Can't center field diaphragm, AO 10

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MichaelBrock
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Joined: Tue Aug 22, 2017 4:47 pm

Can't center field diaphragm, AO 10

#1 Post by MichaelBrock » Sat Jan 12, 2019 8:58 pm

I'm refurbishing another AO 10 microscope for my wife's science class. I have most of it done but one issue is frustrating my attempts to resolve it. When closing down the field diaphragm I cannot center it in the eyepiece view. This is the 1036A illuminator. Adjusting the two screws on each side/front of the illuminator can get it roughly centered left/right (even then it is still a bit to the right of center at it's "left most" adjustment) but nowhere close to centered front/back (the edge of the diaphragm at the at about 3/4 closed is just shy of touching center). Even pushing the top lens fixture as far back as it goes against the spring, it is not centered so I'm guessing that the misalignment isn't coming from the illuminator. There doesn't seem to be any way the diaphragm could be further back than it is now (eg. the attachment of the illuminator to the base has no play in that direction).

So what could be causing this? What's out of adjustment?

einman
Posts: 1288
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Re: Can't center field diaphragm, AO 10

#2 Post by einman » Sat Jan 12, 2019 9:03 pm

mis alignment of the nose turret can cause this. Try adjusting the nose turret while viewing.

There are 3 hex screws as I recall. Movement is sensitive so take your time.

desertrat
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Location: Idaho

Re: Can't center field diaphragm, AO 10

#3 Post by desertrat » Sat Jan 12, 2019 10:15 pm

There are some screws holding the illuminator unit to the frame, from the underside. If you loosen those a bit, you can wiggle the whole illuminator unit around a little. That might help get the diaphragm a little closer to center.
Rick

A/O 10 Series Microstar
A/O 4 Series Microstar
A/O 4 Series Phasestar
A/O 4 Series Apostar
A/O Cycloptic Stereo
Several old monocular scopes in more or less decrepit but usable condition

apochronaut
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Re: Can't center field diaphragm, AO 10

#4 Post by apochronaut » Sun Jan 13, 2019 10:18 pm

There are 6 movable items, 3 with gross adjustment capability and 3 with only wiggle room that could be contributing. In addition to the three mentioned, the stop spring can be malcentered, allowing the objective to be left or right of center, by quite a margin. If it has a non-centering condenser, the condenser mount can be off some, as well as the dovetail in the bottom of the head, although the latter two will contribute only a little to the problem. Once someone starts to fritter with adjustments( including the mirror) in a school microscope, while achieving little success, all of them might have been put out of line at some point. Best start is to center the diaphragm by eyeball in it's mount and adjust the mirror to pass the filament image as close to the center of that as possible, then work up from there.
One of the springs tensioning the diaphragm can get bent when the diaphragm iris is replaced after removal. Not a helpful situation, either.

MichaelBrock
Posts: 91
Joined: Tue Aug 22, 2017 4:47 pm

Re: Can't center field diaphragm, AO 10

#5 Post by MichaelBrock » Wed Jan 16, 2019 5:32 pm

apochronaut wrote:Once someone starts to fritter with adjustments( including the mirror) in a school microscope, while achieving little success, all of them might have been put out of line at some point.
This is definitely the case. My original plan was a full class set of AO 10 microscopes...but it became apparent very quickly that their use was beyond the attention span of a typical 8th grader. I thought "set and forget" but they are continuously adjusting every thing that moves. My wife has been using grant money to slowly purchase cheap chinese student microsopes with almost no adjustability and those are proving more suitable.
apochronaut wrote:... One of the springs tensioning the diaphragm can get bent when the diaphragm iris is replaced after removal. Not a helpful situation, either.
One of the spring arms is indeed broken off but that wasn't keeping the diaphragm "frame" from moving back.
einman wrote:mis alignment of the nose turret can cause this. Try adjusting the nose turret while viewing.

There are 3 hex screws as I recall. Movement is sensitive so take your time.
I was concerned that adjusting the alignment of the nose turret might negatively affect the alignment with the optics in the head but this is ultimately the change I made and it only required a small tweak.

