA can be removed by stacking with Zerene (and presumably with other stacking algorithms), which is interesting and previously unknown to me. Since stacking is often used with higher magnification, LoCA is less problematic in this situation.

One limitation of his test series is that he tested at 1:1, and many times we use our "macro" lenses at 1:2 or less. Jim Kasson tested at 1:2 and got better results with the Nikon 105 f/2.8 VR.

Bill


Good points Bill.

I would like to run some tests at 1:2 and even 1:3 since that is where I personally shoot most but I haven't been able to find the time. I started at 1x since I thought it would be more popular and it is tougher test for lenses, as you mention.

All the best,

Robert



I would be very interested in your opinion and findings in such a test Smile

More specifically, I would like to hear your views on a manual stack test @ 1:2, on a subject like a flower (in optimal light), maybe 4-6 layers deep, using the focus ring.

First compare the image quality of the CV stacked @ f/2.5-f/4 to the Sigma stacked at f2.8-f/4.

Then compare the above CV stacked results to the Sigma at f/8, when it becomes fairly-sharp.

Note also the difference in precision-focusing sensitivity between the two and describe subtle, natural stacking efforts in the focus ring between them. This will be a better way to appreciate the CV 125.

Another big thanks for your time and effort.
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billjanes1



Joined: 30 Dec 2016
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PostPosted: Thu Feb 15, 2018 9:37 am    Post subject: Re: Longitudinal Chromatic Aberration 1X Macro Lens Test Reply with quote

[quote="Doppelgänger"]
RobertOToole wrote:


What makes the Voigtlander 125 such a great macro lens is the fact it is unusually-sharp wide-open and razor-sharp by f/4 (just look at it compared to the Sigma).

When you add to this exceptional bokeh and color-rendering qualities, along with something like 600-degrees of focus throw, you have a lens that is capable of delivering terrific images, which really separate the subject from the background (which is beautifully-rendered), especially when light stacks are employed.


The focus throw of the Voigtlander is very useful for manual focusing, but auto focus lenses have a distinct advantage in that focusing steps can be made very precisely via software and enable automation of the stack. Please refer to Rik's table below for some details.

The screw drive autofocus of the Nikkor 200 mm f/4 is not good for automation, and I have chosen the Sigma 180 mm f/2.8 instead and did not want to wait for Nikon to update their 200 mm lens.



Bill
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rjlittlefield
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PostPosted: Thu Feb 15, 2018 10:01 am    Post subject: Re: Longitudinal Chromatic Aberration 1X Macro Lens Test Reply with quote

billjanes1 wrote:
Please refer to Rik's table below for some details.

Providing some additional links...

The referenced page is at http://zerenesystems.com/cms/stacker/docs/troubleshooting/ringversusrail .

The blue-background slide appears to be an extract from one of my PowerPoint presentations, perhaps slide 24 of "Introduction to Focus Stacking" at http://zerenesystems.com/presentations/4CsWallaWalla20151009/4CsWallaWalla20151009.pdf .

--Rik
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billjanes1



Joined: 30 Dec 2016
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Location: Lake Forest, IL, USA

PostPosted: Thu Feb 15, 2018 11:25 am    Post subject: Re: Longitudinal Chromatic Aberration 1X Macro Lens Test Reply with quote

rjlittlefield wrote:
billjanes1 wrote:
Please refer to Rik's table below for some details.

Providing some additional links...

The referenced page is at http://zerenesystems.com/cms/stacker/docs/troubleshooting/ringversusrail .

The blue-background slide appears to be an extract from one of my PowerPoint presentations, perhaps slide 24 of "Introduction to Focus Stacking" at http://zerenesystems.com/presentations/4CsWallaWalla20151009/4CsWallaWalla20151009.pdf .

--Rik


Rik,

Thanks for the additional information. I did extract the slide from your presentation. I hope that is OK. This is for private use, not publication.

The example of stacking the artificial flower with focus by ring and by rail is instructive. In the past, I have gotten decent results with stacking a flower in Zerene using the rail with my 180 mm lens. I assume the additional focal length would reduce perspective distortion. However, with my Nikon D850 I can use what they call "focus shift" very easily and quickly. In addition, use of the electronic shutter avoids vibration and reduces wear on the mechanical shutter.

