Nice DX vs FX crop factor explanation

I just saw this on another forum and thought it was a nice graphic to explain the difference between DX & FX crop factors.

OTHER FORUM USER said:

Your D3100 is a DX camera, meaning it has a cropped sensor. A FX or full frame sensor is a lot larger so for instance a 50mm is exactly 50mm on a full frame sensor. On a cropped sensor camera, the sensor is smaller, so the field of view is a little different and makes a 50mm lens on a DX camera give you an equivalent of what a 75mm lens would look like on a 35mm full frame sensor body.


You could even use that 18-55 DX kit lens on a full frame camera too, but it will have vignetting.


Here's an idea of what I'm talking about.

Here's another

I don't know how much better I can explain it, but I hope this helps.

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That should be very helpful!

Thanks Joe for finding this explanation! It sure is helpful for a newbie like me! Lol

On a cropped sensor camera, the sensor is smaller, so the field of view is a little different and makes a 50mm lens on a DX camera give you an equivalent of what a 75mm lens would look like on a 35mm full frame sensor body.

If I use a 50mm DX lens on my DX camera, would I see the same image as the owner of a 50mm FX lens on an FX camera?

Sandpatch said:

On a cropped sensor camera, the sensor is smaller, so the field of view is a little different and makes a 50mm lens on a DX camera give you an equivalent of what a 75mm lens would look like on a 35mm full frame sensor body.

If I use a 50mm DX lens on my DX camera, would I see the same image as the owner of a 50mm FX lens on an FX camera?

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No. If standing at the same place, the DX camera with 50mm lens would see the same view that a 75mm lens would see on the FX camera. Assuming same lens and standing in the same place, then DX is a telephoto effect, FX is a wide angle effect.

See FX - DX Lens Crop Factor

A DX lens doesn't mean there isn't a crop factor when it's used on a DX camera. DX lenses are made to just cover the smaller sensor which means they can be made smaller, lighter, and less expensively. A 50mm DX lens is still a 50mm lens and still has the crop factor on DX.

It bugs me how in Nikon's FX promo video for the D600 the guy says something like "and the DX option really lets you reach out there to get the shot..." implying that by switching to DX crop mode, you can zoom in farther. In reality, you are just cropping what would have been a bigger photo.

Blade Canyon said:

It bugs me how in Nikon's FX promo video for the D600 the guy says something like "and the DX option really lets you reach out there to get the shot..." implying that by switching to DX crop mode, you can zoom in farther. In reality, you are just cropping what would have been a bigger photo.

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That's true, but it is the same thing any DX camera would do... and they are favored for reaching out (sports, wildlife, etc). It is a good option on FX cameras, for telephoto effect, but it's the pits for wide angle.

Blade Canyon said:

It bugs me how in Nikon's FX promo video for the D600 the guy says something like "and the DX option really lets you reach out there to get the shot..." implying that by switching to DX crop mode, you can zoom in farther. In reality, you are just cropping what would have been a bigger photo.

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WayneF said:

That's true, but it is the same thing any DX camera would do... and they are favored for reaching out (sports, wildlife, etc). It is a good option on FX cameras, for telephoto effect, but it's the pits for wide angle.

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That's not quite true actually, is it...? If a DX camera and an FX camera are both 16MP then the DX should in theory have more detail per pixel, as it's captured a smaller image area in the same number of pixels (e.g. the DX has 1.5 pixels per blade of grass while the FX has only 1 because there are more blades of grass in the image)?

I am not 'hands on' familiar with the Crop Factor option (haven't played on my D7100 but that's possibly different to FX anyway) but as I understand it it on an FX it just crops the sensor area down to the same area as a DX - so it is doing exactly what BC says, and it's not actually increasing the pixel density, but that is only half of the story of what DX does...? You get the zoom effect, but it won't be the same as if done on an actual DX camera because you don't get this increased pixel density? e.g. In my example above the FX camera will only use 10.6MP in DX Crop mode, so it's image is zoomed more than with full FX and the same lens, but the detail/pixel density is no better (i.e. even though it gains the zoom effect to reach out it's reduced the pixel count used to capture it) - so it's kinda halfway in-between (more zoom than an FX but not the full effect of a DX)...

...or have a missed something completely?

