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01-31-2012, 09:03 PM - 1 Like   #16
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QuoteOriginally posted by Mike Cash Quote
Then I get told off for daring to mention film in my explanation.
Except he didn't tell you off. I was also a little confused as to why you interpreted it that way.


QuoteQuote:
It is like somebody asking what the difference between Judaism and Christianity is and then going, "Waaaa!!!! Don't mention Jesus! Don't care nothing about him. Don't want to hear it."
???

QuoteQuote:
It is ungracious to ask for an explanation of something and then carp about the nature of the explanation, especially when the explanation covers exactly is asked about. If pointing that out makes me the prick, then I suppose I'll just have to be the prick. I don't appreciate being taken to task for doing precisely what I was asked to do just because the person asking did a piss-poor job of making it clear what it was he wanted.
I don't think he carped about the explanation, or was ungrateful for your response, just expressed some further confusion in perhaps a tongue-in-cheek way.

I think it's time for....



01-31-2012, 09:11 PM   #17
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I was confused by the same thing for a long time. Why didn't a 50mm film lens look like a 75mm on my apsc camera?
Here is a way of looking at it. imagine an 8x10 picture. Lets say that is what a 50mm lens is projecting into the camera. lets cut a 1" square out of the middle. it doesn't matter if the camera is apsc, full frame, medium format or large format, that 1 inch square does not change. It will look the same from any camera. out of that 8x10 picture, lets say an apsc sensor is 3x5. it is like taking a 3x5 photo out of the middle of that 8x10. Well a full frame sensor is larger, right? lets say it is 5x7. it is taking a 5x7 picture out of that 8x10. The image is larger because a larger area of light was recorded, not because the lens magnified it different.

Another example. lets take a telescope that has 50x magnification. Lets look at a car that is far enough away that the bumpers are right on the edge of the picture. You can just barely see the whole car. Lets say that is the full frame sensor. now lets take masking tape and put it over the top, bottom and both side edges of the eye piece. you can now only see a portion of the car. The magnification has not changed. The telescope is still 50x magnification. You are simply seeing a smaller portion of the image because tape is blocking it. A smaller sensor sees a smaller portion of the image. A larger sensor will see a larger portion of the image but the magnification is the same. The lens does not change. a 50mm lens is a 50mm lens on any camera, just like a 50x telescope is a 50x telescope no matter what portion you are able to see.
Any 50mm lens will look the same on your camera be it an old film lens or a brand new digital lens.

Here is what crop factor is. Lets take 2 telescopes. One is 50x and can see the whole car. the other has tape on the eye piece blocking part of the car. How much magnification do we need to see the whole car with part of the image blocked by tape? If you assume that the 50x telescope is compared to a full frame sensor, and the telescope with the tape is an apsc camera, the telescope would have to be 33.333x to see the whole car. That is crop factor. A 50mm lens sees the same size image on an apsc camera that a 33.333mm lens sees on a full frame camera. Since the smaller sensor cuts away part of the car, you can zoom out so to speak, to get the whole car back in the picture by using a wider angle lens (one with less magnification). Any 50mm lens will always have the same magnification and give the same image on your camera. You can use a wider lens to duplicate what a full frame sensor sees.

It is often refereed in the other direction though. if you have a 35mm lens on an apsc camera, it sees the same image size as a 52.5mm lens on a full frame camera (35mm x 1.5 crop factor = 52.5). You basically need a wider angle lens on a smaller sensor to see the same thing as a camera with a larger sensor.

I hope that analogy wasn't confusing. Remember everybody, the technical answer is confusing. That is why people have a hard time grasping it until they already understand it. That is why there are no posts asking this with a simple answer that ends the thread. We need some analogy's like this stickied somewhere so that people can understand crop factor (preferably some analogy's that are written a little more clear and concise than mine, lol). I went to Utah valley University and the University of Utah for engineering (dropped out after 3 years due to money but had a 3.8 gpa on a 4.0 scale) and did graduate phi theta kappa from a state school with a degree in gunsmithing. I may not be the smartest but I'm certainly not an idiot and I didn't understand it for quite a while (and was surprised that a 50mm film lens didn't act like a 75mm digital lens), until it was explained to me properly. Or maybe I am an idiot in which case us idiots need simple answers!

