Is it recommended that i get a teleconverter for my nikkor 70 - 300 4.5-5.6 lens??
i am also wondering if my d40 will still be able to autofocus

Thanks

I'm a Canon shooter so I can't directly answer part of your question. I will give you some personal observations on the use of TC's and let you go from there.

TC's can be a less expensive way to achieve a longer focal length and get usable results. There are however some down sides as well.

I don't know the quality of the lens you are asking about, but my guess is that it is a typical consumer lens. It is a bit slow being a 4.5-5.6. With a 1.4X TC you will loose one full stop. With a 2X TC you will loose 2 full stops. On a Canon camera, you would lose auto focus on anything but a 1D series body.

TC's work best with top quality glass. In the Canon realm that means L glass for the most part. TC's are also designed to work with lenses that are at least 100mm or above. When you attach a TC to the lens, not only does it magnify the focal length, it magnifies the flaws in the lens. If the lens is a touch soft you will magnify that softness.

The only two lenses that I consistently use a TC with are my 200mm f2.8L and my 400mm f2.8L. I get very acceptable results with the Canon 1.4X EF TC. I have tried it on my 70-200 f2.8L (comparable to the Nikon version) with mixed results.

The other thing to keep in mind is the quality of the TC. A no name, $50.00 1.5X, or 2X TC is not going to have top quality glass in it. Not only will it magnify the problems of the lens but throw in it's own problems. A top quality TC, such as Nikons top of the line or Kenkos 300DG series are quality glass that will provide better results. Be prepared to pay top price as well.

My suggestion would be to take your body and lens, go to a photography shop and try out a TC if you are wanting one and see if the quality of the images is acceptable to you. You will then have first hand knowledge of whether you body will still auto focus. What may or may not be acceptable to me could be the opposite for you.

Some teleconverters transmit auto focus some don't. They have lens elements and are likely to degrade the image somewhat (pincushion distortion sometimes). If you buy a 2x converter your lens will open to f 9 - f 11 (pretty slow). It might be better to crop the image to get better magnification than to use a teleconverter in some cases.

gryphonslair99 did an excellent write-up response to your question.

"Acceptability" is the open question. What percentage of images you shoot with your 70-300mm are acceptable to you in terms of sharpness? 5%, 10%, 2%, 15%?

To make a rough comparison, if you use a 2x TC, this "acceptability rate" can be divided by 2 - quite a decrease - due to the harder handling and the optimal lighting conditions required. You would have to try it yourself and decide.

Another example why a first-rate lens is required (which theoretically will give a higher success rate in the beginning).

Your lens' max apperture will be too slow with a teleconverter. It will render a max app of f/9 or so and thus will only be able to shoot static objects from a tripod. You'll need at least f/2.8 glass for a TC.

alright thanks for all the feedback

Mitch45,

Found some data on the Nikon site refer to this link it might help: http://www.nikonusa.com/Find-Your-Nikon/ProductDetail.page?pid=2151