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11/08/2007 11:08:09 AM · #1 |
My bokeh entry I have in mind involves some modifications to the lens and before I start I'd like to know which of my lenses I should use to get the best bokeh - the 50mm 1.8 MKII or the 70-200 2.8 on it's long end?
Maybe someone also has the technical explanation, as I believe that there is a specific focal length at which a 2.8 lens would match the 50 1.8 - I'd like to know how to calculate that. Thanks!
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11/08/2007 11:13:41 AM · #2 |
Heres the first thing I found, I will look for a better one. The top equation will give you the best focusing point to get the best dof, but you probably need something a little better, I'll get back if I find one.calculations
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11/08/2007 11:16:01 AM · #3 |
From the same page, just a different link, this gives you a calculator, but you need to know your focusing distance.calculator
Hope this helps.
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11/08/2007 11:33:35 AM · #4 |
The best bokeh comes from having as high a ratio as possible of distance-to-background:distance-to-subject. (for foreground bokeh you'd have distance-to-foreground instead).
The easiest way to achieve high ratios is to have a lens with a short minimum focal distance. My guess is whichever lens has the shorter (I think it's the 50/1.8 vs. the 70-200) focal distance will do you better. This is mainly why macro lenses give very pleasing bokeh.
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11/08/2007 11:37:53 AM · #5 |
Originally posted by DrAchoo:
The best bokeh comes from having as high a ratio as possible of distance-to-background:distance-to-subject. (for foreground bokeh you'd have distance-to-foreground instead). |
That's only a small part of it though - focal length is a huge factor too, as is the aperture.
Consider the bokeh of a 17mm lens 1 foot from the subject at f4, compared to the bokeh of a 100mm lens, 1 foot from the subject at f4. The lens<->subject and subject<-> background distance matters, but so does the other factors.
I'd tend to go for the longer lens to get the better bokeh, particularly as the 50mm 1.8 has that nasty pentagonal aperture blade arrangement, particularly obvious wide open. |
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11/08/2007 11:46:48 AM · #6 |
Well, obviously the aperture has a very important effect, but I took that as basic knowledge and understood.
I'm not sure about your example. My suspicion is that the 100mm would provide a better bokeh, but I'm not positive that would bear out in reality if you took the crop of the 17mm lens to have the field of view be the same as the 100mm.
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11/08/2007 11:51:32 AM · #7 |
| Actually, from a non-technical POV, the best bokeh depends on the placement of subject vs. fore/background, and light on/reflectiveness of fore/background (more so than light on subject). That and colours. |
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11/08/2007 11:51:56 AM · #8 |
Originally posted by DrAchoo:
I'm not sure about your example. My suspicion is that the 100mm would provide a better bokeh, but I'm not positive that would bear out in reality if you took the crop of the 17mm lens to have the field of view be the same as the 100mm. |
Yup, if you cropped about 90% of the shot away, they'd have equivalent depth of field, once you make the angle of view the same.
I'm not arguing that different focal lengths have more or less depth of field though, just effective bokeh for the same subject distance.
however, all other things being equal, the bokeh of the 50mm 1.8 is nastier than the 70-200, so I wouldn't use it unless I wanted particularly geometric bokeh.
Mind you, playing with the aperture shape can be worth it, if you wan to get blue ribbons...
Message edited by author 2007-11-08 11:53:47. |
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11/08/2007 12:00:14 PM · #9 |
how about using a 400mm zoom lense at 5.6?
I̢۪ve accomplished nice background bokeh, but can one accomplish the same for foreground bokeh?
And I have another question, can one get the circular bokeh for a foreground? and how would one be able to differentiate the two
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11/08/2007 12:01:44 PM · #10 |
Oh my, this is well confusing. I think I'll just test both lenses for my particular setup and see which gives nicer results - this shot will involve loads of trial and error anyway.
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11/08/2007 12:02:47 PM · #11 |
Originally posted by JaimeVinas:
how about using a 400mm zoom lense at 5.6?
