Macroscopes - some musings

[palaephatus]

Zoom stereo- and macroscopes are strange animals, when compared to compound microscopes.

Based on a post by Scarodactyl the urge to dig out an old, and due to formatting problems never posted, text was rekindled.
 
For compound microscopes the numerical aperture (NA) is given exclusively by the objective. For zoom instruments it depends also on the zoom range and the entrance pupil of the zoom system. This is only rarely specified from the manufactures; indeed, the only tabulated specifications I have been able to find is for the Nikon HR Plan Apo 1x lens for the Nikon SMZ1500 stereo microscope (http://www.microscopyu.com/articles/ste ... intro.html) and as supplementary material in an article for the Olympus MVX10 with the MVPLAPO 2xc objective. Scarodactyl has provided data for the Leica Z6 APO and Z16 APO macroscopes and the MZ16/MZ16A stereo microscopes.

In general, the NA of zoom microscopes depends on the dimensions of the Common Main Objective (CMO), as well as on the dimensions of the zoom system. This is what Leica has elegantly implemented in their FusionOptics microscope, combining two optical zoom paths of different dimensions, emphasizing resolution and DOF respectively.
 
In the table below I have used the information on the Nikon HR Plan Apo 1x, together with the very useful spreadsheet on camera resolution and relay optics by Charles Krebs. The resolution is calculated as the number of pixels needed to cover the diagonal (22, 23 or 24mm, depending on the instrument), using 2 pixel/detail - in practice one may choose a higher pixel/detail ratio.

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                    Zoom factor                 NA             Pixels/diagonal
---------------------------------------------------------------------------------------

Nikon SMZ1500          0.75                   0.023              2413  
HR Plan Apo 1x         1                      0.029              3043
                       2                      0.052              2727
                       4                      0.085              2230
                       6                      0.104              1819
                       8                      0.118              1548
                       10                     0.128              1343
                       11.25                  0.131              1222
 

As can be seen, the resolution from a top-of-the-line stereomicroscope of yesteryear is not that great, at the highest magnification. Also, one can see that it is very interesting to know the NA as a function of zoom ratio, as one can enter into the region of empty magnification (8-11,25x magnification).

For the Olympus MVX10, subjected to the same calculatory treatment, one can see that the best performance is in the middle magnification region - something that may well also be true for other macroscopes. Conceivably this is a characteristic of the zoom magnification system rather than the objective. For the MVX10 the sweet spot is from 1-4 times zoom factor.

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	            Zoom factor                 NA             Pixels/diagonal
-----------------------------------------------------------------------------------------
Olympus MVX10         0.63                   	0.070              5829 
MVPLAPO 2xc           0.80                     	0.070              4590
                      1.00                      0.110              5770
                      1.25                     	0.140              5875
                      1.60                     	0.190              6230
                      2.00                     	0.230              6033
                      2.50                    	0.295              6190
                      3.20                	0.380              6230
                      4.00                    	0.475              6230
                      5.00                    	0.495              5193
                      6.30                 	0.495              4122


 

The Leica MZ16/MZ16A with the Planapo 5x/0.5 objective is likewise treated below.

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	     Zoom factor                 NA             Pixels/diagonal
-----------------------------------------------------------------------------------------
Leica MZ16/MZ16A      0.71                   	0.084              2962 
Planapo 5x/0.5        1.00                     	0.110              2754
(10447243)            1.60                      0.170              2660
Factor 4x             2.00                     	0.200              2503
FN21                  2.50                     	0.240              2404
                      3.20                     	0.300              2347
                      4.00                    	0.340              2128
                      5.00                	0.400              2003
                      6.30                    	0.450              1788
                      8.00                   	0.490              1534
                     10.00              	0.500              1252
                     11.50              	0.500              1089

Note: According to the data sheet for the Leica MZ16/MZ16A with the Planapo 5x/0.5, this combination vignettes at a zoom factor below 3.2. This is not reflected in the calculated numbers, however, attention is drawn to the fact that the Leica MZ16/MZ16A are stereomicroscopes with two optical paths. The vignetting presumably disappears if the objective is mounted coaxially with either of the optical paths.

