Scope objective thread sizes

[lauriek]

After reasonable success with the trusty Nikon 10x CF plan objective I decided to try to extend my magnification range (I would like a 5x and a 20x to go with this lens!) - I picked up a 5x CF plan Nikon objective in the hope of using this in the same setup. (was quite reasonably priced on ebay!)

It's arrived and it's a huge beast! Obviously not an RMS thread (I am at work atm so don't have the 10x lens to hand) but the thread is massive by comparison, the thing is like a slightly small camera lens!

The thread is roughly 1 inch in diameter. Does anyone know what sort of thread this is likely to be, and what's the best way I can rig this on the front of the bellows. It's quite a heavy lens so I don't think sticky tape will do the job!!

[augusthouse]

Laurie,
First thoughts are that it might be a relay lens for a trinocular or an aux. lens used on a stereo microscope. Could you post some pics when you get a chance?

The prices of the M Plan ELWD and SLWD Nikon CF objectives are a bit scary, eh?

I'm playing around with a CF 20X as mentioned at the link below. WD is only 3mm - but it only cost $75.00 and appears it will be useful for some applications.

www.photomacrography.net/forum/viewtopi ... +objective

Craig

[Gary W Brown]

Good morning lauriek,

From your brief description I think it might be an objective from the Eclipse series which is now discontinued. Is it marked like an objective?
Gary

[lauriek]

It's definitely a microscope objective, just the biggest one I've ever seen! (Bear in mind the 10x CF plan I got a while ago looked pretty big to me, not too much experience with microscopes except cheapo ones before that!)

It's marked on one side:

Nikon JAPAN
5x/0.13
WD 10.0

and on the other side:

CF Plan
5x/0.13
infinity symbol/0 BD

The thread is very close to 1" or 25mm dia, the unit is about 1.25" thick at its widest point. The actual lenses inside appear to be around 7-8mm in diameter (both at the back and front of the unit).

I will definitely take a pic or two tonight and put them up in this thread...

[lauriek]

In fact what the heck, I'm not too busy at work at the moment so here's a quick snapshot of it on my desk next to an AA (LR6) battery for scale!

[Planapo]

Laurie, Threads larger than RMS (about 20 mm diameter) that I know of are the metric M25 and M32. M25 would be very close to your 1 inch guess.
In Nikon brochures I have seen adapters, but they might be hard to find for a reasonable price.

How are you going to project the image of this infinity objective onto the sensor?
And will a 5:1 microscope objective give better results or better ergonomics than a good reversed enlarger lens when used for the same magnifications?

--Betty

[g4lab]

What you have there is a BD objective.
The BD stands for Bright Dark . (sometimes on older cherman objectives HD for Hell/Dunkel )
These are Brightfield Darkfield objectives for incident light. (ie metallurgical and other opaque specimens)

A Brightfield incident light objective is pretty much the same as a transmitted light objective but is usually longer tubelenth 210 or 215 instead of 160 or 170 if it is not an infinity corrected objective. The longer tublength allows them to stick an incident light half silvered mirror accessory into the optical path.

They get fatter in diameter when the darkfield feature is added. This is an annular system of mirrors and/or lenses or a combo of both which provides reflected (incident) light Darkfield illumination. Bausch and Lomb built one once called the TriVert that could do it inside the diameter of a regular RMS thread. But only up to 40x

But most manufacturers opted to just make the objective bigger in diameter which gave them alot of design freedom.

If you could have a reducer fitting made the objective part would work fine for you. Or you might be able to obtain a Darkfield illuminator and actually use the capabilities of the lens.

To see a diagram of how incident light darkfield works go to Microscopy U
or google ultropak which was a Leitz implementation invented in the old days.

The thread is probably a 24 or 25 mm.

But you can't use an infinity corrected objective without an additional lens to uncollimate and refocus the image. Such lenses have focal lengths specific to the series of scopes they are designed to be used with and therefore infinity corrected lenses would be almost impossible to use in a macro arrangement. The refocusing lens is usually placed in th binocular or trinocular head. Sometimes its put in the top part of the stand.

They idea of infinity correction was and is to allow the user to stack different optical modules including more than one at a time if desired and have the resulting tube length not affect the image quality while at the same time not requiring highly corrected optics and relay lenses in things like nosepiece turrets, fluorescence illuminators, regular incident light illuminators, Optovars (mag changer turrets) or othe filter turrets and similar goodies. You stack em as high as you need then have the refocusing lens to bring the collimated image beam to focus. Either on your ocular or your camera projective field plane.

