DX - FX photo explanation of crop zoom

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Moab Man

Senior Member
Wrapping your head around the crop mode can be difficult. After participating in a thread on choosing a next camera, it was asked if the crop sensor is simply cropping down. Now that is an oversimplification, and there were other questions, so I decided to offer a photo explanation so that it may help clear the confusion. All photos were shot from a tripod placed over second base. The hot model, myself, stood in two foot prints for consistency.

On a side note, who would have thought photography was so good for exercise as I ran back and forth between home base, second base, and my camera bag with lenses in the grassy outfield.

Cameras: Nikon D7100 (crop sensor) and a Nikon D600 (full frame). Photos were not edited, auto focused, and no settings were adjusted in the camera other than compensating (shutter speed) for the sunlight fading. Effective focal length calculated using an online calculator.

1. "DX is great for the extra zoom it gives."

No, there is a not an actual zoom happening. The smaller sensor area is taking a smaller slice of the image coming through the lens. This smaller slice is what makes a 50mm lens on a crop sensor have an effective zoom range of 76mm. On a full frame sensor the full breadth of the image coming through the sensor is used thereby keeping it at 50mm.

This image is a 50mm lens on a full frame sensor capturing the full image from the lens.
50mmFX.jpg

This image is a 50mm lens on a crop sensor. The crop sensor is only pulling a slice from the center area of the lens and not the full image. This produces an effective zoom of 76mm.
50mmDX.jpg



2. "So it's just a matter of cropping down the image."

Incorrect, it is not "just" a cropping down of the image. The D7100 and D600 are standing on the dividing line between crop and full frame. Each uses a 24mp sensor.

This image is a 35mm DX lens on a crop sensor camera. The smaller sensor at 24mp allows for this image to be printed at 300dpi (high resolution) at 20"x13.3".
35mmD7100.jpg

Putting this same lens on a full frame camera, triggering a crop mode, gives us the same image. However, due to a small portion of the image being used there are fewer megapixels coming into play. This image has a high resolution print size of 13.1"x8.7" at 300dpi.
35mmInCropModeD600.jpg



3. "You need much more zoom on a full frame to achieve the same of a crop sensor."


This image is a 35mm lens on a crop sensor. Effective zoom due to a crop sensor is 53mm.
35mmD7100.jpg

To achieve the same "zoom" of a crop sensor we must use a 50mm lens on full frame.
50mmFX.jpg

The difference between a 35mm and a 50mm lens may not seem like that much. But, when you are talking serious telephoto reach it become quite substantial in reach and cost to achieve the same image on full frame. A 500mm lens on a crop sensor effectively becomes a 759mm lens. To achieve the same for full frame you're shopping for an 800mm lens. In other words, a crop sensor gives you free additional reach through the "crop factor." However, it bears repeating, there is no actual mechanical zoom happening.


4. "There are benefits to using an FX lens on a DX camera."

Putting a full frame lens on a full frame camera gets you the effective zoom listed on the lens - 200mm is 200mm. As I showed above, triggering the crop mode on the camera with a DX lens loses a lot of pixels. Further pixels are lost when you crop down on the image you want such as sports. Generally, sports shots are cropped tight. for this reason, when it can be afforded, FX lenses are desired because they can give you the additional "zoom" on a crop sensor camera and on a full frame camera pixels are not being lost through the triggering of crop mode.

This image is an FX lens (500mm) on an FX camera and cropped in tight for a sports shot. High resolution print size of 6"x9".
500mmD600SportsCrop.jpg

This image is an FX lens (500mm) shot on a DX camera and sports cropped. High resolution print size of 9"x13". This is a substantial 3" and 4" difference respectively.
500mmD7100SportsCrop.jpg



5. How substantial is the difference?

This first image is the 500mm lens on a full frame sensor and then crop sensor.
500mmD600.jpg 500mmD7100corrected.jpg



6. So how much difference in size are the two sensors? (shot through a 500mm lens)

The inner area boxed in red is what the crop sensor sees. The entire photo is what full frame sees. To create this image I reduced the D7100 crop sensor image until it overlaid the image content of the full frame image. Therefore it is not a "mathematical" sensor size overlay but a content overlay.
SensorOverlay.jpg


7. If I buy a DX specific lens does the crop factor still apply?

Yes, the crop factor and effective resulting zoom is still present.

