using a SMC PENTAX F AF 1.7X ADAPTER with

the 55-300mm DA Pentax lens.

Has anybody used this combination, what are the thoughts from anybody?

Regards

Using a TC with any zoom isn't recommended, though with faster, high quality ones like the 50-135 you may get away with it. The 55-300 is good for it's class, but not good enough or fast enough to use a TC with. The recommendation for the 1.7 TC is that the lens must be f4 or above (or should that be below?).

Thanks Dr Mhuni,
I had tried to find the answer through the forum search but unable to find a specific post.

Regards

The problem I find with this combo is that you are invariably using it at 300mm end, and with 1.7x AFA the max aperture drops from 5.8 to 8.0, tending to me leave scrabbling about for light by increasing sensitivity (and reducing quality) to get a sensible speed both for moving targets and my inevitable shake at 510mm length.

I've read others say that you can only use this combo on manual focus because AF doesn't get enough light, but I have found it fairly reliable on AF so long as it is set on centre. It can scrabble a bit for focus in poorer light. The AFA always needs to be set close to focus point before it kicks in for all shots.

I've also seen the opinion that enlarge+crop at 300mm is likely to be as good as 300+1.7xAFA. I've been meaning to test this, so when I saw your post I went out and took a couple of quick shots this afternoon. First is with 55-300 at 300mm, plus 1.7AFA ie: 510mm, F8@1/180s.


The second is at 210mm enlarged and cropped to match, F8@1/350s.



The third is a living target at 300mm + 1.7xAFA, F8@1/180s.




All are taken on a monopod with SR off, all ISO400. Original images other than crop of second image. The 210mm+crop gets my vote for sharpness over the 300+1.7xAFA, in the poor light today.

I think the loss of quality in the 1.7xAFA shots is not down to the combined quality of the glass, but due to restriction of shutter speed - I can get faster shutter speed at 210mm or 300mm without the 1.7x adapter, and thereby better eliminate the effects of my camera shake or movement of the subject (the bird, not the hay feeder!).

To date I find that I only get the best results with the combo in bright conditions, when the loss of two stops by the adapter doesn't matter so much. Not too much practice so far as I've not had my 1.7x AFA too long. A more experienced photographer with a steadier hand would probably do better than me in poor light. Some of the guys on here working hand-held seem to be human tripods!.

The adapter works well with my DA*50-135 F2.8, which it converts into a 85-230 F4 and I believe it also works well with the DA*60-250 F4, though I don't have one. I've also seen excellent results from others with the DA*300 F4, which would be working as F6.7 with the adapter. That stop advantage over the 55-300's F8.0 seems to make a lot of difference, presumably also helped by the extra quality of the prime.

Having said all that, this combo is all I've got that can reach 500mm and I'm enjoying using it on brighter days and following the philosophy that "you can only shoot with the lens you've got" (I think that's how the the saying goes ), and I will continue to do so until I can afford to splash out on something better - I think the DA*300 currently gets my vote, but I've plenty of time to think about it.

Hope this is some use to you!

all the best

Ed

Ed
Very interesting piece and informative.I agree about the "shed" image with just the 55-300 being sharper...but the blue tit imsge is very acceptable indeed.

Roy

I am very pleased with the 1.7 AFTC and the 50-135mm

link

Regards

Nice birdie, wish i have a 1.7x

I have the 1.7 and 55-300, as yet untested. I will fire off some shots and deliver my verdict.

I've tried it with the Kenko 1.5x Pz-AF Teleplus MC and cropping beat it hands down.
Dave