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Forum: Pentax SLR Lens Discussion 5 Days Ago  
Pentax 300mm primes
Posted By Cee Cee
Replies: 27
Views: 1,515
the closer min focus distance of the DA*300 is an advantage for small birds etc, really annoying to have a bird in your sights then having to back up to get the shot focused
Forum: Post Your Photos! 07-19-2020, 06:39 PM  
Nature Bee at Work
Posted By Cee Cee
Replies: 7
Views: 277
awesome shot, cheers
Forum: Pentax SLR Lens Discussion 07-17-2020, 06:48 PM  
Pentax lens names in Flickr
Posted By Cee Cee
Replies: 14
Views: 880
In win 10, If you right click a jpeg file, and select properties / details it displays the exif data this can be edited directly in windows without the need for other software. what's more if you select a batch of photos and right click then select properties / details, the exif data that is common to all files selected is displayed and can be edited, and is applied across the whole group, this is great for adding name & copywrite info. or any other info common to the selected group.
Forum: General Photography 07-13-2020, 08:08 PM  
A visual guide to bird photography
Posted By Cee Cee
Replies: 16
Views: 1,135
I have all of those shots, except "why" I'll have to try harder. :lol:
Forum: Monthly Photo Contests 06-01-2020, 05:34 PM  
Cherry blossom
Posted By Cee Cee
Replies: 9
Views: 84
beautiful colours & light
Forum: Monthly Photo Contests 05-13-2020, 08:29 PM  
Rose in the rain
Posted By Cee Cee
Replies: 15
Views: 204
IMGP3993as by Colin Chester, on Flickr
Forum: Post Your Photos! 04-30-2020, 11:10 PM  
Landscape Lake Superior at Alona Bay
Posted By Cee Cee
Replies: 6
Views: 223
nice shooting, the silouette of the trees makes for a nice image, cheers
Forum: Post Your Photos! 04-30-2020, 10:51 PM  
Nature Awesomely Beautiful, Amazingly Blue & White Columbine. :)
Posted By Cee Cee
Replies: 14
Views: 290
amazing shot, what a striking image, well done
cheers
Forum: Post Your Photos! 04-30-2020, 10:48 PM  
Nature Go away
Posted By Cee Cee
Replies: 8
Views: 239
I blame my cat for being irresponsible, :D I do the best I can but he has the final say. nice capture BTW.
cheers
Forum: Post Your Photos! 04-30-2020, 10:44 PM  
Nature Coming into
Posted By Cee Cee
Replies: 2
Views: 128
very nice Em, delicate & well captured
cheers
Forum: Post Your Photos! 04-30-2020, 10:41 PM  
Nature Friendly Deer
Posted By Cee Cee
Replies: 12
Views: 197
Nice one, its good when animals co-operate. As I say about birding, the more you go out the more luck you have, or perhaps you could call that experience.

cheers
Forum: Pentax K-70 04-28-2020, 06:17 AM  
Strange behaviour from my K-70...aperture block?
Posted By Cee Cee
Replies: 49
Views: 5,889
it will be interesting to see how you get on, good luck. If it took 5 years for the build up of magnetism to cause the camera to malfunction (in my case) then by reversing the plunger it could take a further 5 years to build up to that point again - by my simple logic. But this is, of course if residual magnetism of the plunger is indeed the only problem.
Forum: Pentax K-30 & K-50 04-27-2020, 08:53 PM  
Sticky: Dark exposure problems on K-30 or K-50? Discussion Thread
Posted By Cee Cee
Replies: 364
Views: 67,540
so which part of what I said is nonsense,

I won't insult you by giving a lesson in magnetic theory 101. But with the plunger in it's original orientation any residual magnetism can only add to the attraction and reversing poles can only reduce the attraction, you must know that to be true.

