Full frame lens on a crop sensor

[francis_d]

<p>Hi, I just picked up a Nikon D90 a few months ago and am progressively picking up things.<br /> <br /> I know that using a full frame lens on a crop sensor will result in a smaller angle of view. For example, take the Nikon 50mm F1.4G. When used on a DX body, the angle of view is equivalent to 75mm (50mm x 1.5) on a full frame body.<br /> <br /> Now, having that 75mm angle of view wouldn't change the focal length of 50mm to 75mm on a DX body would it?<br /> <br /> Just wanted to get that clear in my head.</p>

[luis_g]

<p>No. It's the format that is different. The lens is still 50mm.</p>

[sknowles]

<p>The lens is independent of the camera sensor. The smaller sensor doesn't change the focal length, the angle of view or the image circle of the lens. The smaller sensor only sees the smaller image which is equivalent to the same on a full frame lens of the focal length mulitiplied by the sensor factor, so a 50mm lens produce a similar image, although smaller, of a full frame sensor at 70mm to 80mm (using the 1.4 and 1.6 factor).</p>

[jpo3136b]

<p>The angle of view narrows up <em>as a practical matter</em>, but the focal length stays the same. </p>

[ellery]

<p>I am confused - for all intensive purposes, when you put the 50mm 1.4 on a D90 - what you get is the field of view of say a 75mm focal lengt on a full size sensor....right? </p>

[ben_goren]

<p>Francis,</p>

 

<p>Take a picture with a 35 mm film camera. Take a pair of scissors to the frame until

you’ve cut away half the area, leaving just the central portion. You have just

<em>exactly</em> replicated what happens with a crop sensor camera.</p>

 

<p>Shoot the scene with the longer lens mounted on the larger format, and the wider lens

mounted on the smaller format, and the framing will be the same. You will, however, have to enlarge

the smaller format more to get the same sized print…and right about now you should be

starting to realize there are resultant effects on sharpness, depth of field, noise / grain,

<i>etc.</i></p>

 

<p>The short version is that, photographically, the larger format can do everything the smaller one

can and then some; worst case, you can simply crop the larger format and you have the same

starting point.</p>

 

<p>In the real world, crop sensors often have higher pixel densities (due largely to economic

factors). Those who would be cropping anyways — such as bird photographers who need

1200 mm lenses but only have 800 mm lenses — get better image quality from a crop sensor

camera with a higher pixel density.</p>

 

<p>And, of course, crop sensor cameras are less expensive, smaller, lighter, and may well have

other non-photographic factors that make them make sense. Indeed, if your printer sits on your

desktop, it’s highly unlikely you’d even be able to tell the difference between prints;

it’s mostly only those who buy their ink by the pint and their paper by the roll who benefit

from the larger format.</p>

 

<p>Cheers,</p>

 

<p>b&</p>

[jpo3136b]

<p>Ellery, that is correct. The finer point of understanding the "focal length" part is that when the light comes out the back end of the lens, it has the same qualities it would have, regardless of what camera its bayonetted onto.</p>

<p>When you put the big system lens on the little system camera, you are only intercepting a little part of the cone of light that comes out the lens.</p>

<p>So, you get the same depth of field you would have gotten on the larger system (properties related to focusing, focal length), but you only catch part of the image with the sensor and viewfinder (narrower apparent field of view).</p>

<p>For example, I have a medium format very wide angle lens. Angle of view is about four handspans wide on a 645.</p>

<ul>

<li>That lens is very wide angle on a 645.</li>

<li>That lens has a field of view that's close to a normal lens on a 35mm</li>

<li>That lens has a field of view that's close to short telephoto on a crop DSLR</li>

<li>On all of the cameras, at f/16, I can get a depth of field that will run from about 6 feet (2 meters) on out to several hundred meters (just under infinity).</li>

</ul>

[francis_d]

<p>Thanks for the responses everyone.</p>

<p>Just a quick follow up question taking the Nikon 50mm F1.4G example again. Below is the field of view of the 50mm lens on a full frame and crop sensor camera:</p>

<p>Full Frame: FL 50mm, FOV 40 degrees<br />Crop sensor: FL 50mm, FOV 27 degrees</p>

