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Old Jul 17, 2009, 7:57 PM   #1
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Default TC Madness. . . the K7 made me do it (3 imgs)

Hi All,

Got a K7 yesterday and had a chance to play with it for a couple of hours both yesterday and today. I'll hold off on most impressions until I've had more of a chance to get settled in with it, but I will illustrate one of the main reasons why I wanted to upgrade from the K20 -- that the lower light AF sensitivity would allow me to use either more magnification via TCs or that it would allow me to use at least my 1.7x AFA with slower lenses.

Most look at low light AF sensitivity as just that -- focus in the dark with very fast lenses. I don't shoot too much in the dark, so I concern myself with better AF performance (or any at all) at slower max apertures -- pretty much the same thing in terms of the amount of light entering the AF sensor.

With the DS through the K20, f4.5 max at the lens was about the limit for AF ability with the 1.7x AFA, which was understandable. f8 max is a pretty common limit for AF systems, and most systems automatically default to MF when it senses f8 as the max aperture of the lens. Luckily Pentax doesn't have that limitation. My FA* 300/4.5 + AFA comes out as @ f7.7 (4.5 x 1.7) and this works well until the light drops to medium dark overcast -- that's why I started looking into 300/2.8s -- to allow me to shoot in less than optimal conditions.

Anyway, after playing indoors last night with the K7, I decided to see how far I could push it today. It started out as partly cloudy, and quickly became medium dark overcast. I found a young adult Black Crowned Night Heron hanging out at one of the local lakes, so I grabbed a couple of TCs and started shooting with the FA*300/4.5 and the 1.7x AFA (510mm, f7.7). Then I added the Sigma EX 1.4x APO TC for 714mm f10.7. I had tried this before with the K20 on a bright day and the cam just hunted lock to lock, no matter the target. As I had hoped, the AF system locked focus -- it was slow, but it locked. I shot a bunch handheld, sitting on the ground with my elbows propped up on my knees. I finally remembered to set the FL to 700 for the SR after about 20 shots. Here are some, all cropped and PP'd to taste -- mostly local sharpening, brightening and adding contrast.

K7, FA*300/4.5 + Sigma 1.4x APO TC + P F 1.7x AFA, f8 (actually f11 Av or wide open at the lens), 1/200, ISO 400, SR set to 500mm

This is a full height crop from a landscape frame

K7, same lens combo and settings, except ISO 500, SR set to 700mm

This is about the same crop as above.

The BCNH was pretty much ignoring me, so I went to the car, grabbed the FA*300/2.8, the tripod, and my Tamron F AF 1.4x TC, set everything up, and got some more shots at 1050mm f9.3. It was quickly getting darker, so I had to up the ISO to 1250 to get @ 1/200

K7, FA*300/2.8, Sigma 1.4x, Tamron 1.4x, 1.7x AFA, 1/200, f4.5 (actual f10.7 Av -- wide open at the lens), ISO 1250, SR off, tripod mounted.

This is just an 8x10 crop from the full frame, so it's just cropped some on the sides.
AF was very slow with this combo, but it did lock accurately -- and it had gotten pretty dim.

Bouyed up by these results, I tried a few more lenses when I got home -- the Tokina 150-500 f5.6 AT-X SD which wouldn't AF with the K20 at noon in June with a cloudless sky -- it AF'd with the K7 with the totally overcast sky (no shadows cast) -- pretty quickly too. I really had hopes for the Tamron SP 500/8 mirror, as this would be a killer minature 850mm f 13.6 AF lens, but it wouldn't lock on anything but the highest contrast subjects -- I still have hopes that it might be acceptable on a bright day, but I'm not going to hold my breath. . . The Tokina 80-400 f4.5-5.6 locks focus pretty easily, even though the light is getting pretty low. It needs some contrast to lock in though, but should give very good results with more light. This would give me a viable 136-680 f7.7-9.5 AF zoom that's very compact and light. I'll test these for IQ on a sunny day.

This all is very encouraging to me, and should make all the 70-300, 55-300, and Bigma shooters happy as their lenses might now AF reasonably with a 1.4x TC in good light, making these lenses that much more useful.

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Old Jul 17, 2009, 8:25 PM   #2
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Thanks for sharing the info' . I would love to own just one of the combo u mentioned. Job well done for letting us know what option we in tele

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Old Jul 17, 2009, 8:45 PM   #3
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Nice job Scott!
Unbelievable IQ for such a set up.
Attached Images

Life's a breeze on a Goldwing...
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Old Jul 17, 2009, 9:29 PM   #4
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Scott - thanks for taking the time to test and to share. These are great photos that show both your talent and the strengths of your new camera.
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Old Jul 17, 2009, 10:19 PM   #5
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Very encouraging results, Scott. I don't know how much longer I'll be able to hold off my PBA (Pentax Buying Addiction) if you keep posting this kind of quality.

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Old Jul 17, 2009, 11:33 PM   #6
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Glad to hear that you can do more with your TCs. Pictures look very good! Thanks to good, old (fill in your favorite swear word here) UPS, I'm still waiting for my camera. Amazon shipped it yesterday with 1 day delivery - it arrived in LA early this morning but didn't turn up at the office - and I waited until after 5. Ended up getting caught in a huge traffic jam caused by a bus fire that set the hillside alight, closing several lanes of the freeway and making the normal hour and a half commute take 4 plus hours. I would have missed it if I hadn't waited to see if it would turn up. Needless to say, I'm beginning to regret my order. Not because of the camera but because so much has gone wrong with the rest of it.
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Old Jul 18, 2009, 2:37 AM   #7
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Thanks for trying and posting the results, Scott. Very encouraging. To me it means that when I do get the K7 or it's succeeder, I'll be able to use my 600 mm f5.6 with the 1.7xAFA and get a 1020mm AF lens! I've tried it with the K20, but it doesn't even try to AF.

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Old Jul 18, 2009, 10:20 AM   #8
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A great job, Scott-

Thanks for taking the time to test all those combinations of lenses and TC's.

Sarah Joyce
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Old Jul 18, 2009, 11:09 AM   #9
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I second the thanks for posting these trials. My Sigma 135-400 didn't work too well with the Sigma 1.4X TC on the K20 - Maybe the K7 will do better.
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Old Jul 18, 2009, 11:25 AM   #10
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Since it is so hot out, I have been reading on the other sites about them not liking high ISO - on and on and on....

Your pictures with the detail are wonderful. Your explanation as to why, based on actually taking pictures, and comparison on the AF are excellent - and very instructional. I think that the details in the feathering and the ability to lock AF says it all. The coloring is excellent.

I really like the pictures....
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