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Archive 2013 · Does FOV affect Bokeh?
  
 
sathya_sn
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p.1 #1 · Does FOV affect Bokeh?


Been wondering about this for a while and wanted to hear about thoughts/experience from others on this topic. Is Bokeh strictly a factor of focal length or does FOV also help with it.

What I mean is, I have a 50mm f/1.4 and use it mostly on my 5D3. Was thinking about getting something a little longer for portraits (like a 85mm f/1.8 or 100mm f/2). I also have a 7D where the 50mm itself would be more like a 80mm (FOV).

Assuming there was no difference in Bokeh between a crop & FF camera, will there be a difference in bokeh characteristics between a 80mm FOV and a true 80mm? Not fully sure if this question makese sense but figured I'd ask ...



Mar 31, 2013 at 09:38 PM
curious80
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p.1 #2 · Does FOV affect Bokeh?


This is one of those topics which can quickly turn into heated debated Nevertheless a few points:

1. Suppose you take a portrait on your 5D3 with a 50mm lens and then with a 200mm lens in such a way that the "depth of field" is identical for both shots. In this case the 200mm lens with its narrower FOV will still give you a more blurred background specially if the background is at a distance. The narrower FOV sees less of the background and thus the background is essentially "magnified" more resulting in more blur.

2. However in your example if you take a shot at 80mm on 5D and 50mm on 7D, the FOV is the idential. So the only difference will come from the use of smaller actual focal length on 7D which will result in more DOF and less blur for the 7D shot (assuming identical apertures).

Btw the term bokeh is used primarily to refer to the quality of the out of focus blur rather than "quantity" of it and as such it is determined more by the lens design.



Mar 31, 2013 at 09:57 PM
binary visions
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p.1 #3 · Does FOV affect Bokeh?


FOV does not change the bokeh.

The same FOV on two different crop factors (FF vs. crop) will result in significantly different bokeh, since it will require two different focal lengths or focus distances.

However, simply changing the FOV - i.e. a 50mm lens @ f/1.4 across a full frame sensor vs a smaller FOV on the same lens/settings for a crop sensor - will not affect the bokeh. You are simply cropping the frame.

So, directly, yes. An "80mm FOV" on a DX camera (i.e. a ~50mm lens) will have different bokeh than a real 80mm lens.



Mar 31, 2013 at 11:32 PM
Michael White
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p.1 #4 · Does FOV affect Bokeh?


The biggest factor of bokeh is the design and number of blades used in setting the aperture. The more blades the better the bokeh.


Apr 01, 2013 at 04:07 AM
a.RodriguezPix
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p.1 #5 · Does FOV affect Bokeh?


Leica


Apr 01, 2013 at 04:12 AM
Steve Spencer
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p.1 #6 · Does FOV affect Bokeh?


Michael White wrote:
The biggest factor of bokeh is the design and number of blades used in setting the aperture. The more blades the better the bokeh.


The quality of bokeh is quite subjective, but the number of blades in the aperture is really only important for one factor that appears in only some shots--out of focus highlights. The OOF highlights show the shape of the aperture and more blades generally means more rounded OOF highlights, but the shape of the blades matters as well. Many modern lenses have rounded blades that show nice rounded OOF highlights even with as little as 7 blades. IMO, OOF highlights are not even close to the most important factor in determining the quality of bokeh, however, and can be totally overemphasized. How smooth and how quick the transition from sharpness to blur matters a lot more, IMO. Whether the blur is "nervous," "smooth," or "painterly," all of which are unaffected by the blades also matters more than OOF highlights as well in my view. So, yes the number of blades can affect the bokeh, but IMO it is not even close to the biggest factor and the suggestion that the more blades the better the bokeh is way over simplified to the point of being misleading in my view.



Apr 01, 2013 at 04:28 AM
binary visions
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p.1 #7 · Does FOV affect Bokeh?


Correct me if I'm wrong, Steve, but isn't the transition from sharpness to blur directly defined by the focal length and aperture of the lens?

I always thought that was an inherent property of the depth of field, not something that can be influenced by design. There are some factors that influence each other there - for instance, a long lens not only can give you a shallower DOF but it compresses your image more so the OOF areas appear closer to the subject - but I wasn't aware that you could actually change the optical or blade design of a lens to cause a shift on how quickly the transition to blur occurs.



Apr 01, 2013 at 01:16 PM
justruss
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p.1 #8 · Does FOV affect Bokeh?


Bokeh refers to the quality (I mean that in a descriptive sense, not a single axis sense), not the amount, of background (or foreground) blur.




