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04-26-2021, 05:39 PM   #1
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Test of 4 lenses at the wide end

I have tested 4 lenses at a wider end with some unexpected results.

Method:
I photographed a banknote in the center of the frame with different lenses at different focal distances. In each shot the banknote has the same size on the sensor (i.e. I moved the camera relative to the subject to keep the image same size on the sensor). The lenses were mounted on a KP, on a tripod, shot with a 2-sec. timer, in DNG. Images were looked at 200% magnification in Lightroom and compared side by side for sharpness, resolution, and contrast. I did no image processing (like sharpening), other than occasional minor exposure correction to compensate for changing lighting conditions. Then they were ranked relative to each other for each FL and each f-stop, i.e. for each stop there were four positions: 1, 2, 3, 4 (higher number = better IQ). Corollary: IQ at different f-stops cannot be compared in terms of absolute quality. At times, it was very hard to tell the difference in IQ and I admit that sometimes difference between adjacent ranks is very subjective. When one looks at extremes end in IQ, the difference is rather obvious.

Lenses tested:
Sigma 10-20mm F4-5.6 EX
Pentax DA 16-85
Pentax FAJ 18-35mm F4-5.6 (the only full-frame lens here)
Pentax DA 18-55mm F3.5-5.6 AL

The lenses were tested at 16mm, 18mm, and 20mm, at f-stop of 4.0 (or whatever the largest f-top is available for that lens), 5.6, and 8.0. Sometimes, a lens had f/3.5, but I plotted it as 4.0.


Results:

---------- Post added 04-26-21 at 05:45 PM ----------

Discussion:
16mm: I was surprised to see Sigma outperform the DA 16-85. Sigma is a budget lens, while DA16-85 is a rather respected lens on this forum.
18mm: Again, Sigma is above all at any f-stop, but an even more surprising result is that wide-open DA16-85 looses to FAJ18-35 and DA18-55, both known as very weak lenses! How come? Any ideas?
20mm: DA16-85 is still struggling a lot. FAJ18-35 is the best at f/8! This is not normal. I must have messed up my test.

Attached Images
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PENTAX K-1  Photo 
View Picture EXIF
PENTAX K-1  Photo 
View Picture EXIF
PENTAX K-1  Photo 

Last edited by pentax_amateur; 04-26-2021 at 10:03 PM.
04-26-2021, 05:53 PM   #2
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I would be glad to upload any combinations of images. Let me know what you would like to see for yourself (there are too many to upload all of them).
Here is and example at 16mm wide open.
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04-26-2021, 06:40 PM - 1 Like   #3
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The biggest difference with the DA 16-85mm is that it's a 5:1 zoom whereas the others are about 2 or 3:1. Zooms tend to be optimized for the middle of the range. That would be about 50mm for the 16-85mm.
04-26-2021, 07:17 PM   #4
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Right, but even DA18-55 (which is a CHEAP lens) outperforms DA16-85.
(I do not understand these EXIFs. These images were saved from Excel.)


Last edited by pentax_amateur; 04-26-2021 at 07:29 PM.
04-26-2021, 09:08 PM   #5
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QuoteOriginally posted by pentax_amateur Quote
I have tested 4 lenses at a wider end with some unexpected results.

Method:
I photographed a banknote in the center of the frame with different lenses at different focal distances. In each shot the banknote has the same size on the sensor (i.e. I moved the camera relative to the subject to keep the image same size on the sensor). The lenses were mounted on a KP, on a tripod, shot with a 2-sec. timer, in DNG. Images were looked at 200% magnification in Lightroom and compared side by side for sharpness, resolution, and contrast. I did no image processing (like sharpening), other than occasional minor exposure correction to compensate for changing lighting conditions. Then they were ranked relative to each other for each FL and each f-stop, i.e. if for each stop there were four positions: 1, 2, 3, 4 (higher number = better IQ). Corollary: IQ at different f-stops cannot be compared in terms of absolute quality. At times, it was very hard to tell the difference in IQ and I admit that sometimes difference between adjacent ranks is very subjective. When one looks at extremes end in IQ, the difference is rather obvious.

Lenses tested:
Sigma 10-20mm F4-5.6 EX
Pentax DA 16-85
Pentax FAJ 18-35mm F4-5.6 (the only full-frame lens here)
Pentax DA 18-55mm F3.5-5.6 AL

The lenses were tested at 16mm, 18mm, and 20mm, at f-stop of 4.0 (or whatever the largest f-top is available for that lens), 5.6, and 8.0. Sometimes, a lens had f/3.5, but I plotted it as 4.0.


Results:

---------- Post added 04-26-21 at 05:45 PM ----------

Discussion:
16mm: I was surprised to see Sigma outperform the DA 16-85. Sigma is a budget lens, while DA16-85 is a rather respected lens on this forum.
18mm: Again, Sigma is above all at any f-stop, but an even more surprising result is that wide-open DA16-85 looses to FAJ18-35 and DA18-55, both known as very weak lenses! How come? Any ideas?
20mm: DA16-85 is still struggling a lot. FAJ18-35 is the best at f/8! This is not normal. I must have messed up my test.
Edge performance is something I’d suggest testing also.

