Getting one insted of two ??

Help me out here please.

Today i have a Nikon af-d 80-200mm 2.8 and a sigma 300mm f4 (prime).

I do not have enough space in my backpack to carry them both around. It's to heavy also.

I am thinking of selling both and getting a new Sigma 100-300mm.

I know i am loosing the possibillity to shot at 2.8, but i don't normally use the 80-200 @2.8

What about IQ ??? Will the new sigma 100-300 give me same IQ as the combo i am useing today ??

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Lars

Nikon D300,SB800, SB600
Nikon 80-200mm, 105mm, 50mm, 10-20mm, 17-55mm, 300/4