*Focal Length, Crop Factor and Field of View

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How does sensor size actually affect focal length?

Focal length?  Effective focal length?  Actual focal length?  Crop factor?  Do you get more reach with a crop sensor?  Is it equal to a longer focal length?  There are some misconceptions surrounding what happens when a lens is used on cameras with different sensor sizes.  Let’s have a look at the differences between a full frame, APS-C and micro 4/3 sensor.

We hear about crop factor, effective focal length or angle/field of view in 35mm or full frame terms.  Simply put, a lens’ focal length is the same no matter what camera it is on, as the focal length is a physical measurement, but the angle and field of view that a particular focal length provides varies depending on the size sensor the lens is projecting the image onto.

Focal length is measured by the distance of the focal point from the lens, or the distance from the principal point to the focal point more precisely. The distance from a camera lens’ focal point to its capture medium be it film or a digital sensor, with the lens focus set to infinity determines it’s measured focal length.

The field (or angle) of view that it provides depends on the size of sensor that is capturing the light from the scene in front of said lens which is where we get our “crop factor” or commonly referred to as “effective focal length.”

For our first test, I will be using the same lens on three different cameras.  First, a full frame Canon 5DII, next a Canon 40D (APS-C) and finally a micro 4/3 Panasonic GF1.  Keeping each camera in the same exact position on a tripod I want to explore two things.  Number one, the “crop factor,” how it crops into the image circle projected onto the sensor and the apparent magnification a cropped field of view provides, and number two, the difference in depth of field at the same aperture in these three different sensor formats.

In terms of a full frame or 35mm standard angle/field of view with any particular focal length, a full frame presenting a value of 1, a Canon APS-C sensor provides a crop factor of 1.6x and the micro 4/3’s sensors provide a crop factor of 2x.  To determine the crop factor, simply divide the longer side of the full frame sensor (36mm) by the long side of whichever sensor you need to determine the crop factor for.  For instance, based on the measurements for a Canon APS-C (22.2mm) it is 36 / 22.2 = 1.621… or more simply 1.6x.  To start off with, here is the physical size of each sensor we’re working with in relation to each other.

Full frame, APS-C and m4/3 sensor sizes

Using my 35mm f/1.4 lens on the 3 cameras all following images are sized to fit into a 500 pixel wide file.  As we are not exploring resolution or native file size on this one, we won’t be looking at 100% crops compared with each other or anything, so this should be pretty straight forward.  Let’s begin.

First, we have our field of view.  All shots are at f/5.6 taken with the 35mm f/1.4 Canon lens from the same exact location on a tripod roughly 6 feet away from the point of focus.

Full frame field of view 35mm:

This is what 35mm looks like on a full frame camera.

APS-C field of view = 56mm equivalent:

This is what 35mm looks like on an APS-C cropped frame camera.

And finally the micro 4/3 field of view = 70mm equivalent:

This is what 35mm looks like on a micro 4/3 camera.

Pretty substantial difference in field of view.  All of these show a 35mm focal length, but differ largely regarding field of view provided.  The flowers in the center of the frame fill a lot more real estate the smaller the sensor.  The magnification, based on focal length, from subject to focal plane, is unchanged, but the magnification of the subject created by the cropping of the image circle is increased.

Now, let’s look at depth of field.  Same set up but adjusting the aperture of the lens to f/1.4 to emphasize a narrow DOF:

Full frame at f/1.4:

Full frame depth of field at f/1.4 = 9″

APS-C at f/1.4:

APS-C depth of field at f/1.4 = 6″

Micro 4/3 at f/1.4:

Micro 4/3 depth of field at f/1.4 = 4″

Now, I’d always assumed that the larger the sensor, the shallower the depth of field.  This is true, but only when the subject is framed the same way which requires one to change the focal length to achieve the same angle of view from a fixed location, or alter the distance between the subject and camera which will change the angle of view, but can allow for your subject to occupy the same physical space in your frame while relatively “framing” your subject as it may appear on a different format.  For instance, the above set of pictures were all taken from the same exact location roughly 6′ away from the flower in focus to demonstrate the field/angle of view on the different cameras.  To determine the acceptable area in focus I used the online DOF calculator.  (bookmark it, it helps out quite a bit)  Inputting my aperture as set for the recent 3 pictures above at f/1.4 and the subject distance at 6′, according to the online DOF calculator, the different sensor sizes gave me this information:

