I am thinking of trading in my Canon 50mm f/1.8, Tamron 55-200mm and Tamron 17-50mm as part exchange towards a Canon 70-300mm IS lens. Anyone know what sort of trade-in value I should reasonably expect for these, and a good place in the UK for this? I asked at one local shop recently and was given figures of around £40, £30 and £100 respectively for my lenses; surely I could expect more than 1/3 of the retail price for the Tamrons?

