60x-70x multiple objective comparison. Identities revealed.

[apochronaut]

This is a comparison of 60x to 70x objectives using a stauroneis phoenicenteron as a subject. All variables have been equalized as much as I could do, although for technical reasons the images were taken through three different microscopes. One objective is an 80x objective. One has a very small amount of separation in the rear doublet. I included it comparatively for that reason but also to show it's relative freedom from chromatic aberration, which is quite good for it's era.

I have arranged the objectives in a logical order. Have a look and make as many comments as you wish. I will reveal the ordering system later and also what the specifications and identity of the objectives is as well. There are 12 manufacturers represented and 19 individual objectives.
The images are a very heavy crop, so defects in the resolution are fairly enhanced. The crop was also adjusted to equalize the presented magnification of the image, so the 60x objectives were cropped more than the 80X, etc.

edit. Note the last two images. These are through modern higher end Chinese made planachromats. With the exception of a couple of defective and one very old objective, they are the worst of the lot, even when compared to objectives made before W.W. I. and barely able to separate individual punctae. The N.A.s of .80 and .85 may be real but the precision of manufacture, especially the lens polishing might be in question. The resolution and contrast for objectives carrying the stated specifications are very poor.

[apochronaut]

5 more.

[apochronaut]

5 more

[apochronaut]

Last 4. The dates of manufacture span approximately 125 years, possibly more. The earliest objective is unmarked but I have put it's date to about 1875 and it was supplied on a Leopold Schrauer microscope, although might have been made by E. Hartnack. The most recent objective was made in 2015 and is representative of a standard plan achromat from China. It is likely the same as a Chinese made Olympus objective.

[wporter]

Great work; I love this kind of comparison.

What strikes me right off the bat are the great differences in depths of field. It looks like you were focusing on the central axis structure, it's amazing how some images are much more 'plan' than others.

It must have been somewhat tough to control for how much condenser iris opening to use for different lenses, so as not to throw off the comparisons. Also camera vibrations, although it doesn't look like that was an issue.

[PeteM]

What a terrific project. Thanks for doing this, Apo . . .

[zzffnn]

Thanks for doing this, apo.

A few objectives stood out for me:

DSC02355 seems to be a non plan high NA apo. For my application (COL - pond protists), this is my favorite.

DSC02325 Seems to be a modern plan achromat that has good resolution and contrast.

2353 may be a plan fluorite? But focus point seemed to be slightly different (or is delaminated/has lost of contrast)?

2333 seems to have good potential (plan apo?), but focus point seemed to be slightly different (or is delaminated/has lost of contrast)? I am not sure.

[apochronaut]

Thanks to wporter and PeteM. Yes, I focused on the central area, using two specific well separated punctae as a target. The entire diatom is around 120 um, so the individual punctae I used are around 1 um, which most of the objectives could resolve to some degree. Most of the punctae are well under 1 um. however, and only a few of the objectives, could resolve those.

Fan. Good eyes. You are pretty much dead on.
2355 is a Bausch & Lomb 3mm 61x 1.4 N.A. oil immersion 160mm tube length objective. made around 1930. This was the only apochromat in the group and there were no fluorites. Most older objectives, made after the full understanding of the concept of an achromat was discovered, were not marked achromat. There was an assumption that they were at least that, since that base line was necessary for any decent level of performance. Some however, exceeded what was considered good and most of those contained a fluorite element, in order to raise the N.A. and control chroma. Fluorite objectives, usually contained more than one fluorite element.

2325 is a 1982 AO/Reichert 63x .80 semi-plan achromat infinity corrected for the 34mm parfocal system. This actual objective is the very first prototype sent to AO from the Reichert factory for approval, to be offered for the series 100 scopes. It retained it's spring loaded tip, a feature Reichert needed for their non retractable focus tube stands, that also used modified barrel versions of the AO designed 34mm parfocal infinity objectives. The objective came to me virtually unused, marked with a typewritten label that says; 1303-800 OBJECTIVE APPROVED SUBMISSION PIECE 9/22/82.

