Resolution comparison between BF, Oil DF and PhC

[martinprieto]

Hello everyone,

I decided to make a (not very scientific) comparison to see how much loss of resolution have phase contrast and DF with respect to BF and I was surprised because although there is a loss, it is not as big as I expected (at least for my eyes).
I post it here in case someone might find it interesting.

For the three images I used the same objective (40X Plan Fluor Ph2) and the same camera parameters (only varying the exposure compensation to + 1.3eV for BF, -1.3eV for DF and 0.0eV for PhC). I used three different condersers: 0.9 achromatic for BF, Oil 1.20-1.43 for DF and Zernike (I think it's abbe type) for PhC.

These are the original images:

BF_original_Lo.jpg (62.65 KiB) Viewed 3702 times

DF_original_Lo.jpg (73.63 KiB) Viewed 3702 times

PC_original_Lo.jpg (92.03 KiB) Viewed 3702 times

[martinprieto]

These are grayscale crops of the diatom:

BF_Lo.jpg (135.13 KiB) Viewed 3701 times

DF_Lo.jpg (106.48 KiB) Viewed 3701 times

PC_Lo.jpg (141.63 KiB) Viewed 3701 times

[martinprieto]

And these are grayscale crops of center of the diatom:

BF_Crop.jpg (53.4 KiB) Viewed 3700 times

DF_Crop.jpg (57.51 KiB) Viewed 3700 times

PC_Crop.jpg (59.99 KiB) Viewed 3700 times

[ImperatorRex]

Nice comparison: BF and DF both resolve the punctured structure of this diatom. This is not a surprise since a lens with n.A. 0.65 should already resolve the structure of Stauroneis phoenicenteron.
PC seem not resolve the structure, this may be the result out of the smaller phase ring that does not use the full aperture of the objective? Other thoughts?

[75RR]

Nice detail on the BF image!

[Hobbyst46]

Very nice job! the DF is particularly excellent !
Please, details about the slide - self made ? how were the diatoms cleaned ? which mounting medium ?

[martinprieto]

Thank you all for the comments!

The slide is selfmade, but I have not cleaned the diatoms, I got them from diatoms.NL. I used Pleurax as mounting medium.
I'm agree with you, Jochen, In the case of PC the loss of resolution is probably due to the fact that the NA of the condenser is much lower than in BF and DF. I'm planning to take the same image in BF using a PhC equivalent NA (closing the iris until it matches the phase ring of the lens) to see if the resolution loss is similar.

By the way, just out of curiosity, does anyone know what design the Nikon Oil DF condenser uses?
I think there is only one model and it is the same for the labophot and eclipse era. It's this one:

condensador.jpg (44.5 KiB) Viewed 3633 times

I'm not sure if it is cardioid or paraboloid...
It seems that nowadays, unlike the BF condensers that do indicate the corrections, the manufacturers hardly give information about the DF oil condensers more than the NA.

[apochronaut]

If you look up inside and see a small convex mirror, it is cardioid. It most likely is cardioid, since quality manufactuers were striving for the best possble resolution for DF, coupled to freedom from ca and if they only made one type, cardioid would likely be the choice. Some companies, Bausch & Lomb in particular made both, probably because Paraboloids have slightly lower upper and lower N.A. limits and subsequent wider field coversge, so can work with 10X objectives. I haven't seen any Cardioids that can. Even with a toric lens the AO ones, can only dip down as far as 20X.

very well thought out comparison and well photographed.. No doubt as suggested the dry condenser condition , refuced the N.A. sufficiently to show a visible drop in resolution..