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My friend and I were talking as we were shooting. I will spare you the whole conversation. Which would have more bokeh (granted you had the same framing)? I have no idea how to do the calculation while adjusting for the different subject distances due to different focal lengths.
Well, you can use DOFMaster's online calculator to find out how much you'll have in focus by plugging in the different parameters. That might give you an idea, at least...
Like Sean said, check out www.dofmaster.com:
100mm @ f/2 with a subjectdistance of 10 feet the total DoF is 0.22ft
200mm @ f/2.8 with a subjectdistance of 10 feet the total DoF is 0.08ft
These figures are assuming you are using your Canon Rebel 1000D/XS
Quote:
Originally Posted by Mark Elberson
You know Mark, I started to post example figures just like that. However, then I realized that the subject distance would have to change in order to achieve the same framing. I'm assuming you'd need to double the subject distance in order to get the same framing. Wouldn't that be right? If so, the total DOF using a 200mm lens (assuming the same framing) would be .32 feet.
All of that was going through my head this morning as I was getting ready for work. So I deleted the example I had typed out and just posted the site recommendation until I could think it through without having to do fifteen other things at once. :-)
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Originally Posted by Mark Elberson
The "same framing" (original post specification) would put the 200 @ f2.8 with a subject distance of 20ft, the total DoF is .32ft
The 100 @f/2 wins the shorter DoF calculation but does it produce better bokeh?
The EF 100 f/2 USMhas8 aperture blades, but I can't find any review that tests it's bokeh. Bryan has some nice sample shots and you'll notice in this colorful grass photothat even though the background is blurred there is still a bit of edginess/nervousness to the bokeh. This lens probably has straight rather than curved aperture blades. It would also be interesting to see how the bokeh changes stopped down and subject-distance get's shorter. Bokeh can also change across the frame as well as have oinion like rings in speculars rather than flat circular spots. There is also the dreaded bokeh CA. Uuuoooohhhh!!
The 200 f2.8 has 8 aperture blades as well but I believe that twice the reach will yield better bokeh even though the DoF calculations favor the 100 f2. Looking at Bryans Coneflower Photoit's obvious that whatever is in the background has melted away in to ooF land in a very dreamy manner. Even the stem on the flower is slowly melting away so "buttery smooth".
If all-of-a-sudden Ifell into some major extra coin I would not hesitate to purchase a used 200 f1.8L or the new 200 f2.0L. Even the 300 f2.8L would be very tempting. The creamy bokeh produced by these lenses is the reason they're so highly coveted.
Bokeh seems to be a factor of many things not just DoF and not necessarily the lens design. (Though the more aperture blades and the more curved they are the better.) Also, the FOV vs. focal length playsa major role. For any given aperture, as the fov angle decreases the smoothness of the bokeh increases because less of the background is being rendered by the lens. I have some killer closeups that I took years ago with the el-cheapo Tamron 70-300 f3.5-5.6 Di LD at focal lengths of 180-260 at f4-f8 that have very beautiful creamy bokeh.Often, it's the time of day and the harshness of specular reflections and/or contrast areas like limbs against the skywhich either serve to compliment or detract from a len's bokeh ability. I posted 2 photos of my cat in Postyour Petsthe second one is th EF 50 f1.4 @ f1.4. I find the bokeh extremely pleasing in the ooF areas. I do however, have shots of my son playingin the shadeof a crepe myrtle in bright daylight where the speculars from the surrounding leaves creates an extremely nerve racking bokeh. Same lens in two different situations can yield two different results. The EF 100 f2.8 USM Macro... ? I can't say I've ever been displeased with the bokeh performance of that lens. I'm rambling......
So, my vote is for the longer reaching 200 f2.8....
The 200mm f/2.8 will have more out of focus blur, but the 100mm f/2 will have thinner DOF. The amount of the difference for the background blur will depend on how close you are to the hyperfocal distance. The reason why the 200mm f/2.8 has more blur even though it has a slower f-number is because it has higher magnification.Quote:
Originally Posted by powers_brent
For example, using 35mm and h/CoC=1440 (CoC=0.025mm):
100mm f/2 @ 3 meters: 84mm DOF
200mm f/2.8 @ 6 meters: 118mm DOF
You can see the 200mm f/2.8 DOF is 40% deeper when framed the same way. Even so, it has more OOF blur.
(By the way, bokeh is not the "proper" term for this, because it only relates to the quality of the out of focus blur, not the quantity.)
Thanks guys. I was excited to see so many replies by only 930am! So just to make sure. To get the same framing for different focal lengths the subject distance is proportional to the focal length? (50mm-5ft, 100mm-10ft, 200mm-20ft, 300-30ft, and on and on (even in the reverse direction?)) And just to throw another wrench in the machine. I have the 100mm f/2.0 and the 300mm f/4.0. This is even another question, but I guess I can calculate it now for sure granted the subject distance assertion is correct.
