This is a re-post of something I wrote back in 2013, about my Sigmonster.
My Sigma 300-800mm weighs in at about 12lbs and is a mere 2ft long.
While the lens is capable of taking great photographs, getting a decent shot at 800mm requires an exacting technique because the slightest movement of the camera translates into a huge movement out at the far end. This means you may need to use a remote release, lock the mirror up, drape your arm over the top of the lens without leaning on it, hang a weight from a hook on the tripod, or any number of similar means of dampening any possible vibrations. It also requires a very sturdy tripod and a good stable head.
The real trouble with this beast of a lens is that by the time you get the camera, lens, head, and tripod assembled, you’re humping something over 20lbs. Which means that a two-mile hike across level ground feels like a twenty-mile uphill trek by the time you decide to pack it in. –Especially during summer months here in Las Vegas when the 85 deg temperature at 6 am becomes 100 degrees by 10 and 115 by noon. 🙁
This Blue heron was shot off a monopod -750mm /f8 at 75 meters.
I highly recommend this lens, but only if you really need it. I bought it used for around $4000 back in 2011 and I can buy it used today for only a few hundred dollars more, so it’s still a good deal for a lens of that length and quality.
The problem I had was it was a royal pain to carry around. It was too long, too heavy, and was rarely necessary for the sort of shots I was taking. The end result was that I used it like crazy the first few months, then a bit less the next few months, then it lived in my closet for most of the rest of the time I owned it.