# D7100 crop mode and depth of field



## jl1975 (Mar 31, 2013)

Hi All.  I have a D7100 on order and in the time that I have been waiting, I have been reading up on every aspect of it that I can.  One thing that I have been wondering about is how the crop mode will affect the depth of field.  Now, normally a crop sensor has a different depth of field for a given lens than a full frame does.  Will the crop mode on the D7100 affect the depth of field from the normal mode?  I know that normally the sensor size will change the depth of field, however if you are just using the center portion of the sensor, which effectively is the same as cropping in post, will it be the same?  Will f4 be f4 regardless of crop/normal mode?  I have been going around on this in my head for a while and I can't try it with my camera until I get it in my hands.  Any theories?


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## AaronLLockhart (Mar 31, 2013)

jl1975 said:


> Hi All.  I have a D7100 on order and in the time that I have been waiting, I have been reading up on every aspect of it that I can.  One thing that I have been wondering about is how the crop mode will affect the depth of field.  Now, normally a crop sensor has a different depth of field for a given lens than a full frame does.  Will the crop mode on the D7100 affect the depth of field from the normal mode?  I know that normally the sensor size will change the depth of field, however if you are just using the center portion of the sensor, which effectively is the same as cropping in post, will it be the same?  Will f4 be f4 regardless of crop/normal mode?  I have been going around on this in my head for a while and I can't try it with my camera until I get it in my hands.  Any theories?




crop *mode*? The D7100 is a crop body... it doesn't have a "crop mode." I think you're mistaking it for the D700.


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## coastalconn (Mar 31, 2013)

The D7100 does have a 1.3x crop mode of the crop sensor.. fwiw...It gives roughly 2x equivalent FOV..  How it affects DOF I have no idea


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## AaronLLockhart (Mar 31, 2013)

coastalconn said:


> The D7100 does have a 1.3x crop mode of the crop sensor.. fwiw...It gives roughly 2x equivalent FOV..  How it affects DOF I have no idea




Hmm, I didn't know that. Does the D7000 have this?


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## coastalconn (Mar 31, 2013)

Not on the d7000.  The only interesting thing is that it adds 1 FPS and gives you smaller files with 16 mp instead of 24..  and I think the buffer goes from 8 to 10 or something like that


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## 480sparky (Mar 31, 2013)

How can you double the FOV by using a crop mode??

If you have a lens with 100* FOV, do you get 200* in crop mode? If so, that's a darned good trick!!


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## coastalconn (Mar 31, 2013)

A 100mm lens on a dx body gives you an equivalant FOV of 150mm. (The 1.5 crop factor).  If you use the additional 1.3x mode in the D7100 you end up with almost 200mm eqv.  I think it is like 195mm +/- a few.  Everyone is rounding it up to 2x to keep it simple...


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## Vtec44 (Mar 31, 2013)

DOF shouldn't be affected since it's still the same sensor and lens, but I'm no expert.


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## CouncilmanDoug (Mar 31, 2013)

my understanding is that the dof is the same when you're from the same distance, but if you moved farther away from your subject and kept the same framing as the uncropped fov the dof would be greater.


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## AaronLLockhart (Mar 31, 2013)

When in crop mode, does it still have the same resolution ability? If so, then the DoF shouldn't be affected, since it will be the same effective sensor size.


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## 480sparky (Mar 31, 2013)

You will be recording with fewer pixel, so resolution will be reduced.  And DOF is affected.


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## Vtec44 (Apr 1, 2013)

I'm thinking 1.3x mode, you basically cropping it down inside the camera similar to when you crop it down using a software on your computer.  Since DOF is dependent on aperture, sensor size, and distance to subject, cropping it down in camera or using a software shouldn't affect DOF. I just did that on my D800, cropping 36mp down to 16mp and DOF looks pretty much the same to me.  Then again, I'm near-sighted.


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## 480sparky (Apr 1, 2013)

It will affect the DOF if you enlarge an uncropped image and a cropped image to the same print size.


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## o hey tyler (Apr 1, 2013)

Vtec44 said:


> DOF shouldn't be affected since it's still the same sensor and lens, but I'm no expert.



This is correct. Depth of field is only effected in camera at the time of the shutter actuation. It has to do with aperture, and subject to focal plane distance. Cropping an image won't effect depth of field. If it did, depth of field calculators would be a lot more difficult.


