May need a phase contrast 'scope soon, I'm in the UK...

[mrsonchus]

Hi all, I'm thinking seriously of buying a phase-contrast 'scope to add the capability to my adventures and wondered if anyone had any advice or even one to sell - trouble is I'm in the UK so postage and import may be complicated?
Anyway, I can add this capability (new) to my existing 'scope or buy an extra 'scope dedicated to PC - whatever is my best and most affordable option....
Any ideas out there gratefully received...

[zzffnn]

John B,

With stained thin sections, do you really need phase contrast? Or are you trying to view unstained samples? Oblique does not work well enough for your unstained samples?

You may want to check university surplus sale/auction sites near you (locally, or online in UK). That could get you most for your money.

If you buy a new scope, I do recommend getting a 160TL scope with reasonably -priced trinocular option, since you already have an infinity scope.

Some stands can be used either as 160TL or infinity, depending on which head you use (infinity tube lens comes inside the scope head) - you can swap from infinity to 160TL quickly. Some Nikon and Leitz can do that, though I am not sure exactly which (probably Optiphot and Black Ortholux).

Maybe get a quote for your existing scope system first, then try to see if other approaches can beat that quote? I can help you post a "want to buy" at the other forum, if you know your budget.

I can help you pack and ship from USA too, but most likely the shipping cost would not be worth it. Here is the cheapest shipping method from USA to UK, with an online calculator:

https://ircalc.usps.com/Mobile/Default.aspx

[75RR]

Phase Contrast's forte is viewing transparent protists. I find it most useful in viewing the many denizens that live in a drop of water.
Not sure that it has much to contribute to your area - stained plant sections
Are you planning to dive into drops of water a la Jacques Cousteau?

[mrsonchus]

Phase Contrast's forte is viewing transparent protists. I find it most useful in viewing the many denizens that live in a drop of water.
Not sure that it has much to contribute to your area - stained plant sections
Are you planning to dive into drops of water a la Jacques Cousteau?

Hi 75' - no but I've recently prepared some bespoke unstained slides and have looked at them with a very basic (very, very basic....) oblique setup. Many details were visible and the contrast-enhancement of unstained (Botanical) tissue has 'caught my interest' you may say, in terms of course of Botanicals....

Being able to produce exactly the tissue I desire for myself is a huge advantage of course - I for example know from the aforementioned examination that unstained and sectioned pollen grains yield a host of extra structural information with the use of oblique - and I have similar hopes for PC.

A potentially worthwhile course of study had emerged I suspect; my first intention, as soon as I get a chance, is to learn more of simple oblique technique as possible with my current rig - the possibilities seem endless to me - the game-changer that makes this possible is my great fortune in being able to produce my own slides at will. A fascinating adventure for development later this year - I'll cover this adventure here as and when I get a chance.

Thanks for the input 75' it always helps and stimulates the old grey-matter!

[zzffnn]

^ John B,

I agree with you and suggest perfecting your oblique illumination first. At the same time, prepare a wide variety of sample slides (with different thickness). Then use the return period of that new phase kit for a comparison (with oblique), using your sample slides. Return the phase kit, if it does not perform better.

I will explain in more details in a later post.

[mrsonchus]

^ John B,

I agree with you and suggest perfecting your oblique illumination first. At the same time, prepare a wide variety of sample slides (with different thickness). Then use the return period of that new phase kit for a comparison (with oblique), using your sample slides. Return the first kit, if it does not perform better.

I will explain in more details in a later post.

Good advice old chap - any advice you can give me for basic oblique with my current rig would be really helpful if you get the time.

[75RR]

Might I suggest that you send some unstained slides to a forum member that is both close (for postage costs) and who has Phase Contrast.
If you arrange with them to take some images (perhaps in return for one of your stained slides) you may have your answer.

Note: If you photograph the slides yourself before sending them it will give you a useful benchmark.

[zzffnn]

JB,

Since you are sending me slides anyway, I will send 1-2 of your 4 unstained slides to Rod, who has phase and is very good at oblique. 75RR and gekko may also be able to do that for you. And apochronaut, if he has free time.

I don't have (and don't like) phase.

[mrsonchus]

JB,

Since you are sending me slides anyway, I will send 1-2 of your 4 unstained slides to Rod, who has phase and is very good at oblique. 75RR and gekko may also be able to do that for you. And apochronaut, if he has free time.

I don't have (and don't like) phase.

Great idea Fan, many thanks to you and 75'.

[zzffnn]

JB,

At the risk of repeating what you have already known:

Phase contrast has two issues:

1) halo produced by thick sample, which can reduce resolution significantly. You would need to figure out the tolerable sample thickness, by asking around or experimenting yourself. I am guessing 20 microns or thinner is where that tolerance lies.

