Someone help me understand crop factor pls.

jambredz

jambredz

Veteran
ok after reading tonnes b4 i got my 7d(last week) i've learned to think in terms of 50mm is really 80...28mm is really 44 (full frame lenses) and blah blah on the 7d. Well thats what i;ve grasped from what i;ve read. So i have a Tamron 17-50mm 2.8 (aps-c lens) and my friend is getting a nifty fifty so we can shoot a film soon. Would i be correct in assuming that the canon fifty will look more telephoto (looks like 80) since its full frame in relation to my aps-c tamron at 50mm? Since the tamron is made for this sense size thats truely 50 right?
 
Not quite, Jam. Here's how it works…

Any lens on an APS-C sized sensor will give a field-of-view 1.6x that of the same focal length on a full frame camera. Thus, like you say, a 50mm on a 7D gives you the equivalent FOV of 80mm on a 5DII (full frame). But it doesn't matter whether that lens is for APS-C cameras only (as in the EF-S lenses from Canon) or if it works on full-frame cameras as well (the EF lenses from Canon). So, his "nifty fifty" will give the same FOV as your Tamron set to the telephoto end of the lens.



I hope this makes sense. It does in my drug-addled mind, but sometimes the words are not my friends.
 
50mm is 50mm is 50mm. Any 50mm lens, mounted on any given camera, will give the same field of view as any other 50mm lens mounted on that same camera.

The difference between a full-frame lens or an EF-S lens is not in how "telephoto" they are, it's in how much of the frame they cover. An EF-S lens on a full-frame camera will not cover the full frame; there'll be a big circle of black surrounding the image.
 
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Yeah, since the APS-C sensor is your 7D is smaller than full frame, it will "see" a smaller area from the lens in front of it, making it appear as if it's a longer focal length. So those focal length multipliers to get your equivalent field of view will always be the same when using the same camera, no matter which lens.
 
ohh. koolness. i think i get it now.

sidenote: from using this tamron for the past 3 days i def wanna get an 85 next. it amazes me all the thingsi i see people doing with just a 50mm...then when i;m using it i'm like dang i have to be pretty close to these subjects (sometimes). Coming from dvx where i can zoom in more...the 17-50 just doesnt feel enough. Anyway...thanks for the explanations.
 
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Stephen Mick said:
All hail (the sometimes-accurate) Wikipedia[...]
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I couldn't tell you where I read this—it wasn't Wikipedia—but I did read a while back that Wikipedia is giving encyclopedias a run for their money in terms of accuracy. Wikipedia still gets a bad rap for some reason. The fact that the pages can be changed so easily is perhaps worrisome but the system works, overall. I allow my high school students to use and list it as a reference.
 
five years ago university proffs were very anti-wikipedia.

now they're like... "uh, yeah you could start with wikipedia, but you have to make sure the sources are legit"
 
This is one of these confusing subjects where so many terms get used wrong or mixed up so people misinterpret what is being said. Field of view, angle of view, crop factor, image circle, focal length, focal distace, blah blah blah - are often incorretly used interchangeably, thus the resulting confusion.

All lenses are compared to each other on the same scale, which is why we have the term "equivelant field of view." This measurement/calculation DOES take into account the sensor size and is a way of measuring how a lens will look when used on a camera with a certain sensor.
 
deltoidjohn said:
This is one of these confusing subjects [...] Field of view, angle of view, crop factor, image circle, focal length, focal distace, blah blah blah - are often incorretly used interchangeably, thus the resulting confusion.[...]
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It's simply a circle of indistinctness, err confusion.
 
Can someone confirm or deny that the "crop factor" is irrelevant for T2i/7D video(as regards going for a cinema look)? I recall someone going on at great length about this elsewhere(j. davis?) and the gist was that the sensor size of the t2i/7d are fairly similar to a frame of 35mm film negative in a cinema camera. Thus lenses would cover the same amount of frame on both. So a 50mm cinema prime lens on an Arri covers the same angle of view(more or less) as say the nifty fifty Canon lens on a T2i/7D.

I think most people on here using the dslrs are probably using them for video, so the crop factor should only be an issue if you're using a lens on a 5d, right? At least as far as the Canons go.
 
PastePotPete said:
Can someone confirm or deny that the "crop factor" is irrelevant for T2i/7D video(as regards going for a cinema look)? I recall someone going on at great length about this elsewhere(j. davis?) and the gist was that the sensor size of the t2i/7d are fairly similar to a frame of 35mm film negative in a cinema camera. Thus lenses would cover the same amount of frame on both. So a 50mm cinema prime lens on an Arri covers the same angle of view(more or less) as say the nifty fifty Canon lens on a T2i/7D.

I think most people on here using the dslrs are probably using them for video, so the crop factor should only be an issue if you're using a lens on a 5d, right? At least as far as the Canons go.
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That's what I'm getting from my readings here. I was confused about this myself. I believe it was Kholi that said that the 5D's sensor was bigger then the 35mm film camera's sensor. That the 7D/T2i's sensor are similar in size as the 35mm camera. So I'm guessing that if you compose the same shot with a 35mm film camera, and with the 7D/T2i, the shots will look very similar. As far as the framing is concern when using the same focal length lens. Please correct me if I'm wrong about this.
 
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PastePotPete said:
Can someone confirm or deny that the "crop factor" is irrelevant for T2i/7D video(as regards going for a cinema look)?
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Absolutely.

The "Crop Factory" that is often quoted, is calculated using 35mm STILL photography as the "standard" size. But that has practically nothing to do with cinema. Cinema's film frame is less than half the size of the still frame. So I advocate that we ditch the "crop factor" and start using something called the Cinema Crop Factor, which would relate a given camera's frame size as it compares to 35mm movie film.

Under that scenario, a T2i or 7D would have a Cinema Crop Factor of 1.0.
 
cap10kirk said:
I believe it was Kholi that said that the 5D's sensor was bigger then the 35mm film camera's sensor.
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It is. It's twice the size of 35mm movie camera film. Still film (or the 5D) are 36mm x 24mm; a movie camera's sensor is 22mm x 12mm.

That the 7D/T2i's sensor are similar in size as the 35mm camera. So I'm guessing that if you compose the same shot with a 35mm film camera, and with the 7D/T2i, the shots will look very similar.
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Exactly.
 
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