DIN and RMS?

Cyclops · Post by **Cyclops** » Wed Oct 25, 2006 3:36 pm

Can anyone tell me if these two objective mounts are interchangeable? I am selling an objective with RMS thread and a buyer wants to know if its DIN thread. I have never come across DIN before(apart from film speed!

)
I understand it may be something to do with tube length?
Cheers
Larry

rjlittlefield · Post by **rjlittlefield** » Wed Oct 25, 2006 4:50 pm

Cyclops,

The distinction I know is between DIN and JIS. Both of them use RMS thread, but they're designed for different tube length and more important have much different distance between the shoulder of the threads and the focal plane of the lens.

http://www.techinst.com/faq.asp explains this way:

DIN - Deutch Industrie Norm-international standard used in the manufacture of interchangeable objective lenses. A typical DIN type microscope utilizes 45mm objectives+160mm tube length for a 205mm system length.

JIS Standard-Japanese Industrial Standard -international standard used in the manufacture of interchangeable objective lenses. A Typical JIS type microscope utilizes 36mm objectives+170mm tube length for a 206mm system.

If you look at Edmund Optics, you'll see that the highest-power objectives are very close to 45mm long for DIN and 36mm long for JIS. The text claims that the two can be interchanged, but that was emphatically NOT the case when I accidentally bought the wrong one. My scope is DIN -- using a JIS objective, it would not focus at all.

So... My recommendation is to focus the lens you're trying to sell and measure the distance from turret to slide -- if it's 45mm the lens is DIN, if it's 36mm it's JIS.

Or measure the length of a high power objective (40X, 100X) that works well in the same microscope with the objective you're trying to sell. "Works well" means that the high power objective focuses at the same or almost the same stage position as the objective you're trying to sell. Again should be 45mm or 36mm.

--Rik

Cyclops · Post by **Cyclops** » Thu Oct 26, 2006 3:43 am

Thanks Rik, I just tried to measure as you said, not easy! Closest I could get was 35mm. I'm measuring from the slide to the top of the objective where it joins the nosepiece right?

(Im a little confused as its the thread Im after not its length...)

rjlittlefield · Post by **rjlittlefield** » Thu Oct 26, 2006 4:02 am

Yes, that's the correct measurement. At the Edmund Optics page (http://www.edmundoptics.com/onlinecatal ... uctID=1720) it's what measurement "A" would be for a 100X objective, whose front lens element is much less than 1mm from the slide.

I think your potential buyer is almost as confused as you are. He's asking about "thread", but what he really wants to know is "will this objective work in my microscope?". That's not a matter of thread.

DIN and JIS objectives have the same thread (RMS). You can screw a JIS objective into a DIN microscope. Mechanically, it fits fine. Optically, it won't work. Its focal point will be 9 mm higher than DIN objectives, quite possibly too high to focus at all.

It sounds to me like you have a JIS objective. What brand/model is the microscope that you know it works in?

--Rik

Cyclops · Post by **Cyclops** » Fri Oct 27, 2006 3:23 am

rjlittlefield wrote:
It sounds to me like you have a JIS objective. What brand/model is the microscope that you know it works in?

--Rik

Its a simple chinese model, as stated in my sig

I think the brand is Jiang nan or something like that.
The objectives are unbranded too, but good quality!

Also I found this on a website:
"DIN 58888 RMS thread 55 degree thread angle (objective for microscope) "

rjlittlefield · Post by **rjlittlefield** » Fri Oct 27, 2006 5:45 am

Cyclops,

Important things need to be said repeatedly. Both JIS and DIN objectives use the same mechanical thread. That mechanical thread is called RMS and is specified as 0.8", 36 tpi, 55 degree thread angle, Whitworth form if memory serves. JIS and DIN objectives are compatible mechanically but not optically, as described earlier.

Perhaps the best answer to your buyer would be to tell him that the mechanical thread appears to be DIN, but the focus distance is only 36mm, not 45mm as standard for DIN objectives. Then if his application makes that OK, he'll be happy, and if it doesn't, at least he won't have you to blame.

(This presumes, of course, that the threads really do measure out around 0.8" x 36 tpi and not something completely different. I'd be pretty surprised if they're different, but that has happened before.)

--Rik

Cyclops · Post by **Cyclops** » Fri Oct 27, 2006 6:03 am

I did tell the bidder that I think its compatible, and he has now put a bid on it! If i tell him it may not work optically he might not be too happy. I did say i would get back to him with an update but he bid straight away before i had chance!

rjlittlefield · Post by **rjlittlefield** » Fri Oct 27, 2006 6:23 am

Hhmm... There are a lot of possibilities here. The buyer may not win, in which case all of this is moot. If he does win, and the objective works, then everybody is happy. If he wins, and the objective does not work, he'll be unhappy. If he's unhappy enough, he may demand his money back and/or give you negative feedback on eBay. If he hears additional information, he might get nervous and withdraw his bid unnecessarily. Or he might decide the objective will work fine, and think you're a good guy for getting back to him. Or he might decide correctly that the objective won't work, withdraw his bid, and save everybody a lot of trouble. It's hard to know what will work out best, but worth thinking through the cases.

All the best,
--Rik

DaveW · Post by **DaveW** » Fri Oct 27, 2006 7:42 am

Don't know anything about microscope mounting threads other than RMS stood for Royal Microscopical Society who standardised it. I would have thought BSW=British Standard Whitworth would have been a bit coarse for fine microscope tubes, but do not know. The fine threads we used to put on thin walled tubes was BSP=British Standard Pipe. These have all now been replaced by metric since we joined the EU:-

http://www.boltscience.com/pages/screw4.htm

http://en.wikipedia.org/wiki/ISO_228

There was also a BSF=British Standard Fine:-

http://www.vdwalle.com/knowledgebase/draad/bsf1.htm

DIN was the same as on film. As Rik says DIN was the German Standards Agency just as ASA was originally the American Standards Agency, both now being replaced by ISO=International Organization for Standardization

DaveW

rjlittlefield · Post by **rjlittlefield** » Fri Oct 27, 2006 3:48 pm

Hoping to lay this issue to rest...

See http://www.micrographia.com/tutoria/mic ... 023shi.htm .

Fig. 8. This drawing, which gives the dimensions of the screw thread of the objective, in inches, as adopted by the Royal Microscopical Society, presents the information necessary for the tool or instrument maker so that he can properly fit accessory apparatus to the microscope. The form of thread is Whitworth, pitch, 36 threads per inch. This standard seems to be the only one to which microscope manufacturers consistently adhere. (By courtesy of the The Royal Microscopical Society, London.)

"Whitworth form" describes the cross-sectional shape of the threads, independent of diameter or pitch. See for example http://www.boltscience.com/pages/screw4.htm.

--Rik

Afternote: So I don't have to look these up again, I'll list the critical dimensions here.
The major and minor diameters shown in the drawing are
0.800[+.003-0] and 0.7644[+.003-0] for the female (turret), and
0.7982[+0-.003] and 0.7626[+0-.003] for the male (objective).