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07-15-2015, 05:59 AM - 1 Like   #1
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Depth of field?...can we close this argument once and for all

I am kind of frustrated to continuously see posts where people refer to depth of field (aperture/f stop...whatever you want to call it) as different when you refer to full frame and 67% sensors. i.e f2.8 on full frame and F4 on 67%. I was always under the impression that sensors have nothing to do with it. Sensors just project off what they see. Isn't f stop indifferent. Doesn't the lens solely account for f stop. Please pentaxians. Let's discuss this issue and close it to avoid future confusion.

07-15-2015, 06:06 AM - 1 Like   #2
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Most of the people who have been here a while get it with some exceptions. Then we get someone who posts something and it turns into a 15 page thread...

I just don't participate in those threads for the most part.
07-15-2015, 06:08 AM - 1 Like   #3
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The depth of field at the same focal length never changes, regardless of sensor format.

However, when comparing larger sensors to smaller ones, you'll indeed get less depth of field at the same angle of view with the larger sensor. Let's take a focal length of 24mm on full frame and 18mm on aps-c as an example. Both will deliver the same angle of view, but the full frame lens will have less depth of field since it's a longer focal length.

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07-15-2015, 06:14 AM   #4
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It seems to be very widely believed that a smaller sensor means "less light", and so the aperture must be adjusted for a smaller sensor the same way the focal length is.
The easiest way to say it, is that it's just flat out incorrect. It's simple mathematics. I never had much luck explaining it clearly unless it was in person rather than over the internet. However, this guy has made several videos on this exact subject, and he (though a bit long winded) explains it very well.
Video 1:

Video 2:


07-15-2015, 06:16 AM - 1 Like   #5
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QuoteOriginally posted by Adam Quote
However, when comparing larger sensors to smaller ones, you'll indeed get less depth of field at the same angle of view with the larger sensor. Let's take a focal length of 24mm on full frame and 18mm on aps-c as an example. Both will deliver the same angle of view, but the full frame lens will have less depth of field since it's a longer focal length.
= same lens mounted on the two formats delivers the same DOF.
07-15-2015, 06:16 AM   #6
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QuoteOriginally posted by alamo5000 Quote
Most of the people who have been here a while get it with some exceptions. Then we get someone who posts something and it turns into a 15 page thread...

I just don't participate in those threads for the most part.
Sorry, didn't mean to get anyone uptight, just thought it was a valid post that needed clarification for all users. I know what f stop is, but I thought this may help confusion for others
07-15-2015, 06:21 AM   #7
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https://photographylife.com/sensor-size-perspective-and-depth-of-field
07-15-2015, 06:23 AM   #8
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QuoteOriginally posted by Mattox Quote
Sorry, didn't mean to get anyone uptight, just thought it was a valid post that needed clarification for all users. I know what f stop is, but I thought this may help confusion for others

I'm not uptight about it. I just think it gets old rehashing the same stuff over and over 3 times a week.

07-15-2015, 06:27 AM   #9
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QuoteOriginally posted by Adam Quote
The depth of field at the same focal length never changes, regardless of sensor format.

However, when comparing larger sensors to smaller ones, you'll indeed get less depth of field at the same angle of view with the larger sensor. Let's take a focal length of 24mm on full frame and 18mm on aps-c as an example. Both will deliver the same angle of view, but the full frame lens will have less depth of field since it's a longer focal length.
Yes, I like this explanation.

Depth of field is affected by focal length and aperture size. The sensor / film simply faithfully record what is projected on them.
Larger sensor / film requires longer focal length to create a projection size that will cover them, therefore, you get the effect of using a longer focal length, which we perceive as shallower depth-of-field.

But when we're talking about the total package (i.e the whole camera), it's not wrong to say that we indeed get pictures with more depth of field using APS-C cameras given that we're talking about the same aperture setting.
07-15-2015, 06:30 AM   #10
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He doesn't understand the concept of a focal plain, in his diagram, he has the FX sensor Behind the DX sensor, in reality, the the image circle would be larger than both sensors, they would both be in the same location only one would be bigger than the other... He's drawing the sensors as being located back in the area of circles of confusion, where everything would be out of focus. Where the two lines cross is where the image would be in focus.
07-15-2015, 06:37 AM   #11
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QuoteOriginally posted by normhead Quote
He doesn't understand the concept of a focal plain, in his diagram, he has the FX sensor Behind the DX sensor, in reality, the the image circle would be larger than both sensors, they would both be in the same location only one would be bigger than the other... He's drawing the sensors as being located back in the area of circles of confusion, where everything would be out of focus. Where the two lines cross is where the image would be in focus.
You are correct. Someone pointed that out to him in the comments section, and he clarified that he had drawn it that way for demonstration purposes to help illustrate a specific point about the angle of interception, but that, in hindsight, he could see how it would be confusing for some or be perceived wrong.
07-15-2015, 06:40 AM   #12
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Unless I'm mis-understanding his point, it is kind of critical to his concept.

Last edited by normhead; 07-15-2015 at 08:13 AM.
07-15-2015, 06:48 AM   #13
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QuoteOriginally posted by MyInkIsMyArt Quote
However, this guy has made several videos on this exact subject, and he (though a bit long winded) explains it very well.
This guy is funny.

"jack-crap" was my favorite term.

Last edited by Bunch; 07-15-2015 at 06:54 AM.
07-15-2015, 07:00 AM - 1 Like   #14
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The problem start when people mix DOF with aperture. The aperture is defined by exposure and the numbers on you lens are chosen so that they give one stop difference in shutterspeed (doubling/halving).
A lens aperture is no more defined by DOF than shutterspeed is defined by subject motion.
07-15-2015, 07:07 AM - 3 Likes   #15
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I think it's quite simple: 50mm f2 at 3 meters (or whatever f-stop and distance) will give the same dof on ff-, aps-c-, mft- or whatever-sensors. but because you want to get a specific angle (not focal length), you will take a few steps back when using a smaller sensor - and that changes your dof (further away=more dof).
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