Olympus BX stage keeps drifting down, "focus shifting".

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adamski
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Joined: Fri Oct 21, 2016 11:36 am

Olympus BX stage keeps drifting down, "focus shifting".

Post by adamski »

Hi guys,

I am wondering if any one encountered this problem. I am doing some time-lapse on BX frame, the problem I have is that after few minutes stage drifts down slowly, obviously I lose focus on a subject. I tired to tighten the tension wheel but this does not fix the problem. It seems like stage is moving through fine focus rather than coarse.
Has any one found solution to this issue? Is this normal? Thanks.
Last edited by adamski on Thu Oct 08, 2020 11:33 am, edited 1 time in total.

pbraub
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Joined: Fri Feb 02, 2018 1:23 pm

Re: Olympus BX stage keeps drifting down.

Post by pbraub »

Hi,

drift through the fine focus can happen if the fine focus shaft is not properly lubricated. It needs (quite stiff) dampening grease. Unfortunately Olympus does not tell you which.

Maybe try to lock the fine focus drive in place. Pushing a hefty weight (e.g. a metal block) with some rubber to the side of the drive should be enough to prevent movement.

Peter

enricosavazzi
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Re: Olympus BX stage keeps drifting down.

Post by enricosavazzi »

Just in case, check the friction/brake on the focusing rack before you do any maintenance. This lever may be set too loose. The lever that controls friction is located between the left coarse focus knob and the stand.
--ES

pbraub
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Re: Olympus BX stage keeps drifting down.

Post by pbraub »

enricosavazzi wrote:
Sun Oct 04, 2020 2:56 am
Just in case, check the friction/brake on the focusing rack before you do any maintenance. This lever may be set too loose. The lever that controls friction is located between the left coarse focus knob and the stand.
I agree 100% with enricosavazzi (but i think this is what adamski ment with "I tired to tighten the tension wheel "). Just in case - double or triple check this. And also check if fixing the fine drive in place solves the issue. Pulling the drive apart should be the absolute last thing to do.

This is the friction brake: (please excuse the messy microscope)
PXL_20201004_115608462.jpg

adamski
Posts: 33
Joined: Fri Oct 21, 2016 11:36 am

Re: Olympus BX stage keeps drifting down.

Post by adamski »

Thanks guys for replies,

The wheel on the right is tighten to the maximum, I can barely move the stage up or down. I also taped fine focus wheel with tape but the problem still exists. I found very interesting article "Correcting Focus Drift in Live-Cell Microscopy" on microscopyU. I have the feeling that the problem is to do with heat and expansion etc. I will do bit more checking. It would be interesting to do some testing on your scopes, setting 100x objective and leave it for 10 minutes see if you get a drift too?

Many thanks :)

rjlittlefield
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Re: Olympus BX stage keeps drifting down.

Post by rjlittlefield »

Thermal drift does seem a likely problem.

What are you doing to get the equipment stabilized before starting a photography session?

--Rik

Macro_Cosmos
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Re: Olympus BX stage keeps drifting down.

Post by Macro_Cosmos »

Do you have a dial indicator and one of those temperature thermalcouples? You can use both to try and nail the problem. Set the dial indicator to the stage and make sure it's tightened, then also monitor the temperature. Could be a fun little experiment.

pbraub
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Re: Olympus BX stage keeps drifting down.

Post by pbraub »

adamski wrote:
Sun Oct 04, 2020 1:41 pm
It would be interesting to do some testing on your scopes, setting 100x objective and leave it for 10 minutes see if you get a drift too?
What lightsource do you use? (LED/Hal/etc.)
Epi or transmitted?
Constant illumination or only on during camera exposure?

Pau
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Re: Olympus BX stage keeps drifting down.

Post by Pau »

If drifting down continues over the time (not just until the temperature is constant) it will not be due to thermal expansion.

I don't know if it can happen with BX models but with CH and BH if someone has forced to turn the fine focus knobs in opposite senses they unscrew from the axis and get loose and this leads to the stage going down because it is maintained by the pressure of the bolts inside the fine focus knows over a wavy washer.
Test if it is your problem doing it gently (don't force them), turning the right knob clockwise while maintaining the position of the left one with the other hand.
Pau

adamski
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Joined: Fri Oct 21, 2016 11:36 am

Re: Olympus BX stage keeps drifting down.

Post by adamski »

I will do some tests and will reply with my findings, many thanks.

Lou Jost
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Re: Olympus BX stage keeps drifting down.

Post by Lou Jost »

Turn the microscope sideways or upside down and see if the drift changes direction.

pbraub
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Re: Olympus BX stage keeps drifting down.

Post by pbraub »

Lou Jost wrote:
Tue Oct 06, 2020 6:03 am
Turn the microscope sideways or upside down and see if the drift changes direction.
Im not sure if this will work - i think the bx stages are "preloaded" by gravity. I cannot really turn my scope on the side though. sorry.

I did a quick and dirty test today and the focus shifted a relevant amount during a 15 min break. more than i expected. Will retry tomorrow if i find some time under more defined conditions.

adamski
Posts: 33
Joined: Fri Oct 21, 2016 11:36 am

Re: Olympus BX stage keeps drifting down.

Post by adamski »

Ok, so I can confirm that problem is to do with temperature. I am using normal kohler illumination. When I use microscope "cold" without light there is no shift. I am certain that also changes in ambient temperature will affect the focus. During my tests focus not only was shifted down but also up by a micron or two on couple of occasions. So yes, the only way to do time laps is by monitoring the process and adjust focus accordingly. Maybe if I left microscope running for a while then maybe things would settle? Not sure, haven't tested that yet.

Many Thanks!

Lou Jost
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Re: Olympus BX stage keeps drifting down, "focus shifting".

Post by Lou Jost »

Theoretically, it would reach an equilibrium eventually, but it could take a long time, a few hours at least, and it would require that the surroundings not change temperature much.

enricosavazzi
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Re: Olympus BX stage keeps drifting down, "focus shifting".

Post by enricosavazzi »

The following information does not help if you already have a BX series microscope, but it is related to thermal drift so it might be interesting nonetheless.

A couple of years ago, I ended up ordering an Olympus AX70 stand. It ended up being lost in the mail and eventually returned to the sender, so I never had a chance to test it. However, one of the things that stood out in the online documentation was that the stand had been designed to avoid thermal expansion caused by the halogen light source (apparently by using low-thermal-expansion alloys as well as thermally insulating the stand from the light source and from the conduit and optics carrying light through the base of the stand). So Olympus was aware of problems with thermal expansion and had reduced or eliminated them in the AX series, which was/is their top-level series.

Converting the stand to dimmable LED should reduce the problems with thermal expansion, since a 10 W LED produces much less heat than a 100 W halogen bulb, and with some illumination techniques and magnifications all one needs is a LED dimmed to just 2-3 W. Not using any of the filters built into the base of the microscope (which get hot when inserted into the illumination path) might also help. This is especially true of ND filters, but even the daylight (blue) and green filters do warm up significantly.

A few days ago member praub had asked "What lightsource do you use? (LED/Hal/etc.)". I cannot see that this question was answered in this thread.
--ES

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