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Originally Posted by [1ponders]
Terry and avandonk, what are you feelings on using a 1.4X or 2X teleconverter. Would they degrade the image significantly when used with either a 50, an 85, or a 100 lens?
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The 1.4x and 2x teleconverters only work on some (longer FL) L lenses.For a list see
http://shop.centre.net.au/index.html...1CY&it=product
I have a 300mm F2.8L and a 1.4x teleconverter and there is almost no detectable degradation of image (CA) using the 1.4x.I have heard there is a slight degradation with the 2x.For the cost of one L lens around 100mm you can easily buy two of, 85mm F1.8 USM,100mm F2.0 ,100mm f2.8 macro,and the 135mm F2.8 softfocus (the soft focus can be turned off).
All is not lost though.I am going to modify a 500mm F5 achromat OTA by shortening the tube and then mount a reducer lens to convert it to a 300mm F3. I already have it working at 400mm F4 and the image is no worse than the
native configuration.I suspect a minus violet filter would solve any CA problems.
The 80ed is even a better candidate but I don't want to cut it's tube yet.
Obviously the 80ED would end up being a 360mm F4.5.
When I have it all working and tested on stars will let you know the details.
My aim was to design a reasonable quality fast refractor that was affordable.
Here is a pic of two exposures superimposed with Registar one 600mm F7.5 (80ED) and with focal reducer 0.63 380mm F 4.8.Both the same exposure.The pic with reducer through trees!