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08-03-2017, 09:05 AM   #16
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Bokeh quality, besides having some aspect of personal preference, is also probably highly dependent on the subject and composition of the photograph as well. Certain subjects may work well with weird bokeh, but others won't.

I do think, however, that there could be some attempt at an objective measurement and comparison of lenses, but those measurements would have to be done at the level of a photo, and not based on manufacturer's published specs. I imagine this could be measuring color, contrast, micro contrast, etc., on a photograph of a standardized scene. It still might not turn out to be very possible, but I don't think anyone has even attempted it, so how would we know for sure?

Lenscore.org describes how they rate bokeh; but I still question the rating of bokeh on a 1000-point scale, though maybe they have 100 people rate it from 1-10?



"LenScore™ Bokeh

How to rate bokeh? Certainly a fair question, and one that is frequently asked. Most photographers have a favorite lens when it comes to bokeh, and most of those lenses are fast, medium to long primes. However, some will argue that the smooth bokeh of modern lenses is bland and boring compared to the busy bokeh of a Helios 40-2 for example, and they have a point. Stunning pictures are taken with the Helios, with weird, beautiful bokeh. These images are not great despite the flawed bokeh, but because of it. Thus, it is all a matter of taste.

Or is it? When we discussed the different aspects of a lens we would like to measure, consensus was easily reached regarding measurement of bokeh: physics. A perfect lens does not introduce any kind of aberrations in out-of-focus areas, both in front of and behind the focal plane. No geometrical distortion, no color shift, no chromatic aberrations, no accentuation or attenuation of edges; just pure, mathematically perfect blurring. But that's exactly the kind of bland bokeh mentioned above, isn't it? Yes it is, but as it happens, the vast majority of people - not just photographers - find this kind of bokeh by far the most aesthetically pleasing. It's also the most versatile, as it will never ruin a shot, it will always look good, no matter what kind of picture is taken. Unfortunately, it is also hard to achieve. The lenses coming closest to mathematically perfect bokeh are also top performers in the other categories, and they're usually on the expensive side.

So what about the Helios and all those other lenses with interesting bokeh? In capable hands, they are creative tools able of producing beautiful images impossible to take with a mathematically perfect lens, but they are not good general purpose tools. In most situations, their optically flawed bokeh will lessen the quality of a shot. It is safe to say that for all but a few special applications, clean and smooth bokeh is preferable, and that's why the LenScore™ bokeh score is based on how close a lens' out-of-focus rendering is to mathematical perfection."

08-03-2017, 09:43 AM   #17
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I agree with Norm to a point on this one. Those of us who have an interest in this conversation see the overall tendency to value chart sharpness over character because the numbers are easily understood. Even if you could reliably measure bokeh quality (doubtful) most lenses have bokeh strengths and weaknesses that change with aperture and amount of out of focus. The variables become exponential. Many of us find near focus on the modern high contrast lenses quite distracting and unnatural looking (DA 50 comes to mind). Others like that look.

Then there is the overall usefulness of a lens for specific purposes. As the testing here shows, the 60-250 lens considerably outperforms the 55-300s in optical testing, but if you do a lot of action shooting - you are far better off with the latter lens. I picked up an FA 28-70 f/4 lens that isn't very sharp but renders nicely - and works well for street shooting grab shots because it is so small. If you want stealth for candids and need some reach, I can't think of a better option - even though it isn't optically near the top.

It is important to gather information from several sources, both qualitative and quantitative information have value. As a group, many Pentaxians tend to value qualitative aspects more which accounts for the fondness for old Taks and Limited lenses that often aren't near the top in IQ ratings, but have unusual characteristics. It also likely accounts for rather unenthusiastic responses toward the large zooms that accompanied the K1 introduction despite their high IQ ratings.
08-03-2017, 11:05 AM   #18
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QuoteOriginally posted by dcshooter Quote
We all know by now how much you love and like to boast about your ever expanding Leitaxed Zeiss ZF collection (and really, are they your "own creation," when you are simply spending 5 minutes to remove and reseat 3 screws to put on a replacement mount designed, engineered, produced, and marketed for exactly that purpose by David at Leitax?), but is this thread really necessary?

No need to get upset or defensive if you disagree.
First let me say that I'm certainly not "upset" about the Lenscore website. In fact I still visit this website sometimes. Another popular lens rating website that I visit evaluates most of the same lens characteristics that Lenscore does, however they don't rate bokeh at all. It's a bold, and some might say controversial decision on Lenscore's part to even include bokeh scores on their website. I thought that maybe some here might be interested in learning that there is at least one website that rates bokeh, and that some (me included) might disagree with their bokeh scores.

