185 or 195 listed in finite objective specs?
 Crater Eddie
 Posts: 1827
 Joined: Wed Nov 12, 2014 4:39 pm
 Location: Illinois USA
185 or 195 listed in finite objective specs?
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*
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 BH2 / BHTU with Olympus EP1 MFT camera mounted
LOMO BIOLAM L22
LOMO POLAM L213 / BIOLAM L211 hybrid
LOMO Multiscope (Biolam)
LOMO BIOLAM L22
LOMO POLAM L213 / BIOLAM L211 hybrid
LOMO Multiscope (Biolam)
Re: Conjugate distance value as related to objectives?
I can try ...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
In basic schoollevel 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 comfortlevel ... 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'
Re: 185 or 195 listed in finite objective specs?
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.
Re: 185 or 195 listed in finite objective specs?
For those who may not previously have noticed the numbers to which Crater Eddie refers:
http://www.qualitekinstrument.com/cate ... cessories/
Qualitek lists objectives in 185mm, 195mm, and Infinity versions
MichaelG.
http://www.qualitekinstrument.com/cate ... cessories/
Qualitek lists objectives in 185mm, 195mm, and Infinity versions
MichaelG.
Too many 'projects'
 Crater Eddie
 Posts: 1827
 Joined: Wed Nov 12, 2014 4:39 pm
 Location: Illinois USA
Re: 185 or 195 listed in finite objective specs?
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.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 ?
Excellent, that sums it up very nicely. Thanks very much.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.
CE
Olympus BH2 / BHTU with Olympus EP1 MFT camera mounted
LOMO BIOLAM L22
LOMO POLAM L213 / BIOLAM L211 hybrid
LOMO Multiscope (Biolam)
LOMO BIOLAM L22
LOMO POLAM L213 / BIOLAM L211 hybrid
LOMO Multiscope (Biolam)
Re: 185 or 195 listed in finite objective specs?
It's no problem at all, CECrater Eddie wrote:... I did, sorry. ...
All's well that ends well
MichaelG.
Too many 'projects'
Re: 185 or 195 listed in finite objective specs?
It is a curious number. Are they adding Optical Tube Length plus parfocal distance or what?MichaelG. wrote:For those who may not previously have noticed the numbers to which Crater Eddie refers:
http://www.qualitekinstrument.com/cate ... cessories/
Qualitek lists objectives in 185mm, 195mm, and Infinity versions
MichaelG.
Zeiss Standard WL (somewhat fashion challenged) & Wild M8
Olympus EP2 (Micro Four Thirds Camera)
Olympus EP2 (Micro Four Thirds Camera)
Re: 185 or 195 listed in finite objective specs?
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 preDIN objectives seemed to use). These shorter parfocal objectives are apparently still sold with some cheap microscopes.
Re: 185 or 195 listed in finite objective specs?
Thanks, had missed the minus 10. Adds up nicely now.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 preDIN objectives seemed to use). These shorter parfocal objectives are apparently still sold with some cheap microscopes.
Zeiss Standard WL (somewhat fashion challenged) & Wild M8
Olympus EP2 (Micro Four Thirds Camera)
Olympus EP2 (Micro Four Thirds Camera)

 Posts: 3108
 Joined: Fri May 15, 2015 12:15 am
Re: 185 or 195 listed in finite objective specs?
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.
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.