Which of course leads me to the next question. There is point in the focus (in both the fine and course) where the image "jumps" left/right. As in I can slowly go through the focus range and there is a point where the viewed image shifts a bit to the left/right. I don't notice any movement on either side of this point. Not exactly the end of the world but I'm curious as to where this problem might lie. The point at which the shift occurs does not seem to move around (i.e. it is currently at a constant focus point regardless of the objective). Ideas?

apochronaut
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Re: Can't center field diaphragm, AO 10

#6 Post by apochronaut » Wed Jan 16, 2019 6:14 pm

Since you have now adjusted the nosepiece to be concentric with the field diaphragm, you have to now make sure the objective axis is centered with respect to the telan lens in the head and in fact is concentric with the head in general. If you have a broken field diaphragm tension spring, it doesn't mean that you can't align the nosepiece to it but it is likely that the axis of those two components is now mis-aligned to the axis of the head. Everything needs to be aligned.
If you look into the microscope through a bertrand lens, you will see several vague circles, each representing an optical port, through which the light beams pass. Those need to be as concentric as is possible, otherwise the image bounces back and forth laterally as it ricochets up the tube and the ultimate quality can suffer, depending on the degree of skew. In a very bad scenario, there will be vignetting with the higher power objectives. The image can be o.k.( but not fine), up to the 40X but when you dial up the 100x, an edge of the field will be chopped off.

Regarding the lateral jump during focus, remove the three hex screws surrounding the head dovetail and the Philips screw at the back and lift off the top plate. Sometimes, the grease in the focus track , seen from above at the back of the arm, gets sticky and the ball retainer loses it's position. This can cause the arm to waver slightly because it's lateral registration is determined by the precise location of the ball bearings. You might see that one of the brass retainers sits high. Other possibility, is a mis-alignment of the cast focusing arm as it passages between the mounting brackets. If there is sufficient wiggle in the ball track, that section of the arm could just barely snag one of the brackets causing the lateral movement. Check the rollers right above the nosepiece too. They
might be dirty and slightly moving the nosepiece side to side. The alignment is mostly controlled at the main bearing track but those two rollers lightly guide the nosepiece end. There is some sway there and a bad or dirty roller could be the problem....or dirt or wear on the roller bed.

MichaelBrock
Posts: 91
Joined: Tue Aug 22, 2017 4:47 pm

Re: Can't center field diaphragm, AO 10

#7 Post by MichaelBrock » Thu Jan 17, 2019 11:01 pm

apochronaut wrote:Since you have now adjusted the nosepiece to be concentric with the field diaphragm, you have to now make sure the objective axis is centered with respect to the telan lens in the head and in fact is concentric with the head in general. If you have a broken field diaphragm tension spring, it doesn't mean that you can't align the nosepiece to it but it is likely that the axis of those two components is now mis-aligned to the axis of the head. Everything needs to be aligned.
If you look into the microscope through a bertrand lens, you will see several vague circles, each representing an optical port, through which the light beams pass. Those need to be as concentric as is possible, otherwise the image bounces back and forth laterally as it ricochets up the tube and the ultimate quality can suffer, depending on the degree of skew. In a very bad scenario, there will be vignetting with the higher power objectives. The image can be o.k.( but not fine), up to the 40X but when you dial up the 100x, an edge of the field will be chopped off.
I checked it and everything seems aligned. I'll look into manufacturing a new spring (or picking up another "needs repair" AO 10 with the 1036a illuminator) to make certain it's aligned.
apochronaut wrote:Regarding the lateral jump during focus, remove the three hex screws surrounding the head dovetail and the Philips screw at the back and lift off the top plate. Sometimes, the grease in the focus track , seen from above at the back of the arm, gets sticky and the ball retainer loses it's position. This can cause the arm to waver slightly because it's lateral registration is determined by the precise location of the ball bearings. You might see that one of the brass retainers sits high. Other possibility, is a mis-alignment of the cast focusing arm as it passages between the mounting brackets. If there is sufficient wiggle in the ball track, that section of the arm could just barely snag one of the brackets causing the lateral movement. Check the rollers right above the nosepiece too. They
might be dirty and slightly moving the nosepiece side to side. The alignment is mostly controlled at the main bearing track but those two rollers lightly guide the nosepiece end. There is some sway there and a bad or dirty roller could be the problem....or dirt or wear on the roller bed.
It turns out that the bearing that rides on the side of the arm was completely frozen. I cleaned that and re-lubed it. I also found that one of the brass retainers was slightly bent at the top end and that was providing enough resistance that the two retainers were not staying together. I gently bent that back and it's now much smoother.

Putting it back together, I had to position the arm so that the bearing on the side of the arm was in contact with the bed to keep things "vertical". When I centered the arm there was a distinct "tilt" to the focus.

Thanks yet again for the informative post!

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