185 or 195 listed in finite objective specs?

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Crater Eddie
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185 or 195 listed in finite objective specs?

#1 Post by Crater Eddie » Sun Jul 28, 2019 3:18 am

This might be a dumb question but...
The recent discussion of cheap Chinese objectives has me browsing the offerings again (my grandma always said that I was a glutton for punishment).
I notice that in addition to the usual information, some of the specs include the number "185" and some "195", while others don't say either. I did some googling, but I'm not really sure what this number is. Can someone enlighten me please? This is for a 160mm tube length finite system.
CE

*Edited a bit for clarity*
Olympus BH-2 / BHTU with Olympus E-P1 MFT camera mounted
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MichaelG.
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Re: Conjugate distance value as related to objectives?

#2 Post by MichaelG. » Sun Jul 28, 2019 4:48 am

Crater Eddie wrote:This might be a dumb question but...
The recent discussion of cheap Chinese objectives has me browsing the offerings again (my grandma always said that I was a glutton for punishment).
I notice that in addition to the usual information, some of the specs include the number "185" and some "195", while others don't say either. From googling I believe that this refers to the conjugate distance of the scope's optical system, but I'm not sure how one figures this value (finite system). Professor Google has so far provided only confusion, and a quick search of the forum archives didn't turn up anything useful.
Can someone explain this is simple terms?
CE
I can try ...

In basic school-level physics we learn about lenses having an object distance and an image distance, and that these are related by a simple formula, such that the sum of the two remains constant when one of them is changed ... this is called the conjugate distance.
At this simple level, we assume that the lens is thin, and therefore the distances are measured from a common point.
In reality, things like microscope objectives and camera lenses are complex assembies of elements, and are not thin ... The relationship still holds, but each distance must be measured from its own nodal point.

So ... the physical distance between object and image probably will not be equal to the theoretical sum of the two.

Hopefully: If you search for my emboldened words, you will find a text or demonstration which is at your comfort-level ... if not: I'm happy to take you through it [to the limit of my own ability!]

MichaelG.

.

Edit: I think you edited your post 'for clarity' whilst I was writing that ^^^
... I thought you had mentioned 'conjugate distance' ... was I dreaming ?
Too many 'projects'

PeteM
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Re: 185 or 195 listed in finite objective specs?

#3 Post by PeteM » Sun Jul 28, 2019 5:04 am

If you're looking for a DIN standard finite objective (45mm parfocal obective + 160mm tube length - 10mm for where the eyepiece picks up the image), I believe you'll want a "195." And the "185" would be a short barrel objective.

MichaelG.
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Re: 185 or 195 listed in finite objective specs?

#4 Post by MichaelG. » Sun Jul 28, 2019 11:07 am

For those who may not previously have noticed the numbers to which Crater Eddie refers:
http://www.qualitek-instrument.com/cate ... cessories/
Qualitek lists objectives in 185mm, 195mm, and Infinity versions

MichaelG.
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Crater Eddie
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Re: 185 or 195 listed in finite objective specs?

#5 Post by Crater Eddie » Sun Jul 28, 2019 12:54 pm

MichaelG. wrote: Edit: I think you edited your post 'for clarity' whilst I was writing that ^^^
... I thought you had mentioned 'conjugate distance' ... was I dreaming ?
I did, sorry. Originally I rattled on a bit about what I *thought* it meant, then edited that out and changed the topic. Looks like I was on the right track, should have left it alone. You answered my original question quite well, I appreciate your explanation.

PeteM wrote:If you're looking for a DIN standard finite objective (45mm parfocal obective + 160mm tube length - 10mm for where the eyepiece picks up the image), I believe you'll want a "195." And the "185" would be a short barrel objective.
Excellent, that sums it up very nicely. Thanks very much.

CE
Olympus BH-2 / BHTU with Olympus E-P1 MFT camera mounted
LOMO BIOLAM L-2-2
LOMO POLAM L-213 / BIOLAM L-211 hybrid
LOMO Multiscope (Biolam)

MichaelG.
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Re: 185 or 195 listed in finite objective specs?

#6 Post by MichaelG. » Sun Jul 28, 2019 3:00 pm

Crater Eddie wrote:... I did, sorry. ...
It's no problem at all, CE
All's well that ends well

MichaelG.
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75RR
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Re: 185 or 195 listed in finite objective specs?

#7 Post by 75RR » Sun Jul 28, 2019 4:53 pm

MichaelG. wrote:For those who may not previously have noticed the numbers to which Crater Eddie refers:
http://www.qualitek-instrument.com/cate ... cessories/
Qualitek lists objectives in 185mm, 195mm, and Infinity versions

MichaelG.
It is a curious number. Are they adding Optical Tube Length plus parfocal distance or what?
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PeteM
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Re: 185 or 195 listed in finite objective specs?

