Canon EF-S 55 - 250 MM F/4.0-5.6 Is II Lens -- Photoshop?

I have this lens. It's no "L," but it is silly good for its' price, at the jobs it was meant to do.

Unfortunately, shooting coins is not one of those jobs. Its' minimum focusing distance is 3.6 feet, and at that distance a coin image will be vanishingly small on even a 450D sensor. The kit 18-55 (assuming you have this one too) would be a far better choice, with its' minimum focusing distance of about 10-11". Haven't tried mint on a bellows, but it can be made to do pretty satisfactory whole-face images (max magnification 0.36x) at 50-55mm focal length. You make me wonder what it might do on a bellows.

I'm not deep enough into this to know if a bellows might affect the minimum focus distance of the 55-250. If so, I think you'd be using it zoomed all the way out (55mm), at which point it might become a nice magnifier - optically, it's pretty darn good.

Extension tubes would make the 55-250 into an acceptable coin shooter with decent to exceptional working distance. I have the Kenko set of three and used them on my 70-200 with quite good results. Be sure you get the recent sets that take EF-S lenses rather than an old set that only took EF lenses. Cheaper lenses usually are worst at the corners and coins, being round, don't really use much in the way of corners. I since 'upgraded' to a 100mm macro but you can see a photo of my 2004 set up here:
http://dougsmith.ancients.info/ph2004.html

Let me add that you will wish you had a lens with a tripod collar but we are talking about making do with what you have and the answer is that you can.

In an earlier topic, I asked about extension tubes versus bellows and many said the bellows were better due to their flexibility.

The extension tubes are cheaper, but the bellows are more flexible. This being said, I think I may get the bellows first and then some tubes for other purposes than indoor shooting.

I will take a look at your setup.