The only holding force that's relevant here is the holding force when the shutter is activated and there should be zero holding force as the electromagnetic field generated by current through the coil should perfectly cancel the fixed magnetic field of the solenoid, under these conditions I'm saying that I can detect a clear difference in the required extraction force depending on the orientation of the plunger.
Forum: Pentax K-30 & K-50 04-26-2020, 10:43 PM  
Sticky: Dark exposure problems on K-30 or K-50? Discussion Thread
Posted By Cee Cee
Replies: 364
Views: 67,540
I gather from reading these threads that some solenoids have other quality issues as you say. But I asked similar questions when mine failed, I had just on 5 years and well over 10K activations when it failed. Luckily I had taken a 5 year extended warranty when I purchased, and had it replaced under that warranty. They returned the faulty solenoid to me and I've got to say it looked pristine, and well made, no quality control issues or poor fitting that I could see. And testing it it seemed to work fine with no binding, sloppiness or other issues. Using a spring tension gauge and pulsing the coil with a suitable current to release the plunger I've been able to see a clear difference in the release force required to remove the plunger depending on the magnetic polarity (or the orientation) of the plunger.
Forum: Pentax K-70 04-26-2020, 07:12 PM  
Strange behaviour from my K-70...aperture block?
Posted By Cee Cee
Replies: 49
Views: 5,889
well with CV19 being what it is I have some time on my hands to consider these issues and expel any unwanted gases !

come on, don't you want to fully understand the science here, after all this could possibly lead to novel solutions which don't involve having to track down an old camera from which to remove the solenoid and then replacing the solenoid in their own camera, which involves de-soldering & soldering the coil by people with no soldering skills, which in my experience doesn't always end well.
Do you find it interesting that the "filing the edges of the plunger technique" (to reduce the contact area) has had varied and inconsistent results, perhaps the inconsistency is more to do with which polarity they refitted the plunger! rather than the filing technique.
I must admit the finer points of magnetic theory are perhaps above my pay grade, But reversing the poles on the horse shoe plunger should counteract any residual magnetism, and perhaps provide a simple solution, if not then residual mag (as the primary issue) could be eliminated from the discussion and other theories explored.
Forum: Pentax K-30 & K-50 04-26-2020, 06:28 PM  
Sticky: Dark exposure problems on K-30 or K-50? Discussion Thread
Posted By Cee Cee
Replies: 364
Views: 67,540
let me ask, is it possible you reversed the magnetic polarity the plunger ( flipped it 180` ) when you reinserted it, this would counteract any residual magnetism in the plunger, if indeed the issue is caused by a build up of residual magnetism in the the horse shoe plunger.

I wonder if someone else with a non working camera could try this, just mark to top surface of the plunger with a marker pen, remove the plunger and refit it with the marked side down, this will reverse the magnetic poles and should counteract any residual magnetism in the plunger.
Forum: Pentax K-70 04-22-2020, 06:17 PM  
Strange behaviour from my K-70...aperture block?
Posted By Cee Cee
Replies: 49
Views: 5,889
generally when working with electronics fault finding & diagnoses, if you have no schematics or specifications then it can be of some advantage to have a fully functional unit to do comparisons & checks. Comparing voltage, current or resistance readings can help identify differences between working and non working units and steer you in the right direction quicker than would otherwise be the case. In the case of the K30 aperture problem when the camera is in this transitional stage and can be made to work by a burst of aperture activation then we have the chance to observe, test or measure in both working and non working states. For example if the problem is due and only due to residual magnetisation build up of the plunger then we should be able to detect the the change in magnetism for both working and non-working states.

Further to this, leaving aside test & measurement, just some clear thinking about what could possibly be happening when the camera can be made to function again by multiple shutter activation could steer us in the right direction. If it's just a matter of fixing the camera then there no issue, the solenoid is faulty, so replace the solenoid and the jobs done. But what is the reason the original solenoid can be made to work with shutter activations ? does the the electromagnetic field generated when the solenoid is activated have a degaussing effect on the plunger.

But pondering the question of why the solenoid was good for 5 years & thousands of activations and now it's no good raises interesting questions. Indeed if the problem is solely due to a build up of residual magnetism then perhaps fully degaussing the plunger may be an effective method to repair the camera, I know the problem will eventually re occur but if it takes another 5 years and thousands of activations then that may be good enough for some folk.
But there may be a simpler solution, I've done some bench testing of the solenoid using a spring gauge to measure the force required to extract the plunger when the coil is activated by a pulse of current. Then reversing the magnetic polarity of the plunger by flipping it over, figuring that the reverse polarity would counteract any residual magnetism the plunger and I detected a clear difference in the required force of 50gf. vs 20gf.
So as previously stated if the problem is entirely due to residual mag. of the plunger then reversing the mag polarity should fix the issue. If not then there is clearly more to this problem.

