Wide & Fast

That's not right.

Any 30mm lens, whether it is "digital" or not, will give you a focal length of 30mm.

Using either type of 30mm lens on your digital camera will be like using a 45mm lens on a film camera. That's it.

Yes. Whereas your 50mm 'standard' is now a short telephoto on your K10D, a 30mm 'wideangle' will be more like a 'standard' on the K10D, whether you buy a 'digital' lens or not.

To get a medium wideangle look, you would need a 20mm lens or similar (just to confuse you some more ).

Dan

As you have a digital camera, you can virtually ignore whether any particular lens is "digital" or not, because you can use all lenses that fit the camera.

It's a more important issue for those with with film cameras because a digital lens with a reduced image circle can't be used on a film camera without some serious vignetting (though sometimes with zooms it's just for the wide end).

Iceblinker and I are saying the same thing, just slightly differently. That's why he said 'no' and I said 'yes'.

The 30mm lens will still be a 30mm lens. It won't change to a 45mm lens. But the field of view with the K10D would be narrower than if you put the same lens on a 35mm film camera. That narrower field of view would be the same as if you put a 45mm lens on a 35mm film camera.

Dan

This sort of discussion always reminds me of the old comedy show 'Soap'. The end of the voiceover intro was always "Confused? You will be!"

Dan

Lilly already has a Sigma 10-20mm so she knows what 20m looks like.

A fast lens around 30mm would indeed be good for interiors (too). But I still question whether it needs to be faster than F2.8.

If F2.8 was acceptable, choice would be hugely increased and include more 28mm primes and even zooms like the Sigma 18-50mm F2.8 Macro, Tamron 17-50mm F2.8 and Pentax 16-50mm F2.8.

Well, yes and no. She knows what 20mm looks like, but obviously hadn't realised it would give the same field of view as a 30mm on film, otherwise she wouldn't have been looking for a 30mm lens to give her this view.

Dan

What an amusing discussion!!!

Lilly,
I find myself in exactly the same position as you. I have a wide zoom (particularly a fisheye) and a 50mm f1.4. i also have various zooms that cover the space in between. Like you I find myself needing a "something in between" these focal lenghts (between 17/20mm and 50mm) of very good quality. I think that the real options you have are ONLY prime lenses, because otherwise you are not looking at very high standard IQ (Apart from f2.8 zoom lenses which are indeed very expensive.).
So the choice of primes in that range is this.

- Pentax smc P-FA 28mm f/2.8 AL - Good lens, similar built quality than the FA 50mm - around the focal lengh needed. (28 on film, + 1.5 crop factor on K10d) {42mm equivalent on 35mm film}

- Sigma 30mm f/1.4 (Quality doesn't appear to be so good - and you might really want to wait for something more expensive and better, if IQ is what you are after) {45mm equivalent on 35mm film}

- Pentax FA-31mm f/1.8 ltd - (the best in quality for higher price - but on ebay you can get it from canada for about £470 i think... )
{46.5mm equivalent on 35mm film}

- Pentax SMCP-FA 35mm f/2.0 AL - Same build quality as 28mm and 50mm, and about the same IQ. For a very reasonable price.
{52.5mm equivalent on 35mm film}

- Pentax SMCP-FA 43mm f/1.9 ltd - Build Quality and IQ similar to the 31mm ltd, this is another "special" pentax lens".
{64.5mm equivalent on 35mm film}


By the way, the "crop factor" of digital srl's is a very confusing subject, but it really only applies if you work with both film and digital slr's using the same lenses. If you only use Digital, then you will only be restricted on the wide side of the zooms, as the widest angle will not be as wide as it was on film cameras. So the fisheye (10-17mm)under the crop factor is still a 15-25.5mm which is not exactly "extreme wide".
As Dan and Iceblinker already said, the denomination "digital lens" has only to do with the fact that the area covered by the sensor (23.5 x 15.7 mm ) is smaller than the area covered by the 35mm film. Therefore the lens needs to shorten the angle exposed to the light.

By the way, "digital" lenses produce a lot of vignetting if used on film cameras, for the same reason.
Another thing to consider is the fact that professional FULL FRAME DSLR's will also have problems in using "digital" lenses, and vignetting will be an issue. (Example of this is the new nikon D3; full frame, it has a function that allows only the central 23.5 x 15.7mm of the sensor to be used in order to function properly with "digital" lenses.) )Or at least this is what i understood from my readings... )

Hope this helps,

Cheers,
Nathan

F2.8 zooms are becoming less expensive. The Tamron for example is £259.

Pentax-FA 28mm F2.8 is better than Pentax-F 28mm F2.8 according to some reviews and tests, but actually I found my F version was sharper wide open than an FA I tried. Its auto-focusing is very fast and reliable, and it's refreshing to use such a small and light lens on the K10D. The more commonly available and cheaper A (manual-focus) version has the same optics as the F.

Blimey, what a can of worms I have opened for myself I will have to go away and a very quiet think about all this and try and understand once and for all about this aspect of digital photography. Thank you for your time and especially Nanthan for all that valuable info. I'll be back later!

...Quite frankly, I think this is one of those things that it's best not to think about too much and just accept that there's no difference between digital and non digital lenses on your camera (as far as the amount of the scene that you get in frame, at least).

I don't understand all the physics myself. I don't understand anything, really. I just know a few things

Yes, at least I have established that fact today well you live 'n learn!