Actually it's very easy - you don't have to actually hit focus, just get it near and then the AFA x1.7 takes over and hits focus in an instant (faster than lenses usually focus because no screw / SDM to rotate).

If you are focused at infinity you don't have to do anything !

John is correct - I was referring to the DA*300 earlier.

Dan. Before I bought this lense I would have agreed with you wholeheartedly ...... but not now. Since the lense focuses down to 1.4 metres it's unlikely you'll get any birds closer than that ! I've also never had a problem getting a whole bird in the frame - unless we are talking about ducks, geese or swans from within a few metres then really there is no problem at all.

I've just put up a comparison of two of those lenses and a 500mm :

link

For what it's worth I think the 150-500 may be your best birding lense out of the lot, however the DA*300 is much lighter to carry around all day, and has the best IQ. You can easily add say a Tamron x1.4 lense to it to take you to 500mm - though the IQ is so high that even big crops are not an issue.

Either of those outfits would be great for birding.

Good point.

Actually I forgot .... though as it was exactly the same for all shots then it shouldn't influence the results as far as a comparison is concerned.

Thank you Oggy !

Can't blame you Hefty - IMO it's the best, and most versatile, lense I own !

K10D - yes the 50-135 is renown for it's excellent IQ with a TC installed. With the x1.7 I suppose you must take into consideration that these are 100% crops and the x1.7 is delivering almost twice the added magnification of the x1.4. When viewed at normal size the majority of these are more than acceptable. The Tamron x1.4 is a great little TC but so is the AFA x1.7.

Thank you Sam !

The AFA x1.7 seems to play well with almost all lenses Don !

I really like #1 and #3. That 35 seems to be performing admirably.

Lane Shooting here refers to something quite different - the old lanes, houses and people, full of Old Shanghai !

Thanks Andrew ..... but unfortunately I use Aperture on a Mac. I'm sure someone else will appreciate that tip though.

I like my Isambard Kingdom Brunel shot better - at my daughter's graduation

Recent debates on the virtues or otherwise of certain lense & TC combinations had me resolve to at least check what I have to hand - I need to know, when I go birding in particular, what is going to give me the best results (even though I don't shoot on a tripod very often). This was not designed to be a scientifically perfect test - only to give me real world results under real world conditions.

Methodology
K5 on a tripod + ball head, Manual Exposure (1/250, f8, ISO 200), timer : 2 second delay, SR off, AWB, AF-S, Spot Focus, Centre Weighted Metering. AF or MF (when AF unable to lock focus) : Shot taken on camera focus confirmation (beep).
2 shots per lense per combination - best shot selected, inferior shot deleted.
Subject was a broken white plant pot with blue floral design placed at 15 metres (ca. 16.5 yards or 50 feet).
Note - the camera will not display the exact f stop for some lenses with TCs attached (when the minimum exceeds f so you can calculate the exact stop yourselves from the camera max f stop + TCs. I don't find this particularly relevant for two reasons :
a) you can't reduce this minimum f stop for the lense + TC combination
b) I wouldn't be using faster lenses at those smaller apertures.

Post Processing
Auto Curves all shots to make viewing easier for darker shots.
Resizing for upload to online storage (1250 x 1080) + Forum compression.

Conditions
Bright but overcast. Sun directly behind the tripod (early afternoon). No wind. Sheltered garden. Dog was not permitted to chew, bury or otherwise molest the photographic equipment. A cup of tea was consumer after 1 hour. No toilet breaks.

Lenses Used.
S150 = Sigma 50-150 / f2.8 (this was the lense currently on the camera so I added it to the test anyway) @ 150mm
F210 = Pentax F 70-210 / f4 - f5.6 @210
DA55300 = Pentax DA 55-300 / f4 - f5.8 @300
*300 = Pentax DA*300 / f4
T500 = Tamron BB 500 Mirror / f8
SMC300 = SMC Takumar 300 / f4 - NB. No TC shots taken as I didn't want to risk the adapter getting stuck on one of them ! Also note an error in exposure settings (mistakenly f6.3 instead of f.

Teleconverters Used.
P17 = Pentax AFA x1.7
T14 = Tamron Pz x1.4

Combinations Tested.
S150 (no TC) (+T14) (+P17) - NB. Stacked TCs unresponsive so no shot taken.
F210 (no TC) (+T14) (+P17) (T14+P17)
DA55300 (no TC) (+T14) (+P17) (T14+P17) - NB. Focus lock achieved with P17 only 1 in 5 attempts. MF used for T14+P17 as no focus lock could be achieved in AF.
*300 (no TC) (+T14) (+P17) (T14+P17)
T500 (no TC) (+T14) (+P17) - NB. Stacked TCs - focus lock unresponsive so no shot taken.
Various 300mm @ 100%
Various 500mm @ 100%
Various 700mm @ 100%

Draw your own conclusions !
____________________________

[IMG]http://frogfish.smugmug.com/Other/Test-Shots/Sigma-50-15028-300mm-Test/1246308211_pKGnc-XL.jpg[/IMG]

[IMG]http://frogfish.smugmug.com/Other/Test-Shots/Pentax-F70-210-ALL/1246308284_c5fUq-XL.jpg[/IMG]

[IMG]http://frogfish.smugmug.com/Other/Test-Shots/Pentax-DA55-300-ALL/1246307900_VvWPA-XL.jpg[/IMG]

[IMG]http://frogfish.smugmug.com/Other/Test-Shots/Pentax-DA300-ALL/1246307774_8ZEuP-XL.jpg[/IMG]

[IMG]http://frogfish.smugmug.com/Other/Test-Shots/Tamron-BB-500-ALL/1246308630_SaQQ3-XL.jpg[/IMG]

@300mm

[IMG]http://frogfish.smugmug.com/Other/Test-Shots/Various-300mm-100/1246308616_puxqe-XL.jpg[/IMG]

@500mm

[IMG]http://frogfish.smugmug.com/Other/Test-Shots/Various-500mm-100/1246308864_ikDWD-XL.jpg[/IMG]

@700mm

[IMG]http://frogfish.smugmug.com/Other/Test-Shots/Various-700mm-100-2/1246308959_pbDXP-XL.jpg[/IMG]

Thank you Kris- glad you liked them !

Thanks Piotr !

Cheers Tim - unfortunately I don't have any more in the Bamboo Forest - it was a bit wet and dangerous on those very steep slopes, even in hiking boots.