Crop sensor and lens aperture

[hamlet]

I'm wondering if my d3200 is able to gather the same amount of light from my 50mm at f1.4 as it would on the d600? I mean i know that the more you open the iris in the lens, the shallower your dof becomes because it is letting in more light. Here in this video it shows this example i'm talking about:




I mean if the image on my d3200 is less shallow, then it must mean that my 50mm isn't really shooting at f1.4 when i use it at f1.4 on my aps-c camera. I'm a bit confused here about this.

 

[Mach0]

I didn't watch the video but yes. The quality might not be up to par but the exposure will be the same at the same settings.

 

[astroNikon]

The lens aperture opening itself does not change from a crop vs full frame camera.
Assuming the lens is a FullFrame lens - more glass which allows a "full size" image circle, versus a crop which can have less glass because it only needs a smaller image circle

The FF sensor will have larger individual sensor things, which are larger than on a crop sensor .. for similar sized MP sensors.

The DOF is different between a crop and FF .. Derrel told me a good explanation of which I've forgotten now.

oh yeah.... basically if you create a drawing of heigth & width from the sensor to the subject you get the difference. I'll see if I can find the comparison diagrams.

 

[robbins.photo]

I'm wondering if my d3200 is able to gather the same amount of light from my 50mm at f1.4 as it would on the d600? I mean i know that the more you open the iris in the lens, the shallower your dof becomes because it is letting in more light. Here in this video it shows this example i'm talking about:

I mean if the image on my d3200 is less shallow, then it must mean that my 50mm isn't really shooting at f1.4 when i use it at f1.4 on my aps-c camera. I'm a bit confused here about this.

Well the lens itself will let in the same amount of light on either camera. The thing is that the sensor in the D600 is much larger than the one in your D3200, roughly about two and a half times larger. As a result it's more sensitive to that light and able to do a lot more with it. To put it in terms of Fstops, your looking at roughly a 1.4 Fstop difference.

 

[Braineack]

I mean if the image on my d3200 is less shallow, then it must mean that my 50mm isn't really shooting at f1.4 when i use it at f1.4 on my aps-c camera. I'm a bit confused here about this.

The D600 in that video is sitting closer to the subject to frame it similarly to the D5200, therefore the DOF has been reduced.

Had both cameras been sitting in the same physical location, the DOF would have looked exactly the same.


The amount of light gathered has nothing to do with it--that would change the exposure--it's a factor of the rate of light spread (the distance to the subject, the focal length, and the aperture).

50mm @ f/1.4 is a 35.7mm apertaure opening regardless if it's on a DX or FX sensor.

 

[timor]

Well the lens itself will let in the same amount of light on either camera. The thing is that the sensor in the D600 is much larger than the one in your D3200, roughly about two and a half times larger. As a result it's more sensitive to that light and able to do a lot more with it. To put it in terms of Fstops, your looking at roughly a 1.4 Fstop difference.

Can you explain it a bit better ? If there is the same intensity of light per every square millimetre of the sensor how comes bigger sensor should sense more light ?

 

[Braineack]

The pixel are larger, so there's much more area (2.4x) to gather light over the same instance of time.

 

[robbins.photo]

Well the lens itself will let in the same amount of light on either camera. The thing is that the sensor in the D600 is much larger than the one in your D3200, roughly about two and a half times larger. As a result it's more sensitive to that light and able to do a lot more with it. To put it in terms of Fstops, your looking at roughly a 1.4 Fstop difference.

Can you explain it a bit better ? If there is the same intensity of light per every square millimetre of the sensor how comes bigger sensor should sense more light ?

Well I can.. problem is doing so in such a fashion that the post doesn't become longer than Tolstoy's War and Peace.. lol. Ok, I'll give it a quick stab, and no this is by no means complete but hopefully it will cover the basics.

A sensor in a digital camera has millions of spots that are sensetive to light, called photosites. Each photosite records information about what is being "seen" through the lens, so the more photosites you have and the larger they are naturally the more information that is being collected. A larger sensor allows for larger photosites - and a larger photosite will collect more from a ray of light than a smaller one can. If it helps think of it in terms of water. If you put a coffee cup on the floor and pour water into it, once the cup is full any more water will flow out of the top and simply be wasted. Replace the cup with a bucket, and now you can pour the same amount of water and because of the buckets larger size, it will collect a lot more of the water.

The amount of water your pouring doesn't change (much like the amount of light coming into the camera doesn't change when your using the same aperture) however because you now have row after row of buckets instead of row after row of coffee cups, the amount of "water" or in this case the amount of information from the light captured that is retained is a whole lot more.

 

[timor]

I'm wondering if my d3200 is able to gather the same amount of light from my 50mm at f1.4 as it would on the d600? I mean i know that the more you open the iris in the lens, the shallower your dof becomes because it is letting in more light.
I mean if the image on my d3200 is less shallow, then it must mean that my 50mm isn't really shooting at f1.4 when i use it at f1.4 on my aps-c camera. I'm a bit confused here about this.

