Lens bokeh ability

normhead · 03-11-2020, 08:35 AM

I don't understand the complexities of lens design as it applies to creating great transitions and smooth out of focus areas, but I doubt it's something you can easily analyze. I look at my DA*55 1.4 and the DFA 50 1.4 and the images on the DFA are smoother. I look at the 31 ltd and other 30s, and wide open, the 31 is smoother. Lens designers obviously know how to do this, and it seems to involve more elements and much heavier glass.

I can't imagine the camera companies would just put the information out there on exactly how they accomplish these things so we can do a paper analysis. It has to be proprietary information or everyone would have a DFA* 50 1.4, and nobody else does.

If the DFA* 50 1.4 (and the new lightweight fresnel telephotos) proved anything, it's that some of the older companies can still pull rabbits out of their hats that the more recent companies struggle with.

Last edited by normhead; 03-11-2020 at 09:14 AM.

**luftfluss** · 03-11-2020, 08:45 AM - **1 Like**

Originally posted by kernos

Clicked on the link and it did not work. ??

It's a PDF, so if your browser does not support PDF viewing you likely need to right-click on the link and select "Save".

photoptimist · 03-11-2020, 08:58 AM

Originally posted by UncleVanya

A fair point. I'm not sure what to call this but I'm certain it isn't bokeh as normally defined and discussed.

Indeed!

Maybe what we are talking about here is the "quantity" of the bokeh more so than the "quality" of it.

The "quality" of the bokeh (the texture, shape, aberrations, appearance of the blur circles) certainly does vary from lens design to lens design in ways that are hard (but not impossible) to predict. Moreover, some types of "quality" attributes (e.g., soap bubbles, swirly bokeh, chromatic-fringed bokeh) interact with some types of subject matter for interesting (or ugly) photographic effects.

The "quantity" of the bokeh (the diameter of the blur circles) is a bit more predictable in that stopping down a lens certainly does reduce the amount of out-of-focus blur. Likewise, for a given numerical aperture (e.g., f/4) and subject magnification, the OP is noting how shorter focal length lenses will have less blur than will longer focal length lenses.

Maybe "quality" is the flavor of the blur and "quantity" is the subtlety or boldness of that flavor?

stevebrot · 03-11-2020, 11:00 AM

Yes, the amount of blur is predictable by simple calculation in the same sense as DOF;* The characteristics of that blur, somewhat less so.

Next question...

Steve

*...sort of the same thing?

photoptimist · 03-11-2020, 11:49 AM

Originally posted by stevebrot

Yes, the amount of blur is predictable by simple calculation in the same sense as DOF;* The characteristics of that blur, somewhat less so.

Next question...

Steve

*...sort of the same thing?

They are related but not in a simple linear way.

DoF tells you what shift in subject distance creates a blur circle of threshold size used for the DoF. That DoF number can be used to extrapolate larger blur circle sizes over modest distances, but not long distances. For example, if the DoF is 10 cm for a 30 micron blur circle, it means that an subject shifted by 100 cm lik.ely creates a 300 micron blur circle. But it does not mean that a distant subject (a city light 10 km away or 100,000X the 10 cm DoF) would create a 3,000,000 micron blur circle.

**clackers** · 03-11-2020, 06:22 PM

Originally posted by biz-engineer

A while back, it was said that lens bokeh amount (blur) is a function of aperture diameter, or focal length divided by minimum f number.

Examples:

50mm @ f/1.4 => 50/1.4 = 35.7
100mm @ f/2.8 => 100/2.8 = 35.7
135mm @ f/2 => 135/2 = 67.5
70-200 2.8 zoom @ 200 f/2.8 => 71.43

Looking at those numbers, it looks like the 70-200 f2.8 zoom should be able to produce more blur than the 100 macro lens. But while using the D-FA 100 macro, I was able to produce a lot of background blur when getting close to subject. I realized the focal-length / aperture ratio might give a wrong estimate for lens blur ability. Minimum focus distance should be included but how?

