Author Topic: Seek Thermal Lens Repair  (Read 4807 times)

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Offline jjachim

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Seek Thermal Lens Repair
« on: July 06, 2017, 11:47:33 am »
First time post, so please be gentle.

I dropped my Seek Thermal XR and the lens does not focus anymore.  I have pried the case apart and verified that the image unit is fine, but I am not sure how to take the focusing lens apart to see what is wrong with it.  Any suggestions?
 

Offline Bill W

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Re: Seek Thermal Lens Repair
« Reply #1 on: July 10, 2017, 07:36:18 am »
I don't think there is much to 'take apart' as such, it is a single element lens in a holder on a thread.

What is most likely is that the sensor has moved with respect to the lens and you can no longer get the correct separation to focus anywhere sensible.

Does it focus at any distance ?
A larger lens - sensor separation should make it focus close (like VERY close).  You can use the school lens formula to get a feel for what is going on:
1/f = 1/u + 1/v

Bill

Offline IwuzBornanerd

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Re: Seek Thermal Lens Repair
« Reply #2 on: September 29, 2017, 06:30:05 am »
I recently dismantled the lens assembly on my old Seek XR so I can add some pictorial detail to Bill W's description.

The first image is a view of the inside of the lid of my old XR Seek unit.  I labelled the end of the thing I call a blocking pin.  I call it that because it serves 2 purposes--it prevents you from turning the lens more than 1 turn and it prevents you from unscrewing the bayonet lens mount to remove it from the lid of the camera.  I had been wondering if it had anything to do with either of those things since I was trying to remove the lens from my old Seek XR in order to put a 4" focal length ZnSe lens on it.  I hate to force things but I finally pinched the bifurcated tip of that pin together & pushed it all the way into the lens assembly.  After that I could turn the lens several turns & when I forced it beyond its full CCW travel it unscrewed from its bayonet mount!  Until that time I had not realized that there was a bayonet mount.  A more astute observer might have reasoned that from those curved slots in the cameras lid, but I missed it.

The second image shows the lens assembly parts separated.  I gave the parts my own names, having no knowledge of what the official names might be.  The lens is held in the threaded holder by 2 prongs, one of which you can see in the photo, but the lens did not simply drop out when I pulled the prongs away, so I did not bother pushing it out just for the sake of showing it apart.  The outer shell has 3 pairs of fins that mesh with indentations in the lens mount in order to turn it.  One of those fins is taller than the others and is what hits the blocking pin to limit the focus range.  The outer shell also has 3 tabs which protrude inward just enough to clip the shell to the bayonet ring.  The bayonet ring is metal on the old XR but is plastic on the newer non-XR unit I bought in January.

With that blocking pin removed, the camera can be focused as close as 2 inches.  So if you don't need any closer focus than that, you don't need an additional "bifocal" lens.

The non-XR lens assembly is similar except that the outer shell is less than half the height of the XR shell and there are posts instead of fins to turn the lens.  The third & fourth images show the non-XR lens with the outer shell off.  I trimmed off the top of the blocking pin on that camera & was able to focus it down to about 1 inch.

The outer shell came off the non-XR rather easily just by pushing tweezers under it and prying it off the bayonet ring, but I have not had that luck with the XR lens.  I have to pull the tabs away from the bayonet ring one at a time & push the shell off the ring partway at each tab--AFTER removing it from the camera's lid.  I suspect that the proper way to remove the lens is to pry that shell off first, then remove the blocking pin, and then unscrew the bayonet.  I expect Seek has a couple special tools for that purpose but I am stuck with tweezers & pliers.  The method I described above that I initially used to remove the XR lens is likely not "kosher", as there is a risk of breaking those fins.  In fact, after a couple times of using that technique it did not unscrew the bayonet but the fins started ratcheting on the lens mount as the lens jammed against the top of the shell & started forcing the shell off of the bayonet ring.  Maybe that's still the way to go then, since getting the shell off is what I suspect is the proper first step.  :)

The thread diameter & pitch of this lens mount are the same as that of the lenses on the cheap web cams & "security" cameras I have.  This should facilitate making a lens mount for a telephoto thermal lens.
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Online Fraser

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Re: Seek Thermal Lens Repair
« Reply #3 on: September 29, 2017, 11:00:24 pm »
Nice teardown  :-+

I have worked on webcam type cameras that have been dropped on their lenses and the rotating lens thread had jump down a thread. That in combination with an end stop limit makes the camera backfocus distance incorrect. With thermal cameras the lens normal focus movement distance is usually quite small. If the OP's lens has jumped a thread, it will lose its ability to correctly focus an image onto the sensor.

