apochronaut wrote: ↑Sun Jan 14, 2024 12:00 am
Diffusers always reduce contrast, that's why they are not generally regarded as a first choice option. However, in a system where budgetary requirements are prominent, in order to keep a microscope within a certain competetive price range and compactness, they are used in lieu of a more classic Köhler system, which requires more space.
Originally Köhler illumination was based on a remote illuminator, which is quite distant from the object plane. Condensers were infinity corrected . Early microscopes that applied the Köhler principle to a microscope with an integrated illuminator were mostly larger , with rear entry pumpkin lamps and an illuminator path closer to the original pattern.. The systems in more compact microscopes benefit from a diffuser but the tradeoff is a potential reduction in contrast.
This is a right place to learn and try Kohler illumination! My trouble is, the filament is pretty well focused here, there are two issues:
1. The size of the image is really not big, that's why the light path is quite narrow ( see the right side ), where we would have trouble in some cases.
![Image](https://www.microbehunter.com/microscopy-forum/download/file.php?id=33044)
2. There are some color aberration at the end of this image, which would result in c.a. in the final objective image as well. When we put a diffuser in the light path, see the right hand side, it's much better.
![Filament image comparison on condenser Iris wo and w diffuser.jpg](./download/file.php?id=33053&sid=234af6aa28b4cd9d27ec0f1165c543e9)
- Filament image comparison on condenser Iris wo and w diffuser.jpg (45.76 KiB) Viewed 2627 times
I'm just wondering, maybe a field lens can improve all these by enlarging the filament image so much that only the central part of it is delivered to condenser, no red fringe