[peskywinnets]

Hi there,

I have a Canon 50mm f/1.8 & am pondering buying some Kenko tubes for Macro work.

I was just wondering how the focus performs....I read somewhere that auto focus works only works at an aperture of f/5.8 or smaller - how does this work in reality? (ie is focusing easy enough?...cos with such a small LCD on the Canon EOS-350D it would be a bit of a bind if the focusing isn't precise with the Kenkos)

[onefivenine]

In my experience auto-focus is useless... I manually focus and then move the lens in and out closer to the subject or vice versa.

[jomike]

Originally Posted by peskywinnets

Hi there,

I have a Canon 50mm f/1.8 & am pondering buying some Kenko tubes for Macro work.

I was just wondering how the focus performs....I read somewhere that auto focus works only works at an aperture of f/5.8 or smaller - how does this work in reality? (ie is focusing easy enough?...cos with such a small LCD on the Canon EOS-350D it would be a bit of a bind if the focusing isn't precise with the Kenkos)

Extension tubes do not affect the aperture because they do not place any more glass between the lens and the sensor, they just allow the lens to focus closer by placing the lens further away from the sensor.
Also the camera focuses with the aperture of the lens fully open, then stops the aperture down to the chosen value and takes the picture.
As onefivenine mentioned, all this is academic because in macro you focus manually, usually by choosing a focus point and then moving the camera forward and back while looking through the viewfinder to fine tune the focus point. AF is not accurate enough for this.

Mike

[peskywinnets]

Thanks guys, so if the auto-focusing with the Kenko tubes suck, is there anything to be gained over chinese extension tubes that don't auto-focus.....

http://cgi.ebay.co.uk/CANON-Macro-Ex...QQcmdZViewItem

????

(being unfeasibly tight, you might just have saved me forty odd quid, which is never a bad thing)

[jomike]

The Kenko tubes support AF and metering. I doubt if the cheap ones do either. AF is not that important for macro, but metering is, unless you are prepared to do both manual focussing and metering. The cheap ones might also not fit as well, causing the lens to wobble. Your call.

Some macro links:

http://nocroppingzone.blogspot.com/2...technique.html

http://nocroppingzone.blogspot.com/2...sing-tips.html

http://natureswildscapes.com/index.p...ticles&start=0

Mike

[senu]

Regardless of your intended use.The 50mm 1.8 is not a strong performer in the AF dept
And with macro manual focus ( especially with a very shallow DOF) is a must
Trust me on this , I have the 50mm 1.4 which is way better at this ( but which is 3-4x as costly) not "sharper" but better built and AF is faster and more accurate ( amongst other things) than the 1.8
I am in the middle of a just a multiple Portrait project for over 25 members of a Ward team and found the 30D struggling to AF with the 50mm 1.8 ... manual focus and AV mode ( to decrease aperture) have been my saving grace!!
The 17-85 or 17- 55 USM IS had no such problems