MicrobeHunter.com Microscopy Forum

Clear step by step instructions

https://www.olympus-lifescience.com/en/ ... ieldsetup/

I've looked at this before and having used DF for decades cannot for the life of me figure out how such a confusing instruction document ever got to print.

Presumably this is for the instruction of those that already don't know how to properly do DF. For those of us that are already conversant with the technique, we can muddle through it and understand what they are trying to say but for a novice, I could see it being downright confusing. They start off with an illustration of an oil cardioid type of DF condenser, right smack dab in the center of text that has nothing to do with that condenser. The text is about using a DF stop in a standard condenser, which you establish Koehler illumination on. Then it goes on to say that if you are using a condenser dedicated to DF, remove the first condenser and put in the DF condenser. Why do you need to establish Koehler illumination with the first condenser, if you are going to take it out and put in a DF condenser? And all of this blabber frames a picture of a condenser( Fig. 1) that isn't even relevant to the discussion, just so the confused reader can get even more confused. Worse yet, they don't even reference figure 1 in the section 8 confusing points of instruction later, when the illustration might be relevant.

In the section on High Magnification Transmitted Darkfield Microscope Configuration they again recommend establishing Koehler with a BF condenser then removing that condenser and replacing it with an oil immersion DF condenser. I presume that the reason for establishing Koehler is in order to get reasonable centering?, because once you remove and replace condensers, you no longer have Koehler, nor can you even determine if you have it. They follow up with instructions about adjusting the condenser based on the bright spot appearing in the view and then a paragraph later they just happen to mention that "if an oil immersion condenser is used without oil, light will not emerge from the condenser". Since almost all high N.A. DF condensers are oil immersion, it might have made sense to recommend oiling an oil immersion condenser two paragraphs earlier, when they had newbies searching for a bright circle of light , where none could possibly exist.

There may be aspects of these instructions that are specific to Olympus, such as the recommendation that an iris diaphragm need only be employed with objectives over 1.2 N.A. I haven't found that to be the case, even when I have used systems( such as Olympus) where that is supposed to be the case. Typically down around 1.0 is the case, sometimes lower. With the Reichert Univar and some other microscopes utilizing the same family of optics, they built iris diaphragms into all objectives with an N.A. over .75 and were careful to keep the N.A. of certain objectives below that, so DF could be more easily obtained.

This is a pretty clumsy instructional manual. Needs to be rewritten

75RR wrote:Clear step by step instructions

https://www.olympus-lifescience.com/en/ ... ieldsetup/

Thanks 75RR for the link.. Very clear and concise...

BillT

apochronaut wrote: ↑

Tue Mar 19, 2019 12:52 pm

This is a pretty clumsy instructional manual. Needs to be rewritten

Great point, unfortunately, the dark field technology seems to have been phased out and no one has bothered to perfect the manual.

It's just uploaded content?Creating more content and a route map to it.
Chewing gum for the eyes maybe.

No one has bothered to update the handbook for the dark field technologyretro bowl, and the technology itself seems to have been abandoned.

Dark field is far from abandoned but there are stumbling blocks to using it in it's pinnacle form. DF stops are easy to make and use with a standard condenser but are only really practical up to a 20X objective. Using a 40X is possible but requires very high precision. An oil immersion DF condenser makes DF with 40X and up easy but to achieve high resolution with an oil immersion objective you must have a method of lowering the N.A. to about .2 N.A. below that of the condenser ; so typically in todays world that means , an iris diaphragm in the objective, and that means $$$.
There is an off the shelf 160mm 100X 1.25 achromat with an iris available from india, often paired with an oil cardioid condenser for sale. Could be adapted to most 160mm tube microscopes and the price is attractive. Less than 200.00, even as kit.

apochronaut wrote: ↑

Tue Dec 13, 2022 5:33 pm

Dark field is far from abandoned but there are stumbling blocks to using it in it's pinnacle form. DF stops are easy to make and use with a standard condenser but are only really practical up to a 20X objective. Using a 40X is possible but requires very high precision. An oil immersion DF condenser makes DF with 40X and up easy but to achieve high resolution with an oil immersion objective you must have a method of lowering the N.A. to about .2 N.A. below that of the condenser ; so typically in todays world that means , an iris diaphragm in the objective, and that means $$$.
There is an off the shelf 160mm 100X 1.25 achromat with an iris available from india, often paired with an oil cardioid condenser for sale. Could be adapted to most 160mm tube microscopes and the price is attractive. Less than 200.00, even as kit.

I think 77rr wants to express his complaint about this manual with chaotic logic. If you have a clearer description, please don't hesitate to give me some advice.