Full frame – near limit(in focus): 5.65 ft    far limit (in focus): 6.4 ft.    total area in focus: .75 ft (9″)

APS-C  –  near limit: 5.77 ft    far limit: 6.25 ft     total area in focus: .47 ft (just under 6″)

Micro 4/3 – near limit: 5.82 ft    far limit: 6.19 ft     total area in focus: .37 ft (a hair over 4″)

The final question I want to look at regarding the cropping of a lens’ image circle is how that magnification affects distortion.  If I’m using a 35mm lens on a 2x crop factor micro 4/3 camera, I have the same angle of view as I would with a 70mm lens on my full frame camera, but would I see the decrease in barrel distortion I would going from a 35mm lens to a 70mm lens on my full frame?  Let’s see.  For this comparison, I’m getting rid of the APS-C to simplify things.  This is between the 5DII and the GF1.

Using my trusty Martha Stewart self healing cutting surface, which I mounted to the wall by way of some Scotch tape®, and the 24-70f/2.8, zooming the lens while on the GF1 to 35mm (70mm FOV equivalent) and the 5DII shot at both 70mm and at 35mm (and cropped the 35mm shot to the same frame as the GF1 @35mm/70mm fov), I wanted to see if the center of the lens exhibited the same characteristics as a 35mm focal length or a 70mm focal length for the GF1.

First, the 5DII @70mm:


the GF1 @ 35mm (70mm equivalent FOV):

and finally, the 5DII @35mm and roughly cropped to match the frame from the GF1:

My framing is slightly off, I know.  What I can see though, is when the 5DII is set to 35mm and then the image is cropped, it behaves just like the GF1 does at 35mm effectively cropping to a 70mm field of view by way of the sensor showing the same performance and distortion control.   At 70mm, the 5DII shows a slight pincushion distortion ” )  ( ”  while at 35mm cropped to the same field of view as the GF1 it shows a slight barrel distortion ” (  ) ” as does the GF1 at 35mm.  This makes sense when you consider that the 35mm focal length is the same no matter what cropping takes place, the only thing that changes is the field of view as the smaller sensor uses only the center of the lens’ image circle as shown here:

Please excuse my horrific set up shot here.  I hadn’t really anticipated using it like this.  It is however the full frame from the 5DII shot at 35mm before I cropped into it as shown above.  The white circle represents the full image circle from a full frame compatible lens.  The lighter, larger yellowish rectangle represents the full frame’s use of that image circle while the darker, smaller portion in the center is the area that the micro 4/3 sensor “crops” to and uses.  This is why, even though it has the same field of view as a 70mm lens would have on a full frame camera, it is utilizing the center of a 35mm lens and subject to any optical distortion that the center of the lens has functioning as a 35mm field of view on the full frame camera.  So, in short, the “crop factor” does give extra reach by way of this crop, but it does not act the same way as a lens twice the focal length would on a full frame camera in regards to optical distortion.  Some argue that they would rather have a full frame and just crop it themselves after the fact.  That is fine and dandy, but where that can get troublesome is when resolution comes into play.  Cropping into a 12 megapixel image file captured on a full frame for example to the same field of view as the micro 4/3 sensor provides already at 12 megapixels, is going to suffer quite a bit regarding overall resolution as you are taking those 12 million pixels and throwing nearly 70% of them away leaving you with a 3 or 4 mega pixel image file where you would start with a 12 megapixel file from the smaller, more pixel dense m4/3 sensor.  So, a smaller sensor can offer a benefit to those looking to maintain resolution while gaining “reach” by way of cropping the image circle.  While you do get a cropped portion and the benefits to the sharper area of the center of a lens, it still is subject to any of the optical characteristics of that shorter focal length.

So, while you get reach by way of this crop, you are still using the same focal length, you’re just getting an altered field of view.  You artificially get “reach” by way of this crop, but lose out on the wide end of the scale when using a crop sensor camera.  I say artificially because you’re still using a shorter focal length and do not necessarily gain the same distortion characteristics that longer focal lengths employ.

