Random musings on sensor size...

[michael_young3]

<p>So, I wonder just how useful the metric system and its base 10 measurements is to everyone else. Is it just me who has a difficult time relating 22.3mm to anything but an arbitrary and very fuzzy notion of size? Why did that figure, the width of an APS-C sensor in millimeters, not ring any jarring bells when I first heard it 8 years ago? I realize now that I have a much more innate sense of proportions when relationships are expressed in small fractional powers of 2 (1/1, 1/2, 1/4, etc.: same, half, and quarter). Thirds also are easy enough to imagine, but fifths are pushing it. How exactly does 22.3mm compare with 36mm? Is it just us Merkins who are handicapped? What do our international readers think?<br /> <br /> 22.3mm is just a few hairs shy of 24mm, the height of a 36mm film frame. Thus, an APS-C sensor covers 1/3 the area of a full 35mm frame. APS-C is the center 1/3 crop of a full frame sensor. That's something I can relate to. Did I just not notice while everyone else already figured this out?<br /> <br /> Come to think of it, my most recent other camera was a 6 MP 300D. Its pixel dimensions are an easy to remember 3072x2048. That 3072 is a few pixels shy of the 7D's frame height 3456 pixels (also easy enough to remember). The 300D's pixel resolution is smaller than the 7D's in roughly the same proportion as APS-C to full frame. Of course, anyone else who can multipy 6 MP by 3 in their head and come up with 18 MP beat me to this realization. In my head, I think I just thought of it as simply "way biggerer!" Note the exclamation. Now, I can relate it more precisely: a 7D landscape shot holds a few more pixles than 3 portrait shots from the 300D. Way biggerer, indeed.<br /> <br /> What else? My Mamiya 645 has a frame size of 6x4.5 cm. Dividing its frame diagonal by that of a 35mm frame gives us 1.3. Does that figure look familiar to anyone? 1.3 is the crop factor for APS-H. The 1D sensor is to 1Ds, as 35mm is to medium format. That puts it in perspective. I always thought of APS-H as just fuzzily somewhat larger than APS-C, and a bit smaller than full frame. Nope. It relates to a 35mm frame in the same manner as 35mm relates to 6x4.5. That's easy for me to relate. I can hold a 645 slide next to a 35mm slide, and see and feel the difference. The difference is rather stunning, actually, compared to the picture I used to hold in my head.<br /> <br /> There's more. 22.3mm is just about exactly half of 4.5 cm. APS-C covers 1/12 the area as a 6x4.5 frame. But that is so fuzzy it just frustrates any sense of proportion. That first relationship has meaning, though: APS-C is as wide as half of 6x4.5 is high. I need to stitch 4 shots to cover a paltry 1/3 of the 645 frame. That puts it in proper perspective. I'm looking at a 645 slide this moment, and feeling the difference. APS-C is tiny! 18 MP on that is coming close to angels dancing on a pinhead.<br /> <br /> What brings this up? Some thoughts from another thread about diffraction limited resolution, but that'll have to wait for now. I have a few boxes of slides I just dredged out storage to play with...</p>

[michael_young3]

<p>Oops. I knew that the APS-H stuff just didn't feel right. The crop factor from 35mm to 6x4.5 is 1.7, not 1.3. I'm feeling better about it already. Closer to APS-C to 35mm, but maybe not worth mentioning.</p>

<p>Hmmm. And that whole 6x4.5 thing. I somehow got it in my head that it was the same 2:3 aspect as 35mm. It isn't. The 645 aspect is 4:3. Scratch that whole thought. It needs refinement.</p>

[carbon_dragon]

<p>APS isn't really a "standard" as much as a loose term for a variety of sensors about the size of the old APS film. For instance, my Sony A350 is called APS-C and so is the digital rebel, but the A350 has a crop factor of 1.5 while the Canon is 1.6. I think there is a limit to how much useful resolution can be crammed into a given size of sensor and that the APS sized cameras are probably at that limit now. I don't know what the limit is, but I'm guessing it's something like 12MP give or take a few depending on manufacturer. Then we have full frame which these days tends to be from about 13 to 24MP. I don't know what the full frame rough limit is, but I'll bet in the 20's is probably close.</p>

<p>Even so, the truth is that 10-12MP is probably all you need to do very good 8x10's and pretty darned good 11x14s and that's the biggest I will ever print. I wonder if manufacturers like Canon and Sony will put larger than full frame sensors in 35mm sized cameras in order to trump the other's MPs. What if say Canon put out a 38mm sensor? Of course that would call into question the image circle of the Canon lens line so maybe it's a non starter.</p>

[KenPapai]

<blockquote>

<p><em>"What if say Canon put out a 38mm sensor? Of course that would call into question the image circle of the Canon lens line so maybe it's a non starter."</em></p>

</blockquote>

<p>The sun will rise in the west before that would ever happen. Really? --- details:</p>

<p>The image circle of the EF Canon lenses barely covers 44mm diameter. That just does cover a 36x24 mm sensor/film. I imagine a rectangle 38x24 would not quite fit that circle (its diagonal is 45 mm)</p>

[ben_goren]

<p>Michael,</p>

 

<p>You might find the attached image useful. You might find creating one of your own even more

useful.</p>

 

<p>This should be close to actual size on most monitors.</p>

 

<p>Cheers,</p>

 

<p>b&</p>

[ben_goren]

<p>erk…Photo.net no longer allows GIFs. Let’s see if this one works….</p>

 

<p>b&</p><div></div>

[michael_young3]

<p>Yeah, that's the picture I have in my head, Ben, but somehow the shading in yours makes it look closer to half the 35mm frame. I'll just make a PS action to draw an APS-C frame in every picture.... landscape to landscape, making it a bit more meaningful. I'd swear I did this once already before. But maybe that was 35mm to 645.</p>

[ben_goren]

<p>Michael,</p>

 

<p>In terms of area, an APS-C sensor covers (15.1 × 22.7) / (24 × 36) = 40% of the area of

a full-frame sensor. 40% is close enough to both ^{<small>1</small>}⁄<small>3</small> and ½ that our brains can easily be fooled into thinking

it’s the one or the other.</p>

 

<p>For practical purposes, either “a bit more than a third” or “not quite half”

are both perfectly adequate approximations for these sorts of comparisons.</p>

 

<p>Cheers,</p>

 

<p>b&</p>

[jim_a]

<p>I came across this recently at a Canon booth and included a dime for comparison. Click the image for a larger version:<br>

<a href="http://www.jimarnold.org/blog/wp-content/uploads/2010/01/sensor_sizes_P1040462.jpg" target="_blank"><img src="http://www.jimarnold.org/blog/wp-content/uploads/2010/01/sensor_sizes_P1040462.jpg" alt="" width="600" /> </a></p>

[dan_south]

<blockquote>

<p>Thus, an APS-C sensor covers 1/3 the area of a full 35mm frame.</p>

</blockquote>

<p>As Ben points out it's a bit more than a third.</p>

<p>Also keep in mind that Nikon's APS-C sensors are slightly larger than Canon's (16x24 mm for a 1.5x Nikon crop versus 1.6x for Canon). APS-C is an approximate size depending on who manufactures the chip.</p>

[dan_south]

<p>If you struggle with metric to English unit conversions, keep in mind that 25 mm is approximately one inch.</p>

<p>36 mm is about an inch-and-a-half.</p>

<p>100 mm is about four inches.</p>

<p>A meter is just under 40 inches.</p>