A Riddle for you,: Apo or Planar ?

[Marco68]

I could try a Leica Apo 10x 0.30 lens and i could compare vs a Plan lens 10x on my Leica infinity microscope (DMLS)

Below the pics:
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https://drive.google.com/folderview? ... o_aisAjE_


3 of the above pics have name "..Lens 1" and 3 have name "..Lens 2".. Which ones are made with Apo lens ??

Ps: i am not expert enough, but I see no difference.

[Scarodactyl]

Lighting this yellow will probably suppress the differences quite a bit. I have seen similar effects when looking at insects in amber, color correction doesn't matter as much when everything is yellow.

[PeteM]

Pumpkin stem #2 looked better to me. Didn't check the others. No idea if that's "right."

The most obvious defect comparing an apo to achro objective is color fringing, which as noted above isn't as obvious with a deeply yellow-orange background.

Depending on the objective, the additional lenses and lens surfaces in an Apo objective can reduce contrast if extra care isn't taken with lens coatings and properly illuminating the subject to reduce stray light. A plan achro can look "better" in that case.

Another question -- what corrections are being used to grab this image. Do you have a compatible Leica relay lens or shooting direct to the sensor?

[75RR]

Agree that the yellow cast is negating some of the differences.

Generally the Apo would have a higher NA and therefore be capable of producing an image with better resolution (this is where subject matter and skill come in)

Also the Apo, with proper colour balance, would have a much more pleasing colour - when side by side the achromat would look a little fake.

[MicroBob]

Hi Marco,
the difference between apo and achro ist that the apo projects all clours of the spectrum in one point. This difference becomes visible when you look towards the borders of the image. The ideal object to assess this is just black and white. The achomatic objective will give an image that has colour fringes right next to the structures. A very good object to test this is a stage micrometer. You can get them from China for about 9€. A stained plant section is about the worst object for a test. A diatom slide would be an other useful test object. Or you could mount little bits of aluminium foil under a cover slip.
There are cases were a simple achromat just can't satisfy, but in most cases the image has to be compared directly to that od an objective with higher correction to clearly make the disadvantages visible. And of cause there are no strictly divided groups of objectives with nothing inbetween. Some achromats offer what others might advertise as fluorite. And in China it is already a planapochromat.

Bob

[apochronaut]

Here is how to choose an objective for an optical upgrade on a microscope. There are 10 key questions to be answered, before one pulls the trigger.

1) Is it the correct magnification you need?
2) Is it for the correct application? The specs are on the barrel or can be found in a catalogue( hopefully). Specifically, watch out for the cover slip requirement. It will be either a decimal, usually .17 but sometimes .18 a hyphen - or a 0. Decimals are for cover only, the zero for no cover and the hyphen with either.
3) Is the upgrade necessary to increase planarity? If so then, skip 4 and 5; as long as the intended upgrade is equivalent in application, N.A. and colour correction.
4) Is the N.A. sufficiently higher than the one I am already using? In this I recommend these minimums: .01 for 2-2.5X, .02 for 4-5X, .05 for 10x , .10 for 20X, .10 for 40X, .15 for 60X and .05 for any oil immersion advancements.
5) Are you moving up the ladder of colour correction categories? achromat > advanced achromat > fluorite/semi-apo > apo?
6) Will the objective fit? Is the size/thread correct or can it be easily adapted.
7) Will the objective be properly corrected for the intended system once installed? Adapters, differing lengths and proprietary corrections in the optical tube, can all play a role in throwing an objective's performance off. No assumptions based on optical tube length, fixed or infinity can be made. If you know 100% for sure or you trust someone who does, that's another thing. Sometimes, if the objective is really good and a buy, it is worth sourcing out eyepieces that are designed to work with it, thus circumventing proprietary optical corrections of your system.
8) Is the objective going to be parfocal? This may not matter to you, especially if the objective is for a special purpose and is not going to be used before or after other objectives but for most applications where the objective is ganged with others, it does. Having to watch out for that one extra long objective in the nosepiece is pretty annoying.
9) Is the upgrade worth the cost? How much difference will it make to you.
10) Did you answer all of the above questions satisfactorily?

[Marco68]

Pumpkin stem #2 looked better to me. Didn't check the others. No idea if that's "right."

