Extend focal length of the 70-300mm lens.

Hi everyone,
On the Canon 5D with the new Canon 70-300mm lens, I want to extend the tele. What option should give better result in terms of image quality:
- Using a Teleconverter (I heared the Tamron TC 1.4X is compatible)
or
- Take the shot with the lens only on 300mm, and crop 40% ?
Another or heavier lens is not an option!

If you add the tc on the 75-300 lens, you'll loose 1 stop in that configuration ...

So you'll be shooting with an equivalent f8 lens at the 300mm length.

If you've got the light for that and don't mind the increase in DOF that will give you, then go that route.

I personally found that lens to be a little soft at 300mm (at least the unit that I had was!). The tc will add even more softness to it if it's already soft at 300mm. So be mindful of that possibility.

The conventional wisdom is that if you start with a very sharp L lens and add a 1.4x teleconverter, you can still get pretty sharp results. However, if you start with a normal mushy consumer-grade lens and add a 1.4 teleconverter (or worse yet, the 2x teleconverter), then you get a really mushy image. Also, since prime lenses tend to be sharper than zooms, on the average, they get better final results with a teleconverter.

---Bob Gross---

Taking the shot with the current lens and cropping is a good option, depending on the final output. If it's only for showing in a low resolution on a website, for example, nothing lost there. Ditto for printing anything smaller than an 8" x 10" print. If you planned on printing the results out at 20" x 30" poster size, then it is a different story.

To be honest it all depends on what kind of shots you are taking on whether it makes a real difference. Many of the shots that I take with a TC end up on a web site so the sharpness is not as much of an issue as it could be. That and the tc is the poor mans way out. I would love some better lens but the wallet says no.

I wouldn't put a Tcon on that particular lens as it's image quality already suffers. I don't like to crop either but I think thats the better choice out of the two. It would just be better to buy a lens more suited to your needs IMO. This is I guess one of the down-sides of FF cameras when it comes to reach. But you get every inch squeezed in on the wide side of things. Guess it's the age old problem of not being able to have your cake and eat it too.