Author Topic: Bokeh  (Read 17677 times)

Re: Bokeh
« Reply #50 on: 17 June, 2011, 10:47:41 am »
The bigger the format, the less the depth of field for the same f value. The focal length will vary, simply because the image receiver is bigger. If you use a projector with a fixed focal length lens at home you can see this, you need to move the projector back to get a bigger image, (ie the focal length) and the image isn't as bright when you do, (which equates to the f number).
In cameras the DOF between formats is determined by the size of the glass. So a 6x6 f 4.5 might have the same DOF characteristics as an F2.8 35 mm lens. The medium format lens will have a bigger focal length number because the same size of objective lens has to be further away from the receptor, and the f number is higher because the light is spread over a larger area.

Re: Bokeh
« Reply #51 on: 17 June, 2011, 10:53:09 am »

As the size of the film or sensor increases it needs more light, to acheive the same f value. So the objective lens has to increase in size.

Not true. My 6x6 Rollei TLRs have smaller lenses than my 35mm rangefinders.

The objective lens will be pretty much the same size for a 50mm f 2 lens, or any value, regardless of format. On the rangefinders that is a standard lens, on the TLR that is a wide angle. I just took a look at the only TLR I have, a Lubitel 66 and the lens on that is a f4.5 75mm and it has an objective about the same size as the f2.8 50mm lens from a FED, and therefore the same DOF properties fully open.

Yes, I know this, my point was the lenses are physically smaller. The physical size of the lens has nothing to do with DoF. The reason the focal length changes is to increase or decrease the circle of confusion to obtain the correct coverage for the size of format.

It is the focal length combined with the F-stop that determines the DoF, not the size of the lens.

We are in fact saying the same thing, the combination of f stop and focal length equates to the size of the objective lens, as the format size increases the product of those two values increases and the DOF is shallower.

frankly frankie

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Re: Bokeh
« Reply #52 on: 17 June, 2011, 11:04:45 am »
The bigger the piece of glass on the front, the shallower the depth of field with it wide open.

... and the more expensive it looks, which is why I wrote, on page 1 of this thread, that shallow DoF is largely about willy-waving.
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Re: Bokeh
« Reply #53 on: 17 June, 2011, 11:58:49 am »
The way we look at images has led to a refocusing of our views on depth of field. If we only look at pictures on a monitor a compact is pretty good. It gets everything in focus and has enough resolution for the screen. As the size of the print goes up and the resolving power of the medium increases we need bigger and better lenses to cater for the bigger receptors we need for better resolution.
The bokeh of a lens can be seen as a way of demonstrating its quality within the constraints of the medium of the low resolutions we can see on a computer monitor.

Biggsy

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Re: Bokeh
« Reply #54 on: 17 June, 2011, 12:21:56 pm »
Unlike willies, I find shallow-DoF pictures often rather pleasing to look at.
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Re: Bokeh
« Reply #55 on: 17 June, 2011, 12:37:09 pm »
Unlike willies, I find shallow-DoF pictures often rather pleasing to look at.

Cue shallow-DOF pictures of a dubious nature.

AndyK

Re: Bokeh
« Reply #56 on: 17 June, 2011, 12:42:32 pm »
Most ultra-narrow depth of field effects are just willy-waving, no real pictorial merit that I can see.




A shallow DoF isolates the subject and focuses the viewer's attention:















It can also be used to reduce foreground obstructions:


Biggsy

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Re: Bokeh
« Reply #57 on: 17 June, 2011, 12:55:33 pm »
A shallow DoF isolates the subject and focuses the viewer's attention

Absolutely, and that's often difficult with a small format or slow lens.

Yes some willy waving is done with extreme examples, but that's true of all aspects of photography.  People like to show off their nice equipment (stoppit!).  That doesn't mean the pictures aren't genuinely good as well.
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Re: Bokeh
« Reply #58 on: 17 June, 2011, 01:17:44 pm »
The ultimate Leica bokeh is supposed to come from the pre-aspherical 35mm Summicron, but that's a bit weird; a 35mm has sufficient DOF that you rarely get anything far enough OOF to benefit.