<p>Does that mean in order to get the same field of view as on a full frame camera, you'd have to physically move back from your subject X number of feet when used on a crop sensor camera? But by doing that you wouldn't get the same magnification of your shot (right?) compared to the FF camera.</p>

[jpo3136b]

<p>Not quite, field of view is about the angle. You could <em>intercept a plane of the same width</em> by moving backwards, but that's not quite the same.</p>

<p>If you have an opportunity to experiment with this equipment variety, you will be able to see it for yourself in a very short time. Once you see this happen a few times, it is much easier to visualize than learning about it by reading a description.</p>

[ellery]

<p>Thanks John and others and thanks Francis for asking the question -</p>

<p>I will say Francis that I have a D90 and have a 50mm 1.8 - which comes out to be the "equivalent" of 75mm - I absolutely love this little sucker and it was 130 bucks - it is a bit too long for tight spaces for sure though, but I use it now pretty frequently - but It does leave me wanting for a 35mm prime for indoor use......</p>

[kelly_flanigan1]

<p>A 50mm lens is 50mm lens; like a 12oz CocaCola is a 12 oz Coca cola.<br>

<br /> An analogy might be soft drink sizes at eating places:<br>

<br /> Burger Boy might call their 12 oz Coke a small; Tommies might call it a medium; and old folks home might call it a large coke. Maybe the old folks home calls a 6 oz coke a small coke; thus a 12 0z would be 2X in size?.</p>

<p>One can invent all sorts of references; many folks use full frame 35mm still ie 24x36mm.<br>

<br /> If one puts a 35mm still camera lens on a 4x5 camera; the format is so big one gets a circle; the corners are not even filled; like one of the first Kodak cameras over a century ago. Here is a 35mm F2.8 on a 4x5 camera; one gets a round image; way less than a 4x5 negative.</p>

<p><img src="http://i4.photobucket.com/albums/y148/ektar/35mm%20PC-%20Nikkor%20on%204x5%20speed/tripods-298.jpg?t=1260305432" alt="" width="398" height="424" /></p>

<p><img src="http://i4.photobucket.com/albums/y148/ektar/35mm%20PC-%20Nikkor%20on%204x5%20speed/tripods-296.jpg?t=1260305600" alt="" width="487" height="381" /></p>

[francis_d]

<p>John, thanks for clearing up that up for me. I'll check out the 50mm F1.4G next time I'm at the camera store and compare what I see on my DX zoom lens at 50mm to get an idea. I had a feeling there was more to it than physically moving back, but I'm sure as you say it'll be easier for me to see it myself than read about the visual differences.</p>

<p>Ben, nice analogy with what happens with mounting a full frame lens on a crop sensor camera. I think that's the best explanation I've heard before.</p>

[ellery]

<p>Indeed - Ben's comments do make since I think - sorry to keep this going on, but I can be dense. So when you put the 50mm 1.8 on my D90, you are not TECHNICALLY changing the focal length - you are cutting of or "cropping" the excess that does not fit on the sensor - so what you get is the field of view of a 75mm DX.....</p>

<p>Would there be any optical difference between a 75mm DX prime (if that exists) on the D90 vs. a 50mm 1.8 FX?</p>

[Wouter Willemse]

<blockquote>

<p>Would there be any optical difference between a 75mm DX prime (if that exists) on the D90 vs. a 50mm 1.8 FX?</p>

</blockquote>

<p>Yes, there would be. A "DX lens" of 75mm is 75mm. Meaning, using the cropfactor, it will seem like a 112mm lens. Consider the 18-200VR DX lens. It "acts" like a 28-300 on DX cameras, the cropfactor is still there. If it would start at the equivalent of 18mm full frame, it would be extreme wide angle at the short side; it isn't.<br />The focal length is the focal length. Only the size of the recording medium behind it makes the change in angle of view.</p>

<p>Rephrasing your question: is there any optical difference between a 35mm DX prime (which exists) on the D90 versus a 50mm on FX? The answer would be: none beyond the fact that we're talking 2 different lenses. But the result you'd get from these 2 would be close to equal.</p>