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12-20-2020, 06:24 AM   #1
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Aperture issue with full manual lens

Hi, I have a SMC Pentax 135mm f/2.5 lens, this is the exact lens at link:
SMC Pentax 135mm F2.5 Reviews - K Prime Lenses - Pentax Lens Reviews & Lens Database

I'm trying to use it on the K1 and when I mount the lens the lever on the back locks the aperture wide open and there is no way to stop the lens down. I've tried about everything I can think of and either I am missing some camera setting or the lever needs to be removed.

Do I need to cut the lever that sticks out the back of the lens off? or is there a work around? I'm stumped.

Any help would be appreciated as this lens is pretty sharp wide open and I'd love to see what it can do stopped down some.

Thanks

12-20-2020, 07:13 AM   #2
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Don't cut off the aperture lever!!!

Does the aperture open and close when you move the aperture lever when not mounted on the camera and what position does the aperture ring have when you do that?

Assuming that the aperture works correctly off camera (if the aperture ring is set to 2.5 the lens can't stop down, change the setting to something else), you probably have some settings wrong.
With a K or M lens you have to activate 'aperture ring usage' (my camera is not set to english so the name might be some variation of this) -> it's usually the last setting available in your camera menu.
The camera will only stop down when using M or bulb mode (for Av the camera will use the lens wide open). Green button metering is your best way to meter your shot.

Last edited by othar; 12-20-2020 at 07:24 AM.
12-20-2020, 07:20 AM   #3
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QuoteOriginally posted by othar Quote
Don't cut off the aperture lever!!!

Does the aperture open and close when you move the aperture lever when not mounted on the camera and what position does the aperture ring have when you do that?
The aperture opens and closes fine when I spin the ring if the lens is off the camera. I have the cameras Aperture ring setting #26 set to enable as I've spent the last 4 years using the K1 with manual lenses (M42 Mount). This 135 is the only K mount manual lens I own with the lever that sticks out the back of the lens. (it doesn't have the A or M option on the lens itself)
12-20-2020, 07:26 AM - 1 Like   #4
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QuoteOriginally posted by Durf Quote
This 135 is the only K mount manual lens I own with the lever that sticks out the back of the lens. (it doesn't have the A or M option on the lens itself)
The lens will only stops down when in M or bulb mode.

12-20-2020, 07:28 AM   #5
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QuoteOriginally posted by Durf Quote
The aperture opens and closes fine when I spin the ring if the lens is off the camera.
Does it also open when moving the aperture lever and not the aperture ring?
12-20-2020, 07:34 AM   #6
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QuoteOriginally posted by othar Quote
The lens will only stops down when in M or bulb mode.
Ok, when in M Mode, if I set the aperture ring to say, F8, and look down in to the lens when I snap a pic I see the blades stopping down (closing) when pressing the shutter button. I didn't know the lens/camera operated this way with manual lenses with the lever.....Obviously I have to shoot this lens in M mode!
Thanks for your help!
12-20-2020, 07:36 AM - 1 Like   #7
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When the lens is off camera the aperture on that lens should freely open and close as you turn the ring. When placed onto the camera it will be wide open and you have to use a special method to meter and use it. Watch this and let us know if it helps:



12-20-2020, 07:40 AM   #8
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QuoteOriginally posted by Durf Quote
Ok, when in M Mode, if I set the aperture ring to say, F8, and look down in to the lens when I snap a pic I see the blades stopping down (closing) when pressing the shutter button. I didn't know the lens/camera operated this way with manual lenses with the lever.....Obviously I have to shoot this lens in M mode!Thanks for your help!
You're welcome. The problem for the other shooting modes is, that the camera mount of all DSLRs is a crippled mount (the camera has no idea where the aperture ring is set to when not on the A position) therefore those shooting modes won't work and default to wide open shooting of the lens.
12-20-2020, 07:51 AM   #9
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QuoteOriginally posted by othar Quote
You're welcome. The problem for the other shooting modes is, that the camera mount of all DSLRs is a crippled mount (the camera has no idea where the aperture ring is set to when not on the A position) therefore those shooting modes won't work and default to wide open shooting of the lens.
I'm just having trouble now being able to set the exposure as there isn't a metering scale in the viewfinder like most other cameras have when in manual. Basically having to guess and adjust....

