Spot on FoV driving me insane

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Plasmid
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Spot on FoV driving me insane

#1 Post by Plasmid » Tue Dec 01, 2020 8:25 pm

Im in need of some help in figuring out where the source of a dark spot on the Fov left lower corner is coming from. This is what I've done so far.
Cleaned every glass surface ( except inside of the head)
This includes even the light source.
Additionally Inspected the light bulb and even flipped it around in the event it was coming from a damaged bulb.
Cleaned all the objectives, and Eyepieces.
Its not the objectives or the Eyepieces as changing objectives or rotating the eyepieces has no effect and the spot remains in the same place,
Condenser has also been cleaned inside and out. And rotating the condenser on the dovetail has no effect.
No effect in rotating the field diaphragm.
I have notice that the spot becomes darker as the Microscope starts to warm up, at startup its not so obvious.
Its not the camera, as i get the same result with different cameras.
Any help will be appreciated
https://youtu.be/-m9Ibknqcz0
https://youtu.be/dSjWSOA68IM

apochronaut
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Re: Spot on FoV driving me insane

#2 Post by apochronaut » Tue Dec 01, 2020 8:36 pm

Do you see it with all magnificatons, is it the same size with all magnifications and does it get more obvious if you diminish the light?

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Re: Spot on FoV driving me insane

#3 Post by Plasmid » Tue Dec 01, 2020 9:04 pm

The higher the magnification the more noticeable it is. I ruled out the condenser because I got the same spot using a 1897 condenser from the microstar as well as the condenser from the microlux. Diminishing the light does decrease the spot as well.
Towards the end of that first link video you can see the spot getting more noticeable switching from 20x to 40x

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mrsonchus
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Re: Spot on FoV driving me insane

#4 Post by mrsonchus » Tue Dec 01, 2020 9:11 pm

Sounds very similar to such a frustrating problem I had a while back now with my L Orthoplan - it was a mark on the mirror I eventually discovered....
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Re: Spot on FoV driving me insane

#5 Post by PrecisionInstruments » Tue Dec 01, 2020 9:24 pm

Does adjusting the height of the condenser take it in and out of focus? If so, most likely on mirror or lens close by to it
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Wes
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Re: Spot on FoV driving me insane

#6 Post by Wes » Tue Dec 01, 2020 9:37 pm

I think this is dirt on one (or more..) of a few conjugate planes. I recently cleaned those cause it drove me crazy too! It solved the problem.

Can you post a picture of your scope and also a view of its bottom/base plate?
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Re: Spot on FoV driving me insane

#7 Post by Plasmid » Tue Dec 01, 2020 9:56 pm

Lowering the condenser has no effect on it, the only thing that is consistent is the same spot and that gets worse as the scope stays on 3-4 min after start up

I'll post a pic of the bottom when I get home.

Btw thank you alll for helping oit with this issue.
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hans
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Re: Spot on FoV driving me insane

#8 Post by hans » Tue Dec 01, 2020 9:59 pm

Does the spot look the same through both eyepieces?

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Wes
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Re: Spot on FoV driving me insane

#9 Post by Wes » Tue Dec 01, 2020 10:09 pm

No change when lowering the condenser and the warm up effect argue against a smudge on one of the conjugate planes. I'd still have a look at these though. Check out the binocular head too.
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Re: Spot on FoV driving me insane

#10 Post by Charles » Tue Dec 01, 2020 10:24 pm

You can rule out the binocular head by rotating it and see if the spot moves. What is that slide just below the head in front?

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Re: Spot on FoV driving me insane

#11 Post by Hobbyst46 » Tue Dec 01, 2020 10:28 pm

Perhaps it has to do with the lamp. Is it perfectly centered ?

