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Messages - ecka

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271
Lenses / Re: What lens delivers the strongest background blur?
« on: July 16, 2013, 07:34:20 AM »
I'd like to share a photo shot by a pal on another forum:

He used 200mm f2 to do this shot: tell me if any shorter lens can ever achieve this effect:

hint: subject distance: 17.6m



35 1.4? pfff, not even close

Well, my vote is for 200/1.8 (first page). What I meant with 35/1.4 is that 500/4 is very impractical for what we are discussing here.

Quote
Contrary to popular belief, in order to get most background blur (isolation), you shoot head/shoulder with wide angle (35), half body with medium (50/85) and full body with telephoto (>200), not the other way around.

Wide for full body, tele for close up just gives you flat and boring snap shots.

Yes, I agree :).


272
Lenses / Re: What lens delivers the strongest background blur?
« on: July 16, 2013, 06:44:13 AM »
Just let me guess...
200/1.8? :)

200mm f/1.8 would score a value of 3.1 which means 5th place ( behind 500 f4 but better than 300 f2.8 ).

Good luck with that. The error of this comparison is in the "given magnification".
In reality, for background blur, I'd pick 35/1.4 over 500/4 any day of the week :)

P.S. You forgot 1200/5.6 ;).

273
Yes, you can put a 100mm lens on a P&S (try Pentax Q or Nikon 1) and you are still wrong. I always measure DoF in relativity to reality, not "bokeh balls". :)

Due to different standards, I still call this comparison apples to oranges.

Result: When talking about format affecting DoF, always compare same angle of view, or effective focal length, since comparing different angle of view doesn't make sense.

We are still in disagreement but that's okay.

These are small apples vs big apples of the same taste :)

When comparing different formats using the same lens at the same distance and aperture (different FoV) - DoF is the same.
When comparing different formats using different but equivalent lenses and apertures at the same distance (like APSC+50/1.8 vs FF+80/2.8, same FoV) - DoF is the same.
Cropping the image doesn't change the DoF.

When comparing different formats using the same lens and aperture at equivalent distance (same FoV) - FF DoF is thinner.
When comparing different formats using different but equivalent lenses at the same distance and aperture (like APSC+85/2 vs FF+135/2, same FoV) - FF DoF is thinner.


274
Q2. If you shoot a photo A, then crop the border out leaving a smaller photo B, magnify it back to original size, then in relativity to reality DoF A = DoF B, but in relativity to dimensions of the photograph DoF A < DoF B, because you are not getting closer, you are magnifying it as well as the DoF.

No need to cross my text just because you don't agree with me. Photo is always relative to dimensions of the output, there is no relative to 'reality' to speak of, otherwise your are just muddying the water. When you are comparing two photographs, you compare them at the same output size, otherwise the comparison is just wrong.

"Yeah, put those two photo side by side, B has 2 times larger blur circle in the background, but when you make photo B 2 times smaller, the blur will look just the same!" Well, you are essentially manipulating objectivity to make it suit your theory.

I'm just stating facts. Blur circles ≠ DoF.
DoF A is shallower in both cases, except when you are measuring it in blur circles. By your logic: P&S camera has the biggest blur circles (sometimes thei don't fit inside the image :) ), therefore it produces the thinnest DoF when compared with the same focal length lens on a DSLR. This is wrong in all theories, not just mine.

"thinnest DoF when compared with the same focal length" < This, if you can somehow manage to put a 100mm lens on a P&S, it gives you a huge telephoto equivalence, then DoF will also be a lot thinner than when the lens is mounted on a DSLR. Think about it...

Yes, you can put a 100mm lens on a P&S (try Pentax Q or Nikon 1) and you are still wrong. I always measure DoF in relativity to reality, not "bokeh balls". :)

275
Q2. If you shoot a photo A, then crop the border out leaving a smaller photo B, magnify it back to original size, then in relativity to reality DoF A = DoF B, but in relativity to dimensions of the photograph DoF A < DoF B, because you are not getting closer, you are magnifying it as well as the DoF.

No need to cross my text just because you don't agree with me. Photo is always relative to dimensions of the output, there is no relative to 'reality' to speak of, otherwise your are just muddying the water. When you are comparing two photographs, you compare them at the same output size, otherwise the comparison is just wrong.

"Yeah, put those two photo side by side, B has 2 times larger blur circle in the background, but when you make photo B 2 times smaller, the blur will look just the same!" Well, you are essentially manipulating objectivity to make it suit your theory.

I'm just stating facts. Blur circles ≠ DoF.
DoF A is shallower in both cases, except when you are measuring it in blur circles. By your logic: P&S camera has the biggest blur circles (sometimes they don't fit inside the image :) ), therefore it produces the thinnest DoF when compared with the same focal length lens on a DSLR. This is wrong in all theories, not just mine.

