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 Post subject: lens mm???
PostPosted: Sun Oct 03, 2010 8:18 pm 
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Location: Osijek
hi,

i have been reading this forum for some time now and when it comes to lenses there is always that measurment "= on 35mm".

also what i have learned that focal lenght of the eye is 50mm, and noticed the 50mm lenses,

now my question is if i buy 50mm lens will i have the eye magnification or 75mm that equals on film, and will that mean that i need 35mm lens for eye magnification?

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PostPosted: Sun Oct 03, 2010 8:27 pm 
well what dslr do you have? on a canon a 50mm would be 81mm (I think my maths is correct) on a nikon/sony/pentax it would be 76mm due to the crop factor differences. (providing it's a crop frame dslr). Canon is a 1.62 crop factor and nikon/sony/pentax are 1.52


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 Post subject:
PostPosted: Sun Oct 03, 2010 8:31 pm 
1st of all,you can't buy lenses for your compact camera.

2nd,50mm on a cropped sensor DSLR is ~75mm on a 35mm camera.

3rd,for the focal range to be exactly 50mm,as the human eye sees,you need a ~35mm lens on a cropped sensor DSLR or a 50mm lens of a full frame camera.


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 Post subject:
PostPosted: Sun Oct 03, 2010 10:31 pm 
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@Razvan i have compact (very pleased) and im trying to learn here for the upgrade that is going to come later, i only said "if i buy" so i make understanding the question a bit easier..

@Eagle: i am familiar with the crop factor im just trying to understand when will i have picture with same "look" as when it would be with human eye,

Razvan cleared that for me, thy

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 Post subject:
PostPosted: Sun Oct 03, 2010 10:43 pm 
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Location: Boca Raton, FL, USA
The old film format measurements still exist because of the transition from film to digital - it's hard to let go of what has been used commonly for so long. So '35mm equivalent' still refers to 35mm film cameras. Digital cameras have sensors that come in so many sizes, and the size of the sensor affects how much of the lens' frame actually falls onto the sensor...a smaller sensor is not using the full lens opening circle, which is what is commonly referred to as the 'crop factor' - in other words, how much would you have to crop down the 35mm frame to equal the capture of the smaller sensor. Even P&S cameras have crop factors...but you never really hear them because they usually give you the camera's focal range in '35mm equivalent' terms. But you can always find out what the true lens focal range is by looking on the front of the lens itself...even on P&S cameras. The crop factor is the amount you have to multiply the lens' focal range in order to equal the 35mm sensor/film.

Full frame DSLRs are the ones that match the 35mm film frame in size - so those don't have any crop factor. APS-C DSLRs have smaller sensors than full-frame, and have a crop factor of 1.5x (Nikon, Sony, Pentax) to 1.6x (Canon). Olympus and Panasonic's 4:3 format has a crop factor of 2x. P&S cameras can range from 5x to 7x crop factors.

So, if you put a 50mm lens on a full frame DSLR, you get 50mm. If you put it on an APS-C DSLR, you get a crop equivalent to 75mm (or if using a Canon, you get 80mm). If you put it on a 4:3 Olympus, you get 100mm. If you were to design a P&S camera with a 1/1.7" sensor and a lens with a true focal length of 50mm, you'd get the equivalent of 300mm! Big crop factors on P&S cameras...which is why you'll notice the actual lens on most P&S cameras have a really small lens, with a true focal length range of something like 6mm to 72mm (which would be on a superzoom camera, delivering the equivalent of 36mm to 432mm).

If you have an APS-C camera, you want to look for a lens that will give you the cropped equivalent of 50mm - so rather than look for a 50mm lens (which will be more like 75mm), you would want to look for a 35mm lens, which would be close to the standard '50mm' focal length with the crop factor considered. If you have a full frame camera, then you want to look for a 50mm lens, as you have no crop factor. If you're shooting with a 4:3 sensor camera, then you'll want to look for a 25mm lens.

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 Post subject:
PostPosted: Sun Oct 03, 2010 10:56 pm 
@bakica and i was telling you how to get the focal length on any of the crop frame sensors (other then olympus and sigma) as all you do is multiply focal length by crop factor, so you'd chose a 35mm and multiply it by your camera's crop.


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 Post subject:
PostPosted: Mon Oct 04, 2010 9:51 am 
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Location: Osijek
thank you guys, i finally understand it, the measures on lenses are made for full frame and if you want to know what is the real view on any other camera you need to multiply that range with crop factor..

i have mixed it up in mind a lot before :oops:

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 Post subject:
PostPosted: Mon Oct 04, 2010 1:22 pm 
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The human eyes' focal length is not 50 mm.
It has an the focal length equivalent to a lens with focal length of 50 mm on a 24x36 mm frame(35 mm film or full frame sensor)
In fact the constant factor is the angle of view.
The human eye has an angle of view between 50 an 60 degrees that is, the angle between the horizontal extremes of the image
Any frame size/focal length that yields the human eye angle of view is called a normal lens, and approximates the human vision.
Wider than "normal" angles of view give us the wide lenses, and narrower give us the telephoto lenses.
So a lens that has the same angle of view as the human eye(normal lens) has ~32 mm for a cropped sensor, 50mm for a full frame, 80 mm for a medium format (6X6 cm) and so on.
A 50 mm lens is a normal lens for full frame, a telephoto lens for a cropped sensor and a wide lens for a medium format.

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