90mm f2.8 lens bokeh- no such thing as a stupid question...but

Slidinginfinity

You are all wrong, wrong, wrong!


Bokeh is the direct result of the tiny little magic gnomes that live in walls of your camera lens. How well they do their job is determined by the amount of food pellets they receive each day. If you don't feed your gnomes your bokeh and lens sharpness will suffer.

FoxT

..also is good practice to shake your lens before you use it... this gets the lil critters to wake up & start buzzing around inside the lens, making the bokeh effect more pronounced. In the northern hemisphere you will get best results if you shake your lens from side to side, whilst in the southern hemi it works best if you shake it up & down....

If you listen closely you will hear them sing

"put your left legs in, your right legs out ,do the Hokeh Bokeh & you shake it all about"

charybdis

FoxT wrote: »

There are 2 aspects to Bokeh that I am aware of...
1- "Bokeh Quality" - ie are out-of-focus highlights blurred smoothly or jaggedly. This largely depends on the design of the iris of the lens. Cheaper lenses like the canon 50mm f/1.8 have a 5-blade iris, which can sometimes result in distracting pentagons in out-of-focus highlights. More expensive lenses have more blades in the iris, resulting in softer, rounder oof highlights. THIS ASPECT OF BOKEH IS NOT RELATED AT ALL TO LENS FOCAL LENGTH. ( see the-digital-picture.com for examples)

Yes. Five-bladed aperture diaphragms are for cheap lenses, like those Zeiss ones made for Hasselblad.

FoxT wrote: »

2 - "Bokeh Quantity" - ie how quickly things get blurred as you move nearer or further away from the plane of focus. Here is where it gets interesting.

The above shot was taken with a 70m lens at f/9. Subject distance was about 15cm from the front element of the lens. The figure is about 4cm high. As you can see, the feet are not in focus, I guess they are about 1.5cm behind the plane of focus here.

Now, If I had shot this with say a 180mm lens at the same f-stop, and, critically, with the figure occupying the full frame of the viewfinder ( pretty much as it is here) then the DOF/Bokeh would be identical. The difference is, I would be further away from the subject as using a longer focal length.

So, for a given aperture, bokeh will be about the same regardless of focal length provided the size of your subject in the frame is the same. ( ie for shorter focal lengths you move closer)

OR

For a given distance to your subject, your DOF will be shallower as your focal length increases, provided your aperture stays the same.


Summary:
- Wider aperture gives shallower DOF, regardless of focal length.
- Longer focal lengths give same DOF at any given aperture provided magnification is the same.
- Longer focal lengths give shallower DOF provided aperture & distance to subject remain the same.

Do you not think that there may be a flaw in your description given that you are interchanging the terms "bokeh" and "DOF" very freely?

FoxT wrote: »

Best way to grok all this is to experiment!

I approve of your use of the term "grok", though.

Thecageyone

As good ol' KR says: "Bokeh describes the appearance, or "feel," of out-of-focus areas. Bokeh is not how far something is out-of-focus, bokeh is the character of whatever blur is there."

melekalikimaka

Thecageyone wrote: »

As good ol' KR says: "Bokeh describes the appearance, or "feel," of out-of-focus areas. Bokeh is not how far something is out-of-focus, bokeh is the character of whatever blur is there."

KR is a tool at the best of times

charybdis

melekalikimaka wrote: »

KR is a tool at the best of times

I agree with the more positive interpretation of this statement.

dinneenp

Thread should be renamed to 'bokeh- discuss in 1,000 words or more'....

FoxT

charybdis wrote: »

Yes. Five-bladed aperture diaphragms are for cheap lenses, like those Zeiss ones made for Hasselblad.

And to the minority of photographers who use these, I say 'Good for you'.

Do you not think that there may be a flaw in your description given that you are interchanging the terms "bokeh" and "DOF" very freely?

Yes - wording could be tightened up a bit, and it is also possible that I am incorrect or have missed an important point. If that is the case I would appreciate being told what it is....

charybdis

FoxT wrote: »

And to the minority of photographers who use these, I say 'Good for you'.

