Hello everybody,
I have just acquired an Olympus BHS. I have the 4 “usual” Dplan and BH2-CD 1.25 Abbe condenser. I am still waiting for a BH2-PC condenser, a A 10X PL objective and a Splan apo 10X. I also have a vertical illuminator that I would like to test with neo objectives but they are too expensive for now.
First point:
When used in brightfield mode, are the phase condenser optics any different from the BH2-CD. I have been through a documentation stating that this condenser is using Abbe optics and I am wondering if I will see any difference ?
Second point:
I would like to add darkfield capability since it’s my favorite mode of contrast enhancement. I would like to obtain good result in both direct observation and photography. Right now, I am using my own finger, witch is not the best ^^.
I have learned about the following possibility :
1-The original BH2 or BX dry and oil darkfield condenser (BH2-DCD, BH2-DCW, U-DCD, U-DCW), they seems difficult to find and very expensive.
2-The BH2-PCD condenser with one darkfield stop giving darkfield capability all the way to the x40 (or 20x I am not sure). I know it depend of the objective NA and stopping down capability.An apochronaut post give a maximum theoretical NA of 0.65 for dry darkfield.
3-The amscope DK-200 condenser, either dry or oiled condenser, directly adaptable to the BHS.
4-Any random darkfield condenser than can be more or less easily adapted to the BHS condenser holder.
5-Adding a darkfield stop to the BH2-CD or PC condenser using a removable insert (or, why not, a permanent stop)
The two next link are example of this type of insert
https://www.mccrone.com/mm/machining-a- ... condenser/
https://www.alanwood.net/downloads/olym ... inberg.pdf
My questions are:
1-Can you achieve a good darkfield with oil condenser and low power/low NA objectives ? Correct me if wrong but I guess you loose a some light doing that . Is there any others considerations that make it impractical ? Is the BHS light powerful enough.
2-Is there any difference between using an insert with removable stop and a proper dry darkfield condenser ?
3-In this video you can see the stop used to provide darkfield in the BH2-PCD: https://www.youtube.com/watch?v=QSjlgNy ... lHunsinger.
Why people that use stop in a filter tray (like I was doing with my last microscope) tend to use different stop size matching objectives NA while the manufacturer go for one big stop for all low power objectives.
4-I was also thinking about switching one of the phase insert for a homemade darkfield stop. I still haven't try the phase contrast and I am not sure how useful I will find it. Do you know if this insert is made of a special glass in the original BH2-PCD. That don’t seem the best solution to me but why not.
5-What is, according to you, the best solution for darkfield with this microscope ?
6-What about the best solution for Rheinberg or oblique, Can I expect better result by permanently modifying a BH2-CD than with the Alan Wood insert Kit ?
Sorry for this long post and my uncertain English.
Flo
BH-2 and darkfield
-
- Posts: 608
- Joined: Mon May 24, 2021 1:19 pm
- Location: Devon UK.
Re: BH-2 and darkfield
Low power condensers are the least suited to DF.
Dry will be limited to 0.85 realistically but 0.75 is a more likely limit for 1.25.
Oil would be for 0.5 to 0.9,lower na objectives will only have the centre illuminated.
There are exceptions as always.
If you have a phase telescope and a slide ringing table you can make optimised patches.
Watch glasses with rings made using a fine tip marker will allow you to measure the diameter of the patch needed.
For better contrast and resolution the outer mask should be reduced to leave a gap of around 1mm.
Patches are usually placed near the iris.
There are already threads here to search for DIY DF.
Dry will be limited to 0.85 realistically but 0.75 is a more likely limit for 1.25.
Oil would be for 0.5 to 0.9,lower na objectives will only have the centre illuminated.
There are exceptions as always.
If you have a phase telescope and a slide ringing table you can make optimised patches.
Watch glasses with rings made using a fine tip marker will allow you to measure the diameter of the patch needed.
For better contrast and resolution the outer mask should be reduced to leave a gap of around 1mm.
Patches are usually placed near the iris.
There are already threads here to search for DIY DF.
Re: BH-2 and darkfield
Thank you that help me !Oil would be for 0.5 to 0.9,lower na objectives will only have the centre illuminated.
For the DIY patch I have done some yet with no major problem. But I have never tested a dedicated dry darkfield condenser and was wondering if there is a difference in term of quality.