Which is why i was asking about aperture control to begin with. I will be photographing mainly (hopefully) still subjects & using a mini tripod so slow shutter speeds will not be too much of a problem. A lot of top macro shots are taken with shutter speeds of over a second. I have only used a compact before so dont know what the effects of mirror slap? might be. Camera arrived about an hour ago & am now waiting for battery to charge before i can start playing. As i get more proficient i hope to have a look at image stacking, another way to counter the lack of DOF. By the way Roy you`ve got some nice macros yourself on your website. I particularly like the Bush Cricket. What lens did you use forr that ?
Hi Rob, I think I know what you are asking, but just to confirm:
You want to control DOF by physically stopping down the lens , even though the lens cannot communicate with the camera as you will be using cheap extension tubes that don't have electrical contacts between the lens & body?
I haven't used the type of tubes you are talking about, but have read about this on another forum.
This might not be recommended by the camera manufacturer but it could be worth a try:
With the camera switched on and lens attached, set the aperture in the usual way, then press the DOF preview button and at the same time unscrew the lens from the camera body. It works on my 40D with the same 50mm lens you have and you can see that the lens's aperture blades are held in the chosen aperture position. Then re-connect the tubes between the camera and lens.
As I said, this might not be recommended by Canon, but I'd be interested to see what others think about it. It might be the only way you have to control DOF with the tubes you have.
Best of luck,
Steve
edit, I presume that for macro work using the type of tubes you intend to buy, many photographers would use an old type (ie. legacy lens with built in aperture ring) which would make controlling the aperture a doddle. As others have said, focusing manually would be the way to go and perhaps use shutter priority to fine-tune the amount of light getting through to the sensor. A bit of trial and error will surely reap rewards. With the method I've suggested you would have to set the aperture at first then leave it set at that position for the duration of your shoot, which would surely not be too much of a problem in a 'studio' environment.