I hope this has helped define crop factor for you, I know that going through this exercise has certainly helped me understand it more clearly.

32 thoughts on “*Focal Length, Crop Factor and Field of View”

  1. Thanks for this piece, Tyson. It helps me a lot because it is something I had thought about over the last few weeks since using legacy lenses on my GF1.

    Indeed, someone DM’d me on flickr a few weeks back asking if a wide-angle lens still displayed wide-angle characteristics on M4/3. My immediate answer was “no, it doubles the focal length”.

    This was not the answer they wanted and so a discussion thread was started on the MFT + legacy lenses group which can be found here:

    http://www.flickr.com/groups/1084614@N23/discuss/72157623448900952/

    I read this discussion with interest at the time and felt that on the whole it supported my thinking.

    However:

    Immediately after this I started using my Canon 24mm f/1.4 on my GF1 a lot more and I was noticing images that contradicted what I had said, for example:

    and

    In my (very unqualified and non-professional) eyes despite the fact that they were effectively shot at a focal length of 48mm they clearly exhibit wide-angle characteristics.

    It is a relief to read your article then which explains exactly why i’m seeing this and also gives me additional knowledge as to why the DoF effect seems so much greater with the smaller sensor.

    Thanks again, fortytwenty

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  4. Hi

    just thought i’d add something else. You start with the question:

    Do you get more reach with a crop sensor?

    and come to the conclusion of:

    So, while you get reach by way of this crop, you are still using the same focal length, you’re just getting an altered field of view. You artificially get “reach” by way of this crop, but lose out on the wide end of the scale when using a crop sensor camera. I say artificially because you’re still using a shorter focal length and do not necessarily gain the compression or distortion control that longer focal lengths are usually capable of although

    firstly I think that you get exactly the same angle of view between (for example) a 100mm lens on a full frame and a 50mm on a 4/3 sensor (both mild telephoto) what you don’t get is the same DoF unless you have the aperture the same diameter. You can try this yourself if you like, but I’m sure you’ll find that the images are identical (more so if you keep aperture diameter the same). A 50mm at f2 will be the same as a 100mm at f4 (although the 35mm full frame will have a slightly wider aspect ratio, but that’s another problem altogether…

    secondly I would like to ask what is the compression or distortion you are talking about? If DoF related then that’s solved by matching aperture

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  5. 4020- Glad it helped. It helped me too. I’d based all of my assumptions on crop performance based on what I’d heard and read other folks talking about. By actually spending the time to do this I fine tuned my understanding.

    Chris- with a 50mm lens on a 4/3 (or micro 4/3) sensor you do get the same field of view as you would with a 100mm lens on a full frame. Aperture aside, when speaking of compression and distortion, for all intents and purposes, when using a 50mm lens to gain a 100mm field of view on a 4/3 sensor, you are still seeing through the center of a 50mm lens, not a 100mm lens. This is why I wanted to look at the performance on the GF1 cropping the center of the image circle and exhibiting the same distortion at the 70mm equivalent (at the 35mm focal length) as my 5D did shot at the 35mm focal length in the same cropped center of the 35mm image circle. So on the GF1, I got a 70mm field of view with the same distortion and compression of the center of a 35mm image circle. This is what I was doing with the grid at the end. If you look at the lines, on the 5D, at 70mm it shows slight pincushion distortion and at 35mm, slight barrel distortion. The GF1 at 35mm (70mm equivalent field of view) it shows the same barrel distortion that the center of the 5D frame did at 35mm, not the pincushion distortion of the actual 70mm focal length. This is why I make the comment about artificial reach. Maybe artificial is not the correct term, but while you gain the “reach” by way of the crop, you do not get the same scene/subject compression that a longer focal length would provide from the same physical position, and you are subject to any distortion the lens may exhibit in the center portion of the image circle.

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  6. Hi

    The GF1 at 35mm (70mm equivalent field of view) it shows the same barrel distortion that the center of the 5D frame did at 35mm, not the pincushion distortion of the actual 70mm focal length.

    maybe, but then every lens has different distortions … not sure I see what you’re driving at here

    you do not get the same scene/subject compression that a longer focal length would provide from the same physical position

    I disagree, and would be glad if you could show any example to support this.

