About COL
Re: About COL
It is possible to achieve Phase and COL without a Phase Telescope, though it is a bit hit and miss, what with squinting down the eyepiece tube or trying to decide by the effects if it is properly centered.
I would get a Phase Telescope if you can, not only does it make alignment for Phase and COL quick and painless but it is also useful to check the condition of the objective.
"The 'Phase telescope' is so called because it resembles a miniature telescope which is designed to focus on close distances so as to be able to inspect the phase annuli alignments in phase contrast microscopes. This device is also useful for other illumination techniques and I'd imagine that most microscopists would find it of great use. It can also be used to examine the state of the internal glassware of objectives and to check on optical collimation too. In photomicrography it can be used to spot blemishes such as dust, smears and scratches in the optical system which can spoil an otherwise successful image."
Link to this article (Making a Phase Telescope): http://www.microscopy-uk.org.uk/mag/ind ... phase.html
Link to Micscape COL article:
http://www.microscopy-uk.org.uk/mag/ind ... pjcol.html
I would get a Phase Telescope if you can, not only does it make alignment for Phase and COL quick and painless but it is also useful to check the condition of the objective.
"The 'Phase telescope' is so called because it resembles a miniature telescope which is designed to focus on close distances so as to be able to inspect the phase annuli alignments in phase contrast microscopes. This device is also useful for other illumination techniques and I'd imagine that most microscopists would find it of great use. It can also be used to examine the state of the internal glassware of objectives and to check on optical collimation too. In photomicrography it can be used to spot blemishes such as dust, smears and scratches in the optical system which can spoil an otherwise successful image."
Link to this article (Making a Phase Telescope): http://www.microscopy-uk.org.uk/mag/ind ... phase.html
Link to Micscape COL article:
http://www.microscopy-uk.org.uk/mag/ind ... pjcol.html
Zeiss Standard WL (somewhat fashion challenged) & Wild M8
Olympus E-P2 (Micro Four Thirds Camera)
Olympus E-P2 (Micro Four Thirds Camera)
-
apochronaut
- Posts: 6327
- Joined: Fri May 15, 2015 12:15 am
Re: About COL
The prerequisite for both of those is the possession of a phase condenser. You can achieve very good oblique illumination also, with a condenser fitted with an oblique or offset iris. Sometimes these show up on ebay for very little or are attached to very inexpensive older stands.
Re: About COL
Also: someone on this forum (I think it was zzffnn) mentioned that you can achieve COL by using a darkfield stop and close the condenser iris to leave just a narrow annulus between the condenser iris and the darkfield stop. This assumes that the darkfield stop is located very close (usually right below) the condenser iris.
Re: About COL
Microman2,
Have you compared COL with offset oblique? Offset oblique is easier to set up and image may look better (more 3D) than COL. Take a look at 75RR's image comparison here, between COL and offset oblique (his "oblique 4/6"):
viewtopic.php?t=1860
Some microscopists use an intermediate state between COL and darkfield to get the best comprise among contrast, resolution and camera exposure. That might be the most valuable application of COL. Because high resolution darkfield is technically challenging and hard on cameras. That intermediate state between COL and darkfield is easier, at very high NA, than pure darkfield. Though compared to offset oblique, such is still a bit more difficult to get right.
It should not be too difficult though, at <= objective NA 0.65, to get COL without a phase telescope. Above NA 0.65, centering / aligment becomes difficult and phase telescope does help to produce better-looking COL. Offset oblique does not need to be centered precisely, though you still want to monitor objective back lens.
Were you asking about field lens or field diaphragm? If your light source is evenly diffused without field lens and powerful (e.g., some high-power LED with diffuser lens), then you do not have to have field lens either. Field diaphragm is helpful to cut down stray light/reflections and increase contrast. At high NA > 0.65, when good contrast is required, field diaphragm does help. But if you sacrifice a little resolution by closing down condenser iris very slightly, it can help with contrast.
Have you compared COL with offset oblique? Offset oblique is easier to set up and image may look better (more 3D) than COL. Take a look at 75RR's image comparison here, between COL and offset oblique (his "oblique 4/6"):
viewtopic.php?t=1860
Some microscopists use an intermediate state between COL and darkfield to get the best comprise among contrast, resolution and camera exposure. That might be the most valuable application of COL. Because high resolution darkfield is technically challenging and hard on cameras. That intermediate state between COL and darkfield is easier, at very high NA, than pure darkfield. Though compared to offset oblique, such is still a bit more difficult to get right.
It should not be too difficult though, at <= objective NA 0.65, to get COL without a phase telescope. Above NA 0.65, centering / aligment becomes difficult and phase telescope does help to produce better-looking COL. Offset oblique does not need to be centered precisely, though you still want to monitor objective back lens.
Were you asking about field lens or field diaphragm? If your light source is evenly diffused without field lens and powerful (e.g., some high-power LED with diffuser lens), then you do not have to have field lens either. Field diaphragm is helpful to cut down stray light/reflections and increase contrast. At high NA > 0.65, when good contrast is required, field diaphragm does help. But if you sacrifice a little resolution by closing down condenser iris very slightly, it can help with contrast.