2353 is a Reichert 63x 1.0 oil immersion made around 1960. It was used on stands, such as the Zetopan. It is not labeled achromat and due to it's high N.A., it likely contains some fluorite. I agree that the objective lacks contrast but I cannot find a thing wrong with it, from an exterior examination. It has a tiny W.D. and I have noticed that it likes certain very thin samples better than others. It is a finicky objective to use. I haven't ruled out oil invasion but under a stereo microscope, everything looks o.k.

2333 is a Spencer Lens Co. 3mm 60x .85 from about 1925. I included it, because it has a very small degree of de-lamination in the rear doublet. It is hardly noticeable but degrades the image considerably. One thing of note is the relative freedom from chromatic aberration of this objective, something most companies had trouble with in those days. Spencer had a way of limiting chroma better than their competitors for a period after W.W. I. Likely, they were including fluorite in some of the higher N.A. lenses, not marked as apochromats. They only made a few designated fluorites, a 4mm( 44x) briefly and two versions of a 1.8mm( 95x) a 1.25 N.A. and a 1.30 N.A. The objective immediately before it, 2331, is a Bausch & Lomb 3mm .85 60x made just prior to the Spencer, probably around 1915 or so, in pristine condition. B & L had a co-operative relationship with Zeiss from around the turn of the century up until the first W.W. They were licensed to use some Zeiss designs and visa versa. It's hard to know whether the 60x objective here is a Zeiss or B & L design but B & L continued to use Zeiss designs well after the ending of their formal relationship. Something must have happened between the two companies because B & L went through a huge patent process with all of " their" designs and after late 1925 and for many years after, their objectives were stamped with patent numbers and the grand patent date of Oct. 13 1925.

[billbillt]

WOW!!.. This is a very interesting comparison... To my feeble old eyes, DSC02325 appears to be the best... Just my HO, technical aspects ignored.. Thanks for this!...

BillT

[apochronaut]

Yes, Bill. That is a nice objective. It really can only be used on the AO infinity microscopes up to the series 400 and on the series 400, if a series 100 head is swapped onto it( same dovetail). It also can be used on the Reichert Neovar 2 and possibly one or two other Reichert stands, I am unfamiliar with. It combines, resolution, with depth of field and reasonable chromatic aberration correction too.
Through the eyepieces, the relative differences between objectives were not so apparent as they are magnified so much. Viewing on an average laptop the diatom is a little over 3 times longer than it presented through the eyepieces, so around 2000x. That's a pretty big bump in magnification for those lenses .

What is noticeable is that resolution , although obviously dependent on N.A., is not entirely dependent on N.A. Although some of the older lenses from Europe do not state an N.A., or magnification for that matter: they are just marked 7, or 8, it can be safely assumed that they are .80 or .85, based on comparison to those that are marked. That means the AO/Reichert objective cat. # 1303, has one of the lowest N.A.s of the lot, yet it performs close to the top. Only two of the objectives have an N.A. over 1.0. Four of the objectives were immersion.

[AntoniScott]

Excellent work by Apochronaut. Many thanks. I guess a picture is worth a thousand words.
I should perform a similar photo comparison of images using the eyepieces from different manufacturers.

[Rossf]

Excellent post once again apochronaut! The Hacker 80x .90 is impressive for such a high dry objective-will keep an eye out for one! The most recent Chinese objectives are pretty ordinary by any standards -are these cheapies?
Regards ross

[apochronaut]

I believe Seibert made the Hacker objectives under contract.

[DonSchaeffer]

I never heard of a 70x objective. Does anybody really make one?

[Rossf]

DonSchaeffer I know Leitz made one years ago-a fluorite 70x .90-I only know cos Ive been looking for one for ages!
Regards ross

[zzffnn]

LOMO produced a few versions of 70x NA 1.23 water immersion apochromatic objectives, which are popular with microscopists examining protists.

Objective magnifications go all over the place from 1x to 150x. I have seen: 1, 1.2, 1.3, 2, 2.5, 3, 3.7, 4, 5, 6, 8, 9, 10, 16, 20, 25, 30, 40, 44, 45, 50, 60, 65, 70, 75, 80, 85, 90, 95, 97, 100, 120, 150. Parfocality, thread size and tube length differ though, so mixing them is not easy.

[viktor j nilsson]

Good list, but you're missing the 12x and 63x objectives!