You can induce blur even with a phone lens by getting very close to the subject with a very far background. That ratio means you can get bokeh even with a slow zoom.

I sometimes don't bother shooting sports action in the half of the field away from me because I know the background will be too intrusive.

**Lowell Goudge** · 03-11-2020, 06:36 PM - **1 Like**

Originally posted by biz-engineer

A while back, it was said that lens bokeh amount (blur) is a function of aperture diameter, or focal length divided by minimum f number.

Examples:

50mm @ f/1.4 => 50/1.4 = 35.7
100mm @ f/2.8 => 100/2.8 = 35.7
135mm @ f/2 => 135/2 = 67.5
70-200 2.8 zoom @ 200 f/2.8 => 71.43

Looking at those numbers, it looks like the 70-200 f2.8 zoom should be able to produce more blur than the 100 macro lens. But while using the D-FA 100 macro, I was able to produce a lot of background blur when getting close to subject. I realized the focal-length / aperture ratio might give a wrong estimate for lens blur ability. Minimum focus distance should be included but how?

I have often maintained that it is the relative magnification of two lenses with respect to the ratio of focal distance to background out of focus that matters. For the same subject size, you are closer with shorter lenses, for the same image size, and this changes the perspective and size of the background with respect to sjuject, so longer lenses make bigger blurrier blobs than shorter lenses that reduce things to a confusing mesh of small spots

**kernos** · 03-11-2020, 08:29 PM

Originally posted by BigMackCam

It's working fine for me

Yep its a pdf read issue with firefox.

biz-engineer · 03-11-2020, 11:53 PM

Originally posted by clackers

That ratio means you can get bokeh even with a slow zoom.

Sure, although you are limited by the closest focus distance of the zoom.

**clackers** · 03-11-2020, 11:59 PM - **2 Likes**

Originally posted by biz-engineer

Sure, although you are limited by the closest focus distance of the zoom.

Of course. But if you can't get close to the subject, if the wall behind is much closer to them than your camera is, an expensive wide aperture lens won't do what you want it to do.

Much of the depth of field, up to 2/3 of it according to circumstances, is behind the focal plane.

Choosing a shooting position is so important when arriving at a venue!

biz-engineer · 03-12-2020, 12:20 AM - **1 Like**

Originally posted by clackers

Choosing a shooting position is so important when arriving at a venue!

I see your point. Understood.

normhead · 04-15-2020, 06:58 PM

All you need to know about blur.... you can ascertain by taking a laser pointer making dot on the wall and photographing it out of focus. With a single point of light, you can see, the shape and distribution of light within the circle of confusionof the circles of confusion. If the light is uneven within the circle of confusion you won't get smooth out of focus areas.

Of course to be absolutely definitive you'd have to do it quite a few times from different subject distances and with the single point of light coming through different parts of the lens. But you should be able to see it in your pictures.

Blur is all about the quality of the circles of confusion.

Similar Threads
Thread	Thread Starter	Forum	Replies	Last Post
K1 bokeh vs K10 apsc bokeh	GUB	Pentax DSLR Discussion	44	01-02-2019 02:42 PM
Why does a lens' ability to focus decrease over time?	dflorez	Pentax SLR Lens Discussion	13	11-17-2015 11:03 AM
Misc 100mm f/2.8 Macro WR Bokeh Bokeh Bokeh!	iocchelli	Post Your Photos!	3	03-20-2011 02:22 AM
K-x 18-55mm kit lens macro ability	Muse	Troubleshooting and Beginner Help	50	09-13-2010 11:58 AM
Getting some tele ability on the cheap	tilling	Troubleshooting and Beginner Help	9	07-27-2009 06:45 AM