That is not a function of the objective is supported by the data that the Leica MacroFluo 6.3:1 or 16:1 (the same as the Leica Z6 APO (6.3:1 Zoom) or Z16 APO (16:1 Zoom)) - apparently does not vignette with the eyepieces HC Plan 10×/25. (11507808) when used with the Planapo 5x/0.5 (10447243).

Below is a table encompassing some of the current macroscopes for which data can be readily found. This table now includes the Leica Z6 APO and Z16 APO instruments, where specifications were kindly provided by Scarodactyl.  Data are for the instruments used at the highest possible magnification.

It should be noted, that Zeiss in at least one place have claimed an NA of 0.50 with a FOV of 1.5 mm for the PlanNeoFluar Z 2.3x, however, a manual for the instrument has not been found, and consequently this entry into the table should perhaps be treated with care. If the information is correct, an NA of 0.50 is seen with a zoom factor of 6.67, yielding a total magnification of 15.18 (**). That the highest zoom-factor is not conductive to the highest possible pixel count may also be why the Nikon AZ100 fares comparatively poorly in this exercise.
 
For comparison is included some of the often used Mitutoyo objectives as well as the (rather expensive) Mitutoyo HR Plan Apo 5x and 10x, which fares exceedingly well in this comparison. According to Mitutoyo literature, these objectives covers an image circle of 30mm (in practice for some more, ***).

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Objective               Zoom factor                NA           Pixels/diagonal         WD              FOV@10x ocular
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Nikon AZ100:
AZ Plan Apo 0.5x              8                   0.05             1311               54 mm            5.50 mm (22mm)
AZ Plan Apo 1x                8                   0.10             1311               35 mm            2.80 mm (22mm)
AZ Plan Fluor 2x              8                   0.20             1311               45 mm            1.40 mm (22mm)
AZ Plan Apo 4x                8                   0.40             1311               20 mm            0.70 mm (22mm)
AZ Plan Fluor 5x              8                   0.50             1311               15 mm            0.55 mm (22mm)
 
Olympus MVX10
MVPLAPO 0.63x                 6.3                 0.15             3965               87 mm            5.54 mm (22mm)
MVPLAPO 1x                    6.3                 0.25             4163               65 mm            3.49 mm (22mm)
MVPLAPO 2xc                   6.3                 0.50             4163               20 mm            1.74 mm (22mm)
 
Leica Z6
Planapochromat 1x             4.5                 0.117            3100               97 mm            5.10 mm (25mm)
Planapochromat 2x             4.5                 0.234            3100               39 mm            2.68 mm (25mm)

Leica Z16
Planapochromat 1x             11.5                0.112            1161               97 mm            2.00 mm (25mm)
Planapochromat 2x             11.5                0.224            1161               39 mm            1.04 mm (25mm)

Zeiss Axio Zoom V16
PlanApo Z 0.5x                11.2                0.125            2448               114 mm           4.10 mm (23mm)
PlanNeoFluar Z 1x             11.2                0.25             2448               56 mm            2.00 mm (23mm)
PlanApo Z 1x                  11.2                0.25             2448               60 mm            2.00 mm (23mm)
Apo Z 1.5x                    11.2                0.37             2416               30 mm            1.40 mm (23mm)
PlanNeoFluar Z 2.3x           11.2                0.57             2427               10.6 mm          0.90 mm (23mm)
PlanNeoFluar Z 2.3x **        6.67                0.50             3575               10.6 mm          1.50 mm (23mm)
 
Mitutoyo FS70 ***
Plan Apo HR 5x                1                   0.21             4807               25.5 mm          4.80 mm (24mm)
Plan Apo HR 10x               1                   0.42             4807               15 mm            2.40 mm (24mm)
Plan Apo 5x                   1                   0.14             3205               34 mm            4.80 mm (24mm)
Plan Apo 7.5x                 1                   0.21             3205               34 mm            3.60 mm (24mm)
Plan Apo 10x                  1                   0.28             3205               34 mm            2.40 mm (24mm)
Plan Apo 20x                  1                   0.42             2404               20 mm            1.20 mm (24mm)

The above comparison may be considered crude and I would very much welcome both critique as well as information on instruments omitted above. Further, it would be most useful with links to texts, setting out the intricacies of modern zoom macroscopes. At the end of the day, much more than the NA of system influences the results.