Is there any group of lens users that isn't a minoriy?

FoxT wrote: »

Yes - wording could be tightened up a bit, and it is also possible that I am incorrect or have missed an important point. If that is the case I would appreciate being told what it is....

Depth-of-field and bokeh are not the same thing.

It's more-or-less understood by all parties that "bokeh" is a qualitiative attribute, therefore "bokeh quality" is a tautology and "bokeh quantity" is a contradiction.

It is (contrary to popular belief) not (heavily) dependent on the shape of the aperture diaphragm.

The only thing bokeh depends on is the arrangement and makeup of the elements in the lens. This changes at different focal lengths, apertures, and focus distances; influencing both depth-of-field and bokeh, but they're not the same thing (or even directly related).

Your description of "bokeh quantity" is a reasonable description of depth-of-field, but doesn't say anything about bokeh.

Bokeh describes the blur density distribution of out-of-focus blur discs and their appearance in aggregate.

Different lenses will produce blur discs with different density distributions. One of the most obvious examples is the stereotypical "donut" rings produced by mirror lenses. This property is not dependent on shallow depth-of-field or aperture diaphragm shape.

Another classic blur density distribution is the "double line" or "nisen" shape seen in many 50mm lens designs. The blur discs typically have an appearance of a hard edge which, when many of them are clustered together in the out-of-focus area of a busy background, can have an unpleasant appearance.

Stereotypical "good" bokeh is characterised by blur discs that have soft edges that smoothly blend together when viewed in aggregate.

In conclusion:

bokeh is not: shallow depth-of-field, the shape of the aperture diaphragm, the extent to which something is out-of-focus.

bokeh is: the characteristic blur density distribuiton out out-of-focus areas for a given optical arrangement.

Thecageyone

melekalikimaka wrote: »

KR is a tool at the best of times

You obviously don't get my wit, as I agree. Quoting him to simplify all this Hoo-ha about bokeh says it all about how I feel on it

FoxT

Hmmm, Well I am definitely wrong about the lens iris - it can have an influence but is not as you say the determining factor.


I found this interesting link on Bokeh....

http://www.rickdenney.com/bokeh_test.htm

cnocbui

charybdis wrote: »

It is (contrary to popular belief) not (heavily) dependent on the shape of the aperture diaphragm.
.

I would agree with everything you said except this.

Olympus used a differing number of aperture blades across their OM Zuiko range of lenses - 6, 8 and 9. It has been observed and noted by a number of people that the few lenses with 9 blades had noticeably superior bokeh to the others. Those lenses, not coincidentally I believe, were all 90mm or more in focal length and the most expensive and fast Olympus made.

I am not saying the blades determine bokeh, but that they do play a part in the final outcome. The Minolta/Sony STF 135mm f/2.8 (Smooth Transition Focus) lens was designed to have superior bokeh and happens to have 9 aperture blades. I doubt that was an accident on the part of the lens designers. The Wikipedia article on bokeh also maintains that the aperture blade count plays a part.

I am aware of Mr Denny's tests and conclusions to the contrary, I happen not to agree with him.

ThOnda

This is sooo funny, please, go on

charybdis

ThOnda wrote: »

This is sooo funny, please, go on

OK.

cnocbui wrote: »

I would agree with everything you said except this.

Olympus used a differing number of aperture blades across their OM Zuiko range of lenses - 6, 8 and 9. It has been observed and noted by a number of people that the few lenses with 9 blades had noticeably superior bokeh to the others. Those lenses, not coincidentally I believe, were all 90mm or more in focal length and the most expensive and fast Olympus made.

I am not saying the blades determine bokeh, but that they do play a part in the final outcome. The Minolta/Sony STF 135mm f/2.8 (Smooth Transition Focus) lens was designed to have superior bokeh and happens to have 9 aperture blades. I doubt that was an accident on the part of the lens designers. The Wikipedia article on bokeh also maintains that the aperture blade count plays a part.

I am aware of Mr Denny's tests and conclusions to the contrary, I happen not to agree with him.

I did say "heavily", although I do think their effect is greatly overstated.

