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Author Topic: 4/3 vs APS-C sensor size  (Read 16232 times)
FrankG
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« on: June 15, 2012, 08:31:12 AM »
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4/3 vs APS-C sensor size

We all know and accept that the two most determining factors to image quality are the sensor size (not necessarily the most # of pixels) and the lenses.
I am buying a small compact for when I don't want to take my 5DmkII out for 'street shooting' and want to have maximum image quality so that I dont feel compromised or that I cant make a large print (e.g. 16x20")
I am considering the Nex 7 or the Olympus OM-D.
Both are exccellent but on all counts except sensor size (and that the accessory grip is necessary for my big hands on the Olympus) the Olympus wins out for me - weather sealed, IS in the body, range of lenses, quieter shutter ...
the Nex 7 sensor size is 23.5 x 15.6mm
and the Olympus is 17.3x13mm
All along I've been thinking it has to be the Nex 7 for the larger sensor size, and it just occurred to me that aside from the proportional/ratio difference - one being 3:2 (1:1.5) and the other 4:3 (1:1.3) - they're not all that different (2.6mm in height) -the Olympus 4/3 sensor is really almost the same as using the larger Sony APS-C sensor but cropping the long dimension into the 4:3 format.
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Greg D
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« Reply #1 on: June 15, 2012, 01:13:31 PM »
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4/3 vs APS-C sensor size

We all know and accept that the two most determining factors to image quality are the sensor size (not necessarily the most # of pixels) and the lenses.
I am buying a small compact for when I don't want to take my 5DmkII out for 'street shooting' and want to have maximum image quality so that I dont feel compromised or that I cant make a large print (e.g. 16x20")
I am considering the Nex 7 or the Olympus OM-D.
Both are exccellent but on all counts except sensor size (and that the accessory grip is necessary for my big hands on the Olympus) the Olympus wins out for me - weather sealed, IS in the body, range of lenses, quieter shutter ...
the Nex 7 sensor size is 23.5 x 15.6mm
and the Olympus is 17.3x13mm
All along I've been thinking it has to be the Nex 7 for the larger sensor size, and it just occurred to me that aside from the proportional/ratio difference - one being 3:2 (1:1.5) and the other 4:3 (1:1.3) - they're not all that different (2.6mm in height) -the Olympus 4/3 sensor is really almost the same as using the larger Sony APS-C sensor but cropping the long dimension into the 4:3 format.

Not so sure......  In linear dimensions they seem pretty close.  But if my math is right, in terms of area the APS-C is about a 60% increase over 4/3.  That's quite a bit more and/or bigger pixels......
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FrankG
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« Reply #2 on: June 15, 2012, 02:43:08 PM »
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I think it's only fair to crop the APS (3:2 dimension) to be the same as the 4/3 (4:3 dimension) or 1:1.5 down to 1:1.3 and then compare
That way the long dimension is the same and there is only a 2.6mm short dimension difference....
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Slobodan Blagojevic
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« Reply #3 on: June 15, 2012, 03:10:08 PM »
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I think it's only fair..

Why would that only be fair!? Why wouldn't be fair to crop 1.3 ratio to 1.5 and then compare?
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Slobodan

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AFairley
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« Reply #4 on: June 15, 2012, 03:25:26 PM »
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Really, it all depends on what aspect ratio you generally crop your final images to.  If you do tend to print at "classic" paper ratios, the difference is a lot smaller than if you are used to 2:3 sensors and printing the full frame.
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Guillermo Luijk
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« Reply #5 on: June 15, 2012, 06:47:37 PM »
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Sensor size is useful for two things:
  • Signal to noise ratio: noise, dynamic range, or whatever we call it is improved the larger the sensor
  • DOF: shallower DOF can be achieved the larger the sensor

Between the NEX7 and the OM-D noise differences seem to be very reduced. Shallow DOF is around 1 stop better in the APS sized NEX7, not a great advantage. If really shallow DOF is required FF or larger formats are a better choice.

Michael's review of the OM-D (and he is a NEX7 fan):
"Simply put, the Olympus O-MD E-M5 is a winner, and has now become my preferred camera for travel and urban walk-around shooting"

Regards
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scooby70
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« Reply #6 on: June 15, 2012, 06:59:35 PM »
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Just to be clear...

We do know that sensor size as such does not affect DoF don't we? We do know that with smaller sensors you tend to use wider lenses and that's why you get more DoF?