The most obvious defect comparing an apo to achro objective is color fringing, which as noted above isn't as obvious with a deeply yellow-orange background.

Depending on the objective, the additional lenses and lens surfaces in an Apo objective can reduce contrast if extra care isn't taken with lens coatings and properly illuminating the subject to reduce stray light. A plan achro can look "better" in that case.

Another question -- what corrections are being used to grab this image. Do you have a compatible Leica relay lens or shooting direct to the sensor?

Hi Pete,

Your guess is right ! yes, The Lens #2 is the Apo (actually "S-APO").... sorry, you did not win anything

About the photo: I just use a Samsung S8 smartphone, hand held over the eyepiece. There is for sure some loss in quality vs what I see with my naked eyes, but for the moment I do not know how to do it better: I have made some pictures with my Mirrorless, but the quality was surprisingly even lower.

[Marco68]

Lighting this yellow will probably suppress the differences quite a bit. I have seen similar effects when looking at insects in amber, color correction doesn't matter as much when everything is yellow.

Hi, when I have used this Leica with halogen light for the first time, I was pretty disappointed by the yellow light (vs my previous LED low cost microscope). Now, I am getting used to that and I do not dislike it. If I increase the light intensity, it is getting more white but it is annoying to the view because it is too bright. I was suggested here to buy a blue filter, which I will consider.

[Marco68]

The achomatic objective will give an image that has colour fringes right next to the structures. A very good object to test this is a stage micrometer. You can get them from China for about 9€. A stained plant section is about the worst object for a test. A diatom slide would be an other useful test object. Or you could mount little bits of aluminium foil under a cover slip.


Bob

Thanks Bob,

I did not get what you mean with using "aluminium foil under the coverslip"... can you please explain more ? thanks !

[Marco68]

2) Is it for the correct application? The specs are on the barrel or can be found in a catalogue( hopefully). Specifically, watch out for the cover slip requirement. It will be either a decimal, usually .17 but sometimes .18 a hyphen - or a 0. Decimals are for cover only, the zero for no cover and the hyphen with either.

Thanks Phil,

a very good buying guide !
The S-Apo I have used has a coverslip requirement of .17. Actually I am using low cost coverslips from Amscope and on the box I can read 0,12-0,16 mm. Not sure if this deteriorate the image

[Scarodactyl]

Your guess is right ! yes, The Lens #2 is the Apo (actually "S-APO").... sorry, you did not win anything

Another twist--with Leica 's apo' means 'semi apo'. Apoer than plan but less apo than apo (and not to be confused with their stereo, the S Apo).

[MicroBob]

I did not get what you mean with using "aluminium foil under the coverslip"... can you please explain more ?

A test slide made from bits of thin aluminium foil are very similar to a stage micrometer: No colours, ligh can either pass fully or not at all. When you focus on the object plane you will /will not see colour fringes at the contrasty edges of the objects. Much easier to see than in a stained section or in a plancton sample.

[apochronaut]

Your guess is right ! yes, The Lens #2 is the Apo (actually "S-APO").... sorry, you did not win anything

Another twist--with Leica 's apo' means 'semi apo'. Apoer than plan but less apo than apo (and not to be confused with their stereo, the S Apo).

Proprietary terminology can become annoying for those that understand it and completely confusing for those that don't.

Plan; is not an objective class. It is a qualification based on flatness of field . Plan objectives by definition are achromats, unless otherwise noted, so whatever comparisons are taking place, should be in the context of objective class, without the confusion of the term plan. They are all plan within their intended application but they vary in colour correction.

[MichaelG.]

... I am using low cost coverslips from Amscope and on the box I can read 0,12-0,16 mm. Not sure if this deteriorate the image

With a top quality objective, the degradation of the image should be noticeable.

MichaelG.
.

Useful notes here: http://www.microscopy-uk.org.uk/mag/ind ... jtube.html
and here: https://www.microscopyu.com/tutorials/a ... on-collars
... with a nice interactive demonstration.

[Scarodactyl]

Plan; is not an objective class.

Nor is 'apoer' an adjective--I don't think absolute precision is necessary while joking about Leica's convoluted objective labeling.
It's pretty clesr that 's' is doing a little bit of work on that label while 'apo' is doing a lot. I'm not sure how deceptive it wpuld be in practice but it definitely seems guaranteed to confuse.