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09-03-2012, 09:34 AM   #16
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QuoteOriginally posted by amoringello Quote
Bokeh actually does depend greatly on lens design and aperture. If the aperture is curved or straight, whether is has five blades or nine, it will differ. The lens will also affect the quality of the bokeh, wehther the OOF circle is consistent, has a bright edge, or even donut shaped.
Easy if it's already written down, you just need to quote and btw the one who introduce the word Bokeh into the western countries actually say that this site is the most correct explanation.

QuoteQuote:
Since any image is represented by a large number of images of points, we may attempt to understand the whole by considering the blurring of a single point. An unsharply imaged point is associated with a circle of confusion, or a blur disk. This blur disk is characterized by
- A size.
- A shape.
- The light distribution across the disk.

The size of the disk determines the "amount of blur". The shape of the blur patch does not need to be circular, in which case the designations "circle of confusion" or "blur disk" are misnomers. Nonetheless, for convenience the word disk will be freely used to mean a patch of arbitrary shape. Although the size and the shape of the disk are unmistakable blur characteristics, they do not touch the essence of bokeh as the Japanese intended the word. The distribution of light across the disk does. However, the distinction is not always clear and what follows is intended as an overview of a variety of factors that influence the rendering of OOF image parts. Explanations of the underlying mechanisms will be brief and the reader is referred to other pages for elaborateness.
And really the shape of the aperture does very little to the blur, just compare the DFA100mm and the DFA100mm WR, sure the highlights are more rounded but that's it, nothing of great importance or character defining.

09-03-2012, 09:38 AM   #17
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QuoteOriginally posted by Lowell Goudge Quote
No actually. As I said, check with a DOF calculator, you will find that for the same image size, the depth of field is the same at identical apertures .

I did this calculation once for someone who was looking to do portraits with longer lenses and was wondering about background distance to get similar effects. I used the DOF calculator and found that the setup remains the same I.e. subject to background if you step back proportionally to the change in focal length so that the image size remains the same
but.... the blur disks will appear to be larger in the back ground with the 200mm then with the 40mm even though the DOF is the same.

Sorry but he has a good article about it as well.

http://toothwalker.org/optics/dof.html
QuoteQuote:
DOF versus focal length

The phrase "a wideangle lens has more DOF than a tele lens" is frequently heard. Is it true? Sometimes it is, often it is not. It all depends on the comparison. We may assume that the lenses are compared for the same format and at the same F-number, but what about the object distance? If the object distance is kept the same the wideangle image will indeed show a greater DOF, but also a larger field and, consequently, a smaller subject. On the contrary, if the subject is framed the same way we have an entirely different situation. Now the depths of fields may be comparable or even identical. However, in both cases the photographs are not the same and the comparison is one between two different pictures. The former case concerns a comparison with preservation of the perspective (viewpoint) but with different magnifications, the latter preserves the magnification (the size of the subject on the film) but not the perspective. Ironically, the only case where the images are the same is also the only case where the depth of field is of no importance: the reproduction of a flat object like a stamp or a painting. For such a subject has no depth.
There are samples a bit further down, the funny thing is if you "crop" the blur background so that the subjects are the same size there that the blur is actually the same as well.
So the background is actually blurred just as much but you see more of the background because of the change in perspective.

Last edited by Anvh; 09-03-2012 at 09:44 AM.
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