03-11-2020, 08:35 AM	#31
normhead Pentaxian Join Date: Jun 2007 Location: Near Algonquin Park Photos: Gallery \| Albums Posts: 40,451	I don't understand the complexities of lens design as it applies to creating great transitions and smooth out of focus areas, but I doubt it's something you can easily analyze. I look at my DA55 1.4 and the DFA 50 1.4 and the images on the DFA are smoother. I look at the 31 ltd and other 30s, and wide open, the 31 is smoother. Lens designers obviously know how to do this, and it seems to involve more elements and much heavier glass. I can't imagine the camera companies would just put the information out there on exactly how they accomplish these things so we can do a paper analysis. It has to be proprietary information or everyone would have a DFA 50 1.4, and nobody else does. If the DFA* 50 1.4 (and the new lightweight fresnel telephotos) proved anything, it's that some of the older companies can still pull rabbits out of their hats that the more recent companies struggle with. Last edited by normhead; 03-11-2020 at 09:14 AM.

03-11-2020, 08:45 AM - 1 Like	#32
luftfluss Site Supporter Join Date: Jun 2011 Location: NJ Photos: Gallery \| Albums Posts: 11,627	Originally posted by kernos Clicked on the link and it did not work. ?? It's a PDF, so if your browser does not support PDF viewing you likely need to right-click on the link and select "Save".

03-11-2020, 08:58 AM	#33
photoptimist Pentaxian Join Date: Jul 2016 Photos: Albums Posts: 5,128	Originally posted by UncleVanya A fair point. I'm not sure what to call this but I'm certain it isn't bokeh as normally defined and discussed. Indeed! Maybe what we are talking about here is the "quantity" of the bokeh more so than the "quality" of it. The "quality" of the bokeh (the texture, shape, aberrations, appearance of the blur circles) certainly does vary from lens design to lens design in ways that are hard (but not impossible) to predict. Moreover, some types of "quality" attributes (e.g., soap bubbles, swirly bokeh, chromatic-fringed bokeh) interact with some types of subject matter for interesting (or ugly) photographic effects. The "quantity" of the bokeh (the diameter of the blur circles) is a bit more predictable in that stopping down a lens certainly does reduce the amount of out-of-focus blur. Likewise, for a given numerical aperture (e.g., f/4) and subject magnification, the OP is noting how shorter focal length lenses will have less blur than will longer focal length lenses. Maybe "quality" is the flavor of the blur and "quantity" is the subtlety or boldness of that flavor?

03-11-2020, 11:00 AM	#34
stevebrot Otis Memorial Pentaxian Join Date: Mar 2007 Location: Vancouver (USA) Photos: Gallery \| Albums Posts: 42,007	Yes, the amount of blur is predictable by simple calculation in the same sense as DOF;* The characteristics of that blur, somewhat less so. Next question... Steve *...sort of the same thing?

03-11-2020, 11:49 AM	#35
photoptimist Pentaxian Join Date: Jul 2016 Photos: Albums Posts: 5,128	Originally posted by stevebrot Yes, the amount of blur is predictable by simple calculation in the same sense as DOF;* The characteristics of that blur, somewhat less so. Next question... Steve *...sort of the same thing? They are related but not in a simple linear way. DoF tells you what shift in subject distance creates a blur circle of threshold size used for the DoF. That DoF number can be used to extrapolate larger blur circle sizes over modest distances, but not long distances. For example, if the DoF is 10 cm for a 30 micron blur circle, it means that an subject shifted by 100 cm lik.ely creates a 300 micron blur circle. But it does not mean that a distant subject (a city light 10 km away or 100,000X the 10 cm DoF) would create a 3,000,000 micron blur circle.