Fraser
 

Offline LesioQ

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Re: Seek Thermal Lens Repair
« Reply #4 on: October 03, 2017, 09:02:15 pm »
How would You estimate focal length of SEEK factory optic ? (either Compact or XR).
Less than 8mm ?
 

Offline IwuzBornanerd

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Re: Seek Thermal Lens Repair
« Reply #5 on: October 04, 2017, 08:23:54 am »
In the absence of any stated number from Seek, the focal length is the distance at which images of objects at infinity are focused on the sensor, so with the lens set to where "distant" objects are in focus in the image I made some semi-crude measurements with a metal rule, trying not to scratch either the lens or the sensor.

The distance from the edge of the bottom surface of the lens to the bottom of the bayonet ring is 0.13", the distance from there to the top of the pc board is 0.35", and the distance from the top of the pc board to the top of the sensor module is 0.05".  Adding the first 2 and subtracting the 3rd number gets me 0.43" or 10.9mm, so I'll guess that the XR lens is 11mm.  Without repeating the measurements on the non-XR, but going by the stated field of view numbers, the non-XR would be 6mm.  They are rather thick lenses, though, and the top surface appears curved also so I'm not sure where the distance should be measured from for the official focal length.
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Offline LesioQ

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Re: Seek Thermal Lens Repair
« Reply #6 on: October 04, 2017, 11:20:14 pm »
Oh, thanks! So given the lens diameter of c.a. 5mm that would imply it's brightness to around 2.
Guess that's a field for some improvement.
 

Online Fraser

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Re: Seek Thermal Lens Repair
« Reply #7 on: October 04, 2017, 11:29:18 pm »
The lenses on these types of budget camera are likely a compromise solution that fits within the budget. Adding a suitable higher quality lens will likely bring decent improvement in performance. The problem is in finding suitable replacements. Sadly thermal camera lenses remain a relatively specialist item and so tend to be expensive, even for Chalcogenide glass types.

Fraser
 

Offline Bill W

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Re: Seek Thermal Lens Repair
« Reply #8 on: October 07, 2017, 08:13:47 am »
How would You estimate focal length of SEEK factory optic ? (either Compact or XR).
Less than 8mm ?

Work it out from horizontal field of view and sensor size.


D = Pixels * Pitch/2
D = F * TAN(A)

A being half the horizontal field of view
F is lens focal length

Bill
 
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Offline LesioQ

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Re: Seek Thermal Lens Repair
« Reply #9 on: October 07, 2017, 03:52:19 pm »
That would be the way to go but what are the sensor dimensions ?
I tried to deduct it from pixel size and sensor resolution but came out with too small a numbers.
Perhaps fill factor is less than one (spacing between pixels).
I'm more into CCDs, and there things are somewhat easier, or ... less enigmatic.
Even pinuts aren't disclosed  |O
« Last Edit: July 04, 2018, 06:20:34 pm by LesioQ »
 

Offline IwuzBornanerd

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Re: Seek Thermal Lens Repair
« Reply #10 on: October 07, 2017, 06:59:34 pm »
That angle A is also only half of the stated field of view since you are using half of the sensor size as D (which is probably the correct thing to do).  You would also need  to know if the 20 degree field of view they specify is for the horizontal, vertical, or diagonal dimension.  Using the stated 12um pitch I get 7.0mm, 5.3mm, and 8.7mm respectively, if I didn't screw up somewhere...
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Offline IwuzBornanerd

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Re: Seek Thermal Lens Repair
« Reply #11 on: October 09, 2017, 07:10:51 pm »
I decided to pry the non-XR lens out of its holder so here are a couple views of the naked lens.

