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Old Feb 14, 2010, 8:17 PM   #1
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Default 16mm fisheye to 18mm kit

Harriet,

I'm not sure how scientific my test was here. Since the skies were clouding up by my house I headed over to the beach. A little bit of blue sky still left. I tried to find a spot where I could get the sky in the background and had some vibrant colors. The kids playground at Hampton Beach was it.

The first and fourth images were taken with the kit lens at 18mm. All images with K20 at f8, AV, spot metering, EC at +1, WB - daylight, ISO100, image tone - bright. Shutter speed on 1 - 1/100sec, 2 - 1/1250 sec, 3 - 1/1000 sec, 4 - 1/80 sec. The first one was autofocus, the other three manual focus.

I'm not sure whether it was my testing technique or what. But, the images with the 18-55 kit lens at 18mm are brighter than the Zenitar 16mm. These were taken RAW, imported into PSE8, I adjusted the temperature, tint, etc to all be exactly the same. Not sure if that was a good thing or not. I have no idea what I'm doing.

Anyway, here they are. Any input/suggestions on my process gladly accepted

Patty
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Old Feb 14, 2010, 8:45 PM   #2
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Patty

Something is wrong with your Zen 16mm. At 16mm F8 on a relatively bright day, there is no reason why focus is off in the 3 rd image . The focus is also off to a considerable extent in the 2 nd image as well. Zen should be ultra sharp by F5.6 (unless there is some compression issue in the attachment of this site)
Metering difference is not that big at all (less than 1/2 stop) as there are so many variables - the main one being AF and manual metering.
That is my input

Daniel

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Old Feb 14, 2010, 9:49 PM   #3
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Patty, it takes a little time to get used to the operation of the Z. The camera must be in manual metering mode and manual focus mode. After Framing and focusing you need to either push the AEL button to stop down the lens for metering or with my K-7 push the green button. I am not familiar with the K-20 so I can't tell you specifically what to do.

The shots you took at the Frost Farm looked good. Everything was sharp, so I don't think the lens is the problem.

Lou
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Old Feb 15, 2010, 12:38 AM   #4
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The Z pictures do look a little fuzzier than the kit lens, something I wouldn't have expected. It's not like it's OOF (though I suppose it could be), but it doesn't look like there's anything sharp. I think I'd tend to agree with Daniel - I wonder if there's something wrong with your lens (but think you need to use it some more to make sure).

Isn't the Z a manual exposure lens? While there's often a difference in exposures required by different lenses, yours are very different. 1/100 vs. 1/1250 is a very big difference if you were using the same aperture. If it's a manual exposure lens you'll need to use M mode - if you use anything else the camera will meter, but not stop down the lens at all - perhaps the lens was shooting wide open and softer because of that?

Lou - the K20 has the same green button. It doesn't meter accurately with my manual lenses - some are worse than others (my 24mm f2.8 is way off, the 50 1.7 not as much). The K-7 is far more accurate. With the K20, I usually take a shot or two, check the exposure/histogram and then adjust the shutter speed accordingly.
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Old Feb 15, 2010, 4:36 AM   #5
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Hi Patty,
It's a well known fact that a lot of the Zenitar 16mm f2.8 suffer from an infinity adjustment problem. ie not set correctly at the factory. I had this fault with my own zen ... it isn't too difficult to correct, I followed the instructions on the link below, and though the change in settings seemed minimal, it made a vast difference in the sharpness of results generally. incidentally you will find several hits on this subject with a google search, you may find something that clarifies the situation further. Hope this helps. ... Jack

http://cpicture.net/zenitar/index.html
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Old Feb 15, 2010, 10:40 AM   #6
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Well, like I said I didn't know what I was doing.

I need to redo this experiment. This time with the camera in another mode besides AV. Quickly reading through the manual, I think I can only do this in TAV or M. It's time for me to sit down and really think this through. The images at the Frost Farm were taken with this lens in AV mode. The shutter speed on the ones in the posting are anywhere from 1/1600 sec to 1/4000 sec. I hadn't noticed that until I just looked them all up. I believe they were all at F8. The Pentax Browser is not telling me. Well, except on one that says 1.4. Now I'm thoroughly confused.

With my glasses on it is difficult for me to read all the settings in the viewfinder unless I shift it around. Sometimes I am so focused on what I'm taking a photo of rather than what the settings are telling me.

Another question - if not all the info is always showing in the Pentax Browser with this lens is it that it might not be seated on the camera completely??? Although, I've got some images things show and some it doesn't show and I hadn't removed the lens in between.

Back to the drawing board. I don't think it's the lens. I think it's me.

Patty
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Old Feb 15, 2010, 11:45 AM   #7
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Patty, the Z is a full manual lens. AV mode will not work as the only way to set the aperture is with the aperture ring on the camera. When you set the aperture you want to use with the camera in M mode and then press the AEL button the camera stops down and the camera picks the appropriate shutter speed to go with that aperture.

The aperture ring can be easily tested by setting the aperture ring to infinity and take a picture of a landscape scene. If the picture is sharp all over the aperture ring is working properly.

If you put the Z on your K100D and do as I said and press the AEL button you can see if it is a problem with the stop down of the K-20 as Harriet has suggested.

It may be easier for you to transition to this manual lens in your K100. Keep in mind that this is an all manual lens and not an A manual lens. There are no contacts on the lens to allow the aperture to be set by the camera.

You must also remember to set SR to 15mm when the camera is started with the manual lens attached.

If you want I can meet you on your lunch break one day and go over everything with you.

Harriet- The green button on your camera may or may not be operating the same as Patties and could be an anomaly with you copy of the K20.

Lou
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Old Feb 15, 2010, 11:57 AM   #8
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Thanks, Lou. We're heading out to pick up one of the cars. I'm taking the Zenitar and kit lens with me to find something to shoot it correctly this time. Will report back with what I can do.

Patty
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Old Feb 15, 2010, 8:00 PM   #9
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Lou - the K20's green button works the same way as the K10 and K-7 for M mode, and like the AE-L button on the K100, DS and DL cameras. I've owned all of these cameras at one time or other, except the DL.

Patty - M mode is the only mode where the camera will stop down a manual lens - any other mode and the camera shoots wide open. So TAv won't work either, no matter what aperture you have either the camera or lens set to. You have to use M mode, set the aperture on the lens, then either push the green button to temporarily stop down the lens and let the camera meter, or else use the optical preview button (which you normally use for checking dof) and check the exposure bar to see if the shutter speed set will under or over expose the scene. I always used the green button and then would check the exposure on the LCD to see if I needed to adjust the shutter speed at all.
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