Interestingly any focal length lens has the same DOF with the same aperture and the same SUBJECT magnification. That is if you take a picture with a 35mm and a 60mm lens so that the subject fills the same area of the frame (35mm lens will be at 1/2 the distance of the 60mm), and at the same aperture, then the DOF will be the same.

However, the background on the 60mm image will look softer, because the narrower field of view effectively expands half the amount of background to fill the frame - and hence also expands the blurred area of background making it look less "busy"

That's what you'd think, logically, but in fact, no it doesn't work like that.

Yes it does - here is an explanation better than anything I can conjure up....
Depth of field

Or if you like - bang in the figures to practically any DOF calculator you care to find.

I've just read most of that, and he seems to be saying "sometimes". OK, so I made a blanket statement which doesn't cover everything: DOF in macro is greater at longer focal length for the same magnification, fair dos.

Quote
To a first approximation, on the assumption that the F-number is kept the same, the DOF will not depend on the focal length. However, a closer examination reveals that this is too simple a statement which does not always hold. The general scenario is illustrated in Fig. 2. At a fixed magnification M=0.0025 and F-number N=2.8, we notice that the shorter focal length has more rear DOF and the longer focal length more front DOF. For example, for the 24×36 mm format we may follow the yellow lines (30-µm COC) to conclude that a 100-mm lens comes with 10 m of front DOF and ~ 20 m of rear DOF, whereas a 35-mm lens has 7 m of DOF in front of the subject and several hundreds of meters in rear.

Sorry, but "30" is not the same as "several hundred and seven"

Icidentally, one of the references to that article is the late Sid Ray - he was in fact the lecturer who set the assignment above and then spent weeks over the theory as to why it is so (which I've since forgotten).

Re: Bokeh
« Reply #59 on: 17 June, 2011, 01:57:35 pm »
My Sony NEX 5 has an Intelligent Auto function which pretty much works well all the time. In that setting you can press the centre of the control button and it allows you to vary the 'Background Defocus' using a wheel. It just opens the lens up. You can get this effect without knowng anything about the theory.
Alternatively you can get an adapter for it and use manual focus and aperture lenses in manual mode. I started out using manual cameras, so I know the theory and the practice, but someone new to photography can get the effects with very little effort.

David Martin

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Re: Bokeh
« Reply #60 on: 17 June, 2011, 03:31:02 pm »

As the size of the film or sensor increases it needs more light, to acheive the same f value. So the objective lens has to increase in size.

Not true. My 6x6 Rollei TLRs have smaller lenses than my 35mm rangefinders.

And the lenses I use on my 4"x5" field camera are tiny compared with the lenses on my dSLR

..d
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Re: Bokeh
« Reply #61 on: 17 June, 2011, 03:41:54 pm »

As the size of the film or sensor increases it needs more light, to acheive the same f value. So the objective lens has to increase in size.

Not true. My 6x6 Rollei TLRs have smaller lenses than my 35mm rangefinders.

And the lenses I use on my 4"x5" field camera are tiny compared with the lenses on my dSLR

..d

I'm talking about the diameter of the piece of glass on the front of the lens. You will find that similar diameters give similar depths of field, regardless of format or whether the lens is wide angle or telephoto. What will vary is the f number. The smaller the format of the sensor and the shorter the focal length, the faster the lens will be for the same diameter of glass on the front.

PH

Re: Bokeh
« Reply #62 on: 17 June, 2011, 10:32:12 pm »


16mm Sony lens with +3 dioptre filter. f11 1/160

I don't know what any of them numbers mean*, but that's a cracking shot :thumbsup:

* Well I sort of do if I can be bothered to think about it.

IanDG

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Re: Bokeh
« Reply #63 on: 18 June, 2011, 06:52:20 am »
From my Olympus E620 with 25mm Pancake lens


P6027659 by windy_, on Flickr


P5297568 by windy_, on Flickr

rogerzilla

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Re: Bokeh
« Reply #64 on: 18 June, 2011, 07:51:07 am »
From my Olympus E620 with 25mm Pancake lens


P6027659 by windy_, on Flickr
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rogerzilla

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Re: Bokeh
« Reply #65 on: 18 June, 2011, 11:24:34 am »
To show the problems of wide-angle lenses and DOF, here's a snap from earlier this week:

Forgotten Corner - RangeFinderForum Gallery

This was a 32mm lens (on a compact camera) and the aperture would have been f/3.2, the maximum, because the camera was screaming "slow shutter speed".