[lauriek]

Ahh well - so it sounds like even if I could physically connect this (which I think should be possible with an RMS -> 25mm adapter) - because it's infinity corrected it's not going to work optically.

I'm not sure I understand the whole concept of infinity correction but I understand that it needs an additional lens which I'm not going to be able to add to the equation - even if I could get one from the correct microscope, fitting it in the correct place in a bellows setup sounds unlikely!

If I understand this correctly (I accept I probably don't!!), is it possible if I could physically attach this that it might work but only at one tube length?

ETA

Thanks to all for the help so far!! I really know very little about microscopes and their lenses and accessories. I must be honest whenever I start reading about decent scopes, DIC lighting etc it just goes way over my head with a big whooshing noise! Think I've learnt something important here though - avoid any objectives with the infinity symbol!

Betty at the moment I can get to around 4:1 with my reversed 50 at max extension, and I then go to the 10x nikon at minimum extension, not sure of the magnification with that but there seems to be a gap between the two, so I decided to look for a 5x to supplement what I have already... The OM38mm/f2.8 (wouldn't want the f3.5 I find the 20/3.5 too hard to work with) would do the job nicely but these still go for good money! Guess I'll have to re-ebay this one and keep my eye out for a non infinity corrected 5x CF!

[rjlittlefield]

Laurie,

If you can get it physically mounted without too much trouble, give it a try anyway. Even though it is designed for infinity tube, it can be made to focus like a macro lens. The working distance will increase a bit, the magnification will be off, and the image quality will degrade by some amount that might or might not be significant. When I was looking for info about objectives suitable for bellows work, one of the experienced folks on Yahoo Microscope group confessed that he sometimes used Nikon 10X infinity objectives in finite setups and they worked fine for his purposes. I have no personal experience.

--Rik

[g4lab]

I'm not sure I understand the whole concept of infinity correction but I understand that it needs an additional lens which I'm not going to be able to add to the equation - even if I could get one from the correct microscope, fitting it in the correct place in a bellows setup sounds unlikely!

This is correct. This is why infinity objectives can really only be used to their designed potential on a scope that has a converging lens of the correct focal length ( usually different for each manufacturer and sometimes even for different series from the same manufacturer) Perhaps one day they will enact a DIN standard for the converging lenses too.

If I understand this correctly (I accept I probably don't!!), is it possible if I could physically attach this that it might work but only at one tube length?

You will get an image, but it won't be very sharp. It also won't change mag as much as a regular objective, as you rack it out. You could install it reversed. It still wont be very sharp, but then will throw a converging image, which will crossover at its focal distance inside the bellows, and start diverging after crossover. You probably won't care for the image quality.

Gene

[Joseph S. Wisniewski]

Sorry to be posting on an old thread. I hope Laurie (or someone) is still interested.

The quick answer, Laurie's lens has a 26mm x 36 thread/inch mount. This can be written "M26 x 36 tpi".

Allow me to translate the lens label...

Nikon JAPAN - It's made by Nikon, in Japan
5x - focal length about 50mm
0.13 - NA 0.13 = f3.8 (there are formulas for this stuff)
WD 10.0 - Subject goes about 10mm from the front of the lens

and on the other side:

CF - Chroma free (no CA, good on a bellows)
Plan - PLAN (flat field to 95% of the frame, better than M PLAN)
infinity symbol - infinity optics, needs a tube lens
0 - no cover slide. If this number isn't 0, you can't use it on a bellows
BD - Brightfield/Darkfield. Has that "annular illuminator" discussed elsewhere in this thread.

All Nikon BD (Brightfield/Darkfield) objectives always have the M26x36 TPI mount. This is true of the old CF (210mm tube, 45mm parfocal) objectives for scopes like my old Optiphot 66, as well as CFI60 (infinity corrected 200mm tube, 60mm parfocal) lenses for newer Optiphot 100, 150, 200, or 300.

This M26 x 36tpi mount is sometimes referred to industry wide as a "BD thread". Is shared with Mitutoyo and Olympus BD objectives. Zeiss BD objectives take a different thread, because they're Zeiss.

[Admin edit by Rik: The preceding information about 26 mm threads is not entirely correct. In fact the Nikon 26mm thread has 0.75 mm pitch while the Mitutoyo 26mm thread is 36 tpi. These threads are very close but are not identical. See "Nikon and Mitutoyo objectives have different M26 threads" for full discussion. Some adapters have enough tolerance to work well with both threads, but other adapters that are made to tighter tolerances will work only with the exactly matching thread. If the adapter is inexpensive, chances are good it will work with both.]

