EOS cameras have several settings for file numbering. My guess is you have it set to Continuous and you've wondered why you might ever want to auto or manually reset the count to zero. 

Well, there are few reasons why you'd reset, but I did come across one the other day.  For a variety of reasons I was trying to flatten an LP-E6 batter on an EOS 5D Mark II (it's a long story for a future blog post) and I decided the quickest and easiest way to do it was to shoot a timelapse. Obviously a timelapse will keep the camera active for a long period of time without me having to do anything. 

Now, I'd shot a timelapse sequence to flatten the battery and the counter on the camera was around 7000 when I started. Trouble was, when I came to put the images into a sequence, the counter had gone round to zero and they images were out of order. This meant I had to rename them all (which I did using a very simple automator script which I'll post later this week). Had I reset the counter manually, I would have had all images in one numbered sequence and I could have eliminated the need to rename files later.

As an aside to this, I actually ran two timelapse sequences. One with image captured every two seconds and one with images every second. (You'll have to wait 'til I've got some music and time to edit them to see them!) And I got some interesting results for battery life.

A single LP-E6 battery fully charged gave me, with images captured every second, 10,503 images. Yep, one charge, TEN THOUSAND FIVE HUNDRED AND THREE! Now, there's no IS, no AF etc just the camera being triggered, but o say I was impressed is an understatement. Even with this one after manually resetting the numbering I still had to rename the last 503 files! 

So there you go, a good reason to now and again reset the file numbering manually.  

Do you use manual rest ever? If so, why? Oh and what's the most files you've had from a charge?