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03-01-2007, 08:36 PM   #1
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SMC 50 1.7 aperature setting question...

Am struggling with the manual aperature setting on the 50 1.7.
I want greater DOF in a shot yet when I manually set the aperature ring to say f22, I get the shot at f1.7. If I put the lens on Auto then I get something I don't necessarily want, such as 2.4.

Any help would be greatly appreciated.

03-01-2007, 08:41 PM   #2
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Make sure the custom menu shows use aperture ring and shoot in manual mode using the green button to see shutter speed.
03-01-2007, 08:58 PM   #3
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QuoteOriginally posted by clarenceclose Quote
Am struggling with the manual aperature setting on the 50 1.7.
I want greater DOF in a shot yet when I manually set the aperature ring to say f22, I get the shot at f1.7. If I put the lens on Auto then I get something I don't necessarily want, such as 2.4.

Any help would be greatly appreciated.
Hi Clarence, I'm not sure I understand. Are you saying the camera won't stop the lens down? Even in "M"? Do you have other manual lenses? If so, does the camera stop those down?

NaCl(not sure I understand)H2O
03-01-2007, 09:09 PM   #4
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I guess I have the same lens... I just got it yestaurday and still practicing~

I can only change aperture in Manual mode, not in Av mode, it stays F1.7...

03-01-2007, 09:47 PM   #5
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OK I'll see if I can be a little clearer as I sometimes garble my own thoughts.
#1 Custom menu allows aperature ring OK.
#2 Camera in manual mode.
With the above the lense will stop down temporarily using the green button or I can hold it in position using the funny aperature symbol position on the on/off switch.

What I cannot get is the readout for the f stop. I get F _ _ _ on my rear LCD so I have no way to know for what my shot should be set. Nor do I know if it actually did the stop down. I could know this by examining the DOF of a close shot but didn'tdo that.

How do I set the speed/aperature for this manual lense to get the shot I want outside of using a hand held external meter?

Is there another setting I can use with some coordination of the aperature (either green button or ON/OFF aperature switch) to get it to read the light and let me know at least some starting settings which would allow me to go up/down in either speed or aperature?

Clear as mud??
03-01-2007, 10:10 PM   #6
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QuoteOriginally posted by clarenceclose Quote
OK I'll see if I can be a little clearer as I sometimes garble my own thoughts.
#1 Custom menu allows aperature ring OK.
#2 Camera in manual mode.
With the above the lense will stop down temporarily using the green button or I can hold it in position using the funny aperature symbol position on the on/off switch.

What I cannot get is the readout for the f stop. I get F _ _ _ on my rear LCD so I have no way to know for what my shot should be set. Nor do I know if it actually did the stop down. I could know this by examining the DOF of a close shot but didn'tdo that.

How do I set the speed/aperature for this manual lense to get the shot I want outside of using a hand held external meter?

Is there another setting I can use with some coordination of the aperature (either green button or ON/OFF aperature switch) to get it to read the light and let me know at least some starting settings which would allow me to go up/down in either speed or aperature?

Clear as mud??
With the lens you have on your camera, the camera will not know what aperture setting you are using and that is why your display is showing F--. The only way to confirm you are using the aperture is to look at the aperture ring on the lens itself. You can confirm if the lens is stopping down by using the DOF preview.

If you are using DOF preview through the viewfinder (not using the digital preview) you will see the EV shift from -3 to +3 (0 being proper) as you adjust the aperture and/or the shutter speed.

Hope that helps.
03-01-2007, 10:23 PM   #7
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QuoteOriginally posted by clarenceclose Quote
Clear as mud??
Nop, clear as your 50/1.7

The Original K mount had a pin in the 2-3 oclock position that inserted into the base of the lens when the lens is mounted. This mechanically let the camera know which aperture is currently selected. The camera uses this information to meter as well as to stop the lens to the right position.

If you twisted the ring to F8 position, the camera will know to stop the lens to f8 by releasing the spring loaded aperture pin thingy that sticks out the back of the lens.

Future evolutions saw the addition of electrical contacts along the mount plate.

However, nearing the later MZ film line, Pentax decided to drop the pin located at the 2 oclock position to cut costs. The only way now for a camera to 'know' the aperture is to set it itself and then relay the info to the lens through those electrical contacts.

Using old lenses without this contacts however..is another story. The camera cannot communicate with the lens and so it doesn't know the aperture range and that is why the dslrs will display a "F - -".

This is why you cannot 'use' the lens in Aperature Priority. The camera has no way of knowing what aperture you picked and doesn't know how far to 'stop down' the aperture and will just assume that its wide open.

To use old lenses that don't have "A" on the aperture right, you must shoot in Manual Mode.

> Turn the ring to your desired aperture and press the "AE-L" button.

On Manual, this button stops the lens down for a split second and takes the metering based on the light coming through at that instant. The camera also remembers the how far (distance wise) to stop the lens down.

> Now hit the shutter button and you're done!
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Last edited by FotoPete; 03-01-2007 at 10:55 PM. Reason: added pictures for clarification
03-01-2007, 10:30 PM   #8
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QuoteOriginally posted by Alvin Quote
With the lens you have on your camera, the camera will not know what aperture setting you are using and that is why your display is showing F--. The only way to confirm you are using the aperture is to look at the aperture ring on the lens itself. You can confirm if the lens is stopping down by using the DOF preview.