My focus rail is still useful to position the camera to get the desired field of view.

Regards,

Bill
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rjlittlefield
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PostPosted: Thu Feb 15, 2018 1:21 pm    Post subject: Re: Longitudinal Chromatic Aberration 1X Macro Lens Test Reply with quote

billjanes1 wrote:
I did extract the slide from your presentation. I hope that is OK. This is for private use, not publication.

My major concern is that a link to the original source be maintained. Otherwise there's a distinct possibility of information going stale without warning.

--Rik
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Doppelgänger



Joined: 11 Feb 2018
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PostPosted: Thu Feb 15, 2018 4:57 pm    Post subject: Re: Longitudinal Chromatic Aberration 1X Macro Lens Test Reply with quote

billjanes1 wrote:

The focus throw of the Voigtlander is very useful for manual focusing, but auto focus lenses have a distinct advantage in that focusing steps can be made very precisely via software and enable automation of the stack. Please refer to Rik's table below for some details.
Bill


Good point, if you're shooting in studio.

However, being soft wide-open makes the whole effort not so worthwhile.

Rik's table really only applies to 'most' lenses, not the CV 125.
You can't compare a standard, plastic lens (with a 'loose' 120-240 degree focus throw) to a precision macro lens with a smooth, first class 600+ degree focus throw. Apples and oranges as it gets.
(It's like comparing how a Toyota Corolla handles a mountain road to how a Porsche 911 handles it. The class/handling levels are worlds apart.)



billjanes1 wrote:

The screw drive autofocus of the Nikkor 200 mm f/4 is not good for automation, and I have chosen the Sigma 180 mm f/2.8 instead and did not want to wait for Nikon to update their 200 mm lens.
Bill


Good choice. I'm pretty sure the Sigma 180 is the best of its kind IMO, much much sharper wide-open than its siblings. I've not tried to program stack it on a D850 but I am sure it is nice.



Sigma 180mm f/2.8




Sigma 150mm f/2.8



As you can see in Mr. Otoole's tests, and in Ephotozine's Imatest, the Sigma 150mm is quite dull wide-open, and barely achieves excellence stopped down, while the 180mm f/2.8 (not to be confused with the lesser f/3.5) is well passed excellent, even wide-open, with much better edge to edge sharpness as well. It may not be quite as 'well-corrected for CA in a white-paper/black letter test,' but it is a much better, sharper lens overall.

Having used both, the CV 125 is even sharper wide-open, and the CV also has better micro-contrast, color rendering, and bokeh.

Also, for attempting to stack live subjects, with a precision focus ring you don't need to 'stop' and program a camera (or setup an automated rail) in the field.
With a Class A, precision focus ring you can just incrementally move your left thumb in smooth, ever so slight, incremental steps.
Even the Sigma 180 can't do this smoothly, or precisely, like the CV 125 can. (I can only explain the difference in 'feel' as Toyotas and Porsches again. They're both cars, but ...)

Have you ever tried to follow a butterfly moving from flower to flower, and get a short stack using camera software (or an automated rail)? Not much fun trying to program on a fleeting moment Very Happy

In-camera software is good for static subjects or maybe dead or posed subjects, where you have the time to set it up. Not so much for real-time, fleeting moment stacks.
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Lou Jost



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PostPosted: Thu Feb 15, 2018 8:26 pm    Post subject: Reply with quote

Quote:
In-camera software is good for static subjects or maybe dead or posed subjects, where you have the time to set it up. Not so much for real-time, fleeting moment stacks.


I have to respectfully disagree here; the opposite is true in my experience. You don't "program" anything when taking a bracketed image. Leave the camera always set to bracket. When you find a subject, press the shutter once and watch the magic happen. It is far faster than manually fiddling with a focusing ring, even a nice focusing ring.

Press the shutter again when you want the stack to end.

This will always beat manual focus-stacking.
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Doppelgänger



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PostPosted: Fri Feb 16, 2018 10:37 am    Post subject: Reply with quote

Lou Jost wrote:

I have to respectfully disagree here; the opposite is true in my experience. You don't "program" anything when taking a bracketed image. Leave the camera always set to bracket. When you find a subject, press the shutter once and watch the magic happen. It is far faster than manually fiddling with a focusing ring, even a nice focusing ring.