From the above table can also be seen that a macroscope such as the Nikon AZ100 has a very consistent, if not particularly impressive performance. A slightly more modern instrument, the Olympus MVX10 macroscope is likewise consistent in performance, with a vastly better resolving power. In all the zoom instruments above, the front objectives are of the infinity type and the zoom system enlarges a portion of the "image" projected by the front objective.

One intriguing question therefore is to what extent the front objectives from macroscopes are good over larger areas; i.e. if a front objective can be directly coupled to an ordinary large aperture tele-lens in the role of a tube lens. Incidentally, the preceding should also hold true for front objectives of Common Main Objective (CMO) stereomicroscopes of the infinity type.

Placing an infinity CMO stereo microscope objective in front of a medium tele-lens (135mm f2.0) seems to indicate that this will work. The threaded part of the CMO objective was in this, highly unscientific, test made to rest on the UV-filter while the 135mm lens was focused at infinity. It is currently not known to me if optical parts of the zoom system works as correcting tube lenses, however, as it is a zoom system I am inclined to think that all corrections are made in the objectives.

Looking into using CMO objectives in homebuilt systems may prove a worthwhile exercise.

[Pau]

Hi palaephatus,
This is an interesting post.

I would like to know the source of your AZ100 data, in any case the analysis only at 8X can be too detrimental of the instrument capabilities (of the commented instruments it is the only one I have). I'm preparing a post about it but I always am slow. In the meantime I can say that the 8X zoom range may be nice for visual work, taking low size images or to find and frame the subject but for good quality photomicrography 2X to 4X are the the practical limits, at 1X the corners are somewhat poor and at 6X-8X there is clearly empty magnification (with the Plan Apo 4X 0.40), this is clearly understandable looking at the final magnification in relation with the NA.
I don't think that the zoom could be limiting much the NA from 2X upwards (it clearly does at 1X)

I don't have other macroscope front objectives but the AZ100 ones have a pretty limited quality image circle, so putting them in front of a tele lens like a 135mm is not practical, even on a 200mm it shows pretty poor corners on APSC (but an excellent center!). The 1X Apo of the Wild M5A is worse. I suspect that those wonderful high NA objectives only have a good quality center being the periphery only used for low magnification.
Would like to see experimental info of other models.

[Scarodactyl]

Mm, one of my favorite topics for sure.
Leica does provide NA ranges for both the Z6 and Z16 with 1x and 2x objectives, but only min and max. A 200mm tube lens gives a 1.25x multiplier to nominal mag, and with one it can cover aps-c (though with a little corner shading at min mag, which might be possible to mitigate with a different setup than my current one).

That was compiled before they added the 5x/0.5 objective to their lineup. Note the obvious, that the z16 just gives up a ton of resolution it doean't have to, so that's at least one system where the objectices can deliver a much wider high resolution FoV than they are allowed to.

In the literature for their stereo fluorescence 'fluocombi' system Leica gives granular data for the older mz16 by zoom range, though only with the above mentioned 5x/0.5 adapted onto it


Other than that though it's true most makers stick to giving max NA and/or lp/mm.

I did a personal review of macroscopes a while back, though I haven't tightened it up yet. I think the olympus mvx10 has the best specs, followed by the zeiss axiozoom (though the fully motorized/software controlled nature of this one means it will likely never be very suitable for amateur use), then the z6/Apozoom, then the az100, finally the z16. That said, practically speaking I have only ever had and tried a z6 and a z16 (plus the original m400 makrozoom setup from Wild) and can't speak to the others directly. The combination of lower resolution and shorter working distance on the az100 is particularly puzzling.

