Finding dust speck that does not move

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Jesse
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Joined: Sun Dec 11, 2016 6:40 pm

Finding dust speck that does not move

Post by Jesse »

Hello,

When using a camera to record video with my Nikon E600 microscope via the trinocular port, I see a dust spot on my camera that does not move when I move the stage.

At first I thought it must be on the camera sensor, so I cleaned the sensor using Eclipse cleaning fluid and sensor swabs. I couldn't get it perfectly clean, but it's pretty good now, especially away from the edges of the sensor frame. I determine this by photographing a white sheet of paper with the lens aperture at f32 and zooming in to view the dust specs.

However, the dust speck in video persists.

It shows up as a blob of darkness when using my 20x objective. It becomes more defined in my 40x objective, and it's almost sharp when using my 60x objective. This leads me to conclude it's not a dust speck on the objectives.

Things I've tried:
  • I've blown dust off the mirrors (that I can access) in my Y-IDP attachment.
    I've cleaned the top of my PLI 2.5x lens, but rotating that lens does not change the position of the dust speck, so that's not it.
    I've cleaned the top of my Abbe condenser lens that tilts.
    I've cleaned the top of my Abbe condenser lens that is right above the aperture.
    I've blown dust off the underside of the Abbe condensor lens with the aperture.
    I've cleaned the top of my light emitter lens at the base of the microscope.
What else should I try in what order? This is driving me nuts.

Thanks!

UPDATE: example footage showing problem

before cleaning camera sensor:
https://youtu.be/P2_FDihLfEo?t=2m32s

after cleaning camera sensor:
https://youtu.be/P2_FDihLfEo?t=16m1s

UPDATE2: Just read that if I rotate the camera and the dust spot moves, it's not on the camera. Tried that. Dust spot moves. So camera is thoroughly ruled out as the source of the dust spot.

UPDATE3:
  • I inserted and removed all three filters. No change in the spot.
    I rotated the condenser top lens, no change.
    I moved the condenser using the positioning screws. No change.
    I shifted the Y-IDP mirror and the spot moved a little, but not a lot before the image changed. This is a possibility, but I think it's not the culprit.
    I rotated the lamp house slightly. No change.
I think I've narrowed it down to the field lens and possibly the mirror inside the base between the field lens and the lamp house.

I can't figure out how to remove the field lens on the e600 microscope.

Looks like there might be three screws on top and a circular spring that hold it in place? But I think I would need to remove the turret and stage in order to do that.

Also I found this document which describes removing the bottom: https://www.nano-dyne.com/wp-content/up ... ctions.pdf
Last edited by Jesse on Sat Sep 29, 2018 12:46 pm, edited 2 times in total.

Cactusdave
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Post by Cactusdave »

I guess we have all experienced problems like this at one time or another. It is indeed incredibly frustrating when you can find where the culprit dust is.
I think I've narrowed it down to the field lens and possibly the mirror inside the base between the field lens and the lamp house.
From your description and your careful analysis I would agree that's likely where the problem lies. I'm afraid I have no experience with the E600 and I'm afraid manufacturers can make it distressingly difficult to get at obvious sources of dust problems. I supose that's what keeps service engineers in business. :x
Leitz Ortholux 1, Zeiss standard, Nikon Diaphot inverted, Canon photographic gear

Pau
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Post by Pau »

If it is in the field lens it must focus and defocus moving the condenser knob.
The method to find dirt is to rotate and focus each movable element
Pau

gpmatthews
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Post by gpmatthews »

I've just given my Leitz Dialux setup a spring clean (well, autumn clean!). The most frustrating parts were the camera sensor, where I ended up picking off dust specks individually under a stereo microscope, but still couldn't get everything, and the eyepiece in the trinocular tube: I am using the afocal method of coupling the camera to the microscope and the eyepiece is a Zeiss KPL 8. The most annoying source of dust was the upper surface of the lower lens element in the KPL 8 and almost as fast as one item of dust was removed others floated in or fell from elsewhere in the eyepiece during re-assembly...

The Tominon lens I use on the camera for the afocal coupling was a doddle.

