Re: Is one f-stop worth thousands of dollars?

[Shaun Canning]

Sorry I missed this follow-up question...but yes, with a f2.8 lens the 1.7x AF converter focuses my 300mm reasonably fast. I don't know what slower lenses would be like, but the loss of light with slower lenses will slow down the focus speed. Mark commented that the 'moving mass of lens elements' was the reason for fast or slow focus. The lens elements in the main lens have nothing to do with focusing speed, other than increasing or decreasing the amount of light allowed through to the AF adapter. The AF adapter does not 'focus' the subject lens by moving the lens elements. Rather you focus the subject lens at infinity (or any other point), and the tiny lens element in the AF converter does the focusing for you. The two sets of elements do not mechanically interact, other than for the adapter to pass on the the lens aperture settings in to the camera body.

So, in a nutshell, faster lenses are better for the AF converter. I don't know that I would bother with anything slower than an f4.0 lens. As for noise, well it's not too bad. Turn off the focus conformation beep on the camera, and the focus noise if bearable. If you leave the beep on, it will drive you nuts. The following image was taken using this combo. It's a really bad scan, but you get the idea.

http://www.heritageservices.com.au/images/DSCN0703_JPG.jpg

I have some other examples taken with this lens at http://www.photo.net/photodb/folder?folder_id=238096&ratings=true

Look for the photo's of the white dog, and the bird (Eastern Spinebill)

Cheers

Shaun

Mark Roberts wrote:

" W. Krasowski" <[EMAIL PROTECTED]> wrote:

From: "Shaun Canning" <[EMAIL PROTECTED]>

The 1.7x AF adapters are great. I use one with a Tokina 300 f2.8 MF to give me a 510mm f4.5 as John Mustarde commented. It is a fantastic set-up. You should be able to pick up one of these adapters on e-bay for less than $100.00 USD (I think I paid $89 USD for mine).

Thank you folks for your opinion!

Shaun, Is it fast while AF-ing? What about noise level? It is important to me as I shoot birds mainly.

I've found the AF very fast (as long as you're using it with an 2.8 or so
lens) - probably because the moving mass of the focusing elements is so low.
I've shot mototsports with my Sigma 300/2.8 and the 1.7x AF converter and
even on the old PZ-1p it was plenty fast enough. I have some shots at
http://www.robertstech.com/mid-ohio.htm

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Shaun Canning								
Cultural Heritage Services 						
High Street, Broadford,
Victoria, 3658.

www.heritageservices.com.au/

Phone: 0414-967644
e-mail: [EMAIL PROTECTED]
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