Why are they calling this 50mm telephoto?

jetswing said:
You've got it completely backwards. Pulling back on GH2 to match the crop of T2i with a same lens would produce images with completely different perspectives. You should be putting a wider lens on GH2 and leave the cameras in the same position.
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yes, he has it backwards, but, if reversed, it is still.a valid point. different focal lengths not only have different fov, but render the scene different. longer focal lengths have more spatial compression and thus are more appealing to shoot people with (and the reason we often do not shoot close-ups with wide angle lenses)this all being said, back to the OP's question, or sorta. as a previous poster said, i simply think about my focal lengths choices in regards to the format i am shooting. thankfully, the majority of film-like cameras are very close to Super-35 sized (save for the 2/3" varicams and such). i would just use the lenses for awhile. after a shoot or two, you won't even think about it.
 
A lot of confusion and misconception in this thread...

But to answer the OP's question in literal terms, a telephoto lens is one in which the focal length is longer than the lens itself. The specs say that particular lens is 62mm long, but if the distance, not including the front thread and rear mount, but just from the front lens element to the rear lens element, is shorter than 50mm (even if it is just 49mm) then the lens is by definition a telephoto. It's to do with the design of the lens and the shape of the elements.

This rings true for any lens no matter what the focal length or the field of view they produce. Indeed, many pancake lenses might be considered 'telephoto' by definition, simply because the physical design is so short so the focal length will likely be longer. If a 20mm lens is only 10mm long, then it is a telephoto lens, regardless of crop factor and image plane and format and all the other stuff.

Telephoto has, however, become common terminology for lenses with a narrow field of view. Used in this sense, it is a lot more subjective (as can be seen in the discussion the OP's question has triggered).
 
jetswing said:
IN THE REAL WORLD...mm, focal length, field of view are all the same. If you're shooting with a cropped sensor camera (still or video) in a comparison to 35mm/Fullframe sensor, you must consider the crop-factor when choosing a lens. For example, with Panasonic AF100, the crop factor is 2x. If you need a 50mm, you don't go out and buy a 50mm. Instead you buy 25mm. There's nothing confusing about that! It's a simple math. Of course, you would still call a 25mm lens a 25mm lens but you use it as a 50mm lens. Thus, 25mm becomes 50mm.

I'm not that old nor have ever shot on film but I've shot with both FF and crop sensor cameras along side each other plenty.
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In my opinion the only time you should be using a full frame 35mm still format as a comparison when determining lens selection and crop factors with your current camera, is if you are also shooting video with something like a Canon 5DmkII, which is a full frame camera. So while it is true that if you are comparing the 50mm lens from the FS100's S35mm size frame to a Canon 5DmkII's Full frame, the angle of view goes from 39.6 degrees to 26.6 degrees, and with the 1.5X crop from 50mm to 76.2mm. But, if you were to compare your FS100 to the industry standard Super 35mm film, then you are looking at a 1.1X crop factor. So that 50mm lens on a Super 35mm motion picture camera with a 27.9 degree angle of view, acts like a 52.6mm lens on the FS100 with a 26.6 degree angle of view. Not much difference at all really. Same holds true with the AF100 you mentioned having a 2X crop factor. It's really only 1.4X when compared to Super 35mm film. So a 35mm lens on an AF100 will act like a 50mm lens on a Super 35mm film cam.

Just the thoughts of an old guy who has shot on both sides of the road.

All the Best!

Dave
 
David W. Jones said:
In my opinion the only time you should be using a full frame 35mm still format as a comparison when determining lens selection and crop factors with your current camera, is if you are also shooting video with something like a Canon 5DmkII, which is a full frame camera. So while it is true that if you are comparing the 50mm lens from the FS100's S35mm size frame to a Canon 5DmkII's Full frame, the angle of view goes from 39.6 degrees to 26.6 degrees, and with the 1.5X crop from 50mm to 76.2mm. But, if you were to compare your FS100 to the industry standard Super 35mm film, then you are looking at a 1.1X crop factor. So that 50mm lens on a Super 35mm motion picture camera with a 27.9 degree angle of view, acts like a 52.6mm lens on the FS100 with a 26.6 degree angle of view. Not much difference at all really. Same holds true with the AF100 you mentioned having a 2X crop factor. It's really only 1.4X when compared to Super 35mm film. So a 35mm lens on an AF100 will act like a 50mm lens on a Super 35mm film cam.

Just the thoughts of an old guy who has shot on both sides of the road.

All the Best!

Dave
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The crop factor is always in relation to the 35mm full frame sensor, which what the lenses are based upon.
 
jetswing said:
I guess that's your choice but that still doesn't change the facts.


http://vimeo.com/videoschool/lesson/127/crop-factor
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No it doesn't change the facts. Crop factor can be between any two sensor sizes; Super 35 to 16mm, Full Frame 35mm to APS-H or APS-H to APS-C. Crop factor is NOT always related to full frame.

Also, the abel cine FOV link is a good link because it discusses lenses on different formats in regards to angle of view, thus correctly discusses it.
 
The Crop Factor is based on the 35mm lens system. The sensor size the variable factor but it's always in relations to the 35mm lenses and its focal length. Even lenses made specifically for 4/3 sensor (2x crop factor) are based on 35mm platform.

You can compare the difference in crop factor ratio between different sensor sizes but it all derives from 35mm platform.

Full frame sensor will ALWAYS have zero crop factor. You can claim that FF sensor would have an "x" crop factor to a medium format, for example, but that's really irrelevant for the most part.
 
jetswing said:
The Crop Factor is based on the 35mm lens system. The sensor size the variable factor but it's always in relations to the 35mm lenses and its focal length. Even lenses made specifically for 4/3 sensor (2x crop factor) are based on 35mm platform.

You can compare the difference in crop factor ratio between different sensor sizes but it all derives from 35mm platform.

Full frame sensor will ALWAYS have zero crop factor. You can claim that FF sensor would have an "x" crop factor to a medium format, for example, but that's really irrelevant for the most part.
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Obviously anything that any of us quote or say is not going to have much affect, so I will leave this alone now.
 
[h=2]I guess I never knew that crop factor could so confusing for some. There are only a few different crop factors out there. The crop factor is calculation uses the 35mm as a reference. Any full frame sensor (digital or 35mm film) would have no crop factor.

Crop Factor By Manufacturer[/h] Every digital SLR camera doesn't have its own unique crop factor. Instead, the same crop factor applies to all the cameras from the same manufacturer.

Here are the manufacturer-specific crop factors:


ManufacturerCrop Factor
Canon1.6x
Nikon1.5x
Olympus2.0x
Pentax1.5x
Sony1.5x

http://blog.planet5d.com/2011/11/sensor-sizes-why-do-we-care-and-does-it-impact-video/
http://www.digital-slr-guide.com/crop-factor.html
http://en.wikipedia.org/wiki/Crop_factor
 
hendosan said:
FOV is only one aspect of lens selection, and people place too much emphasis on it. Even though 25mm on a 4/3 sensor has the same FOV as 50mm on a full frame, the way they render images is way different. The perspectives of the two lenses are completely different.
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This is wrong. The perspective of a 25mm on a 4/3 sensor is EXACTLY the same as a 50mm on fullframe. EXACTLY. Don't believe? Do a test. The only thing changes is the DOF and that may confuse some people.
 
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