Her other lenses, like my own beloved Nikon CF M PLAN 20X ELWD, take the old RMS mount.

Nikon CF objectives for either 160mm tube 30mm parfocal (labophot?) or 210mm tube 45mm parfocal take the old RMS (0.8 inch, aka 20.32mm x 36 threads/inch) "Royal Screw".

Nikon CFI60 objectives (aside from BD objectives, as was well covered) elsewhere, take the 25mm x 0.75mm thread.

And, just to be annoying, my Zeiss POL objectives have a 24mm mount, which I shim up to 25mm...

[Joseph S. Wisniewski]

First, some good news. As g4lab mentioned, BD objectives have an annular illumination system. This consists of ports in the back of the lens mount to let light in, and an annular prism that surrounds the lens. The objective has a two part shell (hence the two grip rings) and you can actually unscrew the front of the shell, and remove the prism. This will give you 10mm more free working distance on the 5x objective.

Now, the bad news, three different pieces of it.

First, there is the mechanical issue. BD objectives take a M26 x 36tpi thread. You'll need to somehow rig a mount to put this on the bellows. I suggest having a local machine shop drill and tap the M26 x 36tpi hole in the center of a 50mm disc of 1/4 inch thick aluminum, then either glue or bolt this to a T-mount.

Second, the BD objective annular illumination system must be disabled, or it will let unfocused light from the subject back through the lens mount and wash out the image. If you carefully cut a black annulus (washer like shape) to go over the inner lens mount and fill the gap between inner shell and outer shell, you can seal this thing off from the light. If you ever want to sell the lens, or mount it on a BD microscope, you'll have to poke something through the back ports to knock your annulus out. (there's something that sounds so wrong about that whole last sentence).

Third, not normally a BD problem, but laurie has an "infinity corrected" objective. This means, as Rik pointed out, on a bellows, you need to be slightly farther from the subject than is normal for that objective to get the image to focus at the camera, and this causes curvature of field to go wild.

[dmillard]

Allow me to translate the lens label...


0.13 - NA 0.13 = f3.8 (there are formulas for this stuff)


and on the other side:


0 - no cover slide. If this number isn't 0, you can't use it on a bellows

I would like to add two caveats to Joseph’s extremely comprehensive and comprehensible explanation of the meanings of the markings on microscope objectives (alliteration unintended ):

The f/# of a particular objective does not necessarily follow the formula 1/(2NA). For example, my Nikon CF N Plan Achromat 4/0.13 would be predicted to be an f/3.84 lens. In practice, it measures 1/3 of a stop slower than a Canon 35mm f/2.8 photomacrography lens at the same magnification, making it an effective f/3.14, more than ½ stop faster than predicted by the formula. I don’t know the cause of this divergence (whether the formula, the objective, or the macro lens contribute to the error), but similar discrepancies have been described in another thread: http://www.photomacrography.net/forum/v ... .php?t=424

Failure to use a cover glass of the specified thickness reduces the performance of high NA lenses, but has little or no effect on lenses with smaller numerical apertures. In a table in the back of a 1989 brochure on CF lenses, Nikon indicates that NA 0.25 lenses will suffer no image degradation when used without an indicated cover glass, and NA 0.4 objectives will only lose 3%. The large number of superb images produced on this forum by Nikon’s CF N Plan 10/0.30 lens (marked for use with a 0.17mm cover glass) provide further evidence of the relative unimportance of this designation when using this or similar objectives on a bellows.

David

[Joseph S. Wisniewski]

I would like to add two caveats to Joseph’s extremely comprehensive and comprehensible explanation of the meanings of the markings on microscope objectives (alliteration unintended ):

Well, I've always said alliteracy was one of the greatest problems facing America.

The f/# of a particular objective does not necessarily follow the formula 1/(2NA).

No, but at the objectives stated tube length, it definitely follows the formula:

f=1/(2*TAN(ASIN(NA)))

At any other length, you also have to take into consideration the dreaded "pupilary magnification factor".

For example, my Nikon CF N Plan Achromat 4/0.13 would be predicted to be an f/3.84 lens. In practice, it measures 1/3 of a stop slower than a Canon 35mm f/2.8 photomacrography lens at the same magnification, making it an effective f/3.14, more than ½ stop faster than predicted by the formula. I don’t know the cause of this divergence (whether the formula, the objective, or the macro lens contribute to the error),

That problem is well known. Canon lenses are typically 1/3 to 2/3 stops slower than Nikon lenses stamped with the same speed.

