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Why does cropping reduce dynamic range?
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Feb 25, 2021 12:54:25   #
bleirer
 
When I go to the dynamic range section of the photonstophotos website and plot any full frame camera in full frame mode next to the same camera in crop mode, the dynamic range of the crop mode is always less by the same amount at every point.

So the same camera, the same sensor, the same test conditions, the only difference is that one is measuring the cropped area of the same sensor while the other measures the full frame portion of the same sensor.

So why does cropping alone reduce dynamic range?

Feb 25, 2021 12:54:34   #
bleirer
 
-

Feb 25, 2021 12:55:01   #
bleirer
 
Example using Nikon d850, I don't know why it won't take the whole link, you have to click the Nikon d850 dx mode from the list.

https://photonstophotos.net/Charts/PDR.htm#Nikon%20D850,Nikon%20D850(DX)

 
 
Feb 25, 2021 13:05:15   #
Longshadow Loc: Audubon, PA
 
bleirer wrote:
Example using Nikon d850, I don't know why it won't take the whole link, you have to click the Nikon d850 dx mode from the list.

https://photonstophotos.net/Charts/PDR.htm#Nikon%20D850,Nikon%20D850(DX)


The URL tag should be used to prevent truncation by the parser at various characters, like commas-

https://photonstophotos.net/Charts/PDR.htm#Nikon%20D850,Nikon%20D850(DX)

Feb 25, 2021 13:10:47   #
larryepage
 
bleirer wrote:
When I go to the dynamic range section of the photonstophotos website and plot any full frame camera in full frame mode next to the same camera in crop mode, the dynamic range of the crop mode is always less by the same amount at every point.

So the same camera, the same sensor, the same test conditions, the only difference is that one is measuring the cropped area of the same sensor while the other measures the full frame portion of the same sensor.

So why does cropping alone reduce dynamic range?
When I go to the dynamic range section of the phot... (show quote)


I cannot come up with a reason this would occur. Seems like a pretty good question to ask the Photons to Photos folks.

Feb 25, 2021 13:15:37   #
rmalarz Loc: Tempe, Arizona
 
https://www.dpreview.com/forums/thread/4248398
--Bob
bleirer wrote:
When I go to the dynamic range section of the photonstophotos website and plot any full frame camera in full frame mode next to the same camera in crop mode, the dynamic range of the crop mode is always less by the same amount at every point.

So the same camera, the same sensor, the same test conditions, the only difference is that one is measuring the cropped area of the same sensor while the other measures the full frame portion of the same sensor.

So why does cropping alone reduce dynamic range?
When I go to the dynamic range section of the phot... (show quote)

Feb 25, 2021 13:17:08   #
Bill_de Loc: US
 
[quote=Longshadow]The URL tag should be used to prevent truncation by the parser at various characters, like commas-

Thanks, I wondered why that happened sometimes.

--

 
 
Feb 25, 2021 13:18:53   #
Toment Loc: IL-FL
 
Less data?

Feb 25, 2021 13:19:57   #
bleirer
 
larryepage wrote:
I cannot come up with a reason this would occur. Seems like a pretty good question to ask the Photons to Photos folks.


It's just that it is often stated that cropping of any image, even cropping a photo in post, reduces its dynamic range even though one is using the same pixels from the original image. I thought maybe magnification of noise, but just speculating.

Feb 25, 2021 13:25:16   #
Ysarex
 
bleirer wrote:
When I go to the dynamic range section of the photonstophotos website and plot any full frame camera in full frame mode next to the same camera in crop mode, the dynamic range of the crop mode is always less by the same amount at every point.

So the same camera, the same sensor, the same test conditions, the only difference is that one is measuring the cropped area of the same sensor while the other measures the full frame portion of the same sensor.

So why does cropping alone reduce dynamic range?
When I go to the dynamic range section of the phot... (show quote)


In a word: noise.

The smaller sensor area is noisier (because it's smaller) and so the data is noise swamped sooner.

Feb 25, 2021 13:27:21   #
bleirer
 
Longshadow wrote:
The URL tag should be used to prevent truncation by the parser at various characters, like commas-

https://photonstophotos.net/Charts/PDR.htm#Nikon%20D850,Nikon%20D850(DX)


Thanks. I updated mine.

 
 
Feb 25, 2021 13:31:19   #
bleirer
 
Ysarex wrote:
In a word: noise.

The smaller sensor area is noisier (because it's smaller) and so the data is noise swamped sooner.


Could you expand your explanation a little? If it the same sensor area just a smaller section why does the noise increase?

Feb 25, 2021 13:37:06   #
Bill_de Loc: US
 
bleirer wrote:
Could you expand your explanation a little? If it the same sensor area just a smaller section why does the noise increase?


I was wondering that also.

---

Feb 25, 2021 13:43:17   #
Ysarex
 
bleirer wrote:
Could you expand your explanation a little? If it the same sensor area just a smaller section why does the noise increase?


Noise increases because of the different total areas of the sensor used. Use the whole sensor and you record more total light than if you use the smaller cropped area. Noise will increase/decrease with the total amount of light recorded. SNR is a ratio and goes up or down with the total amount of light recorded.

Try this analogy: You have two cookie pans -- one is 11 x 15 inches and the other is 9 x 12 inches. You put them both out in the rain together and allow them to collect water for 1 minute. That 1 minute is exposure time. After a minute it stops raining and you measure the depth of water in each pan -- it's the same. That's exposure. But now pour the water from both pans into two separate bowls. Do both bowls have the same amount of water? The larger pan collected more water. In the same way a larger sensor will collect more light. Noise (shot noise which is the noise we're concerned with) as a ratio to the signal will decrease with more light collected -- stronger signal.

All else the same, bigger sensors are less noisy than smaller sensors. Noise limits DR.

Feb 25, 2021 13:44:05   #
lamiaceae Loc: San Luis Obispo County, CA
 
bleirer wrote:
When I go to the dynamic range section of the photonstophotos website and plot any full frame camera in full frame mode next to the same camera in crop mode, the dynamic range of the crop mode is always less by the same amount at every point.

So the same camera, the same sensor, the same test conditions, the only difference is that one is measuring the cropped area of the same sensor while the other measures the full frame portion of the same sensor.

So why does cropping alone reduce dynamic range?
When I go to the dynamic range section of the phot... (show quote)


I'm curious too. Makes little to sense to me as well. Since the issue has to do more with firmware, what part of the sensor is included in the produced Raw or Jpeg file. I might expect some weirdness if you just measured the sensor with a DX lens that produces a vignetted round image.

I come from years of film use and as far as I know Tri-X Professional ASA/ISO 320 film has the same dynamic range as 4.5x6cm, 6x6cm, 6x7cm, 4x5", 8x10", 11x14" sizes. Somehow the digital business has the number of pixels included in its calculation. As usual, issues for engineers not photographers. I'd be curious to know what you asked but I have a feeling the answer will not be useful as it is likely an artifact of the method or tool used for measurement. Example, most photographers that use hand held meter for the last 60 years use an Exposure Meter not a Light Meter. We want F-stop, Shutter Speed, ASA/ISO, EV data, not Lux, Lumes, Candles per Square Foot, Foot-Candles and such physics or engineering terms. Or like everyday Kilocalories the nutritionists, medical science, biologists, and chemists typically use, physicists and engineers work in Joules. Though I have seen the energy content of Mexican packaged foods in joules. My point, often our problems are in semantics.

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