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06-05-2014, 11:28 AM   #1
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Using a fixed aperture manual lens and green button

I have a Spiratone 500mm mirror lens that is fixed at f8. This lens attaches to my K500 camera via a T mount to K mount adapter. When using this lens and using the "green button" after composing and focusing, I do not hear any sound like I do with my other lenses and I assume it is because there is no no diaphragm to engage and stop-down as part of the metering process. I assume that is correct and I use the "green button" anyway as I notice seems to be doing its electrical thing since it does adjust my shutter speed when I depress the button.

Something that has me scratching my head is, as I understand it, in order to use a manual lens and the green button, the ISO must be set to MANUAL; however, the best pics with this lens are taken when I leave ISO to AUTOMATIC and use the "green button" prior to taking the shot. It seems to select the needed shutter-speed and ISO setting combination for a good shot.

So now to my question(s):

1. Am I correct in my assumption that a fixed aperture lens using a T-to-K adapter is to be treated just like any other manual lens on my K500. And if not, If not, what is the correct process/steps?
2. Why is AUTO ISO working for me when, as I understand it, the cardinal rule is that ISO must be set to MANUAL.

This one isn't keeping me up at night like Crop Factor did, but it does have me scratching my head.

Thanks!!

06-05-2014, 11:39 AM   #2
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Since the aperture is fixed, you can actually just use Av mode (with Auto ISO if desired) and you won't have to bother with the green button at all. I think that is actually what you are getting with auto iso turned on even in M mode -- you are probably fooling yourself thinking that the green button is doing anything in that scenario (it should change the shutter speed and iso just with changing light without you having to press the button)...
06-05-2014, 11:47 AM   #3
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Use aperture ring should be enabled in settings. Preview set to optical. Green button should be set for "M" and "TAv" modes to Tv shift.

Also on later bodies (the K500 being one of them) the green button will not activate unless a lens is attached. The camera determines this from electrical signals on the pins of the body mount. Every T2-mount I've have seen are painted or coated so the pins do not get grounded. Try carefully covering the pins with a piece of metal foil before mounting the lens. If this works you can remove the coating on the mount to expose bare metal over the area where the contacts would be.
06-05-2014, 02:40 PM   #4
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If it doesn't ask for focal length after mounting the lens, it hasn't sensed that a lens is present. I sometimes use a Spiratone 500 mirror on my K-5, and it normally makes enough contact so the camera knows it is mounted. I assume it is anodized, not painted.

06-05-2014, 03:02 PM   #5
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QuoteOriginally posted by TomB_tx Quote
If it doesn't ask for focal length after mounting the lens.
That might depend on model. I think all mine always ask even with no lens at all as long as shake reduction is turned on and it is in a drive mode where shake reduction is allowed. (Otherwise it won't ask even with a lens.)
06-05-2014, 03:33 PM   #6
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It is an Anodized adapter and yes it does prompt for the focal length when attached.

As for putting it in Av mode, it cannot really be done. The display shows F___ and unable to set aperture via camera. Fully manual with Auto ISO seems to work wrll. I guess it meters based on the light through the lens and seems to work out well.

Just curious as the guide does not really discuss fixed aperture lenses.
06-05-2014, 03:40 PM   #7
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QuoteOriginally posted by ripper2860 Quote
It is an Anodized adapter and yes it does prompt for the focal length when attached.

As for putting it in Av mode, it cannot really be done. The display shows F___ and unable to set aperture via camera. Fully manual with Auto ISO seems to work wrll. I guess it meters based on the light through the lens and seems to work out well.

Just curious as the guide does not really discuss fixed aperture lenses.
Yes, but Av mode still works -- in other words you just point the camera and it will set the ISO and shutter speed. It doesn't need to know what the aperture is or display it. (I'm not saying you can CONTROL the aperture from the body [if it were not fixed], just that you get Aperture Priority -- just because you only have one aperture to choose from is beside the point.) This is generally how m42 screw lenses are used (in Av mode) -- there is no coupling behind the lens and body, it always displays F--, but nevertheless you just set the aperture on the lens (and it immediately goes there, unlike bayonet K-mount lenses that stay open until you fire) and the shutter/iso is adjusted as you do...
06-05-2014, 03:58 PM   #8
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Now I get it. I was trying to set the aperture to f8 on the camera to match the lens. Tried it again in Av mode and it worked with excellent results.

