No.

An ND filter reduces all light passing through it. A polariser, on the other hand, only cuts light in a particular plane, and has a very different effect. It is most well-known for cutting reflections from water, and darkening skies whilst leaving the brightness of clouds unaffected.

In both these cases, an ND filter would simply darken the scene.

They are totally different things.

G

We don't have air. We have hundred mile an hour pure ozone.

G

Yes. In the sense that you could attach a hose-pipe to your nose in order to emulate an elephant.

Simpler to buy a ND filter. Or three.

G

Pentax lens nomenclature is rather arcane. However, for persons of Sherlock Holmesian talents, there are a few obscure clues.

One of these can be found by examining the business end of the lens closely. If it says SMC Pentax-A, then a powerful mind, with the aid of a little opium (or Bowmore's) might eventually conclude that this is an A lens.

Similar reasoning can be applied to those lenses that have SMC Pentax-M inscribed on them. The application of rigorous logic will lead eventually to the conclusion that this is an M lens.

Elementary, my dear Watson? Alas, no. Advanced intellects may think that armed with this insight, they can identify any lens. They would be wrong.

G

I'll expand a little!

It's obvious, of course, but be VERY careful when cutting off a bit of the protruding lug.

If you value your lens, you might ask a lens repairer to do the deed. He might prefer to remove the rear plate before cutting the lug, which will avoid nasty steel filings getting into the lens.

Good luck.

G

Yes.

G

I agree that the Pentax is the best choice, if money is no object. But given what it goes for now, if you can find one, this option looks like a reasonable budget bet.

G

I don't know. This seems to be a three horse race between somebody who can't spell Prometheus and who has no idea how Ebay bidding works (despite feedback of 260), and two relative newbies who may or may not know anything.

Here's some stuff from the web:

Both the 1.4x and 2x TCs show some image vignetting with long telephoto primes like the 300/2.8, 500/4.5 and 600/4. Center sharpness is comparable to the Canon TCs, but edge/corner sharpness is lower. Note that on small sensor (APS-C) digital SLRs like the Digital Rebel and EOS 20D, vignetting will not be a problem and edge quality will not be as large an issue. The Tamron TCs are significantly cheaper than the Canon TCs, so they can be good value. By Bob Atkins.

Good TCs are thin on the ground. I might risk £75.00 if I wanted one badly.

G

I don't know this, but it's probably worth a punt for around £20.00. Tamron lenses are usually quite good.

G

Frankly, trying to determine what is in focus through a darkened viewfinder is very difficult. This is a feature I never use. On a DSLR it is better, if you have the time, to take a couple of pictures at different apertures and then zoom in to see what they look like.

I suspect a majority of photographers never use DOF preview. It's one of those things that reviewers crtiticise a camera for not having, but for many of us it's a complete waste of time.

G