Oblique does well with some thick samples, in comparison.

2) natively low resolution, due to limitation of aperture by phase rings. There are around 3 PC systems of exceptions, but all are very expensive.

Properly executed oblique will not have much resolution issue, while gaining lots of contrast.

[zzffnn]

JB,

I personally do not like the oblique mask that you used (I have tried it before).

I prefer finely graduated circle masks/stops that are accurately placed at objective back lens. At high magnification and NA, a slight misplacement or size change can change resolution/contrast, quite a bit.

Circle temple can be bought online:
https://www.amazon.com/gp/product/B0029 ... UTF8&psc=1

I would cut aluminum foil, based on circle template, then place the mask on a blank slide under condenser.Then center it and offset it for best effect.

[mrsonchus]

JB,

At the risk of repeating what you have already known:

Phase contrast has two issues:

1) halo produced by thick sample, which can reduce resolution significantly. You would need to figure out the tolerable sample thickness, by asking around or experimenting yourself. I am guessing 20 microns or thinner is where that tolerance lies.

Oblique does well with some thick samples, in comparison.

2) natively low resolution, due to limitation of aperture by phase rings. There are around 3 PC systems of exceptions, but all are very expensive.

Properly executed oblique will not have much resolution issue, while gaining lots of contrast.

Hmm, they are very good points Fan, I'm definitely going to try some oblique first - I can also use this technique with certain stained tissue. Much interesting food for though here my friend. As soon as I get a chance I'll start into a basic oblique trial with my existing rig. Thanks again for the good advice.

[mrsonchus]

JB,

I personally do not like the oblique mask that you used (I have tried it before).

I prefer finely graduated circle masks/stops that are accurately placed at objective back lens. At high magnification and NA, a slight misplacement or size change can change resolution/contrast, quite a bit.

Circle temple can be bought online:
https://www.amazon.com/gp/product/B0029 ... UTF8&psc=1

I would cut aluminum foil, based on circle template, then place the mask on a blank slide under condenser.Then center it and offset it for best effect.

That circle-template looks very handy indeed - I'm going to buy one. So, do I understand that having cut the circular mask, it's placed upon a slide then positioned beneath the condenser (presumably as close to the iris's plane as possible) as required? Do I set Kohler as usual - I'm not sure what to 'do with' the condenser's height and iris, or the filed-iris's aperture for oblique - sorry for the stupid question, oblique's quite new to me.

[zzffnn]

That circle-template looks very handy indeed - I'm going to buy one. So, do I understand that having cut the circular mask, it's placed upon a slide then positioned beneath the condenser (presumably as close to the iris's plane as possible) as required? Do I set Kohler as usual - I'm not sure what to 'do with' the condenser's height and iris, or the filed-iris's aperture for oblique - sorry for the stupid question, oblique's quite new to me.

^ Yes, the closer to condenser iris, the better.

Yes, set Kohler as usual with mask partially in, but leave condenser iris fully open first. Then keep field iris and condenser height the same, fully dial in mask and fine tune mask size/placement (by peeking down eye tube without eyepiece, looking at objective back plane). When you are happy with everything, keep them the same, then close down condenser iris very slightly to get the best balance between resolution and contrast/shadow.

Those are good questions.

[gekko]

John, you got good advice. I just want to repeat that phase contrast is generally considered an alternative to staining, and allows examining transparent, colorless objects in the living state. I would like to offer the opinion (for what it's worth) that the slight loss in resolution is only important to people who are examining high contrast objects and need the utmost in resolution from a given objective (and are using fully corrected condensers). Normally I think most people use the condenser aperture illuminating 60 to 90% of the objective's aperture to obtain adequate contrast and in that case the loss of resolution with phase contrast is not too relevant. At least that is what I think, and as usual, I may well be wrong and am open to being corrected.

[Peter]

Hi John,
Might I suggest (recommend) you look into DIC, much better/nicer than phase contrast in my opinion.
Peter.

[c-krebs]

my first intention, as soon as I get a chance, is to learn more of simple oblique technique as possible with my current rig

Everything you have gotten here is good advice. I would strongly recommend taking up the offers to give you some PC examples from your slides.

The ease with which oblique can be utilized depends a great deal on your condenser. Ironically the older condensers that had a swing-out filter tray at the bottom (very close to the diaphragm) were great for this. Newer "styles" that mount the condenser via a dovetail, and have the diaphragm quite far up from the mount are far less convenient. I'm not familiar with your microscope. Can you provide a link that shows the condenser style?

One other "seed" I'll plant... many (not all) PC condensers that use rotating "turrets" for the different annuli can be used quite effectively to obtain oblique lighting. It is not as versatile (variable) as having good access to a location below the condenser diaphragm, but extremely easy and fast.