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01-09-2015, 05:20 PM   #1
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K-50: Getting exosure right on manual lenses?

I bought a Pentax-M 50mm F2, and I already had a Promaster (Tamron) 80-210 AF that has an aperture ring you can set to A or specifically to a manual set position.


I followed the guide here:


https://www.pentaxforums.com/forums/54-pentax-lens-articles/110657-how-use-me...k-x-k-7-a.html



I also configured everything I believe I am supposed to, although the K-50 specific information is scattered around, so for those running into the same issues I took pictures of the menus. I'm going to make a sort of K-50-specific "guide" to make sure I did it right. If I did, people with K-50's can follow this for a bit more specific help. After that, my issue will be below.

First, turn the auto focus switch to "MF" for manual focus:



Might as well set the E-Dial knob to "M' for manual control:



Next, mount the lens and turn the camera ON. If it was already on, turn it off, and turn it back on. It will prompt you to tell it what size lens this is. On my Pentax-M it's on the front (50mm). Hit "OK" to accept your selection:



Next, hit the menu button and move to the tab option shown. Select E-Dial Programming and press "OK":



On the second page of this next window you want the settings for "M"



This lets you select the exposure mode for "M". We want to modify the function of the green button, move to that and press "OK":



Selet "Tv SHIFT" and press "OK":





The green button is now programmed "Tv SHIFT" for the "M" mode.



Next move to this tab on the main menu, and select item #22 (and press "OK"):



We want to select option #2 which is "Enable" and press "OK":



The use of manual aperture control (an aperture ring) is now enabled.




NOW... to the best of my knowledge, based on what I read in that thread... for the K-50 that's about it!


Except... in my case I get some odd results. I set both the Pentax-M and the Promaster to F16. Both of them came out... weird. I am attaching the files here, but the color is strange. All the extended file info should be there other than of course the F16.


I just need help understanding what is at play here. "M" lets me control ISO, shutter speed, and if I wanted to, brightness. I usually leave that at zero. But I see that pressing the green button takes what I assume is a metering for light, and automatically sets shutter speed (but not ISO). Yes?


Hopefully this end of things can be better explained. I already read through a few big web resources on what stops are, bigger numbers are smaller apertures, and how the numbers on the lens correspond with what effective stops work within a given focal range. So then what am I missing here? :/

Attached Images
View Picture EXIF
PENTAX K-50  Photo 
View Picture EXIF
PENTAX K-50  Photo 

Last edited by Suleeto; 01-09-2015 at 05:39 PM.
01-09-2015, 05:51 PM   #2
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Is ISO set to "AUTO"? Try setting it to a set speed, although I think "AUTO" is not available in manual mode.

Are you shooting under fluorescent lights? The phasing on these can throw off the metering and auto WB. Try some outdoor shots.
01-09-2015, 06:23 PM   #3
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Exposure looks good for both shots, but focus is badly off as is the white balance. Neither has anything to do with manual exposure. As for needing a special guide for the K-50...I suppose there might be value there. That being said, the basics are pretty straightforward:
  • Aperture ring enabled
  • M mode
  • Set desired aperture on lens
  • Focus and frame
  • Press green button to have the camera stop down the lens and set the shutter speed
  • Make your exposure
  • Evaluate the exposure and adjust aperture or shutter speed as needed
  • Continue shooting (no need to re-meter) until either the light or the subject changes
This is basically the same flow used with the original Pentax Spotmatic and all other cameras that use stop-down metering. Once you get used to it, you can shoot fast with little thought given to fiddling with exposure.

BTW...you should not need to explicitly set the program line to Tv shift when using non-A contact lenses. When the camera cannot set the aperture, Tv shift is the only option and is what the camera defaults to.


Steve

Last edited by stevebrot; 01-09-2015 at 06:28 PM.
01-09-2015, 06:29 PM   #4
Ole
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First one is out of focus, but white balance seems OKish. The glass is white, the background looks like tungsten light.

Second one looks to be in focus, but for some reason white balance is way off. Since you used a long shutter speed it should have averaged out the issues with fluorescent lights one would think.

I agree with Not a Number, first step is to eliminate the light source uncertainty by shooting outdoors.