---------- Post added 12-20-20 at 07:53 AM ----------

It would probably be much simpler cutting the lever off and just shooting this lens in AV mode to where the camera would meter and adjust the shutter speed like it does with all my M42 lenses! LOL
12-20-2020, 07:56 AM   #10
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QuoteOriginally posted by Durf Quote
I'm just having trouble now being able to set the exposure as there isn't a metering scale in the viewfinder like most other cameras have when in manual. Basically having to guess and adjust....
Green button metering is the way to go.
Set your lens to the desired aperture and push the green button -> the lens will stop down and meter for you (setting the shutter speed accordingly).
If the metering is off, make sure you didn't dial in the wrong exposure compensation, because that will influence the metering
12-20-2020, 08:00 AM   #11
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QuoteOriginally posted by othar Quote
Green button metering is the way to go.
Set your lens to the desired aperture and push the green button -> the lens will stop down and meter for you (setting the shutter speed accordingly).
If the metering is off, make sure you didn't dial in the wrong exposure compensation, because that will influence the metering
I got the green button to meter for me! I really appreciate your help, I was about to give up with this lens.
I just used the green button and shot a few shots with this lens at f8 and it is really sharp. Not bad at all for a 40 year old lens!
12-20-2020, 08:02 AM - 2 Likes   #12
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the " articles " section of the forums can be quite helpful:

QuoteQuote:
Pentax Green Button Guide
A look at one of Pentax's secrets
By johnhilvert in Articles and Tips on Aug 15, 2016

Read more at: Pentax Green Button Guide - Articles and Tips | PentaxForums.com

QuoteQuote:
How to Use Manual Lenses on Pentax DSLRs
Virtually all K-mount and M42 lenses are compatible!
By PF Staff in Tutorial Videos on Apr 29, 2013
Read more at: How to Use Manual Lenses on Pentax DSLRs - Tutorial Videos | PentaxForums.com

and this thread might help as well

QuoteQuote:
How to use/meter Manual & M42 Lenses on all Pentax DSLRs (K-1, K-3, K-5, K-30, etc)Report Post
Posted By: Adam, 08-12-10, 05:24 (Offline)
Many Pentax DSLR owners want to use M42 screwmount (Takumar) lenses, or M or K manual lenses, on their cameras because of the low cost and relatively high image quality of these lenses.
Read more at: How to use/meter Manual & M42 Lenses on all Pentax DSLRs (K-1, K-3, K-5, K-30, etc) - Page 23 - PentaxForums.com
12-20-2020, 08:05 AM - 2 Likes   #13
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QuoteOriginally posted by Durf Quote
It would probably be much simpler cutting the lever off and just shooting this lens in AV mode to where the camera would meter and adjust the shutter speed like it does with all my M42 lenses! LOL
For metering maybe, but not for focusing. You would have to open up and stop down the lens repeatedly to get a good focus.
The way it is now might be more tricky to get a correct exposure at first but after you have that dialed in you can shoot away without meddling with the aperture ring.
12-20-2020, 08:14 AM - 1 Like   #14
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I can't add to the excellent guides posted above. But I'll just say that your lens is known as a "auto aperture" lens. The main benefit compared to real fully manual, where the aperture doesn't move when taking the photo, is that you can focus wide open for accuracy and a brighter viewfinder. After a few days you get used to "green button metering". It's not as quick as using newer lenses but I don't find it too cumbersome. It reminds me of the Zenit camera I used a while ago, metering required stopping down the aperture by half pressing the shutter.

Another option is to adapt it to a mirrorless camera, then you can set and maintain the lens at a given aperture.
12-20-2020, 08:23 AM   #15
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QuoteOriginally posted by aaacb Quote
I can't add to the excellent guides posted above. But I'll just say that your lens is known as a "auto aperture" lens. The main benefit compared to real fully manual, where the aperture doesn't move when taking the photo, is that you can focus wide open for accuracy and a brighter viewfinder. After a few days you get used to "green button metering". It's not as quick as using newer lenses but I don't find it too cumbersome. It reminds me of the Zenit camera I used a while ago, metering required stopping down the aperture by half pressing the shutter.

Another option is to adapt it to a mirrorless camera, then you can set and maintain the lens at a given aperture.
I'll quickly adapt and get used to the green button metering with this lens. I was surely scratching my head though trying to figure out how to use it! LOL (I thought I knew everything! haha)
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