Accuracy of Correction Collar scale markings?

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Lou Jost
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Accuracy of Correction Collar scale markings?

Post by Lou Jost »

I bought an expensive Nikon Super Fluor 40x objective on eBay with NA=0.90, and when I got it, I found that its correction collar was immoveable. After applying lots of force I was able to get it to turn, but the force is so great that it is impractical to adjust the collar while looking at a subject through the microscope. So I am thinking of alternatives. I can easily measure any coverslip to very high accuracy, and then I could set the correction collar to match the measured thickness, using the thickness scale on the correction ring. But this will only work if the scale is accurate. Does anyone have experience regarding the accuracy of the scale markings on correction collars? I know the best policy is to check the effects visually, but in this case it is impossible. If these scales are known to be very inaccurate, I might just return the objective.

PeteM
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Re: Accuracy of Correction Collar scale markings?

Post by PeteM »

Lou, I've had some luck freeing up correction collars - though not with your $$$ objective.

First step is to apply gently a bit of heat to get the grease moving. $20 will buy a pencil-like hot air gun to apply controlled heat. If it frees up with a bit of warmth, chances of a fix are pretty good.

Second step is to open the objective up enough to see how it might be lubed. Perhaps the shroud simply removes. A drop of solvent (lighter fluid) left for a good while, followed by a drop of instrument oil and gentle exercising has done the trick in a couple instances. I like soft jaw connector pliers to safely grip the objective while "exercising" the correction collar. If this doesn't free things up, you could always return the objective.

As for the accuracy of the markings, I suspect there's some variance from objective to objective as well as a potential for damage - but also that a like-new Nikon objective should be pretty close. If there are signs the objective has been opened up (tell-tale signs from the rear), that's not a good sign and all bets are off.

You could get a rough idea of how well yours is calibrated by making up a set of slides with various measured cover slips and compare to the markings. If a .17 cover slip with the objective set to .17 looks better than either a .15 or a .19 cover slip, that might give you some confidence.

Macro_Cosmos
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Re: Accuracy of Correction Collar scale markings?

Post by Macro_Cosmos »

Unfortunately, it is always better to fiddle with the collar and follow the standard routine of having it at 0.17mm first, and going higher to find the best image quality, rarely will you find yourself going lower than 0.17mm (to the other direction) but I've had three cases where that was needed. They were antique slides using quite outrageously thin coverslips.

You are able to measure coverslips, what about the mounting media, the thickness of the sample and how deep it is situated with respect to the coverslip? Assuming directly underneath the coverslip, 0.17 would be good. What if the sample is thick and you want to image somewhere deeper? The diatoms I deal with can often be thicker than 200um, placing the correction collar at around 0.2 often gives a good balance.

Well, this is just my two cents. As for the accuracy, I cannot imagine a $1500+ objective being inaccurate. Perhaps you can get a wafer chip (shame the ones I distributed to America got crushed...) and mate it with a precisely measured coverslip using Norland's optical adhesive (Norland 87 RI=1.52), then compare. You can use some simple subtraction to calculate the total thickness above the wafer.

Lou Jost
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Re: Accuracy of Correction Collar scale markings?

Post by Lou Jost »

Thank you both for the advice...Returning it would be a long a difficult process from here, so I will try to live with it and see if I can loosen it up.

Scarodactyl
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Re: Accuracy of Correction Collar scale markings?

Post by Scarodactyl »

Better at least get a partial refund, unless it was a real steal I guess.

Lou Jost
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Re: Accuracy of Correction Collar scale markings?

Post by Lou Jost »

Better at least get a partial refund, unless it was a real steal I guess.
It was claimed to have been in working order, and it was sold with no return option. I opened a case with eBay because it was defective, and the seller offered to refund 50% and let me keep it. I will probably do that and try to make it work.

viktor j nilsson
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Re: Accuracy of Correction Collar scale markings?

Post by viktor j nilsson »

Odds are pretty good you'll get it working, and that it turns out to be a good deal. I've freed up three Nikon objectives with siezed correction collars: a a Plan 40x 0.55 LWD, a CF Fluor 40x 0.85 and a CFN Planapo 40x 0.95. The planapo was just this week. I bought it "as-is for parts" on eBay for a good price ($150), and that is how objectives like that should be sold, as it's impossible to know how they perform without using the correction collar. Even minute changes in the cc setting has a huge effect on image quality. I felt pretty good about the odds, though, and with a tiny bit of work I now have a fully functioning objective for a fraction of what they'd normally cost.

In both cases, it was enought to add a few tiny drops of light oil (from the Nye hobbyist kit) along the edge of the collar, heating for a while with a hair dryer, and letting it sit to soak in for a few days. I was actually surprised to see how good it got. The Fluor could be turned with quite a bit of force when I got it, and is still a little uneven. But the planapo was completely stuck, but is now working better than the fluor. Definiately worth trying before disassembling.

But if that hadn't worked, it is often fairly stratightforward to disassemble them a bit and give it a good clean. The CC mechanisms that I have seen have not required assembly of the lens stack, just the outer barrel.

Lou Jost
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Re: Accuracy of Correction Collar scale markings?

Post by Lou Jost »

Thanks for that encouraging information! Will any light oil work? My choices here in the Andes are fairly limited.

viktor j nilsson
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Re: Accuracy of Correction Collar scale markings?

Post by viktor j nilsson »

I am not an expert on oil/grease compatibility, but I would guess that any light synthetic oil would work fine. Sewing machine oil should do fine.

Lou Jost
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Re: Accuracy of Correction Collar scale markings?

Post by Lou Jost »

Thanks, it turned out to be easy to take apart and clean. It works so lightly now that I think I could move it just by blowing on it jejeje.

But, removing the housing spoils the calibration! The reference line for the correction collar scale is on the housing, which has no set screws to define a correct axial orientation. It rotates freely. I'll have to recalibrate it myself as well as I can.

PeteM
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Re: Accuracy of Correction Collar scale markings?

Post by PeteM »

Lou, at least some correction collars have physical stops at the high and low points. If yours does, it should be possible to get close by centering the marked range and the actual range. That could be good enough given that actual observation is best to tweak things once you're in the ballpark.

Lou Jost
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Re: Accuracy of Correction Collar scale markings?

Post by Lou Jost »

Pete, that would have worked. But I just did the calibration: measured a coverslip thickness, then optimizing the correction collar setting, and then rotating the housing so that the reference line matched the measured coverslip thickness. All is well!

Scarodactyl
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Re: Accuracy of Correction Collar scale markings?

Post by Scarodactyl »

Congrats! Sounds like you got a nice deal in the end.

Lou Jost
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Re: Accuracy of Correction Collar scale markings?

Post by Lou Jost »

And now I know how to fix Nikon correction collars! I have another high-end objective with a similar problem, and I can see it uses the same system. I'll fix that today.

viktor j nilsson
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Re: Accuracy of Correction Collar scale markings?

Post by viktor j nilsson »

Super happy to hear it worked out for you! Well done.

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