I've acquired a used #1096 toric darkfield condenser and I'm a bit puzzled comparing it to my other DF condenser. It's my understanding that I should get a central circle of light with a 10X objective as I bring the oiled condenser up to the slide. With this one I get full darkfield across the entire FOV. Even the 4X only shows a slight shadowing around the periphery. Makes it a devil to center. Anyone have any experience with this?
Cheers, Al.
A.O. Toric darkfield condenser
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Greg Howald
- Posts: 1186
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Re: A.O. Toric darkfield condenser
You might use a centering telescope to center the condenser.
Other than that try removing the eyepiece and looking through the tube to center.
Good luck.
Greg
Other than that try removing the eyepiece and looking through the tube to center.
Good luck.
Greg
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apochronaut
- Posts: 6327
- Joined: Fri May 15, 2015 12:15 am
Re: A.O. Toric darkfield condenser
There were two versions I know of for that condenser. one, probably of later production had a thin ring embedded in the glass that could be used for centering.
I've used both and never really found the ring to be necessary.
This is the method I use. First off though, there will be some parcentering variance between objectives and between each objective in the various nosepiece ports. For every nosepiece and objective assembly, I do a best case parcentering but of prime importance for DF is to have the 100X objective as close to being exactly parcentered with whatever objective you use to center the condenser, as is possible. Generally, the 400 series microscope's nosepieces and objectives are quite precise so there are no major issues but with DF every little bit off center increases the level of assymetrical ca. The 1096 condenser is generally ca free. Proper parcentering keeps it that way.
I usually use the 4X for centering. With the 4X, the fully illuminated defined central spot is about 1500 microns wide, with a corona around it of a somewhat lower illumination, totalling about 2000 microns. With the 10X, that 1500 micron spot doesn't quite cover the 20 mm f.o.v. of the eyepieces, although with the corona, a 10X objective is reasonably useable, although not perect to the edge of the field. The 1096 condenser produces a fully lit field with a 20X objective.
Install the condenser and place the oil drop on top. Raise the condenser until the oil touches the slide and there is the characteristic flash of light in the slide. Then back off the condenser until the smallest oil bubble possible is still connected between the condenser and slide. Looking through the microscope, you will see a central black spot, surrounded by a fairly well illuminated circle . Adjusting the condenser up and down will define the spot, which is as usefull as anything for centering the condenser. If the surrounding circle if light is not uniform; in other words if the dark central spot bleeds into the surrounding area, your objective , condenser and or stage are not in parallel planes.
First off, check to see if the condenser and stage are parallel, then check the objective against them.
I've used both and never really found the ring to be necessary.
This is the method I use. First off though, there will be some parcentering variance between objectives and between each objective in the various nosepiece ports. For every nosepiece and objective assembly, I do a best case parcentering but of prime importance for DF is to have the 100X objective as close to being exactly parcentered with whatever objective you use to center the condenser, as is possible. Generally, the 400 series microscope's nosepieces and objectives are quite precise so there are no major issues but with DF every little bit off center increases the level of assymetrical ca. The 1096 condenser is generally ca free. Proper parcentering keeps it that way.
I usually use the 4X for centering. With the 4X, the fully illuminated defined central spot is about 1500 microns wide, with a corona around it of a somewhat lower illumination, totalling about 2000 microns. With the 10X, that 1500 micron spot doesn't quite cover the 20 mm f.o.v. of the eyepieces, although with the corona, a 10X objective is reasonably useable, although not perect to the edge of the field. The 1096 condenser produces a fully lit field with a 20X objective.
Install the condenser and place the oil drop on top. Raise the condenser until the oil touches the slide and there is the characteristic flash of light in the slide. Then back off the condenser until the smallest oil bubble possible is still connected between the condenser and slide. Looking through the microscope, you will see a central black spot, surrounded by a fairly well illuminated circle . Adjusting the condenser up and down will define the spot, which is as usefull as anything for centering the condenser. If the surrounding circle if light is not uniform; in other words if the dark central spot bleeds into the surrounding area, your objective , condenser and or stage are not in parallel planes.
First off, check to see if the condenser and stage are parallel, then check the objective against them.
