You are going to need a much bigger zoom than 250mm. The best way would be to use a telescope with camera adapter and shoot through that. For a camera lens, you're gonna need something big. I don't know the size of Mars on the 27th, but I do know that to fill a 35mm frame with the Moon, you need something like a 2500mm lens. I was actually thinking of renting a 1200mm Canon L lens for the day with an EF 1.4x or EF 2.0x extender. On my Canon EOS 10D, that would equate to a lens of: with 1.4x Extender - 2688mm ~F/8 lens with 2x Extender - 3840mm f/11 lens With the 2x, the Moon would be about 35mm wide on a regular film frame. -=>Donald