which is the real DIN 160mm objective?

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petew
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which is the real DIN 160mm objective?

#1 Post by petew » Fri Jun 11, 2021 12:27 am

Recently I bought a trinocular microscope.
All the objectives on this big microscope are physically longer than my small introductory monocular microscope.

What puzzles me is both sets of objectives are marked the same, supposedly they are to DIN 160mm standard.

Here is a picture of the two 40x objectives side by side from both my microscopes:
https://drive.google.com/file/d/16P-43u ... sp=sharing

According to this website, a 40x DIN objective should measure 44.5mm:
https://www.smsoptical.com/Accessories% ... 0Sheet.htm
The one off my trinocular is exactly that, the one off my monocular is only 33mm.

So even though all the objectives are marked the same on both microscopes, would it be correct to say the shorter ones on the introductory monocular are not really DIN 160mm standard objectives?

tgss
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Re: which is the real DIN 160mm objective?

#2 Post by tgss » Fri Jun 11, 2021 1:10 am

Hi petew
The DIN standard for objectives specifies not only the mechanical tube length (160mm), but also the parfocal distance of the objective, i.e. the intended distance from the objective mounting flange to the object, which for a DIN standard objective is 45mm. So your longer objectives appear to be manufactured to the DIN standard. The shorter objectives comply with the DIN standard for mechanical tube length but not for parfocal distance. Many microscopes manufactured before the DIN standard became generally accepted used parfocal distances in the 33mm range. Another important dimension associated with the DIN standard is sometimes called the optical tube length, usually quoted as 150mm for DIN microscopes. This is the distance from the objective mounting flange to the intermediate (sometimes called primary) image. DIN eyepieces are therefore manufactured on the understanding that the intermediate image will be formed 10mm below the top of the eyetube.
Tom W.

petew
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Re: which is the real DIN 160mm objective?

#3 Post by petew » Fri Jun 11, 2021 2:16 am

Thanks for the great explanation!

Perhaps the parfocal distance should also be part of the markings on each objective?
Physically they are easy to tell apart, but when buying an objective online, I have not seen parfocal distance ever mentioned :-)

The practical newbie mistake I made with all this is that I bought a 60x and 20x objective of the same "series" as these shorter parfocal quasi-DIN objectives for my monocular intro microscope, assuming that since they were supposed to be DIN standard, I would be able to use them interchangably on a better microscope.

But not only are they not parfocal, they are also not practically not interchangeable, since it's not physcially possible to raise or lower the stage enough on either microscope to get the objective into focus should I switch objectives between the 2 microscopes.
Oh well, I didn't pay that much for those quasi-DIN objectives, so small price to pay to learn the hard way!

Thanks again

apochronaut
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Re: which is the real DIN 160mm objective?

#4 Post by apochronaut » Fri Jun 11, 2021 11:53 am

In order to determine an objective's parfocality, you need a high magnification example of the objective series. Low magnification and l.w.d. examples are often much shorter than the parfocal length. An immersion example will be less than 1mm shorter than the parfocal length.
In general there are a whole bunch of individual companies between 32 and 36 2/3 mm. 32, 33, 34, 35, 36 and 36 2/3, with several companies using the same length.
The odd 36 2/3 length originated as an imperial measure used by Bausch & Lomb since the early part of the 20th century, which was then copied by Olympus from American microscopes that arrived with Occupied Japan and subsequently became metricized.

There were a few that standardized for many years at 37mm: Leitz, Wild, Reichert and a couple of others.

45mm became the default for most companies by the late 80's/90's.
Around 2000 as spatial requirements grew in order to add better corrections, 60mm and longer parfocal lengths began to be used, along with wider bodies and therefore a larger diameter threaded section.

Bausch & Lomb abandoned the short objective format in the 60's, solving the space requirement early on by splitting the objective up and placing a common back lens section in the nosepiece, effectively making a roughly 60mm parfocal length, although with the removeable lower objective section looking like they are regular 45mm parfocal objectives.
Last edited by apochronaut on Fri Jun 11, 2021 12:12 pm, edited 1 time in total.

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75RR
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Re: which is the real DIN 160mm objective?

#5 Post by 75RR » Fri Jun 11, 2021 12:08 pm

.
Here is a linked image showing some of the terminology
.
Image
Zeiss Standard WL (somewhat fashion challenged) & Wild M8
Olympus E-P2 (Micro Four Thirds Camera)

MichaelG.
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Re: which is the real DIN 160mm objective?

