I acquired this 1.5x teleconverter as an intermediate step between using a telephoto lens and using one with a 2x teleconverter. I had hoped that using a lower power teleconverter would improve the image quality as well as being a boon to handholding as the loss of light would be lower. A 2x teleconverter makes a lens 2 stops slower, so a 100mm f/2 lens would become a 200mm f/4 lens with a 2x teleconverter attached. Supposedly a 1.4x or 1.5x teleconveter leads to a single stop of light loss, but actually a 1.5x teleconverter leads to 1 and 1/6th stops of light loss, you can feel free to round down to a single stop (I do). So a 100mm f/2 lens actually becomes a 150mm f/3 lens and a 400mm f/5.6 becomes a 600mm f/8.4.
Vivitar 1.5x teleconverter size comparison to Vivitar 2x teleconverter
The Vivitar 1.5x teleconverter appears to be multicoated as near as I can tell based on the reflections. Most 1.4x teleconverters are 4 elements and this 1.5x teleconveter looks like it probably is as well (it is very, very thin). The Vivitar 1.5x teleconverter is very tiny. It is around 20mm thick without lens caps on and weighs less then 100g (2oz). The teleconverter was $19 from KEH in BGN condition (though it looks brand new, no blemishes whatsoever on it). Anything other then 2x and to a lesser degree 3x teleconverters seem to be very hard to come by for OM cameras. So far I’ve seen a pair of 1.5x Vivitar teleconverters on KEH and some months back I saw a Soligor 1.5x teleconverter on Ebay and that has been it. I primarily bought the lens to extend the reach of my Sigma 400mm f/5.6 lens as well as my Vivitar 70-210mm f/3.5 when I need a zoom lens with longer reach. I am also using it with my Tamron 35-70mm f/3.5 macro to give higher magnification (instead of 1:2.8 I can now go to 1:1.9 with the lens and making it an equivelent of a 105mm macro lens, though pretty slow at an effective f/5.2).
Size comparison Zuiko 50mm f/1.8, Vivtar 1.5x teleconverter, Vivitar 2x teleconveter
At a guess I would say if you don’t mind stopping down a stop or two the image quality loss won’t be very noticable and with only a single stop of light loss this is much more doable then with a 2x teleconverter where you are lossing 2 stops of light. The few pictures I have taken with my sigma 400mm f/5.6 and the vivitar 1.5x teleconverter on I did notice some loss in image quality. I’ll have to do some better testing to see if this can be solved with stopping down a couple of stops or not. Some of it could also be because of my handholding technique which is still not stellar combined with the total focal length now being 600mm instead of 400mm. I’ll try shooting a test roll with my Sigma 400mm f/5.6 wide open a f/8 and f/11, with the vivitar 1.5x teleconverter on 1 and 2-stops down and with the vivitar 2x teleconverter 1 and 2 stops down as well as the same setup with my vivitar 135mm f/3.5 (at f/4, f/5.6 and f/8) and the teleconverters. I’ll try to eliminate the handholding issues by using a bean bag to rest the lens and using mirror lockup.
Eventually I would love to get a Zuiko 1.4x teleconverter to test against the Vivitar 1.5x teleconverter, but unfortunately due to the design the zuiko 1.4x teleconverter will not work with all lenses since it has elements that protrude from teleconverter barrel (which is why I didn’t try to get one at this time).
A couple of sample images with the vivitar 1.5x teleconverter (first two, Sigma 400mm f/5.6 + Vivitar 1.5x teleconverter last one Tamron 35-70mm f/3.5 macro + Vivitar 1.5x teleconverter)