ATM Filtering a non acromat

[Antonio de Ugarte Postigo <ugarte@mad.servicom.es>]

Hello everybody,
        I've bought a really cheap ($60) 500mm f/4.8 triplet
I looks great and its Zeiss Jena. I've built the tube asembly 
fot it and it works really good visually. The problem is that 
it isn't color corrected (it couldn't be perfect). I would like 
to use it for photography, and I have thought of using it with a 
color filter. My questions are:
What would be the diference in the image quality between placing 
a big filter before the objective or a small one inside the tube?
In the case that I used a small one where should I place it?
Thanks.

Antonio De Ugarte Postigo
Boadilla del Monte (Madrid)
SPAIN
ugarte@mad.servicom.es