BTW - green button doesn't work. I just saw the camera adjusting ISO and shutter speed for light conditions as I moved the camera slightly to review the info screen.

Thanks.

06-05-2014, 04:05 PM   #9
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QuoteOriginally posted by ripper2860 Quote
Now I get it. I was trying to set the aperture to f8 on the camera to match the lens. Tried it again in Av mode and it worked with excellent results.

BTW - green button doesn't work. I just saw the camera adjusting ISO and shutter speed for light conditions as I moved the camera slightly to review the info screen.

Thanks.
Yeah, the green button will only work with camera in M mode and auto ISO turned off as you previously learned...(and possibly only with an conducting-mount lens, but if that is true it is not true with all models). Now, you should also be warned that some claim that using Av in this way the meter results will be less accurate (in some cases grossly so), but it has always worked fine for me...
06-05-2014, 05:52 PM   #10
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Using a fixed aperture lens follows the same procedure as using a K, M or screw mount lens - there is just no aperture ring to adjust. Av mode works best with these lenses when they are wide open. A fixed aperture lens is always wide-open always stopped-down.

Here are the directions for using manual focus "A" lens, K, M and M42 lenses on the K50. The K500 is virtually the same camera as the K50 without weather sealing, the electronic level and focus points so these should pertain to the K500 too. These instruction neglect to say that ISO should not be set to "Auto".:

Using Older Lenses on the PENTAX K-50 | Ricoh Imaging Support
Q: Can I use older PENTAX lenses on my K-50

A: Yes. PENTAX A-series lenses (lenses with an "A" setting on the aperture ring), can be used as manual-focus lenses in all exposure modes on a PENTAX K-50.

Early PENTAX K-series, M-series and S (screw) mount lenses without auto-aperture control (an A setting on the aperture ring) can be used in Manual exposure mode using stop-down metering and manual focus. This is the exposure mode which will give accurate exposures when using these older lenses on our digital SLRs. If older lenses without an "A" setting on the aperture ring are used in Av (Aperture Priority) Mode, an exposure error may occur.

Note: Using PENTAX S (screw) mount lenses on a PENTAX DSLR requires the use of a Pentax Mount Adapter K.

To set up your PENTAX K-50 to use older PENTAX lenses:

STEP 1: (Customizing the Green Button)
Press the Menu button

Using the 4-way controller on the back of the camera, navigate to E-Dial Programming on pg.4 of the Rec. Mode menu.

Navigate to pg. 2 of the E-Dial Programming menu, highlight the first line and press the right button on the four-way controller. Press the down button to highlight the first line, then press the press the right button on the four-way controller. Press the down arrow on the four-way controller, highlight Tv SHIFT, press the OK button on the back of the camera, then press the MENU button several times to exit the Rec. Mode menu.

(This setting allows easy and accurate exposure metering using older lenses without an "A" setting on the aperture ring. When the camera's Green Button is pressed in Manual exposure mode, the lens "stops down", the camera's meter measures the light passing through the lens, and an appropriate shutter speed is automatically set based on that measurement).


STEP 2: (Enabling the use of the lens aperture ring)
Press the Menu button

Press the left button on the four-way controller once to get to pg. 4 of the Custom Settings menu.
Press the down button on the four-way controller and select Using Aperture Ring
Press the right button on the four-way controller, then the down button, highlight Enable and press the OK button.
Press the Menu button to exit the Custom Settings menu

STEP 3: (Setting Shake Reduction)
Shake Reduction is compatible with older PENTAX lenses (PENTAX M-series, K-series and Screw-mount lenses) but you will need to manually select the closest matching focal length from the Input Focal Length menu. To do this:
Turn the camera off. Mount the non-"A" series lens. Turn the camera on.

The Input Focal Length screen will appear. Use the rear e-dial to select a focal length which is closest to the focal length of the lens you are using and press the OK button on the back of the camera. If you are using a zoom lens, choose a focal length close to the midpoint of the zoom range of the camera.

STEP 4: (Using Older Lenses)

The camera has now been setup to use older (early K-series and M-series) PENTAX lenses on your K-50. To use these lenses:

a) Set the camera to Manual exposure mode and Manual focus.
b) Focus the lens and set the desired aperture (i.e. f/8) on the lens aperture ring.
Once again, without the pins shorted out the green button will not activate. This is the same problem people experience when using extension tubes that do not have contacts and bare metal mounts.