This image is from a DX specific lens: Tokina 11-16mm shot at 14mm. The effective zoom due to the crop factor gives us an image approximating 21mm.
14mmDX.jpg

This image is from a Rokinon 14mm FX lens. On a full frame it will give us a 14mm photo. Putting this FX lens on a crop sensor camera would give us an image like the image above because a crop sensor pulls a small slice from the center of the image.
14mmFX.jpg



**My personal thoughts and opinion.

When I shoot sports I prefer a crop sensor for the effective zoom of a crop sensor. However, if I am shooting in lower light I have to make the decision between having quite a bit less zoom with no high ISO noise and improved low light capability. Or, do I live with the higher noise in low light on my crop sensor to get better reach. With that said, the low light capability of the D7100 is pretty darn good. But... full frame is still clearly king in low light and high ISO.

In my opinion, buy FX lenses when able. Generally, it's better glass and the lens can be used equally on both crop and full sensor cameras. DX lenses can be used on both, but you sacrifice image print size when used on full frame due to the triggering of crop mode because a DX lens is only putting through a smaller image in the center of the FX sensor leaving the outer area of the FX sensor with no image coming through.

And I have no idea as to why this image below has attached itself to this thread. So I guess you can all take a moment to stare at me, the eye candy in each photograph.
 

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Philnz

Senior Member
Wrapping your head around the crop mode can be difficult. After participating in a thread on choosing a next camera, it was asked if the crop sensor is simply cropping down. Now that is an oversimplification, and there were other questions, so I decided to offer a photo explanation so that it may help clear the confusion. All photos were shot from a tripod placed over second base. The hot model, myself, stood in two foot prints for consistency.

On a side note, who would have thought photography was so good for exercise as I ran back and forth between home base, second base, and my camera bag with lenses in the grassy outfield.

Cameras: Nikon D7100 (crop sensor) and a Nikon D600 (full frame). Photos were not edited, auto focused, and no settings were adjusted in the camera other than compensating (shutter speed) for the sunlight fading. Effective focal length calculated using an online calculator.

1. "DX is great for the extra zoom it gives."

No, there is a not an actual zoom happening. The smaller sensor area is taking a smaller slice of the image coming through the lens. This smaller slice is what makes a 50mm lens on a crop sensor have an effective zoom range of 76mm. On a full frame sensor the full breadth of the image coming through the sensor is used thereby keeping it at 50mm.

This image is a 50mm lens on a full frame sensor capturing the full image from the lens.
View attachment 102701

This image is a 50mm lens on a crop sensor. The crop sensor is only pulling a slice from the center area of the lens and not the full image. This produces an effective zoom of 76mm.
View attachment 102690



2. "So it's just a matter of cropping down the image."

Incorrect, it is not "just" a cropping down of the image. The D7100 and D600 are standing on the dividing line between crop and full frame. Each uses a 24mp sensor.

This image is a 35mm DX lens on a crop sensor camera. The smaller sensor at 24mp allows for this image to be printed at 300dpi (high resolution) at 20"x13.3".
View attachment 102694

Putting this same lens on a full frame camera, triggering a crop mode, gives us the same image. However, due to a small portion of the image being used there are fewer megapixels coming into play. This image has a high resolution print size of 13.1"x8.7" at 300dpi.
View attachment 102695

To get the same zoom factor of the 35mm on a crop sensor camera we have to step up to a


3. "You need much more zoom on a full frame to achieve the same of a crop sensor."

This image is a 35mm lens on a crop sensor. Effective zoom due to a crop sensor is 53mm.
View attachment 102694

To achieve the same "zoom" of a crop sensor we must use a 50mm lens.
View attachment 102701

The difference between a 35mm and a 50mm lens may not seem like that much. But, when you are talking serious telephoto reach it become quite substantial in reach and cost to achieve the same image on full frame. A 500mm lens on a crop sensor effectively becomes a 759mm lens. To achieve the same for full frame you're shopping for an 800mm lens. In other words, a crop sensor gives you free additional reach.


