what size extension tube required

[iwols]

hi all read various charts but still puzzled,what size extension tube would i need for a 1:1 macro with a nikon 18-70mm lens please or the 70-300mm nikon lens,which would be the best to use as well thanks guys,also is it worth the extra for auto focus,or are you better using manual focus anyway

 

[petersmart]

Well a set of auto focus extension tubes beats a manual set hands down - it's not just about the AF but also about the exposure - at least on the Canons an auto set will also mean the aperture also works as intended, otherwise you will be shooting wide open.

As to getting 1:1 the rule of thumb is that if you have say a 50mm lens then you need 50mm of extension to give you a 1:1 reproduction on the sensor.

Normally extension tubes come in a set of 3:

http://www.amazon.co.uk/Polaroid-Fo...H18Q/ref=sr_1_3?ie=UTF8&qid=1338845645&sr=8-3

which can be joined together to give various lengths, but as you can see a complete set adds up to approx 70mm so using lenses longer than this won't give you a 1:1 reproduction.

However I often use my 70-300mm L IS USM lens on my Canon 1Ds MkII at 300mm with a set of tubes and get extremely good pictures with it:

http://www.talkphotography.co.uk/forums/showthread.php?p=4709566#post4709566

especially since I don't need to get too close to get these pics.

But you also have to remember that you will also have very small DOF so you have to use a small aperture and, usually, flash.

But if you are intent on taking macro shots a set of extension tubes is, in my opinion, an absolute necessity.