What impact does lens magnification have in this example?

[Colin O]

This may be an obvious one, but I just can't get it straight in my head.

 

Say I take a photo of a billboard using a 24-Megapixel full-frame camera with a 300mm lens, and then, from the same position, take another photo of the billboard using a 24-Megapixel APS-C camera with a 200mm lens. Seeing as the two images are taken from the same position and the lenses have pretty much the same angle of view (in combination with their respective sensors), the two images should be pretty much the same, but, all other things being equal, what impact (if any) does the higher magnification of the 300mm lens have on the first image compared to the second?

[lornesunley]

<p>Not too much effect, other than that introduced by the quality of the lens.<br>

Both have the same magnification - angle of view - so there should be no impact on the image.</p>

[Colin O]

<p>Thanks for the response. It's my understanding that magnification is independent of film/sensor size and is only related to focal length, whereas angle of view is a function of both focal length and film/sensor size. So the angle of view in my example is the same, but I think the 300mm lens has a higher magnification by definition.<br>

And this is where I become uncertain - because of the combination of the full-frame sensor being physically larger, and the fact that both images have the same pixel dimensions, I'm wondering if the higher magnification of the 300mm lens has any impact/advantage.</p>

[michael_darnton2]

<p>No, but the larger size of the sensor may have an advantage in speed vs noise in difficult situations.</p>

[Peter_in_PA]

<p>Taken at base ISO from a sturdy tripod, I bet no one would tell the difference.</p>

<p>There is slightly deeper Depth of field on the APS-C image of course, but you're shooting flat art in daylight? You can compensate with aperture.</p>

[James G. Dainis]

The 300mm lens would have narrower depth of field for any given aperture but since this is a flat billboard it wouldn't matter.

[Ed_Ingold]

<p>The perspective is determined by distance from the subject. The focal length determines the field of view. In the example presented, the distance is the same in either case, and the field of view of the 300mm lens on a FF sensor is nominally the same as that of a 200mm lens on an APS-C sensor. Depth of field is related to the absolute magnification of the image and aperture. That said, a longer lens and larger sensor has more magnification in this example.</p>

<p>Quality is another, ambiguous issue, depending on what is important to the application, or in the eyes of the beholder. Resolution, noise, color and contrast are possible factors. There are incredibly good APS-C sensors (e.g., Fuji X-Pro1) and lesser FF sensors. All else being equal, larger sensors will have more resolution, or larger cells with proportionately less noise. If we compare two exceptional sensors with comparable quality glass, size may make little difference.</p>

<p>Leica digital users often select a APS-C sized Fuji X-Pro or Sony NEX camera as a backup. None of these cameras has an anti-aliasing filter, and all can be adapted to use Leica M lenses. From examples I've seen, it is very hard to see a difference.</p>

<p>The most important factor is what pleases you, or your customer. Perhaps it's something as mundane as meeting deadlines (i.e., less editing and adjustment).</p>

[ellis_vener_photography]

The only thing I can think of is that if you use the same aperture setting on both lenses and you are using a tripod, you'll have shallower depth of

field with the 300mm /FX combination than with the 200mm/DX combo.

 

But that isn't a "lens magnification" issue related to format size differences, just the difference between the two focal lengths.

[JDMvW]

<p>Two examples of lens and position of camera principles<br>

First, just the other day, Frode Langset's example at http://www.photo.net/casual-conversations-forum/00clOs <br>

and<br>

here is a reworking of a page from the Life Library of Photography series in pdf format:</p>

[frode]

<p>OK, I will show the images anyway. The 70 mm should have been taken with f/5.6 (or the 300 mm with f/4). The differences between the two should therefore have been even more pronounced because the 70 mm image should have had an even larger depth of focus.<br>

Ps. I don't have a camera with the needed 5.5 mm x 3.6 mm sensor, but I used the same camera for both images and trimmed away everything in the 70 mm image that came from outside the central 5.5 mm x 3.6 mm part of the sensor (aka cropped the image) ;-)</p>

<p>Sorry for the mess. I hope this will illustrate the differences anyway.</p>

<p>Cheers,</p><div></div>

[James G. Dainis]

The first thing the OP said:

 

"Say I take a photo of a billboard ..."

 

 

If I remember correctly, billboards are usually flat.

[Ed_Ingold]

DOF would affect the appearance of objects in front of or behind the billboard.

[ellis_vener_photography]

"James Dainis , Aug 14, 2014; 07:40 p.m.