4. "There are benefits to using an FX lens on a DX camera."

Putting a full frame lens on a full frame camera gets you the effective zoom listed on the lens - 200mm is 200mm. As I showed above, triggering the crop mode on the camera with a DX lens loses a lot of pixels. Further pixels are lost when you crop down on the image you want such as sports. Generally sports shots are cropped tight. for this reason, when it can be afforded, FX lenses are desired because they can give you the additional "zoom" on a crop sensor camera and on a full frame camera pixels are not being lost through the triggering of crop mode.

This image is an FX lens (500mm) on an FX camera and cropped in tight for a sports shot. High resolution print size of 6"x9".
View attachment 102696

This image is an FX lens (500mm) shot on a DX camera and sports cropped. High resolution print size of 9"x13". This is a substantial 3" and 4" difference respectively.
View attachment 102697



5. How substantial is the difference?

This first image is the 500mm lens on a full frame sensor and then crop sensor.
View attachment 102698 View attachment 102699



6. So how much difference in size are the two sensors? (shot through a 500mm lens)

The inner area boxed in red is what the crop sensor sees. The entire photo is what full frame sees. To create this image I reduced the D7100 crop sensor image until it overlaid the image content of the full frame image. Therefore it is not a "mathematical" sensor size overlay but a content overlay.
View attachment 102700


**My personal thoughts and opinion.

When I shoot sports I prefer a crop sensor for the effective zoom of a crop sensor. However, if I am shooting in lower light I have to make the decision between having quite a bit less zoom with no high ISO noise and improved low light capability. Or, do I live with the higher noise in low light on my crop sensor to get better reach. With that said, the low light capability of the D7100 is pretty darn good. But... full frame is still clearly king in low light and high ISO.

In my opinion, buy FX lenses when able. Generally it's better glass and the lens can be used on both crop and full sensor cameras. DX lenses can be used on both, but you sacrifice image size for print when used on full frame in crop mode.

Wow. Thank you for all the time that you must have put in to this post. It has helped my understanding a great deal. I am buying all the old film lens that I can get my hands on.( if the price is right.) so am I right in thinking they are all Full Frame Lens?
"On a side note, who would have thought photography was so good for exercise as I ran back and forth between home base, second base, and my camera bag with lenses in the grassy outfield." Now that is a good excuse to "Give Her in Doors" for getting more gear:very_drunk:

 

PaulPosition

Senior Member
Wow. Thank you for all the time that you must have put in to this post. It has helped my understanding a great deal. I am buying all the old film lens that I can get my hands on.( if the price is right.) so am I right in thinking they are all Full Frame Lens?
You're right, at least as long as you're talking 35mm film camera's which full frame sensors are sized like (I have no idea what sort of lens "large-format" camera used to use).
 

Marcel

Happily retired
Staff member
Super Mod
You're right, at least as long as you're talking 35mm film camera's which full frame sensors are sized like (I have no idea what sort of lens "large-format" camera used to use).

Normal lens on a 2-1/4" camera was 80mm, 4x5 around 190mm, 8x10 350mm is my memory serves me well.
 

skater

New member
I'm sorry...I totally got distracted by the fact that he's not actually holding a bat.

This is a great post, though. It'll help us make the decision on whether we want to go full frame or not for the next camera. Thanks!
 

§am

Senior Member
Very useful indeed - thanks :)

So to summarise really I would say;


  • 50mm FX lens on a FX body = equivalent 50mm (1x zoom)
  • 50mm FX lens on a DX body = equivalent of 75mm (1.5 zoom)
  • 50mm DX lens on a FX body = equivalent 50mm (1x zoom)
  • 50mm DX lens on a DX body = equivalent 50mm (1x zoom)


It's important to remember that the focal length does NOT change on a lens - its the equivalent length that is chaging
 
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PapaST

Senior Member
Thanks for that great write up. But, we really need to work on your stance. Leaning into the plate too much and your strike zone is a mile high. ;)
 

Moab Man

Senior Member
I'm sorry...I totally got distracted by the fact that he's not actually holding a bat.

