I've been wanting to test my stable of OM-mount telephotos for some time. Someone became interested in purchasing one, and I thought I'd better make sure it wasn't a prize of some kind before I got rid of it!
Carol came running into the house, shouting, "There's a pair of eagles in our neighbor's tree!" They stayed there for over an hour, giving me an opportunity to test almost every telephoto of 180mm or more that I own. (I did not try the Zuiko 85-250/5, nor did I haul out the Celestron C8.)
• Soligor 180mm ƒ3.5 T-mount
• Zuiko 180mm ƒ2.8
• Tamron 300mm ƒ2.8
• Zuiko 300mm ƒ4.5
• Vivitar 500mm ƒ8 macro mirror
• Zuiko 500mm ƒ8 Reflex
• Zuiko 600mm ƒ6.5
• Bausch & Lomb 800mm ƒ10 mirror
• Celestron C90 1000mm ƒ11 mirror
In addition, I tested many of these with the two Olympus teleconverters. Due to it's protruding front element, some lenses would not accept the Olympus 1.4X-A teleconverter.
So, what did I learn? Bottom line: with the exception of the wide-open Zuiko 180/2.8, the Zuikos bested everything else. (The 180/2.8 joined that group when stopped down to ƒ5.6.)
• The lenses were mounted on an Olympus E-300, via an OM-->4/3rds adaptor.
• The E-300 was on Benbo #1 tripod with a Manfrotto 310 Mini-Gear Head.
• The E-300 was set to remote trigger, with a one-second mirror pre-fire.
• The E-300 was set to aperture priority -- you can see the shutter speed in the detail page for each image.
• The mirrors, of course, were tested at their sole aperture; other lenses were tested wide open and stopped down two stops.
• Color balance was (unfortunately) set to automatic -- there appears to be considerable color differences between lenses, but with it set to automatic, it's hard to say that it's all the lens' credit or blame!
• From each test image, I cropped approximately the same view, to give an idea which lens/converter combo would give the best results, regardless of focal length.
• Other than re-sizing and cropping, no post-processing was done to any of the images.
The cropped results were a bit surprising: you're better off cropping the center of the Zuiko 300/4.5 than using any of the non-Zuiko mirrors! So focal length may not be worth as much as megapixels when you need "reach."
My overall pick? I'd read some bad reviews, but the Zuiko 600/6.5 redeemed itself in my eyes, with the Zuiko 500/8 Reflex a close second.