The first thing the OP said:

 

"Say I take a photo of a billboard ..."

 

If I remember correctly, billboards are usually flat."

 

Geometrically speaking, a billboard may be a flat plane but have depth when looked or photographed from any any

excepting the perpendicular .

[Colin O]

<p>I'm not actually taking photos of billboards, I just used that in my example to hopefully exclude depth of field from the discussion! Because here I am not wondering about depth of field differences, but rather about differences in the detail at the focus distance resolved by different lenses, but the same FoV and pixel count.</p>

 

<p>If one was taking a photo of a billboard with a single camera, of course a 300mm lens would be preferable to a 200mm lens (assuming the field of view with the 300mm lens covers the billboard). That's because a 300mm lens has greater magnification than a 200mm lens and so resolves greater detail.</p>

 

<p>Think of my scenario this way:<br>

A 300mm lens is projecting its more more magnified image onto a larger sensor which has 24 million imaging pixels.<br>

A 200mm lens is projecting essentially the same image onto a smaller sensor, but still onto 24 million imaging pixels.<br>

So what's the difference? The 300mm lens magnifies details in the scene to a greater extent, but is this entirely negated by the fact that in both cases the image is being "sampled" by the same number of pixels? Or does the 300mm lens' greater magnification somehow resolve greater detail onto its 24 million pixels? I think it must be the former, no?<br>

(As Michael says, the larger sensor could have dynamic range / lower noise advantages at high ISO, but I'm just really considering well-lit conditions for this comparison.)</p>

 

<p>PS. One other thing - it's possible I'm using the term "magnification" differently to how others are. I'm talking about magnification in terms of the image that a lens projects onto the focal plane. Whether there's a large or small sensor positioned at the focal plane has no bearing on the magnification level of the image that the lens is projecting there.</p>

[ellis_vener_photography]

"PS. One other thing - it's possible I'm using the term "magnification" differently to how others are. I'm talking about

magnification in terms of the image that a lens projects onto the focal plane. Whether there's a large or small sensor

positioned at the focal plane has no bearing on the magnification level of the image that the lens is projecting there."

 

The correct term is reproduction ratio. In your two cases your reproduction with both lenses on both format cameras is

either 1: infinity or close to it.

[ellis_vener_photography]

If the area as measured in pixels on one one sensor covered by the billboard is the same area as measured in pixels on

the other , the answer would seem to be that the resolution is equal. However this ignores two very real technical aspects:

 

- differences in sensor technology

 

- the differing acuity of both lenses.

[q.g._de_bakker]

The term reproduction ratio is just as correct as magnification.<br>Reproduction ratio, scale and magnification are all the same thing. A ratio or scale of 1:2 equals a magnification of 0.5x (1 over 2, 1/2, i.e. 1:2). They all express the relation between the real life size of something to the size of the same thing in reproduction.<br>Confusion can occur regarding what the reproduction is: the image on the sensor or the image on the final print.<br><br>The magnification, or scale, or reproduction ratio in the image projected by the longer focal length lens is larger than in the image projected by the smaller lens.<br>To capture the same angle of view, you will thus need a larger sensor behind the longer lens.<br>If both same-angle-of-view images then are captured using the same number of pixels over the long side, and both printed to the same size (or viewed on teh same size display), the scale, reproduction ratio and magnification will then be the same in both images. And the resolution, meassured in pixels per subject, will be the same too.<br>Assuming that the same f-stop was used, DoF will be the same as well. Unsharpness outside DoF will increase faster in the image made using the longer lens. But DoF itself will be the same.<br>Resolution depends not just on magnification. It is entirely possible to have a highly magnified image that resolves less detail than a much less magnified image. That far from uncommon phenomenon is called "empty magnification". Big does not always equal more or better. So the assertion that a 300 mm lens resolves more detail than a 200 mm lens because the magnification in the image it projects is larger is not necessarily true, could be false.<br><br>A reproduction ratio if 1:infinity is only achieved when the subject is infinitely far away, and it's size in the image is infinitely small.<br><br>Differences in lens quality and sensor technology will indeed have to be considered as far as the image quality is concerned. It mostly affects the smallest detail that will be resolved. But not scale, reproduction ratio and magnification.<br>Since DoF depends on the visible difference between unsharp and sharp, the level of sharpness of that which is said to be sharp will make a difference. That's why DoF appears larger when using less good lenses, and vice versa.

