Canon 450D Main dial not working

The AV mode is for setting the aperture (ie Depth of Field).
To change the ISO setting turn the Mode dial to the P position and then turn the Main dial (next to the shutter button) to the ISO setting you require.

On right hand top of the camera there is a Mode dial. Move the dial to Av (aperture priority) then rotate the wheel in front of this dial to set the F stop. The shutter speed will automatically adjust by the light meter.

First, make sure you're in the manual exposure mode, not manual focus mode, as set by turning the mode dial to the "M" position.
In manual exposure mode, turning the main command dial should change the aperture, while turning the subcommand dial should change the shutter speed.
If the two command dials don't have the expected effect, reply to this post and we can troubleshoot further.

Solution 1 • Unlock focus area selector. • Auto-area AF selected for Custom Setting 2 (AFarea mode): choose another mode. • Press shutter-release button halfway to turn monitor o?¬? or activate exposure meter • Memory card is full, locked, or not inserted. • Flash is charging. • Camera is not in focus. • CPU lens with aperture ring attached without locking aperture at highest f/-number. • Non-CPU lens is attached: rotate camera mode dial to M. • Mode dial rotated to S after shutter speed of bulb selected in mode M: choose new shutter speed • P, S, A, and M modes: lower ?¬? ash. • Digital Vari-Program modes: turn ?¬? ash o?¬? Turn long exposure noise reduction o?¬? Turn long exposure noise reduction o?¬? Press multi selector up or down or rotate sub-command dial to choose photo information displayed Select All for Playback folder. Note that Current will automatically be selected when next photo is taken • Select On for Rotate tall. • Photo was taken with O?¬? selected for Auto image rotation. • Camera orientation was changed while shutter-release button was pressed in continuous shooting mode. • Camera was pointed up or down when photo was taken Use Nikon-approved card. • Card may be damaged. Contact retailer or Nikonauthorized service representative. • Delete unwanted ?¬ les or insert new memory carD

You need to understand the relationship and teractivity of aperture, shutter speed and iso. In Av mod, you choose the aperture and the camera makes thw shutter speed agjustment, In Tv mode, you set the shutter speed and the camera makes the aperture adjustment, In manual, you have to set both shutter speed and aperture manually. If the ISO mode is set to AUTO, the camera chooses the sensors sensitivity to light automatically. Change to specific ISO
(200-400 for daylight and 799-1600 for night). Take a picture in AV mode and note what shutter speed the camera chose. Then switch to TC mode choose the same shutter speed and see if camera chose the same aperture(f-stop) you chose in first shot. Change to Manual and choose same f-stop and shutter speed the camera chose for you in the other modes. Compare all three photos. They should be almost if not exactly the same exposure wise.
In Tv mode choose a dlowers shutter speed, In Manual choose a combo of slower shuuter and wider f-stop(smaller number). Read your manual.

If your camera is a Rebel XS you should have a dial on the top right with a series of letters and icons. To set your camera so you manually control the shutter speed turn this dial too "TV" (Time Value). This setting will allow you to select the shutter speed and the aperture will open or close to achieve the correct exposure. The "M" is (Manual) where you would select both the shutter speed and aperture "AV" is (Aperture Value) where the user selects the aperture they want and the shutter speed increases or decreases to obtain a proper exposure. The "P" (Program) mode allows the camera to automatically select the shutter speed and aperture

Steve - the Nikon dSLR cameras are very capable. Check the position of the mode dial:



The image above has it set to "P" or Program mode. Change it to "AUTO" and take a picture of a well lit scene (preferably outside in the daytime). You should get a properly exposed image. If the mode dial is set to "M" or Manual mode, the shutter speed is probably too low, and the aperture either too small or large if the image is dark or light, respectively. You'll have to turn the knobs on the front AND rear to adjust BOTH shutter speed and aperture (f-stop) to find the right combination of exposure time and aperture opening allowed into the camera to suggest motion (more blurry with a slow shutter - or more sharp with a fast shutter), in addition to DOF or depth of field.

You may have a similar issue when set to "P". If you are in this mode, the camera will attempt to determine the best shutter and aperture settings for you. You can veiw the settings chosen in the view finder. Likewise, you may override either shutter speed or aperture changing the aperture OR shutter speed control knobs. The camera will automatically change the other - to provide a properly exposed image.

Review the manual here. Page 39 details the mode dial and how it works. Page 18 discusses the
"Digital Vari-Program" modes depicted by the icons, and the "AUTO" label. These modes should be avoided, unless you are happy with "snapshot" type pictures. The most creativity will come from using the camera in one of the other modes: M,A,S or P. Taking the time to learn them will greatly increase your enjoyment of the camera and resulting images.

I hope this was a good starting point for you & good luck!

In Programmed (P), Shutter-priority (S), and Manual (M) modes, turn the main command dial (the one in the back). In Aperture-priority (A) mode, turning the subcommand dial (the one in the front) controls the aperture and changes the shutter speed to suit.

This all assumes you haven't gone into the menus and switched the functions of the two command dials.

Which mode are you on? When you zoom in, the maximum aperture size decreases to f/5.6 in the kit lens. Sometimes it may be too dark or shutter speed too slow so the camera doesn't shoot. If you're in "P" (program) mode, full auto mode or any of the Basic Modes, the aperture/shutter is auto. In other modes (Av, M, etc) you can turn the dial on the top of the camera to adjust shutter speed to a lower number.

No. You can only use the camera in manual mode, setting the shutter speed to, say, 1/125 sec and the aperture: according to the working aperture on the flash. The flash has to be in auto mode. The physical connection between the camera and flash can be either a standard PC cord, originally supplied with the flash plus a hotshoe-to-PC-female "cube", or an SCA305a cable plus an SCA301 standard foot. Of Metz 45 series only the 45CL4 Digital together with an SCA3102 M4 module is dedicated to the Canon EOS digital series.