Considering a 2x converter..

[Tobyh]

Originally Posted by nightshade

One thing to watch out for is that the rear glass element of your lense
does not touch the converter glass elements during zooming

Ok now I am confused how could this happen if it's meant to be compatible? Are you speaking from experience here Nightshade>? It's something I just would never have even thought about!

[jasongallier]

If it is all compatible then try it, just be careful! Have a look at the rear element in the lens and see how far back it travels when zoomed and focus is changed.

My canon 100mm macro can't be used with converters because the rear element of the lens would hit the front converter element - glass on glass is not a good idea! However I can put a small extension tube between the two then it would work fine but I rarely use that combination.

As for light issue - if you are using a ring flash you should be fine but remember that the increased focal length will mean reduced depth of field but that may well be off set by the increased physical distance you are away from your subject!!! Now it could get confusing

Jason

[glsammy]

Originally Posted by Tobyh

Ok now I am confused how could this happen if it's meant to be compatible? Are you speaking from experience here Nightshade>? It's something I just would never have even thought about!

It's quite common. On the Sigma 50-500mm, you can't use the converter at the 50mm end, because the glass hits the rear lens! Mind you why you would want to use it at 50mm is another question! You do have to be careful though when it's fitted as if you try and lock the zoom, again it'll hit the rear lens, just be careful with whatever lens you use one with.

[joekid]

ive used lots of converters in the past 20 or so years, and the latest one on a sigma 400mm 5.6 apo lens,the lens was great on its own ,i tried the 2 times sigma apo version but it didnt quite have the edge on selective enlargements, so i tried the 1.4,which was lots better,and with good film gave good results,you need to use a firm tripod, for best results,and remote release/if your camera has mirror lock up use that too(if quality is the thing) but ive used it gently pressing the release with good results, the more you pay the better the results,, do a little home work before parting with your cash ,, good luck fella.

[Matt Hunt]

Hi

I am using the Sigma 2xTC on the 100-300mm f4 and find I am getting acceptable results but having manual focus only is hard on moving objects (so far I've tried birds and Spitfires!). Having said this, I am wondering if this is a lens focusing issue at infinity since using the converter at less than 300mm has produced results.

For this combination there are no clearance issues.

Hope that helps.

Matt

[joekid]

i would save up for a while, a two times converter will slow things down more and take the edge off things,if its for macro stick with the extention tubes/ no loss of light/,,theyre is some expensive converters but again designed for fast lenses and will cost as much as a decent macro lens, catch 22 and only one way out,good luck fella,look for quality used lenses,