Press the shutter again when you want the stack to end.


Isn't bracketing different from in-camera stacking? (Forgive my ignorance, but I've not used in-camera stacking before, only an automated macro rail.)

I was under the impression in-camera stacking had to be re-configured for depth based each new subject/position in the field?

Do you just set your camera for (say) 10 images, and that's it? I would imagine the depth of each click would have to be re-configured based on differences in subject, or are you satisfied with just "one" depth for everything you shoot?

Example: I've manually-stacked from 3 to 50 images with the CV 125, using my real-time assessment of the subject, and simply determining how many subtle rotations of the focus ring I am going to make.

I'm trying to envision how you can render different creative decisions like this, in an automated setup, without re-configuring the settings within your camera.



Lou Jost wrote:

This will always beat manual focus-stacking.


In speed, possibly, if you never change your preferred configuration.

Still, not only would I personally find a "set" number of stacks limiting, but the glaring issue remains that a manual-focus lens which renders each image better (meaning sharper, better color/bokeh) than an AF lens being stacked will produce better end results, especially with wide-open aperture stacks, where you're trying to render the background beautifully. (E.g., a manual-stacked Otus result vs. a program-stacked zoom.)

That said, being as sharp as it is wide-open, I could see the Sigma 180 f/2.8 (not the 150) producing sharp results stacked like this, but I personally prefer the CV 125. It is made for beautiful rendering wide-open.


Last edited by Doppelgänger on Fri Feb 16, 2018 11:32 am; edited 1 time in total
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ChrisR
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PostPosted: Fri Feb 16, 2018 11:32 am    Post subject: Reply with quote

Doppelganger, these matters aren't relevant to this thread and would be better addressed in the Technique, or Beginners' Macro sections.
I suggest you actually try, and demonstrate the benefits you're claiming before making some of these assertions.
However, you seem to be mostly interested in praising your lens, as you're doing it at every opportunity, so expect us to doubt your impartiality. Wink
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Lou Jost



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PostPosted: Sat Feb 17, 2018 11:36 am    Post subject: Reply with quote

Doppelganger, I was referring to "focus bracketing" throughout, though I just called it "bracketing" sometimes, for brevity.

There is no need to choose the desired depth of the stack (ie number of frames) in the field. That's a decision you can make in Zerene. The automatic bracketing is so fast that you can just leave the number of frames set to some high number and let it go. So as not to waste card space, press the shutter a second time when you see the zone of focus has passed the subject. If it didn't go far enough, press the shutter again and the camera continues to bracket where the last set left off.

The step "size" setting normally doesn't need to be changed. It is really not the step size in microns but a measure of the degree of overlap between steps. The distance moved between each shot is calculated based on chosen f/stop and magnification. It will do this calculation much faster than a human can, with no chance of error. There is also no chance that the stack will be accidentally ruined due to misjudgement.

I suspect I could do quite a few deep automated stacks in the time it would take to do one manual stack of the same depth.

The question of lens quality is a separate issue; I don't have the CV 125mm so can't comment on that. I am sure it is a great lens, and many old manual lenses do better than many of todays' automatic lenses. Convenience (ease of use) does have to be considered, though, when making a lens choice, especially for field work. A 150mm Printing Nikkor with beta ring is optically better than the Apo Lanthar by far, according to tests (it has almost zero CA), but it is hard to work with, so few people use it in the field. Lens choice is a balancing act and reasonable people can come to different decisions depending on the amount of weight they put on different criteria.

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cactuspic



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PostPosted: Thu Feb 22, 2018 8:06 am    Post subject: Reply with quote

Thank you Robert. I always appreciate the care and precision that you apply to your testing. I also have a bit of a cautionary tale, because I did not use the test information correctly at first. In particular, I love the sharpness and overall quality of the images produced with my Sigma 180 mm 2.8. I had not seen the same degree of cr in my images as evidenced in the test. It was only after I read the entire thread that I understood why. Probably 90+ percent of my images with the 180mm are focus stacked botanicals. It is my understanding that stacking mitigates that type of ca to some degree.

Again, thank you for the time and effort taken. It is very helpful.
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