If you are using DOF preview through the viewfinder (not using the digital preview) you will see the EV shift from -3 to +3 (0 being proper) as you adjust the aperture and/or the shutter speed.

Hope that helps.
I have the M50mm F1.7, I use the green button to show the shutter speed based on the aperture ring setting and ISO. My normal sequence is to set the aperture ring, frame and focus, press green button, if speed not acceptable, adjust ISO, press green button again to see new shutter speed. Use the DOF preview if I wish to see the result without taking the image, adjust aperture and repeat steps until satisfy. The whole process is very quick except for DOF preview otherwise your eye never leave the viewfinder.

03-01-2007, 10:36 PM   #9
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QuoteOriginally posted by FotoPete Quote
> Turn the ring to your desired aperture and press the "AE-L" button.

On Manual, this button stops the lens down for a split second and takes the metering based on the light coming through at that instant. The camera also remembers the how far (distance wise) to stop the lens down.

> Now hit the shutter button and you're done!
I forgot about that one Pete. Good one!
03-01-2007, 11:32 PM   #10
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I spent alot of time on forums and stuff so when I got my GX-1L, the transition was pretty smooth despite most of my lenses being of plain K Mount. Then I eventually discovered why the procedure must be done and how the "Crippled KAF" came to be.

(I added some close up photos of the Kmount on my previous post.)
03-02-2007, 06:39 AM   #11
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OK, I understand what you are getting at now.

QuoteOriginally posted by clarenceclose Quote
OK I'll see if I can be a little clearer as I sometimes garble my own thoughts.
#1 Custom menu allows aperature ring OK.
#2 Camera in manual mode.
With the above the lense will stop down temporarily using the green button or I can hold it in position using the funny aperature symbol position on the on/off switch.

What I cannot get is the readout for the f stop. I get F _ _ _ on my rear LCD so I have no way to know for what my shot should be set. Nor do I know if it actually did the stop down. I could know this by examining the DOF of a close shot but didn'tdo that.

How do I set the speed/aperature for this manual lense to get the shot I want outside of using a hand held external meter?

Is there another setting I can use with some coordination of the aperature (either green button or ON/OFF aperature switch) to get it to read the light and let me know at least some starting settings which would allow me to go up/down in either speed or aperature?

Clear as mud??
As others have said, the reason you get the F___ is because there is no electronic communication between camera and lens. After reading FotoPete's post I guess there used to be a mechanical connection but that's gone too. From my understanding this is what happens when you mount a manual K mount lens on your camera: (and if I say something wrong I'm sure those more in the know will correct me)
1. To improve focusing, framing etc there is a small tab that protrudes from the rear of the lens. This lever allows the lens to be wide open when it is mounted on the camera.
2. You set your aperture and push the appropriate button on the camera (dont have the K10D, on the DS it's the AE-L button, on the M setting it tells the camera to move that small tab in the back of the lens to meter the light at the aperture youve selected) On the DS there is a distinctive elongated cliiiick sound as this happens. It then makes the calculations necessary and displays the appropriate shutter speed for the available light and aperture selected. If you like that particular speed, fine, take your picture. If the speed is not acceptable, change a parameter (aperture, ISO, EV, etc) and go thru the process again. It sounds a lot more time consuming than it is. Unfortunately you do not know the aperture unless you stop and look and note it down...I hate taking notes whilst shooting, so I don't bother.
You really don't know that the camera has stopped down the lens, you have to take that on faith.
3. When you press the shutter the camera agains moves that small tab to stop down the lens, and opens the shutter for the caluclated time. The lens remains stopped down during this and then springs back open when the shot is completed so that you have a nice bright viewfinder for your next shot.
As an experiment what you can do is examine your manual lens off the camera. Take off the caps. Stop down the lens to a small aperture, you will see the diaphram closed down. Move the little sprng loaded tab protruding from the back of the lens, you will see the diaphram open. If you release the tab the diaphram will close down again. This is what your camera does (in reverse) when you press the shutter or the stop-down button.

NaCl(now I've probably confused you completely)H2O
03-02-2007, 06:47 AM   #12
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HAHA, That's a great image FotoPete! As others have said, you MUST be in M mode. Since you can have the camera meter for you (and set the shutter speed) by pressing the green button, you are kind of in a pseudo-Av mode, since you set the aperture on the lens using the ring, and the camera decides which shutter speed to use.

If you are in Av mode, the camera body will NOT stop the lens down to your selected aperture, so it will ALWAYS shoot wide open (and meter wide open), so if you want to shoot at f/1.7, then you can use Av mode.


I believe this is all spelled out in the manual (at least it was for the DS)
03-02-2007, 10:36 AM   #13
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I have to tell you all that I am most greatful for your considered attention and information.

I will apply what you have taught and am very appreciative.

Hopefully I will get by the mechanics and take some horse images for posting.
03-07-2007, 03:17 PM   #14
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hi clarence
i will bring to you a contribution(may be it 'll works)
i bought last week a very special lens k mount.it's not a real manual even if officialy it is one) but neither an auto.

so ,after checking a lot of way of using, i discover how its work well:

1) use it on manuel position
2) choose your aperture directly on the ring
3)adjust the speed according the choice of your aperture and the light
4) shoot without using the AEL position

Conclusion : if it's work for you ,you win a step
don(t forget to tell me if it's work or not for you,just to know i i am the owner of an exclusive lens !!!
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