Dark Field Condenser vs DYI Filter/Patch

[Nreekay]

Hey Folk,
I am new to this site and is my first time posting a question. Hello!! Is there a reason why someone would buy a dedicated dark field condenser instead of making their own? I cannot seem to find anything on the web.
Please let me know your thoughts
Thanks,
NReekay

[dtsh]

Hey Folk,
I am new to this site and is my first time posting a question. Hello!! Is there a reason why someone would buy a dedicated dark field condenser instead of making their own? I cannot seem to find anything on the web.
Please let me know your thoughts
Thanks,
NReekay

In my limited experience, darkfield patches work fine 90% of the time; there is some fiddling around finding the right size, but once figured out they work pretty well and deliver the desired effect. The darkfield condenser produces a nice cone and tends to work better, especially at higher magnifications.

If you're exploring it, I'd try finding a patch that works for your microscope to experiment with it; you can make your own patches if you're handy. If you like the result, I would consider a darkfield condenser an upgrade and I think it would allow one to do more with darkfield. I have two darkfield microscopes, one with a manufacturer designed darkfield stop and the other with a darkfield condenser; both work great. I think the condenser is better, but that could be a bias.

[Nreekay]

Hey Folk,
I am new to this site and is my first time posting a question. Hello!! Is there a reason why someone would buy a dedicated dark field condenser instead of making their own? I cannot seem to find anything on the web.
Please let me know your thoughts
Thanks,
NReekay

In my limited experience, darkfield patches work fine 90% of the time; there is some fiddling around finding the right size, but once figured out they work pretty well and deliver the desired effect. The darkfield condenser produces a nice cone and tends to work better, especially at higher magnifications.

If you're exploring it, I'd try finding a patch that works for your microscope to experiment with it; you can make your own patches if you're handy. If you like the result, I would consider a darkfield condenser an upgrade and I think it would allow one to do more with darkfield. I have two darkfield microscopes, one with a manufacturer designed darkfield stop and the other with a darkfield condenser; both work great. I think the condenser is better, but that could be a bias.

Thanks very much for your reply! I appreciate it. I think I might then just splurge a little and get a dedicated condenser.

[zzffnn]

DIY darkfield patches do not work well above NA 0.65 (usually 40x objective, below that patches work just fine).

Dedicated darkfield condenser has mirrored internal surface for better light efficiency and can also provide better optical correction.

[BramHuntingNematodes]

Yeah stops work ok for under the 40x, kind of iffy for an achromat 40x, unusable for a 40x fluorite or Apo or anything of a higher magnification.

Also, if you were doing diascopic fluorescence you would want a darkfield condenser to shoot maximum abs. freq onto the sample but get a minimum of it into the objective.

[Nreekay]

DIY darkfield patches do not work well above NA 0.65 (usually 40x objective, below that patches work just fine).

Dedicated darkfield condenser has mirrored internal surface for better light efficiency and can also provide better optical correction.

Thank you!
Are you able to tell me if the oil DF condenser can work with lower magnification? I’m just wondering which one to buy. Dry or oil?
Thanks again

[Nreekay]

Yeah stops work ok for under the 40x, kind of iffy for an achromat 40x, unusable for a 40x fluorite or Apo or anything of a higher magnification.

Also, if you were doing diascopic fluorescence you would want a darkfield condenser to shoot maximum abs. freq onto the sample but get a minimum of it into the objective.

Thanks very much! I’m very much just learning. I have no idea what diascoptic fluorescence is, but I’m gonna look it up right now!

[apochronaut]

The quality of dark field imaging is dependent on how highly corrected the condenser is. There are various designs of DF condensers but they all have in common the fact that they correct for ca and other aberrations better than an abbe condenser. With higher N.A.'s they are also more precise, so the image circle is centered and therefore uniformly dark.
An unfortunate aspect of DF condensers is that most of them have a limited range of N.A. under which they will work. With oil condensers that limitation is controlled by the size of the illumination circle that they create. With most, they can only fill the field of a 40X objective or greater. They will work at lower magnifications but they will only illuminate a central spot of the field. About 80% +- of the field at 20X and 30% or so at 10X. Most oil condensers will fill the field of a 25X objective, one of the logical reasons that 25X objectives exist. Certain designs such as the AO and Reichert toric oil DF condenser will fill the field down to a 10X objective.
On the other hand dry DF condensers have a limited maximum N.A. of about .90., so while they will fill the field of high magnification objectives, the fact that the aperture of the objective needs to be about .2 N.A. lower than the condenser aperture, limits their application to objectives with an N.A. of about .75 or so.

I am guessing that your 60X objective is .85, so a dry condenser will likely not work with it but it should work with the other objectives, other than the 100X.
With an oil condenser, you would have 40X, 60X and 100X.

