MicrobeHunter.com Microscopy Forum

Hello to you all,

As a phase contrast kit is pretty expensive I've decided to make my own or at least to find a cheap effective solution and I 've got the first results :

I bought on ebay some Phase contrast objectives (LOMO Ph x10 ; x20; x40; x90) and yesterday I received the X10 and X40.

they are in good state and as my microscope cant produce a proper Köhler illumination setting I had no other choice but make a phase annulus painted with black pen on a glass plate put on my lighting system and set the height of the condenseur in order to project a matching size image of the annulus at the back focal plan of the phase objective.

With the x40 it was quite easy as the annulus can be quite large and despite the lack of precision of my first trial the results i got are pretty encouraging.

Judge by yourself..

now I'm trying to draw more precise annulus and especially for the X10 its not easy as it has to be rather small.

The problrm with my Bresser is that i tried to ajust it in Köhler illumination by removing the frostes glass but the focal length of the lens isnt short enough to allow me to project the filament image on the condenser diaphragm and also I found out that the diaphragm of the condenser IS NOT at the focal plan of the lens of the condenser !!!

If some of you own a BRESSER with KÖhler could you check if the diaph is at the focal plane because it seems in this range of microscope that the condensers are made the same...

To be continued...

Pretty good results for a DIY anulus. Regarding your problem setting up Köhler illumination after removing the frosted glass, you can either use the condenser height adjustment knob to focus the field diaphragm within the field of view of a focused test subject (with a closed condenser aperture diaphragm). If you have a phase telescope (or a pin-hole ocular) you can use them to look at the back focal plane to focus the filament of the light bulb there (again, using the condenser height adjustment).

there's no field diaphragm on my microscope unfortunately but the idea of checking for the filament image on the back focal plan is a pretty good one ; i'll try tonight to see if its possible ; if not there's another option : trying to image the condenser diaph on the back focal plan and then i'll know if its possible to put my annulus at this location into the condenser.

thanks a lot for the tip

I've just made some new experiments

1) i've transformed a finder (sort of tiny astronomical telescope used to aim at stars and search quickly in the sky and orientate the telescope) into a phase telescope and aim at the phase plate inside the phase objective.

result a : I cant project an image of the filament on the back focal plan of the objective : focal length and geometry of my microscope dont allow it

result b : indeed when i adjust the height of the condenser i can get a somewhat sharp image of the phase annulus and set the correct size to match and also center both elements precisely.

result c : if instead of the annulus i put a piece if transparent ruler i can measure directly the diameter and width of the annulus of the phase plate inside the objective and then draw it properly on the piece of transparent plastic

result at the eyepiece : when everything is well set the vision is mindblowing!! I had never seen protozoa like that before. The vision is quite magical. (I'm posting a video of a vorticeli "having fun" with a chilomonas on youtube).

ps: without the frosted glass the image is much brighter but there are much diffraction artefacts and détails are blurred compared to the vision WITH the frosted glass where the background is darker but the gain in definition is greater.

At least it shows one important thing : phase contrast is possible event without Köhler illumination as long as you have a proper condenser.

https://youtu.be/w-HdZBGWl_4

here is the video

I've just measured the diameter i'm suposed to draw and the visual results are even better : better contrast and resolution better too (i'll post a video soon)

Hello chrisimbee-nice kludge to get it working-is it possible to posts photos of the objectives used (especially the back side) I’m starting to understand some of the symbols relating to different properties on lomo objectives -looks like positive phase from the slight white halo around objects-they made fluorescent versions as well and would like to see what they look like-have a couple of “luminescence” bright field objectives and they do have an quite a different look to standard BF objective-would love to see what the “luminescence” phase versions look like. If you can’t afford DIC then phase is definitely second best and one thing I’ve learned in life is second best is still way better than 3rd or 4th best! I’m a firm believer in the aesthetics of phase being an asset in itself-it tames super white background (less headaches) and frankly its just a super cool optical trick! I never get sick of phase!
Have fun with it
Ross

Hi Ross

here are the photos

PS : i cant correct the order of the photos but i guess you'll be able to know wich is wich

I re upload this one in case it didnt work (i dont know why you cant correct the order but never mind)

If phase annulus is moved closer to condenser bottom lens (for example it can be stuck there using double-sided tape), DIY phase images should improve further.

Agree with Fan. The image of your phase diaphragm should be conjugate with the phase annulus in the objective , when the condenser is focused perfectly on the sample. Where you are placing the phase diaphragms is more typical of the ideal location of a DF occlusion. Typically, phase condensers are optimized to work at maximum N.A. dry and focused in a Köhler condition for phase, yet also work as an oil immersion condenser for B.F., although not all fullfill that requirement.
With a focused subject on the stage, the diaphagm and phase annulus in conjugate focus , the condenser iris diaphragm should also be focused enough to see the leaves . When this condition is met, the condenser will also be adjusted for Köhler, if such exists for the microscope or, it's best case scenario if not; assuming the illumination system has been made in such a way as to project an acceptably dispersed circle of light at the image plane.

thanks , i know all of that but my microscope cannot be in kohler mode ; its impossible as this model isnt designed for a kohler illumination.

The lamp position in respect to the position of the lens of the illumination system makes it impossible : the focal lengh isnt adequate and the image of the filament (when i search for it with a screen and after i remove the condenser) is at a distance above the stage where i'm supposed to put the glass plate preparation. So i cant produce the filament image at the focal plan of the condenser.

Plus the fact that Bresser condenser isnt set properly either : the diaph isnt at all at the focal plan of the condenser lens either!!!

Even if I tried to use double tape to put my annulus at the right place (wich could improve even more the device as the image of the annulus would project exactly at the back focal plan of the objective where the phase plate is) the filament image wont be at the right place as in köhler .

Still the great thing is that so far with the x40 it works already pretty well :

https://youtu.be/2Fi6uhKK1cw

but there could be 2 solutions on my microscope to get kôhler :
1) adding another field lens to project the filament at the right place and buy a proper condenser 37mm wich has its diaph at exactly the focal plan of the condenser.

2) unsrew the microscope from its base to put some piece of would in order to get more height for the illumination system to project the filmament image at the focal planof the condenser.

3) buy a new genuine kohler microscope but i suspect this ine isnt either a true Kohler :
I mean it seems that the same condenser as mine and if so the diaph isnt at the right place either..

The field diaph they addes helps into kohler and if i had one on mine I can too focus the image of it but still the place where to put the field diaph is a precise place.

The only thing i have no information about it the focal lengh of the lens in the illumination system ; it could different than mine (= much shorter) and then could produce an image of the light source at the required place.

I have bought on ebay a spare condenser ....and i'm expecting it.. but i think i should probably buy a proper one.

to be continued

Amoeba with CP LOMO x40 Ph+ but this time I made a phase annulus drawn on the blue filter wich if frosted and meant to be put in the filter holder under the condenser..

It works fine too