Longer focal length for wildlife

zeroastigmatism · 2011-05-12T21:19:50+0100

Hi Need some feedback please on a telephoto topic. I have a Pentax Kx DSLR and want to do some Butterfly/Moth/Insect photography. This isn't necessarily macro shots I want to make, but mainly at distance (500mm to 10m or so) for the purpose of species identification. Currently I use a Tamron SP 70-210 f/3.5 with an adaptall. It is a good quality lens and I can get to less than a metre from the subject. However, I need greater focal length for image scale. My options I have considered are - 1. A good quality 2X teleconverter or maybe a 1.4X or 1.5X with a spacer to increase to about 2X should I need it. I can also use a 2X converter on my Tamron SP 90mm f/2.5 manual lens, as 180mm with macro facility would be very useful. 2. Putting hands deep into my pocket and go for a Sigma 120-400mm APO lens with K fitting. First question. Is my current telephoto zoom of high enough quality to take a 2X converter and still produce sharp results at 420mm? If so what is the best converter I should be looking for, bearing in mind it is image quality I am after. Q2. With a converter in place, can I still get to the same level of close focus at one end and infinity at the other? Q3. Will I see a momentous difference at 400mm with the Sigma APO, over the Tamron 210 + converter at 400mm? The advantage of the Sigma may be image quality and exposure time at 400mm, against the advantage of the converter being its usefulness on both Tamron lenses and the macro facility of the 90mm SP. Anyone have experience of either of these choices, or even both? Many thanks for your help. 0astig