I̢۪ve accomplished nice background bokeh, but can one accomplish the same for foreground bokeh?
And I have another question, can one get the circular bokeh for a foreground? and how would one be able to differentiate the two |
It's actually probably easier to get foreground bokeh than background bokeh, anyway, given the typical 1/3rds/ 2/3rds in focus regions for non-macro focusing. So its more likely that foreground elements will be out of focus for equivalent focus point/ subject distances.
In reality you probably want to be shooting through something. Differentiating the two might be interesting, I suppose it needs to obscure the actual in focus subject, sort of like this
Message edited by author 2007-11-08 12:06:26. |
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11/08/2007 01:40:51 PM · #12 |
Originally posted by Gordon:
Originally posted by DrAchoo:
I'm not sure about your example. My suspicion is that the 100mm would provide a better bokeh, but I'm not positive that would bear out in reality if you took the crop of the 17mm lens to have the field of view be the same as the 100mm. |
Yup, if you cropped about 90% of the shot away, they'd have equivalent depth of field, once you make the angle of view the same.
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Are you sure about this? Have I misinterpreted? I would have thought that the 17mm lens would exhibit greater DOF and less bokeh, rather like the 'crop factor' argument.
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11/08/2007 01:50:05 PM · #13 |
From what I have learned 3 things affect the dof, distance, aperture, and focal length. If you want the most shallow dof then you get closer, open your aperture up wide, and use your longest focal length. I haven't played with that calculator I first posted to see how accurate it is, but to use an example. If you stood the same distance from your subject and took a shot with your zoom and your fixed lens, both at a 2.8 your zoom lens would have a more shallow dof every time. Somebody correct me if I'm wrong, especially since that is how I was taught it, and if I'm wrong I need to know.
ETA: And your zoom at the 200mm side would be more shallow than at the 70mm side.
Message edited by author 2007-11-08 13:50:48.
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11/08/2007 01:53:32 PM · #14 |
Originally posted by travis_cooper:
From what I have learned 3 things affect the dof, distance, aperture, and focal length. If you want the most shallow dof then you get closer, open your aperture up wide, and use your longest focal length. I haven't played with that calculator I first posted to see how accurate it is, but to use an example. If you stood the same distance from your subject and took a shot with your zoom and your fixed lens, both at a 2.8 your zoom lens would have a more shallow dof every time. Somebody correct me if I'm wrong, especially since that is how I was taught it, and if I'm wrong I need to know.
ETA: And your zoom at the 200mm side would be more shallow than at the 70mm side. |
The only problem being that getting close and using a long focal length make it difficult, often, to get the subject within the frame.
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11/08/2007 01:55:43 PM · #15 |
Originally posted by Mr_Pants:
The only problem being that getting close and using a long focal length make it difficult, often, to get the subject within the frame. |
Technicalities, or course you still need to choose the option that will let you compose your shot the best.
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11/08/2007 02:00:37 PM · #16 |
Originally posted by Mr_Pants:
Are you sure about this? Have I misinterpreted? I would have thought that the 17mm lens would exhibit greater DOF and less bokeh, rather like the 'crop factor' argument. |
If the subject remains the same size in both shots, its only the angle of view that changes, not the depth of field or bokeh. However, you'd have to move the lens to get the subject the same size in each case.
The background would be substantially different, but the depth of field is essentially the same at different focal lengths, for the same aperture and subject size. (The key to all of this is the same subject size - this is far different to the same camera/subject distance, for example) |
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11/08/2007 02:05:08 PM · #17 |
Originally posted by Gordon:
Originally posted by Mr_Pants:
Are you sure about this? Have I misinterpreted? I would have thought that the 17mm lens would exhibit greater DOF and less bokeh, rather like the 'crop factor' argument. |
If the subject remains the same size in both shots, its only the angle of view that changes, not the depth of field or bokeh. However, you'd have to move the lens to get the subject the same size in each case.
