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Condenser settings?
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dragonblade



Joined: 18 Oct 2014
Posts: 148

PostPosted: Tue Feb 27, 2018 9:11 pm    Post subject: Condenser settings? Reply with quote

I'm a bit puzzled by online instructions for setting the height of the condenser. They seem to contradict the workings of my own microscope. There's a youtube video that recommends raising the condenser close to it's maximum height when using the 40x objective. Though when I do this, the image becomes pretty dim. And another online source states that lowering the condenser leads to a darker image. Though when I lower my condenser, the image becomes brighter instead.

As you see, I'm still struggling with basic microscopy skills.
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GaryB



Joined: 29 Jul 2016
Posts: 521

PostPosted: Tue Feb 27, 2018 10:33 pm    Post subject: Reply with quote

I had the same issues myself. Some of it depends on your lighting, is it built in? It would help to know what scope type you are using.

The general gist is that with in built lighting, focus on a specimen, close the iris down on the light source (field iris/diaphragm) and focus the condenser to this iris. You should see the iris opening come into focus. When the iris is in focus by raising or lowering the condenser (not the objective) then the condenser is in the correct position. Open the field iris so it's just out of view.

Remove an eyepiece and close the condenser iris until it's a little way into view looking down the eyetube. This is Kohler illumination. Your system may have a different setup.

I'll see if I can find additional pics to help

https://www.youtube.com/watch?time_continue=125&v=dYP0uBxE0AA

these are the steps and it's basically the same for all scopes, even those using a desklamp. The specifics will depend on your particular microscope.
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dragonblade



Joined: 18 Oct 2014
Posts: 148

PostPosted: Tue Feb 27, 2018 11:13 pm    Post subject: Reply with quote

Gary, thankyou for the detailed reply. Very insightful. I'm using an Indian-made monocular microscope with a built-in LED light - exact model is the RM-600. Do I close the iris down all the way or only partially? If I open the iris all the way again, would the previously adjusted condenser height still be correct? Also, do I need to perform this step every time I change an objective? Another youtube video suggested that different objectives required different condenser heights / settings.

I wasn't even aware that my microscope has a condenser iris - is that separate from the main iris?

Edit: Ive just watched the video again. I think the condenser iris might be the main iris - the one that I normally use. I don't think my microscope has a field iris. With the lack of a field iris, is there some other technique that I can use to adjust the condenser to the right height?
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GaryB



Joined: 29 Jul 2016
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PostPosted: Tue Feb 27, 2018 11:42 pm    Post subject: Reply with quote

could you snap a pic of the scope and post it here, I could then give a better informed answer.

In the meantime here's where the terminology fits. Your scope may or may not have some of the following...

Field iris. This is an iris that is attached to the lighting system. It's normally placed where the light exits the base. This limits light flooding the subject causing glare. Ideally, opening size should be adjusted to suit objectives, though many don't go through the whole thing every time you swap objectives. With a 40x objective it'll need to be mostly closed to be visible for the condenser to see and focus on it, once in focus, open it until it's just outside the view as you look down the eyepiece.

Condenser iris. Usually at the base of the condenser. Used to increase contrast and limit glare. Normally closed down just so it shows a little when looking down the eyetube with no eyepiece.

Condenser should be focused on the field iris (if you have one), this sets the correct position relative to light source to give even illumination.
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GaryB



Joined: 29 Jul 2016
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PostPosted: Wed Feb 28, 2018 12:31 am    Post subject: Reply with quote

ok, looked at the scope and it doesn't have a field iris so we'll take a different track. The light included with it is probably a very poor choice. Do you have a mirror like the one shown in the picture here?



If so, a better lamp would be something like this



With this type of standard desklamp I have a 60W led bulb and some black card with a hole which acts like a field iris. Place the lamp about 10 inches from the microscope, aim the mirror at the light through the hole in the card, then focus the condenser on the edge of the hole in the card. You'll need to fiddle about with the mirror to get the thing aimed properly but once you get the card in focus, move the mirror back so you just see the light and not the edges.

It sounds complicated but you can do it all looking through the scope while doing it. Have the condenser iris open while doing this, then once it's set, close the iris a little, you'll see things get more contrasty. Too much and you'll kill the resolution. This will give you near optimal lighting.

I use this lamp with my antique Bausch and Lomb brass microscope. It looks a lot different to yours but it's parts and operation are essentially the same and this light works very well.
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dragonblade



Joined: 18 Oct 2014
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PostPosted: Wed Feb 28, 2018 12:58 am    Post subject: Reply with quote

Gary, thanks for those instructions. Yea I admit the LED light with mine is not the best but I prefer it over the mirror when using the 40x lens - brighter image. Can something similar be done (with a cutout hole in cardboard) when using the LED light? Don't suppose I can place a piece of cardboard with a cutout hole on or close to the base?
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Pau
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Joined: 20 Jan 2010
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Location: Valencia, Spain

PostPosted: Wed Feb 28, 2018 2:14 am    Post subject: Reply with quote

Dragonblade,
All this depends of the condenser and illumination setup, and also of the magnification (in fact the NA) of the objective.

The standard instructions to get the condenser regulation right are for standard microscope design: collimated illumination (almost parallel rays) and an Abbe or superior condenser.

