Does having a crop sensor camera really "magnify" anything?

[realdereal]

I'm hearing several different views on this anytime I try to find the answer.
Can someone tell me plainly if there is truly any -actual- reach in a crop sensor,
or if it just truly the same image with the sides cut off of a full frame image.

So many say the conversions of a lens from crop to full frame etc. But if you just
cropped the image in post, would you not then find the same exact image.

Is there truly a reach advantage with a crop sensor? Or is it just our
perception.

[AlwaysOnAuto]

I suggest you read some of the fine tutorials on this site that discuss this subject.

[xpatUSA]

I'm hearing several different views on this anytime I try to find the answer.
Can someone tell me plainly if there is truly any -actual- reach in a crop sensor . .

Plainly, no, there is not truly any actual [more] reach in a crop sensor. Depending on what is meant by "actual reach", I suppose.

. . or if it just truly the same image with the sides cut off of a full frame image.

A better way to look at it, IMHO.

So many say the conversions of a lens from crop to full frame etc. But if you just
cropped the image in post, would you not then find the same exact image.

I've never liked the word 'crop' any more than I like the 35mm equivalent numbers dished out for lenses. It is surprising in this day and age when full-frame lenses and DSLRs are in the minority, yet the literature is still being published as if we all started out with 135 format SLRs and have to be constantly referred back to those archaic times in order to 'understand' the later stuff.

A bit like my early hobby learning in 'modern' i.e. solid state electronics, where anything about transistors was always explained by tube (valve) analogies which were of no use to me, having learned nothing about them.

rant over

[chauncey]

Using it narrows your field of view giving the impression of magnification.

[NorthernFocus]

Nowadays with so many choices in bodies out there, you can't rely on many common generaliztions any more. There is no simple answer unless you compare two specific camera bodies.

Maybe the easiest way to think about this topic is to consider how many megapixels an image contains. More megapixels equates to more detail which compares to magnifying an image. So if shooting with a "cropped" sensor results in a higher resolution image than shooting the same image with full frame and then cropping to the same end result, then the cropped sensor does have the same net result as a longer lens (aka more magnification). For example:

- Let's say you stand in the same spot with a full frame Nikon D4 and cropped body Nikon D7000, each with a 300mm lens. Both cameras have 16MP sensors. If you take the same shot with both cameras then crop the D4 image to match the composition of the D7000, the result would be a 7.1MP image compared to the same content but at 16MP for the D7000. So in that case, yes, the D7000 has the effect of "magnifying" the image aka more "reach".

- On the other hand, if you conduct the same exercise above with a 36MP D800 and the D7000, the cropped D800 image would be 16MP. So you end up with exactly the same resolution as the D7000. So no effective magnification.

[Donald]

Please do look at the tutorials on this site, as suggested above. It explains the whole thing very clearly.

I actually find the 'discussion' that goes on about a lens giving you 'x' on a crop frame body and 'y' on a full-frame body' a complete waste of time. Unless I have both a full frame and a crop frame body, the point is meaningless. On my crop frame body, I get what I get from a lens. The fact that someone with a full frame body using the same lens would get a different field of view, is irrelevant to me.

[Adrian]

There is a degree of real world relevance though Donald. For example, my wife and I travel with a Canon 5DIII full frame and either a 7D or 70D crop body. We share a bunch of L lenses - so if we are out an about we can go wide or go long simply by choosing which body/lens combo. It's horses for courses: the 5DIII is much better in low light and for wide angle. If we want to pull in birds in flight, the 7D or 70D with a tele is a better bet than the 5D with the same lens.

It seems to me that at times it is handy to have say 24m pixels on a smaller sensor than the same number on a bigger sensor. At one time I thought naively that a full frame was an upgrade, but I quickly realised they are two different tools.

Doesn't the Nikon 810/800 actually do both in some interpolated way?

Adrian

[JR1]

Please do look at the tutorials on this site, as suggested above. It explains the whole thing very clearly.

I actually find the 'discussion' that goes on about a lens giving you 'x' on a crop frame body and 'y' on a full-frame body' a complete waste of time. Unless I have both a full frame and a crop frame body, the point is meaningless. On my crop frame body, I get what I get from a lens. The fact that someone with a full frame body using the same lens would get a different field of view, is irrelevant to me.

Good reply

[dje]

Doesn't the Nikon 810/800 actually do both in some interpolated way?

Adrian, I'm not sure about the D810 but my FF D610 has what they call a DX mode. This crops the image down to APS-C sensor size and is intended mainly for the situation where you are using a DX lens on the FX camera. I don't know whether it does any interpolation to upsize the cropped image but I must test it out some time.

Dave

[NorthernFocus]

....Doesn't the Nikon 810/800 actually do both in some interpolated way?...

The 800/810 has a DR crop mode that simply captures a portion of the image off the sensor the same size as a DX sensor and ignores the rest. There is no interpolation involved. So you get a 16MP image rather than the full 36MP full frame image. I frequently shoot in DX mode.

