Jump to content


Photo

Is Köhler Illumination a significant advantage?

  • Please log in to reply
8 replies to this topic

#1 cloud_cover

cloud_cover

    Viking 1

  • -----
  • Posts: 563
  • Joined: 17 Aug 2010
  • Loc: Restaurant at the End of the Universe

Posted 10 June 2014 - 04:30 AM

Hello!
I'm thinking of getting a biological microscope for home observation and to interest the kids who will soon start schooling.
Looking at these 2 models:
OMAX 40X-1600X PLAN Biological Compound Microscope with Kohler Illumination S...

OMAX 40X-2000X Lab LED Binocular Compound Microscope with Double Layer Mechan...

I realize one uses PLAN objectives while the other does not but I'm wondering if the Kohler illumination is sufficient cause to get the more expensive model, or would the basic model suffice.

On the other hand, a new Olympus CX21-LED with Plan objectives is about $1000. Hmmmm..... but that's too pricey for me.

#2 Hikari

Hikari

    Viking 1

  • *****
  • Posts: 940
  • Joined: 05 Jan 2011
  • Loc: Maine, USA

Posted 11 June 2014 - 08:56 PM

Kolher illumination is fundamental in a compound microscope. However, if this is for fun and for the kids, I am not sure if it would be worth it. If you find the microscopy addictive and want to really pursue it, then it might be better to invest in a good instrument. And in that case, I would then recommend the business and industrial section of ebay for a biological or research microscope. Depending on the vintage, they can be very reasonable.

#3 cloud_cover

cloud_cover

    Viking 1

  • -----
  • Posts: 563
  • Joined: 17 Aug 2010
  • Loc: Restaurant at the End of the Universe

Posted 11 June 2014 - 11:04 PM

Thanks! The trouble is I don't live in the USA and my electricity supply is 240V, which would blow most of the vintage microscopes being sold as their transformers are strictly 110V only, so unless I want to add on another bulky AC voltage transformer (which is not the best thing to have with inquisitive and meddlesome children about!), most of the ebay scopes, including all the Nikon/Zeiss/Olympus scopes are out of the question for me!
I've also dropped by a few local warehouses selling second hand microscopes - the condition of the objectives and sometimes the body itself can be fearsome and unlike a telescope most ebay sellers will not post photos of the objective lens itself.
Was looking at their phase contrast kit (Omax) - pricey but results can be interesting, if I learn to do it right :)
For me I've always loved using optics - be it telescopes or microscopes although I haven't learnt the art of preparing good slides just yet :)

#4 Hikari

Hikari

    Viking 1

  • *****
  • Posts: 940
  • Joined: 05 Jan 2011
  • Loc: Maine, USA

Posted 12 June 2014 - 12:57 PM

I was not suggesting you get a used microscope until you had some time with the model you want to buy. Manufacturers do make microscopes for other countries in the world and you can get microscope working at 240V.

However, if you do want techniques like phase contrast then you need a sub-stage condenser and kohler illumination. I still would go for the simple model and see if you get the microscope bug. If it is addictive, then look into buying a better scope.

#5 EJN

EJN

    Vanguard

  • *****
  • Posts: 2241
  • Joined: 01 Nov 2005
  • Loc: 53 miles west of Venus

Posted 12 June 2014 - 02:37 PM

Looking at these 2 models:
OMAX 40X-1600X PLAN Biological Compound Microscope with Kohler Illumination S...

OMAX 40X-2000X Lab LED Binocular Compound Microscope with Double Layer Mechan...


I am beginning to really like LED illumination, it doesn't get hot and cook the
specimen like Halogen bulbs do.

What really caught my eye was the first scope listed has a quintuple nosepiece,
having the 20x objective is really useful. If they made a trinocular version
I would consider buying one, but alas apparently they do not have that.

I took this picture of a diatom with a 60 year old Bausch & Lomb microscope using
an LED illuminator, and it looks like it loses nothing vs. Kohler illumination.
This was taken with a 97x oil-immersion objective.

Attached Files



#6 Hikari

Hikari

    Viking 1

  • *****
  • Posts: 940
  • Joined: 05 Jan 2011
  • Loc: Maine, USA

Posted 13 June 2014 - 03:11 PM

LED in and of itself does not mean there is no kohler illumination. Your 60-year old scope I assume still uses it sub-stage condenser and so you still have kohler illumination.

#7 NGC704

NGC704

    Explorer 1

  • -----
  • Posts: 98
  • Joined: 18 Jul 2011
  • Loc: League City, Texas

Posted 10 September 2014 - 10:13 AM

"Student grade" microscopes with simple illuminators give fine views, all other things being equal. Upgraded "Kohler illumination" means capable of giving better views; in reality it'll be everything from not noticeable, to dramatically improved, just depends on what you're doing and/or what you're looking at. However, "Kohler" implies or outright indicates a general upgrade as well: better lighting system in general with more features, and often other upgrades as well, such as next level of optics, a mechanical stage, etc.

 

Tell ya what's funny: Practically NO microscope made today gives "true" Kohler illumination, but rather a modified (simplified) version at best -- which, then, means it is not Kohler, but critical, or Nelsonian illumination. I won't get into all that here, but suffice it to say that a microscope that claims "Kohler" should include one particular feature that's very good to have; namely, a field diaphragm in addition to the condenser diaphragm. This allows you to adjust the size the light bundle for each objective to suit its numerical aperture, or N.A. But this is a finer point, and not (really) applicable to beginners.

 

So ... is it worth it? Nobody can answer that but you since it depends on what you can afford, etc. But if it means the difference of whether you can get a scope or not, then it's a no-brainer: by all means get one without, and never look back! I would consider a mechanical stage much more "worth it", myself.

 

Guess you could say it's kind of like a clock drive on a telescope, where it's awful nice to have, and advanced users tend to consider it indispensable; but it certainly isn't necessary, especially for a beginner.


Edited by NGC704, 10 September 2014 - 10:16 AM.


#8 Hikari

Hikari

    Viking 1

  • *****
  • Posts: 940
  • Joined: 05 Jan 2011
  • Loc: Maine, USA

Posted 14 September 2014 - 11:18 AM

Tell ya what's funny: Practically NO microscope made today gives "true" Kohler illumination, but rather a modified (simplified) version at best -- which, then, means it is not Kohler, but critical, or Nelsonian illumination. I won't get into all that here, but suffice it to say that a microscope that claims "Kohler" should include one particular feature that's very good to have; namely, a field diaphragm in addition to the condenser diaphragm. This allows you to adjust the size the light bundle for each objective to suit its numerical aperture, or N.A. But this is a finer point, and not (really) applicable to beginners.

 All of the research instruments in my lab are Kohler. There is no research microscope made today (and for the last 75 years or so) that does not use Kohler. Critical illumination simply is not used as every single dust spot in the illumination pathway would be shown in the specimen plane. 

 

The field stop, just like the field stop in a telescope, does not change the N.A. of the system. The aperture stop changes the N.A. of the condenser. The field stop is to control flare in the system.



#9 NGC704

NGC704

    Explorer 1

  • -----
  • Posts: 98
  • Joined: 18 Jul 2011
  • Loc: League City, Texas

Posted 30 September 2014 - 10:54 PM

I'll gladly step aside and let a more knowledgeable microscopist take the lead. May take a seat in the audience and ask a few questions?

 

Could you clarify what the field stop and aperture stop is on a microscope, and how they translate to telescope optics? 

 

Also, I have never been able to understand Numerical Aperture to any meaningful degree, wonder if you'd care to expound upon that a little?








Cloudy Nights LLC
Cloudy Nights Sponsor: Astronomics