Edit:
Just a little related info. A 50mm full frame lens (old film lens if you like) and a new designed for digital (and designed for apsc) lens have the same magnification. That is why they both work the same on your camera. The full frame has larger glass so that it can project a larger image, large enough to cover a full frame sensor (or the equivalent size in film). The lens designed for apsc has glass that is smaller in diameter that projects an image just large enough for an apsc sensor (ti's generally cheaper to make smaller glass). They still have the same magnification, but if you use the apsc lens on a full frame camera, the corners will be dark as the glass is not big enough around, but the magnification will still be the same.

Last edited by ripit; 01-31-2012 at 09:22 PM.
02-01-2012, 03:40 AM   #18
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QuoteOriginally posted by jsherman999 Quote
I don't think he carped about the explanation, or was ungrateful for your response, just expressed some further confusion in perhaps a tongue-in-cheek way.
This was also the way I read it...

QuoteOriginally posted by jsherman999 Quote
Except he didn't tell you off
No he didn't...

And as for his "piss poor job"... I remind you for a second time that this is a beginners forum... As such, a lack of understanding often raises imperfectly formed questions... Something most forum members are well used to..

Like I said before... Normally your advice is sound and it's my belief that you are indeed a credit to the forum...
But I really do think you've handled yourself quite badly in this partictular thread... That is why I 'took you to task".
I think you possibly misread the OP's tone (which in my opinion was playfully sarcastic)

Best
Dave
02-01-2012, 07:33 AM - 1 Like   #19
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thanks for "defending" me Dave... hahaha.
i was trying to be silly, and i do understand how i may have annoyed him and how it could have been taken as bitching though.
also, as this is probably very obvious to anyone who gets crop factors.
to me, it wasnt, and my particular learning style works alot better when i can phrase teh quaetion a certain way, take out the variables taht confuse me and are irrelevant (in this example, film). the thing is, to someone "in the know" like him, understands WHY film is used comparatively. but to me, i didnt want crop factors explained, and i could care less. i jsut wanted to know why people say teh 1.5 thing. and everyone else on here helped me understand taht very clearly, i think he just went a little to in depth and missed the actual point, whic again, to be fair, i may not have been entirely clear on.
then again, that's exactly why i asked a simple yes/no question:
if it was answered i would get exactly the answer i need without worrying about whether anyone understood what my question is, as i could put 2 and 2 together after that point.

for future help on this topic, it should be kept in mind by the "pro's" that the beginners asking this question probably dont care about film or image sensor size. they jsut want to know what lenses will work what way. to a beginner, crop factor is hearing soemwhere that lenses act differently on different cameras, and nothing more.
i have been doing photography for about 10 years now as a hobby and professionally. i could tell you how to set up any shot on teh planet reasonably well... but i haev always used digital lenses on digital cameras, and (canon) film lenses on film cameras back in teh day, and never thought 2x about this... now that i want to purchase an FA77 or 43 since teh DA's lack their character, i suddenly became worreid that teh 43 might act like a 62 and the 77 liek a 110 or whatever. and suddenly all the crop factor conversations ive heard over the years without caring came back to me with a vengeance. these lenses are expensive and after putting in my order i had an "oh shit moment" but now i'm fine.

thanks again, everyone.

02-01-2012, 07:42 AM   #20
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QuoteOriginally posted by ripit Quote
I was confused by the same thing for a long time. Why didn't a 50mm film lens look like a 75mm on my apsc camera?
Here is a way of looking at it. imagine an 8x10 picture. Lets say that is what a 50mm lens is projecting into the camera. lets cut a 1" square out of the middle. it doesn't matter if the camera is apsc, full frame, medium format or large format, that 1 inch square does not change. It will look the same from any camera. out of that 8x10 picture, lets say an apsc sensor is 3x5. it is like taking a 3x5 photo out of the middle of that 8x10. Well a full frame sensor is larger, right? lets say it is 5x7. it is taking a 5x7 picture out of that 8x10. The image is larger because a larger area of light was recorded, not because the lens magnified it different.

Another example. lets take a telescope that has 50x magnification. Lets look at a car that is far enough away that the bumpers are right on the edge of the picture. You can just barely see the whole car. Lets say that is the full frame sensor. now lets take masking tape and put it over the top, bottom and both side edges of the eye piece. you can now only see a portion of the car. The magnification has not changed. The telescope is still 50x magnification. You are simply seeing a smaller portion of the image because tape is blocking it. A smaller sensor sees a smaller portion of the image. A larger sensor will see a larger portion of the image but the magnification is the same. The lens does not change. a 50mm lens is a 50mm lens on any camera, just like a 50x telescope is a 50x telescope no matter what portion you are able to see.
Any 50mm lens will look the same on your camera be it an old film lens or a brand new digital lens.