DF is more useful at high magnifications , so you if I were you , I would buy an oil DF condenser and use a stop for the 4,10 and 20X magnifications in the abbe condenser.

[Nreekay]

The quality of dark field imaging is dependent on how highly corrected the condenser is. There are various designs of DF condensers but they all have in common the fact that they correct for ca and other aberrations better than an abbe condenser. With higher N.A.'s they are also more precise, so the image circle is centered and therefore uniformly dark.
An unfortunate aspect of DF condensers is that most of them have a limited range of N.A. under which they will work. With oil condensers that limitation is controlled by the size of the illumination circle that they create. With most, they can only fill the field of a 40X objective or greater. They will work at lower magnifications but they will only illuminate a central spot of the field. About 80% +- of the field at 20X and 30% or so at 10X. Most oil condensers will fill the field of a 25X objective, one of the logical reasons that 25X objectives exist. Certain designs such as the AO and Reichert toric oil DF condenser will fill the field down to a 10X objective.
On the other hand dry DF condensers have a limited maximum N.A. of about .90., so while they will fill the field of high magnification objectives, the fact that the aperture of the objective needs to be about .2 N.A. lower than the condenser aperture, limits their application to objectives with an N.A. of about .75 or so.

I am guessing that your 60X objective is .85, so a dry condenser will likely not work with it but it should work with the other objectives, other than the 100X.
With an oil condenser, you would have 40X, 60X and 100X.

DF is more useful at high magnifications , so you if I were you , I would buy an oil DF condenser and use a stop for the 4,10 and 20X magnifications in the abbe condenser.

Now this is excellent advice! Thank you so much for taking the time to write this all out! Very informative, and very much appreciated!
Eric

[Nreekay]

The quality of dark field imaging is dependent on how highly corrected the condenser is. There are various designs of DF condensers but they all have in common the fact that they correct for ca and other aberrations better than an abbe condenser. With higher N.A.'s they are also more precise, so the image circle is centered and therefore uniformly dark.
An unfortunate aspect of DF condensers is that most of them have a limited range of N.A. under which they will work. With oil condensers that limitation is controlled by the size of the illumination circle that they create. With most, they can only fill the field of a 40X objective or greater. They will work at lower magnifications but they will only illuminate a central spot of the field. About 80% +- of the field at 20X and 30% or so at 10X. Most oil condensers will fill the field of a 25X objective, one of the logical reasons that 25X objectives exist. Certain designs such as the AO and Reichert toric oil DF condenser will fill the field down to a 10X objective.
On the other hand dry DF condensers have a limited maximum N.A. of about .90., so while they will fill the field of high magnification objectives, the fact that the aperture of the objective needs to be about .2 N.A. lower than the condenser aperture, limits their application to objectives with an N.A. of about .75 or so.

I am guessing that your 60X objective is .85, so a dry condenser will likely not work with it but it should work with the other objectives, other than the 100X.
With an oil condenser, you would have 40X, 60X and 100X.

DF is more useful at high magnifications , so you if I were you , I would buy an oil DF condenser and use a stop for the 4,10 and 20X magnifications in the abbe condenser.

Now this is excellent advice! Thank you so much for taking the time to write this all out! Very informative, and very much appreciated!
Eric

Does the brand matter? I have an Omax scope, and so was just gonna order the Omax brand.

[BramHuntingNematodes]

The brand should be able to fit your condenser holder is the biggest concern . There is also the paraboloid v cardioid. The cardioid is more efficient, but more finicky about stuff like centration and slide thickness also more expensive. Unless you are doing a lot of immersion lens work the paraboloid or even a dry dark field condenser might be a better fit. For high na lenses you will want versions with an iris or, somewhat difficult to find, funnel stops to tamp down glare.

[Nreekay]

The brand should be able to fit your condenser holder is the biggest concern . There is also the paraboloid v cardioid. The cardioid is more efficient, but more finicky about stuff like centration and slide thickness also more expensive. Unless you are doing a lot of immersion lens work the paraboloid or even a dry dark field condenser might be a better fit. For high na lenses you will want versions with an iris or, somewhat difficult to find, funnel stops to tamp down glare.

Thanks very much, BHN! Much appreciated!

[Greg Howald]

My oil dark field condenser works at 10, 20, 40 and 100x, but the 100x objective has a built in iris. What a difference.
Greg

[Nreekay]

My oil dark field condenser works at 10, 20, 40 and 100x, but the 100x objective has a built in iris. What a difference.
Greg

Thanks Greg! I appreciate your note.
I did manage to make a couple of darkfield stops. They work well, but only at 4x and 10x, not at 40. I think I’ll just have to pick up an oil filter