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  7. Hi Chris,

    Every lens having different distortions is beside the point made. My point was that the 35mm focal length used on the lens I was using for this test, whether or not its image circle is being cropped exhibited the same distortion in the center of the lens for both the full frame camera and the m4/3 camera. While it cropped to a 70mm field of view, it did not provide the same distortion as the same lens at 70mm, ultimately showing me that when cropping by way of a small sensor, I’m still getting characteristics of the wider focal length, just the center of the lens at that particular focal length. It was merely done to prove to myself that when we talk about “crop” giving us more reach, we’re still getting the center portion of a frame from a shorter focal length and subsequently subject to any distortion the center of the frame may exhibit be it barrel or pincushion which tends to be different in many lenses of the actual focal length when looking at a cropped frame/field of view equivalent. In this case, using the 24-70 lens at 35mm and at 70mm, I saw barrel distortion at 35 on both the full frame and the m4/3 (70mm e-fov) while at 70mm I saw pincushion distortion. Not surprising really, but I wanted to see it for myself.

    I guess regarding scene and subject compression, I will have to do another test as I guess I’m not accurately describing myself and honestly, speaking from assumption (we all know what assuming can do). From say a fixed position 6′ away to the point of focus (or 10′, or 20′, etc) a shot using a 300mm focal length should exhibit a different compressional relationship between subject and background all other variables staying constant than would a 30mm focal length shot from the same location based on variance in depth of field, etc no? Perhaps I am wrong and should certainly follow up with a test, but simply put, as the focal length of a lens increases, the depth of field gets shallower and visually compresses space, making objects in the scene appear closer together than they actually are. This is the way I understand compression from an optical standpoint and the standpoint that I was referencing. Cropping into the frame taken with say a 30mm focal length to match the 300mm frame, in my understanding, we would see a very different compression assuming all other variables were constant.

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  8. Hi

    thanks for taking the time to address my questions.

    Every lens having different distortions is beside the point made.

    but if I’m summarising you right:

    My point was that the 35mm focal length …exhibited the same distortion in the center of the lens for both the full frame camera and the m4/3 camera. While it cropped to a 70mm field of view, it did not provide the same distortion as the same lens at 70mm, ultimately showing me that when cropping by way of a small sensor,

    you essentially say that the difference is that the distortions of the 35mm when used as a cropped lens on a 4/3 camera don’t have the same distortions as a 70mm on the full frame.

    no?

    I’m still getting characteristics of the wider focal length,

    or you could be getting the distortions of that lens over another. You’d need to try some other 35mm lenses to be sure that they all have the same barrel distortions.

    It was merely done to prove to myself that when we talk about “crop” giving us more reach, we’re still getting the center portion of a frame

    which I would have thought was the meaning of what I get when I crop an image. If I print a full frame image out to 10×8 , and then crop it back to a 5×4 I’ll have the same effect.

    cropping

    from a shorter focal length and subsequently subject to any distortion the center of the frame may exhibit be it barrel or pincushion which tends to be different in many lenses of the actual focal length when looking at a cropped frame/field of view equivalent.

    yes .. and so it appears that you seem to be saying the same as me, different lenses have different distortions.

    no?

    I guess regarding scene and subject compression, I will have to do another test as I guess I’m not accurately describing myself and honestly, speaking from assumption (we all know what assuming can do).

    I’ll be doing that test on the weekend, I only have film for full frame (no 5D as at now) so I’ll be testing:

    50mm on G1 vs 100mm on Full frame
    100mm on G1 vs 200mm on Full frame
    150 (using a zoom) on G1 300mm on full frame

    all at equal apertures (diameter) and at “normal” settings too

    I’ll post them on my blog

    seems like a reasonable way to get out of the house at easter 😉

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    • Hi Chris,

      I love the conversation. It’s why I started the blog.

      You’ve said:

      “or you could be getting the distortions of that lens over another. You’d need to try some other 35mm lenses to be sure that they all have the same barrel distortions.”

      But I wasn’t looking to test a variety of different 35mm lenses or lenses at the 35mm focal length. I wanted to show 1 lens’ performance on different sensors and how cropping into the image circle of any one given lens performs. I think this may have gotten out of hand as I merely wanted to prove that the center of the lens, whichever lens you happen to use, by way of a crop will exhibit the same characteristics in the center regardless of which camera you have it on as obvious as it seems.