When teaching the microscope use with Oly CH clone microscopes (Abbe condenser but non collimated light source and no field aperture diaphragm) my quick instructions to get it right (critical illumination) was to raise the condenser on top, lower it "just a bit", full open the diaphragm, focus the sample and close the diaphragm just until begins to darken "a bit".
Not very precise but it has worked well with hundreds of students

If you post details and pictures of your microscope illumination and condenser it could help
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GaryB



Joined: 29 Jul 2016
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PostPosted: Wed Feb 28, 2018 2:17 am    Post subject: Reply with quote

Yes you can. You can place anything over the light as a reference to focus on. It doesn't need to stay on there, it'll just be a focus reference for the condenser. The issue there is that you'll effectively be focusing on the diffuser and that becomes very close to *critical lighting* which is not as smooth and uniform as Kohler. I don't know what your current light looks like so I'm guessing based on common designs I'm aware of.

Anyway, a small lamp with a 60W equivalent LED bulb (most supermarkets carry them) will give a very bright even illumination with a 40x that'll probably produce a better overall image as it'll set the condenser properly which is needed for good image quality. If you get the look you're happy with using your existing light, all well and good. If not there is a cheap alternative Very Happy
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dragonblade



Joined: 18 Oct 2014
Posts: 148

PostPosted: Wed Feb 28, 2018 4:56 am    Post subject: Reply with quote

Thankyou both of you for the tips. I do have a desktop lamp around somewhere that I could use in combination with the mirror. Would be interesting to try it out and see how it goes. Annoying thing about removing the mirror is that it's almost impossible to avoid hitting it with another component of the microscope. You've got use a bit of force to remove it and it's such a narrow space. I wouldn't be surprised if there's a scratch or two on the mirror as a result.

I'm not sure of the wattage of the bulb in this lamp though. It's really bright - maybe too bright for viewing through a scope. Good thing 60 watt bulbs are readily available.
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GaryB



Joined: 29 Jul 2016
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PostPosted: Wed Feb 28, 2018 3:15 pm    Post subject: Reply with quote

Well the reason I was saying a 60watt equivalent LED bulb is because they have very good frosted bulbs which give excellent smooth light with no hotspots. They cost a little more but it's well worth it for microscopy.

good luck!
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dragonblade



Joined: 18 Oct 2014
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PostPosted: Wed Feb 28, 2018 11:45 pm    Post subject: Reply with quote

Gary, I'm curious if the distance between the desktop lamp and the cardboard iris is critical or is there some leeway involved? Thanks again.
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GaryB



Joined: 29 Jul 2016
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PostPosted: Thu Mar 01, 2018 1:28 am    Post subject: Reply with quote

There is leeway, it's mainly so that when you focus in front of the bulb, the lamp bulb itself is not in focus with the specimen. When the lamp and specimen are in focus at the same time it's called 'critical lighting' and can be distracting because you can't always tell if you're seeing the lamp frosting (or even the filament in a standard bulb) or the specimen when observing. So when you focus on the the iris (or hole in this case) it's just to defocus the lamp and give a smooth, even background for your specimen. It gives a clean uncluttered view so all you are seeing is the specimen on the slide.

The distance is not critical but I'd put it an inch or two away from the bulb. The size of hole you'll need will be a process of widening until it's clear of the view when looking through the scope. Start off with a hole about an inch across, focus the condenser on it, then cut the hole bigger until you clear the view. No other adjustments of lamp, mirror or condenser position are necessary. Finally, adjust the condenser iris until it just starts to darken the view a little then enjoy!

Hope this helps get the results you want.
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dragonblade



Joined: 18 Oct 2014
Posts: 148

PostPosted: Thu Mar 01, 2018 1:53 am    Post subject: Reply with quote

Gary, thanks for the explanations. I guess I could fit a cardboard iris within the microscope itself and make sure that it's a distance away from the built in light source (provided there's enough space.)

Focusing with the condenser iris wide open and then closing down makes sense. This is similar in principle to photography where you preferably focus with the aperture wide open where the depth of field is shallowest. However on the microscope, do you have to open the iris back up every time you refocus? I don't mind this in photography when using old, manual lenses but doing it in microscopy sounds like a bit of a drag.
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GaryB



Joined: 29 Jul 2016
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PostPosted: Thu Mar 01, 2018 2:12 am    Post subject: Reply with quote

No, set the iris and leave it there. Once these things have been set there is only some minor things that need adjusting but mostly you can leave things alone. In the more dedicated individuals here, there are constant adjustments being made to optimize each objective by adjusting the field and condenser iris's to match but for many people, most things can be left alone unless you notice something amiss. For example, with a 10x objective, the hole in the card might be a bit small, so you just flip it out the way and flip it back when you are using the 40x again. A relatively minor annoyance.

I wouldn't try to fit the card to the microscope itself, the condenser may not focus that close. To test things, use something like a pencil and try to focus the condenser on it, this will let you know how close the iris can be to the condenser. Put the pencil tip in the line of sight, If you can focus on the pencil, you can place the iris there. Keep moving it back until you can focus on it.
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dragonblade



Joined: 18 Oct 2014
Posts: 148

PostPosted: Fri Mar 02, 2018 9:49 am    Post subject: Reply with quote

Good tip about using the pencil. I assume the further away the iris is from the light source, the better? Out of curiosity, roughly how far away would a field iris be from a microscope's light source?
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