Why did the 18-55 crash at f8?
04-26-2021, 10:00 PM   #6
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QuoteOriginally posted by UncleVanya Quote
Edge performance is something I’d suggest testing also.
I did! I just have to process the images.

QuoteOriginally posted by UncleVanya Quote
Why did the 18-55 crash at f8?
To me, the question is How did it do so well wide-open! It is a cheap kit lens. Here it is against the Sigma and FAJ:
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04-26-2021, 10:15 PM   #7
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If you photographed at the same focal length and had to move the camera then there is breathing, meaning they are not really the same focal length at short distance.
How much did you have to move them and it would be intetesting to know which is widest at each length.

04-26-2021, 11:52 PM   #8
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Sigma EX is years old but still it was "professional" lens with good reputation.
I owned and used one for years, only recently I passed it to my niece.
FAJ is a FF lens so you use its sweet spot on the crop body.
Pentax had / has always reputation for providing above average IQ on kit lenses.
The 16-85 is just a longish zoom upmarket kit lens with obvious compromises.
04-27-2021, 12:25 AM   #9
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All the lenses you tested are on a high level IQ wise. Even the 18-55 is a very good kit lens.
All these lenses have there issues on the short end.

Thus you are testing a very good lens (Sigma) on it's sweet spot against a very good lens (16-85) on its weak side. Outcome is predictable, don't you think so?
On the other side, if the image you posted for the 16-85 at 16 mm and 3.5 is exemplary for the whole of the test images taken with it, I would say you have issues with your copy of the lens. Might it be decentering or focusing.

Here are the tests opticallimits did with the lenses. Mind you they are all taken with different megapixel sizes and the Sigma 10-20 is tested with a Nikon.
But the performance of a lens scales rougly with sensor size, i.e. if you get 80% of possible resolution on a 10 MP sensor you will get something a bit below of 80% on a 16 MP sensor with a good lens.

Pentax SMC-DA 18-55mm f/3.5-5.6 AL - Review / Test Report - Analysis
Pentax HD DA 16-85mm f/3.5-5.6 ED DC WR - Review / Test Report - Analysis
Sigma AF 10-20mm f/4-5.6 EX DC HSM - Review / Lab Test Report - Analysis
04-27-2021, 04:02 AM   #10
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The Sigma seems like a robust performer. I love my 18-55, it's really, surprising good at many occasions.
04-27-2021, 04:13 AM   #11
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QuoteOriginally posted by pentax_amateur Quote
I would be glad to upload any combinations of images. Let me know what you would like to see for yourself (there are too many to upload all of them).
Here is and example at 16mm wide open.
Here the Sigma seems to be doing much better.
04-27-2021, 04:36 AM   #12
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That’s a terrific pile of work you have done.

How’d the sigma and kit lens shoot at 85?

(Some sacrifices/trade offs are made to be something the others are not ie a short tele)
04-27-2021, 06:13 AM   #13
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QuoteOriginally posted by pentax_amateur Quote
16mm: I was surprised to see Sigma outperform the DA 16-85. Sigma is a budget lens, while DA16-85 is a rather respected lens on this forum.
Not surprised that a lens performs better in the center of its focal range.

QuoteOriginally posted by pentax_amateur Quote
DA16-85 looses to FAJ18-35 and DA18-55, both known as very weak lenses! How come? Any ideas?
DA18-55 is not weak per se.

QuoteOriginally posted by pentax_amateur Quote
I must have messed up my test.
Two possible issues that I see.

1-How did you focus? Using focus peaking in live view, or with the viewfinder? The later will lead to errors, especially if you have not fine-tuned the AF.

2-You are not always comparing identical apertures.

A better way would have been to compare identical apertures, and consider anything wider to be a bonus. for instance, say the 18-55 offers only F4, and the 16-85 offers F3.5, that wider aperture is a bonus, and at F4 you can compare apples to apples.

There are more elements than just pure sharpness to define if a lens is "well regarded". It's certainly part of it but doesn't tell the whole story.
04-27-2021, 06:50 AM   #14
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QuoteOriginally posted by swanlefitte Quote
If you photographed at the same focal length and had to move the camera then there is breathing, meaning they are not really the same focal length at short distance.
How much did you have to move them and it would be intetesting to know which is widest at each length.
There is a little breathing, but I don't think it affects the outcome. While FL may not be exactly the same, they are very close.
04-27-2021, 06:52 AM   #15
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QuoteOriginally posted by i_trax Quote
Sigma EX is years old but still it was "professional" lens with good reputation.
I owned and used one for years, only recently I passed it to my niece.
FAJ is a FF lens so you use its sweet spot on the crop body.
But FAJ is voted multiple times as the worst Pentax lens ever in another thread, and I have to agree. In my experience, it is a pretty bad lens. I disagree with the whole idea of "sweet spot" of ff lenses on a cropped format. If you take a bad image and blow it up x1.5... I don't see how it may become good.

QuoteOriginally posted by i_trax Quote
The 16-85 is just a longish zoom upmarket kit lens with obvious compromises.
Yet, it is recommended above 20-40 Limited in another thread for its wide angle. My surprise here is that DA16-85 is doing so badly at the wide end, which is its selling feature. What is the point of a lens with wide angle capability if it does so badly at those FL?

Last edited by pentax_amateur; 04-27-2021 at 07:10 AM.
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