Larger sensor just a luxury?

[EchoingWhisper]

From Cambridge in colour -
One might initially think that throwing away image information is never ideal, however it does have its advantages. Nearly all lenses are sharpest at their centers, while quality degrades progressively toward to the edges. This means that a cropped sensor effectively discards the lowest quality portions of the image, which is quite useful when using low quality lenses (as these typically have the worst edge quality).

On the other hand, this also means that one is carrying a much larger lens than is necessary — a factor particularly relevant to those carrying their camera for extended periods of time (see section below). Ideally, one would use nearly all image light transmitted from the lens, and this lens would be of high enough quality that its change in sharpness would be negligible towards its edges.

So, a FX lens is actually larger than DX lens. "Ideally, one would use nearly all image light transmitted from the lens." So if a DX lens is made the same size as a FX lens, the same amount of light in FX lens is transmitted to the DX lens, then the noise performance and depth of field would be the same.

 

[bentcountershaft]

If you have a 7D (crop) and a 5D (full) and use the same 200mm EF lens on both using the same aperture value and the same distance to subject then the 5D will have a slightly shallower DOF.

 

[Dao]

I realised I'm slightly wrong. The reason larger sensors' lenses are larger is because their focal length is longer compared to smaller sensors at an equivalent focal length. But it is still similar - they are larger - so if we make DX's lenses larger too then it will have the same low light performance.

Focal length is the optical property of the lens. So even if someone managed to mount that on the iPhone, the focal length is the same. Just like a race car performance tires(tyres). If someone manage to mount them on a Toyota Prius, the tires performance properties are the same. It just that the Prius is not able to take full advantage of it.

Since Toyota do not need to spend that kind of money nor the consumer want to do that, so it is better to get a smaller, less perform tires on it.

Same thing apply to lens. I strongly believe the cost of making and using (require less processing power) a smaller sensor is much lower than a full frame. So manufacturers go that route and create the cropped sensor.

And because of the cropped sensor, the lens manufacturers now can create a fast zoom lens with smaller glass (possible lower cost). With less glass => less weight => do not need sturdier lens housing => even less weight.

 

[Dao]

If you have a 7D (crop) and a 5D (full) and use the same 200mm EF lens on both using the same aperture value and the same distance to subject then the 5D will have a slightly shallower DOF.

I believe they will have the same DoF. However, if you frame the subject so that the size appear to be the same, then the one in 5D should have a shallower DoF. In order to do so, the 5D camera will need to move closer to the subject. So the DoF change due to subject to camera distance change.

 

[Dao]

From Cambridge in colour -
One might initially think that throwing away image information is never ideal, however it does have its advantages. Nearly all lenses are sharpest at their centers, while quality degrades progressively toward to the edges. This means that a cropped sensor effectively discards the lowest quality portions of the image, which is quite useful when using low quality lenses (as these typically have the worst edge quality).

On the other hand, this also means that one is carrying a much larger lens than is necessary — a factor particularly relevant to those carrying their camera for extended periods of time (see section below). Ideally, one would use nearly all image light transmitted from the lens, and this lens would be of high enough quality that its change in sharpness would be negligible towards its edges.

So, a FX lens is actually larger than DX lens. "Ideally, one would use nearly all image light transmitted from the lens." So if a DX lens is made the same size as a FX lens, the same amount of light in FX lens is transmitted to the DX lens, then the noise performance and depth of field would be the same.

What that line means is lens usually perform the best in the center. And DX sensor only use the center region, so overall image is better. There are examples that fall into that category. i.e. The Sigma 70-200mm f/2.8 lens. It border performance is not as good as the center, so when that lens is test with a DX body, the MTF charts are not bad at all, however, when it test with a FX body, MTF charts show weakness on border performance.

Again, even if the DX lens make the same size as a FX or big enough for full format camera, it is going to be the same.

 

[2WheelPhoto]

From Cambridge in colour -
One might initially think that throwing away image information is never ideal, however it does have its advantages. Nearly all lenses are sharpest at their centers, while quality degrades progressively toward to the edges. This means that a cropped sensor effectively discards the lowest quality portions of the image, which is quite useful when using low quality lenses (as these typically have the worst edge quality).

On the other hand, this also means that one is carrying a much larger lens than is necessary — a factor particularly relevant to those carrying their camera for extended periods of time (see section below). Ideally, one would use nearly all image light transmitted from the lens, and this lens would be of high enough quality that its change in sharpness would be negligible towards its edges.

So, a FX lens is actually larger than DX lens. "Ideally, one would use nearly all image light transmitted from the lens." So if a DX lens is made the same size as a FX lens, the same amount of light in FX lens is transmitted to the DX lens, then the noise performance and depth of field would be the same.

What that line means is lens usually perform the best in the center. And DX sensor only use the center region, so overall image is better. There a examples you find that fall into that category. i.e. The Sigma 70-200mm f/2.8 lens. It border performance is not as good as the center, so when that lens is test with a DX body, the MTF charts are not bad at all, however, when it test with a FX body, MTF charts show weakness on border performance.

Again, even if the DX lens make the same size as a FX or big enough for full format camera, it is going to be the same.

True for non-pro lenses that don't perform on the outside, but not a good argument at shooting DX over full frame. Its no secret if one wants the best image quality, camera body, most functions, pro durability and sealed up body, and an overall pro-level its full frame all the way.

6 pages of funny right here LoL and another 6 pageswill never reverse the roles of FF > DX and DX > than 3/4 and 3/4 > cell phone sensor.