Apr 01, 2013 at 02:14 PM
Johnny B Goode
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p.1 #9 · Does FOV affect Bokeh?


a.RodriguezPix wrote:
Leica


i lol'd



Apr 01, 2013 at 11:35 PM
sathya_sn
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p.1 #10 · Does FOV affect Bokeh?


Reading through all the responses it does sound like the 85 would probably have a better/different bokeh than the 50 on a crop. If nothing else because of differences in lens design.

Browsing some of the pictures taken with a 85 f/1.8, it does seem like that would be a good addition. Just have to wait for the finances & a good deal to line up Thanks everyone for all the helpful responses ...



Apr 02, 2013 at 01:56 AM
 

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binary visions
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p.1 #11 · Does FOV affect Bokeh?


A lens with a longer focal length is, all else being equal, going to produce a shallower DOF and more compression in the image, which often leads to more pleasing bokeh.

As mentioned above, there are some design aspects to a lens that can improve or worsen the bokeh but if it's a clean or attractive defocused area you're after, longer focal lengths are usually a better bet than shorter ones.



Apr 02, 2013 at 01:02 PM
dsjtecserv
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p.1 #12 · Does FOV affect Bokeh?


Sathya, I think you need to be clearer about what you mean by "bokeh" in your question. Strictly speaking, bokeh refers only to the aesthetic quality of the out of focus objects. As several people have pointed out, that quality is primarily a function of the individual lens design characteristics; it isn't a direct function of focal length at all. Thus you couldn't make a generalization that a 85 1.8 will give better bokeh-- it depends on which 85 1.8.

On the other hand, several people have responded as if you were talking about the depth of field, or the degree of blur, or the transition between the two. If that's the case, then this could be very focal-length dependent, depending on exactly what characteristics you are interested in.

So perhaps you could provide a little more detail about what you are curious about, which might help the answers be a bit more focused.

Dave



Apr 03, 2013 at 06:00 PM
sathya_sn
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p.1 #13 · Does FOV affect Bokeh?


Dave, I like the out of focus effects that wide open apertures create. For portraits I really like the near 3D effect those generate. So, I guess I was talking more about the depth of field although that is one of the factors of the bokeh.

I realize that multiple factors play into this and as far as I can tell, 1) size of the sensor (FF Vs Crop), 2) the aperture size (obviously) and 3) the focal length of the lens and 4) the one that I didn't factor in, which is the lens design (number of elements/shape of elements etc).

My question was about the 3). I have a 50mm f/1.4 that I use on 5D3 and I was thinking about getting a 85mm f/1.8. Thats when I was wondering whether the real focal length and the FOV create a difference in the Out Of Focus effect on the picture.

I guess what I really asking is, if there were to be a 80mm f/1.4 EF-S, if I put the 50mm on the 7D first and then the 80mm on the 7D, will the out of focus effect be similar between the two lenses or will the 80mm EF-S have a better Out of focus effect since it is a 80mm real focal length as opposed to the 50mm lens which is more of a 80mm FOV in the 7D.

I'm starting to realize that it may be more of a theoretical question since in reality we can't ignore the FF & Crop effect and the design of the lens. And I prefer to use the 5D3 for portraits anyways.



Apr 04, 2013 at 02:46 AM
dsjtecserv
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p.1 #14 · Does FOV affect Bokeh?


Well, first let me clarify a couple of things: First, "bokeh" is not synonymous with "background blur"; bokeh is a subjective impression of how "nice" the blur looks. So while it is true that you must have blur before you can evaluate whether that blur is attractive, and in order to have blur you must have limited depth of field, depth of field itself isn't a factor in whether the blur is attractive or not. On the other hand, design of the lens does directly affect how attractive the blur is.

Second, I'm not sure whether or not you are assuming that the "real focal length" is something different on EF-S lenses. For all lenses that you would attach to a DSLR, the focal length is just that, whether the lens was designed for an EF-S or EF mount. In your fourth paragraph, it seems that you are assuming that the 50 mm focal length of the lens EF is less real than the 80 mm focal length of the EF-S lens just because it has been mounted on a 7D. In fact they both quite real, and they will each give a field of view proportional to the their stated focal length when mounted on a 7D. They will not give the same field of view, even if the 80 mm lens is an EF-S.

At any rate, the simple answer is that the depth of field is a function of focal length, subject distance, and f-number, and well as the degree of enlargement needed to produce a standard-sized print viewed at an assumed distance. The relationships among those factors, and how they work out to a bottom line, is fixed and predictable, and doesn't depend on differences between lenses. So if the focal length of two lenses is different, and all of the other factors are held unchanged, the depth of field will be different, by a predictable amount. This is not affected by the design of the individual lens, assuming that its marked focal length and f-numbers are reasonably accurate.

