Cant get length of Image Sequence correct without Time stretching

Hi.

I have scanned, frame by frame, 1 small Reel of Super8 Film ( 3 min 20 seconds )


I have 3600 jpg images to import as an image sequence.


I am using Vegas pro 12


I know how to import the sequence. That's not my problem.


When I import the Video file created from the 3600 images, it runs for 2 min 24 seconds,
when in fact it should be close to 3 min 20 seconds in order to make the timing of everything look right.


I do know how to time stretch, but I don't want to have to do this to 5,000 Reels every year.


I just want to set up the settings so that all of my image sequences hit the timeline and are at the correct
playback speed.


Has anyone done the maths on this scenario before ?


I am in PAL 25f per second
Super8 films has 18 frames per second
3600 frames = 3600 jpg images and should = 3 min 20 ( approx )


When I go to preferences in Vegas and click on Editing tab
and adjust " New still image length ( seconds ), it doesnt seem to make
any difference if I choose 1 second, 5 second or 0.05 seconds for each image. ...... I still get
an incorrect speed on the timeline, forcing me to make eye judgements in time stretching the video.


Any help or advice appreciated.


cheers
Scott