Originally posted by ivoire A 300mm + 1.5 or 1.7TC + good stealth technique is affordable and very adequate. If you are taking a planned trip and need a long lens its probably a better idea to rent one. I've looked at the Sigma 500mm but it would sit in its case 300 days out of the year. $4600 buys a lot of other equipment/vacation/shooting time.
I agree -- and stealth technique is important regardless of how long you're shooting. 300mm is about my limit for both portability and afford-ability. With a premium quality 300 f4(or 4.5), you can stretch it to 420 or 510mm and retain AF. This is about the optimum setup if you plan to walk around and take opportunities as they come either handheld, or with a light tripod or monopod.
Here's one from the summer with a K100DS+ FA*300/4.5 +1.7x AFA handheld
With a 300/f2.8, you have more versatility, but the size and weight can become restrictive, as can be the price. With the f2.8 max aperture, and the optical quality of any lens of this class available for the K mount, TCs can get you 420 f4 (1.4x), 510 f4.8 (1.7x), 600 f5.6 (2x or 2 stacked 1.4xs), or 714 f6.7 (1.4x stacked on a 1.7x). With the 1.7x AFA, and the choice of Tamron or Sigma 1.4x AF TCs, I have AF with all of these combos.
Here are a couple of examples at 714mm, using different bodies and 300/2.8s. These were both shot from a tripod w/Wimberley Sidekick
K-7, FA*300/2.8 + Sigma 1.4x APO TC + F 1.7x AFA
K20, same lens/TC combo at very close range, cropped to vertical from a landscape frame. I'd like to see a crop from a 300mm shot that matches this for feather detail -- and this is with
stacked TCs. . . anyone?. . .
And one at 420mm at very close range and close to max aperture (f3.2), cropped to vertical from a landscape frame. This one's handheld.
K20, Sigma EX 300/2.8 APO, Sigma EX 1.4x APO TC
The hidden advantage of using this class of lens with TCs is the Minimum Focusing Distance. All the alternatives for the K mount that are reasonably available -- the Tamron SP 300/2.8 LD (IF), Sigma EX 300/2.8 APO, and the FA* 300/2.8 ED (IF) are 8', 8', and 6' respectively. The Sigma EX 500/4.5 has a MFD of 13 ft. The old K 500/4.5 has an MFD of about 30' IIRC!!! The F* and FA* 600/4 ED (IF)s MFD are over 15'.
IMO, any of the 300/2.8s are the best birding option if you can work with a tripod. If you're looking to go handheld, then a 300/4 or 4.5 with a TC is your best option -- compare the size and weight to a Bigma -- with the latter
fully extended to 500mm
Just my couple of ¢ worth. . .
Scott