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01-30-2018, 01:55 PM   #1
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K-50 - apreture failures?

Hi, half-crying, half-devastated.. but hello once again after a 1 or 2 days.

I have K-50 from 2,5 year, so I'm out of warranty (which last in Eu for 2 years - yay!). I often use old manual Tokina for macro shots (with pentax mount) and switch to KIT 55-18 1.35/5.6.

Lets start with the beginning:
A week or so ago I was doing a session of my painted figurines. I shot first with rather high settings, something like 1/90, f8 iso 100 or so in a very dim light. It was not too bright, so I changed the settings to lower ones. It shocked me a bit that the shots were almost dark, I tried a few times more with the same results, checked my hand-made diffusor, and after a few another tries and adjustings of the difusor the shots started to be lighten correctly. I thought it was diffusor's fault.


Today I treid to do some shots of a citation in a book (I know, rather unusuall use for the camera). I started once again with rather high settings in almost completely dark room - the text was there but rather dim (I deleted the shot, and I don't
remember the details). I then tried to go lower - 1/30, f5.6, ISO 800 - the shot was... darker than one before. I recalled the situation from before a week described above here... So I tried to go even lower, with ISO ~52.000, lowest apreture and ~1/10. Shot was even darker. I adjusted diffusor again hoping it is something with it once again, but this time trying to adjust it didn't help.

So I then tried to go up with the settings. 1/50, f14 and iso 800 - shot was brighter, 1/50 ISO 800 f32 - was what it should be - white background with nice dark letters on it. What the hell?

So did some tests without any diffusor - only built-in lamp; I pointed the camera on a dim lamp:
1/180, ISO 800, f5 - dark, only bulb was a brighter dot
1/180, ISO 800, f32 - bright!

So I did a test without a lamp:
1/10, ISO 800, f5.6 - dark with only a bulb visible
1/10, ISO 800, f40 - completely THE SAME result as above

I was terrified by then. I thought that either software or aprreture in my lens is faulty.

I'm not sure which was next, 1 or 3:
1) I probably unmounted the lens, checked the .."lever" of the apreture if it can be levered up manually and down automatically- and it looked OK
2) I then did a test once again and get the same bad results
3) checked how the world looks like when I lever the mirror (Raw/fx button in my case) and still looking on a lamp went up from f5.6 to f40 - everything looked completely the same (dark)
4) checked the same thing going down from f40 to f5.6... IT STARTED WORKING! Both ways.

I've checked the manual but they do not list any similar problem...
I've searched google, and found a mention about apreture block but nothing about apreture settings working "upsidedown".
I'm out of ideas what the hell happens to my camera. Any thoughts? Any help? :<

01-30-2018, 02:18 PM - 1 Like   #2
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Sounds like aperture block failure. Common problem. Plenty of threads on the K30 & K50 forum. You can start here:

Dark exposure problems on K-30 or K-50? Read me first! - PentaxForums.com

I have been using my K-30 with old manual lenses for over a year now. Didn't want to put money or effort into fixing it.
01-30-2018, 02:50 PM   #3
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No. No.. that cannot be.. :x

And to be more serious, mentioned article does not cover situations where the apreture works "upside-down". Maybe, the issues have similar output, but are two different things. If anyone other have some thoughts/had the same issue, I'm here to listen...
01-30-2018, 04:10 PM   #4
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Sounds like classic early stages of aperture block failure. At first the aperture is unreliable, then it stops opening altogether.

01-30-2018, 04:20 PM - 1 Like   #5
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For near free, you can file down a part. Or use AA batteries. Or even better, buy a 30 ohm solenoid and replace the one that's in there. Or get it professionally repaired.

You do have options, Geb, this forum contains all the info you need to know.
02-04-2018, 12:43 PM   #6
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As for now, I send the e-mail to polish authorised service. Twice. No response from them since I wrote first post in this thread :3
02-05-2018, 07:25 PM   #7
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QuoteOriginally posted by iheiramo Quote
Sounds like aperture block failure. Common problem. Plenty of threads on the K30 & K50 forum. You can start here:

Dark exposure problems on K-30 or K-50? Read me first! - PentaxForums.com

I have been using my K-30 with old manual lenses for over a year now. Didn't want to put money or effort into fixing it.
Are you using M42 lenses, or manual K mount lenses?


