Teleconverter Question
 

Hi All

I am fairly new to using a dslr and have got a sony alpha 200 with the standard sony 18 to 70 mm lens as well as a sigma 70 - 300 mm lens and was looking at getting a sigma 2.0x Teleconvertor.

Is there any disadvantages to using one in terms of loss of picture quality and will it also work with the sony brand lense.

thanks in advance.

Andrew

Don't know about Sony cameras or the Sigma 70-300 lens Andrew but in general 2x tc's degrade the image quality a lot. It is only on the very best quality prime lenses that you can get away with a 2x tc (300 f2.8, 500 f4, 600 f4 etc.)
A 1.4 tc would be a better bet but even then I would not like to say how good it would be with your 70-300 (I know on the Canon 70-300 any tc is poor and you lose AF).

Hopefully someone with the same combo as you can give you some advise but until then I would be very weary about spending any cash on a tc - just my 2p worth.

I've never used a 2x t/con, only a 1.5x, that degraded the image quality quite significantly, it also reduced the effective maximum aperture by one stop. General consensus is, as Roy says, that a 2x will degrade image quality even more. You will also lose 2 stops of light with a 2x t/con, i.e. a lens which is normally wide open at f/5.6 becomes an equivalent f/11 lens. So, you can hopefully see you'll need a LOT of light to get an acceptable shutter speed, especially as you'd be using a "600mm" lens on a DX format dSLR - about 1/1000th would be needed for shake free images hand held.

You really are on a hiding to nothing using t/cons, of any magnification, with anything other than the very, very best quality lenses (ideally primes - not zooms). You're after a big, good quality lens on the cheap. I'm afraid if it was that easy, everybody would have one.

When I used my 1.5x I found it was actually just as satisfactory, if not better, to do a selective from on the image taken without using the t/con.

If you want a converter go with a high quality f1.4. To check if Sigma's converter will work with your 70-300 you will have to check it out on the Sigma website as it will only physically fit certain lenses without causing damage due to it's physical design. A very good converter which will fit is the Kenko 1.4 Pro 300. However you may lose autofocus with the combo which again you will have to check out on the Sony website this time as many "cheaper" cameras will not autofocus with a converter if the main lens is slower than an f4. For instance in the Canon line up you have to go to a Series 1 professional camera.

Thanks guys will probably just save up for a bigger lens then.

Andrew