Is this...

a) Suitable for an istDL ?
b) worth getting regardless of the lack of auto focus?
c) a useful lens, ( I only have the kit lens and an old manual everything 70 -162mm lens )

http://cgi.ebay.co.uk/Sigma-UC-28-70mm-f3-5-zoom-Pentax-PKA-fit-UV-caps_W0QQitem...

The difference between the long end of the kit lens (55mm) and the long end of this (70mm) is fairly insignificant - your kit will give a similar field of view by walking two steps forward. At the same time this doesn't go as wide as your kit (the difference between 18mm and 28mm *is* significant) which means you'll be pretty much duplicating what you already have but with a reduced range and lack of AF. It'll work fine on your camera but why would you want it? If it were me I wouldn't bother, even for a fiver.

If you're looking at bulking up your lens collection and want something genuinely good yet cheap (which will give you something you don't already have covered) then I'd suggest looking out for a Pentax M50/1.7 - there are plenty floating around on eBay and they tend to fetch between £10-20.

The 1.7 was often sold as a kit lens back in the film days and isn't as glamourous (or fast) as its 1.4 sibling, however, 1.7 is still very quick compared to your current lenses and the optical (and build) qualities are exceptional - a real step up from what you've used thus far. The focal length makes it great for portraits and the ability to shoot with razor-thin depths of field and in low light (without flash) will be a real eye-opener.

The downsides are no autofocus and no automatic shooting modes - you'll have to meter manually and set your own aperture/shutter speed (just like folks did when the lens was new), this is quite straightforward though and the results will be worth it.

This one finishes tomorrow and looks quite good, I reckon it'd be a better spend of your money than the Sigma...

I would be very wary of buying any lens that had such a serious fault, plus the probability that someone with limited knowledge has had the lens open and removed some of the mechanism.

There are plenty of mint, intact lenses around at very reasonable prices.

Er, John's referring to the Sigma here, not the Pentax I linked to - just to clear that up (had me frantically reading the description again!)

Thanks folks.
You pretty much confirmed what I thought, but when I saw the price, I did wonder whether it might just be worth it.

I'm not desperate, yet, to increase the amount of lens' I have, ( I need to learn to use what I already own ), but ever mindful of a bargain, I tend to keep an eye on ebay.

OK, I just had a look at the 50mm lens on my Super ME. It has 1:2 50mmm written on it, but nowhere does it say 1.7 or 1.4
So..is this an f1.2 lens, or am I being to simplistic jumping to that conclusion?
If it is, is this any good? I just put it on my digital camera and it works well, so either way..it is another lens

It sounds to me like a 50mm f2 lens you have there. Still a very useful lens, try it on your DSLR and see.

Your lens has a maximum aperture of f2 (1:2) and f1.2 lens is labelled 1:1.2

Thanks.
I think I'll read up on what the numbers mean

Is the "f" number measured the same as I would with my telescope, ie, focal length divided by diameter of front ( objective?) lens? My scope is 1m long with a 100mm lens so is an f/10, which I would refer to as a "slow" telescope.

Presumably the same applies in photography,the smaller the "f" number the "faster" the lens?

The smaller the f number, the wider the aperture and the faster the lens.

A 50mm lens with a 25mm diameter is f2. A 100mm lens with 25mm diameter would be f4.

This explains why many zoom lenses have variable apertures. The glass diameter stays the same, so everything else being equal as the lens zooms the f number must change.

In the days before multi-coating a good deal of light was lost in a lens because of internal reflections. This gave rise to the T number (transmission) for the purposes of exposure calculation. The T number gave the actual transmission of light. It has not been used for many years.