[Donald]

... my wife and I travel with a Canon 5DIII full frame and either a 7D or 70D crop body.

And that is exactly my point, Adrian. You are in the category of having both types of body, so the question is relevant for you.

[DanK]

Kristen,

I don't consider this question a waste of time. Sensor size has important effects.

I suggest that you separate two terms. "Magnification" really means how large the image on the sensor is, compared to the size in real life. This is completely unrelated to sensor size.

When people talk about magnification from smaller sensor sizes, they are talking about something else: how big the image is, not in absolute size, but relative to the area captured by the sensor. This is how I use the term "reach." In other words, given a particular focal length of lens, a subject that fills the frame on a crop sensor camera will not fill the frame on a full frame camera. The image is the same size, but it fills less of the larger sensor.

Some people say, well, you can just crop the image from the full-frame camera and get the same thing. that is only true if the pixel density is the same, which it usually is not. When the pixel density is higher on the crop, you will get more pixels on the subject with the crop than with a FF.

So, if you are thinking in terms of the frame (how far away can I be with a given lens and still fill the frame?), the answer is "farther away with a crop sensor camera." You can offset this with a FF by using a longer lens.

this is why many wildlife photographers prefer crop-sensor cameras.

[Donald]

I don't consider this question a waste of time. Sensor size has important effects.

Just for the purposes of clarification and the avoidance of doubt, I never suggested that Kristen's question was a waste of time. As you will read if you look at my post, I pointed Kristen towards the tutorials on here as a source of information to understanding the issue.

[benm]

Adrian, I'm not sure about the D810 but my FF D610 has what they call a DX mode. This crops the image down to APS-C sensor size and is intended mainly for the situation where you are using a DX lens on the FX camera. I don't know whether it does any interpolation to upsize the cropped image but I must test it out some time.

Dave

On a D800 the DX mode simply crops the image, thereby using fewer pixels. The only advantage, besides file size, is you get a slightly faster frame rate.

[JR1]

Just for the purposes of clarification and the avoidance of doubt, I never suggested that Kristen's question was a waste of time. As you will read if you look at my post, I pointed Kristen towards the tutorials on here as a source of information to understanding the issue.

+1

[DanK]

Just for the purposes of clarification and the avoidance of doubt, I never suggested that Kristen's question was a waste of time. As you will read if you look at my post, I pointed Kristen towards the tutorials on here as a source of information to understanding the issue.

No offense intended. I was responding to your third sentence, which I apparently misunderstood.

[DanK]

Kristen,

I just thought of another way to explain this. suppose that you held a magnifying glass over a piece of white paper and obtained an image of something that is 1 inch (2.54 cm) square. Now, suppose that you hold the glass so that it doesn't move, and someone else replaces the paper with a smaller piece. What would happen to the size of the image? Nothing, of course. However, the image would take up a larger share of the smaller piece of paper.

This is exactly analogous to the difference between sensors differing in size.

The complication is just that in the world of digital photography, the smaller sensor usually crams more pixels into a square cm.

[William W]

. . . if you just cropped the image in post, would you not then find the same exact image.

No.

Similar but not the exact same.

The differences might not be relevant to some people and might be relevant to others. And that relevance may also depend upon each shooting situation and also what cameras are used for the comparison. Much of this is about pixel density as Dan mentioned.

Donald makes a very good point - if you have only ONE camera FORMAT and/or are not considering more than one format, or maybe changing formats, then likely the answer is not of much practical relevance to you.

I have a dual format DSLR kit, I always have because that was a purposeful strategy when I changed over my gear from Film SLR cameras: one reason was so I could purposely leverage the 'reach' advantage of lenses with an APS-C Format Camera and more generally, at any one time carry fewer lenses in my bag.

WW

[ajohnw]

The extra reach is a bit missleading. From comments that kick about it's easy to get the impression using m 4/3 as an example as the sums are easier, crop factor 2, that say 300mm on m4/3 is the same as 600mm on full frame. Unfortunately it isn't for a very simple reason - the resolution of the lens that is used. Say both lenses had top notch full frame lens performance - reckoned to be able to resolve 45 line pairs per mm on the sensor. The full frame sensor is bigger which basically means it has more space for lines and will because of this resolve finer detail, very loosely speaking twice as much.

In practice "top notch" m 4/3 lenses get to more like 55 line pairs per mm according to tests so things aren't as simple as that but they are when full frame lenses are used on crop bodies. In loose terms it is possible to take a crop view out of a full frame one with software. Comparing pixel densities is difficult. Resolution tests charts shown in some reviews are always black and white. Colour images are interpolated from a block of 4 pixels. There is no saying just what the software used will do when the sensor information is converted to an image. Some people have been know to think that cameras know when they are photographing a test chart - after a fashion they are probably correct - the software probably does this automatically as it's working on a black and white image.

To be honest my personal view is that there are cameras about of all types that have far more pixels than the optics can really make use of.

John
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