On Tue, 17 Feb 1998 11:56:46 +0100, "Per Nordenberg"
<per.nordenberg@xxxxxxxxxx> wrote:
>Frank, I know we´ve been through this before (perhaps you and some other
>listmembers remembers),
> but I don´t think your 200/4 changes into a 340/4.5. I have an IS-3000/B-300
>combo myself and I was as surprised as you perhaps will be when I learned this.
>
>These front converters or front extenders do not affect the main lens in the
>same way as ordinary converters (which are put between the body and the lens)
>do. In technical terms they are referred to as Galileo telescopes. Ordinary
>converters affect lens speed but not close focus, but these extenders affect
>close focus but not lens speed (quite an astonishing statement, right?).
>These facts are also reflected somewhat in the small instruction leaflet
>to the B-300, although I didn´t understand this at once. It says: "This
> telephoto conversion lens can be easily attached to the lens of the
>Olympus IS-3/IS-3000. WITHOUT CHANGING THE APERTURE SETTING, THE FOCAL
> LENGTH IS MAGNIFIED 1.7 TIMES (300 mm)."
>
>The conclusions of the earlier discussion was as far as I can remember
>(have it archived on another PC but no monitor to use) that there is no
> easy way to confirm that the lens speed remains unchanged and that
> these extenders did this with the help of the human eye.
I missed the earlier discussion, and certainly didn't take part in it.
Why would it be difficult to measure the lens speed, or aperture?
BTW, I mentioned the figure to show that this was a good performance -
only 10 percent speed loss. But let me try to explain what I did.
With a normal 1.7 teleconverter, the 200/4 would have changed into
a 340/6.8. Olympus (seconded by you) claims that this B-300 converts
it into a 340/4.0... or at least that is how I translate the figures
from the instruction leaflet which strictly spoken apply for the IS3
only.
I measured (through the lens with an OM-4T and checking values with a
handheld meter) that this was not completely true for the OM setup I
used.
Focusing on a large brick wall magnification was indeed 1.7 times as
high as with the plain 200 (just counting numbers of visible bricks).
But keeping the - apparent - aperture at 4.0 the needed exposure time
rose slightly, from 1/250 to about 1/225. (I call it apparent
aperture, because the 200 was still on the camera, and it was the
aperture mechanism of this lens that was used in metering, not taking
into account the influence of the teleconverter).
I concluded that the effective maximum aperture of the combination had
become somewhat smaller, from the original 4.0 to (about) 4.5.... and
I think this is a beautiful performance, compared to the 6.8 you would
have expected with ordinary converters. Maybe the increase is so small
that Olympus has decided to call it 'without change ...' and
considered the scale being logarithmic this may be justified.
On the IS3, in aperture priority mode, you can also see the needed
exposure time becoming slightly longer when putting the extender on.
Please correct me if I did something wrong here. But I think that we
say basically the same thing: the maximum aperture (and consequently
the speed of the lens) remains almost constant.
>
>My experience with the B-300 is mostly positive. As you say you can
>only use it at the extreme 180 mm tele position on the IS-3. I´ve find
> it somewhat difficult to mount at times since the threads are very fine
>threaded, but when once mounted you can practise handheld shooting almost
>as with just the IS-3. The combo is a bit frontheavy and you must rest it
>in your left hand though. Other drawbacks are you cannot use filters with
> these extenders and that the front element on the B-300 is rather
>unprotected (the convex surface of the element protruds somewhat and
>there is no lock that keeps the cheap plastic lens cap in position
>and it frequently falls off). I haven´t found any significant
> decline in sharpness when using it, and I sure would want the
> wide converter as well if I could find one. It´s interesting that
>you can fit it to all OM lenses with a 55 mm thread, although
>I don´t have any myself. Hmm.. a 65-200F4 / B-300 combination would
>certainly be interesting. BTW, I paid 1 350
>SKR for mine used but in mint condition. I´ll look forward to hear your
>results.
>
>Best regards,
>Per Nordenberg
>Sweden
To paraphrase some Guy known to us all: Ah! I do have a beautiful
65-200 in stock. And a 200 as well! Please email if interested ;-)
Best wishes - Frank.
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