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Re: Spot on FoV driving me insane

#12 Post by Plasmid » Tue Dec 01, 2020 10:28 pm

Unfortunately it does, its more visible with either one of the cameras that i normally use but it is still visible with the eyepieces, I took apart the cat 181 and thoroughly cleaned them and swapped them with a WF10/18mm and the spot was still there.
I noticed that the 12v 20watt bulb had a slight discoloration on one side, and so I reversed it to make sure that wasn't it.
The way the image of the spot moves over the sample makes me want to take the whole head apart for cleaning, before I do, im going to try and see if one of the other heads I have will fit and recreate it.

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Re: Spot on FoV driving me insane

#13 Post by mrsonchus » Tue Dec 01, 2020 10:42 pm

Try the mirror before you start to dimantle - this really did solve this problem for me...
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Re: Spot on FoV driving me insane

#14 Post by Plasmid » Tue Dec 01, 2020 11:13 pm

mrsonchus wrote:
Tue Dec 01, 2020 10:42 pm
Try the mirror before you start to dimantle - this really did solve this problem for me...
The mirror next to the bulb correct?

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Re: Spot on FoV driving me insane

#15 Post by Plasmid » Tue Dec 01, 2020 11:18 pm

In an an effort to eliminate the bulb as a possible causation , the manual calls for a 12v 20w, of which I have no spares just 6v 20w. Shopping around the prices for the 12v 20watt vary from sub $10 to $30 per bulb , is there a particular brand I should go for or avoid. My understanding is that its commonly refered to as a G4 bulb, is that correct?

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Re: Spot on FoV driving me insane

#16 Post by PeteM » Tue Dec 01, 2020 11:58 pm

I'm with Hobbyist that it's likely in the illumination system and possibly heat-related.

You've already ruled out the eyepieces and objectives, since it doesn't rotate with them. Not sure if you've tried the suggestion to rotate the head - but such a defect should also be apparent by removing the head and looking through it or with a centering or phase telescope.

Could well be that if you take a look you'll see damage on a mirror, a defect on a lens or bulb, or simply a bulb or reflector out of alignment. There should also be instructions for your scope on how to see an image of the filament and get that centered for Kohler illumination.

I've had better luck with new old stock Japanese or German-made bulbs off Ebay than with cheap Chinese ones. You do want the proper model (and cross-referenced identicals), since filament size and placement will vary within various G4 pin 12v 20 watt bulbs. Scope dealers will commonly sell the right bulb for about 3x of what it might cost elsewhere.

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Re: Spot on FoV driving me insane

#17 Post by mrsonchus » Wed Dec 02, 2020 12:03 am

Plasmid wrote:
Tue Dec 01, 2020 11:13 pm
mrsonchus wrote:
Tue Dec 01, 2020 10:42 pm
Try the mirror before you start to dimantle - this really did solve this problem for me...
The mirror next to the bulb correct?
Yes, the mirror that reflects the light into the condenser. My system was showing an annoying blue mark that didn't move whatever element of the illumination and image train I moved or cleaned - until I discovered the mirror-mark. Like magic a long-standing and very elusive problem was solved much to my delight.
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Re: Spot on FoV driving me insane

#18 Post by hans » Wed Dec 02, 2020 2:42 am

In addition to rotating the head as Charles suggested, could also try rotating the nosepiece slightly and see whether the spot moves sideways.
PeteM wrote:
Tue Dec 01, 2020 11:58 pm
I'm with Hobbyist that it's likely in the illumination system and possibly heat-related. ...
mrsonchus wrote:
Wed Dec 02, 2020 12:03 am
Yes, the mirror that reflects the light into the condenser. ...
The warm-up behavior is confusing, but I think this test points to the spot being somewhere on the objective side of the specimen:
PrecisionInstruments wrote:
Tue Dec 01, 2020 9:24 pm
Does adjusting the height of the condenser take it in and out of focus? ...
Plasmid wrote:
Tue Dec 01, 2020 9:56 pm
Lowering the condenser has no effect on it...