01-10-2015, 12:03 AM   #5
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I shot outdoors but left that chip at home. What I can tell you is that all the shots had a similar issue with hue being off. This weekend I'll take shots outside with the Pentax-M and then shoot the same subject with the kit lens on auto everything @ 50mm for comparison. I mean, there should be differences between the two lenses, sure, but not this much. Not when I see Pentax-M 50mm F2 example shots in the "Pentax-M Club" thread.... and they look nothing like this, indoors or out. Those look real to life. Mine looks filtered through a weird color shift.

Hell, my cell phone is getting better color and sharpness.

---------- Post added 01-10-15 at 12:02 AM ----------

Oh and ISO is NOT set to "auto". All the extended file info is there to see, those example shots are attachments uploaded directly to the forum.
01-10-2015, 02:05 AM   #6
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Ok so I set the Pentax-M aside, and just played with the 18-55 WR kit lens.

First, I set it to auto (that will be picture #1)...
Then I observed what settings the automatic mode selected...
And THEN I set it to "M" and set the same ISO, aperture, and shutter speed.

First pic is full AUTO, second is "M" with as close to identical settings as I could set. Here also is the EXIF for both:


Image 1, AUTO


Image 2, "M" (manual)


Same exact lighting from a normal incandescent bulb in a desk lamp. ????????

This is with the AF lens. So it's not the lens. It's something with settings in the K-50. Is there some sort of image processing in AUTO that is happening to make things look more "real"? Why is the RGB so different with the manual mode?
Attached Images
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PENTAX K-50  Photo 
View Picture EXIF
PENTAX K-50  Photo 
01-10-2015, 08:30 AM   #7
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The second shot clearly is overexposed and the lens is quite a bit less sharp in the second photo as well. This could indicate that the lens on the camera didn't stop down when taking the second photo. But, I also wonder if you have some negative exposure compensation set when taking the first photo in Auto Mode? Such compensation wouldn't be applied when you switch to Manual Mode and also could explain the results you got in the second shot.
01-10-2015, 01:08 PM   #8
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Other than the settings described in the "guide" above, AUTO is as it came from the factory.

When you say "overexposed", are you talking shutter speed?

01-10-2015, 02:26 PM - 1 Like   #9
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Overexposed is when too much light reaches the sensor; the photo is washed out to some extent. This could be the result of the shutter being open too long, or the lens aperture was to large, or the ISO setting was too high (or a combination of these). None of this should be applicable here because you simply transferred the setting used in AUTO to MANUAL.

Maybe it's time to reset the camera to it's default setting using the MENU. Then try your test again using the kit lens. Don't make any menu adjustments/settings changes before doing the test again. Remove and replace the lens to ensure it is mounted properly. Use a tripod if you have one. Otherwise, place the camera on something solid so it doesn't move at all between the two shots. Use the four-way controller on the back of the camera to select the 2 second delay for the shutter. Set it to AUTO and ensure the switch on the side of the camera to AFS. Half press the shutter to focus, then fully press the shutter to take the photo. I'd then move the switch on the side to MF as the camera doesn't need to refocus for a second shot. Set the model to MANUAL and input the aperture, shutter, and ISO settings. Take the second shot. The lighting when taking the two shots needs to be identical. No flash. The results should be identical. If not, perhaps you have problem with the camera and/or lens, with the lens not reaching the proper aperture.
01-11-2015, 11:35 AM   #10
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OK I reset it... and it worked! Images in order of attachment:

- Full AUTO.
- Reproduced shutter, ISO, and stop from previous AUTO image.
- Third image, with a very quick swap to the Pentax-M, absolutely NO settings altered.

Success! Thank you for the reset suggestion! I wonder what went wrong :/

Side note... resetting (to default) did NOT change "Using aperture ring" back to "Disabled".
Attached Images
View Picture EXIF
PENTAX K-50  Photo 
View Picture EXIF
PENTAX K-50  Photo 
View Picture EXIF
PENTAX K-50  Photo 
01-12-2015, 08:52 AM   #11
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This is off topic, but how did you get the screen captures of the camera's lcd menu items?

Thanks
01-12-2015, 09:12 AM   #12
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Carefully holding my Samsung Galaxy Note 3 phone and using a dustcloth as a light blind. Had to take lots to get "straight-ish" shots, and even then some minor cropping of edges.

But when other K-50 noobs see this, it will help. I wonder if I should add that part of my OP to the manual lens mounting guide...?

Last edited by Suleeto; 01-13-2015 at 12:02 AM.
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