      “you essentially say that the difference is that the distortions of the 35mm when used as a cropped lens on a 4/3 camera don’t have the same distortions as a 70mm on the full frame.

      no?”

      Yes, they do not exhibit the same distortion as they are two different focal lengths that happen to have the same field of view by way of the crop factor. This being one of the situations many folks not used to the concept of crop factor seem to have a hard time ‘getting’ and I just wanted to put it into a simple example.

      “or you could be getting the distortions of that lens over another. You’d need to try some other 35mm lenses to be sure that they all have the same barrel distortions.”

      Again, this is beside the point I was making. I wanted to look at one lens for the sake of determining how that one particular lens, regardless of which lens it was, performed when used with different sensor sizes / a cropped image circle. Different lenses will provide different distortions even different lenses at the same focal length. There is no uniform distortion assigned to focal length. Different lens designs can adjust for rectilinear distortion, or amplify it (like a fisheye for instance). But I’m not sure if that is what you are implying or are just saying that I should run the same test I’ve done here using one lens, with others to see if by way of a crop it is consistent with my argument?

      “which I would have thought was the meaning of what I get when I crop an image. If I print a full frame image out to 10×8 , and then crop it back to a 5×4 I’ll have the same effect.

      cropping”

      Exactly. Putting it into a readable format helping those of us that may not quite grasp that was why I did this. I had always assumed this, but never done the test to visually see it in first person. Merely filling in the blanks by showing examples.

      “yes .. and so it appears that you seem to be saying the same as me, different lenses have different distortions.

      no?”

      Yep. But this conflicted a little with your statement from above which is what had me a little confused.

      I look forward to your blog post. If you wouldn’t mind, for the sake of continuity, could you link it in the comments here so that anyone stumbling across this in the future can follow it?

      I appreciate the conversation and like the clarifications through the back and forth. It is helping me be more concise in my semantics. Easter weekend might find me looking for a bit of outside testing myself 🙂 Here’s hoping my corner of the world drys out a bit and I get a little sun.

      Cheers,

      Tyson

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  9. Hi Tyson

    I was the one who started the thread on the Flickr group that Fortytwenty referred to.

    I also shared the idea that a lens had a focal length and that this won’t change (and this at least still holds true). The perspective distortion you get with a lens would be the same when recorded on different sized sensors. What would change is the size recorded, the crop factor.

    However, people try to get as close to the subject as possible as it preferrable not to have to crop an image. If someone wants to take a head and shoulder protrair with a 50mm lens, they would have to move closer if the lens in mounted on a full frame, and they would have to step back when the lens is on a M4/3.

    Moving closer of further away from the subject is what affects the perspctive. The same happens with our eyes, as things look different as we get closer to objects.

    This is also the reason that when taking portrait, people use a lens that allows the to get further away so that the result puts less emphasys on the nose.

    Cheers

    Cosimo

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    • Hi Cosimo,

      Thanks for commenting here as well.

      You mention:

      “I also shared the idea that a lens had a focal length and that this won’t change (and this at least still holds true). The perspective distortion you get with a lens would be the same when recorded on different sized sensors. What would change is the size recorded, the crop factor.”

      Yes, by size it is the amount of the image circle that is “cropped”. I think the biggest confusion that accompanies this conversation is when we use terms like “effective focal length” or when we would make a statement like “a 24mm lens will be a 48mm lens on a 4/3 sensor” while the field of view would be that of a 48mm lens, semantically it can be confusing to some as it can be read like it would act like a 48mm lens would on a full frame camera in all ways when that isn’t entirely true. This is what we are all hoping to iron out I assume.

      “However, people try to get as close to the subject as possible as it preferrable not to have to crop an image. If someone wants to take a head and shoulder protrair with a 50mm lens, they would have to move closer if the lens in mounted on a full frame, and they would have to step back when the lens is on a M4/3.

      Moving closer of further away from the subject is what affects the perspctive. The same happens with our eyes, as things look different as we get closer to objects.

      This is also the reason that when taking portrait, people use a lens that allows the to get further away so that the result puts less emphasys on the nose.”

