Dear Fellow Pentaxians:
The PIPE Here once more...unfornuately, the Pentax FA 80-320 lens I recently tried out from an Internet vendor that specializes in Pentax gear

didn't work out as hoped, from its

"ratchety" manual focus...I was able to get my purchase price back in full from the vendor, earlier this month, for that lens.
I've been thinking of another, currently avalable lens for "really getting 'out there' " with my K100D to grab nice, detailed images of Radio Control model and full sized aircraft in flight, and from my quarter century duration of experience with my K1000SE film Pentax, and starting this year with the K100D, a maximum focal length of 300-to-400mm would be best for the models, and 200-to-300mm is best for full scale aircraft.
The Vivitar Series One original production 70-210mm manual K-mount all manual lens that I acquired some time ago from KEH.com, and used a whole lot with the K1000SE for many, many years, has been tried out successfully on static test shots outdoors at home with my K100D, and it COULD be a usable lens in a pinch on my K100D DSLR (with an effective focal length range of about 105-310mm on my K100D) to get nice fly-by and other action shots of aircraft in flight with....that "AE-L" button on the K100D (same functionality as the "green button" on the K10D for this need) allows me to get that stopped-down preview, to help select a good set of aperture and shutter speeds to use in all-manual mode on my K100D (almost ALL my aviation shooting is done in all manual mode with the K100D...hard to beat!)
But the ease of use of my DA 50-200 Pentax digital autofocus lens this year, at times, just could not be beat, and I'm wondering if the lens that could end up being called the "Li'l Bigma" in Sigma's lineup for K-mount needs...their DG series f/4.5-5.6 135-400mm autofocus lens, shown at their site at
Sigma - Lenses , might be a decent choice for aviation photography with my K100D.
I do have a question or two, for ANYONE here that might have used that lens on any of the Pentax digitals, be they K-digitals or the earlier "Star-ist" series DSLRs...the MOST important ones are...
1: The 135-400 lens has a handle under the barrel, apparently like the 50-500 "Bigma" unit...has this been a help or a hindrance?
2: From the appearance of the lens in photos of it, it DOES have a dedicated aperture ring on it...
does this lens even HAVE an "A"-style automatic aperture setting on it in any way to allow the camera body (like my K100D does) to set the aperture, or would I have to use the AE-L button all the time with it, to get usable aperture settings to shoot in all-manual mode?
3: How smoothly does the manual focus operate on this Sigma lens when the lens is on the camera...is it smooth, or somewhat "ratchety" from the autofocus drive mechanism?
It's going to be later next summer before I'll have the money to get one of them...a decent priced site with it was found at
Sigma Zoom Telephoto 135 400mm f/4.5 5.6 APO DG Aspherical Autofocus Lens For Pentax from one of the NYC-located online vendors...but I'd thought I'd ask here first to see if anyone else might be able to pass along their experiences with a Pentax DSLR, be it "Star-ist" or K-Series, and that particular Sigma DG-series 135-400 zoom tele lens I've mentioned here.
Hope to see some answers "over time"...as I stated earlier, I'm not in a big rush to get it just yet!
Thanks in advance and Yours Sincerely,
The PIPE....!