I have been conducting extremely long aperture priority auto exposures with the Pentax LX - some lasting minutes to hours, as shown in some examples below.
Using Kodak Gold 100 for about 15minutes
Using Kodak Ektar 100 > 40 minutes.
Using Kodak Gold 100. Fired the shutter about 9pm and found it had closed after 4am
The Pentax LX is the only camera ever - by any brand or make, that can aperture priority auto expose a scene for as long as it takes - or batteries dies, all the while checking the scene lighting for changes and adjusting exposure time accordingly. Unfortunately, there is no indicator when the LX has completed it's exposure so I have to occassionally check by looking into the viewfinder to see if the mirror has come back down. I posed the question before if there was an accessory that would help with this and someone here recommended to check the X-sync terminal but I cannot find that thread to give proper credit. Thanks to you, I finally got around to doing this and the solution works!
The X sync terminal provides a normally open connector and closes when the shutter is fired for the duration of the exposure. I simply needed an X sync connector, an indicator - in this case I used an LED, and a battery in series that provides power to the LED when the shutter is fired and opens once the exposure is done. Below is what I put together very quickly to try it out. Top picture shows the LED off as the shutter hasn't fired yet and the bottom shows the LED is on as the shutter has fired. BTW, my solder skills are up to NASA standards and this is just very fast and loose prototype . . .
Larger version ->
Shutter open indicator
I tested it using the manual exposure times as well as in aperture priority mode for >30 minutes successfully.
I've also tested it on some of my other bodies and they work accordingly but probably not needed unless it is capable of the very long auto exposures.
I suppose I could use a piezo electric buzzer for audio queue but this battery LED can last an exposure a couple of days long so it maybe a match for the LX.