When using a converter you multiply f stops just as you multiply focal
length. Using a 1.4x converter costs one full stop and a 2X converter
costs two full stops. From f/2.8 the 1/3 stop increments are:
2.8, 3.2, 3.5, 4, 4.5, 5, 5.6.
As you can see, 3.5 is only 2/3 stop smaller than 2.8 and 4 is a full
stop but only one stop down. If you used a 1.4x converter on the
100/2.8 it would become a 140/4 (1.4x100 and 1.4x2.8). While the
100/2.8 with a 2x converter ends up at 200/5.6 and is slower than the
200/f5 it's only 1/3 stop. If you started with the 135/2.8 and used a
1.4x converter you'd be very close to the 200/4 at 189/4.
Chuck Norcutt
r.burnette@xxxxxxxxxxxxx wrote:
> You are probably right, Chuck. I was thinking that the two stops
> derived from the 2X would comprise f3.5 then f4.
>
> Robert
>
> ----- Original Message ----- From: Chuck Norcutt
> <chucknorcutt@xxxxxxxxxxxxxxxx> Date: Saturday, December 16, 2006
> 17:22 Subject: [OM] Re: Newby Intro + Zuiko prime lens question To:
> olympus@xxxxxxxxxx
>
>
>> Good advice for Louis but I have a few comments.
>>
>> Your math got a bit confused on the 100/2.8 with 2X. That becomes
>> a 200/5.6 so it's not actually faster then the 200/5. Drat!!!
>>
>>> Chuck Norcutt
>
>
>
>
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