---------- Post added 04-23-20 at 12:01 PM ----------



See my comments above, maybe this could work providing the plunger is the only issue , perhaps try flipping the plunger (180`) before going to the trouble making a replacement.
Forum: Pentax K-70 04-18-2020, 06:51 PM  
Strange behaviour from my K-70...aperture block?
Posted By Cee Cee
Replies: 49
Views: 5,889
"Magnetic Solenoid" is not my term. It is the name a manufacturer of these types of solenoid uses. I'm not sure about the word push, nothing is pushed here. The plunger is held in position by the fixed magnet, the electrical coil when activated counteracts the fixed magnetic force and allows the plunger to be removed by some other mechanical force. Activating the coil doesn't eject the plunger.
Forum: Pentax K-70 04-18-2020, 04:18 PM  
Strange behaviour from my K-70...aperture block?
Posted By Cee Cee
Replies: 49
Views: 5,889
I agree "armature" is the wrong term here, although I've generally considered the "armarture to be the moving part of a motor assembly,( as in a simple DC motor ) but this is incorrect. By definition the armature is the part of a electrical machine that carries ac current (the armature windings) (Wikipedia) So in fact there is no "armature" at all in this device. "Plunger" is a good term to describe the removable part of the solenoid, perhaps the other part with the coil & magnet is best referred to as the solenoid "Body".

---------- Post added 04-19-20 at 09:23 AM ----------



once again agreed, but studying or considering what happens in this transitional phase when the camera is sometimes working and sometimes not working gives important clues to understanding the nature of the failure.

---------- Post added 04-19-20 at 09:50 AM ----------



I didn't word particularly well and clearly I got this wrong, but regardless my main point here was that the magnetic structure changed or the relationship between the magnetic circuit and the electrical circuit changed.
Forum: Pentax K-70 04-14-2020, 05:55 PM  
Strange behaviour from my K-70...aperture block?
Posted By Cee Cee
Replies: 49
Views: 5,889
Just my take on what's happening here..

The coil assembly has a fixed magnet which keeps the armature engaged, energizing the coil creates an opposing magnetic force which allows the armature to be withdrawn. Over time the armature retains some residual magnetism, it reaches a tipping point where the magnetic field produced by the coil is no longer strong enough to overcome the the combined force of the fixed magnet and the magnetized armature and allow the armature to be released. The action of activating the coil produces a reverse magnetic field to cancel the fixed field, this also has a demagnetizing effect on the armature, so firing shots in quick succession demagnetizes the armature and puts it the other side of the tipping point and the camera starts working normally again. Left alone, the armature will again be re magnetized and will fail again.
The issue I believe is that the manufacturer of the magnetic solenoid changed the magnetic structure and upset the balance
Filing the armature can work because it reduces the coupling to the fixed magnet and slows the build up of residual magnetism.
I'm not sure that degaussing the armature will work long term, at best it could only return to it's natural state which will make the camera work but the problem will eventually re occur, as the core issue of the magnetic structure of the coil assembly hasn't been addressed. If you wish to experiment then try the other solutions and see, but if you just want to fix the camera then I think changing the coil would be the best solution.
Forum: Post Your Photos! 02-26-2020, 03:04 PM  
Nature Mango or Tango (I'm not sure which Toucan was which.)
Posted By Cee Cee
Replies: 3
Views: 263
what an interesting creature, nice capture, cheers
Forum: Post Your Photos! 02-26-2020, 02:59 PM  
Nature Big cluster
Posted By Cee Cee
Replies: 2
Views: 195
beautiful, I like the way you've cropped it, .... my little Frangipani currently has some blooms, the first for several years, they are a joy to photograph:).
Forum: Post Your Photos! 02-26-2020, 02:53 PM  
Nature And the rains
Posted By Cee Cee
Replies: 2
Views: 187
nice one EM, white can be tricky, cheers
Forum: General Photography 02-23-2020, 04:51 PM  
Not all of us are rich
Posted By Cee Cee
Replies: 89
Views: 3,805
I have a K30, Sigma 17-70 F2.8-4.5, DA55-300, Tamron 90m f2.8 in my bag (and a very tight budget), I never feel it's the gear that limits my photography, its always me, creativity, skill & commitment. Same goes for a whole lot of manual lens I've accumulated over the years.
Forum: Post Your Photos! 02-19-2020, 03:28 PM  
Nature Putting My Best Foot Forward
Posted By Cee Cee
Replies: 4
Views: 227
perhaps he's wants to tie your laces together
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