Crop Factor Myth: Your Lenses are NOT 1.5/1.6/1.3x Longer

In last week's video on why 50mm Prime Lenses are NOT Portrait Lenses I had a ton of questions about the crop factor of smaller sensor DSLRs. This video will show you what is actually happening with your camera and dispel the myth that your lenses are magically longer with a crop sensor.

[sovernsectwarren]

You also have to multiply the apertures too as well so a 200mm F2.8 lens on 1.6X crop is actually a 360mm F4.5 lens in terms of image noise and background blur.

So distance perspective does change because you have to backup to obtain the same shot with a crop body as you would with a 35mm body or FF body.

[islanderiam]

Great video, this is a huge myth that so many mistakenly believe. A 50mm lens is still a 50mm lens regardless if it is on an FX or a DX format, it’s just being cropped on a DX camera and giving you a different ANGLE OF VIEW, but the focal length did not change.

BTW: What software are you using to record your screen? Thanks!

[insanelypositive]

thanks for the video...you mean to say if i use a full frame body on my 400mm lens, then crop it to 1.5 times in my laptop...it gives exact result like shot from a crop body of similar specs?

[wiscflank]

Good point, but how about demonstrating with a wide lens, with a lot of geometric deformation. Then we'll see that the crop sensor acts only on framing but the lens deformation remains the same. (And I think 50mm is a good portrait lens, but that's IMO)

[cazillo]

Its not 'equal' the image is being cropped as illustrated by the video.

[cazillo]

It should be equivalent, although you will have a dof change to get the same image fx vs dx.

[cazillo]

the point of the video is that the image area is being cropped, the lenses are not longer. You seem to have missed that point.

[TheErikBallew]

We are talking about the Same sized box, as he just did what the cropped sensor already does...

I doesn't zoom in or walk closer to the subject, it crops the image the lens if feeding it.

[Elusive_Pete]

To simplify. The comparison of cropped sensor vs full-frame only makes sense when it's a FF lens being used on both bodies.

An APSC 100mm on an APSC body would have roughly the same field of view as a 100mm FF lens on a FF body. The reason is because the optics are designed to squeeze the image onto the appropriate image circle.

Here is a way you may understand it easier: Image the sensor sizes are the surface area of a light on spot mode (APSC) and flood (Full frame). Each of those sources are to target a certain surface area. The APSC would take the portion of the FF image that it sees (60 percent of the image circle) and blow it up to encompass the entire sensor.
The field of view is effectively longer because it naturally zooms a part of the image.

On the flip side, the native lenses are designed to fit the same field of view onto a smaller sensor.

[cazillo]

Video is talking about how lenses change their focal length, not mp changes.

[kentak]

Erik, please explain why Nikon's tech specs for their 50mm lens says the DX Format Angle of View is 31.5 degrees and the FX Format Angle of View is 47 degrees? Is that not a narrower field of view for the DX format?

[mantalow]

Greg i think you are missing the point of what people mean with the magnification. it means the picure taken on a 1.6x crop sensor at say 200mm minus any movement or depth of field will be the same as one at 320mm on a full frame. For example my 50mm on my 1.6x crop bady will have the exact same field of view as an 80mm lens on a full frame.

[happyhc]

If I understand correctly, your point is at the same focal length and subject-to-lens distance, the perspective is the same for FX and DX. Or more generally, it doesn't matter what the sensor size is. Now I have trouble understand this (more extreme case): I have a Canon S95 which has focal length 6-22.5mm (crop factor 4.66), when shooting at 6mm it is not distorted that much, with a 6mm lens on FX camera I would imagine all kind of distortion. How to explain this?

[Guggle]

Greg u r missing just one point I think. when using a DX Body with 50mm lens u dont have to get as close as to the subject unlike when you use it on a FX body. Thus there s much less distortion when using a 50mm lens on a DX body...

[wladius]

For better comparison you could have included a picture at 75mm from FX (let's say from 70-200?) and compare it against the picture at 50mm from DX (since x1.5~75mm), the difference might be more clear that way.

[Anthelix]

Hi Greg ! Thank you for your video.
DX and cropped FX give you the same result because you are at the same distance to your subject.
But this video doesn't prove anything about the link or the lack of link between distance and perspective distortion.
You should try with a 50mm on DX vs 50mm on FX and 50mm on DX vs 75mm on FX without cropping, and with the same framing, which is what really matters on field.

[laztod]

It's pretty obvious to me that if I put a 70-200mm on my D3000 that its not going to become a longer lens physically...however because of the cropped censor using the centre portions of the lens, it gives the lens a longer feel optically, with further reach. It's in no way cropping the image as such resolution wise, just using a smaller portion of the lens elements. What you've shown us here is how using the cropped sensor mode in your D3S can be used to attain an OPTICALLY longer focal length.

[burnbarrelmedia]

Only if you "assume" the image is cropped. Cropping a FF picture is different than using a DX camera.

[WaltPark]

A more controlled test would be to use a ff body, a crop body, a zoom lens that can be used on both, and then frame the same pic from a stationary tripod, only using the zoom to adjust the the frame. Then show side by sides, with the exif info. Photography is about perspective and the one you give in this vid is from a FF pov, without considering the apsc pov.

[charlesmilton]

I am fairly new, and it took a while to understand the concept. As I understand it, the focal length of a 50mm lens is 50mm from the center of the curvature of the lens to the sensor. The amount of magnification is the same, regardless of the sensor size. When comparing a DX vs. FX, the DX image area is smaller - the angle from edge to edge of the sensor is more narrow. So a 50mm lens on a DX body had the field of view that would look about the same as an 85mm on a FX body. So if you want a "normal" field of vew using DX, you have to go to about 35mm to make it look like 50mm. The issue is that you get the characteristics of that 35mm lens including the distortion and lack of compression.