What is the Numerical Aperture of the 20x objective?
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It's 0.40
Louise
What is the Numerical Aperture of the 20x objective?
There's not much to see - it's just a (new) cheap Chinese lens from Ebay:75RR wrote: ↑Thu Jul 09, 2020 9:02 pmI don't think it is supposed to work. This is what microscopyu says: https://www.microscopyu.com/microscopy- ... ifications
Most manufacturers have now transitioned to infinity-corrected objectives that project emerging rays in parallel bundles from every azimuth to infinity.
These objectives require a tube lens in the light path to bring the image into focus at the intermediate image plane.
Infinity-corrected and finite-tube length microscope objectives are not interchangeable and must be matched not only to a specific type of microscope,
but often to a particular microscope from a single manufacturer.
Can you provide a photo of it
Well it's only a cheap plan achromat to start with. Sorry the image was a bit dim... Anyway I've just taken this one with the 10x (NA=0.25) 160mm Non Plan Achromat (the one that came with the scope so many years ago!) which I've cropped to approximate a similar size, and another using the 40x (NA=0.17) Plan Achromat 160mm (from same Chinese source):apochronaut wrote: ↑Thu Jul 09, 2020 11:27 pmThat's a pretty dismal image. Tons of spherical aberration and increasing off axis ca.....especially for a 20X of only .4 N.A., which should have some resistance to spherical aberration due to the low N.A. Reports of people using infinity objectives in finite systems successfully and visa versa are not very common and a lot of them have to be taken with a grain of salt. Usually it is with lower N.A. objectives where sometimes it is difficult to see the effect of spherical aberration.I do know of some instances but not many.
There are not a lot of differences between made in China objectives within the two broad categories of 160mm or infinity. They are very good at changing the barrels and using the same optical formulas in many barrel styles. It gives the consumer the impression that there are all these choices and all this technology in what are essentially very basic microscopes but in reality they are just choosing barrel styles and a few other irrelevant features that any decent microscope should have.
I would have thought that one could confirm it is an infinity objective by removing the microscope head and holding a paper over the light beam that it produces.Scarodactyl wrote: ↑Fri Jul 10, 2020 5:23 amHave you taken them apart or something like that to confirm that? Or more just from testing samples and getting the same performance? It'd love to hear more about that (though it may deserve its own thread).
Here is a compact description of the difference :LouiseScot wrote: ↑Thu Jul 09, 2020 4:57 pmI've never quite understood exactly what a tube lens does in terms of aberration and maybe also colour correction?
Thanks for any expertise/advice
I think you need to allow for different browsers etc ... I had no luck in my search using your suggested parameters.
Hi
Just turn on your microscope as you would normally do, focus on a slide, then take off the head and place a paper over the light beam from the 'infinity' objective.In any case, comparing the finite and 'infinity' objectives by using them as magnifying glasses doesn't show any obvious differences ...
Hi75RR wrote: ↑Fri Jul 10, 2020 12:29 pmNo need for a magnifying glass, just turn on your microscope as you would normally do, focus on a slide, then take off the head and place a paper over the light beam from the 'infinity' objective.In any case, comparing the finite and 'infinity' objectives by using them as magnifying glasses doesn't show any obvious differences ...
Move it up and down to see if the diameter of the beam changes.
It ain't necessarily so. On the BX50 imaging system showed above, I believe that it was the objective, tube lens and camera; if one had used the dedicated Olympus camera like the DP70, DP73 etc, it would be the objective, tube lens and camera, plus a reducing lens between the camera and tube lens (optional, to cover a larger portion of the FOV).LouiseScot wrote: ↑Fri Jul 10, 2020 12:24 pm...At the end of the day, there is really just the objective lens and the camera, from an imaging point of view.
I was just talking about my setupHobbyst46 wrote: ↑Fri Jul 10, 2020 12:49 pmIt ain't necessarily so. On the BX50 imaging system showed above, I believe that it was the objective, tube lens and camera; if one had used the dedicated Olympus camera like the DP70, DP73 etc, it would be the objective, tube lens and camera, plus a reducing lens between the camera and tube lens (optional, to cover a larger portion of the FOV).LouiseScot wrote: ↑Fri Jul 10, 2020 12:24 pm...At the end of the day, there is really just the objective lens and the camera, from an imaging point of view.
Yet there are other options in hobby use, for example, for finite (160mm) tube optics : (1) objective + camera body; (2) objective + eyepiece + camera body; (3) objective + eyepiece + camera lens + camera body (aka afocal). Each of which may be the winner in image quality, depending on the equipment.
It is true that the objectives are the heart of a microscope, but you do have to place them in a 'good' stand.Maybe I would be better off just getting a new scope complete with, hopefully, better objectives, after all?