Indeed I do post a lot about Zeiss lens performance on Pentax K1 cameras. I know of no one else who's tested as many different Zeiss lenses on the K1. I do know that some here appreciate my sharing my opinions on this subject, and even a few have purchased Zeiss lenses based on my comments and have been pleased with their purchases.

I agree that converting Zeiss "Classic" lenses with Leitax adapters is easy to do. However, converting the newer and more complex Zeiss "Milvus" lenses is much more involved than "removing and reseating 3 screws on a replacement mount".

As far as my comment about creating lenses, I was not referring to my adapting of Zeiss lenses from F to K mount. Rather I am also into purchasing old Xray/TV/Projector lenses and modifying/adapting/creating unique hybrid lenses out of them for use on my various digital cameras. I've currently got over 20 such lenses in various stages of development. Usually, these unique Frankenlenses are total failures and end up in the trash. But every once in a while I end up with something that I like, keep and use (see attached photo of a homemade tilt/shift lens - in K mount no less). So far I have not talked about or posted images from these unique lenses on this forum because I don't believe there would be wide interest in it by forum members.

Last edited by Fenwoodian; 12-23-2017 at 12:12 PM.
08-03-2017, 01:43 PM   #19
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Personally, I'd love to see a poll with Zeiss lenses compared in a blind test to lenses from other companies, just t find out if the average for user would even prefer their images. There are several trains of thought here, one would be that Pentax users aren't all that interested in Zeiss lenses, because manual focus is already a pin before you even discuss the price, so it's starting with 2 strikes against it. Then if is likely based on other polls I've done, people prefer images taken with other lenses more, then that would be strike three. To my mind, you can't use lenses tests to proclaim Zeiss lenses "the best". I need to see images from five of the top 50mm lenses, Sigma Art, Pentax 50 macro, SMC Pentax 50 1.4, Zeiss 50 and possibly the new 50 1.4 when it comes out. I have to look at the kind of image I'd shoot, and the ZIess is at a tremendous disadvantage, because my favourite 50 is the macro, and in a blind test decide that one of the lenses was noticeably different, and find out afterwards it was the Zeiss. Until that happens I am not willing to conceed I'd take a Zeiss lens even if it was given to me.

The possibility exists that not only would I not find the Zeiss lens better, I might not even rate it as one of the top three. What I find lacking for the discussion of Zeiss lenses and lens ratings is those kinds of doubts. It needs to be proved that the lens ratings systems have some kind of meaning in terms of user appreciation before any discussion of their superiority can be entertained. When I can be told after some reliable research that 60% of people would choose a Zeiss lens instead of something else for their own use based on blind testing on the way they use their cameras (which is not pixel peeping or test charts), that might be good enough for me to consider them top o the line. That would be a pretty convincing accomplishment.

But there are no such tests and all this is innuendo, conjecture and mis-information. The assumption of excellence based on insufficient data and test charts.

I'm happy to concede they do well on test charts. I'm not willing to concede that test chart photography has a direct correlation with 3D photography and how people rate the images they take with their cameras. My polls with 75 to 100 participants suggest that rendering properties other than test chart resolution matter more.


Last edited by normhead; 08-03-2017 at 01:49 PM.
08-03-2017, 02:11 PM - 1 Like   #20
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The quality of bokeh of a lens is precisely that...quality.
I think it is best explained in 'zen and the art of motorcycle maintenance' that quality simply cannot be objectively defined. The very act of trying to define it, is to fail to understand it.

/philosophy
08-03-2017, 02:30 PM - 4 Likes   #21
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To my mind, perceived image quality based on what a lens does will always rest on a mixture of objectively measurable (of which photoptimist has compiled a fairly comprehensive list above) and subjective criteria, or personal taste. Sometimes what is objectively "inferior" may actually appeal to us, or we may find it objectionable in one situation, and prize it as adding character or an artistic effect in another.

Make no mistake, I'm all for technological progress and manufacturers always striving to come up with better lenses that keep pushing the envelope of what we can do in photography. However, I think it is a good thing if lens designers are also practical photographers with a keen sense that photography is both technology and art, instead of solely trying to cater for the measurebating masses who, despite their purchasing power, have done so much to ruin photography already. Maybe it's not untterly fair, but that "standardized lens bokeh measuring protocol" Fenwoodian is hoping for unwittingly reminds me of dxomark's peceptional megapixel BS.