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Re: Spot on FoV driving me insane

#19 Post by Greg Howald » Wed Dec 02, 2020 2:54 am

Just bought a pack of 20 watt twelve bolt halogen bulbs on Amazon for under $15.00.
Greg
Seems silly but I had a similar problem last month. Problem was obstruction from the filter holder not being fully in place.

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Re: Spot on FoV driving me insane

#20 Post by mrsonchus » Wed Dec 02, 2020 3:02 am

Update to reply I mistakenly-gave above....

I actually meant the mirror that's below the field diaphragm not the mirror that's in the lamp-holder behing the bulb - just re-read the post and saw my careless answer - sorry.
The mirror last in line (usually under) before the field-diaphragm is the one to check...
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Re: Spot on FoV driving me insane

#21 Post by apochronaut » Wed Dec 02, 2020 11:43 am

Presumably your bulb has some kind of focus mechanism? ....and a reflector? You can rule out the bulb by focusing it. If the smudge changes, then it is the bulb or reflector. If not, then....

Rotate the head . If the smudge rotates with the head, then it is somewhere between the telan lens if it has one and the cement in the beamsplitter. If the smudge is there in both eyepieces but darker in one than the other, it is most likely in the cement layer. If if is the same in both then it is on the surface of the deviating prism : likely the back surface, which would be the upper, presuming there is only one in the head. That's all only if it rotates with the head.

Could be mirror if it doesn't.

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Re: Spot on FoV driving me insane

#22 Post by Plasmid » Wed Dec 02, 2020 12:00 pm

Heres a couple of pics with no condenser
The head rotated
The field diaphragm closed and open

I also took apart the botton part and cleaned it and nothing.
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Re: Spot on FoV driving me insane

#23 Post by Plasmid » Wed Dec 02, 2020 12:04 pm

More pics of illumination parts
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Re: Spot on FoV driving me insane

#24 Post by mrsonchus » Wed Dec 02, 2020 12:15 pm

Ah - you have just one mirror - the one behind the bulb. Place a piece of frosted filter or even greaseproof-paper/tracing paper over the top of the light port (on top, on the outside) to see if the mark is above (then it will still be visible) or below (where the frosted glass/paper will diffuse the mark) where it will be changed/diffused - this should tell you if it's 'in the base' or above the base's light-port....
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Re: Spot on FoV driving me insane

#25 Post by Plasmid » Wed Dec 02, 2020 12:21 pm

Thank you let me give it a try, will report back......

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Re: Spot on FoV driving me insane

#26 Post by hans » Wed Dec 02, 2020 5:14 pm

Plasmid wrote:
Wed Dec 02, 2020 12:00 pm
Heres a couple of pics ... The head rotated
If I am interpreting the photos correctly they appear to show the spot in the same place on the phone with the head at two different angles? If so I think that is a pretty good indication that the spot is somewhere in the head, not in the illumination system.

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Re: Spot on FoV driving me insane

#27 Post by apochronaut » Wed Dec 02, 2020 5:42 pm

You need to rotate the head more than a little. Try 90° . It does look like the spot has moved but with a more extreme movement you should be able to see it travelling around an axis.

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Re: Spot on FoV driving me insane

#28 Post by Plasmid » Wed Dec 02, 2020 5:45 pm

Ok so I tried mrsonchus approach and that confirmed han's suspension, that the problem was indeed inside the head; a dirt particle with a smudge on the right side first set of the lens inside the head. I'm very happy to report the problem has been fixed.

Thank you all for the help could not have done it without the help, there still some visible dust particles at higher mag but nothing some air can take care of. :)

Ps.....It is still a mystery as to why it got worse when the operating temp of the lamp increased
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Re: Spot on FoV driving me insane

#29 Post by mrsonchus » Wed Dec 02, 2020 5:48 pm

Well done! Great when these awkward blighters finally give-up!

Onward-ho! :D
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Re: Spot on FoV driving me insane

#30 Post by Hobbyst46 » Wed Dec 02, 2020 5:55 pm

Bravo for the solution.
The intensity of halogen light can increase in the first few minutes.

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