Although the reproducibility of quality of images from new unbranded objectives has been questioned, I doubt that they went so far as to mark a finite optics objective with the "infinity" sign...LouiseScot wrote: ↑Fri Jul 10, 2020 12:42 pm...Using the 20x, doing the projection on to a piece of paper gives a changing circle of light which comes into focus at a point above the head - I'm guessing at ~160mm! Same with 10x finite objective. So I really need better quality finite objectives from somewhere...
It is strange but the objective behaves as a finite one. I don't think the UK based Ebay supplier normally even offers infinity objectives. Perhaps it was one in a 'bad batch'. I could ask the supplier but I bought it over a year ago now so would feel a bit silly!Hobbyst46 wrote: ↑Fri Jul 10, 2020 2:29 pmAlthough the reproducibility of quality of images from new unbranded objectives has been questioned, I doubt that they went so far as to mark a finite optics objective with the "infinity" sign...LouiseScot wrote: ↑Fri Jul 10, 2020 12:42 pm...Using the 20x, doing the projection on to a piece of paper gives a changing circle of light which comes into focus at a point above the head - I'm guessing at ~160mm! Same with 10x finite objective. So I really need better quality finite objectives from somewhere...
I was going to only get the one Nikon objective just to try, to compare. I don't know why the make of stand would make a huge difference when the objective is just being used like a camera lens. The stand I have is fine for 160mm objectives although the focus resolution isn't as good as I'd like (I'm sure a Nikon stand would be better for that!), but with only achromats, it's probably ok. I could probably do with a better camera. The one I have is ok-ish (It's a Touptek 5M with Aptina sensor and 2.2um pixels) but tends to be a bit grainy.75RR wrote: ↑Fri Jul 10, 2020 2:07 pmIt is true that the objectives are the heart of a microscope, but you do have to place them in a 'good' stand.Maybe I would be better off just getting a new scope complete with, hopefully, better objectives, after all?
The one you have is not going to do them justice.
If you want to get some nikon objectives then fine, but also get a Nikon stand.
All the other bits that you will need such as a condenser and eyepieces and anything else you want is available and compatible.
That is the beauty of a modular system, everything you need is designed to work well together. No guesswork, no bodging.
I know you are not overly keen on used but they are affordable, originally cost many thousands of pounds and you can return it if it is not as described.
If the camera is an eyepiece camera, so is being used without eyepiece, the Nikon CF objective is expected to perform very well, since it is inherently corrected for aberrations.LouiseScot wrote: ↑Fri Jul 10, 2020 3:50 pm...I could probably do with a better camera. The one I have is ok-ish (It's a Touptek 5M with Aptina sensor and 2.2um pixels) but tends to be a bit grainy.
Yes it's a small EP type camera. It's only parfocal if I actually use it in place of an eyepiece. Usually, I use it in the trinocular position. In either case I'll use the monitor screen to focus on. The pollen is probably not the best subject as the grains are opaque and 3d.Hobbyst46 wrote: ↑Fri Jul 10, 2020 5:05 pmIf the camera is an eyepiece camera, so is being used without eyepiece, the Nikon CF objective is expected to perform very well, since it is inherently corrected for aberrations.LouiseScot wrote: ↑Fri Jul 10, 2020 3:50 pm...I could probably do with a better camera. The one I have is ok-ish (It's a Touptek 5M with Aptina sensor and 2.2um pixels) but tends to be a bit grainy.
Regarding the previous images you posted - can it be that the viewing eyepieces and the camera were not exactly parfocal ? I am using an eyepiece camera from time to time, each time I install it have to carefully adjust parfocality.
The Toupview software is very good, IMO.
Hi SteveFungusMan wrote: ↑Wed Jul 22, 2020 1:19 pmThis was a very informative post - like everything in a nutshell.
Louise, what have you decided at the end? I am also a fan of the Motic BA310 or BA410. There are online shops selling it from EU too. The BA410 would be around 3000Eur including transport etc. and it is a bit above average.
Anyway, I just wanted to ask if you have decided.
Steve.
Yeah, most objectives that I've looked at - Euromex Oxion, Motic and AmScope seem to be of the Olympus 180/45mm variety.apochronaut wrote: ↑Wed Jul 22, 2020 3:51 pmThe Chinese infinity microscopes are patterned after the 3 of the microscope systems they have been asked to make the cheaper optics for. Each objective type is usually produced in 3 versions. Olympus pattern, with a 180mm reference length, Nikon R.M.S with a 200mm reference length and Nikon 60mm parfocal with a 200mm reference length.
There are also a few designs that appear to be possibly purchased or swiped from other discontinued systems. The ones I have seen look unique and are usually on some more expensive equipment.