Hva gjør en teleconverter?

[eiengen]

Lurer bare på en ting jeg, har ikke spesielt greie på ting og må derfor bare spørre meg frem. Hva gjør en teleconverter?

[s-ki]

Hei!

Ta en titt her, så skulle vel det gi svar på ditt spørsmål.

 

http://www.cyberphoto.se/index.php?http://...ligor/65200.php

 

mvh

s-ki

[dottnett]

Ordboka her på akam.no er nede for telling så jeg tok et kjapt søk på o'store internett;

 

http://www.faqs.org/faqs/rec-photo/lenses/faq/

"Q33. What is a teleconverter?

 

A. A teleconverter is a device that enlarges the center portion of

the normal frame to fill the whole frame. In 35mm systems where the

frames are 24x36 millimeters, a 2X teleconverter expands the central

12x18 mm to fill the full 24x36mm frame.

 

Q34. How does a teleconverter affect exposure, focusing, depth of

field and image quality?

 

A. A lens of focal length f and f-number N with a teleconverter of

magnification K attached will behave in all respects like a lens of

focal length K*f and f_number K*N.

 

If the aperture diameter and focus are left untouched and an ideal

teleconverter is attached, the lens will focus at the same distance,

the image, including the diffraction effects and lens aberration

effects, will be K times as large, the exposure will need to be K^2

times longer, the hyperfocal distance will be multiplied by K and the

depth of field will be divided by K. A practical teleconverter will

also contribute some of its own aberrations. (See the technical

notes.)

 

On the other hand, if you open the aperture to keep the same effective

f-number and hence the same exposure time, the image will be enlarged

by K, the diffraction will be unchanged, the depth of field will be

divided by K^2 and the hyperfocal distance multiplied by K^2. The

aberrations are increased by three effects: the lens is opened to a

larger aperture, the teleconverter multiplies those (probably larger)

aberrations by K, and then combines them with some of its own.

 

Since the focusing is unchanged, the minimum focusing distance is the

same whether or not a teleconverter is attached. (See the technical

notes.)

 

Q35. What is the difference between using a teleconverter at the time

the picture is exposed vs. enlarging more in the printing process?

 

A. Assuming the aperture diameter is the same in the two cases, the

teleconverter case will require K^2 times the exposure while the

enlarging case will enlarge the grain in the film K times as much.

The teleconverter adds some aberrations of its own, while enlarging

more will make aberrations in the enlarging lens more apparent. All

other effects are identical. In 35mm format, grain is usually the

dominate factor in image quality.

"