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I'm wanting to purchase a telephoto converter lens but was wondering are extension tubes/rings sufficient?
I have a D80 with 18-55 and 70-300 kit lens and 90macro lens. My aim is to get a bit more 'length' out of the lens without losing quality (have enough probs taking reasonable pics without making it harder )

TIA

Linda

Linda,

with the lenses you have, it is a waste of time to use a teleconverter (TC). I'm not even sure if it would work on the 70-300. Even if it would work, you would lose too much light, the image quality would go way down.

Extension tubes are different, they don't actually make your lenses "longer". What they will do is allow you to focus closer so you will in effect get a "macro" lens from your 70--300. You already have the Tamron 90mm which is a great macro lens and you can focus it very close.

Typically, you would put a TC on a lens that has an f-stop of f2.8 or f4. Note that a 1.4 TC, you lose one-stop, with the 1.7TC, you lose 1.5 stops and with the 2.0TC you lose 2 stops. On a slow lens you would only be able to use the TC in bright conditions, likely on a tripod.

HTH,

André

Linda, Andre is pretty much right on the money here.

Essentially extension tubes are a completely different thing to teleconverters.

Plus you would not want to use a TC on anything other than a f/2.8 or f/4 prime, or a f/2.8 zoom in my opinion. You will lose speed and quality, and if your lens is already quite slow as it is, you are never going to be happy with the results of sticking a TC on it.

I have the 70-200mm 2.8 and the 2x TC, and with the TC on it's nearly impossible to get good shots with low noise outside of bright daylight hours. Anything above 2.8 and your in trouble. At night i just take the TC off. It's not worth the effort, and noise you get.

Thanks for the feedback people - I knew it was worth posting my 'question'
Will now throw that thought away until I get better lenses.


Linda

The best way to demonstrate what extension tubes do is to observe what your lenses do when you focus on something close. Note: this only works with lenses that are not internal focusing (IF). I'm pretty sure the Tamron 90mm macro is not internal focusing.

As you focus on something closer, the front of the lens extends so you can focus. The big difference between a macro lens and a regular lens is the macro lens can extend further allowing it to focus on closer objects.

An extension tube moves the lens further away from the focal plane and basically achieves the same result that you get when you focus the lens on something close. The difference being that the extension tube adds to the amount of movement you already get from the lens and so you can focus on something even close.

The extension tube has little effect on the focal length of the lens so it will not give you any more reach from the lens. As the tube lets you focus on something closer, you really should look as it as decreasing the reach of the lens.

If you want more reach, you would be better off buying a longer lens. If you want to do macro with more reach than your 90mm, a Sigma 150mm f/2.8 or Sigma 180mm f/3.5 would make a big difference.

What others have said.

I'd just like to add that with tubes you'll lose the ability to focus at infinity (for the reason Andrew explained). Infinity focus is achieved at minimum lens extension. With tubes you'll push the lens out.

Cheers
Steffen.