      For my test here I wanted to eliminate the variable of framing by way of altering the distance between the subject and camera to account for the cropped field of view, but yes, I agree. The one thing that I am interested in and Chris’ upcoming blog post should help me understand is the affect of focal compression from a fixed location. The same shot from a fixed distance with varying focal lengths and the relationship it has with compression compared to cropping images from varying focal lengths from that fixed position to match a longer actual focal length. Doing this with different sensor sizes adds a new element to it, but when we understand how a cropped image circle affects the image captured, when included into a test of this nature, should provide consistent results with what we’ve come up with here.

      Thanks for stopping in and helping continue the conversation.

      I am getting quite a bit from all of this.

      Cheers,

      Tyson

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  10. Great write up! Regarding pincushion/barrel distortion, you also need to consider what the image processing engine does to correct these. I mention this because with the Panasonic LX3 there was some evidence that lens distortion correction was even applied to RAW files.

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  12. Hi Blork,

    Thank you. It is a good point and one I will have to look into. In regard to the LX3, I believe that the distortion correction was enabled because of the integral lens and it’s ability to communicate with the camera and processor. In this case I’m not sure if the GF1 would be able to anticipate and therefore correct for distortion because I’d removed any electronic connection between the body and lens, not to mention it was a canon lens as well. It didn’t know what to correct for essentially, and as far as I am aware, the in camera processing isn’t quite to the point where it can recognize distortion purely by itself quite yet. I may be wrong. I know that with proprietary combinations camera companies have been able to adjust for distortion, and in canon’s case they have an “illumination” adjustment as well that for any given canon lens on a newer canon body, it can help with vignetting during jpeg compression, etc but I’m not too sure about the ability to do so for other lenses from other manufacturers and the like. Thanks, and if I can find out definitively, I’ll check back in.

    Cheers,

    Tyson

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  13. Sorry Tyson, I haven’t been back to see your answer until today.

    I am further confused. I received this morning a 28mm lens which I have fitted with an adaptor to my E-PL1.

    The first thing I noticed, was that it seemed to actually behave like a wide lens, and certainly not like a standard 56mm lens.

    This actually contradicts what I wrote on my previous post on here.

    I believe (and I will need to speak to a friend of mine who understands physics, of which optics is a branch) and confirm. But at the moment I am tempted to think that the factor which affect the perspective are two, and they work together.

    I think these would be the focal length (how the rays enter and leave the lens) and the distance from the subject. It could be (but really I don’t know) that perhaps a 24mm lens would have a perspective compression which is similar to something in between 24 and 48. Maybe a third of the way, like a 32mm equivalent.

    I would also like to point out, that when I speak about perspective (I am not really that good with technical terms, so I might use the wrong one) I do not refer to barrel and pincushion distortion, but to hot things appear flattened when using a long lens, and how they appear deep when using a wide one.

    I suppose another test would be to take a few object of the same size, placed at different distance and photograph them with a 50mm lens on a M4/3, and with a 100mm lens on a full frame.

    This should result in an image of the same size. But if the difference between the first object and the one further away is larger in the wide lens, this would mean that the lens is not equivalent in focal length.

    Did I make that clear? I feel words are failing me.

    Regards

    Cosimo

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    • Hi Cosimo,

      Simply put, from my tests here, while you will gain a 56mm field of view with the 28mm lens on the EPL1, you will still be seeing through that 28mm lens albeit just the center portion. This said, the center of the cropped image circle is still subject to any distortion that lens exhibits.

      Briefly, pincushion distortion is when it appears that the center of the lens is pulling back in as if a pin was pushed into the center. Like this (kinda) ” ) ( ” where the parenthesis would represent the edges of the frame. Pincushion distortion is more common on longer focal lengths. Barrel distortion is the opposite, where the center of the frame appears to be bulging out ” ( ) ” more common on wide angle lenses. I hope this helps.

      Cheers,

      Tyson

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    • I have no problems whatsoever man. I like bouncing back and forth. I just had a read through and appreciate the detail you’ve gone into. I’d highly suggest anyone looking at clarifying respective dof and sensor/film size to read through the above link.