 

[Dao]

Yes, and border performance may not be too important for some shooters since the subject that need to be sharp is closer to the center. And the background is blurred anyway.

 

[mjhoward]

"Ideally, one would use nearly all image light transmitted from the lens." So if a DX lens is made the same size as a FX lens, the same amount of light in FX lens is transmitted to the DX lens, then the noise performance and depth of field would be the same.

Wrong. And if you need an explanation as to why, re-read all of mine and everyone elses other responses.

 

[molested_cow]

Okok here's an analogy, not sure if this will work for you.

You got two cups. One with 5cm diameter and one with 10cm diameter, both have the same depth. Put both in a down pour and see which will collect more water at the same period of time.

A larger sensor vs a smaller sensor of the same pixel count, means the size of each pixel is different. If each pixel is like a cup, then a larger pixel will "collect" more light than the smaller pixel at the same given time.
You kept arguing that they will receive the same amount of light if the light source is the same. However it seems that you are quantifying the light by the number of photons that YOU ALLOW to hit the pixels, which is unrealistic. In the real world, the amount of light is controlled by the aperture and shutter open time, which means at the same given time, there will definitely be more photons hitting on a larger pixel than the small one.


Another way to look at it is, take the D700 sensor and turn it to DX mode(6mp). Its noise performance at DX mode will be the same as FX, which is better than D90 which has a 12mp DX sensor.

 

[bentcountershaft]

If you have a 7D (crop) and a 5D (full) and use the same 200mm EF lens on both using the same aperture value and the same distance to subject then the 5D will have a slightly shallower DOF.

I believe they will have the same DoF.

Not according to my depth of field calculator. There's a reason those calculators ask what format of film/size of sensor the camera has.

 

[EchoingWhisper]

If you have a 7D (crop) and a 5D (full) and use the same 200mm EF lens on both using the same aperture value and the same distance to subject then the 5D will have a slightly shallower DOF.

Sorry, depth of field is determined by circle of confusion, aperture and subject - sensor is not a factor.

 

[Dao]

EchoingWhisper

Hope this will clear things up. Diagram quote from dpreview

Assuming shutter speed and ISO value are constant.

What will make the image casted on the sensor brighter?
The answer is the aperture.

What if I make the lens bigger and keep the aperture the same?
Same brightness.

So what a larger lens can do?
To create a larger image circle at the focal plane. => wider Angle of View (AoV) / Field of View (FoV) = See more sky around the eagle

What if I use a smaller sensor?
Same brightness. But the eagle is cropped and I cannot see the tip of the wings. (In other words, I can say narrower AoV/FoV)

What if I use a FX sensor, but use a DX lens?
Same brightness. But the eagle is cropped by a black circle and I cannot see the tip of the wings.


Please note that, no matter what I use for the recording medium, P&S sensor or medium format, the focal length is the same. Brightness is the same.

 

[EchoingWhisper]

Okok here's an analogy, not sure if this will work for you.

You got two cups. One with 5cm diameter and one with 10cm diameter, both have the same depth. Put both in a down pour and see which will collect more water at the same period of time.

A larger sensor vs a smaller sensor of the same pixel count, means the size of each pixel is different. If each pixel is like a cup, then a larger pixel will "collect" more light than the smaller pixel at the same given time.
You kept arguing that they will receive the same amount of light if the light source is the same. However it seems that you are quantifying the light by the number of photons that YOU ALLOW to hit the pixels, which is unrealistic. In the real world, the amount of light is controlled by the aperture and shutter open time, which means at the same given time, there will definitely be more photons hitting on a larger pixel than the small one.


Another way to look at it is, take the D700 sensor and turn it to DX mode(6mp). Its noise performance at DX mode will be the same as FX, which is better than D90 which has a 12mp DX sensor.

Not really true, two lens with the but covering a smaller sensor, light density is highly. The magnifying analogy is surprisingly accurate to what I am thinking.

Another way to look at it is, take the D700 sensor and turn it to DX mode(6mp). Its noise performance at DX mode will be the same as FX, which is better than D90 which has a 12mp DX sensor.

Not true. Because at 100%, the D700 sensor in DX mode will look better. But if you display both at the same size, you'll realise both have the same noise performance.

 

[EchoingWhisper]

EchoingWhisper

Hope this will clear things up. Diagram quote from dpreview

Assuming shutter speed and ISO value are constant.

What will make the image casted on the sensor brighter?
The answer is the aperture.

What if I make the lens bigger and keep the aperture the same?
Same brightness.

So what a larger lens can do?
To create a larger image circle at the focal plane. => wider Angle of View (AoV) / Field of View (FoV) = See more sky around the eagle

What if I use a smaller sensor?
Same brightness. But the eagle is cropped and I cannot see the tip of the wings. (In other words, I can say narrower AoV/FoV)

What if I use a FX sensor, but use a DX lens?
Same brightness. But the eagle is cropped by a black circle and I cannot see the tip of the wings.


Please note that, no matter what I use for the recording medium, P&S sensor or medium format, the focal length is the same. Brightness is the same.

Not trying to say you're wrong. You're entirely right, but it's just that at the same total light level, the DX will always get higher density of light, therefore it will not be worse than FX, in terms of SNR.

 

[Dao]

Not really true, two lens with the but covering a smaller sensor, light density is highly. The magnifying analogy is surprisingly accurate to what I am thinking.

This is what I keep trying to show you. IMAGE CIRCLE. Larger lens has larger image circle. Smaller lens has smaller image circle.

You assumption was wrong and that make you believe what you believe. You assume when DX lens change into a FX lens, the image circle remain the same, which is not the case.