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12-26-2013, 02:34 PM   #1
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How do I get this manual lens to work?

I got the Pentax Asahi 100mm f4 macro lens today. I put it on camera and switched to manual mode. I can see through the lens, but it's flashing "F" and won't let me take a photo.

What do I do to the camera settings to tell it to let me take photo ?

Additional info: I have the Pentax k-r

12-26-2013, 02:36 PM   #2
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https://www.pentaxforums.com/forums/58-pentax-beginners-corner-q/110658-using...x-dslrs-f.html
12-26-2013, 02:37 PM   #3
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Enable Manual Focus?

Hello Michael,
This question comes up a lot. Here's the guide;
https://www.pentaxforums.com/forums/54-pentax-lens-articles/110657-how-use-me...-x-k-7-a.html?
Hope this helps!
Ron
Oooppps! See I was 1 minute late!
12-26-2013, 02:40 PM   #4
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You need to set use aperture to permitted in the custom settings. That's a great lens, you will like it once you get to using it.

12-26-2013, 02:56 PM   #5
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OK, I watched this video and did what it said, even though the k-r is a little different.


Now, do I have to use the aperature ring to select what "F stop" I want to use?
I'm curious as to which F setting is best for macros. The aperature ring goes from 4 to 32.

Last edited by Michael Piziak; 12-26-2013 at 03:21 PM.
12-26-2013, 03:19 PM   #6
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One other question , what is this "tv shift" that I set my green button for ?
12-26-2013, 03:31 PM   #7
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It strictly depends on what your lighting conditions are.

Ultimate Exposure Computer

http://www.shutterfreaks.com/Tips/Exposure/exposure111.pdf
12-26-2013, 03:35 PM   #8
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Setting the green button to Tv shift causes it to choose shutter speed based on the meter reading.

12-26-2013, 03:39 PM   #9
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ok, I took a few photos with the lens. This is the lens I got off eBay for $25 because there was crud on the inside of the outer element. But I don't think the crud is affecting it. Here's some photos.
It's my understanding that the aperature ring is used to set the F stop, right? And also, when I push my green button (set to tv shift), it picks the exposure and shutter speed, right?
Trying to learn here

Last edited by Michael Piziak; 12-29-2013 at 08:20 AM.
12-26-2013, 03:44 PM   #10
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But I manually set the ISO, right?

Also, this is probably stupid question, but when camera is first turned on and wants me to set focal length, I just choose 100 since this is a 100mm macro lens, right?

Last edited by Michael Piziak; 12-26-2013 at 04:07 PM.
12-26-2013, 03:59 PM   #11
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QuoteOriginally posted by Michael Piziak Quote
it picks the exposure and shutter speed, right?
If set to Tv shift, then it selects the shutter speed that corresponds to the correct exposure given the aperture set on the aperture ring and the ISO selected. ISO should be selected manually.

For a basic understanding of how all this works try a book by Brian Petersen "Understanding Exposure". It explains how all the variables come together.
12-26-2013, 04:17 PM   #12
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QuoteOriginally posted by Michael Piziak Quote
ok, I took a few photos with the lens. This is the lens I got off eBay for $25 because there was crud on the inside of the outer element. But I don't think the crud is affecting it. Here's some photos.
It's my understanding that the aperature ring is used to set the F stop, right? And also, when I push my green button (set to tv shift), it picks the exposure and shutter speed, right?
Trying to learn here
  • But I don't think the crud is affecting it. - Initially no, however if it is mold or fungus, it will just keep growing and eventually obscure the lens. Not a good thing.
  • It's my understanding that the aperature ring is used to set the F stop, right? - Yes, the aperture ring is used to manually set the f stop to the desired value. Aperture and f stop refer to the same item. The aperture is the variable size hole the light goes thorough in the lens. The f stop is the value indicating how large or small the hole actually is.
  • And also, when I push my green button (set to tv shift), it picks the exposure and shutter speed, right? - Yes, once you set the aperture, you push the green button and it will set the shutter speed (which is the same thing as the exposure). Also, if you have the ISO set to automatic, the camera can select the ISO also (see your next question).

QuoteOriginally posted by Michael Piziak Quote
But I manually set the ISO, right?
Yes, or you can set it to Auto (see page 98 in the manual). If you set it to auto, then the camera will select the ISO along with the shutter speed, trying to balance everything for what it thinks will be the best resulting picture.
  • Also, this is probably stupid question, but when camera is first turned on and wants me to set focal length, I just choose 100 since this is a 100mm macro lens, right? - Yes

12-26-2013, 04:43 PM   #13
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QuoteOriginally posted by interested_observer Quote

Yes, or you can set it to Auto (see page 98 in the manual). If you set it to auto, then the camera will select the ISO along with the shutter speed, trying to balance everything for what it thinks will be the best resulting picture.



I tried to set the ISO to auto, but it doesn't have that option. My camera is in M mode and Manual switch selected in front. Perhaps that is only an option with an automatic lens?

p.s. Thanks for all the knowlede you gave me here
12-26-2013, 07:49 PM   #14
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QuoteOriginally posted by Michael Piziak Quote
I tried to set the ISO to auto, but it doesn't have that option. My camera is in M mode and Manual switch selected in front. Perhaps that is only an option with an automatic lens?

p.s. Thanks for all the knowlede you gave me here
I actually prefer to use the Av mode. I think that most folks around here use Av more than the Manual mode for manual lenses. With manual lenses (M42 screw mount, K and M lenses) you can use either M or Av modes. In this way you can select the aperture (f stop value) on the lens' aperture ring and with the rear thumb wheel control the shutter speed (or exposure). You should also be able to set the ISO either to a value or to auto. See page 98 of the manual. You should be able to set a ISO value (ISO 200) or a range ISO 200-1600, where the camera selects the best iso for the image within the range that you had previously selected.

hope that helps...

12-27-2013, 09:31 AM   #15
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QuoteOriginally posted by Michael Piziak Quote
Now, do I have to use the aperature ring to select what "F stop" I want to use?
I'm curious as to which F setting is best for macros. The aperature ring goes from 4 to 32.
The aperture affects the amount of light that comes in It also affects the depth-of-field. So make your choice based on your needs. When you close down too far (f/16 or higher like f/22 or f/32), you will get poorer results due to diffraction.

QuoteOriginally posted by Michael Piziak Quote
I tried to set the ISO to auto, but it doesn't have that option. My camera is in M mode and Manual switch selected in front. Perhaps that is only an option with an automatic lens?
Auto-ISO is not available in M mode. M-mode with auto-ISO is called TAv and is not available on your camera (as far as I know).

QuoteOriginally posted by interested_observer Quote
I actually prefer to use the Av mode. I think that most folks around here use Av more than the Manual mode for manual lenses. With manual lenses (M42 screw mount, K and M lenses) you can use either M or Av modes.
Are you sure about K and M lenses in combination with Av?
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