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06-17-2010, 06:26 PM   #1
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Aperture recognition on k10

I have a k10. It has been good for 2 years. Images are sharp. Light control is good. Color is good. Now my Problem.
I have a Kit lens which is a 18-55. 3.5-56. In dim areas the camera says the widest opening i can get on the lens is 5.6. I put a prime Pentax 100mm 2.8 and the K10 says it can go to 2.8. Good. If i put a prime 50mm on the K10 the camera says i can go to 1.4.... Good...If i put on my Sigma 120-400 4.5-56 on the camera the camera says i can go to only 5.6........ I have a favorite Sigma 70-300 that i have used for years and i can only go to 5.6 on it too......

Have i done something stupid with settings or do i have a problem with firmware or software....

Thanks for your thoughts.

Old Coot

06-17-2010, 06:33 PM   #2
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at what focal lentth

the lens at minimum focal length is the fastest but at the longest focal length will be F5.6

focal length is important in this
06-17-2010, 07:01 PM   #3
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Largest aperture 3.5 of the kit lens when it's at 18mm, and changes to 5.6 when its focal length is about 45mm.
06-17-2010, 08:18 PM   #4
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Focal Lenth

????? I have never set the Focal Lenth..... I pulled off a lens and found it was set to 35mm. I reset it to 40mm and i got the Aperture up to 4.5......The lens should be at 3.5..... I tried higher than 40mm but i could not get better. I tried lower than 35mm for fun but did not do any better.
The Sigma 120-400 also got 4.5.....And that is as big as it goes.......So some of my problem is solved.
I don't have the 70-300 Sigma lens as it is into the cleaners for dirt i got into it while taking pictures of Steam Boat Rock up on the Columbia River.
I did a reset to default settings with no help.The Prime 100mm and 50mm still work at 40mm

Old Coot

06-17-2010, 10:36 PM   #5
Ash
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Old Coot - there may be some misunderstanding here.
You change focal length with every turn of the zoom ring. If you have your kit lens set at 18mm, the largest aperture should be f/3.5 as Ken T states above.

If there is trouble getting to this value, try cleaning your camera mount's electrical contacts and do the same on the lens's contacts.
06-17-2010, 10:49 PM   #6
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Ok Coot . Would you do this so you can understand what Lowell and I talked about .

- Set your K10D at TAv (it doesn't matter if wether TAv or Av) ; mount your kit lens on and turn its zoom ring to its widest position which is 18mm; turn the e-dial which is the one you asigned to adjust aperture, turn to open aperture and you will see you can get to 3.5 .

Now you will notice that as soon as you turn the zoom ring out of that 18mm position, you don't have aperture of 3.5 anymore, and if you zoom more to about 45mm mark, or more, you will have the aperture reading of 5.6 .
06-18-2010, 09:52 AM   #7
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Thank You All for the help.....

Thanks for the help Ash, Ken T, Lowell Goudge," I, You All " have it figured out. Like i said the Primes are good. My KIT LENS 18-55 was driving me nuts. I did as sugested and tried to set it manually. I could not turn the focus "ring" ????? The lens was off the camera. I tinkered with it and got it to move. I wiped as much of the barrel as i could and twisted the barrell parts for 5 minutes....... I put the 18-55 back on the camera and it worked to the 3.5 opening..... seems the lens was dirty. I use newspaper plastic covers as much as i can but it is hard to protect lenses

I do a lot of out door photo"s in the Northwest. I take my Pentax out in rain, snow, and salt water spray sometimes. That is why i bought it. Tough as a brick. I am going to up grade to the WR lenses as they come available. I do not use my primes much accept when i need extra sharp pictures or ..... and have time to compose the picture...... Critters in the woods or bad weather sometimes don't accomadate me sometimes.

Thanks for the heads up on focal lengths. i will pay more attention to it in the future.... Have a good "Picture Perfect Day".......


Old Coot
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