I personally would have thought that the most determining factor for image quality wasn't the sensor size as such but rather a more complex mix of things including the sensor design. For example, it's possible to have a MFT sensor that has bigger pixels than an APS-C sensor and that could affect signal to noise and DR as could having on chip widgets, or not, and such like...
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Guillermo Luijk
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« Reply #7 on: June 15, 2012, 07:13:56 PM »
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We do know that sensor size as such does not affect DoF don't we?

No we don't. If we keep all variables (focal length, aperture and subject distance) constant, the larger the sensor the larger the DOF, but the framing changes too since the FOV is wider. If we adapt focal length and/or subject distance to match the framing (in case we modify subject distance, perspective also changes), the larger the sensor the shallower the DOF.
« Last Edit: June 15, 2012, 07:17:06 PM by Guillermo Luijk » Logged

scooby70
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« Reply #8 on: June 15, 2012, 08:12:29 PM »
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So using two different cameras with different sized sensors with the same lens, aperture and subject distance changes the DoF?

OK.
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sunnycal
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« Reply #9 on: June 16, 2012, 12:58:16 AM »
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I think it's only fair to crop the APS (3:2 dimension) to be the same as the 4/3 (4:3 dimension) or 1:1.5 down to 1:1.3 and then compare
That way the long dimension is the same and there is only a 2.6mm short dimension difference....

While by no means a universally true, you do have a point there. The 3:2 size lends itself to more cropping as it is many times either too wide or too tall. With 4/3rd there is usually less need of that.

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torger
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« Reply #10 on: June 16, 2012, 02:46:22 AM »
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So using two different cameras with different sized sensors with the same lens, aperture and subject distance changes the DoF?

DOF and sensor size is a favourite subject to be categoric and state opposite things. It depends on how you see things and which variables you adjust etc.

For landscape photography where you want maximum DOF a smaller sensor size won't help you since you need to open up the aperture to avoid diffraction to keep the resolution. But since smaller sensors typically have lower resolution one can accept more blurring and thus it appears one have more DOF.

If you want as short DOF as possible you'd want the format that can have the largest aperture in relation to the sensor size, which is full-frame where you can get say f/1.2, which is considerably shorter DOF than f/1.0 on 4/3 sensors. One can multiply with the crop factor to compare, 4/3 has 2x crop factor so f/1.0 on that corresponds to 1.0 x 2 = f/2.0 on full-frame.

Video/film cameras tend to have small sensors, the idea is to have fairly large DOF with large apertures so you get a lot of light on the sensor so you can film with the fixed shutter speeds you have. A drawback with large sensors when you need large DOF is that you need a smaller aperture so the shutter speed goes up.
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ErikKaffehr
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« Reply #11 on: June 16, 2012, 03:09:09 AM »
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Hi,

The way I see it:

There are two advantages of having larger sensor size:

1) A larger sensor collects more photons, that's good for noise and DR.

2) A larger sensor would potentially resolve fine detail better using the same quality lens

3) Shadow noise depends much on sensor technology while factors 1-2 do not.

Regarding DoF it may matter little. With a larger sensor you may need to stop down more but a larger sensor will have better ISO and also better edge contrast on small detail (MTF), so you may stop down a bit more and still achieve the same quality. The 4/3 systems seem to have some very good lenses, but that advantage goes away if you stop down excessively.

In summary, I'd say that general image quality will be better with an APS-C sensor, especially as the Sony sensors seem to best of breed. Regarding DoF you will probably something like stopping down one stop more on APS-C.

Regarding cropping, what is relevant is how you crop. I usually crop according to image content and not to paper format.

You could also consider waiting a couple of months? Some interesting things may show up at Photokina. With digital we are not really bound by old film formats. Some new interesting concept with larger or smaller sensors may show up.

Best regards
Erik


4/3 vs APS-C sensor size

We all know and accept that the two most determining factors to image quality are the sensor size (not necessarily the most # of pixels) and the lenses.
I am buying a small compact for when I don't want to take my 5DmkII out for 'street shooting' and want to have maximum image quality so that I dont feel compromised or that I cant make a large print (e.g. 16x20")
I am considering the Nex 7 or the Olympus OM-D.
Both are exccellent but on all counts except sensor size (and that the accessory grip is necessary for my big hands on the Olympus) the Olympus wins out for me - weather sealed, IS in the body, range of lenses, quieter shutter ...
the Nex 7 sensor size is 23.5 x 15.6mm
and the Olympus is 17.3x13mm
All along I've been thinking it has to be the Nex 7 for the larger sensor size, and it just occurred to me that aside from the proportional/ratio difference - one being 3:2 (1:1.5) and the other 4:3 (1:1.3) - they're not all that different (2.6mm in height) -the Olympus 4/3 sensor is really almost the same as using the larger Sony APS-C sensor but cropping the long dimension into the 4:3 format.

