suntouched Loc: Sierra Vista AZ

I have a 300 mm f4 Pentax lens- used on K3-2 camera. It hunts and hunts and hunts- for BIF and more so with T/C on. Every now and then it will catch focus but it's a rarity. Does better with no T/C but still slow as molasses for BIF. Anyone found any settings that improve catching focus? If not for the lens being such an excellent one, I wouldn't keep trying.

MT Shooter Loc: Montana

Is your TC a 1.4x or a 2x? With a 2x you will not make it any better as your camera cannot AF past F6.3 and the 2x makes that lens a 600mm F8.

suntouched Loc: Sierra Vista AZ

It's a 1.4

MT Shooter Loc: Montana

Have you checked the rear lens element for fingerprints or smudges?

lamiaceae Loc: San Luis Obispo County, CA

What AF mode are you using AF.S, AF.C or AF.A? You are not set to AF.A are you? Here is a Review that may help. It seems to be a great lens, but fussy AF by some reviewers.

https://www.pentaxforums.com/lensreviews/SMC-Pentax-DA-Star-300mm-F4-SDM-Lens.html

You probably should only use the matched 1.4x T/C. Yes, I know 300mm or 420mm is pretty minimal for wildlife. I have Pentax K-3, K-5, K-20D cameras and even with my longest lens, a cheap used Pentax FA 100-300mm I can barely reach birds unless they are near me. If it is a 1.4x is it a matched AF model, I have T/C that are either totally Manual or AE. AF is the pricey type! It is the same with Extension Tubes for macro, they come in several types, Manual, AE, AF.

I'm mostly shooting close-up so most of my lenses are short, falling between 19mm and 135mm, with only a few longer. My best two "digital" lenses are likely my smc-Pentax-DA 35mm Macro f/2.8 Limited Lens, and my smc-Pentax-DA* 16-50mm f/2.8 Zoom. Both bought new costing me more than a camera at the time. I also have 30+ Pentax K, M, A, FA, DA, and Takumar Screw Mount M-42 lenses. The Super-Takumars are great, but not easy to use!

Can you take your 300mm f/4 off "A" and use an aperture (click stops) ring with the camera and lens and/or body set to MF? If so, you might try, what does Pentax call this, "Catch In" focus; You manually focus slowly and when the camera detects FOCUS it takes the picture. It works for Pentax/Takumar M-42, K, M, A lenses. You may need to press the Pentax Green button on the back for correct AE for any M-42, K or M lenses. But I guess that might not help you for BIF. Good luck.

suntouched Loc: Sierra Vista AZ

No but I will.

RWR Loc: La Mesa, CA

The lens can only respond to signals from the camera. You may be trying to focus on too many points at once, or the camera's autofocus sensor may not be sensitive enough for the scene. Not all cameras are equal in this respect. You might check the user's manual for conditions in which autofocus is not recommended.

speters Loc: Grangeville/Idaho

There are (rare) occasions, that I use my Pentax 300/f4 for shooting birds in flight, but I use manual focus, because I use it on my Canon. Mostly I do not use that lens for birds, but had situations, were that was the only somewhat longer lens I had on me. Certainly don't get a high keeper rate doing that, but when I hit, the images turn out very well!

radiojohn

If you think you have trouble, pity those trying to shoot indoor sports!

Sadly, this is why pro sports shooters spend so much money on lenses and bodies. It's a "get the right tool for the job" situation. Back when point 'n shoots were used, I had countless students hoping to catch indoor sports action shots with f/8 lenses and cameras that topped out a ASA400. Sometimes they got lucky, most times not.

agillot

you are right about birds shots , i find 800mm is about right .especially for small birds .

GENorkus Loc: Washington Twp, Michigan

I have found a couple 3rd party T/C units to not work at all on long lenses. Only normal to mid range lenses. Not even my 70-200.

Another thought, by saying "action shooting", it might be that anything to get a focus lock on what eve has changed.

I have had a similar problem going for birds in trees. After thinking about it, i thinking about it,
it was because there were several tree branches in the way.

Those branches had my camera thinking the subject was less footage away. When the wind blew, the branch moved and I got a clear but futher away shot and the auto focus changed back and forth. (I remedied that by going to manual focus.)

digit-up Loc: Flushing, Michigan

I have a wonderful 60-250 that isn’t great for birding, but I must say, it is a great lens otherwise. At one point, after a few weeks of persnickety focusing, it just quit focusing at all. I mailed it off for repair, and it is now one of my favorites. Pentax has been known for focusing ISSUES. But...I still believe that Pentax makes great glass. I knew you were a FUJI fan, as I am now, to, but I didn’t know you also shoot Pentax. I bought my first Pentax (spotmatic) while in VietNam, 1968-1969. Have a nice new year and I hope you find a solution. BOB

alandg46 Loc: Boerne, Texas

I use a 300mm f-4 on a K-5. It locks on quickly except for a subject in motion. This unfortunately is a Pentax weakness. I love Pentaxes and I love that lens, but not when I'm doing birds. I really had to work at it and still had only a 50% or so success rate. I can't imagine trying with any extender. That's why I have a Nikon D500 with a 200-500mm 5.6 now too. I have the 1.4 extender. It slows it some, but it is satisfactory and even with the extender beats the hell out of my Pentax gear.