      One thing I had done here that differed from your most recent post was using the same exact lens on all three cameras from the same location which when keeping with your explanation of focal length over aperture diameter equaling the ratio determining the dof, lined up with my understanding, I’d just not applied the equation. Where a proprietary micro 4/3 lens is physically built smaller to accommodate the smaller sensor and image circle, it’s ratio is still consistent by way of physical construction as a 20mm lens is still a 20mm lens and f/2 for instance is still f/2 for that measured focal length, just built in accordance to actually project for the smaller image circle. Now this is where I become a bit clouded, optically speaking, are these lenses capable of being built to exhibit similar optical distortion to that of a focal length twice the length on a full frame equivalent for instance? (I assume so as the focal length is, in this case, relative to sensor size and for the sake of “standard” a measurement of the diagonal.) A 20mm full frame lens is usually pretty distorted, even in the center. So, when cropped by a 4/3 sensor, it’s still subject to a fair bit of distortion in the center of that lens. (But, would a 10mm m4/3 lens be able to exhibit the same optical distortion as the 20mm lens would, not a 10mm focal length built for a full frame?) While I haven’t done anything to test the distortion on the 20mm Lumix lens (built for the micro 4/3 system for those not familiar), I feel like the images I’ve gotten from it are more consistent with a standard focal length, distortion wise, not an ultra wide angle. So many questions… We just need to find someone willing to fund our tests 🙂

      Thanks for coming back to this Chris. I look forward to your future blog posts.

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  15. I’ve been shooting for years with no formal photography classes and never truly understood the crop factor. I’ve had 7 or more high end cameras (Getting the Mark II very soon!) and never really understood this because most people over explain using tech terms and formulas that you would only learn having been formally taught photography. I just knew “closer makes fuzzy backgrounds”. 🙂 I can’t thank you enough for how well written this is and taking the time to share it. (The pictures almost explain it alone!).

    Thank you so much,

    Eric

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  20. Does this mean a 35mm lens on a 4/3 has a magnification of square?
    Another world a 200mm 35mm lense is 4x magnification on 35mm camera but a 16x magnifiction on 4/3 (4 to power of 2 ). And a 50mm 35mm lense if it is 1:1 magnification on 35 mm camera will only be 4x magnification on 4/3 camera (2 to power of 2). am I correct? Do you square the magnification of 35mm lens on 4/3 camera?

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  21. After looking at it again I found my mistake. I beleive you use just 4x formula for any 35mm lenses if used on 4/3. another word a 50mm (1:1 magnification of 35mm camera() will hace 1×4=4 times mag on 4/3 camera and a 100mm 35mm lens will have: 2×4=8 times mag on 4/3.
    Right?

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    • Hi Essi,

      I’m not exactly sure. Are you trying to determine the crop factor, or ability to enable 1:1 “macro” magnification? I’m not quite picking up the “4x formula” but I’ll be the first to admit my relative density from time to time as this may be inquiring about something over my head and beyond my mathematical paygrade 🙂

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  22. This is an amazing article. Thanks a bunch for the good read.
    I started getting into the micro four thirds format, with the GF1, and I went with legacy lenses instead of the costly and few native autofocus only lenses. As I prefer manual focus to autofocus, I always did wonder if I ended up getting less or more distortion by using the center of the legacy glass. Legacy lenses are designed to fill full frame sensors (film back in the day) so I always thought that even though legacy lenses over resolve the micro four thirds sensor, that they would reduce distortion.
    It is very interesting to see that distortion is still present even though you are using the “best” part of the lens, the middle center.
    Thanks again.

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    • Hi Anthony,

      Thanks for taking the time to comment. All technical specs, optical formulations and resolution tests aside, I have to say, I love that the current digital reality enables so many of us to utilize so many different combinations. To me gear is in no way a necessary factor when making a good image, but by being fun and enabling a multitude of possibilities it can give a photographer tools to help spur creativity and enjoyability. If we’re not getting paid to shoot, it better at least be fun right!?

      Cheers,
      Tyson

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  23. Pingback: *Everything you need to know about digital photography. Two years of tips, tricks and various freebies, revisited. «

  25. Wonderful read… Thanks for sharing your knowledge… I got to know a lot about photography just by going through most of your posts… Especially the lens, aperture, and trifecta ones…

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