u/EmotionalCouple9032

Hi, I am looking for the lightest possible lens for some casual birding during my hikes. I am a geologist by profession, so I can't carry too much gear. I do possess an OM-5, which i can pair with the 75-300ii or pana/oly 100-400 lens. Although the latter is small compared to others in its league, I suspect that it wont fit my sling bag. Carrying a heavy backpack is not an option. So i invite comments from people who have experience with this setup. I intend to use the lens during day time only. Any other suggestions are welcome. I want decent enough image quality to post on IG.