[frode]

<blockquote>

<p>Assuming that the same f-stop was used, DoF will be the same as well.</p>

</blockquote>

 

 

I won't elaborate on this since this is a discussion that the OP specifically do not want, but interested people can read Bob Atkins' excellent article about this here on photo.net: http://www.photo.net/learn/optics/dofdigital/

 

 

(Btw: I honestly believed, obviously incorrectly, that the rules about keeping strictly to the matter was not that strict in a "casual photo conversation", that is why my previous post was a bit on the side, sorry about that, won't happen again)

 

Cheers,

 

 

[Alan Marcus]

<p>The degree of magnification yield is based on the diagonal measure of the format. This might seem weird but we buy TV’s and computer monitors based on diagonal measure. Also, study after study reveals that we tend to view pictures at a distance about equal to the diagonal measure. A full frame format measures 24mm height by 36mm length. The diagonal measure of this rectangle is about 45mm. By rights if we mount a lens with this dimension as the focal length, the view delivered is said to be “normal”. Technically it will be about 45⁰ with the camera held horizontal. If a 50mm is mounted, the angle of view becomes 46⁰. Because 43.3mm is a weird value, opticians chose 50mm as “normal” for the FX (full frame).<br>

<br>

Thus 50mm is the basis for magnification. Mount a 100mm and the results are 2X magnification. Mount a 300mm and the yield is 6X. Astronomers also use the 50mm base. An astronomical telescope, 2 meters in focal length (2000mm) is said to deliver 2000 ÷ 50 = 40(written as 40X) when a camera is used at the 2000mm (prime focus) position. <br>

<br>

If the same lens is mounted on a DX (compact digital), the image produced by the lens is the same as to magnification. After all, the focal length is a constant. However, both the FX and DX are miniature cameras. Thus the images they make are practically useless unless magnified. We display on a TV or computer monitor and we see an enlarged view. Same is true if we make a print. <br>

<br>

Now the DX format measures 16mm height by 24mm length. The diagonal measure of this format is 30mm. Thus mounting a 30mm delivers a “normal” view 43.6⁰. Note the ratio of the diagonal is 45 ÷ 30 = 1.5. This is the so called crop or magnification factor. In other words, a DX which is 1/1.5 = 0.666 = 66% of an FX, must be blown-up 1.5X more to yield an equivalent image. </p>

[q.g._de_bakker]

I'm not sure about those studies concerning viewing distances. Sounds much like lab studies that do not have much relevance for real life situations. People tend to view pictures the way the viewing circumstances 'dictate', not according to considerations about image size. Pictures in books and magazines, in photo wallets etc. are viewed at reading distances, whether they are book size or half that. Pictures on billboards are viewed at whatever distance they are presented.<br>More or less the same with pictures on gallery walls. Small pictures on gallery walls invite people to come closer, yes. But still no adherence to a diagonal-rule.<br>On the whole, the 'rule' is that people view images the way they find most comfortable.<br><br>Magnifications in photography are hardly ever expressed as a factor of the angle of view of a 50 mm lens. With binoculars and telescopes, yes. But, say, a 3x zoom, is one that has a largest focal length that is 3x that of its shortest focal length. And 1:1 or 1x magnification in photography means that the subject appears the same size on film (or sensor) as in real life. Not that it appears as large as it would using a 50 mm lens.<br><br>Magnification is the result of focal length and subject distance. That means it will be larger when using a longer lens than when using a shorter lens at the same distance. The 300 mm lens in the OP's question will have more magnification than the 200 mm. That also means that (assuming a big enough image circle on both), the shorter lens will have a wider angle of view. If you use a smaller sensor behind the shorter lens, so that the angles of view are equally big, the image projected by the longer lens still has more magnification. The suggestion in the OP's question is that it also shows more detail, because of that. If the sensors behind both lenses capture the same angle of view, and the same number of pixels, resolution of detail will be the same (X number of pixels per width of the billboard = X number of pixels per width of the billboard). Magnification 'per pixel' will also be the same.<br>The OP's question is if that means that the higher magnification of the longer lens (and it's supposed higher level of detail) and larger sensor is then lost.<br>The answer is that it probably is. (And considering that longer lenses tend to have a lower resolving power than shorter lenses, i.e. that the gain in detail level isn't as big as it is supposed to be, the result may even be worse. But that depends entirely on an unknown: the performance of both lenses to be used.)