#6 Post by MichaelG. » Fri Jun 11, 2021 12:28 pm

75RR wrote:
Fri Jun 11, 2021 12:08 pm
.
Here is a linked image showing some of the terminology
.

Ah, yes ... I remember it well ;)
https://www.microbehunter.com/microscop ... din#p85168
Too many 'projects'

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patta
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Re: which is the real DIN 160mm objective?

#7 Post by patta » Fri Jun 11, 2021 12:53 pm

Likely, your small introductory microscope was made following the infamous Chinese standard "185", not following the DIN. 185 is the length in mm of "a" in the image of the previous post. All else is the same, just the length "b" is 35mm instead of the DIN's 45mm, so "a" too is shorter. The tube length "m" is 160mm for both.
The 185 standard is the most common for current economy microscopes. Chinese vendors usually write that in the specs; or they write "195" for the DIN objectives ("a"=195mm for DIN). 99% of the costumers (us, me included) has no idea what this 185 or 195 stands for, and we buy wrong objectives. Maybe that is a sophisticate fraud scheme to sell more objectives.

Length of the objectives, "a", "b", "d" are a nightmare for vintage microscopes, always different and never written. Lomo was the worse, each single objective has a different random length; and they made a fool of us writing the specs with incomprehensible characters. We are so lucky today that the Chineses decided to write the length as 185 mm, instead of weird things like "five twelfth of an arm's length" or "五点五周期寸".
Last edited by patta on Sat Jun 12, 2021 9:34 am, edited 11 times in total.

MicroBob
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Re: which is the real DIN 160mm objective?

#8 Post by MicroBob » Fri Jun 11, 2021 12:56 pm

When looking for used objectives of higher power one can copy the image into irfan view and mesure length and thread diameter to determin the object distance / parfocal distance.
In Klaus Henkel's "Mikrofibel" there is a table with specification values for different manufacturers.

Bob

petew
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Re: which is the real DIN 160mm objective?

#9 Post by petew » Sat Jun 12, 2021 12:56 am

patta wrote:
Fri Jun 11, 2021 12:53 pm
99% of the costumers (us, me included) has no idea what this 185 or 195 stands for, and we buy wrong objectives. Maybe that is a sophisticate fraud scheme to sell more objectives.
Ah ha, I think you've help me to decode buying objectives online, thanks!

Looking at sellers of these "185" objectives on amazon, I see they do 1 of 3 things:

a) no indication of "185" anywhere, they just show a picture of the objective with 160 marked on it, so you assume it is fully DIN standard (this was the case with the 60x I bought)

b) the write "185" somewhere in the description or title with no indication of what it refers to, again showing just picture of 160 marked on the objective (this was the case with the 20x I bought)

c) I see some more honest ones describe the objective as "185 conjugate distance", whatever that means to dummy buyer, but now I know that is "a" in the diagram that was posted earlier.

petew
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Re: which is the real DIN 160mm objective?

#10 Post by petew » Sat Jun 12, 2021 1:52 pm

I just found one of Mr. Microbe Hunter Oliver's youtube videos on "conjugate distance/parfocal distance":
https://www.youtube.com/watch?v=-4HzdclIW3A

I thought I already watched all of his videos twice, but must have missed this one :-)

In my work, we say "a little knowledge is a dangerous thing"

Armed with my new little knowledge of 185 vs 195,
I went ahead and ordered a "195" 20x objective for my trinocular scope, coming from China, of course.

It doesn't say DIN standard or anything, it just says 195 in the title and "160mm tube length" in the description and nothing else except a picture of the objective with typical 160 markings on it.
From the picture, it looks to be of the same "series" as the DIN objectives on my trinocular.

I'll see in 6 weeks if this one turns out to be of the real DIN :-)

DrPhoxinus
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Re: which is the real DIN 160mm objective?

#11 Post by DrPhoxinus » Sat Jun 12, 2021 4:26 pm

Like so many others I got suckered into unknowingly buying a 185 objective. Subsequently I bought an extender to get it close to 45 mm.

I will never confused 185 and 195 again

Gerard

EYE C U
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Re: which is the real DIN 160mm objective?

#12 Post by EYE C U » Sun Jun 13, 2021 6:06 pm

i bought the wrong ones for a scope i set up for grand kids... 10mm spacers under the stage fixed it right up no problem

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