[zzffnn]

Yep, forgot that big one 63x 1.4 which is popular among diatomists, as I don't use it.

12x is not common? I can see it go between 25x and 6x.

[Scarodactyl]

Don't forget that old classic, the 2.8x objective.

(They have since started labelled them as 3x from what I can tell).
Some of the wonky magnifications come from microscope systems with mandatory built in magnification factors above the objective. Of course I assume the ones Apo was working with would have been marked by their focal length rather than their magnification which moves the goalposts somewhat as to what qualifies as a nice round number.

This collection really is a tour de force. I imagine it took as much time to match them up to the best correcting optics as the rest together.

[AntoniScott]

I recently saw a short video of a company offering a 100x "dry" objective, claiming the image quality was equal to a similar 100x oil immersion. The video looked like the dry performed equally as well. I'm not sure how it would work out in the real world. Oil immersion is messy, I guess that's why 60x objectives are popular although not as good as the oil immersion. I have a 50x oil immersion (Olympus) that has spectacular image quality, equal to or better than a 40x.
I haven't seen anymore about this 100x dry.

[Scarodactyl]

It'a not uncommon to have 100x and even 150x dry objectives for metallurgical usage. I have a 100x/0.90 and it's really not bad. But compared to an immersion objective it's just not going to measure up.

[apochronaut]

Some of the last planachro objectives AO released for the series 100 microscopes were #1866 40X .55 L.W.D. and # 1867 100X .90 L.W.D. In the release literature, they refer to them as " the best optics we make". Their target market use were quick smears. Both were recommended for the 1820 inverted microscope too. Both had exceptional quality for planachros. A higher N.A. objective in an immersion format does have to look through interference from unhomogenious mediums often, reducing the effective N.A. whereas a smear without cover can provide a very sharp image without oil. Also , very often users dispense with oiling the condenser, so all of a sudden the best case scenario for a 1.25 N.A. objective working at peak, is about 1.13 or so if the sample is homogenious and it often isn't. All of a sudden, an excellent .90 100X objective can start to look pretty useful

[apochronaut]

LOMO produced a few versions of 70x NA 1.23 water immersion apochromatic objectives, which are popular with microscopists examining protists.

Objective magnifications go all over the place from 1x to 150x. I have seen: 1, 1.2, 1.3, 2, 2.5, 3, 3.7, 4, 5, 6, 8, 9, 10, 16, 20, 25, 30, 40, 44, 45, 50, 60, 65, 70, 75, 80, 85, 90, 95, 97, 100, 120, 150. Parfocality, thread size and tube length differ though, so mixing them is not easy.

Prior to the advent of extremely controlled and precise glass production lens designers were more at the beck and call of nature when it came to glass production. In more ways than one. Sand was the base material for glass and kiln operators wore protective clothing and head gear made out of thick wool. That puts a whole different spin on the phrase " I FELT it get hot all of a sudden".
Glass batches were inconsistent and as much as the glass could still be worked to yield perfect lens making material, a slightly different blend of component elements from a particular collection of sand could yield glass of a different refractive index, thus rendering a production that required some tweaking in element dimensions or shimming to get the desired corrections and as well maintain a consistent N.A., which as a more important specification than the absolute magnification factor. Some companies rounded off a particular objective's magnification and others marked them as accurately as they could. More complex objectives with more elements were more vulnerable to variability since there were more glass elements that could slightly vary. It kept the drafting department busy!
Spencer and Bausch & Lomb are the makers I am most familiar with. A quick run down of some pre 1955 magnifications that Spencer marked on some of their objectives. 25mm achromat : 5.1X, 5.3X, 5.7X. 4mm achromat : 43X , 44X. 3mm apochromat 57X, 58X, 60X. 2mm apochromat : 82X, 85X, 90X. 1.8mm achromat : 95X, 97X, 98X, 100X. 1.5mm achromat: 113X, 115X.

[MichaelG.]

… thus rendering a production that required some tweaking in element dimensions or shimming to get the desired corrections and as well maintain a consistent N.A., which as a more important specification than the absolute magnification factor. Some companies rounded off …

Those are very important points, which are sometimes lost on beginners … a reality-check which clearly explains why we must calibrate an eyepiece-micrometer or a photographic system.

MichaelG.