It was my job to bring the camera equipment and my imaginary friends job to bring the baseball equipment. I'm not sure if he let me down or not.
 

Moab Man

Senior Member
Thanks for that great write up. But, we really need to work on your stance. Leaning into the plate too much and your strike zone is a mile high. ;)

LOL, this is my I'M TRYING TO BREATHE stance. I was in a literal race against the setting sun to get these shots finished. My daughter laughed her butt off because in the photos I have this belly hanging out. I don't actually have a belly but learned to belly breathe to extend the lungs when bike racing. However, none of that matters to the camera or my laughing daughter.

As for the stance... I don't play imaginary baseball very well. :)
 
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Blade Canyon

Senior Member
So it's safe to say this?

Using DX mode on a D600 (10mp DX area) is no different than just cropping a D600 pic shot in FX mode.

BUT, shooting the same lens on a dedicated DX camera with 24mp packed into the DX space gives a better image quality than a cropped D600 FX shot.

Right?
 

Pretzel

Senior Member
It was my job to bring the camera equipment and my imaginary friends job to bring the baseball equipment. I'm not sure if he let me down or not.

Of course he didn't let you down... your imaginary friend OBVIOUSLY brought you an imaginary bat. What else would he bring!?

(FWIW, it's much easier to hit imaginary home-runs than real ones)

Great write up, friend. We might link to it for those who ask the question in the future. :)
 

Moab Man

Senior Member
[MENTION=15302]Blade Canyon[/MENTION]
That's the general idea. None of this really matters a whole lot unless you have images printed in large sizes. I regularly print in poster sizes so it's a factor for me to consider. If I was shooting for 8x10 and smaller a or just for a computer screen a 6MP camera would do me just fine. This is where all this mega pixel upsizing really means nothing for most people as few print images and even fewer print large.
 

Moab Man

Senior Member
Of course he didn't let you down... your imaginary friend OBVIOUSLY brought you an imaginary bat. What else would he bring!?

(FWIW, it's much easier to hit imaginary home-runs than real ones)

Great write up, friend. We might link to it for those who ask the question in the future. :)

I don't know about it being easier to hit a home run. Never saw the ball coming and I got hit in the face right after shooting these images - broke my nose.

I've seen the question so many times and it can be a nightmare without pictures to understand so I figured it was the least I could do for a forum where we all learn so much from each other.

If I could have found my imaginary friend I would have charged the mound after he hit me with the imaginary ball. Maybe next time my imaginary friend might meet my real bat.
 

Moab Man

Senior Member
Wow. Thank you for all the time that you must have put in to this post. It has helped my understanding a great deal. I am buying all the old film lens that I can get my hands on.( if the price is right.) so am I right in thinking they are all Full Frame Lens?
"On a side note, who would have thought photography was so good for exercise as I ran back and forth between home base, second base, and my camera bag with lenses in the grassy outfield." Now that is a good excuse to "Give Her in Doors" for getting more gear:very_drunk:


Correct, they would be full frame as the full frame reference is based off of the 35mm film size. Glad this helped you out.
 

DraganDL

Senior Member
Just don't forget that with a modern software like phshop...zoom_pro... you can FREELY choose virtually ANY "print size", so the cropped photo can be printed as if it was NOT being cropped at all. Of course, since this procedure is a form of "enlargement made through the use of a software", the real quality of such print would be reduced - still, generally, quite acceptable for many (photographers)...:rolleyes:

I did this a few years ago - I was a member of the team of authors of a book about the local zoo (where I also am employed on the regular basis). We had a lots of old photos, previously scanned in a low resolution (100/150 dpi)...
 
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PapaST

Senior Member
I was kidding. But that is a great write up. It's what makes this forum so great. Thanks for taking the time.
 

Moab Man

Senior Member
I was kidding. But that is a great write up. It's what makes this forum so great. Thanks for taking the time.

That's how I took it. For humor I was sharing the visual of what it took to get these shots running back and forth racing against a setting sun and I'm out of breathe. I thought I looked pretty composed all things considered. :)
 
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skene

Senior Member
Good write up. Should help those in unfamiliar territory when it comes down to choosing between the 2.
 
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