I bought a second hand Dynax7, with fresh batteries sometimes unexpected camera does not react on releasing the shutter. But only when releasing the shutter to take picture. Display at the back stays operational, but display in viewfinder goes black. Only cure is pulling power switch of and on again.

Carl Zeiss is exceptional which results for greater sharpness and less Chromatic aberrations. and also its a well known brand with almost 125 years of history. Usually a stuck lens is caused by dirt getting into the gap between the lens barrel sections. The simplest thing to try is a freshly recharged battery, which might just have the power to overcome the resistance. Plugging in an AV cable sometimes blanks the screen, leaving just a bit more battery power for the lens. Every product we make is backed by an industry leading, limited lifetime, transferable warrant. ZEISS warrants for a period of 2 years from the date of original purchase that the product is free from defects in material and workmanship. An extended warranty for one additional year is available by registering the product within 4-weeks of the date of purchase at the ZEISS product registration. Zeiss lenses really show high-end performance. On the other hand, these lenses also show some weaknesses - the most obvious being the lenses' measured sharpness. ... So although these lenses are masterpieces of build quality, their results may not always be as good as expected.

Sure you did not turn the dial to mirror up?
Always chack all settings on the camera, if something unexpected happens. Like you can press the shutter release button and it won't take a picture. You left the dial in the setting for remote release. I can't believe there is anything wrong with the camera. Just a setting.

The most common causes of blurry pictures are not holding the camera still and correctly pressing the shutter release button or using a slow shutter speed.

Let\'s talk about properly holding your camera first. Always hold your camera with both hands. With an SLR such as yours, grip the left side of the camera with your left hand and cradle the camera from underneath with your right hand using you thumb and index fingers to zoom. Hold your arms so that both elbows rest on either side of your chest and brace the top of the camera against your forehead. This forms a rigid triangle of support.

The second thing you must do is properly press the shutter release button. Do not poke the button because you will jerk the camera and that can cause blur. Instead, start to press the button gradually increasing the pressure until the shutter trips. It should trip almost by surprise. This is very similar to how a marksman pulls the trigger on a gun.

Assuming that you are holding your camera correctly, not "punching" your shutter button and your camera is not defective, here are two easy ways to solve your problem. First, you could use the manual exposure mode and keep your shutter speed at 1/500 second or faster. Second, go to the "S" shutter priority mode and set the shutter speed above 1/500 second. Your camera will automatically adjust the f-stop (lens diaphragm opening) and "film speed" for proper exposure. Please let me know if this resolved your problem.

The most common causes of blurry pictures are not holding the camera still and correctly pressing the shutter release button or using a slow shutter speed.

Let\'s talk about properly holding your camera first. Always hold your camera with both hands. With an SLR such as yours, grip the left side of the camera with your left hand and cradle the camera from underneath with your right hand using you thumb and index fingers to zoom. Hold your arms so that both elbows rest on either side of your chest and brace the top of the camera against your forehead. This forms a rigid triangle of support.

The second thing you must do is properly press the shutter release button. Do not poke the button because you will jerk the camera and that can cause blur. Instead, start to press the button gradually increasing the pressure until the shutter trips. It should trip almost by surprise. This is very similar to how a marksman pulls the trigger on a gun.

Assuming that you are holding your camera correctly, not "punching" your shutter button and your camera is not defective, here are two easy ways to solve your problem. First, you could use the manual exposure mode and keep your shutter speed at 1/500 second or faster. Second, go to the "S" shutter priority mode and set the shutter speed above 1/500 second. Your camera will automatically adjust the f-stop (lens diaphragm opening) and "film speed" for proper exposure. Please let me know if this resolved your problem.

Maybe the two items are not compatible

From the manual:
"If the error display is not canceled when the shutter release button is pressed again, insert the Dark slide, half-press the shutter release button while pressing the roll film holder's manual film advance button to wind up the film, then contact your nearest Mamiya agent or service center."

If you need a manual, you can download one from
http://butkus.org/chinon/mamiya/mamiya_645af/mamiya_645af.htm

Wow, four days ago.

I would think that the camera has dropped the shutter by now.

There is a mode in the camera that holds the mirror up out of the way for sensor cleaning but this is defaulted as soon as the power is shut off and then turned back on again.

Or the camera was set in manual mode "Bulb" and is waiting for the next command from the photographer to "drop" the shutter "takes a second press of the shutter button.

The lens may be loose (unlocked) and giving a bad command to the camera.

The Canon 40D has a shutter capable of 60,000 actuation so if you are close to this I'd say the shutter has been shot out of it.

Also sometimes the shutter release button sticks and gives the feeling or appearance of a stuck shutter.

Shutter switch also known as a release button have been an issue sometimes where dirt and oil from a person hands get down into the button.

To release shut the camera off, take the battery out, remove and reinstall the lens, shift the taking mode to "P" program or full automatic green box.

This camera is somewhere between fifteen and thirty years old. It is highly unlikely that spares would be available, and it would be extremely expensive to have it repaired in any case, most artificers familiar with the internal layout having probably retired years ago. Maybe the camera should be retired too ?

Try these procedures.

Take the lens off and continue pressing the shutter untill it doesn't react anymore, you should then have a normal menu without the error message.Put your lens on and you're all sorted.Cheaper and less hassle than sending it to Nikon.
olly