03-11-2020, 06:22 PM	#36
clackers Otis Memorial Pentaxian Join Date: Jul 2013 Location: Melbourne Photos: Albums Posts: 16,397	Originally posted by biz-engineer A while back, it was said that lens bokeh amount (blur) is a function of aperture diameter, or focal length divided by minimum f number. Examples: 50mm @ f/1.4 => 50/1.4 = 35.7 100mm @ f/2.8 => 100/2.8 = 35.7 135mm @ f/2 => 135/2 = 67.5 70-200 2.8 zoom @ 200 f/2.8 => 71.43 Looking at those numbers, it looks like the 70-200 f2.8 zoom should be able to produce more blur than the 100 macro lens. But while using the D-FA 100 macro, I was able to produce a lot of background blur when getting close to subject. I realized the focal-length / aperture ratio might give a wrong estimate for lens blur ability. Minimum focus distance should be included but how? You can induce blur even with a phone lens by getting very close to the subject with a very far background. That ratio means you can get bokeh even with a slow zoom. I sometimes don't bother shooting sports action in the half of the field away from me because I know the background will be too intrusive.

03-11-2020, 06:36 PM - 1 Like	#37
Lowell Goudge Site Supporter Join Date: Jan 2007 Location: Toronto Photos: Gallery \| Albums Posts: 17,891	Originally posted by biz-engineer A while back, it was said that lens bokeh amount (blur) is a function of aperture diameter, or focal length divided by minimum f number. Examples: 50mm @ f/1.4 => 50/1.4 = 35.7 100mm @ f/2.8 => 100/2.8 = 35.7 135mm @ f/2 => 135/2 = 67.5 70-200 2.8 zoom @ 200 f/2.8 => 71.43 Looking at those numbers, it looks like the 70-200 f2.8 zoom should be able to produce more blur than the 100 macro lens. But while using the D-FA 100 macro, I was able to produce a lot of background blur when getting close to subject. I realized the focal-length / aperture ratio might give a wrong estimate for lens blur ability. Minimum focus distance should be included but how? I have often maintained that it is the relative magnification of two lenses with respect to the ratio of focal distance to background out of focus that matters. For the same subject size, you are closer with shorter lenses, for the same image size, and this changes the perspective and size of the background with respect to sjuject, so longer lenses make bigger blurrier blobs than shorter lenses that reduce things to a confusing mesh of small spots

03-11-2020, 08:29 PM	#38
kernos Site Supporter Join Date: Feb 2013 Posts: 456	Originally posted by BigMackCam It's working fine for me Yep its a pdf read issue with firefox.

03-11-2020, 11:53 PM	#39
biz-engineer Pentaxian Join Date: Feb 2015 Photos: Gallery Posts: 12,247 Original Poster	Originally posted by clackers That ratio means you can get bokeh even with a slow zoom. Sure, although you are limited by the closest focus distance of the zoom.

03-11-2020, 11:59 PM - 2 Likes	#40
clackers Otis Memorial Pentaxian Join Date: Jul 2013 Location: Melbourne Photos: Albums Posts: 16,397	Originally posted by biz-engineer Sure, although you are limited by the closest focus distance of the zoom. Of course. But if you can't get close to the subject, if the wall behind is much closer to them than your camera is, an expensive wide aperture lens won't do what you want it to do. Much of the depth of field, up to 2/3 of it according to circumstances, is behind the focal plane. Choosing a shooting position is so important when arriving at a venue!

03-12-2020, 12:20 AM - 1 Like	#41
biz-engineer Pentaxian Join Date: Feb 2015 Photos: Gallery Posts: 12,247 Original Poster	Originally posted by clackers Choosing a shooting position is so important when arriving at a venue! I see your point. Understood.

04-15-2020, 06:58 PM	#42
normhead Pentaxian Join Date: Jun 2007 Location: Near Algonquin Park Photos: Gallery \| Albums Posts: 40,451	All you need to know about blur.... you can ascertain by taking a laser pointer making dot on the wall and photographing it out of focus. With a single point of light, you can see, the shape and distribution of light within the circle of confusionof the circles of confusion. If the light is uneven within the circle of confusion you won't get smooth out of focus areas. Of course to be absolutely definitive you'd have to do it quite a few times from different subject distances and with the single point of light coming through different parts of the lens. But you should be able to see it in your pictures. Blur is all about the quality of the circles of confusion.