One reason I did that was to see if there was a second piece of glass in there, in front of the lens, to protect it.  I wondered about that because the thing appears to be "fogged" on the inside.  But I said " I can't see through the lens so how can I be seeing fog on the inside of it?".  So I checked to see if there was a shield in front of the lens.  There is no such thing there, so what is it I'm seeing in that lens surface?  Can anyone explain the appearance in the third image?  The 2 XR lenses I have don't look anything like that and I have not identified any effects of that "grubbiness" in the images.
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Online Fraser

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Re: Seek Thermal Lens Repair
« Reply #12 on: October 09, 2017, 08:41:21 pm »
I have not seen that exact pattern on a thermal camera lens before, but I have seen plenty of damaged Anti-reflective coatings that have been worn away or blistered.

What I can say is that if the images remain OK, do not be too concerned. You cannot polish the lens as that would remove the AR coating. Sometimes a lens can look pretty awful in the visible light spectrum, but it still performs fine in the thermal energy spectrum. Was this lens like this from new ? If so, it is likely an issue with the AR coating process but it may still function OK.

Fraser
 

Offline Bill W

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Re: Seek Thermal Lens Repair
« Reply #13 on: October 09, 2017, 10:47:59 pm »
The  'grubby' is damaged coating, as Fraser says, leave well alone as any attempt at fixing it will make more fall off and the picture get worse.

No coating is about 20% transmission, at each surface.

Bill

Offline LesioQ

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Re: Seek Thermal Lens Repair
« Reply #14 on: October 09, 2017, 11:24:08 pm »
...

No coating is about 20% transmission, at each surface.
Hey You mean 80% reflection withour AR ?! I doubt that. 20% less transmission - pehaps, like 90% down to 70%
 

Offline Bill W

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Re: Seek Thermal Lens Repair
« Reply #15 on: October 10, 2017, 12:12:07 am »
...

No coating is about 20% transmission, at each surface.
Hey You mean 80% reflection withour AR ?! I doubt that. 20% less transmission - pehaps, like 90% down to 70%

No, I do mean 20% transmission, it is germanium we are talking about here.  Even some coatings such as 'hard carbon' coating are only 80% or so transmission.

Had some windows done once and the coating on one side got missed off.  :palm:

Bill

Offline LesioQ

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Re: Seek Thermal Lens Repair
« Reply #16 on: October 10, 2017, 12:29:22 am »
So what would be the transmission with AR coating ? 4-fold improved ?!  :o
 

Offline Bill W

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Re: Seek Thermal Lens Repair
« Reply #17 on: October 10, 2017, 12:48:18 am »
So what would be the transmission with AR coating ? 4-fold improved ?!  :o

There's 3 grades of coating:
Hard Carbon - around 80% - Proof against almost anything, so good for 'sand exposed with windscreen wiper'.
High durability - around 92% - OK for externals that either don't get trashed or can easily be replaced.
High efficiency - around 97% - only ever use inside a dry clean box.

There's also some loss in the germanium itself so there isn't such a clean answer.  It also depends a little on what you are looking at, raw germanium transmission falls across the 8-14um band

However even a lens as bad as the image posted above still has quite a lot of coating in place so might only be down to 70% overall especially if the internal surfaces are OK.


Bill

Offline IwuzBornanerd

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Re: Seek Thermal Lens Repair
« Reply #18 on: October 10, 2017, 07:40:06 am »
Wow, thanks guys.  I had not thought about coatings.  Very interesting.

I don't know if that lens looked like that when I first got it.  I noticed it recently when I was examining the camera after it had been drenched when a thunderstorm blew rain at the opposite side of the house from where the prevailing wind had been blowing.  It was that incident that caused me to finally crack the camera open (it was not wet inside, thankfully).  If the reflection had significantly changed since I got the thing I expect the temperature readings would be noticeably lower and I have not observed that so I think it's okay.

For comparison purposes, I'll post images of the old & new XR lenses.
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Offline Bill W

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Re: Seek Thermal Lens Repair
« Reply #19 on: October 10, 2017, 09:34:01 pm »
If the reflection had significantly changed since I got the thing I expect the temperature readings would be noticeably lower and I have not observed that so I think it's okay.


