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07-27-2010, 07:40 PM   #1
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Digital Sensors

Hi all,

Well i know the differences between the film cameras and digital cameras but i still have some issues with the sensors...

First of all, i've already read and a friend explained the pros and cons of CMOS and CCD but i didn't ask about sizes and useful pixels. I mean, i get lost when i see charts and drawings of the different sensors, which are the useful areas and i definitely start to cry (not literaly) when i hear full frame.

After that, i start thinking how it may affect the sensor size with the focal length. I'm studying Filmmaking* so i understand that a lense with certain focal length behaves as a telephoto or wide angle depending when you change the film format. So, can anyone explain me what is the "1.5" (don't know if thats the correct number) difference of lenses when in digital photography?

*As some may know, i'm from Argentina. Don't really know if "Filmmaking" is the correct translation of the career i'm doing.
**Also, my sincere apologies with my English, i'm kinda rusty and it's quite hard when using technical words. If you see some TERRIBLE misspellings; please, let me know, i'll really apreciate the correction xD

07-27-2010, 08:03 PM   #2
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Sensors that are smaller than 24x36mm (the 35mm film format) change the field of view (or angle of view) of a lens from what it would look like on the larger sensor.

This change makes it look like the lens has a longer focal length (in reality the focal length never changes). This multiple of the focal length varies from brand to brand.

Pentax uses 1.5x, Canon is 1.6x I think, and Olympus, using an even smaller sensor, is 2x.
07-27-2010, 08:34 PM   #3
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QuoteOriginally posted by tehSancho Quote
Hi all,
First of all, i've already read and a friend explained the pros and cons of CMOS and CCD but i didn't ask about sizes and useful pixels. I mean, i get lost when i see charts and drawings of the different sensors, which are the useful areas and i definitely start to cry (not literaly) when i hear full frame.
"Full frame" just means "the same size as the traditional 35mm film camera film frame", which I understand was long ago called "miniature format" (as opposed to medium format or large format).

QuoteOriginally posted by tehSancho Quote
After that, i start thinking how it may affect the sensor size with the focal length. I'm studying Filmmaking* so i understand that a lense with certain focal length behaves as a telephoto or wide angle depending when you change the film format.
Then you already understand! Really!

QuoteOriginally posted by tehSancho Quote
So, can anyone explain me what is the "1.5" (don't know if thats the correct number) difference of lenses when in digital photography?
1.5 (or 1.6 for Canon entry-level cameras) is just the ratio between the sensor used in that camera and the 35mm film format, and it simply expresses how much narrower the lens behaves, as you say above. So a 50mm lens is a normal lens on full-format, but the 1.5 narrower field of view makes it a short telephoto on a 1.5-crop dSLR.

QuoteOriginally posted by tehSancho Quote
*As some may know, i'm from Argentina. Don't really know if "Filmmaking" is the correct translation of the career i'm doing.
Filmmaking is a very broad term, ranging from coming up with ideas, writing the thing, actually making it, and distributing it. You might be studying all of that, or you might be focusing on a more particular part, like cinematography, which is the photographic aspect in particular.
07-27-2010, 08:34 PM   #4
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So, my DA L 18-55 (which i think is exclusively prepared for DSRL and the focal length is that in the CMOS), in a analogue camera would work like a 1.5 times smaller focal length (i'm not saying i will do that, just an example), while a Vivitar 50mm 1.9 will behave as a (50 x 1.5) mm in a DSRL?