I also found extensive dust in the condenser elements, but this wasn't so bad to address even though there were many surfaces (Leitz ICT - DIC - condenser with flip out lens and integral rotating polariser, multi-position turret for DIC prisms and phase annuli, plus compensator slider). Fortunately most were already reasonably clean and most of the dust was on the externally accessible lens elements.

The glass over the field aperture removes easily on the Dialux stand in question, so that was also easy to access and clean.The mirror was OK.

In all, a nightmare, but worth doing- even if I couldn't achieve perfection.
Graham

Though we lean upon the same balustrade, the colours of the mountain are different.

Jesse
Posts: 69
Joined: Sun Dec 11, 2016 6:40 pm

Post by Jesse »

Pau wrote:If it is in the field lens it must focus and defocus moving the condenser knob.
The method to find dirt is to rotate and focus each movable element
Well, this is frustrating. The dust speck does indeed focus and defocus using the condenser knob. I had a moment, finally, to tear the microscope down and clean the field lens and the mirror below it. I filmed the process, so I should be able to share it soon. However, the dust speck is still there.

Are we sure a dust speck that focuses and defocuses using the condenser knob indicates the field lens? Could it indicate something else? Maybe one of the glass elements between the field lens and the lamp housing? I'm stumped.
Last edited by Jesse on Sat Sep 29, 2018 12:46 pm, edited 1 time in total.

Pau
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Post by Pau »

Are we sure a dust spec that focuses and defocuses using the condenser knob indicates the field lens?
No, it is indicative of the dust being placed in the light train before the condenser
Could it indicate something else? Maybe one of the glass elements between the field lens and the lamp housing?
Yes, of course

If it is focused at the image plane when you set the microscope for Kölher (together with the field diaphragm) it must be placed at a conjugate plane with it, somewhere between the lamp and the field diaphragm (of course if not placed at the field diaphragm level glass)
Time ago I found some weird lines at my images. When searching the cause I discovered a tiny spider making its web inside the microscope base halfway of the light path :roll:

If it doesn't focus at the image plane...in most cases you can just forget it.
Pau

Jesse
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Joined: Sun Dec 11, 2016 6:40 pm

Post by Jesse »

After editing the footage... it could still be the field lens. It looks to be in pretty bad shape, even after cleaning. It looked clean to the naked eye, but the camera had a much better view.

I think the next thing I try will be to rotate the field lens. I'll need to strip the microscope down to do this, remove the field lens cover and tension spring, then reassemble everything without the field lens cover and tension spring. Finally, I'll rotate the field lens using tweezers and see if the speck rotates.
Last edited by Jesse on Sat Sep 29, 2018 12:47 pm, edited 1 time in total.

Jesse
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Post by Jesse »

Here's the tear down video if anyone is curious. I'm linking to 7:36 where the field lens has already been removed. Dusty in there. https://youtu.be/g-W9CEiEpPA?t=7m36s

ChrisR
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Post by ChrisR »

That looks frustrating. This may be an "ignorant" question, as I have little experience; have you eliminated the projective eyepiece? (rotate 90°?)
Chris R

Jesse
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Joined: Sun Dec 11, 2016 6:40 pm

Post by Jesse »

ChrisR wrote:That looks frustrating. This may be an "ignorant" question, as I have little experience; have you eliminated the projective eyepiece? (rotate 90°?)
If by "projective eyepiece" you mean the relay lens in the trinoc tube, then yes, I've rotated it with no result. Also the dust speck shows up in both the camera and the binocular eyepieces.
Last edited by Jesse on Sat Sep 29, 2018 12:47 pm, edited 1 time in total.

Jesse
Posts: 69
Joined: Sun Dec 11, 2016 6:40 pm

Post by Jesse »

I had a moment today to work on this, so I removed the objective turret and the stage, then removed the field lens cover. Finally, I reassembled everything and rotated the field lens using a pair of tweezers. dust specks do not move. It's not the field lens.
Last edited by Jesse on Sat Sep 29, 2018 12:47 pm, edited 1 time in total.

Jesse
Posts: 69
Joined: Sun Dec 11, 2016 6:40 pm

Post by Jesse »

Gah. I was wrong. The dust is on the relay lens. I thought I saw it through the binocular eyepieces, but that must be another dust speck in a similar place. Lifting up the f-mount tube enough so that I could rotate the relay lens while viewing the camera output revealed the problem.

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