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03-30-2016, 04:33 AM - 1 Like   #1
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A number of Pentax lenses tested on FF sensor.

I have just stumbled upon this Swedish site and their article about FF and Pentax lenses. Despite the old date (28feb), i have not found this has been posted here before.
As quoting the site - this is a review of six full frame prime lenses for the new Pentax K-1 DSLR. Completed with their MTF charts showing each lens performance on a full frame sensor.

You can easily translate this to English via google translate. (from Swedish)

TEST: Sex fasta fullformatsobjektiv för Pentax K-1

03-30-2016, 04:44 AM   #2
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QuoteOriginally posted by sunCrm Quote
I have just stumbled upon this Swedish site and their article about FF and Pentax lenses. Despite the old date (28feb), i have not found this has been posted here before.
As quoting the site - this is a review of six full frame prime lenses for the new Pentax K-1 DSLR. Completed with their MTF charts showing each lens performance on a full frame sensor.

You can easily translate this to English via google translate. (from Swedish)

TEST: Sex fasta fullformatsobjektiv för Pentax K-1
Thanks. Three FA limited are tested there!
03-30-2016, 05:43 AM   #3
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QuoteOriginally posted by starjedi Quote
Thanks. Three FA limited are tested there!
Not to mention the FA35, FA50 and 50 Macro!
03-30-2016, 06:02 AM - 1 Like   #4
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I was a little shocked to read "Test: Sex fasta fullformatsobjektiv för Pentax K-1" Then I realized it wasn't translated yet.

03-30-2016, 06:06 AM   #5
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interestingly that such old glas still gets such high marks! however the jewel the 31/1.8 is said to have severe vignetting and not really that good sharpness wide open. Surely its 1.8 but owners say the 31mm was to be very sharp, even wide open. Is their copy at fault perhaps?

How do you compare such results to other brands offerings, is pentax well set? Interestingly they consider some lenses to be too expensive, can we expect prices to go down in the future?
03-30-2016, 06:41 AM   #6
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QuoteOriginally posted by quh86 Quote
interestingly that such old glas still gets such high marks! however the jewel the 31/1.8 is said to have severe vignetting and not really that good sharpness wide open. Surely its 1.8 but owners say the 31mm was to be very sharp, even wide open. Is their copy at fault perhaps?

How do you compare such results to other brands offerings, is pentax well set? Interestingly they consider some lenses to be too expensive, can we expect prices to go down in the future?
Most people agree that the 31 is soft wide open, but sharpens up quickly when stopping down.

Pentax is well set, unless you want Zeiss Otus "quality", and even then sigma is producing close seconds that will likely find their way to K mount if the K-1 takes off.

Thanks OP for the article!
03-30-2016, 07:43 AM   #7
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QuoteOriginally posted by jeffshaddix Quote
Most people agree that the 31 is soft wide open, but sharpens up quickly when stopping down.

Pentax is well set, unless you want Zeiss Otus "quality", and even then sigma is producing close seconds that will likely find their way to K mount if the K-1 takes off.

Thanks OP for the article!
A good copy of FA 31 should be sharp from F1.8. However, de-centering issue due to sample variance can drop down the sharpness at wide open significantly.

For the vignetting, it sounds to be normal for FF wide angle lens, at least on par with Zeiss 35 F2. However, the latest lens like Tarmon 35 1.8 do much better.
03-30-2016, 08:30 AM   #8
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03-30-2016, 01:41 PM   #9
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QuoteOriginally posted by quh86 Quote
interestingly that such old glas still gets such high marks! however the jewel the 31/1.8 is said to have severe vignetting and not really that good sharpness wide open. Surely its 1.8 but owners say the 31mm was to be very sharp, even wide open.
On APS-C you're always getting the sharper inner half of rhe lens' image circle.

FF will reveal the softer outer half.
03-30-2016, 06:04 PM   #10
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QuoteOriginally posted by starjedi Quote
A good copy of FA 31 should be sharp from F1.8. However, de-centering issue due to sample variance can drop down the sharpness at wide open significantly.
Have there been any definitive tests to show this? I know there's sample variation, but are there any objective tests between multiple copies that show the MTF increase at 1.8 is more than marginal?

Not doubting you, just curious.
03-30-2016, 07:12 PM - 3 Likes   #11
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QuoteOriginally posted by jeffshaddix Quote
are there any objective tests between multiple copies that show the MTF increase at 1.8 is more than marginal?
On my optics bench I have tested 26 copies of the pentax SMC-FA 31mm f/1.8 Limited - My own copy of the FA31 is perfectly centered: and produces excellent resolution and contrast across the full format frame even at f/1.8*. Compared to the rest of the samples tested there was in some cases a considerable variance in optical performance, but the variance is no greater than that of any other AF lens manufacturer like Canon, Nikon and Sigma.

It has occurred to me I should plot the lens variation data and post it onto pentax forums, but the problem is I have a LOT of data, and a LOT of lenses. These things take time to verify and put into an visual format and there are instances where certain lenses are so rare I don't have enough samples to make any reasonable reports on sample variation.

* Though I will state that contrast is somewhat lowered at f/1.8 in the corners, resolution is still quite high.

Last edited by Digitalis; 03-30-2016 at 11:41 PM.
03-31-2016, 04:43 AM - 1 Like   #12
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QuoteOriginally posted by Digitalis Quote
there are instances where certain lenses are so rare I don't have enough samples to make any reasonable reports on sample variation.
I think a lot of people would still appreciate seeing an isolated datum (or rather the data on one lens) in that case, accepting the limitations that rarity brings. Any systematic assessment (with limitations admitted) is better than none at all.
03-31-2016, 06:22 AM   #13
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QuoteOriginally posted by pathdoc Quote
I think a lot of people would still appreciate seeing an isolated datum (or rather the data on one lens) in that case, accepting the limitations that rarity brings. Any systematic assessment (with limitations admitted) is better than none at all.
Agreed, and thanks for speaking up Digitalis - 26 copies of the 31 is plenty for significant results.

I'm glad to know some copies show good resolution at 1.8, hopefully better than the lens review sites suggest.

I'm currently doing the rounds at B&H swapping out the 16-85 because of decentering. If I recall correctly, Sigma announced improved assembly practices a couple years back with their global vision - I wonder if there has been a tangible improvement to their reliability on proper centering...
03-31-2016, 07:35 AM   #14
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QuoteOriginally posted by jeffshaddix Quote
I wonder if there has been a tangible improvement to their reliability on proper centering...
The answer to this is a qualified NO.

QuoteOriginally posted by pathdoc Quote
I think a lot of people would still appreciate seeing an isolated datum
I thing presenting the data as a range than as a specific point would be more valuable here, as variation is inevitable.

Last edited by Digitalis; 03-31-2016 at 07:43 AM.
03-31-2016, 07:54 AM   #15
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QuoteOriginally posted by Digitalis Quote
I thing presenting the data as a range than as a specific point would be more valuable here, as variation is inevitable.
Oh, it is, and for the garden-variety in-production or easily available old glass I completely agree. But for lenses that are so uncommon that most of us would never see one, let alone own it, assessment of a single example has its uses (if only prurient interest). For true collectors' items, sufficient numbers for a statistically representative sample may not even exist.

The trouble, as always, is with people who don't know how to interpret such single examples in the context of the implicit caveats. "This lens is factory-fresh, new in box" is a different matter from "This lens spent fifty years in backpacks travelling to all corners of the earth, kicking around under the owner's bed and getting slobbered, carried about and repeatedly buried by their bull mastiff dog." Quality issues and bench-test results have different implications in each case.
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