Now, you appear to be asking more about what is out of focus rather than what is in focus. Several people above gave answers regarding how focal length affects how blurry an out-of-focus background appears, and how quickly the transition from sharp to blurry occurs, so I won't repeat them. But I do want to reinforce that to the extent that this depends on focal length, it is the actual focal length of the lens, which doesn't depend on whether it is an EF-S or EF (or DX vs. FX) lens. It also doesn't matter whether is is a crop or full frame camera, assuming you are comparing results on the same camera. so the whole crop/full frame EF-S/EF distinction is, I think, irrelevant to your question.

I hope that helps provide a little more context so that the excellent answers you got from others make more sense.

Dave



Apr 04, 2013 at 06:00 PM
sathya_sn
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p.1 #15 · Does FOV affect Bokeh?


Dave, really appreciate your detailed answer... I get the part about the smoothness of the bokeh being different from the DOF.

But I'm not sure if I understand with part about the differences in EF-S/EF lens. My understanding is, if there was a EF-S 80mm mounted on 7d and a EF 128mm mounted on 5D3, they both would have the same FOV. Or in other words, if I were to put a EF 80mm on 5D3 and a EF 50mm on Crop (7D), they both would have the same FOV.

This is based on things I've read where a EF-S (Canon) or DX (Nikon) 18-200 will produce the same FOV as a 27-300 (in the Nikon world where the Crop is 1.5). Is my understanding of the EF-S/EF incorrect?



Apr 04, 2013 at 09:56 PM
dsjtecserv
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p.1 #16 · Does FOV affect Bokeh?


No, you've misunderstood the significance of EF-S lenses. The are the same as any DSLR lens in that their focal length is stated as what it actually is; there is no adjustment factor applied. Because they are only intended for use with Canon "crop sensor" cameras, EF-S lenses are designed to take advantage of the fact that they don't need to project the image back to as large a sensor as a full frame sensor. This allows the designer to do some things to make the lens smaller and/or lighter than would otherwise be necessary. But in all other respects -- including the focal length -- they work the same as any other lens.

Any lens of a given focal length, when mounted on (for instance) a 7D would give a field of view that is equivalent to a lens of about 1.6 times that focal length mounted on a full frame camera. That is a function of the relative size of the sensor, and has nothing to do with the lens. The multiplier is the same regardless of the lens: a lens of 80 mm (whether EF or EF-S) would give a field of view equivalent to a 128 mm lens mounted on a full frame. A lens of 128 mm, mounted on a 7D, would give a field of view equivalent to a 205 mm lens mounted on a full frame.

The same thing would be true of Nikon's FX and DX lenses, except, as you note, that the multiplier would be 1.5. The key thing is that the field of view comparison is done based on the relative sensor sizes (only), not on the lens type; the stated focal length is always the actual focal length, and the difference in sensor sizes works the same way regardless of lens type.

Hope clear it up for you.

Dave



Apr 05, 2013 at 01:15 AM
sathya_sn
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p.1 #17 · Does FOV affect Bokeh?


Dave, I guess, I'll fully wrap my head around this one of these days Thanks for the help. Browsed through your collection in pbase. Some excellent shots you have there.


Apr 06, 2013 at 03:07 PM
dsjtecserv
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p.1 #18 · Does FOV affect Bokeh?


I think you basically had it already, but I think you were thinking that the APS-C designation meant more than it does. And consequently you were giving more significance to that in your thinking about bokeh, depth of field, and degree of blur. I hope the response as a whole were a useful response to your questions.

Oh, and thanks for your comment on my pictures.

Dave



Apr 08, 2013 at 01:15 PM
uscmatt99
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p.1 #19 · Does FOV affect Bokeh?


I think we need to be careful not to oversimplify what depth of field means. You can in fact take two lenses with the same focal length, at the same aperture, mounted on the same camera and have significantly different depths of field. The on-line calculators are a simplified model based on assumptions. In the Zeiss thread on the Alt forum, I've seen many examples of this. Specifically compared pairs include the Zeiss 50/1.4 Planar and 50/2.0 Makro-Planar, as well as the Zeiss ZF.2 35/1.4 and Leica R 35/1.4. The 50mm comparison is the most dramatic. At the same aperture, the Makro-Planar has much more depth of field than the Planar. The ZF 21/2.8 also has more depth of field than expected based on DOF calculators.


Apr 08, 2013 at 01:49 PM
dsjtecserv
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p.1 #20 · Does FOV affect Bokeh?


Why? What exceptions to the physics embodied in the calculators do these lenses accomplish? And if different assumptions are made, why would they not apply equally to all lenses?

Dave



Apr 08, 2013 at 04:40 PM
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