That is correct, and is a good simple test especially if you know it was OK beforehand.
On a camera of unknown history though, a detector going up to air and coating loss will give exactly the same symptoms.

regards
Bill

Online Fraser

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Re: Seek Thermal Lens Repair
« Reply #20 on: October 10, 2017, 09:59:01 pm »
In case readers do not know what Bill means about "up to air", it is a term used to describe the loss of the hard vacuum in the microbolometer module. Such a loss of vacuum is devastating to the sensors performance.

Fraser
 
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Offline jjachim

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Re: Seek Thermal Lens Repair
« Reply #21 on: October 28, 2017, 09:13:11 pm »
Thanks for all the good information.  I was kind of hesitant to just start ripping this thing apart but with all the additional data, it seemed like a manageable task.  So my original issue was that I had dropped it and then I could not get it to focus.  After prying the metal lid off the unit I found that I could get it to focus if I extended it out a mm or so.  I then pushed in the retaining pin and the lens now spins freely around and around.  I could not get the lens to unscrew from the bayonet mount.  All I could do is put a dental probe into one of the little holes next to the lens and try to rotate it, but it would not budge.  Since the threads are plastic, I did not want to force them of have the tool slip and damage them or the lens.  So I gave up on that part.  But I did decide to push on the lens.....and it moved.  Not sure exactly how far, but more than it should.  I put whole thing loosely back together and tried it.  It was better, but still not what it was supposed to be. So I took the lens part and tapped it firmly on the table and got the lens to move again.  Then I was more careful pushing the the lens and only moved it a bit.  Then I tested it.  I repeated this process until it was very close to what it was supposed to do.  I can focus out to infinity and probably down to 4 feet.  Good enough for me.  The lens seems to be a pressure fit inside the threaded mount.  I could put a drop of super glue around the edge right now and it might be a permanent fix for the lens movement, but I am going to hold off the see if it moves with just regular handling.
 

Offline LesioQ

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Re: Seek Thermal Lens Repair
« Reply #22 on: October 28, 2017, 09:48:04 pm »
Watch out for the superglue. Cyanoacrylate glues do emit lots of gaseous contamination, depositing it on surrounding optics (up to 1/2 inch distance, I estimate).
For optics better use UV curing glue.
 
 

Online Fraser

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Re: Seek Thermal Lens Repair
« Reply #23 on: October 28, 2017, 09:56:08 pm »
DO NOT apply superglue anywhere near the lens. Very bad idea as the cyano glue vents nasty gases and causes residues to form on the lens. Remember the lens is coated so removing such contamination is very risky.

Use only low vapour glues near lenses. Water based general purpose glues are likely safe to use but be aware that some 'string' and can drop glue across the lens..... very bad. I prefer to use a car acrylic lacquer touch up kit to secure lenses. The lacquer is very controllable, dries hard and acts like a screwlock or weak glue. Perfect for holding delicate optics in place within their housing. I always work on the lens with its edges fully exposed to avoid risk to the lens faces.

Fraser
« Last Edit: October 28, 2017, 10:06:14 pm by Fraser »
 

Offline IwuzBornanerd

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Re: Seek Thermal Lens Repair
« Reply #24 on: October 29, 2017, 06:39:55 am »
The lens is held in the holder by a couple of plastic prongs that have to be pried away from the lens in order to push the lens out of the holder.  If the lens is still in the bayonet mount this will not be possible.  You can see one of the prongs in the image showing all the parts apart--it is isolated from the threads by a gap on each side. 

I'm having trouble visualizing what you are describing, so let me ask a couple questions for clarification.  When you said you put a dental probe into "one of the little holes next to the lens", are you talking about the gaps I jut mentioned?  If you are looking at the lens in the bayonet mount these will appear as a pair of slots in the plastic close together on opposite sides of the lens--or if if the lens is screwed in almost all the way they will be little square holes.  Thinking while I type, I suspect that is the case.  It also sounds like the threads are mangled.  Can you post a clear, close-up photo of a side view of the lens with the outer shell off & the lens screwed out as far as you can get it to go?  And take a good close look at those threads.  If they are not nice & smooth they are messed up.  You might be able to improve them by carefully running a sharp tweezers tip along in the groove, if you can tell for sure where the groove is supposed to be.

Is the bayonet mount that the lens screws into also plastic on your camera?  It's metal on my old camera but plastic on the new non-XR (I haven't taken the new XR apart yet, so I don't know about that one).
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