As you can see, most of it is in focus.
Hard work sometimes pays off in the end, but laziness ALWAYS pays off NOW.

AndyK

Re: Bokeh
« Reply #66 on: 18 June, 2011, 12:33:13 pm »
To show the problems of wide-angle lenses and DOF, here's a snap from earlier this week:

Forgotten Corner - RangeFinderForum Gallery

This was a 32mm lens (on a compact camera) and the aperture would have been f/3.2, the maximum, because the camera was screaming "slow shutter speed".

As you can see, most of it is in focus.

That is why wides are favoured by street shooters. They can set the hyperfocal, which on wides is very deep, and forget about having to focus.

simonp

Re: Bokeh
« Reply #67 on: 18 June, 2011, 08:18:55 pm »
I’ve experimented with depth of field before, here are some pics I took back in 2009, of my pompino’s drivetrain:

Bokeh - a set on Flickr

At the time I didn’t know what “bokeh” was.  Think I might experiment some more.

Of those 4 I like this one best:


Untitled by SimonP2006, on Flickr

rogerzilla

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Re: Bokeh
« Reply #68 on: 10 July, 2011, 09:39:19 pm »
Average-to-iffy bokeh from the Summicron Dual Range 50mm at f/2.8.  The Elmar and Summar 50s are much better in this respect, although worse in many other respects.  Generally, lenses with the best bokeh are not the very sharpest in the plane of focus.  The Summicron DR was said to have the highest resolving power of any camera lens at one point in time, although you can't see it with film or any 35mm digital sensor.

Hard work sometimes pays off in the end, but laziness ALWAYS pays off NOW.

Jakob

Re: Bokeh
« Reply #69 on: 04 August, 2011, 12:24:37 am »
I had forgotten about this one:

rogerzilla

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Re: Bokeh
« Reply #70 on: 13 August, 2011, 09:03:48 pm »
I shot this at Buscot Park this afternoon (the M3 has been serviced and is now like new, yay).  Note how much better the bokeh is on this old Elmarit 90mm than on the Summicron shot I previously posted.

Hard work sometimes pays off in the end, but laziness ALWAYS pays off NOW.

Dr.Doo

Re: Bokeh
« Reply #71 on: 13 August, 2011, 10:31:51 pm »
Love playing with DoF...especially when urbexing and doing detail shots

However here's shallow Dof and bokeh ...the subject is a bench in the Grim Town


Nikon D100 w. 50 1.8....f2.2 - 1/4000sec


rogerzilla

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Re: Bokeh
« Reply #72 on: 13 August, 2011, 10:46:16 pm »
The irony is that the Leica style tends towards very shallow DOF and selective focus, yet the nature of the camera means you can't actually see any focus effect in the viewfinder - so it's always a bit of a surprise when you get the negs.  I'm not sure whether the digital M9 has live preview or not, but at least you can take another shot if it's too blurred or not blurred enough.  As I am using a 1960 camera and film, I actually took this shot at three different apertures, and it turned out that my first guess (f/5.6) was the best.

Here's another shot using the Summar 50mm, an ancient uncoated lens designed for the Leica III.  This has the best bokeh of all of them, but only between about f/3.2 and f/6.3 (it has the old German f-numbers).  The composition is weaker though (I really need a 135mm lens to nail these guys and get four heads lined up next to each other).



Hard work sometimes pays off in the end, but laziness ALWAYS pays off NOW.

IanDG

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Re: Bokeh
« Reply #73 on: 15 August, 2011, 05:26:37 am »
This was shot with a Leica II


Fence Post, Willow Glen by windy_, on Flickr

rogerzilla

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Re: Bokeh
« Reply #74 on: 15 August, 2011, 06:34:33 am »
What was the lens?  The Elmar 50/3.5?
Hard work sometimes pays off in the end, but laziness ALWAYS pays off NOW.