Overall I like my z6 an awful lot, and as an all-rounder combining comfortable viewing and examinatio with the mag range that mitutoyo objectives do poorer on it's a complementary addition. Speaking practically it is probably overkill for the type of photography I do (gems and minerals, where routine stereo microscopes are still the most prevalent tool).

[palaephatus]

Hi Pau,

The data on the AZ100 is from the "AZ100 technical handbook.pdf", the copy of which looks as if scanned from paper. According to the datecode I downloaded my copy in 2015.

Attached to this post is a picture of a table from p40 - for some reason I cannot attach the pdf-file, which is at any rate 12.2 mb.

I agree that the numbers for the AZ100 are too conservative, and would very much like to see some more detailled data on the variation of the NA of the telescope system.

Palaephatus.

[palaephatus]

Hi Scarodactyl,

What exactly is the 1.25x Y-tube? Looking in the sales material made me none the wiser, but possibly better informed (or overlooking the obvious). It looks as if the FOV with 10x oculars at 1x zoom factor is 18.4 mm.

Excellent catch on the MZ16 data(!), which will be made into a separate table.

Palaephatus

[Scarodactyl]

The y tube has a prism which splits the light in two and terminates in a mount that accepts a Leica stereo microscope head (which has a 200mm tube lens in each light path). It is a creative, weird (and dare I say it, dumb) solution to putting a head onto them. I assume they do it that way because they don't have a compound head with a non-compensating tube lens, and they already had the prism made for adapting compound objectives onto stereo microscopes. It does suggest a weird lack of care though, since having the light split in half before it can ever reach a camera is not a good arrangement, worse if it has a fixed 50/50 split for the photo port. Better to put it on an M420/M400 head or a Nikon infinity head.
The nominal mag being lower is weird, and goes back to the original m400. I think the zoom objective may have been designed as a standalone camera lens before the head with a 200mm tube lens was added. Otherwise it would just be stupid to mark the mag that way and then slap "1.25x" onto the head, and Wild engineers were no dummies. But no guarantees on the history there.
So just to be clear, the 18.4mm FoV is at the 1.0x zoom setting, not at 1.0x mag. At .8x zoom setting it fully covers the 23mm Fn of the provided eyepieces, though it will cover much more in practice.

[palaephatus]

The original post has now been updated with information for the Leica Z6 & Z16 macroscopes, as well as for the Leica MZ16F & MZ16FA stereo microscopes.

Palaephatus

[Scarodactyl]

Thanks! These calculations are very handy, and the results are a bit different from my expectations. I'm a bit surprised how well the z6 matches up to the axiozoom in particular, and how well the macroscopes match up to the m plan apos in general.

[Lou Jost]

I have the big heavy Leica PlanApo 2x front objective. It is chroma-free, I don't see any CA in the image. When attached to a tube lens, the center is perfect but there is what I would describe as exaggerated perspective, and there is a lot of distortion in the edges. I am hopeful that there is some method to make it work. Most of the image is fantastically sharp.

[Pau]

Hi Pau,

The data on the AZ100 is from the "AZ100 technical handbook.pdf", the copy of which looks as if scanned from paper. According to the datecode I downloaded my copy in 2015.

Attached to this post is a picture of a table from p40 - for some reason I cannot attach the pdf-file, which is at any rate 12.2 mb.

I agree that the numbers for the AZ100 are too conservative, and would very much like to see some more detailled data on the variation of the NA of the telescope system.

Palaephatus.