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## 480sparky (Apr 1, 2013)

o hey tyler said:


> Vtec44 said:
> 
> 
> > DOF shouldn't be affected since it's still the same sensor and lens, but I'm no expert.
> ...



Then why does a crop sensor have a different DOF than a full-frame one when all else is the same?


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## o hey tyler (Apr 1, 2013)

480sparky said:


> Then why does a crop sensor have a different DOF than a full-frame one when all else is the same?



Because on a crop sensor, you are framing the same shot at a different distance than you would with a full frame body. If the D7100 has crop lines for the smaller format size, you would have to move back to frame the same shot. If you chose not to move, and just engaged the crop mode, the DOF would be the same but the resolution would be smaller. 

Since you have a full frame camera, take a photo of a ruler with a macro lens. Go for 1" of DoF. Crop that image as much as you would like, the depth of field doesn't change from 1".


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## AaronLLockhart (Apr 1, 2013)

o hey tyler said:


> 480sparky said:
> 
> 
> > Then why does a crop sensor have a different DOF than a full-frame one when all else is the same?
> ...



^ Those are personally my thoughts.

However, I was waiting on someone to say something else so that I didn't say something and then someone come in and tell me I was an idiot for posting "noob" comments. (Not implying what you said was noob, Tyler. However, if the comment would have come from me, it would have certainly been dismissed as such.)


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## o hey tyler (Apr 1, 2013)

AaronLLockhart said:


> ^ Those are personally my thoughts.
> 
> However, I was waiting on someone to say something else so that I didn't say something and then someone come in and tell me I was an idiot for posting "noob" comments. (Not implying what you said was noob, Tyler. However, if the comment would have come from me, it would have certainly been dismissed as such.)



I am just a noob dude. Don't give me too much credit.


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## 480sparky (Apr 1, 2013)

o hey tyler said:


> 480sparky said:
> 
> 
> > Then why does a crop sensor have a different DOF than a full-frame one when all else is the same?
> ...



No, I'm not framing anything different.  I'm standing in the same spot.  I just use the same lens at the same aperture on two difference cameras.

Try taking a DOF calculator and punching in some numbers with a crop sensor camera.  Now change ONE THING: use a full frame. Why is the DOF suddenly different?


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## AaronLLockhart (Apr 1, 2013)

480sparky said:


> o hey tyler said:
> 
> 
> > 480sparky said:
> ...



Because the physical sensor is larger. Which is the point. When you have the same sensor area... DoF shouldn't change. (Or so I would think).

It's not like the camera is flipping back and forth between two separate sensors. It's the same sensor, with the same area, and if the "print size" is the same, then it would use the same number of active pixels, just change the "crop factor." Crop factor could be changed in a camera simply by having a mechanism that moves the sensor closer and further from the back lens element (I'm not saying that is how full frame switch between full frame and crop frame modes, just implying that it COULD be done that way). This wouldn't change the depth of field, only the crop area.


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## 480sparky (Apr 1, 2013)

Full Frame:








Crop Sensor:








Once again I will ask:  If the sensor size makes no difference as to DOF, then why does every DOF calculator need the sensor size in order to figure DOF?


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## Vtec44 (Apr 1, 2013)

480sparky said:


> Once again I will ask: If the sensor size makes no difference as to DOF, then why does every DOF calculator need the sensor size in order to figure DOF?



It makes a difference when you have two different sensors.  However, I don't think cropping mode changes the sensor size but just changes the image size on the exact same sensor.  

BTW, the D7000 is front focusing.


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## 480sparky (Apr 1, 2013)

Vtec44 said:


> .............BTW, the D7000 is front focusing.



I tried not to move the focus ring, but I may have when I changed cameras.

I went round and round in this thread, and I'm still confused.


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## TheLost (Apr 1, 2013)

Somebody correct me if i'm wrong (and i'm sure somebody will)... 

But DOF is due to the angle of light coming through the aperture:





Now if you look at FX vs. DX you'll see why FX has a slightly better DOF:





So ends my lesson on DOF!

As to the D7100 crop mode:

My answer is....  No! On the D7100 1.3x crop mode has no affect on DOF.  Why? because the light is still hitting the sensor at the same angle.  The sensor is just ignoring the data from the outside (to created the 1.3x crop).  As somebody said before... 1.3x crop on the D7100 is EXACTLY the same as cropping the image in software.  However, The camera is moving less data around so it speeds things up (FPS and buffer flushing).. that is the benefit of having the body do it for you.

