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Messages - PavelR

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46
Lenses / Re: Focal Distance: furthest possible maintaining blurred BG
« on: November 25, 2012, 06:11:22 PM »
If you crop just the tower from both images, and view them at the same size on the screen, they will look identical.  That means the blur is identical. 

Examples from http://toothwalker.org/optics/dof.html.

100mm f/4:


28mm f/4:


The car to the right of the subject has more blur with the 100mm lens than with the 28mm lens, right? 

 

Wrong. Same blur. That's the case even in your extreme example.

I'm not saying it looks the same, the tower and car do look more blurred with the longer focal lengths. Like I said, it's good illusion.
Thx for the link - there is deep explanation we all agree with (I suppose).
And our different view on the last posts is nicely summed up by paragraph:
---
This is true when we speak of the absolute blur. The absolute blur is given by the blur disk diameter of a point in the background, such as the highlight reflections off the cars in the street. However, when we speak of the relative blur we must relate the blur disk size to the "image magnification" of the background. And that magnification is larger with the 100-mm lens too. As a matter of fact, the relative blur of the backgrounds is identical.
---

47
Lenses / Re: Focal Distance: furthest possible maintaining blurred BG
« on: November 25, 2012, 05:30:32 PM »
Exactly.  Your eyes are being fooled. The blur is the same. That it doesn't look that way is an illusion. But...it's a good illusion.
I think that we need to define "background blur" now, because it does not look like the same COC at 200mm and 400mm.
And what about my extreme examples in the previous post? Do you still call it: "my eyes are fooled"?

Background blur is already well defined, you are not using it in its common context. As I said, the towers are both blurred exactly the same, below is an image where I have made the tower the same size from the 200 and 400 shots, they are exactly the same.

 You are not referring to how blurred an object is, you are referring to how big objects at different distances are in relation to each other. That is perspective, not depth of field. For a same sized subject and aperture a longer lens shot from further away will give you a bigger apparent background object, hence the illusion of it being more blurred.
You did the operation which affects DOF - you changed magnification - look at: http://en.wikipedia.org/wiki/Depth_of_field

48
Lenses / Re: Focal Distance: furthest possible maintaining blurred BG
« on: November 25, 2012, 05:06:07 PM »
No, look again, the actual blur of the tower is the same, BUT the tower is much bigger with the 400, you are looking at the effects of perspective in those shots NOT depth of field.
Yes - the tower is bigger and blurred part is bigger too - thus better blur in my eyes.
In the extreme smallness, the tower will be one pixel width -> perfectly "in focus" = the worst background blur possible, for me...
Opposite extreme: the tower fills whole background = one gray color around the subject = the most blurred background (little boring thus I do not call this "the best" though still good example of the biggest isolation).

You're confusing what is in the background vs. how much that background is out of focus.
It is not confusion of those characteristics, but sum of all that make final subject isolation, which OP was asking about. There is only one place (distance from camera) which is in the perfect focus, all other things at other distances are blurred, but if you use longer focused distance or bigger F number or smaller FL the blur is smaller ~ even invisible on the final picture...
Another example: shooting straight en face with 50/2.8 both eyes are sharp pretty the same, but shot with 300/2.8 = it is easy to say which eye was focused on.

49
Lenses / Re: Focal Distance: furthest possible maintaining blurred BG
« on: November 25, 2012, 04:22:14 PM »
Exactly.  Your eyes are being fooled. The blur is the same. That it doesn't look that way is an illusion. But...it's a good illusion.
I think that we need to define "background blur" now, because it does not look like the same COC at 200mm and 400mm.
And what about my extreme examples in the previous post? Do you still call it: "my eyes are fooled"?

50
Lenses / Re: Focal Distance: furthest possible maintaining blurred BG
« on: November 25, 2012, 03:28:23 PM »
No, look again, the actual blur of the tower is the same, BUT the tower is much bigger with the 400, you are looking at the effects of perspective in those shots NOT depth of field.
Yes - the tower is bigger and blurred part is bigger too - thus better blur in my eyes.
In the extreme smallness, the tower will be one pixel width -> perfectly "in focus" = the worst background blur possible, for me...
Opposite extreme: the tower fills whole background = one gray color around the subject = the most blurred background (little boring thus I do not call this "the best" though still good example of the biggest isolation).

51
Lenses / Re: Focal Distance: furthest possible maintaining blurred BG
« on: November 25, 2012, 03:10:40 PM »
---CUT---
 This means, as has been said, that 600 f4 has exactly the same dof as a 17mm @ f4 if the subject is the same size in both frames. The images look quite different, but that is because of perspective, this series of images might help. http://www.luminous-landscape.com/tutorials/dof2.shtml
---CUT---
The images of FL 200mm and 400mm in the link prove my point of view - blur of tower is much bigger at 400mm.
+ I did lots of shots within the 50mm-300mm range and I know there is no way to get any comparable background blur if it is used 50/2.8 and 200/2.8 for the shots with the same framing...

52
Lenses / Re: Focal Distance: furthest possible maintaining blurred BG
« on: November 25, 2012, 02:59:13 PM »
My guess would be the EF-800mm F/5.6
My too.
I use/d 85/1.4, 135/2, 200/2, 300/2.8 and the most blurred background I've got with longer FL.
FL does affect the isolation of the subject more than open [wide] aperture.
(Using the same framing of a human body / face.)

