RiceHigh's Pentax Blog: "Round" Lens Diaphragm? See This! :-o

Tuesday, November 23, 2010

"Round" Lens Diaphragm? See This! :-o

When some Pentaxians rave about the "round" diaphragm of the "new" DFA 100 Macro lens of Pentax, which has only 8 aperture blades actually, I think we need to look at something that is really great in this regard, which came from the old days:-

Could you count how many aperture blades this lens has? It has 16! And, most importantly, the opening is really perfectly round, no matter at *any* f-stop that it is set!

Well, a circle is essentially a multi-polygon with numerous number of sides. So, how a lens with 8 blades could be "perfectly round" when it is only 8, just? :-)

Related:-

DFA 100 Macro WR - Brief Hands-on Impressions

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j viviano · 746 weeks ago

Compare this image with the DFA 100 stopped down if you plan on being at all fair...

4 replies · active 746 weeks ago

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RiceHigh 110p · 746 weeks ago

A lens with 8 aperture blades will not be as round as a lens with 16. Just admit it. It's simple geometry afterall.

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j viviano · 746 weeks ago

Why don't you show us. I'd like to see the difference.

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RiceHigh 110p · 746 weeks ago

I simply won't bother to show you obvious things as simple as that a square is a square and a circle is a circle. I'd rather use my time to do some more meaningful things else!

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Anu · 746 weeks ago

This is a vast oversimplification. Not all blades are equal - some are totally straight while others are rounded a bit or even lots.

Anyhow, I do agree, that 16 blades does allow for round bokeh highlights, especially in the center.

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syam · 746 weeks ago

Oh brother

See this people. http://www.pentaxforums.com/forums/pentax-slr-len...

I think this shows how circular it can get....

And don't bullshit how it is not perfectly round, If you want that get a meyer gorlith or one of the m39 lenses, which by the way you can use on Pentax dslr via adapters. But I don't think you will get AF or the superior coating or WR. Not too mention these lenses were not designed for color per se. So your point is rather moot.

1 reply · active 746 weeks ago

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RiceHigh 110p · 746 weeks ago

Can you see the wave-form aperture opening near wide opened of the DFA WR lens (the last photo)? At that aperture, I am sure that the old version of (the same optical formula) DFA will have a rounder aperture (but not a waved one)! And, from the photo above, it is still not as perfectly round as the Konica lens I shown above, that's simply geometry, I feel obliged to say again!

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syam · 746 weeks ago

Which photo is that? But you do have to admit, that for only 8 blades, the specular highlights are very round.

Just to add, the blades are not straight, they are curved so..... catch my drift?

I would like to point out the supposedly bokeh king the Leica 35mm f/2 Summicron 4th Ed has also 8 curved aperture blades. And the Olympus ee i use to have a square aperture but still produce nice bokeh.

So what I'm saying here is that how much does the aperture shape affects the bokeh or quality of the photo - I don't know but what i do know is that it affects the shape of the specular highlights. All in all, the number of aperture blades is really down on the list of my priorities.

Furthermore take into account that the aperture is stopped down when taking a picture using a modern slr, I shudder at the thought of the amount of friction produced or the reliability of such a design using that many aperture blades.

2 replies · active 746 weeks ago

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j viviano · 746 weeks ago

They ARE round. There is no use in having extra blades.The pictures offer round specular highlights from wide-open to f11, after which OOF rendering becomes hard to differentiate from any lens (even the kit).

Maybe it's not perfectly round inside of the lens, but can you see it in the pictures...? Oh right, that's what we are supposed to be doing.

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Anu · 746 weeks ago

A small correction to above - it is easy to get quite a bit of OOF at f/11 and beyond - when shooting at macro distances one often has to close the aperture lots just to get enough into sharp focus.

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RiceHigh 110p · 746 weeks ago

>> Which photo is that? But you do have to admit, that for only 8 blades, the specular highlights are very round.

The last photo.

>> Just to add, the blades are not straight, they are curved so..... catch my drift?

You've missed the most important point. A 8-blade aperture won't help the user to get round bokeh for *all* f-stops. If you made the blades too curved, wide apertures will suffer, the last photo is a really good illustration, the near wide opened aperture opening is in waved form, which is actually totally not desirable, although at f/5.6 you get a perfectly round opening. That's the case of the new DFA WR 100.

In contrast, if you make the blade side straighter, i.e., the case of the old DFA, there will be no waved opening near wide opened. But then at stopped down, the octo-polygon shows its corners!

So, the perfect solution? There is only one technical answer: More blades are needed! If not, the old German lens makers did not need to include so many blades, neither did some very old serious bokeh lens made by the Japanese!

Sometimes I really thought that some Pentaxians are just so brand-blinded to see the world more for better things. They only knew and defended to death that everything that Pentax made is the best! That, but indeed at the end, just like a frog that looks up the world under a well, which is only partial, very partial.

1 reply · active 746 weeks ago

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j viviano · 746 weeks ago

This has nothing to do with brand. I don't see any real difference in picture quality past 9 blades, period. I would assume that is why most companies don't make these designs anymore (not jus Pentax!)

The problem, Rice, is you make general statements about photography which are incorrect, and furthermore blame Pentax for these made-up deficiencies! ON top of that, you have a habit of only reporting certain things (albeit, incorrectly), and spinning your headlines to be either neutral or negative.

YOU are the one with a brand-based agenda, most of us don't really care and just want to take pictures.

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syam · 746 weeks ago

Oh that waveform on the blade itself! I tot you meant the photos (I was wondering how u were able to see waveform distortions with all that)

Actually my reply to your current post is in my previous post, so please, please re-read again. Again its not bokeh, its highlights. From the photo you can see that the specular highlight at f5.6 is quite round at f11 less so but still good.

The leica 35mm have that aperture design as well but would you say that it is a bad lens because it only have 8 aperture blades?

To say that I'm a pentaxians would be quite wrong. Currently I have no Pentax DSLR, I have a couple of their film cameras though but what I do have is a Canon 5d , contax camera and the Zeiss glasses, minolta and canon film cameras and a Sony compact. And the camera I lust after the most is an Olympus OM1....

3 replies · active 746 weeks ago

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RiceHigh 110p · 746 weeks ago

The "highlights" you mentioned is *part* of the bokeh!

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syam · 746 weeks ago

owie...... please google......

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RiceHigh 110p · 746 weeks ago

Google won't help you if you're not willing to learn..

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John · 746 weeks ago

What's more interesting to know is, why are lenses not made like this anymore, is it really that much more expensive to add some diaphragm blades, or do recent lens designs not allow it?

3 replies · active 746 weeks ago

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RiceHigh 110p · 746 weeks ago

It's a matter of cost concern, of course.

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John · 746 weeks ago

I don't get it, I bought this lens for over 5000 hk$ after it just came out, I'd gladly would have paid 500 to 1000 hk$ more for this.

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Anu · 746 weeks ago

As Rice says, it is (mostly) a cost thing - it is quite a bit more expensive to do that kind of assembly instead of a more manageable amount. Then there is the issue of reliability - many more moving mechanical parts with tight tolerances...

Personally, I prefer fewer aperture blades - I occasionally have to build aperture mechanisms, and that is not exactly my idea of fun. More blades would mean more life wasted ;) Besides, I mostly shoot wide open...

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Tuesday, November 23, 2010

"Round" Lens Diaphragm? See This! :-o

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