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Auto focus problem on 20d/100-400l usm is plus 2x exteneder


31 May 2005 2:35AM
I need help!!!

im fairly new to this and on last friday brought canon 20d, 100usm macro, 100-400l is usm, 2x exrender and aload of other stuff.
Upon using the 100-400 i thinks its great, but when i put the extender on aswell i cannot auto focus because it will not go any lower than f11, it says on the box it needs to be f 5.4 or lower to focus, also i seem to be getting noise with the extender on, i am using it mainly in apeture priority, is there a rule of thumb or such like i need to know so as to get the most from my 800mm, i have one shot in my PF so far from using 800mm that was not too bad but the others well not so good.
Any help would be much appreciated

Cheers Luke J

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digicammad e2
11 22.0k 37 United Kingdom
31 May 2005 2:45AM
Luke when you put on the extender you will be losing 2 stops of light due to the extra glass, perhaps more. Long zooms are notoriously slow anyway and the extender worsens this. Manual focus is a fact of life with that setup.

In general if you want to use a long zoom and extender together you need either plenty of light or to increase the iso speed.

Re the noise you report, this is probably due to the longer exposures or higher iso you are having to use, unless the extender is dusty. :0)

Ian
goatster e2
10 399
31 May 2005 2:47AM
Ian, beat me to it.

Luke from the Canon description for the 2x convertor:

Quote:With the Extender attached, the f-number decreases by two stops. Auto-focusing is possible with lenses whose maximum aperture is f/2.8 or faster.


Agree with Ian re noise, check your ISO settings (althought the 20 is known for low noise) and shutter speed.

Tony
31 May 2005 2:49AM
Thanks for that, i was using iso 100/200 on them maybe need to go higher in fair i was shooting the shots a bit dark to capture better detail then when i went to lighten them up thus i was getting noise, i was also using manual focus on them, need some practise on that front....
thanks again

luke

the blue tit in my PF was shot at iso200 but i did have a bright wall in the background maybe this is why it come out better??
ahollowa e2
10 1.1k England
31 May 2005 3:56AM
You were probably under exposing the shots. I had this problem and thought my 10D was noisy at high ISO. What infact was hapening was I was setting the speed and the camera was running into the widest apperture and underexposing when I wasn't looking!! I tried the otherday increasing the ISO so the histogram moved back to the right and the shots wern't under exposed and most of the noise disappeared. I would love to lay claim to this idea but there was a very informative thread that ran on here a couple of weeks ago discussing whether the long held view that you should always under expose a DSLR actually held water. Apparently the decision was it doesn't!!

cheers

Al.
cambirder e2
10 7.2k England
31 May 2005 9:02AM
A 2X converter on a f5.6 lens is not a combination I would recommend. I know it's an IS lens but I think working without a tripod a 800mm is not going to produce good results, and MF is not easy when you have such a narrow DOF and you are looking through a dark view finder.

I find it difficult enough with a 1.4x on my 400mm f5.6 prime lens (although I now have AF with that combo as I've upgraded to a 1D) personaly I would not persist with the 2x and return it for a refund unless you plan to buy some fast glass in the near future.
u08mcb 10 5.8k
31 May 2005 9:08AM
Also if you're patient and sit still, you'll be able to get closer to your bluetits and fill the frame at much smaller focal lengths. 200mm should be easily done, again provided you don't move too much and stay quiet for a while.

800mm would be of more use when taking photographs of much more timid "wilder" birds than those that frequent gardens but as Paul correctly says, 2x TC plus a starting aperture of f5.6 is pretty much unworkable.

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