Yes. There is a six-fold difference between 50mm and 300mm, so to get the same field of view (not angle of view), you need a six-fold difference in subject distance.Quote:
Originally Posted by powers_brent
The 300mm will have slightly more diffuse OOF blur and deeper DOF. (When framed the same for distances far from the hyperfocal distance.)Quote:
Originally Posted by powers_brent
Calculating OOF blur is much less common than calculating DOF. The only calculator I know of is Bob Atkin's:
http://www.bobatkins.com/photography/technical/bokeh_background_blur.html
I plugged in your numbers and used a 2 meter focus distance and typical 35mm 8x10 CoC values:
http://thebrownings.name/images/2009...r-100mm-f2.png
http://thebrownings.name/images/2009...r-300mm-f4.png
William Castleman has done some testing and written an article about Bokeh and Background Blurring with Canon Lenses. See
http://www.wlcastleman.com/equip/reviews/aps-c_port/bokeh.htm
Great point Sean and valuable lesson! Thanks for bringing that to my (and everyone else's) attention.Quote:
Originally Posted by Sean Setters
Quote:
Originally Posted by Johnny Rasmussen
That's a good read Johnny. I've seen that before.
His comparison of the 50 1.4 vs the 50 1.2 is really good as well.
Thanks for the link.
Something that bryan pointed out about bokeh and focal length is that telephoto lenses may or may not have less blur, but because of their field of view, given the same framing on the subject, they will have less background detail to start with, and as such the blur will seem like more. In other words, longer the focal length, there's less to blur out. Even if you could adjust aperture to match depth of field, the blur will be qualitatively different between focal lengths. longer focal lengths will likely have a more uniform blur with less variation in color/contrast.
Ignoring the qualitative impact of the aperture shape and other variables I can't recall...
Quote:
Originally Posted by powers_brent
I think it depends on what you mean by "more bokeh". One can quantify "depth of field", but how does one quantify bokeh? This isn't just a rethorical question... I would be interested if anyone has an answer, but I suspect that "more bokeh" is something that depends on perception.
It seems to me that an important step in answering this question is to ask what happens to bokeh when you crop. Does a cropped picture appear to have more, less, or the same bokeh as the original? This is the same question as "does a lens with a given aperture produce more bokeh if it is slow or fast?" (or equivalently, "long focal length or short focal length")?
If you say a cropped picture has the same bokeh as the original, then only aperture matters. So 200mm f/2.8 has exactly as much bokeh as a 100mm f/1.4 (and thus it has "more bokeh" than a 100mm f/2). If we accept this, we can quantify the bokeh a lens has very simply (the "amount of bokeh" a lens has is simply its aperture).
My impression is that bokeh probably stays the same or increases when you crop. (If it increases, the 200mm f/2.8 is even more favored over the 100mm f/2).
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Originally Posted by Daniel Browning
Interesting, but... does he say *what* he is calculating? How does he define OOF blur? Do all these numbers come together to make a single measure of bokeh?
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Originally Posted by Jon Ruyle
Jon, you are using a very wrong definition of the word bokeh. I think you are doing it intentionally, since others in this thread have been doing it, but I think something should be said.
Bokeh has nothing at all to do with this thread. In his original post, powers_brent used the word "bokeh", but what he meant was "background blur". There is no such thing as "more bokeh" or "less bokeh". It's an attribute like someone's face. You don't say that someone has "more face" or "less face", but an "ugly face" or a "pretty face" (or specific qualities about their face, such as symmetry, feature size, etc.). In the same way, we talk about specific qualities of bokeh, such as highlight edge softness and overall comparisons like "uglier bokeh" and "prettier bokeh".
However, it does make perfect sense to talk about "more OOF blur" and "less OOF blur". Most photographers only care about background blur, since they don't use foreground blur in most of their compositions. So usually, what they really mean by "bokeh" is just "quantity of background blur".
So there are three very different things here:
- Quality of the OOF blur (bokeh)
- Quantity of the OOF blur
- DOF
You can have any combination of the three:
- Deep DOF
- High quantity of OOF blur
- Poor quality of OOF blur (harsh bokeh)
Or:
- Thin DOF
- Low quantity of OOF blur
- Good quality of OOF blur (smooth bokeh)
In this thread, the poster asked about bokeh, which is completely separate from DOF and quantity of OOF blur. But what he meant was quantity of background blur, not bokeh.
Quote:
Originally Posted by Jon Ruyle
The bokeh is the exact same, but the background blur (if any) changes in relation to the subject.
Quote:
Originally Posted by Jon Ruyle
You can answer that question definitively for background blur (or OOF blur), though even that will vary based on proximity to the hyperfocal distance, but not for bokeh.
Quote:
Originally Posted by Jon Ruyle
Yes, it's all on his web page.
Quote:
Originally Posted by Jon Ruyle
Diameter of a point source specular highlight at a given distance from the plane of focus.