Re: A.O. Toric darkfield condenser
Thanks you guys,
O.K. making some progress. Staying with the 4X and dropping the condenser waaay down has helped. One of the things that had me confused was the 10X. surprisingly I get full darkfield illumination right across the FOV, no vignetting whatsoever that I can detect. No little circle on my condenser either, I must have the older version. I do get a dark spot with the 4X, enough to center it although it is long gone by the time I get a reasonably defined circle of light.
I may have an issue with something out of plane. with the 10x the black area extends to the right as the condenser is lowered although I wonder if that due to it not being parcentered with the 4X. I'm not familiar with the correct way to verify everything is in the same plane. I'll keep experimenting but at least I feel like I'm going in the right direction now.
As to getting the 100x centered I am going to pull it and put the 4X in its place when I center the condenser. I don't normally have the 4X in the nosepiece anyway so I might as well swap it there. I may end up using the 218F for the higher magnifications, I have been swapping it back and forth with the 1096 a lot and so far I'm getting consistently better results with the 218 on anything over 40X.
All the help is very much appreciated!
Cheers, Al.
O.K. making some progress. Staying with the 4X and dropping the condenser waaay down has helped. One of the things that had me confused was the 10X. surprisingly I get full darkfield illumination right across the FOV, no vignetting whatsoever that I can detect. No little circle on my condenser either, I must have the older version. I do get a dark spot with the 4X, enough to center it although it is long gone by the time I get a reasonably defined circle of light.
I may have an issue with something out of plane. with the 10x the black area extends to the right as the condenser is lowered although I wonder if that due to it not being parcentered with the 4X. I'm not familiar with the correct way to verify everything is in the same plane. I'll keep experimenting but at least I feel like I'm going in the right direction now.
As to getting the 100x centered I am going to pull it and put the 4X in its place when I center the condenser. I don't normally have the 4X in the nosepiece anyway so I might as well swap it there. I may end up using the 218F for the higher magnifications, I have been swapping it back and forth with the 1096 a lot and so far I'm getting consistently better results with the 218 on anything over 40X.
All the help is very much appreciated!
Cheers, Al.
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apochronaut
- Posts: 6327
- Joined: Fri May 15, 2015 12:15 am
Re: A.O. Toric darkfield condenser
Swapping the 100X and 4X might not keep you parcentered. Remember that everthing with the 4X is magnified 25X with the 100X. The 100X is also a little longer so any mechanical variance will increase.
While there seldom is a problem, most variances are less than 10 microns, it makes life a lot easier to be able to just dial up through the magnifications with full confidence that once centered, the condenser will be so with every objective. It is really easy to do so.
Put a BF condenser in the stand and take all the objectives out of the nosepiece except the 4X. Then find a fairly high contrast but small target on a slide with a thin coverslip and center it using the 4X. Then successively move the 4X objective around the nosepiece , noting the two ports side by side that have the closest registration with each other. Install the 4X in one and the 100X in the other, starting in the rotation direction you prefer. Then check the 100X dry, to test how parcentered they are. You don't need to oil either the condenser or objective to parcenter them. Hopefully they are dead on or close but if not, reverse their order and see. It is better to have them parcentered than being in your preferred direction of rotation. Then fit the rest of the objectives in sequence. You will have to center the DF condenser every time you use it and you do not have the benefit of an iris diaphragm or field diaphragm to do so. The 100X objective is the most sensitive to a condition of decentering, so it helps to get it right based easily on it's known relationship with the 4X.
While there seldom is a problem, most variances are less than 10 microns, it makes life a lot easier to be able to just dial up through the magnifications with full confidence that once centered, the condenser will be so with every objective. It is really easy to do so.
Put a BF condenser in the stand and take all the objectives out of the nosepiece except the 4X. Then find a fairly high contrast but small target on a slide with a thin coverslip and center it using the 4X. Then successively move the 4X objective around the nosepiece , noting the two ports side by side that have the closest registration with each other. Install the 4X in one and the 100X in the other, starting in the rotation direction you prefer. Then check the 100X dry, to test how parcentered they are. You don't need to oil either the condenser or objective to parcenter them. Hopefully they are dead on or close but if not, reverse their order and see. It is better to have them parcentered than being in your preferred direction of rotation. Then fit the rest of the objectives in sequence. You will have to center the DF condenser every time you use it and you do not have the benefit of an iris diaphragm or field diaphragm to do so. The 100X objective is the most sensitive to a condition of decentering, so it helps to get it right based easily on it's known relationship with the 4X.