Has anyone used the Kenko Pentax teleconverter?

ben searle said:

ben searle wrote:

I was thinking of using this Kenko teleconverter with my 70mm Limited on a K5.

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www.srsmicrosystems.co.uk

Has anyone tried it? Better than cropping 70mm to same area?

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I have one of these TCs but I haven't done any direct comparisons of resolution using it v cropping. I briefly owned the 1.4X version (I sent it back because it was advertised as the Pz version but wasn't), and I did do some comparisons with that one. I took real-world pictures rather than test charts so my results are only subjective but I can't see any difference in resolution between lens A + TC v Lens B without, when the FL of B is about 1.4X A. I don't see any plus or minus cropping v using TC either.

These results were using good primes at their sweet spot of f/5.6-f/8t: FA50/1.4, DA70/2.4 and Sigma 105/2.8.

For the 2X version, here's a shot with it + DA70/2.4 (the combo you're interested in). Nominally f/5.6 so f/11 equivalent; K20D. Re-processed just now with CS6 and detail enhancement with Topaz Detail.


K20D, DA70/2.4 + Kenko 2X TC

As I say, I don't think there's any visible gain (or loss) compared to cropping. However, it's very much more convenient composing the image.





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Gerry
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First camera 1953, first Pentax 1985, first DSLR 2006

Many thanks for taking the trouble to process and post this.

As you say, may be no real gain over cropping, but I can see autofocus should also be much easier when the subject matter is larger. Did you find that worked ok?

Ben

2x TCs don't yield the best results.

Joe

ben searle said:

ben searle wrote:

As you say, may be no real gain over cropping, but I can see autofocus should also be much easier when the subject matter is larger. Did you find that worked ok?

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It's so long since I used the DA70 + 2X TC that I can't remember anything about AF. I therefore did a quick test this morning; test chart on bedroom wall, camera on tripod about 3.5m away. Using QS to pull the lens to infinity or closest, then letting the camera AF I'd say the TC slows things down by a tiny fraction: the bare lens snaps to focus effectively instantly; with the TC there's a barely perceptible delay - at a guess I'd say 0.1s without TC, 0.2s with it. Not enough to make any difference in practical shooting.

Shooting a test chart breaks the rules of ideal AF - that is, don't use closely repeating patterns. However, this particular chart didn't seem to cause problems. I'd say, though, that AF wasn't perfect with either. That may be calibration: I've calibrated the body + lens but not at this range, so there may be a slight discrepancy. I got slightly better results using LV.

I set the lens to f/2.8 and left it there: in terms of DOF that's like f/5.6 with the TC, which might have a minor influence on focus. In terms of resolution I'd have done a bit better by setting f/4 (about 4% more lp/ph according to Photozone).

Having taken the shots I processed them in CS6. The lens has a bit of LCA, which I reduced as far as possible by de-fringing. I cropped the TC version to 3200px square (easy to divide by 2) and the non-TC version to 1600px square; this should have equalised the size of the chart in the frame but in fact it isn't quite (so the TC isn't exactly 2X). Then I used Topaz Detail to show the definition of the lines better. Finally I resized both to 20cm square.

Here are the results (look at original size for the full effect).





Note that I didn't set things up at the correct distance for true measurement of resolution (although I wasn't that far off) so you can't use these shots to say what resolution the lens gives. Topaz Detail can't increase resolution but it does improve local contrast so that the resolution is easier to see.

I reckon version #1 shows something like 70-80 l/mm; #2 about 100-110l/mm (note this chart gives l/mm as opposed to the lp/ph given by PZ).

Several caveats, of course: my focus might have been different between the two (although I picked the best of three or four for each); the magnification of not-exactly 2X might have an effect; my resizing might have an effect. However, I can't think that any of these, or even all three combined, can make a difference of almost 2:3.

So which is which? #2 is the one with the TC, so in this simple test it seems pretty clear that it's worth using the TC.



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Gerry
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First camera 1953, first Pentax 1985, first DSLR 2006

I noticed that you use Topaz Detail. Would you recommend it or any of the other Topaz products?

rondeann said:

rondeann wrote:

I noticed that you use Topaz Detail. Would you recommend it or any of the other Topaz products?

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I recommend Topaz Detail very strongly. Like any software it can be overdone but used properly it can bring out a lot of details beyond what ordinary sharpening can do. It has independent control of fine, medium and coarse features. The fine control is roughly equivalent of conventional sharpening, but an auxiliary part of it can also reduce noise.

I also have Topaz InFocus, a more conventional sharpening tool. It's pretty good but I rarely use it because I can nearly always get what I want from Detail. A quirk in the Topaz mentality means that you can save your own presets in Detail but not in InFocus, so Detail is more convenient.

I bought Noise Ninja several years ago because a review at the time raked it equal with Topaz DeNoise but cheaper. With the improved NR in ACR and the auxiliary control in Topaz Detail I haven't used it for a couple of years. If you haven't already paid for other plug-ins I'd say buying the full suite from Topaz would be a good deal.

Incidentally, once bought you get free updates. I bought the original version of Detail and I'm now on V3 at no extra cost.

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