Re: [APML] teleconverter lens questions

["Bill Ronald" <ronaldb@home.com>]

> Take your 50mm f1.4 lens and a two times converter:  It becomes an 
> 100mm f2.4, a two stop increase.

Actually it becomes a 100mm f2.8 lens, a two stop increase <g>.

(The square root of 2 is approx. 1.4, and the square root of 8 is approx.2.8.)

I have used both 2x and 3x teleconverters on the Sun and Moon and there is a 
definite "softening" of the image.  However, sometimes it is the only way to 
get the eclipse shot when you have traveled to the "middle of nowhere" for it.  
 Vignetting as isn't obvious with these nice round objects, but the solar 
corona definitely falls off.  Also, a small f5 refractor ends up as approx. f10 
and  f15 respectively, and the only control you have is the shutter speed.  
Unless you have a nice bright object, this also puts it right in the worst 
speed range for camera  vibration.

Cheers ... Bill

Bill Ronald, Vancouver, B.C.
ronaldb@home.com
Secretary/Webmaster - RASC Vancouver Centre
http://members.home.net/rascvc/index.html
49 15'00"N : 123 10'40"W

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