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'Noise' when viewing at higher magnifications
Posted: Tue Jul 07, 2020 10:38 am
by Luca
Hi,
I was hoping someone might help me work out what's going on...
When I looked through the lower magnification objectives I can see things pretty well, but when I get up to the highest ones, suddenly it's like I'm trying to see through layers of murk. There are lots of dark spots that move around. I'm reasonably sure the issue is with my eyes - is it just grime on the surface of my eye? Is there anything I can do about it? Why would it happen only at the higher magnifications? I wear contact lenses as well and was wondering whether that might make it worse.
Any advice or help would be appreciated - and if someone's asked this before please do feel free to direct me to another thread!
Re: 'Noise' when viewing at higher magnifications
Posted: Tue Jul 07, 2020 1:06 pm
by MicroBob
Hi Luca,
by moving or turning individual components you can single out the source of the obstractions. It is true that imperfections and dust show up more when observing with higher powered objectives. These also show faults in eyepieces or in camera objectives. The obstractions might be mouche volantes in your eyes. The final solution would be a clean camera setup coupled to a monitor.
Bob
Re: 'Noise' when viewing at higher magnifications
Posted: Tue Jul 07, 2020 1:57 pm
by BramHuntingNematodes
Luca wrote: ↑Tue Jul 07, 2020 10:38 am
Hi,
I was hoping someone might help me work out what's going on...
When I looked through the lower magnification objectives I can see things pretty well, but when I get up to the highest ones, suddenly it's like I'm trying to see through layers of murk.
how high we talking about? I assume oil is being used appropriately?
Re: 'Noise' when viewing at higher magnifications
Posted: Tue Jul 07, 2020 2:19 pm
by Charles
Welcome Luca,
If rotating the eye pieces, objective or moving the condenser does not move the 'spots', it maybe what is termed as 'eye floaters', which usually can not be removed and which can be more pronounced with higher power optics. After awhile and focusing/concentrating on the specimen, the floaters become less apparent.
Re: 'Noise' when viewing at higher magnifications
Posted: Tue Jul 07, 2020 5:56 pm
by Luca
MicroBob wrote: ↑Tue Jul 07, 2020 1:06 pm
Hi Luca,
by moving or turning individual components you can single out the source of the obstractions. It is true that imperfections and dust show up more when observing with higher powered objectives. These also show faults in eyepieces or in camera objectives. The obstractions might be mouche volantes in your eyes. The final solution would be a clean camera setup coupled to a monitor.
Bob
Great tip! I already checked it wasn't on the slide by moving it. Now I've also tried rotating the eyepiece - not that. Can't work out how to rotate the objective (hope I'm using the right terminology). But because the spots move around when I move my head, it seems likely that the problem is on the surface of my eyes? Is that a sensible assumption?
And yes - I'm hoping to get my DSLR hooked up, and if my eyes are the problem that should solve it. There's something quite nice about looking directly through the eyepiece though, isn't there
Re: 'Noise' when viewing at higher magnifications
Posted: Tue Jul 07, 2020 5:58 pm
by Luca
BramHuntingNematodes wrote: ↑Tue Jul 07, 2020 1:57 pm
Luca wrote: ↑Tue Jul 07, 2020 10:38 am
Hi,
I was hoping someone might help me work out what's going on...
When I looked through the lower magnification objectives I can see things pretty well, but when I get up to the highest ones, suddenly it's like I'm trying to see through layers of murk.
how high we talking about? I assume oil is being used appropriately?
It happens when I use the 40x objective, with either of the two eyepieces I have, which are 16x and 5x.
No! I have no idea how to use oil, appropriately or inappropriately! What should I be doing?
Re: 'Noise' when viewing at higher magnifications
Posted: Tue Jul 07, 2020 5:59 pm
by Luca
Charles wrote: ↑Tue Jul 07, 2020 2:19 pm
Welcome Luca,
If rotating the eye pieces, objective or moving the condenser does not move the 'spots', it maybe what is termed as 'eye floaters', which usually can not be removed and which can be more pronounced with higher power optics. After awhile and focusing/concentrating on the specimen, the floaters become less apparent.
That's what I was worried it might be - so if I just persevere it might improve?