Mycenius said:

That's not quite true actually, is it...? If a DX camera and an FX camera are both 16MP then the DX should in theory have more detail per pixel, as it's captured a smaller image area in the same number of pixels (e.g. the DX has 1.5 pixels per blade of grass while the FX has only 1 because there are more blades of grass in the image)?

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That's true, it is less. The D600 is 24 megapixels and "only" 10 megapixels in DX mode. But it still is 3,936 × 2,624 pixels, not that shabby. It will still print 8x10 inches, and anything smaller.
The D800 is 36 megapixels, and 15 megapixels in DX, 4,800 × 3,200.

So you may as well shoot in Fx and crop afterwards.

Well, there are other considerations too. I just got back from a long vacation, and took 1500 pictures. On a D800, Raw is 40 MB, which would have been about double the size of my 32 GB memory card. So I shot DX when I could, and FX when I needed wide angle (a 24-120mm lens is anything but wide angle for DX). Still had room for a few hundred more on the card. And other than the wide angle, I see absolutely nothing wrong with the DX shots. It is a great option to have.

WayneF said:

That's true, it is less. The D600 is 24 megapixels and "only" 10 megapixels in DX mode. But it still is 3,936 × 2,624 pixels, not that shabby.

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Which is a lot less than it's native 6,016 x 4,016 in FX, and less than the D7100's 6000 × 4000 DX. As Rick (& BC) say - might as well just crop unless you gain 'physical' reach from the actual zoom effect on the lens...

WayneF said:

The D800 is 36 megapixels, and 15 megapixels in DX, 4,800 × 3,200.

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Which again is a lot less than it's native 7,360 x 4,912 in FX, and less even than the D7100's 6000 × 4000 DX (at 24MP).

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WayneF said:

Well, there are other considerations too. I just got back from a long vacation, and took 1500 pictures. On a D800, Raw is 40 MB, which would have been about double the size of my 32 GB memory card. So I shot DX when I could, and FX when I needed wide angle (a 24-120mm lens is anything but wide angle for DX). Still had room for a few hundred more on the card. And other than the wide angle, I see absolutely nothing wrong with the DX shots. It is a great option to have.

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I don't think anyone is saying that Wayne, and the image file size thing for data capacity is a different factor again, and is a valid point - we were just talking more about the benefit of the FX crop from a zoom (i.e. x1.5) effect and the image benefits. Space constraints is a whole 'nother kettle of fish...!

IMO - From an image quality/benefit perspective I think the crop factor function is a two-edged sword - you may gain some zoom benefit on FX cameras (I need someone more technical in the know to tell me if I am wrong or right on this), and the smaller file size benefit, but you sacrifice pixel density (i.e. IQ) for printing large images and/or limit your options to do more detailed cropping in post processing...

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Mycenius said:

IMO - From an image quality/benefit perspective I think the crop factor function is a two-edged sword - you may gain some zoom benefit on FX cameras (I need someone more technical in the know to tell me if I am wrong or right on this), and the smaller file size benefit, but you sacrifice pixel density (i.e. IQ) for printing large images and/or limit your options to do more detailed cropping in post processing...

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Any FX zoom benefit is towards wide angle. 24 mm on FX is 24mm and rather wide. The 24mm on DX is 36 mm effective comparison, really a normal view lens for DX, not wide angle at all.

But on DX, 200mm is 300mm effective view (compared to FX), and on FX, same lens is "only" 200mm. For that reason, DX seems pretty important to sports and wildlife photographers. But yes, FX could be cropped the same DX size, with maybe a few less pixels, but still a lot, and still same view as DX.

FX is a sensor 1.5x times larger dimensions than DX, so it has 2.25x area to have more pixels, or it could have larger pixels, or possibly a combination of both. Larger pixels are favored for their lower noise, which allows much higher ISO to be used. New sensors like the D7100 are improved and very good, but the D800 also is, even with 36 megapixels, still seems to lead (on usability of highest ISO).

So, you would buy FX for one or both of those reasons, more wide angle, and/or higher ISO with lower noise, or like the D800, possibly those two plus the resolution of more pixels (36 mp).

You would not buy FX for its telephoto performance, and not just because it can also do DX (and other) crops, but it can do that too. So more choices (but we cannot say DX could simulate FX).