Advantage of Bigger Sensor?

[Lijo]

For the DoF calculator consider the following values https://www.cambridgeincolour.com/tu...calculator.htm

Aperture - f/2
Focal Length -35
Focal Distance – 6m

Now we test three different sensors for the DoF calculation
1. With 1’’ sensor, the DoF is 1.39 m
2. With 1/1.8’’ sensor, the DoF is 0.78m
3. With 1/2.3’’ sensor, the DoF is 0.67m


My understanding was, smaller the value of DoF better the quality of the pictures. [But in the above calculation, the smallest DoF is given by the 1/2.3’’ sensor. ]. If this is not the case, what is the purpose of a bigger sensor?


References:
• Sony Cyber-shot DSC-RX100 with 1’’ sensor, 3.6x Zoom and F/1.8 - 4.9
• NIKON COOLPIX P7700 with 1/1.7’’ sensor, 7.1x zoom and F/2.0-4.0
• Canon PowerShot SX160 IS with 1/2.3’’ sensor, 16x zoom and F/3.5.0-5.9

[tomdinning]

For the DoF calculator consider the following values https://www.cambridgeincolour.com/tu...calculator.htm

Aperture - f/2
Focal Length -35
Focal Distance – 6m

Now we test three different sensors for the DoF calculation
1. With 1’’ sensor, the DoF is 1.39 m
2. With 1/1.8’’ sensor, the DoF is 0.78m
3. With 1/2.3’’ sensor, the DoF is 0.67m


My understanding was, smaller the value of DoF better the quality of the pictures. [But in the above calculation, the smallest DoF is given by the 1/2.3’’ sensor. ]. If this is not the case, what is the purpose of a bigger sensor?


References:
• Sony Cyber-shot DSC-RX100 with 1’’ sensor, 3.6x Zoom and F/1.8 - 4.9
• NIKON COOLPIX P7700 with 1/1.7’’ sensor, 7.1x zoom and F/2.0-4.0
• Canon PowerShot SX160 IS with 1/2.3’’ sensor, 16x zoom and F/3.5.0-5.9

Don't you know about the 'Size Counts' rule, Ligo?
I don't know where you got the idea that DoF makes better picture. DoF is simply an element of design you can apply to your pictures to obtain particular effects and to enable you to manipulate your focus. It has nothing to do with good or bad pictures, just different ones.

[DanK]

For an explanation of sensor size and DOF, look here: http://photo.net/learn/optics/dofdigital/.

A larger sensor allows one to use larger photosites for any given number of pixels. This allows better performance--greater dynamic range, lower high-ISO noise, slightly less effect of diffraction, and arguably slightly better detail. For some purposes (e.g., low-light landscapes printed large), these will be important. For many uses, the differences in image quality will not be substantial. It also allows smaller DOF at a given lens's maximum aperture, which allows one greater separation of subject from background.

My understanding was, smaller the value of DoF better the quality of the pictures.

Nope. Sometimes the photographer wants wide DOF, other times narrow. It all depends on what you want to accomplish.

[Manfred M]

In a nutshell, every image taken by anything other than perhaps a view camera, needs to be enlarged to be viewable.

The more you enlarge an image, the more the lens defects become visible. The other issue is the raw material to be enlarged; once you get very small photodiodes, you start getting issues with diffraction as well as lens resolution, i.e. adding more sensors does not improve image quality. Another issue with very small sensors is that they are are not as efficient at collecting light and do not perform well at higher sensitivity levels (i.e. introduce sensor noice). A larger sensor helps reduce all of these issues.

A larger sensor also allows use of DoF as a creative element; but contrary to your asserting, shallow DoF is not always desireable. Landscape photography is just one instance where the photographer will often try to have everything in focus.

[William W]

For the DoF calculator consider the following values https://www.cambridgeincolour.com/tu...calculator.htm

Aperture - f/2
Focal Length -35
Focal Distance – 6m

Now we test three different sensors for the DoF calculation
1. With 1’’ sensor, the DoF is 1.39 m
2. With 1/1.8’’ sensor, the DoF is 0.78m
3. With 1/2.3’’ sensor, the DoF is 0.67m


My understanding was, smaller the value of DoF better the quality of the pictures. [But in the above calculation, the smallest DoF is given by the 1/2.3’’ sensor. ]. If this is not the case, what is the purpose of a bigger sensor?

You are asking many questions about Depth of Field (DoF): and also you are asking many questions about small sensor cameras and you seem to want to buy a small sensor camera, but, it seems that you also want to be able to make very shallow DoF.

Firstly - the comparison you made above is flawed: because if you used a 35mm lens on each of those three different sensor camera you would get a different Field of View for each.

Secondly - (as already mentioned) a shallow Depth of Field does not necessarily make a good photo.

Thirdly - IF you want to make images with a very shallow Depth of Field, then the larger the sensor size of the camera then generally the easier it will be for you to do that.

Fourthly - there are also other advantages for buying larger sensor cameras: but if you speak to many Portrait Photographers one advantage they most likely will mention, is the very shallow DoF one can attain more easily and especially whilst using the lens stopped down a bit - and that is one reason why now I use 135 Format Digital Cameras (aka "Full Frame Digital) for most of my Portrait work.


