In general, we don't with digital photography, as many effects can be approximated in Photoshop.

However, remember that a filter works by not just changing colour temperature, but by actually removing part of the light that is allowed through to the sensor. This, if haze scatters blue light then we remove it and we have reduced haze. We haven't affected the colour temperature of the overall spectrum of light allowed in. If we let the blue light through and deal with it afterwards, the scattering and contrast reduction have been allowed to happen and it's too late to correct that.

As regards WB, I would be aiming to relect the nature of the ambienmt light and would shoot JPEG with a fixed Daylight WB.

If you use AWB the camera will try and correct to what it sees as a neutral grey overall, so the effect of any dramatic natural lighting and indeed of a filter will be reduced or even removed.

To adjust the dioptre properly you need to point the camera at a blank wall or sky and make sure the etched lines on the focusing screen are sharp. Then you eye is focusing naturally on the screen when it's relaxed and you will be able to manually focus much easier.

Just open the aperture and the shutter speed increases. No need to change modes. However, a high ISO will help in low light situations and also something to compensate for subjects that add shake to your shooting naturally, such as burlesque strippers. Perhaps a drink seeing you're at a bar.

If you use filters on digital remember not to use AWB, otherwise whatever the filter colour is may be "corrected" by the camera. Use daylight or another setting that suits your style.

I can see that there is a clear misunderstanding here about what the first article is saying, which is not new in any respect.

DOF increases with using smaller apertures, but it is also true that the resolution of a lens falls off either side of an optimum aperture, usually about two stops down from open aperture. So a good f2 lens might peak at f4 or f5.6.

There a a couple of consequences here. True, wider apertures might give sharper images, so stopping down to f22 will result in a less sharp image. But this has nothing to do with whether the lens is in focus or not. This relates to the ability of the lens to render those in focus areas sharply.

This we have a balance to achieve between using the "best" aperture for sharpness and the "best" aperture for DOF. To maximise DOF and with a good lens, it';s clear from tests that pereformance can hold up well to f11 and maybe even f16 and those are the apertures I would choose. It works well.

A further caveat is that less expensive zooms aften break the peaking rule and can actually improve down to f16. This is the sign of a less good lens, but it does at least unify our "best" points.

It's very easy to get bogged down by all this and that's why I try to talk about simple "rules of thumb" that we can use and find OK, most of the time. The more pedantic we are, the less true anything becomes.

People get great results with spotting scopes, providing they are good scopes. Even simple point-and-shoot cameras can be attached via adapters and give syurprisingly impressive shots. The K-5 will of course be much better and have a faster response time too, so some action can be caught.

In good light f12 should be fine, just increase the ISO to ensure a high enough shutter speed.

The Pentax lens is superb and can be found fo amazingly low prices. I would unhesitatingly recommend it.

The Sigma lens I have not tried, but being aware that Sigmas can vary quite a bit and that they reverse-engineer, I tend to avoid them. I don't like the feel of thr finish either!

It's one of those things beginners and everyone else has to learn about.

Pentax have at least been photographically consistent and correct in the labelling of their lenses. If it's going to be a 5-15mm then they list it as such, with the "35mm equivalent" provided for the purposes of those who can't visualise in terms of a new format. New users could happily ignore that information and just be told that, for example, a 50mm lens is a short telephoto.

Graduated filters do allow for progressive reduction in part of the colour spectrum, that's how filters work. For example, a graduated warming filter will remove more blue at its densest part, this making the sky progressively warmer.

There are likewise graduated colour filters for black and white photography that increase contrast in the sky, but leave the foreground relatively untouched.

I would suggest you search eBay and camera fairs for what you want at low prices and old and new filter catalogues for ideas as to what has been/is available. Pentax made some oddd double-coloour filters at one time for special effects, so all sorts of oddments can be unearthed.

Pity you didn't post this when I've had lots of odd filters on eBay, but sadly they are all gone now.