Ok - page 242 of the K-m manual documents how to do it
The bottom row of the column:
All Lenses - M (Manual) mode
Hope that helps!
Matt

Judith - my guess is you have an old lens without the "A" position
Let me explain:

The K1000 (and similar) had a special mechanical "finger" that let the camera read where the aperture ring was set to. The camera takes a meter reading with the lens wide open (ie at it's smallest f-number), and would calculate the shutter speed for the aperture that you had selected. When you press the shutter button the K1000 would close down the aperture (say to f/11) and use the correct shutter speed.

However... Pentax removed this "finger" linking on all the dSLR cameras Many have asked for it to be added on at least some cameras, but alas, they don't have it. If your lens has an "A" setting, then the camera can choose the aperture - and knows about it. However, with lenses without the "A" setting, the camera will meter wide-open and expect the lens to remain wide-open when you take the shot.

Consequently, if you have a zoom lens that has f/4 as its widest aperture, but you have rotated the aperture ring to f/8, then the shot will be 2-stops underexposed

As Pete says, Pentax added the ability to perform "stop-down-metering" on most of the digital bodies. I'll download the K-m manual and see how it's done...

Matt

Here are some images that show the kind of edge distortion you'll get (Googled these - with Nikon & Tokina lenses... but you'll get the idea)
1) http://static.photo.net/attachments/bboard/00I/00IM8t-32857184.jpg

2) http://static.photo.net/attachments/bboard/00I/00IM8r-32857084.jpg

3) http://www.billmajoros.com/photoalbum/categories/new/WideAngle/frames/dog-3.html

That said, there are situations where 12mm and wider is useful. You have to weigh up whether it's worth the price of the 10-20 or 12-24

... of course, for portraits you can always use your feet and the 18-55 and just move further back

Matt

Just compare like-for-like

If you are comparing lenses on the same body, then compare 28mm against 10mm or 12mm.

If you were used to using a 28mm on 35mm film and want that on digital then compare the angle of view - so your old 28mm on a 35mm film body would give the same AoV as 18mm on digital.


Looking at your kit list, I suppose your original question should have been "How much wider is 10mm compared to 18mm?" (since you already have the 18-55 kit lens). Answer - appreciably wide, but not necessarily more useful (See my reply about 12mm for portraits!... think there was a couple of images on another thread that showed the face distortion at 12mm...)

Matt

So sorry to hear the news
Matt

Glen,
Just a question... why are you trying to use HS mode for wireless flash?
(ie what's your situation that requires it)
Matt

Shim,
The centre looks about right for the FA80-320. Not sure about the edges - but the subject isn't that helpful.
Best thing is to try and take a shot square-on of a brick wall. That'll show if you have any centering issues (i.e. you need a subject that is definitely flat) Take the shot on a tripod (if possible) and with a range of apertures.

Matt

Erm, page 143 clearly says "High-speed flash sync" - Built-in flash "No"

Page 145 under "Using High-Speed Flash Sync Mode" is specifically using tethered AF540/360 in HS.
Page 145 under "Using in Wireless Mode" says:
EDIT: Are you confused by the "or using the built-in flash with an external flash"? Certainly the features list specifically says that the pop-up cannot do HS.

Matt

You can do wireless high speed P-TTL using two flash guns - one on the hot shoe and one remote (e.g. an AF360 on the camera triggering an AF540, etc).

The pop-up on the K20D cannot do HS mode at all (neither normal nor as a controller) AFAIK, the *ist-D was the only dSLR that offered HS on the pop-up.

Sorry!
Matt

You definitely do NOT want to do family portraits at 10mm
In a rectilinear lens, the edges distort the geometry - so a square looks an odd oblong shape. (In this respect the fisheye are better - they curve, but a square still looks a square.)
The faces of people on the edges are distinctly odd if taken close.

The widest I'd go for a portrait group is 16mm (e.g. DA16-45, or my current DA17-70 )

And, as many have experienced, unless you have a truly impressive landscape, taking a shot at 10mm or 12mm can give an underwhelming shot. It takes a lot of practice and skill to get a really good super wide angle shot.

Matt