Here is what crop factor is. Lets take 2 telescopes. One is 50x and can see the whole car. the other has tape on the eye piece blocking part of the car. How much magnification do we need to see the whole car with part of the image blocked by tape? If you assume that the 50x telescope is compared to a full frame sensor, and the telescope with the tape is an apsc camera, the telescope would have to be 33.333x to see the whole car. That is crop factor. A 50mm lens sees the same size image on an apsc camera that a 33.333mm lens sees on a full frame camera. Since the smaller sensor cuts away part of the car, you can zoom out so to speak, to get the whole car back in the picture by using a wider angle lens (one with less magnification). Any 50mm lens will always have the same magnification and give the same image on your camera. You can use a wider lens to duplicate what a full frame sensor sees.

It is often refereed in the other direction though. if you have a 35mm lens on an apsc camera, it sees the same image size as a 52.5mm lens on a full frame camera (35mm x 1.5 crop factor = 52.5). You basically need a wider angle lens on a smaller sensor to see the same thing as a camera with a larger sensor.

I hope that analogy wasn't confusing. Remember everybody, the technical answer is confusing. That is why people have a hard time grasping it until they already understand it. That is why there are no posts asking this with a simple answer that ends the thread. We need some analogy's like this stickied somewhere so that people can understand crop factor (preferably some analogy's that are written a little more clear and concise than mine, lol). I went to Utah valley University and the University of Utah for engineering (dropped out after 3 years due to money but had a 3.8 gpa on a 4.0 scale) and did graduate phi theta kappa from a state school with a degree in gunsmithing. I may not be the smartest but I'm certainly not an idiot and I didn't understand it for quite a while (and was surprised that a 50mm film lens didn't act like a 75mm digital lens), until it was explained to me properly. Or maybe I am an idiot in which case us idiots need simple answers!

Edit:
Just a little related info. A 50mm full frame lens (old film lens if you like) and a new designed for digital (and designed for apsc) lens have the same magnification. That is why they both work the same on your camera. The full frame has larger glass so that it can project a larger image, large enough to cover a full frame sensor (or the equivalent size in film). The lens designed for apsc has glass that is smaller in diameter that projects an image just large enough for an apsc sensor (ti's generally cheaper to make smaller glass). They still have the same magnification, but if you use the apsc lens on a full frame camera, the corners will be dark as the glass is not big enough around, but the magnification will still be the same.
also, now that i do understand this- this is teh best explanation i have read anywhere, on proffesional photography magazines websites or any forum. seriously.
it made me realize the big problem: that peopel dont think about magnification and image size as 2 separate thigns. for example, i dont care so much if a lens is 10 or 15mm, i want it to capture from teh left wall to right in my bathroom, know what i mean? so you completely explained that part that has eleuded so many other explainers.
02-01-2012, 02:36 PM   #21
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When faced with a question about the "1.5x" thing it is impossible NOT to include a mention of film in the explanation. To then get complaints for mentioning film in the explanation is exasperating.

To on top of that also get "you're confusing me more" and remarks about no longer caring or wanting to understand it.....where I was raised and where I have spent my entire adult life that would be considered an inconsiderate, ungrateful, and downright rude reaction to what was a sincere attempt to do a kindness for a stranger.....not "playful sarcasm". Playful or not, sarcasm can hardly be considered an appropriate reaction to a sincere attempt at helpful kindness from a stranger.

There was nothing in my explanation that called for a sarcastic response. Call me an argumentative pr*ck all you want.

And quit giving me crap about this being the beginner's corner. I'm doing this via Tapatalk and didn't notice it, for one thing. For another, the "after so many years" in the thread title led me to believe I must have been on some other subforum.

He gets to be sarcastic and gets a total pass.

I resent the unwarranted sarcasm and I'm an argumentative pr*ck.

Last edited by Mike Cash; 02-01-2012 at 02:43 PM.
02-01-2012, 05:41 PM   #22
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Wikipedia has a great entry on crop factor. Basically, the FOV doesn't change just how much image is exposed.


02-01-2012, 05:47 PM   #23
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QuoteOriginally posted by mtroute Quote
Basically, the FOV doesn't change just how much image is exposed.
If that explanation made sense to you, great. But it would only confuse most beginners.

