Replacing short (older) ojectives with long (newer) objectives.

[AntoniScott]

A question was asked in a previous posting about replacing the old shorter objectives with the newer longer ones. I'm guessing that the question being asked was to determine if the larger (newer) objectives had better optical quality that the shorter ( older) objectives. My response ( with reservations) would be to say definitely not.

I have two microscopes. One is an older Japanese Bristoline ( I believe a subsidiery of Kyowa) , probably from the 1970's or earlier but in excellent optical condition. The other is a newer Olympus from around the late 1980's, or newer, that uses the larger style objectives is commonplace today. I have ehaustively compared the optical quailty of both and have concluded there is no difference ( if the older objectives are still in good condition).
That being said, microscopes from the late 1980's like the Olympus BH2, CH2, or Nikon's, were extremely expensive instruments at the time, well out of the reach of most amateur microscopists. Today the market is flooded with inexpensive and poor quality miroscopes, posing as professional instruments. Their new looking and shiny large style objectives are equally as poor in optical quality in some instances, but are within the reach of most amateur micrsocopists.
Amateur microscopists, such as myself, prefer to own an older Olympus microscope and look for additional objectives on Ebay, etc. Since the standard four objective array available on most micrsoscopes is usually, 4x, 10x, 40x and 100x oil, I wanted a 20x and a 60x. Prices and quailty can range widely from cheap to extremely expensive. Preferred objectives such as from Olympus may have been of superb optical quality when new but were damaged during use ( i.e. scratched objective lens), especially one like 60x.
Older objectives like the "short" versions from the 60's and 70's may have been superb optically at time of introduction. Although the objective lens is scratch free due to careful user use, time has caused dust to settle inside the objective barrel, a cloudy film of unknown origin may have settled on the inside glass, which is difficult to remove even with high pressure compressed air, or the cement used to glue lenses together, may have yellowed over time, or a common condition called "delamination" may have occurred.
When you do find used objectives from old scopes like Bausch and Lomb, Spencer, American Optical, etc, that are in good condition you can be assured that their optical quality will be everybit as good as, or far better than the inexpensive "new" long objectives flooding the market today.

One way to decide if you have a good recent purchase lens, is to perform A-B comparisons. If a new 40x is to be tested, remove the objective next to the 40x ( 10x or 100x) on the microscope and replace it with the 40x to be tested. Going back and forth between the two 40x objectives looking at the same specimin under the same lighting, can determine if the newly acquired objective is better or not as good as the original.
Antoni

[Leitzcycler]

I have the same experience. I have old short barrel objectives in my Olympus FH and they work just fine. Extensive objective comparison and aiming at perfectionism with the image quality is fine if that's the part of the hobby. Otherwise the most important is that you get the information from the image you need.

Happy Valentine's Day!

[apochronaut]

I believe that the theoretical design of recently manufactured mass market objectives is basically good. Non-plan objectives especially are a pretty basic design with only a few optical elements and if that theory was realized into practice while upholding it's integrity, that would be good too. However, the throughput is very high and poor Q.C. , resulting in both internal and external misalignment plagues a high percentage.
Old school objectives were put together by craftsmen and exhaustively tested by experts, and both groups had the freedom to make use of time as an ally. Part of that arose from the era and part from philosophy. Inexpensive commodities in todays world are made in an atmosphere where time is viewed as an enemy.

[PeteM]

A question was asked in a previous posting about replacing the old shorter objectives with the newer longer ones. I'm guessing that the question being asked was to determine if the larger (newer) objectives had better optical quality that the shorter ( older) objectives. My response ( with reservations) would be to say definitely not. . .

I did get a grin out of the "definately not" but "with reservations" answer to the question, "do newer long barrel objectives have better optical quality than their short barrel precursors?" And would even agree that some of the better short barrel objectives are outstanding - essentially indistinguishable in image quality.

However, it seems to me that there have been at least two significant improvements from the "short barrel" era to day's best "long barrel" objectives.

The first is improved anti-reflective coatings. As a very rough guesstimate of the effect (and others may know better), Edmund Scientific's article on coatings suggests that an uncoated lens loses 4% of light at each lens surface. An Apo lens might well have 10 elements and 20 surfaces. The earliest objectives had no coatings -- and later -- partially effective coatings. Edmund also suggests that today's better coating technologies can cut losses at each surface from 4% to 0.1%

So, uncoated we might have .96 to the 20th power . . . or 44% transmission through an uncoated Apo objective.

With a coating that cuts reflection in half (to 2%) we might have .98 to the 20th . . . or 66% transmission.

With current best-in-class coatings we might have 99.9 to the 20th . . . or 98% transmission

There's also the potentially more significant issue of where that 66%, 34%, or 2% of stray light goes. At the very least stops have to be carefully designed in to preserve contrast. My own experience is that the new fatter barrel (Leica, Nikon) infinite objectives have far better contrast than their precursors. How much of this is more space for optical elements and how much is due to improved coatings -- don't know.

The second is wider flat fields of view at a given price point. Early scopes might have struggled to get 14mm FN. The best deals in short barrel scopes might me up around 18mm. Excellent finite Leitz (Laborlux), Nikon (Labophot, Optiphot), Olympus (BH2), and Zeiss (Standard) models might be up around 20mm. Today 22mm is pretty much the standard for a mid range pro scope.

Somewhat related to even longer barrel lengths is working distance at higher magnifications. Many high numerical aperture short barrel objectives can only peer a short distance below the cover slip. One of Nikon's claims to fame for the 60mm parfocal CFI objectives is this longer working distance compared to their earlier efforts.

A big plus cost-wise for hobbyists has been the advent of CNC lens grinders. Most anyone can copy a good lens design and accurately produce it at low cost. They might (and often do) screw up assembly, put a cheaper coating on, and so on -- but getting the geometry right is no longer just for the most renowned makers.

[AntoniScott]

Interesting discussions, for sure, regarding old and new objective, lengths, etc. When I suggested to not replace old "short" objectives with the newer "long" objectives, "with reservations" of course that meant that not all short obejectives are necessarily better just as not all long objectives are necessarily better. A $1200 Olympus "long" objective is hopefully gping to be better than a $25 Chinese-made counterpart, both are long objectives.
Since I am definitely in the category of a microsope enthusiast and couldn't afford a new Olympus, Zeiss or Nikon microscope, I satisfy my needs through used equipment. The market is flooded with used objectives from high end manufactureres, all of varying condition, due to use, abuse or misuse. Doing side by side A-B comparisons of similar used objectives can expose differences in optical quality that were not apparent through visual external examination.

Regarding the comments about superior image quality of the newer lenses because of coatingsm etc. I'm sure this is true, as technology always moves forward, but to the enthusiast looking to not spend a fortune, the used market has a lot to offer.

And of course, any objective will yield an image, It is up to the microscopist to determine if that image is what they expect.

When I started out in microscopy (as a hobby) decades ago, I was perfectly satified with the inexpensive scopes such as from Lafayette Radio and Electronics. As I progressed, I was looking for something better. If the only microscope available was a mega-expensive Leitz, Zeiss and later Olympus, I would have never experienced microscopy.