From the same lens DoF is same, no matter what the medium size. Size of the sensor doesn't change the physics of the lens, circles of confusion falling on the medium are of the same size and those are responsible for your apparent sharpness of the image. Standard CoC for full frame 50mm lens is 0.03 mm. DoF on both sensor is the same, when you compare straight prints from both cameras made in such a way, that objects in both prints have exactly same size.

 

[WayneF]

Can you explain it a bit better ? If there is the same intensity of light per every square millimetre of the sensor how comes bigger sensor should sense more light ?

No, you are confusing exposure with depth of field. They are NOT at all the same thing (as you are trying to say).
A f/1.8 lens is a f/1.8 lens, and it lets in the same amount of light as any other f/1.8 lens, and onto any sensor (same exposure at f/1.8).
A FX sensor is merely a wider view of the wider scene (uncropped), but it is not a brighter view.

Because FX is a wider uncropped view, then if using the same lens on both FX and DX (which obviously projects the same image onto either sensor, no difference), then a DX camera (which will crop the image) has to stand back 1.5x greater distance in order to see the same view as FX. This is the 1.5x crop factor of the DX sensor.

DOF is affected by aperture, focal length and subject distance. You are changing subject distance, in order that they look alike. Any DOF differences with same lens at same aperture can only be caused only by the greater distance (for same view). Or sharpness is affected by sensor size (might appear changed) since we have to enlarge the smaller DX sensor image more, to appear same size as the larger FX sensor image.

See FX - DX Lens Crop Factor

 

[Mike_E]

Another dynamic is the inverse square law.

Yes, reflected light is far more linear than a point source but it's not perfectly linear. The further you are away from a subject let less light you will get from that subject even though your camera will give you the same meter reading. This sounds counter-intuitive but the background/foreground comes into play with the meter reading at distance.

The fix for this is to use (or get) a basic understanding of the zone system and to use spot metering.

 

[timor]

Well the lens itself will let in the same amount of light on either camera. The thing is that the sensor in the D600 is much larger than the one in your D3200, roughly about two and a half times larger. As a result it's more sensitive to that light and able to do a lot more with it. To put it in terms of Fstops, your looking at roughly a 1.4 Fstop difference.

Can you explain it a bit better ? If there is the same intensity of light per every square millimetre of the sensor how comes bigger sensor should sense more light ?

Well I can.. problem is doing so in such a fashion that the post doesn't become longer than Tolstoy's War and Peace.. lol. Ok, I'll give it a quick stab, and no this is by no means complete but hopefully it will cover the basics.

A sensor in a digital camera has millions of spots that are sensetive to light, called photosites. Each photosite records information about what is being "seen" through the lens, so the more photosites you have and the larger they are naturally the more information that is being collected. A larger sensor allows for larger photosites - and a larger photosite will collect more from a ray of light than a smaller one can. If it helps think of it in terms of water. If you put a coffee cup on the floor and pour water into it, once the cup is full any more water will flow out of the top and simply be wasted. Replace the cup with a bucket, and now you can pour the same amount of water and because of the buckets larger size, it will collect a lot more of the water.

The amount of water your pouring doesn't change (much like the amount of light coming into the camera doesn't change when your using the same aperture) however because you now have row after row of buckets instead of row after row of coffee cups, the amount of "water" or in this case the amount of information from the light captured that is retained is a whole lot more.

I know that explanation, it only explains, why larger sensors produce less noise giving cleaner images (that's why people buy them). You try to convince me, that larger sensors because of larger photosites records more light then it is there ? Maybe they have this ability, but shouldn't they keep ISO standards ? What you are saying ISO 100 on FF sensor equals ISO ... 250 on APS sensor ?

 

[timor]

Can you explain it a bit better ? If there is the same intensity of light per every square millimetre of the sensor how comes bigger sensor should sense more light ?

No, you are confusing exposure with depth of field. They are NOT at all the same thing (as you are trying to say).

Thank you Wayne, I am not confusing anything here. I am asking Robin why larger sensors can do more with the same amount of light.

 

[WayneF]

Can you explain it a bit better ? If there is the same intensity of light per every square millimetre of the sensor how comes bigger sensor should sense more light ?

No, you are confusing exposure with depth of field. They are NOT at all the same thing (as you are trying to say).

Thank you Wayne, I am not confusing anything here. I am asking Robin why larger sensors can do more with the same amount of light.

My apology, I incorrectly confused you with the OP. I was speaking of the video in the first post here.

 

[timor]

No, you are confusing exposure with depth of field. They are NOT at all the same thing (as you are trying to say).

Thank you Wayne, I am not confusing anything here. I am asking Robin why larger sensors can do more with the same amount of light.

My apology, I incorrectly confused you with the OP. I was speaking of the video in the first post here.

No problem.