Pity camera makers don't describe lenses in terms of angle of view, rather than "equivalent" focal lengths.

02-01-2012, 11:01 PM   #24
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QuoteOriginally posted by baro-nite Quote
If that explanation made sense to you, great. But it would only confuse most beginners.

Pity camera makers don't describe lenses in terms of angle of view, rather than "equivalent" focal lengths.
Equivalents are misleading. But AOV ratings would be even more confusing on dSLRs and the like because frame sizes aren't standard. Or rather, are many standards. My K20D's sensor (28.1mm diagonal) isn't nominal APS-C (30.1mm). Canon uses an APS-H sensor that may or may not be nominal (34.4mm). So how do we qualify interchangable lenses?

An AOV rating *would* work on fixed-lens cams -- and would totally brainwhack the 99.9% of humanity that's functionally innumerate. (I'm too close to that crowd myself, ever since I lost my best slipstick.)

And I'll just bet that if lenses *were* rated by AOV, we'd have the usual bitter arguments about whether 1 degree or 2mm difference is significant. That old standard of 50mm on a a FF cam has AOV= 47 degrees. For nominal APS-C, 35mm gives 47 degrees. For my K20D, it's 32mm. On APS-H it's 40mm. And the AOV of a 'normal' lens on a 3:2 frame is 53 degrees. Those are the numbers. Now let's fight!
02-02-2012, 12:17 AM   #25
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QuoteOriginally posted by baro-nite Quote
Pity camera makers don't describe lenses in terms of angle of view, rather than "equivalent" focal lengths.
Might make it easy to compare P&S. But will not help for interchangeable lens systems; my M50 will be marked as what? 40/27/47 And next we put it on APSc and it's no longer correct.

Focal length is the only variable that accurately describes a lens regardless of where it is used (to my knowledge).

Last edited by sterretje; 02-02-2012 at 12:24 AM.
02-02-2012, 05:27 AM   #26
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QuoteOriginally posted by sterretje Quote
Focal length is the only variable that accurately describes a lens regardless of where it is used (to my knowledge).
Yes, of course. I was thinking mainly of the P&S market, where "equivalent" is bandied about a lot. If you have a P&S with a "28-105mm equivalent" zoom range, you're in for confusion when shopping for an APS-C camera.

I said "camera makers" rather than "lens makers" thinking of camera-lens combinations rather than lenses alone. Restricting the idea of equivalence to angle of view would be helpful in terms of leaving DOF out of it. Only reasonably simple way I can think of is to include a table of this in each camera's specs. I'm just musing; I don't expect it to ever happen.
02-02-2012, 08:54 AM   #27
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QuoteOriginally posted by sterretje Quote
Might make it easy to compare P&S. But will not help for interchangeable lens systems; my M50 will be marked as what? 40/27/47 And next we put it on APSc and it's no longer correct.

Focal length is the only variable that accurately describes a lens regardless of where it is used (to my knowledge).
Actually there are a few variables that accurately describe lenses independant of format.

- Focal length defines obviously the principle lens characteristic,
- Aperture defines explicitly the lens in terms of exposure,
- minimum focus distance plus focal length, or conversly magnification, define the maximum magnification of a lens (subject reitive to focal plane image)
- mount defines what camera systems it can be used on,

just like 50mm is always 50mm F2 is always F2.
02-02-2012, 09:15 AM   #28
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QuoteOriginally posted by Lowell Goudge Quote
Actually there are a few variables that accurately describe lenses independant of format.
You're right, but in the line where this discussion was (AOV vs. FL) I took the low level approach; after all, a magnifying glass is also a lens
02-02-2012, 11:14 AM   #29
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QuoteOriginally posted by sterretje Quote
You're right, but in the line where this discussion was (AOV vs. FL) I took the low level approach; after all, a magnifying glass is also a lens
Yes, with a fixed focal length, an F number that is focal length over diameter, and a minimum focusing distance of the focal length and a magnification ration that is infinite.

and by the way it is also capable of tilts and shifts.

but yes focal length is the only constant in terms of FOV etc when mixing formats.
02-02-2012, 11:25 AM   #30
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QuoteOriginally posted by baro-nite Quote
If that explanation made sense to you, great. But it would only confuse most beginners.

Pity camera makers don't describe lenses in terms of angle of view, rather than "equivalent" focal lengths.
Hence the illustration...
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