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Possible to hit cover slip with objective using fine focus?

 
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dragonblade



Joined: 18 Oct 2014
Posts: 135

PostPosted: Sun Dec 17, 2017 4:03 am    Post subject: Possible to hit cover slip with objective using fine focus? Reply with quote

Tonight, Ive been viewing a rotifer on a slide with water from a bird bath. As always, I'm using the golden rule of only using fine focus with the higher powered objectives. However, I'm observing something unusual which I haven't noticed before. I'm using the 40x objective and at a certain point during the fine focus knob's travel, I can see everything shift position (left / right.) Then everything shifts back to it's original position when I turn the focus knob in the opposite direction. I never notice this when focusing with a camera lens in the real world. And it's happened a number of times tonight.

I'm not hitting the cover slip with the objective, am I? Viewing from the side, it's impossible to tell because the gap between slide and objective is so narrow. If I was making physical contact, would I be able to feel it or hear an audible sound? I hope I'm not doing harm to the front glass element of the objective.
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dragonblade



Joined: 18 Oct 2014
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PostPosted: Sun Dec 17, 2017 5:01 am    Post subject: Reply with quote

After I reach that point (when everything shifts position) I can still continue to focus / rotate the focus knob. It's not reaching a stop / dead end so perhaps it's not hitting the cover slip.

By the way, this microscope did not come with any microscope lens cleaning tissues. It did come with a soft, orange cloth. Do you reckon it would be okay to use this for cleaning the front glass elements of the objectives?
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Pau
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Joined: 20 Jan 2010
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Location: Valencia, Spain

PostPosted: Sun Dec 17, 2017 8:05 am    Post subject: Re: Possible to hit cover slip with objective using fine foc Reply with quote

dragonblade wrote:
...I'm not hitting the cover slip with the objective, am I? Viewing from the side, it's impossible to tell because the gap between slide and objective is so narrow.

Likely you are.

The gap will be very small but if present you could be able to see it with very lateral light

Quote:
If I was making physical contact, would I be able to feel it or hear an audible sound? I hope I'm not doing harm to the front glass element of the objective.

You will hear a sound when you crack the cover or the whole slide. Usually it doesn't damage the objective although it could, be careful to avoid contact of the front lens with the liquid, if it happens clean it as soon as possible.

Quote:
After I reach that point (when everything shifts position) I can still continue to focus / rotate the focus knob. It's not reaching a stop / dead end so perhaps it's not hitting the cover slip

It depends of the microscope design, with some ones the same stop works for both focus while with others it doesn't, even the fine focus may not have any limit, is the fine focus able to travel the whole distance. You can test it with a lower power objective after setting adequately the limit for the coarse focus as I explained you in another thread.

Cleaning objectives must be done with lens cleaning paper wet with the adequate solvent (this can vary between makers, alcohols are adequate in many cases)
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dragonblade



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PostPosted: Sun Dec 17, 2017 6:52 pm    Post subject: Re: Possible to hit cover slip with objective using fine foc Reply with quote

Thankyou for the reply.

Pau wrote:

Likely you are.


It's likely I'm what?

Pau wrote:

It depends of the microscope design, with some ones the same stop works for both focus while with others it doesn't


What I mean is if say the objective is hitting the cover slip (making physical contact with it) the stage will not be able to move up any further. Theoretically, it would stop when the objective hits the cover slip, at least that's what I assume. I wouldn't think it would be physically possible to rotate the focus knob any further. Whereas I could rotate the focus knob past the point where I noticed the left / right shift of the subjects.

Or perhaps the stage would be able to move past the point where the objective hits the cover slip since there would be some space between the cover slip and slide (after all, there is a small volume of water in between.) So yea I guess it could continue to move some distance past the cover slip before hitting the slide.

At the time, I was trying to focus on some vegetation in my water sample. If the objective was hitting the cover slip, it seems odd that that is unavoidable when focusing on a particular object in my sample.

Pau wrote:

even the fine focus may not have any limit, is the fine focus able to travel the whole distance.


As I mentioned in that other thread, there seems to be a built-in stop limit for the fine focus knob. Just hope it’s set correctly.
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Pau
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Location: Valencia, Spain

PostPosted: Mon Dec 18, 2017 1:25 am    Post subject: Re: Possible to hit cover slip with objective using fine foc Reply with quote

dragonblade wrote:
Pau wrote:

Likely you are.


It's likely I'm what?

You're hitting the cover slip with the objective tip
Because your 40X is almost for sure spring loaded, it is applying pressure to the cover and so displacing and/or squashing the subject although not breaking the slide while the spring is working, if you pass this point it will break

Quote:
Pau wrote:

It depends of the microscope design, with some ones the same stop works for both focus while with others it doesn't


What I mean is if say the objective is hitting the cover slip (making physical contact with it) the stage will not be able to move up any further. Theoretically, it would stop when the objective hits the cover slip, at least that's what I assume. I wouldn't think it would be physically possible to rotate the focus knob any further. Whereas I could rotate the focus knob past the point where I noticed the left / right shift of the subjects.


I have no experience with your model, but don't assume so much, better test it to get your own experience

Quote:
Or perhaps the stage would be able to move past the point where the objective hits the cover slip since there would be some space between the cover slip and slide (after all, there is a small volume of water in between.) So yea I guess it could continue to move some distance past the cover slip before hitting the slide.

At the time, I was trying to focus on some vegetation in my water sample. If the objective was hitting the cover slip, it seems odd that that is unavoidable when focusing on a particular object in my sample.

Those objectives have very small working distance, is the slide is too thick you will have this situation for sure even with the best microscopes, and also the image of the parts situated far of the cover will be degraded for optical reasons.

Quote:
As I mentioned in that other thread, there seems to be a built-in stop limit for the fine focus knob. Just hope it’s set correctly.

Again, test if there is such stop and, if present, if you can regulate it. Hopes give nothing practical while experience does.
Anyway this is not tragical, just with practice and care you can live without that stop.
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