Olympus 75-300 vs Panasonic 100-300

Ok, I am just considering a rental for an upcoming trip to San Diego and the SD Zoo. Currently use the Oly 40-150mm F5.6, and while it is reasonably sharp, it's is a bit short for the zoo. We visited the SD Zoo and Safari Park in 2007, and I did Ok with only 280mm of reach (Canon 70-200 F4 L IS + 1.4x on FF).

The way I see it:

Olympus Advantage:

• Lighter and smaller (under 1 lb while the Panny is just over 1 lb)
  
• Zoom ring direction is familiar (the Panny zoom ring turns in the opposite direction)
  
• 25mm more zoom on the short end
  
• No potential IS/IBIS conflict with Olympus OMD Camera
  

Panasonic Advantage:

• 1/2 stop faster at the long end (the big difference!)
  
• Perhaps better built in IS performance than what I can get out of my aging EM-5 IBIS (plus Oly lens).
  

I think it really comes down to 1/2 stop slower, which is not insignificant, vs lighter/smaller. Any thoughts or hands on experience with these lenses. The Panny 100-400 is of course better but at 2+ lb, it is non-starter for me. Also, don't really know how the build in IS of the Panny lens will interface with the camera's IBIS. Ideally, IBIS will automatically turn off when the lens IS is activated (and turn on when the lens IS is off), but it would be a real PITA if I have to manually shut down IBIS to use the lens IS (will likely forget to turn IBIS on with my Oly lenses).

If you do not change lenses a LOT and you are shooting casual stuff. I found that I can work with both Panasonic and Olympus zooms. So I have to turn the zoom ring in the other direction, not a big deal.

But in sports or fast action, were I have a very very short time to zoom, I rely on muscle memory to zoom the lens in the correct direction. Then it is critical for the zoom rings to work the way my muscles are trained. I gave up on the Sigma zoom after about 20 minutes, as it zoomed in the opposite direction from my Nikon, and I kept loosing shots by turning the zoom ring in the wrong direction.

Since I do shoot sports, I went with the Olympus 75-300, to keep my sport lenses zooming in the same direction.

BTW, I do NOT shoot sports with both Olympus and Nikon at the same time. The zoom rings turning in opposite directions is too confusing. Ideally I should have gotten Panasonic lenses for sports, but it is too late now.

In full daylight, the slightly slower Olympus should not be an issue. Will you be shooting wide open, likely not.

re IBIS, check your menu setting.

There is a setting (at least on my EM1) to set the IBIS to be ON if there is no lens IS, or turn OFF when there is lens IS.

Thanks for your feedback. I never used a zoom lens that did not zoom out when turned counter clockwise (Olympus and Canon) so it may become a bigger issue than I thought to rent a Panasonic for a week or two. My EM-5 does not have a documented feature to automatically turn off IBIS when lens IS is detected. It may work that way, but is not stated in the owner's manual. Zoos can have subdued light and many animals require a high shutter speed to freeze movement. I find myself at 2000 ISO (or higher) regularly when shooting at the Bronx Zoo at F5.6 with the 40-150mm.

I will have to figure this out and decide what to rent, or simply go with what I currently have.