If the two of you are guessing based on the maximum physical size of the aperture, then the winner is actually the 600 f/4. The 400 f/2.8 and the 800 f/5.6 are tied for second.

800 / 5.6 = 142.857
600 / 4 = 150
400 / 2.8 = 142.857

If you're going off focal length, then the 600 with a 1.4x teleconverter would beat the 800 without one.

At the same time, there's really not any significant difference in actual aperture size between them, just a small fraction of a stop: stop the 600 down to f/4.5 (a third of a stop, one click of the wheel) and it's now got a 133mm physical aperture.

If you were trying to decide between the three, your decision should be made primarily on focal length needs and you shouldn't give any consideration to the physical aperture. Indeed, they might all actually be the same, what with rounding and all: 600 / 142.857 = 4.2, which is closer to f/4 than f/4.5.

Cheers,

b&
Hmm, than the winner should be Sigma 200-500/2.8.
I did not take into account TC because it also blur subject :-D
(I do not have the experience of a difference between magnification by crop of a sensor [narrower DOF] and  prolonged focus distance [wider DOF]. I have only crop bodies 1.5x and 1.3x.)

53
Lenses / Re: Focal Distance: furthest possible maintaining blurred BG
« on: November 25, 2012, 02:40:18 PM »
My guess would be the EF-800mm F/5.6
FL does affect the isolation of the subject more than open [wide] aperture.

Not quite.  Contrary to popular opinion, Depth of Field is not affected by focal length only the physical size of the aperture (when maintaining subject height).  To maintain subject height in the image the subject distance must be increased as you increase focal length (in other words, you have to step back when using a longer lens).  Now, greater subject distance increases depth of field but a longer lens with the same f-number (eg. f/2.8 ) has a physically larger aperture which decreases depth of field.  It turns out the the increase of DoF due to increases subject distance is almost exactly offset by the decrease in DoF due to the physically larger aperture with the result that focal length does not affect DoF.
I do not know math behind the scene, but you hardly find the real aperture size of any lens with selected F stop. Thus the real aperture size is not attribute I can use to choose lens to shoot with. I know subject isolation ~ DOF of my lenses and longer FL isolate the subject more than shorter; even if I need to step back to maintain the framing & prolong focus distance.

54
Lenses / Re: Focal Distance: furthest possible maintaining blurred BG
« on: November 25, 2012, 10:03:18 AM »
My guess would be the EF-800mm F/5.6
My too.
I use/d 85/1.4, 135/2, 200/2, 300/2.8 and the most blurred background I've got with longer FL.
FL does affect the isolation of the subject more than open [wide] aperture.
(Using the same framing of a human body / face.)

55
Lenses / Re: 24-70 or 70-200??
« on: November 21, 2012, 10:40:48 AM »
I guess you're talking about the 24-70F2.8L2 and the 70-200ISF2.8L2. Both are really excellent lenses with full frame and are complementary. Since your 50L1.2 covers the middle of the 24-70 focal range, you should get the 70-200. It is the best compromise. Of course if you have the money, you should get both and still keep the 50L2 for very low light or shallow dof work.
+1

57
Portrait / Re: Shooting a soccer portrait for a friend
« on: November 14, 2012, 06:29:56 AM »
I think it would help the image if the background was less distracting.  I like the pose and what you were going for though.
+1

58
Lenses / Re: Best solution for organizing numerous lenshoods
« on: November 14, 2012, 06:27:37 AM »
I just leave them reverse mounted on each lens thy belong to, simple
+1

59
Lenses / Re: do image stabilisers decrease image quality?
« on: November 07, 2012, 06:44:06 PM »
EF 70-200mm f2.8L IS II
Image Stabilization & a very sharp lens

300/400/500/600 II superteles.  Image Stabilization & even sharper.

What, no love for the 200/2IS? The sharpest of them all.
+1

60
EOS Bodies - For Stills / Re: 1d4 or 1d3 +lens
« on: November 05, 2012, 12:27:08 PM »
My ability to shoot sports with a 50D went up greatly when I got a 70-200 IS f/2.8. Put your saved money toward a better camera in a year or two and go for great glass. A 1D4 with your current glass will get you mediocre shots but at a great frame rate.
+1
Glass, AF or good MF, the reasonable ISO + correct exposure time make the image look great, not fps...
(Or 5d3 for better low light AF. I have 1d4 and FPS do not help much in 95% of sports, you need to catch the exact moment.)
Are we in agreement that better glass with a 50D will be better that a kit lens with a 1D4?  Or not?  My sports shots did get better when I paired my 50D with a 70-200 IS f/2.8 and improved a bit more when I went to a 7D.  Saving my $ for a 1Dx.  I'd like to get the shots in between the ones I get with the 7D as the frame rate goes from 8fps to 12fps.
We are in an agreement.
(Better glass improve the technical quality of an image the most. I listed some characteristics that influence an IQ the most.)
(I have set 9fps on my 1D4, because AF needs more time to follow the subject than it is available in the highest FPS, but generally fps do not help me in group indoor/outdoor sports or any athletics disciplines - only one moment is the best and it is needed to press the shutter release just before the moment. I've also used spray and pray :-) with new camera, but now one shot at the best time is better technique for me...)

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