Lens question

Hello.

 

I have a question regarding lense focal lengh increase on digital

SLR's. Is it true no matter what type, make, model lens that i buy for

my D70, im always going to get a 3rd increase on the optical range. If

so if i buy 17-55 it will actually be 27-82mm,

 

Any help would be appreciated.

True....

I've never used any of my lenses on a film camera, so on a D-SLR a 17-55mm lens is just a 17-55mm lens. My mind thinks in terms of a D-SLR because that is all I know. The only time the 1.5x factor is relevant is if you shoot both film and digital. Otherwise, 17-55mm is simply a unit of measurment.

To be precise, the 17-55mm would have the 35mm equivalent focal length of 25.5-82.5mm on your D70.<div></div>

It's actually a 50% increase in EFFECTIVE focal length as compared to using a lens on a

full-frame camera, (insert endless discussion here about cropping factor vs focal length).

 

Yes the 17-55 becomes the appx. equivalent to a 27-82.

Thanks for the quick response.

 

So, a nikon 17-55mm DX is giving me a true 17-55mm?

But at the same time, understand that the 17-55mm DX Nikkor will still retain the same depth of field characteristics as a 17-55mm full-frame lens mounted on a 35mm camera. The focal length is immutable; only the size of the imaging area has changed.

No, actually it's not any kind of difference in focal length. A 17 to 55 mm lens is still a 17 to 55 mm lens no matter. To focal length doesn't magically change when you mount the lens on a DSLR, just like it doesn't magically change into nothing when you remove it from the camera. What changes is the angle of view captured by the camera. The full from a standard 35 mm film camera has a larger capture area than the typical DSLR sensor. Think of it as an in camera cropping factor and you've got it.

So the fact is that the sensor on digital cameras are 1/3 smaller than that of a standard 35mm. So that basically means im getting a slightly cropped version on a 35mm shot. Which i suppose why they say you get an increase of .3

 

So if i got use to using a 17-55 with my F100, and used it @17mm all the time, if i then used my D70 @ 17mm i wont be getting the same picture.

 

So do i then need to compensate and drop down to 15mm to achieve the same shots that i was use to achieve with my standard 35mm??

"So if i got use to using a 17-55 with my F100, and used it @17mm all the time, if i then used my D70 @ 17mm i wont be getting the same picture."

 

 

Yes, though the 17-55mm is a DX lens, so at 17mm, it does not project a large enough image circle to cover a full 24x36mm frame without vignetting. If you needed a wide pro zoom that would work at 17mm on both a D70 and an F100, you would want to get the 17-35mm f/2.8 lens.

 

 

"So do i then need to compensate and drop down to 15mm to achieve the same shots that i was use to achieve with my standard 35mm??"

 

 

Umm, if you were using a 35mm focal length lens on a 35mm camera and wanted to acheive about the same field of view with your D70, you would want to use a 24mm lens (24mm times 1.5 equals 36mm).

Like many have said, there is NO CHANGE IN FOCAL LENGTH.

 

Digital cameras have a smaller sensor, covering about 44% of the area that the 36 x 24 mm negative used to cover. This means that the images you shoot with a 50 mm lens will now have the field of view that a 75 mm lens would give you on a 35 mm camera. That's a 50% increase, not one third.

 

If you want to use your lenses like you used to (50 being a normal, 85 being a head and shoulders portrait, 35 being a full body lens, etc) then you can get a Canon 5D for about $2,600 or wait for Nikon to come up with a FF camera.

 

It's easier to do the math and think of your 35 mm as the normal lens, with anything above being telephoto and anything below being wide angle.

 

Ignacio

This is one of those questions that's easier to understand if you shoot multiple formats

(Personally, I shoot 35mm and 6x6 right now). Focal length is focal length. Angle of view at a

given focal length is dependant on sensor size/image format.

 

So on a 6x6 SLR, 50mm is a nice wide angle, on a 4x5 view camera it's massively ultra-wide.

On 35mm it's a hint longer than 'true' normal (Which is actually 43mm) and on a DX-format

sensor it's a nice portrait telephoto. It's still 50mm and still has roughly the same DoF across

all formats.

Not that this is the case of this lens, but if you use to read the DOF scale to selectively focus objects in your scene, mind that they refer to the circle-of-confusion on film format. That is, if you think things are going to be in focus on your digital sensor, they will not be... more than a stop (1 1/3) difference to be expected.

Matt, if you use a 17-35 on your F100 you'll need to use a 12-24 on your D70 to get nearly the same view through the viewfinder. The 12 won't be quite as wide on D70 as the 17 is on F100, but very close.