I’m not going to kid myself that Sony’s 18-250 DSLR lens (based on a successful Tamron design) is a stellar performer to rival Canon’s L glass or similar. That would make it far too good to be true. After all, it covers a very wide focal length range, so much so that you can pretty much leave it on the camera and forget about ever needing to change lenses. On my Sony A100 that range is the 35m equivalent of 27mm, a decent wide angle, all the way through to a whopping 375mm at the long end.
It can though produce some very sharp, highly detailed pictures, with plenty of bite and rich colours, even if it doesn’t quite perform at a consistent enough standard to stop the more serious Canon and Nikon users being a bit sniffy about it. For example, it can be a tad soft at longer focal lengths unless you stop down.
For me it’s a revelation. For a year after I acquired my DSLR I was using an ancient Tamron 28-200 (71D) which was starting to really frustrate me with its softness, wishy-washy colour and general lack of punch. It performs far worse on the DSLR than it ever did when I used it with my old Minolta film SLR. By comparison, the Sony lens is contrasty and sharp, occasionally bordering on the 3 dimensional.
Not something a professional would use but a godsend to a reasonably keen amateur who doesn’t want to cart a shedload of gear around everywhere.
There are drawbacks. The maximum aperture at the long end is F6.3 so you need a fair bit of light, and as I mentioned above you really want to be stopping down if you can. The A100’s built in image stabiliser helps quite a lot. You can with a DSLR just ramp the ISO rating up as needed, but I try to avoid going beyond ISO 200, or if desperate 400, with the A100 because noise starts to become an issue.
There is a lot of barrel distortion at extreme wide angle. I quite like the effect but you can get rid of it quite effectively using say PT Lens.
Some users have complained focusing is a bit slow, but I haven’t found that to be a problem. Then again I am more of a landscape than action photographer.
The focusing speed may have been more of an issue with the original Tamron design on which the Sony lens is based. The Sony variant is reckoned to focus faster and have better bokeh.
Maybe the biggest downside, from a long term perspective, is that it is a DT lens, that is it is designed for the 24mm sensor size. It would be no use to me if I ever traded up to an A900 or some other future Sony full frame DSLR. If you listen to Scott Bourne of TWiP fame you will hear that it is only a matter of time before all new DSLRs are based on full frame 36mm sensors, even if it could be a while.
I couldn’t care. I’m just delighted to at last have a lens I can truly enjoy right now.