#8 Post by PeteM » Sun Jul 28, 2019 5:16 pm

As noted above, I believe it's parfocal distance + tube length - MINUS the distance (10mm for DIN) where the eyepiece picks up the image. Seems to be the only way the math works out. And I've bought "195" objectives which are DIN finite compliant and seen what must have been "185" objectives which have around a 35mm parfocal distance (33 to 37mm what what major makers of older pre-DIN objectives seemed to use). These shorter parfocal objectives are apparently still sold with some cheap microscopes.

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75RR
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Re: 185 or 195 listed in finite objective specs?

#9 Post by 75RR » Sun Jul 28, 2019 5:36 pm

PeteM wrote:As noted above, I believe it's parfocal distance + tube length - MINUS the distance (10mm for DIN) where the eyepiece picks up the image. Seems to be the only way the math works out. And I've bought "195" objectives which are DIN finite compliant and seen what must have been "185" objectives which have around a 35mm parfocal distance (33 to 37mm what what major makers of older pre-DIN objectives seemed to use). These shorter parfocal objectives are apparently still sold with some cheap microscopes.
Thanks, had missed the minus 10. Adds up nicely now.
Zeiss Standard WL (somewhat fashion challenged) & Wild M8
Olympus E-P2 (Micro Four Thirds Camera)

apochronaut
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Re: 185 or 195 listed in finite objective specs?

#10 Post by apochronaut » Sun Jul 28, 2019 8:39 pm

The numbers relate to the conjugate distance of the microscope optical tube and follow the DIN 58887 standard of 150mm.

Prior to China becoming a major budget line OEM for the established companies, they had developed an in house industry , likely based on copying the Nikon system, which used a 35mm parfocal objective design coupled to a 160mm tube length. The conjugate distance is 150 mm, the point where the objective intermediary image is collected by the eyepiece, 10mm down the tube. China still manufactures student microscopes to that standard, using 185mm conjugate distance objectives.
The bulk of their internationally known and OEM production however , is based on an additional DIN standard relating to the microscope objective parfocal length of 45mm. The DIN 58887 is still adhered to, so the extra 10mm of objective length , calls for a 195mm conjugate distance.

dburner
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Re: 185 or 195 listed in finite objective specs?

#11 Post by dburner » Fri Nov 06, 2020 12:12 pm

Two more questions about this

1. If i have a microscooe with 185 objectives, if i swap all of them with 195 objectives would that be ok? Does the condenser have to be in a special position?
2. Are 195 objectives better in general than 185?

Greg Howald
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Re: 185 or 195 listed in finite objective specs?

#12 Post by Greg Howald » Fri Nov 06, 2020 12:39 pm

If you have a microscope that came originally with short barrel objectives, then yes, you can install the objectives with the longer barrel length, but there is one sacrifice I noticed.
The scope that comes with short barrel objectives is usually very small in its overall size. It is designed for short objectives. By installing the longer objectives the first thing you will notice is a lack of space between the objective lens and the stage, to the point that it can be cumbersome to put the specimen on the stage.
This is the only difficulty. The longer barrel objectives will perform properly. But can be very difficult to work with if you do not have a mechanical stage.
All that I have told you is based upon personal experience and nothing else. No science here. Just trial and error.
Greg

dburner
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Re: 185 or 195 listed in finite objective specs?

#13 Post by dburner » Fri Nov 06, 2020 1:11 pm

Greg Howald wrote:
Fri Nov 06, 2020 12:39 pm
If you have a microscope that came originally with short barrel objectives, then yes, you can install the objectives with the longer barrel length, but there is one sacrifice I noticed.
The scope that comes with short barrel objectives is usually very small in its overall size. It is designed for short objectives. By installing the longer objectives the first thing you will notice is a lack of space between the objective lens and the stage, to the point that it can be cumbersome to put the specimen on the stage.
This is the only difficulty. The longer barrel objectives will perform properly. But can be very difficult to work with if you do not have a mechanical stage.
All that I have told you is based upon personal experience and nothing else. No science here. Just trial and error.
Greg
Yes it would seem that lowering the stage at maximum gives at most extra 15mm. Soo yeah not too much room left then.

One question still remains are the 195 ones better in general than 185? :)

Greg Howald
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Re: 185 or 195 listed in finite objective specs?

#14 Post by Greg Howald » Mon Nov 09, 2020 12:26 am

195s generally meets the industry standard. 185s don't have to do that, but I've had no trouble with them. I have a small scope that came with 4, 10 and 40x. The scope performs well. I have now ordered 185s in 20, 60 and 100x. I can not respond to their performance level as I have not yet received them. I wonder if the 1 watt led bulb in the scope will provide enough light for higher magnification and all I can do is wait and try them out.
Basically if your scope is designed for 185s you should use only 185s on it. If your scope is designed for 195s and you install 185s the result may well be that the stage will not raise high enough for you to obtain focus.
I guess what I'm saying so far as quality or which is best, is that what is best is what size objectives your scope is designed to utilize.
Greg

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