I have both sitting in my "if K-30 fails" collection, and I'm wondering which I should actually lug around with me?
02-05-2018, 11:07 PM   #8
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QuoteOriginally posted by reh321 Quote
Are you using M42 lenses, or manual K mount lenses?


I have both sitting in my "if K-30 fails" collection, and I'm wondering which I should actually lug around with me?
K mount. I've started collecting M series primes and have experience only with them, but as long as lens have an aperture ring it should work.

04-13-2018, 06:46 PM   #9
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Get a AA battery adapter, use lithium batteries and never look back! True story.
04-21-2018, 01:57 PM   #10
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My K-50 just started to act up while on a vacation a week ago. First photo after being turned off for a while was very underexposed, most others after that were OK. I use NiMH AAs for power. I tried the aperture exercise method using the RAW/FX button and that seemed to help, got through my vacation with minimal issues, but dreading that it would soon fail completely. I did not have any manual aperture lenses with me, so I would have been out of luck. The camera had about 8000 exposures when the problem started. Camera manufactured May 2014. A failure this early is wholly unacceptable.

I just ordered a used K-5 IIs to use as a prime, will think about replacing the solenoid in the K-50 with a white once after I am comfortable with the "new" body. I have K mount lenses that I like for general walk-about, particularly happy with the Pentax 18-300 zoom as a vacation lens, especially for gardens where I vary from taking vista photos to looking into details of tiny flowers. Hope the K-5 holds up better or I will have to replace the whole system. I was spoiled by years of using Olympus OM-1s where I never had a failure. Even my Praktica Super TL never had a failure, despite being made in East Germany and having a terrible reputation.
04-21-2018, 02:20 PM   #11
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QuoteOriginally posted by Spacedave Quote
My K-50 just started to act up while on a vacation a week ago. First photo after being turned off for a while was very underexposed, most others after that were OK. I use NiMH AAs for power. I tried the aperture exercise method using the RAW/FX button and that seemed to help, got through my vacation with minimal issues, but dreading that it would soon fail completely. I did not have any manual aperture lenses with me, so I would have been out of luck. The camera had about 8000 exposures when the problem started. Camera manufactured May 2014. A failure this early is wholly unacceptable.

I just ordered a used K-5 IIs to use as a prime, will think about replacing the solenoid in the K-50 with a white once after I am comfortable with the "new" body. I have K mount lenses that I like for general walk-about, particularly happy with the Pentax 18-300 zoom as a vacation lens, especially for gardens where I vary from taking vista photos to looking into details of tiny flowers. Hope the K-5 holds up better or I will have to replace the whole system. I was spoiled by years of using Olympus OM-1s where I never had a failure. Even my Praktica Super TL never had a failure, despite being made in East Germany and having a terrible reputation.
I believe, but do not know, that the design of this mechanism is over thirty years old - it looks like the sort of thing Asahi would have put into bodies when they first enabled bodies to control the aperture. My Super Program was one of the first of those bodies. I used it for eleven years, then used it as seldom-needed backup for eleven years. I still use it on occasion, over thirty years after I purchased the camera, and the aperture control mechanism still works fine. If you were spoiled by Olympus, I was spoiled by Pentax.

I used Canon for a number of years, but came back to Pentax when I had two Rebels in a row experience processor failure {total shutter count of the two around 5K} If you experienced regrettable performance from Pentax, I experienced regrettable performance from Canon.