Re: 'Noise' when viewing at higher magnifications
Posted: Tue Jul 07, 2020 6:19 pm
by BramHuntingNematodes
Luca wrote: ↑Tue Jul 07, 2020 10:38 am
It happens when I use the 40x objective, with either of the two eyepieces I have, which are 16x and 5x.
No! I have no idea how to use oil, appropriately or inappropriately! What should I be doing?
Whenever the objectives get higher magnifications and numerical apertures, everything also gets more finicky and more prone to lose quality. Also, for Numerical apertures at or in excess of 1, a drop of special oil is required on the cover slip that the lens then dunks into. Without this oil, an objective with an NA of 1.25, for instance will not form a clear image at all.
On the other hand, using oil with objectives with NA below 1 is not at all recommended as the oil can seep into these lenses (they are not specially made for oil as high NA lenses are) and cloud them. 40x achromats typically have an NA of .65, so oil is probably not the issue, although if you have a 90x or 100x then it definitely would be. At .65, coverslip thickness also is not incredibly important. Maybe the lens itself has some issues?
I have plenty of floaters, and these certainly appear in microscope work, but I think it's unlikely that you never noticed them until now. You could also try adjusting your eye's iris diaphragm by turning the light brightness down.
Re: 'Noise' when viewing at higher magnifications
Posted: Tue Jul 07, 2020 6:26 pm
by Luca
BramHuntingNematodes wrote: ↑Tue Jul 07, 2020 6:19 pm
Whenever the objectives get higher magnifications and numerical apertures, everything also gets more finicky and more prone to lose quality. Also, for Numerical apertures at or in excess of 1, a drop of special oil is required on the cover slip that the lens then dunks into. Without this oil, an objective with an NA of 1.25, for instance will not form a clear image at all.
On the other hand, using oil with objectives with NA below 1 is not at all recommended as the oil can seep into these lenses (they are not specially made for oil as high NA lenses are) and cloud them. 40x achromats typically have an NA of .65, so oil is probably not the issue, although if you have a 90x or 100x then it definitely would be. At .65, coverslip thickness also is not incredibly important. Maybe the lens itself has some issues?
I have plenty of floaters, and these certainly appear in microscope work, but I think it's unlikely that you never noticed them until now. You could also try adjusting your eye's iris diaphragm by turning the light brightness down.
I haven't had my microscope for very long, so from what you're saying, and from others, it's definitely sounding like floaters. That's a great tip about turning the lights down - I will try that...
Re: 'Noise' when viewing at higher magnifications
Posted: Tue Jul 07, 2020 6:39 pm
by BramHuntingNematodes
Keep at it. I have fiddled with my microscope a long while before getting comfortable enough with it to know how to set it up instinctively.
Re: 'Noise' when viewing at higher magnifications
Posted: Tue Jul 07, 2020 9:30 pm
by DonSchaeffer
It's difficult to focus the 40x and 60x objectives. They focus very close to the subject and if the cover glass is too thick or the subject is too thick and it raises the cover glass too high, you may not be able to focus at all because you bump into the glass. If there is curvature in the subject you will get all kinds of distortion. Water on the subject or gelatine-like surfaces often cause light bending that wrecks your focus. With that said, if you focus very slowly and carefully using the fine focus knob where you can, you will find a sweet spot and the image will pop into focus. You may need to darken the condenser to get sufficient contrast. Once you have the focus you can move around the subject without having to refocus much. I really enjoy the high-power objectives because you can see extraordinary detail with them under the right conditions. However, subjects are not all suitable for high magnification.
I wouldn't use the oil immersion objective at all. I bought a 60X dry objective to replace it.
Re: 'Noise' when viewing at higher magnifications
Posted: Wed Jul 08, 2020 4:08 am
by 75RR
Luca wrote: ↑Tue Jul 07, 2020 10:38 am
When I looked through the lower magnification objectives I can see things pretty well, but when I get up to the highest ones, suddenly it's like I'm trying to see through layers of murk.
There are lots of dark spots that move around.
The fact that they move around would indicate that we are talking floaters.
Adjusting the viewing angle by changing chair height and your posture will help as well.
Re: 'Noise' when viewing at higher magnifications
Posted: Wed Jul 08, 2020 9:47 am
by Luca
Thanks all - that's incredibly helpful!