What are peoples thoughts on teleconvertors ??

Thanks in advance for your help.

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Teleconverters work. Buy the best you can afford. For a longish lens "on the cheap" the 300 mm 4.5 Tair telephoto with the Russian Fotosniper outfit is a remarkable good image maker. It is a M42, but a simple adapter will allow you to mount it on your telextender. In such a configuration, the spring-loaded aperture must be stopped down by the user hitting a lever under the lens.