I believe, but do not know, that they switched suppliers, and the new supplier used a material that has some characteristic that no one ever thought of testing, but that caused issues over time, and they have now switched away from that supplier. As far as I know, no one has ever reported similar issues with the K-7, K-5, K-3 series. I believe, but do not know, that these series, and the K-1, and the KP, use a completely different design {stepper motors come to mind}.
04-21-2018, 11:59 PM   #12
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QuoteOriginally posted by Spacedave Quote
My K-50 just started to act up while on a vacation a week ago. First photo after being turned off for a while was very underexposed, most others after that were OK. I use NiMH AAs for power. I tried the aperture exercise method using the RAW/FX button and that seemed to help, got through my vacation with minimal issues, but dreading that it would soon fail completely. I did not have any manual aperture lenses with me, so I would have been out of luck. The camera had about 8000 exposures when the problem started. Camera manufactured May 2014. A failure this early is wholly unacceptable.
It is not about being acceptable or not... you have to accept it: It is the solenoid which as usual failed. So change it against the only true solution,
i.e. the white solenoid.

---------- Post added 04-22-18 at 12:04 AM ----------

QuoteOriginally posted by geb88 Quote
No. No.. that cannot be.. :x

And to be more serious, mentioned article does not cover situations where the apreture works "upside-down". Maybe, the issues have similar output, but are two different things. If anyone other have some thoughts/had the same issue, I'm here to listen...

You need to study the "mentioned articles" a bit better because your symptoms are for sure the faulty green solenoid!
Nothing is upside down, that your camera works with aperature values very high IS TYPICAL! There is nothing upside down.

---------- Post added 04-22-18 at 12:09 AM ----------

QuoteOriginally posted by reh321 Quote
I believe, but do not know, that they switched suppliers, and the new supplier used a material that has some characteristic that no one ever thought of testing, but that caused issues over time,
Or the manufacturer switched from having them made in Japan to production in China.
Because thats how it was.

QuoteOriginally posted by reh321 Quote
... and they have now switched away from that supplier.
How do you know this?


QuoteOriginally posted by reh321 Quote
As far as I know, no one has ever reported similar issues with the K-7, K-5, K-3 series. I believe, but do not know, that these series, and the K-1, and the KP, use a completely different design {stepper motors come to mind}.
There have been no reported issues with the K20D, K7, K5 and K3 because there cannot be an issue.
Because the do use this complety different design.

There have never been any reported issues of ANY Pentax prior the K30!
04-22-2018, 04:20 AM   #13
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We basically agree

QuoteOriginally posted by photogem Quote
Or the manufacturer switched from having them made in Japan to production in China.
I'm just not willing to assume particular nation of origin

QuoteOriginally posted by photogem Quote
How do you know this?
Slightly different color suggests slightly different materials, most likely from changing suppliers, although same supplier could have made changes to keep costs down

QuoteOriginally posted by photogem Quote
There have been no reported issues with the K20D, K7, K5 and K3 because there cannot be an issue. Because the do use this complety different design.
I'm insufficiently familiar with older models to guess which would use the ancient design, but we agree on the models of concern to the OP.

QuoteOriginally posted by photogem Quote
There have never been any reported issues of ANY Pentax prior the K30!
Not here at least
04-22-2018, 04:22 AM   #14
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I suppose @photogem probably could be less aggressive, at least I take it that way :/ But thanks for the information anyway.

What I mean by "upside down effect" is what was not mentioned anywhere (also regarding "appreture block" issue). My camera takes dark pictures on low appreture (like 4.5f) and takes bright pictures in the same time on higher papretures (like 40f) and then -after several shots - it turns back to normal eventually. It looks more like a software issue to me, but since I didn't found similar issues in the internet I started the thread here.

Peace and love.
04-22-2018, 06:20 AM   #15
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I have followed a few of these threads about the aperture block problem, and at various points there has been mention of replacing a faulty green solenoid with a white one from an old camera. Different models of old camera have been mentioned, but I seem to recall that in some cases it has been said that the magnetic force created has been stronger.

Is there anywhere on the forum, a list of suitable cameras from which a donor solenoid can be extracted - be it from the aperture block assembly or the pop up flash? If not, then perhaps one of those who have taken an active part in such repairs may be in a position to create a list. Just a thought, I'm sure it would be of interest.
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