Portrait at Sunset
Canon EOS 5D and 135F/2L

WW

[Lijo]

because if you used a 35mm lens on each of those three different sensor camera you would get a different Field of View for each.

Apologies for my ignorance if the following is a foolish question:

1. For getting same Field Of View, can I use more focal length on a bigger sensor camera? Is it like I can use 45mm focal length on a 1/1.8’’ sensor to get same field of view of a 1/2.3’’ sensor with 35mm focal length?
2. What you mean by "if you used a 35mm lens"? Do you mean I changed the f/stop to get 35mm focal length?

[William W]

1. For getting same Field Of View, can I use more focal length on a bigger sensor camera? Is it like I can use 45mm focal length on a 1/1.8’’ sensor to get same field of view of a 1/2.3’’ sensor with 35mm focal length??

IF you used a 35mm lens on a 1’’ sensor camera, then the FoV would be the same:

a) AS IF you used a 20mm lens on a 1/1.8’’ sensor camera
b) AS IF you used a 17mm lens with a 1/2.3’’ sensor camera

2. What you mean by "if you used a 35mm lens"? Do you mean I changed the f/stop to get 35mm focal length?

No.

I simply meant that if you want to compare Depth of Field using the CiC calculator, then you must change the Focal Length of the Lens when you change the Format of the Camera, so that you are comparing the same Field of View: thus making the DoF comparison, meaningful.

WW

[Lijo]

you must change the Focal Length of the Lens

Thanks for the answer. Still I would like to know one more thing. Won't the focal length get changed when we change the zoom on a compact camera?

[Manfred M]

Thanks for the answer. Still I would like to know one more thing. Won't the focal length get changed when we change the zoom on a compact camera?

When you zoom in or zoom out, you are changing the focal length; so long as we are referring to what some manufacturers "optical zoom". Based on this view, changing focal length and zooming are the same thing.

Some point & shoot cameras refer to "digital zoom". This is really just cropping the image and showing the cropped area.

[William W]

Thanks for the answer. Still I would like to know one more thing. Won't the focal length get changed when we change the zoom on a compact camera?

What Manfred wrote.

Thanks Manfred.

WW

[Dave Humphries]

The only other thing to bear in mind is that many P&S and bridge cameras have the focal length marked/reported as if they are Full Frame cameras, so setting the zoom on each to "35mm" (on some of those cameras you list) might actually give the same angle of view.

However, in terms of using the DoF calculator, as Bill and Manfred say, you must do that calculation to ensure you are comparing like with like.

For example, I have two small cameras;
On my Nikon P510 bridge camera, setting the lens to "35mm" actually uses a 'real' lens focal length of 6.3mm.
On my Canon S100 P&S camera, setting the lens to "35mm" actually uses a 'real' lens focal length of 7.6mm.
The latter has a slightly bigger sensor than the former.

To compare them on DoF calculator, I'd need to dial in the 6.3 and the 7.6 figures.

Cheers,

[Lijo]

On my Nikon P510 bridge camera, setting the lens to "35mm" actually uses a 'real' lens focal length of 6.3mm.
On my Canon S100 P&S camera, setting the lens to "35mm" actually uses a 'real' lens focal length of 7.6mm.

Thanks, Dave. Since I am an absolute beginner, I have one more question :-). Which focal length do I get from EXIF Data? "35mm" or the 6.3mm? If I get only 35mm from EXIF data, how can I get the real value for entering in calculation?

[William W]

Which focal length do I get from EXIF Data? "35mm" or the 6.3mm?

I don't know about all miniature format digital cameras, but we use a few Canon PowerShot cameras and the EXIF they record is the actual Focal Length:


Matt_Levy_London Paralympics_Gold Medal_2012

*

(EXIF should be attached to the image, but if you can’t see it then here is the relevant part of it)



***

If I get only 35mm from EXIF data, how can I get the real value for entering in calculation?

IF the camera records the EXIF DATA as the “equivalent 35mm format” Focal Length, then you can divide that number by what is now termed the “Crop Factor” of the camera you used.

For example, the FORMAT of a Canon SX40HS (the camera used to make the image above) is: 1/2.3inch.
This format has a “Crop Factor” of (approximately) 5.64

Therefore, if we wanted to know the “equivalent” Focal Length in 35mm Format, we would MULTIPLY the actual FL of the SX40 Camera.

So, the EXIF states the lens was at 22.95mm – so the “equivalent” in 35mm would be about: 22.95 * 5.64 ≈ 129mm

Obviously if the camera reported the EXIF as “equivalent 35mm FL” the EXIF would read: 129mm


***

Note that a 129mm (or a 135mm lens) is a “nice” FL when used on a 35mm camera, for a Tight Bust or Head and Shoulders Portrait.

Importantly that is what matters the most, how the image looks in the viewfinder and NOT the actual numbers.

I would encourage you to learn how to see these elements of the Craft of Photography, no matter what camera you use.

I do not understand why you might be concentrating on these minute details of Focal Length and Depth of Field?

I have no issue with you wanting to know all this knowledge, actually I find it quite interesting: but I am not sure how this technical detail will assist you in choosing a camera for purchase.

Is choosing a camera for purchase your main aim?


WW