Comparing entirely different lenses that happen to have different numbers of blades in their aperture diaphragm then declaring any differences between them are due to the number of blades isn't exactly a rigourous test. Do you think that two lenses of the exact same composition apart from having different amounts of aperture blades would look drastically different?

Why did they stop a 9 blades when making the STF 135mm? Many lenses have more than 9 blades, so surely a lens designed explicitly for "superior bokeh" would have more, given that it's such an important factor?

Also, the people commenting on the "superior bokeh" of the lenses with more rounded aperture diaphragms probably also subscribe to the idea that the determinant in what makes "good bokeh" is the shape of out-of-focus points of light.

Thecageyone

Does it not depend on whether the blades are straight or rounded? Straight 6 blades usually = Hex bokeh, rounded 9 blades - better chance of perfect circles.

FoxT

lessons learned from this thread:

1 - don't argue the toss with charybdis. It doesn't matter if he is right or wrong, at the end of the day it is just gets too hard...

2- To be fair, Charybdis is right a lot of the time,& I have learnt from him/her in the course of the thread. Thank you Charybdis! ( I mean that, not ttp*)

3 - a quick look at wikipedia or the luminous landscape, or similar, BEFORE YOU POST, can often mean that you learn something worthwhile, and can lead to your post being even more better than the one you had in mind.( I am talking about me, here ;( )

4- some people on this forum can come across as being self righteous or somewhat aggressive - but if you put that aside, you can still learn from them.

5 - If I ever woke up in the morning & found myself in bed beside one of these people I would reach for the colt 45 that I keep handy...

That is all,really.
-FoxT

* ttp = Taking the pi**

Promac

FoxT wrote: »

lessons learned from this thread:

1 - don't argue the toss with charybdis. It doesn't matter if he is right or wrong, at the end of the day it is just gets too hard...

So true.

charybdis

FoxT wrote: »

1 - don't argue the toss with charybdis. It doesn't matter if he is right or wrong, at the end of the day it is just gets too hard...

Promac wrote: »

So true.

Would you guys feel better if I made it easier?

FoxT wrote: »

2- To be fair, Charybdis is right a lot of the time,& I have learnt from him/her in the course of the thread. Thank you Charybdis! ( I mean that, not ttp*)

You're welcome.

FoxT wrote: »

3 - a quick look at wikipedia or the luminous landscape, or similar, BEFORE YOU POST, can often mean that you learn something worthwhile, and can lead to your post being even more better than the one you had in mind.( I am talking about me, here ;( )

Do people actually not do this?

FoxT wrote: »

4- some people on this forum can come across as being self righteous or somewhat aggressive - but if you put that aside, you can still learn from them.*

Damn straight.

FoxT wrote: »

5 - If I ever woke up in the morning & found myself in bed beside one of these people I would reach for the colt 45 that I keep handy...

FoxT

charybdis wrote: »

Would you guys feel better if I made it easier?

I'd feel much better,but would learn less. I post here to learn, I post in the pervy forums to feel good. 2 different things, entirely!

FoxT

charybdis wrote: »

Do people actually not do this?

ehhmmm

charybdis

FoxT wrote: »

I'd feel much better,but would learn less. I post here to learn, I post in the pervy forums to feel good. 2 different things, entirely!

Honestly, One of the main reasons I participate here is to learn. Not necessarily by learning from what others have to say, but learning from having to more closely examine my own understanding of things and having to express it in an intelligible and coherent way.

Thecageyone

You just seem to over complicate the straight forward at times Char

FoxT

And, finally... this was the colt I had in mind...

Promac

Nice bokeh with no circles:

cnocbui

charybdis wrote: »

OK.

I did say "heavily", although I do think their effect is greatly overstated.

Comparing entirely different lenses that happen to have different numbers of blades in their aperture diaphragm then declaring any differences between them are due to the number of blades isn't exactly a rigourous test. Do you think that two lenses of the exact same composition apart from having different amounts of aperture blades would look drastically different?

Drastically no, noticeably yes.

