My kit had nothing useful for birding, or for basking reptiles... and that just could not be.  It came to the point where I even had to hire a Canon 100-400mm for my trip to WA.  The situation needed to be addressed while I still have some time to dedicate to photography and the geographic opportunities of our current migratory lifestyle.

I've read all the reviews on the Tamron 150-600mm and decided that it was unlikely I could find a better lens for the dollars.  There are some very, very compelling reasons to like this lens:

• 600mm - that's a fantastic long focal length and certainly in the useful range for birding.
• 150mm - that's a useful close focal length, and happens to be the same as my macro lens, so it's a familiar start point.
• x4 zoom - wow!  The felxibility this lens provides when compose your shots and adjust where you have no control over the range to you subject etc, is just wonderful.
• Size & weight - it's not a small lens, but it's not a monster life some of the faster primes.  I've hand held it now for a few hours at a time with no big issues.
• Cost - If, like me, you can't afford big fast prime glass this lens will let you get shots and shoot subject that you'd simply miss without it.
• Image quality (IQ) - I think the image quality of this lens, even at 600mm can be very good (as the image below demonstrates).

Pandion haliaetusPandion haliaetus (Osprey)

IUCN Status: Least Concern.

Taxonomy is hard. According to some there are actually four species/sub species of Osprey (see wikipedia for details). However the study that made this differential (base on genetics) was not adequately peer reviewed (checked by other scientists) and so is not acknowledged (see the ICUN link).

The boundaries of what is a "species" are not hard and fast. Nature refuses to be easily categorised and labelled. It's fluid, flexible and changing; as is our understanding of it. That makes it both messy and intriguing: but increasingly alien to people living in increasingly sterile, clean, prescribed, modern lives.

Now to provide a balance, there are a few things I'm not 100% happy with:

• Image Quality (IQ) - while the IQ can be very good, often it is not.  I've been shooting hand held, but at very high shutter speeds (1/1600) so that should eliminate a lot of steadiness issues.  Some shots look wonderful even pixel peeping at 100%, but a lot are not as sharp as I would like.  Now, I realise my expectations are not fair or appropriate... because I'm comparing it to the shots I see my mate getting with his Canon 500mm f4 (that's a > $10,000 lens), and I've already said that on some shots IQ is very, very good.... but not consistently.  NOTE: I don't have a lot of experience with long glass, so it is possible this is a technique issue on my part.
• AI Servo -  I got this lens with birding in mind and I'll admit I'm pushing what's possible shooting birds in flight.  However even when I've tried using AI Servo on my kids riding tricycles, or a helicopter doing a simulated sea rescue (ie not moving much), the results with AI servo have been..... ordinary.  It seems slow, and simply doesn't appear to track very well.  Once again, this is new territory for me.  I'm trying on big(ish), slow(ish) sea birds and struggling.  At the moment, I can't see it tracking smaller, faster birds at all.  I'd been pumped for shooting the insanely agile rainbow lorikeets in flight, but doubt I'll be able to.

So, the short version is that I'm generally very happy with the lens, and hopefully that as my technique improves, I'll get more consistent results and my keeper ratio should go up.  The AI servo issue has me a bit worried, but I'm hopeful that a rumoured firmware upgrade might improve that.

At some point I'll post a follow up to let you know how I get on with the lens in a few months.