I already had got this document but still I don't understand where the Pixels/diagonal data at your table come from. The fact that 1311pix being the exactly same for all objectives seems suspiciously not experimental

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Objective               Zoom factor                NA           Pixels/diagonal         WD              FOV@10x ocular
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Nikon AZ100:
AZ Plan Apo 0.5x              8                   0.05             1311               54 mm            5.50 mm (22mm)
AZ Plan Apo 1x                8                   0.10             1311               35 mm            2.80 mm (22mm)
AZ Plan Fluor 2x              8                   0.20             1311               45 mm            1.40 mm (22mm)
AZ Plan Apo 4x                8                   0.40             1311               20 mm            0.70 mm (22mm)
AZ Plan Fluor 5x              8                   0.50             1311               15 mm            0.55 mm (22mm)
 

As I said, at 8X "resolution" on sensor is poor -lots of empty magnification- but at lower zoom settings sharpness is very good. I have no experience with the SMZ1500 but I have with the SMZ1000 with Plan Apo 1X and for photography the AZ100 is vastly superior.

22mm is the FN of the AZ 10x22 eyepieces but the 0.6X phototube is meant for direct projection on 2/3 with 11mm diagonal sensor, this is equivalent to FN of 18.3mm at the nominal magnification

[fufkuns]

I'm resuming this post after a few years' break, because the topic of macroscopes particularly interests me.
My work is as a botanical researcher and I frequently use stereoscopic microscopes as well as a macroscope to observe and document small structures of the plants and flowers I study.
In our research center we use a Leica Z16 APO macroscope with a 1x Planapo objective. I am lucky enough to have the same instrument at home, which I bought some time ago for a price that I would define as ridiculous. I present to you a photograph of it in its current configuration. Compared to when I purchased it, I changed the focus drive to have one with coarse/fine control (an unfortunately expensive beast), indispensable in my opinion for z-stacked photography.

I understand that it is possible to adopt planapochromatic objectives of greater magnification compared to the classic 1x, but in this configuration the Z16 APO has the advantage for my applications of reaching the type of magnifications that I use most frequently (around 100), but of allowing me to at the same time to document general structures with lower magnification simply by using the zoom function, without having to replace the objective.

For readers of the forum who are more interested in photographic topics, I first want to offer you a comparison between the result that can be obtained with the completely apochromatic system of the Z16 APO macroscope (above) and that obtainable with a common steroscopic microscope (below, in this case an M80 with 1x Plan lens, without AX carrier for lens decentration), both taken at 70x magnification. The image depicts the pollinarium of an orchid. Despite the reduction in quality due to the transformation of the original image into a JPEG of medium quality, the difference in quality between the two systems is evidently very pronounced.

With the same zoom, but at a lower magnification (about 20x), I created the following image, which shows the gynostemium of an orchid, an image that I needed to obtain with sufficient quality for a publication I have in progress.

At the minimum magnification of 7.1x (with Y-tube) I can document whole flowers:

Here, at the same minimum magnification, is a Z-stacked image produced with the Z16 of the tips of two fountain pen nibs (one of my hobbies), followed by the tip of one nib at the higher magnification.

Reading Scarodactyl's comments on the performance of the Z6 APO zoom made me curious to see how much, in the field, the image quality differs between the two systems, considering the limitation of the Z6 in terms of the maximum magnification it reaches with the Y -tube of only 45x. With a 2x or a 5x objective this limitation could be resolved, and in that case a higher resolution capacity could be of great interest.

If any of the readers have experience (and maybe some images) in respect, I would be very interested to know.

[Lou Jost]

Thanks very much for this. Those are very nice photos. I'm also an orchid researcher and have similar needs. I have the 2x Leica PlanApo but not the dedicated Z scope for it. I have been struggling to make an optical system that uses this gigantic objective. Do you know what kind of optics your scope uses above the objective?

[Lou Jost]

Ah Franco! I just noticed your name on the photo. Hi! Nice to see you here.

[Lou Jost]

Franco, I am puzzled by the magnifications given. I don't think they follow the conventions of this forum. We use the magnification of the image on the sensor. The "70x" image looks more like a 7x image. A 70x image on a full frame sensor would have a horizontal field of view of only 0.5mm but your scale bar shows the FOV is much larger.

[fufkuns]

Hi Lou! Great and truly unexpected to meet here each other!

Did you have the Planapo 2x for the Leica M system or that for the Z system?