Searched through all the forums and online, still can't decide on a telephoto for travel use, so seeking some opinions. I am primarily a < 100 mm equivalent focal length person, and will typically use some combination of fast primes (PL25, O45 on the way, either P14/PL15/O17 in future) and the versatile and weatherproof O12-50. I will be using it primarily for daytime travel to capture interesting details in the distance, and those unique compression shots. Secondary use as a 'zoo' lens, mostly for interesting animals I come across rather than actual zoos or serious wildlife stuff. As part of a kit, the telezoom will be taken and used for specific shots/scenarios only. Because it's for travel, I'd like it to be light and not too large for taking along in addition. As I will be using it purely as a telephoto, sharpness across the frame at the far ends seems to be more important than the close ends. And because I will be using it as an occasional day time lens, the P35-100 and O40-150 f/2.8s are overkill and outside the money/weight criteria. I am not considering any of the superzooms either because they don't go wide enough, are heavy and large, are not weatherproof, are way more expensive, and do not appear to perform well at the telephoto end. OIS is not of much concern as I have an E-M5. Focusing speed might matter though, I've not heard much about focusing speed of Panasonic telezooms vs the O40-150 on an Olympus body. So it seems my choices come down to the usual suspects: O40-150, P45-150, P45-175, P45-200, as well as the rogue element of the unreleased mini 35-100 that goes with the GM1. My current thinking is as follows: Price: P45-200/O40-150, both easy to find used in NZ. Telephoto IQ: P45-150/O40-150? Weight/size: O40-150/P45-150/P45-175 Feature: P45-175 for its power and non-extending zoom? But occasional shutter shock issues? Having never used a telephoto zoom on an ILC before, how bad is the 'gas pump' effect? Does it just go into the lens or into the sensor cavity as well?