Why did they stop a 9 blades when making the STF 135mm? Many lenses have more than 9 blades, so surely a lens designed explicitly for "superior bokeh" would have more, given that it's such an important factor?

Law of diminishing returns i would imagine. Turn that question around - why not just
three blades?

From a rather dense Zeiss technical paper on bokeh, this comment was made"

In summary we can say that the shape of
the iris can become visible in the picture
either obviously as a decorative feature or
as a disturbing artefact and that it can betray
interesting facts about the lens to us.
However, the iris can remain totally invisible
in many pictures. Yes, and if we use a lens
with the aperture fully open, it can of course
play no role at all.

Nevertheless or perhaps in just such a case
there can be major differences in the bokeh.

http://www.zeiss.com/C12567A8003B8B6F/EmbedTitelIntern/CLN_35_Bokeh_EN/$File/CLN35_Bokeh_en.pdf

Also, the people commenting on the "superior bokeh" of the lenses with more rounded aperture diaphragms probably also subscribe to the idea that the determinant in what makes "good bokeh" is the shape of out-of-focus points of light.

In my case, I do not principally consider out of focus highlights.

In the other recent thread about the top 6 portrait lenses, I note that two have 8 blades, 2 have nine, two I could find no spec for and the also mentioned sigma has 9.

charybdis

cnocbui wrote: »

Drastically no, noticeably yes.

I would say it is unnoticeable in all but very few circumstances.

cnocbui wrote: »

Law of diminishing returns i would imagine. Turn that question around - why not just
three blades?

I'm not saying there isn't reason to use more aperture blades, but one would think that - assuming the lens was designed for bokeh superiority and that the number of aperture blades is an important factor - they would've designed it with more. There's a Pentacon 135mm f/2.8 lens that has 19 aperture blades, for example. Why would they put so much effort into building a lens for this expressed purpose, only to fall short on the number of blades?

cnocbui wrote: »

From a rather dense Zeiss technical paper on bokeh, this comment was made"

From the exact same paper:

Zeiss wrote:

Sometimes the phenomenon of the individual
iris images is equated with “bokeh’; under this
heading one finds collections of pictures in
which iris images are mixed with photos of
soap bubbles. But this is not what is meant by
“bokeh”. In the iris image the lens is reading
the cards to a certain extent but what
significance has all this for the reproduction of
image areas in which there are no highlight
areas?

In the following examples of photos we will see
that one should not over-estimate the
significance of the shape of the iris

cnocbui wrote: »

In my case, I do not principally consider out of focus highlights.

Fair enough, but you can't speak for the other people's statements you're using to support your argument.

cnocbui wrote: »

In the other recent thread about the top 6 portrait lenses, I note that two have 8 blades, 2 have nine, two I could find no spec for and the also mentioned sigma has 9.

That's probably true, but I don't know what it proves. As I said earlier in the thread, all the lenses designed by Zeiss (the people whose whitepaper you just quoted) for Hasselblad have five-bladed aperture diaphragms.

cnocbui

charybdis wrote: »

That's probably true, but I don't know what it proves. As I said earlier in the thread, all the lenses designed by Zeiss (the people whose whitepaper you just quoted) for Hasselblad have five-bladed aperture diaphragms.

It proves that the lenses I could find the data for all have closer to 9 plades than 5.

The Zeiss 85mm f/1.4 Planar T* was one of the ones with 9 aperture blades. You were saying? :rolleyes:

charybdis

cnocbui wrote: »

It proves that the lenses I could find the data for all have closer to 9 plades than 5.

That is true, but I still don't know what you think it proves.

cnocbui wrote: »

The Zeiss 85mm f/1.4 Planar T* was one of the ones with 9 aperture blades. You were saying? :rolleyes:

I said:

charybdis wrote: »

the lenses designed by Zeiss for Hasselblad have five-bladed aperture diaphragms.

humberklog

Promac wrote: »

Nice bokeh with no circles:

Now I'd have that that's good control of DOF but not Bokeh. Am I way off?

FoxT

I agree - my (improved ) understanding of bokeh is that it is the rendition of out-of-focus highlights, and I don't see any in this pic.