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FORUMS Canon Cameras, Lenses & Accessories Canon EF and EF-S Lenses 
Thread started 20 Jan 2013 (Sunday) 06:58
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Amount of background blur 135mm f2L vs. 70-200mm f2.8l IS II

 
Wilt
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Feb 20, 2013 17:15 |  #31

At the distance that I recall at which I was focused, it would have captured an area of about 1 x 1.5'. Irregardless, while the values plotted and the profile of the curves change with the framed area used by the program, nevertheless the shorter FL lens is plotted with the greater amount of blur in the near background (2') and intermediate background (20'), but which show more blurred at the longer FL (larger aperture diameter) in the photos.

IMAGE: http://i69.photobucket.com/albums/i63/wiltonw/smallerframe_zps5edb115c.jpg
IMAGE: http://i69.photobucket.com/albums/i63/wiltonw/largerframe_zps0a18c83b.jpg

So why is that?!

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johann3s
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Feb 21, 2013 01:30 |  #32

It is because you are moving the wrong way. I said for smaller subject sizes the advantage for the longer lens becomes more clear. And what do you do? You show me a plot for a field of view of 10 meter. You clearly did not understand it. By the way the assesment of which test shot has more blur for the closest subject (the small pole) is highly subjective to me anyway. You could argue for both as the difference is too small to draw a clear conclusion.

@JeffreyG: As for why I let users not simply enter a value for subject distance, is because to me this is not as intuitive. What I want to do is link this calculator to actual photography, and then it is easier to think of what you want to capture in your photo, then how far you actually need to be in order to achieve this with a given focal length.




  
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agedbriar
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Feb 21, 2013 07:56 |  #33

I find this quite useful:

http://toothwalker.org​/optics/vwdof.html (external link)




  
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Wilt
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Feb 21, 2013 10:33 |  #34

johann3s wrote in post #15634736 (external link)
It is because you are moving the wrong way. I said for smaller subject sizes the advantage for the longer lens becomes more clear. And what do you do? You show me a plot for a field of view of 10 meter. You clearly did not understand it. By the way the assesment of which test shot has more blur for the closest subject (the small pole) is highly subjective to me anyway. You could argue for both as the difference is too small to draw a clear conclusion.

@JeffreyG: As for why I let users not simply enter a value for subject distance, is because to me this is not as intuitive. What I want to do is link this calculator to actual photography, and then it is easier to think of what you want to capture in your photo, then how far you actually need to be in order to achieve this with a given focal length.

You're getting very defensive and accusatory in your tones, guy! Calm!!!! I am trying to UNDERSTAND, not persecute you!

You clearly missed the point of the two plots which I displayed. As I was unable to necessarily reproduce the information about exactly what shooting distance and frame area was used in the test shot, I chose TWO EXTREMES, 1) head and shoulders framing, and 2) a very large area framed. Therefore the curves show the expected blur at 1m behind the subject and at 10m behind the subject, which BOTH of my targets (the PVC fitting, and the apple) fall within. So it should be possible to see in one graph or the other graph that one of them echoes the test shots taken months ago, as the conditions of the shoot were somewhere IN BETWEEN the two framing extremes which were graphed, shouldn't they??


As for me not understanding....I wrote to you suggesting that you explain HOW to INTERPRET your graphs, for those who do not understand the topic. If I, who have read considerable amounts about the topic of background blur, cannot read your graphs correctly, you can't expect a lesser understanding person to correctly interpret your graphs either, should you? Q.E.D. :cool:


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johann3s
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Feb 21, 2013 11:36 |  #35

Sorry about my tone before. This is probably the last thing I will post in this discussion, since it seems we are just talking on a different wavelength.

It is not clear to me what you are trying to achieve. I think you can understand and interpret the graphs perfectly. Furthermore I think the explanation given on the website as it is now is clear enough to be able to understand the graphs. The only thing which is bothering you is that your test shots indicate something else, but to me these shots are not clear enough. The differences are to small, and therefore open to discussion, to draw conclusions which can actually validate the tool. And that is what you are trying to do. Especially since even the sizes and distances you give are no more then a rough estimate.

Secondly, I understood perfectly the point of your two plots. The thing I commented on is, especially given the subject size you stated of your sample shots, that you had chosen the wrong extremes, since even your own test shot did not fall within these boundaries. Think about it.

So, feel free to use or not use the tool. Just as you like. As for myself I trust the math (which I did not develop myself, but is confirmed by multiple sources on the web). And it is also clearly stated on my website, that this is just the theoretical part, and there might be differences between lenses.




  
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Wilt
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Feb 21, 2013 11:49 |  #36

I am simply wanting to find the most reliable graphing device, so as to actively use it in future discussions in helping others!

  • I have one DOF calculator which is the gold standard, and ignore results of most other DOF calculators...except for macro
  • so I have another calculator for macro work.
  • now I see (in this thread) four background blur graphing programs, the curves seem to deviate in shape from one another -- post 4 and post 18 are very different from the S-curve shape of the other two... so which is the best of the four, are any accurate and in what circumstances?!


That is why I am trying to dig into this with you...to your credit YOU have replied, but no one else has replied about theirs!

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johann3s
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Feb 21, 2013 12:05 |  #37

Yes, but don't miss that the plots in post 30 and in my calculator use a logaritmic scale, this can be seen if you look at the x-axis. This is, at least in my case, done because otherwise it would be difficult to have a clear view both at the near and far distance. This causes the S-curve. :)




  
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Wilt
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Feb 21, 2013 12:21 |  #38

johann3s wrote in post #15636197 (external link)
Yes, but don't miss that the plots in post 30 and in my calculator use a logaritmic scale, this can be seen if you look at the x-axis. This is, at least in my case, done because otherwise it would be difficult to have a clear view both at the near and far distance. This causes the S-curve. :)

Thank you for pointing that out...taking values for one of the lenses plotted in post 18 and putting them on your logarthmic plot, I confirm that this does change that curve to one resembling the curves for the two lenses which you plotted. Graphs of both post 4 and post 18 used a linear scale. My degree of skepticism has been greatly reduced by this single bit of clarity!


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BTNorris
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Feb 21, 2013 18:30 as a reply to  @ Wilt's post |  #39

Any chance one of you nice people with both lenses could post a couple of real-life comparisons? Thanks!


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Xcelx
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Mar 02, 2013 06:53 |  #40

Wilt wrote in post #15629367 (external link)
Now we have a 'Battle of the Blur' calculators, as there is no universal agreement, but great disagreement!

We have a veritable conflict of findings! Post 4 seems to align with my actual testing, while post 18 and 19 and 22 would indicate otherwise. (Using the post 22 program, the graph of 116mm f/4 vs. 193mm f/6.3 would have the 116mm winning the blur battle, with curves similar to the 135 f/2 vs. 200 f/2.8)

One thing came to my mind is focus breathing, what if your lens focal length isn't what is stated in the exif? The aperture you calculated might not be correct when the focus isn't at infinity.




  
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Wilt
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Mar 02, 2013 11:22 |  #41

Xcelx wrote in post #15667770 (external link)
One thing came to my mind is focus breathing, what if your lens focal length isn't what is stated in the exif? The aperture you calculated might not be correct when the focus isn't at infinity.

A very valid possibility!
If the 135 f/2 were 5% longer, and the 200 f/2.8 were 5% shorter than rated, they could indeed swap positions in actual aperture size so that the lens with greater blur is the shorter FL


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Amount of background blur 135mm f2L vs. 70-200mm f2.8l IS II
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