On 7 Dec 01 at 19:01, Malcolm Stewart wrote: > I have the Minolta Monocular converter, and I've tried using it with my 500 > f8 RF, 300 f4.5 MD and a few others. Not a really worthwhile experience. > Before you spend money, I suggest you try it out using adhesive tape or > whatever to hold it roughly in place. The converter has a focal length of > 10mm and so you get an effective magnification of "lens focal length in mm" > / 10mm. i.e. 10-40x on your zoom. What really kills it is the small exit > pupil, making viewing seriously deficient. Your zoom would offer something > like 0.7 to 0.8mm (approx. filter diam./ 40) at the long end, and I > think you'll find it quite difficult to view in comfort. Give it a try > before committing yourself.
Hmmm....;)) First, entrance/filter diameter on a 100-400/4.5-5.6 lens at 400mm is 400/5.6 = 71mm. Second, with magnification 40x (400mm lens divided by 10mm ocular), the exit pupil then becomes 71/40=1.8mm....at the wide end, 100mm, this would become 100/4.5 = 22mm entrance diameter, and an exit pupil of 22/10=2.2mm. Third: we are talking about a functioning IS, which means that normal rules of minimum exit pupil in relation to hand-held 'eye-ergonomy' do not apply (6mm minimum, as in a 42x7 binocular)....otherwise Fujinon wouldn't have made a mechanical image stabilized 40x16 with a price tag of US$5k and more....nor would Zeiss have made a 60x20 IS unit with a similar price tag.....once that exit pupil is rock steady, you don't need that large diameter as much, at least not in daylight (in daylight, 3mm is enough for a contracted eye pupil, at night, enlarged, it becomes 6mm). -- Bye, Willem-Jan Markerink The desire to understand is sometimes far less intelligent than the inability to understand <[EMAIL PROTECTED]> [note: 'a-one' & 'en-el'!] * **** ******* *********************************************************** * For list instructions, including unsubscribe, see: * http://www.a1.nl/phomepag/markerink/eos_list.htm ***********************************************************