Tuesday, January 15, 2019

Sensor Size doesn't effect the Depth of Field

Ok, VUEmbers .... here is the thing. I am big advocate of doing things with own hands and to verify stuff before I start believing on things over the internet. I often heard and read from the internet that larger the sensor, shallower the depth of field. So i thoughts lets test this and see what exactly happening in the world of photography by having 3 different digital formats. Here is the breakdown with real-world examples of the following 3 digital Format,

From Left to Right,

Full Frame: Nikon D700 + 24mm f/1.4G
APS-C: Fujifilm X-T20 + 16mm f/1.4
Micro 4/3: Panasonic GH5s + 12mm f/1.4

All these 3 digital formats cameras are covered by their respect focal length lenses which covers the same angle of view (84 degrees) which are 24mm (for full frame), 16mm (for APS-C) & 12mm (for Micro 4/3). All these 3 lenses are having a maximum aperture of f/1.4 in common, which means they pass the same amount of light regardless of being the different focal lengths in reality. Therefore, the exposure on all 3 formats is the same except that Nikon highlights are little more than usual (my mistake). Settings on all 3 formats cameras were as follows,

ISO:200 | f/1.4 | 1/100

Now this quick test I did is not for the quality of the Bokeh or how lenses/sensors are rendering the image. It's more about why the depth of field (Area in focus) is different in all 3 images regardless of being three f/1.4 lenses in common.

Now some of you already know the answer in detail and most of you will say well it's because of the bigger sensor size. Well in reality (and as the caption of this blog says) sensor size has nothing to do (directly) with the depth of field. As three different formats capturing 3 different "area or angle of view" in the real world, therefore, in order to obtain the "EQUAL" angle of view we have to design the lenses with different focal length which ultimately leads us to the famous term of "crop factor". Now let me clear at this point right away that this crop factor has no connection what so ever with the depth of field. It is just a reference to understand and bringing down different digital formats at one level. It's just like if someone ask you how many centimeters in 1 inch and you quickly say it's 2.54 centimeters or 25.4 millimeters and all will give you equal length in physical world.

1 inch = 2.54 centimeters = 25.4 millimeters

Same goes for the angle of view. All below 3 focal lengths will be giving me the same angle of view.

24mm (FF) = 16mm (APS-C) = 12mm (Micro 4/3)

Are you guys with me so far? I hope so. Now the big question is why depth of field is changes by changing the format regardless of having f/1.4 lens. The answer is FOCAL LENGTH. As we know that depth of field is changes by the following 3 parameters.

- Aperture (All were f/1.4 in this case)
- Distance of shooting (were the same in all 3 cases)
- Focal length (longer focal length produces more shallower Depth of Field)

So, as you can see, when you change the format and try to achieve the same angle of view by keeping aperture constant, the only parameter which is makes the bigger impact practically speaking is the focal length. This is why when you move to medium or large format cameras and try to achieve the same angle of view with constant aperture, you will end up using longer focal length lenses on the medium/large format cameras causing massive shallow depth of field which make these format stands out. You can check sample image of the medium format using this link where image was taken by Fujifilm GFX 50R with 45mm f/28 lens (equivalent to 35mm f/2 for full frame, or 23mm f/1.4 on APS-C).

Now let me share with you the 3 examples next which I took using the same aperture, shutter speed and ISO value also from the same distance.

 Full Frame


Micro 4/3

I hope you will find information useful and it will help you in making great images. If you still kind a confuse and not able to get what i explained, then i suggest to check out this video from fstopper.coom people who explained it well then me i guess. Please do visit our Facebook group VUE for more technical stuff related to Photography.

Happy Clicking Guys.

Babar Swaleheen

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