QuoteOriginally posted by mattdm Quote
Filmmaking is a very broad term, ranging from coming up with ideas, writing the thing, actually making it, and distributing it. You might be studying all of that, or you might be focusing on a more particular part, like cinematography, which is the photographic aspect in particular.
Right now i'm studying the whole. I'll do another career to focus on cinematography xD (and some courses on Photography as a hobby and reinforce some aspects of lighting). In a few years time you'll have an Argentinian Director of Photography that once asked about focal length in pentaxforums.com!!! xD


Last edited by tehSancho; 07-27-2010 at 08:43 PM. Reason: for not double-posting
07-27-2010, 08:39 PM   #5
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QuoteOriginally posted by tehSancho Quote
So, my DA L 18-55 (which i think is exclusively prepared for DSRL and the focal length is that in the CMOS), in a analogue camera would work like a 1.5 times smaller focal length (i'm not saying i will do that, just an example), while a Vivitar 50mm 1.9 will behave as a (50 x 1.5) mm in a DSRL?
This is over-thinking (not your fault; I think everyone does it at first!) The lenses are sold with their real focal length, regardless of what format they're designed for. So an old Vivitar 50mm will give you exactly the same field of view as the DA L set at 50mm, no matter what camera you mount it on.

The difference is that if you put that DA L on a film camera and took a picture, you'd probably see round shading in the corners, because it doesn't necessarily produce an image circle big enough to cover a whole film frame. (This lets the designed-for-smaller-format lenses be smaller, lighter, and cheaper.)
07-27-2010, 08:58 PM   #6
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If you aren't VERY familiar with 35mm still film cameras, forget about "crop factor", whether it be 1.5x or 1.6x or 2x or whatever. That factor is only useful if you are mentally translating the FOV or AOV (field or angle of view) from 35mm film to smaller dSLR sensors. A lens is a lens; it remains the same lens whether it is on a Hasselblad 6x6, a Yashica 135, a Pentax dSLR, or an Olympus m43 camera. Smaller frames (film or sensor) just see less of the image projected by that lens, that is all.

A lens behaves the same, no matter what format it feeds. Perspective remains the same; DOF (depth of field) only changes slightly. This is noticed especially by people used to small P&S (point-and-shoot) cameras. A P&S zoom lens may say that it is equivalent to 34-136mm on a 35mm camera, but it's really a 7-28mm zoom feeding a small sensor. 28mm has great DOF, no matter what camera it is on. But the P&S user is sad or angry when they use a 90mm lens on their dSLR, the 'equivalent' of a 135mm lens on a 35mm camera, and they do not get sharp pictures. What is wrong? Their expectations, of course.

Cut out a picture from a magazine. Draw on it a rectangle that is 44x33mm. That is the sensor size of a new Pentax 645D medium-format dSLR. Now draw a rectangle inside that, 36x24mm. That is the size of a FF (full-frame) 35mm film frame. Now draw a rectangle inside that, 24x18mm. That is the size of HF (half frame) film, or a 35mm cine frame, or the APS-C sensor in a Pentax Kx. The picture remains the same, but each smaller format sees less of it. Now think of enlarging the 24x18 or 36x24 frames to 645 size. Those smaller frames, blown up, will show less detail. That is why the same lens has slightly less DOF on small formats.

By the way, your English usage and spellings are just fine.
07-27-2010, 09:07 PM   #7
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QuoteOriginally posted by tehSancho Quote
First of all, i've already read and a friend explained the pros and cons of CMOS and CCD
Great! Now I suggest forgetting about all that, as it just doesn't matter to the end user. The differences are relevant to folks designing cameras, or writing technical articles about them, but the difference to the photographer is zero.

QuoteQuote:
can anyone explain me what is the "1.5" (don't know if thats the correct number) difference of lenses when in digital photography?
It means if you are already very intimately familiar with 35mm film (not just *any* film, but 35mm film in particular), then in order to understand how a given lens will behave on a digital camera that happens to use APS-C sensor size, you would multiply by 1.5 to find the focal length that would behave the same ont he 35mm film camera you already know so well. If you *don't* already know 35mm film cameras very well, then you can completely forget all this, too.

QuoteQuote:
*As some may know, i'm from Argentina. Don't really know if "Filmmaking" is the correct translation of the career i'm doing.
In English, this term means you make movies. Motion pictures. Cinema.

Not sure if that's what you mean, but aside from that, you're doing great with the English!
07-27-2010, 09:29 PM   #8
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Just great...

It's amazing how you learn something every day.

Thanks all.

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