(waiting for everybody to tell me where im wrong... going to get popcorn.. brb)


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## crimbfighter (Apr 1, 2013)

480sparky,

What was your camera to subject distance on your test shots, or were either of these images cropped? I only ask because both images have the same FOV, which would lead me to believe you moved the camera to obtain the same FOV, or cropped the images. Obviously, if the camera to subject distance changed, it would effect the focusing distance, which would effect the DOF at any given aperture, explaining why the DOF got larger if you moved the camera farther from the ruler to obtain the same FOV. Certainly don't mean to sound condescending, just trying to wrap my own head around it, as well..


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## 480sparky (Apr 1, 2013)

crimbfighter said:


> 480sparky,
> 
> What was your camera to subject distance on your test shots, or were either of these images cropped? I only ask because both images have the same FOV, which would lead me to believe you moved the camera to obtain the same FOV, or cropped the images. Obviously, if the camera to subject distance changed, it would effect the focusing distance, which would effect the DOF at any given aperture, explaining why the DOF got larger if you moved the camera farther from the ruler to obtain the same FOV. Certainly don't mean to sound condescending, just trying to wrap my own head around it, as well..



They were shot from the same spot.  Ruler is on a table, cameras on tripod. The only thing I changed was the camera.  I then edited them in post to make them the same size & FOV.


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## crimbfighter (Apr 1, 2013)

480sparky said:


> crimbfighter said:
> 
> 
> > 480sparky,
> ...




Understood. That blows my theory out of the sky...


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## Derrel (Apr 1, 2013)

Yes, the crop-mode on the D7100 will change the depth of field. Not by a whole heck of a lot, but a small amount. At each given picture angle, you will have more depth of field when shooting to a smaller sensor than you will when shooting to a larger sensor. Now that the base MP count is 24MP, and the crop-mode is a healthy 16 MP in the D7100, that makes for a kind of nifty feature. Nikon has offered multi-size captures for some time now. Where it REALLY comes in handy is when shooting events, or long-lasting things like say, baseball games, or multi-hour events. And it's VERY handy when you have say, a shortish zoom lens, like an 18-35 or 18-55, or whatever, and you'd like to get some frame-filling, or narrow-angle-of-view shots, right in-camera. Just use the crop-mode!

Depth of field changes with the size of the recorded image field; a smaller image sensor, or smaller film, has MORE depth of field at a given picture angle than does a larger film or sensor capture shooting the same picture angle. For example, a semi-wide angle field of view shot at f/4.5 on a P&S with the teeeenie-tiny, pinky-fingrnail-sized sensor has *great* depth of field when the lens is focused at 5 feet. An APS-C camera, not nearly so much. A 24x36mm camera has even less DOF. A 120 rollfilm SLR shooting 6x9 cm images has VERY little DOF when shot at f/4.5 at 5 feet.

6x9 cm film with a 65mm lens at 5 feet at f/4.5. DOF is 1.1 feet total DOF, from 4.51 feet to 5.61 feet.

An APS-C sized capture shot with a 20mm lens at 5 feet at f/4.5 is 3.85 feet total DOF, from 3.74 to 7.55 feet.

Both cameras will have "similar" picture angle of view.


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## jl1975 (Apr 1, 2013)

Thanks everyone for the responses.  Nothing like a little lively discussion, right?  I'll be sure to experiment with it once I have the camera.


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## nmoody (Apr 1, 2013)

Please excuse the horrid pictures, this was quick and dirty and the only ruler I own. I have a D7100 and have taken two shots. One with 1.3x from mode and the other DX (as it is labeled in the camera) Exif data is intact so you can see my settings.

1.3x





DX


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## 480sparky (Apr 1, 2013)

Tick marks are too small and not enough contrast to even see.


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## 2WheelPhoto (Apr 1, 2013)

I'm lost, why not just do the extra crop in post?


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## 480sparky (Apr 1, 2013)

2WheelPhoto said:


> I'm lost, why not just do the extra crop in post?




Smaller image = less memory needed, faster buffer clearing, smaller files.....


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## Derrel (Apr 2, 2013)

2WheelPhoto said:


> I'm lost, why not just do the extra crop in post?



Why not just get the image right in camera?

see where this is headed>>>?


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