Lense selection help - Canon 30d

[guy1]

I am going to make an investment for recreational purposes into a Canon 30d from my old Canon Elan II.  I plan to buy the camera body, and 430ex flash to double my rebate dollars.     I also will keep my Canon 50mm f1.8 lense.

I will use this camera for just about everything, portrait work with my kids, local sporting events, beach shots, family vacations, and everthing else.  I like to take shots and  blur the background to make the subject jump out.  

I am trying to decide between the Tamron 17-50 f2.8 and the Tamron 28-75 f2.8 lense as my "standard" lense.  Considering the 1.6x factor, these lenses are equilvalent to 27-80 and 45-120 respectively.  I was considering the Canon 70-200 f4 L as an additional lense purchase (equivalent to 112-320).  

If I go with the Tamron 17-50 and the Canon 70-200 f4 L lense I will have an effective gap between 75 and 112.....and if I go with the Tamron 28-75 I will overlap on the long side but my widest will only be an effective 45mm....18mm short of the effective size of the Tamron 17-50.   Also, if I ever go to full image sensor the Tamron 17-50 will be useless.  

What do you think is the best match?  Any other suggestions, combinations??

[giles]

If I go with the Tamron 17-50 and the Canon 70-200 f4 L lense I will have an effective gap between 75 and 112.....and if I go with the Tamron 28-75 I will overlap on the long side but my widest will only be an effective 45mm....18mm short of the effective size of the Tamron 17-50.   Also, if I ever go to full image sensor the Tamron 17-50 will be useless. 

I would not be concerned about a 'gap' from 50 to 70mm.  I suppose there has been an occasion sometime that I've wanted longer than 50mm and shorter than 70mm, but I can't think when.

Not having anything wider than 45mm equivalent would be constraining IMHO, and if you ever end up with a "useless" 17-50mm lens you can sell it.  The millions of crop factor DSLRs aren't going to  disappear even when/if full frame becomes affordable in the price range of the current 30D, and besides, that isn't going to happen this year or next!

Giles