What is a good telephoto focal length and aperture for planets?

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Blood N Guts Murphy
Blood N Guts Murphy Regular Member • Posts: 268
What is a good telephoto focal length and aperture for planets?

What is a good telephoto focal length and aperture? I have a few vintage options which are long. Not sure if they will be too dark with a teleconverter on each end. I have:

  1. APSC cameras, one 16MP and one 24MP.
  2. Pentax 135mm f3.5
  3. Teleconverter that goes onto the end of the Pentax 1.5x
  4. Just received today a Teleconverter that goes behind the Pentax 2x
  5. 200mm f4 Super Takumar
  6. Teleconverter that goes behind the Tak (maybe this makes the aperture f8 in light terms?)
  7. Have one or two more similar bits on the way (I got an awful Ensinor 135 2.8 today and have the same spec Miranda on the way). I just think the Pentax IQ could be bettered (as it was by the Super Takumar which was far better for aberrations and sharpness.

Thanks.

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