Originally posted by woodywesty I guess I didn't think that the jump from 60-250mm F4 to 135-380mm F4 would take us from $1,400 to $5,000 or more? That's a pretty big jump. It may be that the best option in the end is to get the DA300mm F4 and the new TC or even better the Sigma 300mm F2.8 along with the new TC. I'll wait and see how it all shakes out.
250/4 = 6.25 cm = 30.68 cm^2 = $1400
380/5.6 = 6.78 cm = 36 cm^2 = $??
380/4 = 9.5 cm = 70.88 cm^ 2 = $???
560/5.6 = 10 cm = 78.54 cm^2 = $7000
Not a perfectly linear correlation of course, longer lenses are more expensive by 20-40%, zooms are often more expensive than 'comparable' primes by 20-40%, etc., etc., etc.
I'd expect a new Pentax 380 f/4 to be $4500 to $5000.