KurtM- I have owned and still own multiple stereoscopes. I currently own a Bausch & Lomb Stereoscope 7. I purchased multiple SZ7's before I finally settled on this one ( though I have several partial pods). The majority were either out of alignment or the optics were degraded due to use for electronic purposes. I have and currently own several Chinese models including an Amscope ZM-1t, a Ken-a-vision T22001, and sorted other brands not really worth mentioning. I currently own a swift 80 series as well as an American Optical Cycloptic 56M. My last major purchase, prior to the SMZ-U was the Nikon SMZ-2T.
With each purchase I sought to obtain better resolution as measured per specs at the lowest possible price. Specification for stereoscopes generally involves the NA and the resolution given as line/mm or micrometers. Resolution being the smallest distance discernible between two points. As manufacturers have improved their optics the NA's have increased, as well as the resolution, with the 2 being related by various equations about which I won't pretend to be very knowledgeable. In addition they have sought to increase zoom ratios as well. In short the measure of the lowest to the highest magnification.
Unless you employ a micrometer or use such items as a slide with diatoms etc. the easiest way to observe changes in resolution is by the crispness of the image as you increase magnification. One reason it took me so long to purchase this scope is because I often wondered if the performance improvements would be worth the cost of admission. To be clear I NEVER pay what the average asking price is for a scope on E-bay. Patience is a virtue. Having never seen any of the stereoscopes I own prior to purchasing them, I was taking some chance in terms of cost/benefit ratio with each attempt to "upgrade". I must say the B&L SZ7 is an impressive scope, given the age, with specs still close to many of the newer lower end Nikon/Olympus scopes in terms of lines/mm but has a smaller FOV and poorer contrast. It has a resolution of 300 lines/mm with a 10X eyepiece and 1X auxiliary objective. Though I have not seen the specs with the 2X auxiliary objective, based on an old ad (
http://pubs.acs.org/doi/abs/10.1021/ac6 ... ode=ancham) i imagine it would be roughly 600 lines/mm. Interestingly enough, current manufacturers often tout resolution, claiming "best in class", but you have to dig to get the actual numbers in most cases. This could be because they now offer a choice in objectives including apos with varying magnifications. The higher mag objectives give you better resolution, that is they increase the ability to discern the distance between 2 points thus more lines/mm. So when they do give out the resolution in terms of lines/mm it is with their highest available mag auxiliary objective. Unfortunately, I do not have all the specs so I simply used those as a starting point. Keep in mind I have spent hours in researching these scopes with every purchase before I let loose of my money. Also keep in mind that many times I sold my current scope when I upgraded to offset the cost of the "upgrade" .
For comparison to the B&L which was the standard in its day, 1960's:
Olympus SZX-7 ~300 Lines/mm with 1X objective at 56X 600 lines/mm with the 2X objective at 112X
Olympus SZX9 same as SZX-7 higher zoom ratio
Olympus SZ51 max 415 lines/mm
Olympus SZ61 max 424 lines/mm
Olympus SZX12 max 800 lines/mm
Nikon smz 1500 with 1.6X objective 630 lines/mm
Nikon SMZ-800 640lines/mm with 2.0x objective (planapo)
Nikon SMZ1000- 300 lines/mm with 1x objective
So where is the improvement, at least in the lower priced lines, that is those scopes costing less than 5 figures?
-Improved ergonomics
-improved CA
-Higher zoom ratios
-Larger Working Distances
Those who have had the privilege of owning or using both the Olympus SZH, SZX-9, and the SMZ-U tend to favor the SMZ-U over the SZH but say the SZX-9 is a tad bit crisper but not significant. I was tempted to go for a used SZX-7 or SZX-9 for this reason but this deal came up.
So now after throwing all this out there (and I have a lot more) how do you determine if the SMZ-U is worth the cost differential over the B&L 7 or the SMZ-2T? You have to try them. Literally put them side by side and compare.
The difference between the B&L SZ7 and the newer scopes lies mostly in the contrast, FOV, working distance and required lighting. Not as much in the resolution as you might think.
In short The SMZ-U has a much larger FOV, a brighter image, and better contrast. After some experimentation, I found this is in part due to superior eyepieces. The eyepieces that come with the SMZ-U have a much wider FOV and are just plain better. The 20X has an FOV of 15 vs the SMZ-2T at 12.5. I put the SMZ-U eyepieces on the SMZ-2T and lost some working distance but gained in clarity and FOV.
My question ever since I purchased the SMZ-2T was- Is it worth the price difference to upgrade to an SMZ-U? SMZ-2T's go for about $1000 with stand on E-bay while SMZ-U's go for about $2000, on average, with a broad variation in stands available etc. Is the SMZ-U worth a $1000 more vs the SMZ-2T. My answer is NO! However, it has its advantages beyond optics. For example, when photographing you can take photos and still observe the specimen through both eyepieces. You can't with the SMZ-2T. The SMZ-U is also modular. You can add or replace damaged components rather easily. You can not with the SMZ-2T, or any of the other scopes mentioned for that matter.
Given I paid less for this SMZ-U then the avg price for an SMZ-2T..took some dickering and a lot of patience but.. it was worth it. Even my wife saw the difference right away and she was pissed I bought it. In fact when she looked into it her first comment was --wow this has better image and I don't have to use one eye! You would have to have read an earlier post to understand that statement.
And when compared to a new Chinese Amscope ZM-1T costing about the same price, ..the used SMZ-U is superior in every way. Of course I am referencing the price I paid.
Oh and the Amscope ZM-1T is not as good as the SMZ-2T either, but the difference lies mostly in the contrast and lower magnification with a 1x objective.
It is my opinion that marginal improvements come at great cost in microscopy. When you buy used you eliminate much of that great cost.
Hmm..I have rattled on enough. I have lots to say in terms of working distance between all these scopes but I will save that for another day.