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02-06-2009, 10:10 AM   #1
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TeleConvertor Query

Hi people!

As always I have done a search for this, but I either get 100's of hits (that don't seem related) or nothing at all .....

Anyway, I've recently taken delivery of a Sigma 100-300mm f4 + 1.4TC.

When I'm using these together my K10D doesn't seem to realise there is a TC there - it still lets me select an apperture of f4 for example even though I know the minimum apperture is f5.6?

Is this normal behaviour?

It still lets me take pictures and everything else seems to respond as expected but I thought it would be clever enough to realise that the TC is there and restrict minimum apperture to f5.6?

Thank you

Lee

02-06-2009, 11:00 AM   #2
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Yes, it's normal. The same physical lens opening that worked out to f/4 without TC works out to f/5.6 with TC. Set the lens to f/4 and it *will* be f/5.6 in reality. Set it to f/5.6 and it will be f/8 in reality. And so on. But unless you're tying to use the "sunny 16" rule, or the "guide number" rule for calculating aperture with flash, you don't really need to think about that. The camera produces the right results without you having to do a thing to compensate.
02-06-2009, 11:36 AM   #3
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If you set the camera at F4 you should see it select a proportionally slower shutter speed when using the TC compared to lens only. An interesting test would be to check the shutter speed selected by your camera if you choose F5.6 with just the lens (no TC) and compare that speed to F4 with the lens + TC.
02-06-2009, 11:56 AM   #4
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As Marc states, normal behavior. You got a great combination! If you have any desire for the 2x EX converter, even though the Sigma web site says that you lose autofocus capability, it still works on my copy. Enjoy! The perfect air show or sports lens.

02-06-2009, 12:21 PM   #5
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There are a couple of "cautions" I would like to put into this discussion.

FIrst, some TCs have a chip internally that actually do modify the apature back to the camera, sigma is NOT one of these.

Second, if you are using a K10D or K20D, adding a TC to this lens can introduce a perminant exposure error, tending towards over exposure.

I use both 1.4x and 2X TCs on my sigma 70-200 F2.8, and find I need about -.7 stops with the 1.4X and -1.3 stops with the 2X TC to compensate for the metering error.

Note the metering error has been discussed to the death already.

Also note that the focal length is also fed directly through the TC hence your shake reduction will not be correct.

As far as focusing with an F4 lens and 2x TC, I have once (perhaps foolishly) stacked both 1.4x and 2X on my 70-200 F2.8, and it would hunt a little but on a bright day could get focus confirmation. Bt 560 mm F 8 is not all that great.
02-06-2009, 01:14 PM   #6
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Thanks to everyone for the replies.

I haven't had much of a chance to play with the lens and TC much yet but will hopefully be posting photo's soon
02-06-2009, 01:18 PM   #7
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QuoteOriginally posted by Lowell Goudge Quote
...

Second, if you are using a K10D or K20D, adding a TC to this lens can introduce a perminant exposure error, tending towards over exposure.

I use both 1.4x and 2X TCs on my sigma 70-200 F2.8, and find I need about -.7 stops with the 1.4X and -1.3 stops with the 2X TC to compensate for the metering error.

Note the metering error has been discussed to the death already.
This I was not aware of! Guess I just ignored those threads. Time to give the search engine a little exercise.
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