If you don't want to try the foil try this: Mount one of your other lenses (preferably a K or M series lens) and confirm that when in manual mode pressing the green button stops down the lens and sets the shutter speed (provided you have the green button set as above). You should hear the mechanical noises of the actuator, lever and iris moving and looking through the lens see the iris close down (if not set to wide-open). Even with aperture set to wide open you should still hear the actuator and levers.

Now remove the lens and press the green button. Nothing should happen. No noise, the actuator on the side of the mirror box nearest to the grip (right side) should not move.

On the K10D, K20D and perhaps some others the lever will activate without a lens attached when I press the green button or DOF preview. At some point Pentax decided to change this but I haven't been able to find in which model line this was changed.
06-05-2014, 08:53 PM   #11
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Thank you. I will verify all settings and make sure I fully understand the steps.

My T2 - PK adapter is not conductive and does not short out the contacts, so "green button" method does not work with this lens. Works fabulously with my M lenses and A lens (with aperture set via the lens) and camera set to manual focus / manual ISO. While I can just set the camera to Av mode when using the T2 lens, I like the idea of using one process (green button) for any of my manual and T2 mounted lenses I think it might just be easier if I could find a more appropriate mount adapter that would let me use the "green button". Is there a electrically conductive T2 -> PK adapter that would short out the required contacts? If so, can someone recommend?

Thanks!!
06-06-2014, 08:01 AM   #12
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QuoteOriginally posted by ripper2860 Quote
Thank you. I will verify all settings and make sure I fully understand the steps.

My T2 - PK adapter is not conductive and does not short out the contacts, so "green button" method does not work with this lens. Works fabulously with my M lenses and A lens (with aperture set via the lens) and camera set to manual focus / manual ISO. While I can just set the camera to Av mode when using the T2 lens, I like the idea of using one process (green button) for any of my manual and T2 mounted lenses I think it might just be easier if I could find a more appropriate mount adapter that would let me use the "green button". Is there a electrically conductive T2 -> PK adapter that would short out the required contacts? If so, can someone recommend?

Thanks!!
You can't truly use "one process" simply because bayonet K-mount lenses always stay wide open until you fire the shutter no matter what the aperture on the lens is set to -- that's why you need the green button which stops the lens down for a second to the selected aperture and takes a meter reading. Whereas other adapted lenses -- m42 & t-mount for instance, will never have a mechanical aperture coupling to the body -- they stop down as you turn the aperture ring (i.e. they physically need to be stopped down BEFORE you hit the shutter). It is annoying that the newer bodies require contact for the green button to work (it works fine even with no lens on my K5) if that's true, but anyway I do find it preferable to just use Av mode for non-bayonet adapted lenses. (And somewhat prefer m42s to non-A K-mount lenses for this reason.)
06-06-2014, 09:25 PM   #13
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Thank you. Makes sense and it would be far too easy if there was a singular process irrespective of the lens type. I do not own an M42 lens as of yet, as I really prefer the A lenses when I can find them in the Focal Length I want. I'll likely pick one up w/ an adapter just so I can gain some experience and add a Takumar family lens or two to my lens portfolio. They seem to be built like tanks, have quality glass and still relatively affordable. If they are anything like my Helios 44K-4, I'll really take a liking to them.

An additional note: I do believe that the "green button" IS metering and setting shutter speed with NO lens attached (as long as ISO and Camera are set to MANUAL). I removed the lens and pointed to a bright area of a room -- and pressed the "green button" -- the shutter speed changed and held. I then pointed to a dark section of the room and pressed the "green button" and the shutter speed changed to a slower speed and held. Pointing to the brighter section and pressing again, resulted in shutter speed changing to a faster speed and holding. It seems the K500 "green button" does work with a T2 adapter and lens to set the shutter speed via "green button". While this seems to work, I do prefer using the Av program setting with ISO set at automatic, as it does take a lot of the guess work out of finding the best settings. It gets me in the ball-park and I adjust ISO or Shutter speed from there by going to MANUAL program mode.

Again -- thanks!!

Last edited by ripper2860; 06-08-2014 at 03:34 PM.
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