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07-21-2009, 10:44 PM   #1
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K-7 and the Pentax 18-250mm zoom

I received my K-7 on my birthday, and this is my first outing with it. At first I wasn't thrilled by its softness. I discovered that it was front focusing. I adjusted the lens focus in the menu to a -2 and it seems to have corrected the problem.

I was at the San Juan Capistrano Mission in Southern California and took a few shots. As it was mentioned in a another post, the K-7 does tend to expose a bit on the hot side. In the harsh lighting that I had this day at the mission, I set the EV to ranges of -1.5 to -0.5. In ordinary lighting though, the EV was set at 0.0 and exposed nicely

Here are a couple of shots that I took at the mission... I will post more later...

This is a shot inside the mission displaying different lighting effects on the surroundings.... This one is at -1.5EV



Here it is again at EV0.0


Exposure can be corrected using multi-exposure methods suuch as HDR..

Here is an example of a 3-shot HDR tonemapped image using Photomatix:


Here is the same image using Photomatix's Exposure-Blended function.... this gives the picture more color in the sky while not having the extreme contrast of the tonemapped image.



This one was taken at the center court fountain and had lotus flowers... this was also at -1.5 EV..



Alex


Last edited by AlexM; 07-22-2009 at 11:19 AM.
07-22-2009, 05:33 AM   #2
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QuoteOriginally posted by AlexM Quote
I was at the San Juan Capistrano Mission in Southern California and took a few shots. As it was mentioned in a another post, the K-7 does tend to expose a bit on the hot side. In the harsh lighting that I had this day at the mission, I set the EV to ranges of -1.5 to -0.5. In ordinary lighting though, the EV was set at 0.0 and exposed nicely
I also find that the K-7 in Matrix metering has a tendency to mimic Nikon cameras in allowing more blown highlights. Good or bad thing, depends on how you look at it... You have a bright sky with deep shadows, how the camera can know which one to prioritize?

I notice also that some lenses can be consistently off by +/- 0.5 EV. For example on my K20D, the Sigma 10-20mm needed +0.7 while my 16-50 often needed -0.3.
07-22-2009, 06:44 AM   #3
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Hey Alex - thanks for posting these. I have the 18-250 (my boat lens), as well and I appreciate seeing example shots produced with it coupled to a K-7.

Jer
07-22-2009, 07:39 AM   #4
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Me Too!

I also Have the Pentax 18-250mm zoom and I'm getting the K7 within the next month. I am looking forward to the front and back focus adjustment, but my question has to do with AF. Once the focus has been adjusted what would you say is the difference in focusing speed and accuracy over other Pentax DSLR's? I currently have the K10D, but any comparison would be helpful.

Thanks,


Last edited by Pentax_XTC; 07-22-2009 at 07:40 AM. Reason: Typos... :)
07-22-2009, 10:59 AM   #5
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The K-7 AF is pretty speedy in bright light and locks quickly and accurately. Low light though is another matter... Even though Pentax provided an AF illuminator, it doesn't work very fast and many times did not lock at all when in very low light and objects had a low contrast. The AF light only comes on under the same conditions as the raised flash on the K10/20D. Pentax REALLY needs to correct this problem with the AF light. Another thing I believe Pentax should add in a firmware update is to add a new menu item that permits AF in movie mode, regardless of the noise that could be generated in the sound. Lenses with SDM would not generate any noise at all IMHO...

Alex
07-22-2009, 11:30 AM   #6
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Updated my original post with additional images...

Alex
07-22-2009, 07:06 PM   #7
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I've been very impressed with the AF speed and accuracy of the K-7.
In bright light, focus hunting has never been an issue with previous Pentax bodies, but the focus travel speed was e.g. going from close focus to infinity for screw-drive lenses was a problem.
The K-7 does that travel noticeably faster.

The big difference in AF speed and accuracy has been in available light - all the typical indoor situations under artificial lighting, just bright enough to shoot handheld at high ISO. A lot of my photography is taken under such conditions. Interiors of homes and public buildings e.g. churches, halls, indoor events, night time functions on stage.

The K-7 will lock AF focus where the K10D and K20D will focus hunt for several seconds or just give up.
I previously considered the slow zoom lens nearly useless indoors for that reason, but with the K-7, I'm finding it very much usable indoors, combined with its pretty good high ISO performance.
With a large-aperture lens like the FA50 or DA70, available-light AF is a breeze.

The green AF-assist light only lights up in very dim light, or a dark/dimly lit object in an otherwise well-lit room. It has limited range - OK for portrait work, but not much of use in a big room. I've really only used it in conjuction with the on-board flash, which is rare.

With an AF540, the camera will trigger the Flash's Red Spot Beam. That bit is still slow and clunky, I wish Pentax could improve it..

Last edited by kittykat46; 07-22-2009 at 07:14 PM.
07-24-2009, 12:13 PM   #8
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Here is a shot I took yesterday with the K-7 / Pentax 18-250. No "sharpness" problems here



As with the k20d, I find the 18-250 on my camera the most. Alex, a "superzoom" lens is not a good indicator for AF tests in darker conditions. As kitty mentions, the small max aperture on a lens like the 18-250 makes it harder to AF in dark conditions. This is not a Pentax issue. It is a matter for all similar lenses on all cameras.


Last edited by PentaxPoke; 07-24-2009 at 12:20 PM.
07-24-2009, 01:05 PM   #9
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QuoteOriginally posted by AlexM Quote
The K-7 AF is pretty speedy in bright light and locks quickly and accurately. Low light though is another matter... Even though Pentax provided an AF illuminator, it doesn't work very fast and many times did not lock at all when in very low light and objects had a low contrast. The AF light only comes on under the same conditions as the raised flash on the K10/20D. Pentax REALLY needs to correct this problem with the AF light. Another thing I believe Pentax should add in a firmware update is to add a new menu item that permits AF in movie mode, regardless of the noise that could be generated in the sound. Lenses with SDM would not generate any noise at all IMHO...
The AF illuminator works well for me but I would agree that Pentax is too conservative and use it only when it's very dark. If they could use it 1 or 2 EV sooner, it would be better IMHO.

The 18-250 is f/6.3 at the long end and this could cause a problem because most modern AF system won't work that well past f/5.6, especially in low-light.

AF in movie mode would be better if CD-AF was not that slow with a lot of back and forth movement. This would be very distracting on a video and you're better off with manual focusing IMHO.
07-25-2009, 09:24 PM   #10
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QuoteOriginally posted by ManuH Quote
The 18-250 is f/6.3 at the long end and this could cause a problem because most modern AF system won't work that well past f/5.6, especially in low-light.
I never had a problem focusing with the 18-250 on my K100D at the long end.
Isn't f/8 considered to be the threshold?
For a 2 x teleconverter, a f/4 lens is the minimum which pans out to f/8.

The image by PentaxPoke looks more like what I would expect in terms of sharpness than the palm tree shots of the OP. It is probably a difference in JPEG settings or downscaling method.
07-25-2009, 10:09 PM   #11
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QuoteOriginally posted by Class A Quote
The image by PentaxPoke looks more like what I would expect in terms of sharpness than the palm tree shots of the OP. It is probably a difference in JPEG settings or downscaling method.
I am also wondering what shutter speed Alex used. The tree leaves, palms, and some of the tall plants seem to be a bit blurred. Especially in the multi-exposure HDR shots. The lack of sharpness may simply be movement of the scenery.
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