What is so wrong about providing us with commented bokeh samples in real-world reviews, and letting us otherwise form our own opinions based on what we rationally know about bokeh and subjectively prefer about it?

BTW, in pursuit of superior bokeh - of which I cannot recall having seen compelling demonstration yet - the engineers have already sacrificed our beloved starbursts with the latest-generation Limiteds. I can't shake the feeling that perfect bokeh can also become a fixation, an obsession that is not always worth the trade-offs. Just my two bits.

---------- Post added 08-04-17 at 12:09 AM ----------

@Rondec: One thing I like a lot about your posts on this forum is how you illustrate your (routinely informed) opinions with actual images, Vincent.

Personally, I actually I find it hard to fault the "busier", but also colour-punchier, more lively bokeh produced by the DA*55, at least in the provided sample. I would argue that, instead of distracting from the main subject, it adds another layer of interest, another level of complexity, without making the image complicated. Reminds me of boldly used watercolours. As others have noted, the DA50 behaves in a similar way, which I happen to like in the attached two hoar-frost images.
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Last edited by Madaboutpix; 08-03-2017 at 03:30 PM.
08-03-2017, 04:19 PM   #22
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QuoteOriginally posted by Fenwoodian Quote
Bokeh is not easy to evaluate and rate. Maybe someone needs to come up with a standardized lens bokeh measuring protocol that, once and for all, brings uniformity to this here-to-for subjective lens characteristic.
I agree. The problem is that bokeh is not just a linear spectrum from "good" to "bad". Its character. And it might fit some subjects better than others. I think reviewers should find ways to describe the character. For example
-Smooth, soft
-Swirly
-has onion rings
-coma, distorted into shapes
-Harsh, jagged
-Mirror lens doughnuts

Bokeh could be reduced down to a number of characters. Most of them would depend on basic lens type (like typical Tessar bokeh, or famous Biogon bokeh, or mirror lens bokeh which can be fun, or terribly distracting).
Then people would just get the facts and decide what kind of bokeh they want. Sometimes mirror lens bokeh can be very creative. Other times it can ruin a photo because it distracts too much from the subject.

So I think bokeh should be 'reviewed' in two ways:
a) The "bokeh size" (DoF, CoC, aperture, magnification) (I'm not sure I explained this point well. I meant the things that 8mm f3.5 has less of than 135mm f1.8. One has smaller bokeh blur and large DoF, the other is a bokeh monster)
b) Bokeh type(related to lens genus) + specifics (related to optical corrections, elements, aperture blades, construction materials and tolerances)

08-03-2017, 07:53 PM - 4 Likes   #23
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I will admit that I am one who has purchased Zeiss lens influenced by Fenwoodian's comments but I have been most influenced by the lack of new Pentax lens to choose!

Can I get the same results with other lens that I get with Zeiss? I don't know, but I think the results have helped motivate me to take better photos. Call it a placebo effect if you want.

25mm Distagon:
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08-03-2017, 09:30 PM - 4 Likes   #24
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I think the background vegetation in Rondec's third shot is just centimetres from the focus point, and in the first two, metres away. Relative distance means a lot.

I find the DA*55 bokeh to be beautiful, with nine curved aperture blades:





08-04-2017, 06:18 AM - 1 Like   #25
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QuoteOriginally posted by Fenwoodian Quote

As far as my comment about creating lenses, I was not referring to my adapting of Zeiss lenses from F to K mount. Rather I am also into purchasing old Xray/TV/Projector lenses and modifying/adapting/creating unique hybrid lenses out of them for use on my various digital cameras. I've currently got over 20 such lenses in various stages of development. Usually, these unique Frankenlenses are total failures and end up in the trash. But every once in a while I end up with something that I like, keep and use (see attached photo of a homemade tilt/shift lens - in K mount no less). So far I have not talked about or posted images from these unique lenses on this forum because I don't believe there would be wide interest in it by forum members.
I, for one, would love to hear more about your unique hybrid lenses. I've got a number similar projects (2.5 X teleconvertor from the front group of a dead zoom, high-mag macro with reversed 8mm movie camera lenses, polaroid camera lens, etc.)

There's are several "lens clubs" and threads for unusual adapted lenses such as:

The impossible lens club?! - PentaxForums.com

The "Projector Lens" Club ... - PentaxForums.com

franken-lens - Tagged Pentax Forum Threads - PentaxForums.com

Or you could start your own frankenlens club if those are too tame.

P.S. That tilt-shift is awesome!
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