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04-03-2010, 02:53 AM   #1
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Over-exposure with TC

Just wondering if anyone had similar experience, and advice, on exposure with a teleconverter?

The Sigma 100-300/4 is a nice marriage on the K20. Just for a little more reach I recently added a Sigma APO 1.4x TC. Although it is pretty useless with most my other lenses I thought it was the best fit for the 100-300/4. Well had my first test today and it seems the rig with TC is now over-exposing by two stops. Is this normal? I tried spot, centre-weighted and matrix metering and each seems to over-expose....though spot a little less.

I fear light leaks but a web-search says that a teleconverter can require a little adjustment...but two whole stops

I'm used to winding the EV up or down for my older glass (K or M) but not with the newer AF offerings.

Looking forward to others experience as the longer reach is good but not at the expense of blowing highlights....

04-03-2010, 04:55 AM   #2
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Its ddue to the focusing screen, which has a funny characteristic which impacts the metering , combined with the fact thY the sigma TC does not correct the lens aperture but feeds the lens data right through

the K10D is the same

search for posts on metering with manual lenses for mor details
04-03-2010, 11:40 AM   #3
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I've noticed strange readings with TC's. If you have PhotoMe you can read off the meter readings with and without the TC to get the exact difference. Just type LV in the search box. I use the value for Segment 1.

It might have something to do with the values of TC's being just nominal one's i.e. a 2x could be 3x on certain lenses.

I just use trial and error to find the correct exposure when using a TC.

shim
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