I'm trying to use an external intervalometer for my Fujifilm HS25EXR. It works and snaps pictures on the timer, but for some reason it won't overide the shutter speed. I'm trying to do some night sky photography and the longest the HS25EXR goes at ISO 800 is 4 seconds. I need roughly 15-25s. The higher the ISO the faster the shutter. I was looking through the camera menu to see if I could turn something off but its just not working.
When the HS25EXR is in Auto mode, it limits the shutter speed to 1/4s (the shutter speed will display as 4, but this means 1/4s. 4s typically displays as 4".
I would suggest putting the camera into M (or at least a non-Auto mode), which should then allow you to expose up to the camera's limit, which is 30s. And make sure that the interval at which you're setting the images to be taken is longer than your shutter speed.
Actually, the HS25EXR has a software limitation that decides the max shutter speed of the camera according to the ISO value. At ISO 100, you can get a shutter speed of 30s but as the ISO increases the shutter speed is automatically reduced. So far, I haven't found a way to override this but if you do, be sure to share it...
The Fuji Finepix HS25EXR does not have a Bulb mode and so the shutter-speed is not controlled by the interval timer. There is no way to get longer shutter-speeds.
You can simulate them by stacking images and add the exposures together. This will not give exactly the same result but astro-photography is done like that quite often.