Older EF 75-300 Image Stabilization Lens

kenko doesn't work with it...the lens projects too far...if you want to use a TC already you may want to look into the 70-300IS...it works with the kenko 1.4

I own the 75-300 IS and just ordered a refurbished 55-250 IS from Adorama for $199 to see if it is better (faster focus, sharper at max focal length, better IS). I don't know about the 70-300 IS but it is supposed to be much better at 300mm than the original 75-300 IS. I've heard that the 55-250 IS lens is sharper at 250mm than the 70-300 IS lens is at 300mm. I assume the 70-300 IS is probably a better lens overall than the 55-250 IS but not by much and probably not worth the additional cost unless you need FF. I'd pick up a 70-200 f/4L and a teleconverter/extender rather than get a 70-300 IS myself. You might find a used 100-400L for about $1000 if you're lucky or you could also look for a used Sigma or Tamron tele for half that.

As far as using a teleconverter with an EF-S lens, my Promaster 1.7x TC (probably made by Kenko or Tamron) doesn't work with my 18-55 IS lens and neither do my Kenko extension tubes. The EF-S lens mount diameter is too large or extends too far to mount on the TC or extension tube. I could probably modify the extension tubes to make them work, but don't see a good reason to do that.

shaftmaster wrote in post #7413661
I've heard that the 55-250 IS lens is sharper at 250mm than the 70-300 IS lens is at 300mm. I assume the 70-300 IS is probably a better lens overall than the 55-250 IS but not by much and probably not worth the additional cost unless you need FF.

the 70-300IS is sharper than the 55-250IS...but yeah i agree the degree to which it is better might not be worth the cost...when i bought it though there was no 55-250IS...also i enjoy using it with my 1.4 to get 420mm reach

Thanks for the info. Everyone has been a big help. I wish I could afford an L lens but hat is beyond my budget, and so is the 70-300 IS at this time. The only longer L lens I might be able to swing is the old 100-300 5.6, but that lens is pretty slow. I am leaning towards the 55-250 IS.