Has anyone ever used LWD condenser?

[osterport]

I came across a Motic LWD Achromat condenser, and compared it with normal abbe condensers.


However, its NA is quite low, which results in lower resolution compared with normal condensers like N.A. 0.9.

Maybe it's designed for low magnification objectives? It's quite expensive even it's Achromat. The question is, in which scenario is it useful? I had thought it's for inverted microscope, in which you can illuminate live specimen from certain distance, but it turned out to be for upright one: BA410e

https://www.tedpella.com/mscope_html/BA410e.aspx

[Phill Brown]

More useful for inverted scope.
Would work ok for lower na, maybe 2x.

[MichaelG.]

I think tis probably gives the game away:
https://www.fishersci.fi/shop/products/ ... 0/15425302

The long working distance facilitates its use with phase contrast accessories

MichaelG.
.
See also: https://moticeurope.com/en/lwd-achromat ... hragm.html
which is rather light on that important detail

[PeteM]

As you and Phill suggest, on an inverted microscope you'd want more working distance between the top (bottom side when inverted) of the condenser and the stage - in order to fit Petri dishes and the like.

For your Motic version -- lower numerical aperture condensers on an upright microscope often fill a large and even field of view - useful for, say, 1x to 4x objectives. Yours should be fine up to 40x (which is also often the upper limit for inverted scopes).

[einman]

Most dedicated inverted scopes have an na of 0.55 or less. The LWD objectives commonly used, tend to have a lower na compared to their normal distance counterparts. Thus, the two work well together. Having a condenser of 0.9 na and objectives of 0.65 or less would have no benefit.

[osterport]

I think tis probably gives the game away:
https://www.fishersci.fi/shop/products/ ... 0/15425302

The long working distance facilitates its use with phase contrast accessories

MichaelG.
.
See also: https://moticeurope.com/en/lwd-achromat ... hragm.html
which is rather light on that important detail

Thanks all for the feedback!
About phase contrast, I have a question: given the light only goes through a small hold in the phase contrast ring, does it mean the actual phase contrast objective N.A. is lower?

My phase contrast objective is 40x/0.75, I see Olympus ph objective is also 40/0.75. With LWD condenser NA 0.65, does it fit or actually phase contrast by nature is lower N.A. than what it labeled for brightfield?

[PeteM]

. . .
About phase contrast, I have a question: given the light only goes through a small hold in the phase contrast ring, does it mean the actual phase contrast objective N.A. is lower?

My phase contrast objective is 40x/0.75, I see Olympus ph objective is also 40/0.75. With LWD condenser NA 0.65, does it fit or actually phase contrast by nature is lower N.A. than what it labeled for brightfield?

It's a good question, and I suspect with two answers. Numerical aperture is usually defined as a geometric relationship - the angle of view of an objective. The wider that angle, the more light it takes in, and (usually) the higher the resolution. By that geometric definition, a .75na brightfield and a .75na phase objective have the same angle of view and the same numerical aperture. Indeed those two objectives are likely otherwise identical, except with the addition of a phase ring inside the one.

Still, the area of the objective occupied by the phase ring inside (maybe 5%?) isn't contributing to resolution. So, numerical aperture no longer fully tells the story of achievable resolution. The difference usually isn't obvious in casual observation, but in comparing something like an Olympus UPlan Fl 20s or 40x phase objective and the same objective without the phase ring - the latter is clearly a bit sharper. I especially see this with DIC.

[einman]

I agree with PeteM. The resolution of my leitz objectives with the phase ring always seem to be slightly less sharp although the na listed on the barrel is identical between the two. Also specimen thickness can result in some additional distortion when using a phase-contrast set-up.

[apochronaut]

The N.A. of a any specifiic objective with a phase annulus at it's back focal plane is the same as the same objective without the phase annulus. If that were not the case, manufacturers would mark phase objectives with a different N.A. A phase objective will produce an image with lower contrast and of slightly less definition than the same objective without the phase annulus due to a small amount of spherical aberration caused by the presence of the phase annulus, when only an ordinary illumination wavefront is used.
There is an N.A. reduction taking place during phase use by virtue of the appropriate phase condenser diaphragm inducing a condenser N.A. reduction that then causes the open portion of the condenser to overlap the annulus of the objective at the back focal plane but the objective N.A. remains unchanged. In this scenario it is the adjustment of the condenser against a fixed objective state that makes the system work.

A vaguely comparable situation but somewhat the opposite exists when higher resolution DF is used. In this scenario, the objective is also marked with it's functional N.A. but it must be either naturally or mechanically caused to be sufficiently lower than the condenser N.A., so that no light enters the objective directly. In this scenario it is the objective that is the N.A. adjustable component against s fixed state of the condenser.

In both systems a variance from the ideal will result in image formation but there will be increased scatter and uncontrolled interference in the illumination beam, such that a degradation of the image contrast , resolution and background homogeneity will form, somewhat proportionate to the degree of deviance from the ideal N.A.