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Guillermo Luijk
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« Reply #12 on: June 16, 2012, 03:34:03 AM »
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So using two different cameras with different sized sensors with the same lens, aperture and subject distance changes the DoF?

Correct, this is basics in photography. Using two different cameras with different sized sensors with the same lens, aperture and subject distance changes the DOF and the FOV on a print of the same size and observed at the same distance.

You will perceive a larger area in front of and behind your subject to be in focus in the larger sensor copy, because the projected circles of confusion in that copy will be smaller. This is what DOF is about.

Regards
« Last Edit: June 16, 2012, 03:39:05 AM by Guillermo Luijk » Logged

Guillermo Luijk
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« Reply #13 on: June 16, 2012, 03:42:51 AM »
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For landscape photography where you want maximum DOF a smaller sensor size won't help you since you need to open up the aperture to avoid diffraction to keep the resolution. But since smaller sensors typically have lower resolution one can accept more blurring and thus it appears one have more DOF.

This is wrong. In a smaller sensor, at the same aperture you suffer more from diffraction, but you need to stop down less your lens yo get the same DOF. In the end both effects compensate, and no format size is specially better to achieve large DOF's. An APS-C camera at f/11 will provide the same DOF and diffraction blur as a FF camera at f/16.

Regards
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torger
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« Reply #14 on: June 16, 2012, 04:45:12 AM »
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This is wrong.

I guess you did not really read what I wrote. I explained why smaller sensors may appear to have more DOF, I do know that if you want to achieve a specific resolution and you can choose aperture at will a smaller sensor won't help you.
« Last Edit: June 16, 2012, 04:58:54 AM by torger » Logged
stevesanacore
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« Reply #15 on: June 16, 2012, 05:48:39 PM »
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From my understanding, depth of field cares not what size the image area is. Depth of field is dependent on focal length and F-stop. On a Minox or an 8x10 camera a 100mm lens at f5.6 will have the same depth of field. Unless my memory serves me wrong - I have discussed this subject many many times in my career.
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We don't know what we don't know.
Guillermo Luijk
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« Reply #16 on: June 16, 2012, 06:11:54 PM »
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I guess you did not really read what I wrote. I explained why smaller sensors may appear to have more DOF, I do know that if you want to achieve a specific resolution and you can choose aperture at will a smaller sensor won't help you.

Right, I read too quickly and thought you meant larger sensors are better to achieve large DOF's. My apologies.

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thefl
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« Reply #17 on: June 17, 2012, 04:26:32 PM »
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If we adapt focal length and/or subject distance to match the framing (in case we modify subject distance, perspective also changes), the larger the sensor the shallower the DOF.
We do recognize that your explanation actually confirms what scooby70 already said - sensor size itself does not directly affect DOF?
Your mentioned change of focal length/or subject distance for adaption towards the same angle of view is what causes the change regarding DOF, not the sensor size itself.
Sure, the sensor size is the reason for making these changes in order to get useful comparisons as it dictates which angle of view corresponds to which focal length, but it's not the primary cause for any differences regarding DOF.

Greetings
« Last Edit: June 17, 2012, 04:30:38 PM by thefl » Logged
Guillermo Luijk
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« Reply #18 on: June 20, 2012, 01:53:41 PM »
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Your mentioned change of focal length/or subject distance for adaption towards the same angle of view is what causes the change regarding DOF, not the sensor size itself.

If you keep all parameters the same and use different formats, you get different DOF: larger DOF with larger format. This means sensor size changes DOF itself.

If in addition to changing the format size you alter focal length (or subject distance) to preserve the framing (for example), you alter DOF in two ways simultaneously: larger format will tend to increase DOF, while larger focal length (or closer subject distance) will reduce DOF; and the second effect (DOF reduction) will prevail. That is why a FF camera produces shallower DOF for the same aperture and framing than an APS or 4/3 camera.

Just enter any values on Dofmaster, change format (and only format), and see if DOF changes or remains the same. If it changes, you will agree that format size changes DOF itself.

Regards
« Last Edit: June 20, 2012, 02:01:36 PM by Guillermo Luijk » Logged

Tom Frerichs
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« Reply #19 on: June 20, 2012, 06:13:52 PM »
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From my understanding, depth of field cares not what size the image area is. Depth of field is dependent on focal length and F-stop. On a Minox or an 8x10 camera a 100mm lens at f5.6 will have the same depth of field. Unless my memory serves me wrong - I have discussed this subject many many times in my career.

You left out one other factor.  The size of the acceptable circle of confusion, which is directly impacted by the final print size and viewing distance.

Tom Frerichs
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