OK, on a more serious note, these calculations never work quite right for very low magnification objectives.

The CF N Plan Achromat 4/0.13 is a 210mm tube lens, is it not? That makes it a 52.5mm f3.81, and puts the clear aperture at 13.77mm. Except that it's not. Measure your front element diameter. Probably around 8mm...

Why? Because it's a retrofocus lens. Nikon CF lenses have a 45mm parfocal length. That puts the front node of the lens behind the mounting flange. So, to combat this, the lens has negative front elements. The overall effect is a reduced size front element, and an entrance pupil closer to the subject (and therefore smaller) than you'd expect from a lens of that focal length. And our old friend the pupliary magnification factor has to be taken into consideration. This means that the clear aperture really is 13.77mm only at one magnification, 4x. If you tested at a higher magnification, the small front element occluded the entrance pupil, and the lens tested slower than it should have.

The Canon 35mm f2.8 has a clear aperture of 12.5mm. If you tested both lenses at 4x, you'd probably find the Nikon to be 1/3 stop faster than the Canon at 4x. At higher magnifications, the Canon would catch up to the Nikon, and then pass it in speed.

but similar discrepancies have been described in another thread: http://www.photomacrography.net/forum/v ... .php?t=424

Interesting article. Doesn't take the bellows factor into consideration when reporting apertures, though, so the results are a bit skewed. I'll address that in another post, so as not to dilute this one.

Failure to use a cover glass of the specified thickness reduces the performance of high NA lenses, but has little or no effect on lenses with smaller numerical apertures. In a table in the back of a 1989 brochure on CF lenses, Nikon indicates that NA 0.25 lenses will suffer no image degradation when used without an indicated cover glass, and NA 0.4 objectives will only lose 3%. The large number of superb images produced on this forum by Nikon’s CF N Plan 10/0.30 lens (marked for use with a 0.17mm cover glass) provide further evidence of the relative unimportance of this designation when using this or similar objectives on a bellows.

Definitely. Good caveat on that one, David.

Not a problem for that 0.13 NA lens at all. Definitely something to be concerned about on my 0.5 NA M Plan 40 ELWD, though.

[Joseph S. Wisniewski]

I don’t know the cause of this divergence (whether the formula, the objective, or the macro lens contribute to the error), but similar discrepancies have been described in another thread: http://www.photomacrography.net/forum/v ... .php?t=424

Interesting thread. Doesn't take the bellows factor into consideration when reporting apertures, though, so the results are a bit skewed.

That's why there are statements like

In contrast, the Olympus 38mm macro lens actually has highest resolution wide open at f/2.8, and starts to degrade noticeably at f/5.6.

Of course the 38mm lens "degrades" at f5.6. That's a clear aperture of 6.8mm. I don't know what the author's bellows setup looks like, but my most frequently used setup (WizWerks 25mm conical RMS T-mount adapter, T-mount, Nikon PB-4 bellows, Nikon PK-13 ring, any old Nikon camera) gives you a range of 156-296mm flange to sensor. That's effective f28 at minimum extension, f43 at max. A typical APS crop sensor camera starts to show diffraction limiting at about f16, by f28 it's gone mushy.

You want a good stack out of the Oly 38mm f2.8? Shoot it wide open. Even then, you're at f22 at max extension, enough to soften things up a bit.

That's why I keep a 25mm f2.5 Photar around, it's got a full stop over my 25mm f3.5 Luminar. That full stop matters...

I want to mount the optical capsule of a 55mm f2.8 Micro-Nikkor in a short mount, and pit it against a rare 50mm f2.8 Photar and my 63mm f4.5 Luminar. I love the Luminar, but it's a bit slow on the bellows.

And that's why I'm not concerned that the aperture control on my 16mm f2.5 Luminar is sticky. You can't stop that lens down, ever. Wide open, on the bellows, it ranges from f24 to f46.

The thread was really starting to resolve all this, and then it just "stopped".

Rik noted the problem of diffraction and effective aperture, but didn't actually do the calculations that would have shown him the light...

Tom Webster noted the aperture relationships of a set of Luminars.

Charles Krebs stepped in with the pupillary magnification factor equations, but he didn't note how high those often are on microscope objectives. P > 3 is not uncommon.

And there it stalled.