Quote:
Originally Posted by Jon Ruyle
No, they're separate.
Thanks Daniel. Your post (and Bob Atkins page) helped me understand some stuff.
Quote:
Originally Posted by Daniel Browning
Yes, I was using the word in the way I thought Mr. Powers Brent intended, even though it isn't how I would have used the word.
Quote:
Originally Posted by Daniel Browning
Okay, that makes perfect sense. Of course, if you really want to quantify blur with a single number (and thus answer which lens has more) you have to specify which given distance you care about . (Correct me if I'm wrong, but I think if that "given distance" is close to infinity, only aperture matters. If the "given distance" is close to zero, only f number matters.)
In addition, I guessed that by "bokeh" the OP wanted to also take into account another feature of long lenses: they magnify background details more. I *thought* this contributed to our perception of a blurred background (quite separate from how big the OOF disk of a background point will be), giving an additional advantage to the long lens. Maybe I'm confused about this as well, though.
Quote:
Originally Posted by Daniel Browning
According to Bob Atkins (not that I nececarily would take his word over yours [:)]), bokek is a combination of quality and quantity of OOF blur. This is what I thought the word meant, too, though I never tried to check a definitive source.
Quote:
Originally Posted by Jon Ruyle
No, you idiot. 1) This is only true if the subject is far from infinity. 2) there is diffraction (which favors the longer lens, aperture being the same).
Think before you post next time, loser head.
Thanks for the kind response, Jon.
Quote:
Originally Posted by Jon Ruyle
When in Rome. [:D]
Quote:
Originally Posted by Jon Ruyle
You're quite right.
Quote:
Originally Posted by Jon Ruyle
I think so too.
Quote:
Originally Posted by Jon Ruyle
Agreed.
Quote:
Originally Posted by Jon Ruyle
I think one of the ways in which the increased magnification of the background affects our perception of background blur is by increasing the size of the OOF disk on the sensor (though in a very different way from which f/number affects the OOF disk.) One other way that someone else mentioned in this thread is by having less background to begin with.
Quote:
Originally Posted by Jon Ruyle
That's not the impression I get. Bob says:
<p style="padding-left: 30px;"] "While the quality of blur - bokeh - is in itself a "fuzzy" concept and
something that's quite difficult to predict or control, the quantity of blur can be
calculated quite easily and it's something over which the photographer has control through
choice of focal length and aperture."
To me it seems like he treats bokeh as quality only.
Thanks again, Jon.
I wish I could keep up with this thread because it's a fascinating subject. Maybe one of you guys who understands it in detail could post some images that illustrate your points? Speaking on behalf of the "no question too stupid" contingent [;)], it would be much easier to understand if we could see it.
Thanks and I hope someone can come up with a way to illustrate this.
Jeff
[View:http://farm3.static.flickr.com/2682/4234224849_ff11394af8.jpg]
XS with Canon 100mm f/2.0 @ 2.0, 1/200 sec, ISO 100. Kodak P20 shot thru @ 1/16 camera right and Canon 430EXII bare @ 1/64 left behind snowman. (http://www.flickr.com/photos/brentpowers/4234224849/in/photostream/)
http://farm5.static.flickr.com/4041/...97794c215e.jpg
XS with Canon 300mm f/4.0 @ 4.0, 1/200 sec, ISO 100. Kodak P20 shot thru @ 1/4 camera right and Canon 430EXII bare @ 1/16 left behind snowman. (http://www.flickr.com/photos/brentpowers/4234227817/in/photostream/)
If the framing is not exact does the test not count? They are framed almost the same, just slightly different. The OOF blur seems more diffused with the 100mm lens. Or is it just me? What may I have done wrong? Or is that what I should expect?
Quote:
Originally Posted by powers_brent
Looks that way to me, too.
I think that is because the background is pretty close to the focal plane. If I understand things right, when the background is close, f number matters more. When the background is far, aperture matters more.
Quote:
Originally Posted by Daniel Browning
Yup, I agree with your interpretation of that quote. But he also says: "While "Bokeh" is a measure of both the quantity and the nature or
quality of background blur, this program only calculates the quantity."
Perhaps he is taking the precise definition of the word less seriously than we are [:)]
Quote:
Originally Posted by powers_brent
I agree with Jon. If you repeated the test with human-sized focus distances, I think you would get different results.
Quote:
Originally Posted by Jon Ruyle
I see now, thanks. You're right.
Quote:
Originally Posted by Daniel Browning
Well everybody on this forum knows that the both of you (quite specifically you two) delve into the technicals of photography. But I ask these questions hoping that you two will answer and set all my mistakes, misconceptions, etc. correct. I literally post these questions and think in my head, "what will Daniel and Jon have to say?" I learn a lot by your exchange. Thanks for all the information.
EF 135mm F2 L my choice. Hook on 1.4 crop censor