1) SMC Pentax DA 1:4-5.6 50-200mm ED, with 52mm UV filter, moderate use, $110
2) Nikon 3T (1.5 diopters) Closeup Lens for 52mm, very slightly used, $40
3) Nikon 4T (2.9 diopters) Closeup Lens for 52mm, very slightly used, $50
4) Tiffen Linear (movable) Polarizer, 52mm, moderate use, $20
$200 (+ shipping) for all four.
In case you've not heard of "Closeup Lenses", also called "Diopters": they decrease the focus distance, giving you a lightweight and economical way to turn any lens into a macro by simply threading them onto the front of your primary lens, like a filter. These two can be "stacked" (both mounted at one time) for combined effect. Photo below shows the DA 50-200 with the 3T plus a UV filter mounted. (Obviously, this photo was not taken with the DA 50-200.)
On the 50-200 lens at 200mm, the 4T Closeup lens chops the minimum focus from the standard 4.5 feet down to about 1 foot, with all the increase in magnification that implies. See dragonfly below, using 50-200 and 3T Closeup lens.
With these high-quality two-element Nikon close-up lenses, there is VERY little sacrifice in IQ, edge to edge. The big trade-off is, they drastically reduce the lens's maximum focus distance. Thus, since you lose the ability to focus at inifinity, you wouldn't leave one mounted all the time -- it can be a bother to repeatedly install to go macro and then remove to shoot birds.
More advantages: they do not decrease available light, like a tele-converter would, nor change a lens' range of apertures. Nor do they prevent auto-focus, within their focal range -- you can leave everything in AutoFocus mode.
The Tiffen is a Linear Polarizer, meaning that you can align its axis toward the sun to get maximum effectiveness. Yes, the 50-200's hood has a small access tab for the polarizer -- this is why Pentax put the access tab in the hood. And in case you were wondering, the 50-200 filter mount never rotates, so you do NOT have to worry about the polarizer angle while focusing or changing zoom.
You're already familiar with the Pentax 50-200 itself, but I'll provide a 100% crop sample, anyway. Here's a hummingbird from about 6 feet away, handheld, 1/180s, 200mm, f5.6 (wide open), ISO 400, with Lightroom sharpening. (Caution: forum software has reduced the size about 50%, so it's no longer really 100% crop.
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