276
Don't get me wrong, there are many brilliant photographers, but in most cases I'm inspired by some of their works and not by their philosophies or personalities. Sometimes even a bad photographer gets lucky and shoots an insanely, unbelievably, stunnishing photo (?perfect). So, for me, this question cannot be answered.
I'm mostly influenced by the online photographic communities and I'm happy being a part of it.

277
How do you define 'DOF'?

Q1. If you shoot photo A using FF+50, then photo B using APS+35, at same F number DoF of photo B > photo A

Q2. If you shoot a photo A, then crop the border out leaving a smaller photo B, magnify it back to original size, DoF of photo B < A, but since the framing has changed, it's not the same photo anymore.

And that's it. DoF on two different format has two trends fighting against each other. One tends to decrease DoF (entrance pupil size), another tends to increase it (magnification or CoC). So here's the answer:

Answer 1. When comparing using the same Angle of View (effective focal length), larger sensor always has less DoF.

Answer 2. When comparing using different Angle of View, like comparing two different photos, it DOESN'T MAKE SENSE.

It seems most of the arguments and 'confusions' are around point 2, which is not a valid argument at all. Different Angle of View can never give you the same photo, you are comparing apple to orange.

Q2. If you shoot a photo A, then crop the border out leaving a smaller photo B, magnify it back to original size, then in relativity to reality DoF A = DoF B, but in relativity to dimensions of the photograph DoF A < DoF B, because you are not getting closer, you are magnifying it as well as the DoF.

278
Lenses / Re: What lens delivers the strongest background blur?
« on: July 16, 2013, 04:16:08 AM »
Just let me guess...
200/1.8? :)

279
This has been confusing for me for a long time thank you everyone for clarifying it.

Here's my new understanding.
• Physically the DOF does not change because your not changing the lens (ie. set up a shot,  switch a crop to a FF, and you'll just get a wider field of view but same DOF).
• But in practice it essentially does change (ie set up a shot, switch bodies, now move the came to have the same field of view, now the DOF of the crop camera photo will be larger. Same goes for not moving the camera and changing focal length).

Bingo! :)

280
This is a confusing topic because the term "1.6 x crop" is a bit confusing to some. You hear that when you mount a 100mm lens on an APS-C camera it behaves like a 160MM lens on a FF camera. Really, what it means is that the field of view is the same as if you had a 160m lens on a crop FF camera, but it does not mean you have a 160mm lens.

The lens remains a 100mm lens. It's optical qualities do not change, it's depth of field does not change, it's aperture does not change. When you mount that lens on an APS-C camera you are using a sensor that will only sample the center 40% of the image ( 1/(1.6^2)).

If you were to use a FF sensor with 46Mpixels that was built with the same technology as an 18Mpixel APS-C sensor, the center part of the FF image capture would be ABSOLUTELY identical to that of the APS-C image.

So, sensor size has no effect on DOF or aperture.

Good explanation, with wrong conclusion. Using similar logic we can say that lens-sensor combo has no effect on DoF as well, only subject (scene) size and distance matters. DoF is not a constant describing the lens or the sensor, but it is described by the combination + distance.

281
Let's try to help

DoF ~ focal length * aperture * subject distance

in this "equation",

Focal lenght =
- on FF, just the number you see on the lens/EXIF
- on ASP-C/H, number of the EXIF * 1,6/1,3

thus just changing the sensor changes the focal lenght and by repercussion the DoF.

I can't find a simpler way to put it.

Wrong. The only thing that changes is the field of view. Focal length stays the same.

282
DoF ~ focal length * aperture * subject distance
If you want to shoot the same picture using the same lens with both FF and crop sensor cameras, you need to be closer to the subject with FF camera to get the same framing and that's the only difference.


That is only part of the story, and there are many ways to tell it........


Well, for me it is a very simple thing and I gave a simple answer to the question "Why?". You don't need to write a book to answer a simple question, because that's how people get confused.

283
Lenses / Re: Indoor Lens recommendations?
« on: July 15, 2013, 02:59:54 AM »
You will like the 40mm....I would add that with the STM focus motor, it will serve you well for indoor video too...

How will the STM focus motor help with video, given that the OP has a 60D?

by magic?....my mistake, i thought he wrote 6d

Not even by magic lantern.  ;)

The 6D doesn't AF during video, either. Just the T4i/650D, T5i/700D, and the EOS M. The 70D will have it, too.

Well, 6D has no AF tracking mode for video, but it does AF just fine, using the same slow hunting LiveView CDAF. From what I've seen, only 70D actually does AF tracking during video. T4i/650D, T5i/700D, and the EOS M are just trying to :).

284
DoF ~ focal length * aperture * subject distance
If you want to shoot the same picture using the same lens with both FF and crop sensor cameras, you need to be closer to the subject with FF camera to get the same framing and that's the only difference.

285
EOS Bodies - For Stills / Re: 70d + 70-200 II vs. 5d III
« on: July 13, 2013, 05:28:11 PM »
I think that for a serious job 5D3 + 70-200/2.8L'IS'II'USM is a must, but I would prefer 5D3 + 135L.
5D3 + 24-70VC + 135L should do.

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