Aperture questions about a SFXn

Not quite sure what you're getting at there, David.
Most zoom lenses quote two maximum apertures ie. 3.5 / 5.6 (to use your example), this means that the maximum is f3.5 at the shortest focal length (toward wide-angle) and f5.6 at the long end (toward telephoto). This is because you lose light as you increase the length of the lens. A 'fast' telephoto would have to be very large (diameter) and therefore heavy and expensive - such lenses are designed for specialist use and carry a professional price tag.

The lens only stops down to the aperture setting chosen, by the camera or the photographer, when you fire the shutter. This enables you to see the subject clearly up to the point of exposure. The depth of field preview function found on some cameras, enables you to close the aperture down to the setting that will be used for the final exposure so that you can see how much of the foreground and background will be in focus for the actual shot.
Obviously, the image seen through the viewfinder will darken as the aperture closes but it gives you a very good actual view of the depth of field. Some cameras feature a graphic representation on the LCD display and / or in the viewfinder and you can refer to the depth of field scale on the lens eg. you know how far away the subject is because the lens tells you, you then look for the distances before and after the subject distance as indicated by the aperture markings on the lens barrel.
If you look at your 50mm 1.7 lens (I'm presuming autofocus F series), focus at 1m and you'll see three white lines marked 22, 16 and 5.6, the depth of field extends from 0.8m to 1.5m at f22, approx 0.85m to 1.3m at f16 and 0.95m to 1.1m at f5.6 (you can calculate the precise figures if you wish or refer to pages 52 and 53 of the SFXn manual).

For cameras that don't have a depth of field preview function, there is a way to cheat - set the aperture and depress the lens release button, then very carefully turn the lens (approx halfway) as if you were going to remove it. The aperture will stop down to the setting you chose and hey presto you have a preview function!
As the lens is effectively half removed from the camera at this point, be very careful not to allow it to fall off and remember to re-fit it properly.

BTW, the sub-modes I referred to previously are actually called 'wide' 'standard' and 'tele' - sorry for any confusion.

Hey that's a nifty trick Kimbo! Though I was real carefull and never let go of the lense (and probably won't do it very often, but really neat to see. Thanks.

Sorry if I messed up on my explanation about the zoom numbers. Suffice it to say, "what you said" lol. Anyway I get it now.

I just bid on a KX on ebay so with luck I'll have a reg dop to play with.

Oh just cause it was a cool picture, I printed out the first page of the K series literature, that shows all 4 of the camera types lined up. I set the zoom percentage in the PDF at 100%, for maximum clarity, (though it was real small at that level), and printed it out on my HP 8450. Then I scanned it in my flatbed in a high enough rez to be about half page size, and let a graphics program blow it up to full page. Then I printed it out at high quality on some nice heavy glossy paper. Trimmed it to fit an 8 by ten and framed it. Haven't put it on the wall yet. My mom asked why I would want to frame a picture of camera's, and I told her I think their beautifull. Hey beauty is in the eye of the beholder, (or camera holder
Hope this aint infringing on some copyright Kim C.