Having a few problems with my macro extension tube...

[fishiboii]

Hi, I recently purchased a cheap macro extension tube for around £10. I'm pretty happy with it, it does the job just fine. Obviously it sends no data from the lens to the body, so with using my 600D with it's stock lens it locks the aperture to 0, which I had expected. The plan was to get myself a cheap manual lens so that I could manually change it's aperture. But I was wondering, is there no way of locking the aperture? I've heard about it but I've never researched it in too much detail. Plus i need to know if anyone does it so that I don't end up damaging my camera / lens in the process. I can't really use it at the moment, the depth of field is microscopic. Here's a random shot:


5p by FishSticks., on Flickr

I guess it could be good in some situations but I want more freedom with aperture. Thanks for any input.

 

[Bitter Jeweler]

Can you set your aperture, hold your DoF preview button down, then remove the lens to set the aperture?