The background would be substantially different, but the depth of field is essentially the same at different focal lengths, for the same aperture and subject size. (The key to all of this is the same subject size - this is far different to the same camera/subject distance, for example) |
I understand that moving the camera to frame the subject the same would give pretty much the same effect in terms of DOF, but I asked the question, as you mentioned cropping 90% of the frame away. Something which would not give the same result.
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11/08/2007 02:15:25 PM · #18 |
Originally posted by Mr_Pants:
I understand that moving the camera to frame the subject the same would give pretty much the same effect in terms of DOF, but I asked the question, as you mentioned cropping 90% of the frame away. Something which would not give the same result. |
I tend to think of cropping as moving my feet, just as much as throwing away pixels, or switching camera bodies.
//www.luminous-landscape.com/tutorials/dof2.shtml
Message edited by author 2007-11-08 14:17:22. |
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11/08/2007 02:16:15 PM · #19 |
Originally posted by Mr_Pants:
I understand that moving the camera to frame the subject the same would give pretty much the same effect in terms of DOF, but I asked the question, as you mentioned cropping 90% of the frame away. Something which would not give the same result. |
I agree, I don't think cropping comes into this equation at all, that just means you see less of the picture, it shouldn't affect your dof.
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11/08/2007 02:22:08 PM · #20 |
Originally posted by Gordon:
I tend to think of cropping as moving my feet....
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OK, I wasn't familiar with your particular nomenclature.
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11/08/2007 02:28:13 PM · #21 |
Originally posted by Mr_Pants:
Originally posted by Gordon:
I tend to think of cropping as moving my feet....
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OK, I wasn't familiar with your particular nomenclature. |
I've been using primes too much this year I think. |
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11/08/2007 03:11:32 PM · #22 |
For all practical purposes DOF is solely dependent on the physical size of the aperture used and the actual point of focus. Focal length is irrelevant. A 25mm aperture on on a 50mm lens will deliver exactly the same DOF as a 25mm aperture on a 200mm lens, assuming both lenses are focused to the same distance. But that 25mm aperture is f/2.0 on the 50mm lens and it is f/8.0 on the 200mm lens.
R.
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11/08/2007 03:44:31 PM · #23 |
Originally posted by Bear_Music:
For all practical purposes DOF is solely dependent on the physical size of the aperture used and the actual point of focus. Focal length is irrelevant. A 25mm aperture on on a 50mm lens will deliver exactly the same DOF as a 25mm aperture on a 200mm lens, assuming both lenses are focused to the same distance. But that 25mm aperture is f/2.0 on the 50mm lens and it is f/8.0 on the 200mm lens.
R. |
Though the practical outcome of that is that focal length is critical ;) |
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11/08/2007 04:05:15 PM · #24 |
Originally posted by Bear_Music:
A 25mm aperture on on a 50mm lens will deliver exactly the same DOF as a 25mm aperture on a 200mm lens, assuming both lenses are focused to the same distance. But that 25mm aperture is f/2.0 on the 50mm lens and it is f/8.0 on the 200mm lens.
R. |
Ah, I think this is intersting. Doesn't that mean that if you keep the f/ ratio consistent and zoom in, the aperture in terms of mm becomes bigger and the DOF shallower?
Edit: Oh hold on, I think I got it - the DOF doesn't actually become shallower, but the bokeh becomes bigger due to perspective?
Message edited by author 2007-11-08 16:09:35.
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11/08/2007 04:10:10 PM · #25 |
Originally posted by gloda:
Doesn't that mean that if you keep the f/ ratio consistent and zoom in, the aperture in terms of mm becomes bigger |
This, in large part, is why cheaper zoom lenses tend to change minimum f-stop as you zoom them further out - the physical aperture stays the same but the focal length has changed.
More expensive lenses are constant maximum f-stop through their zoom, because the physical aperture has to change dynamically with focal length. But it means your 70-200 will be f2.8 at 70mm and 200mm, instead of a cheaper zoom that might be 3.5 at one end and 5.6 max aperture at the other end. |
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