Help!! Parfocal length of old objectives, once and for all

[patta]

Hello,
I am trying to collect the parfocal length of old objectives, so to choose the right extender.
Please help me , by confirming the measures you know, or contributing with new. The subject is messy and extensive.
Here below the image current table where I collected the values from forums and manuals.

You can view the update table and maybe contribute at the following link:
https://docs.google.com/spreadsheets/d/ ... sp=sharing

Prize!! the best contributor will receive a personalized parfocal extender with length of its choice.
I'm publishing the design of a set of extenders for 3D printing, https://www.thingiverse.com/thing:4567179, so to have the lenghts tabulated somewhere will be great.

Image of parfocal length table one

Parfocal_lengths_one.png (86.18 KiB) Viewed 6753 times

[BramHuntingNematodes]

I have many B&L objectives from the 1960s and prior. They are not all parfocal with each other. I don't know if they are supposed to be like that or are just old and abused. I can take some measurements.

[75RR]

.
Zeiss West Parfocality = 45mm

This is from page 11 in the Zeiss Optical Systems Brochure

http://www.science-info.net/docs/zeiss/ ... ystems.pdf
.

[patta]

They are not all parfocal with each other.

That's not good news for me!

Zeiss West Parfocality = 45mm

Ok I will start adding also the data (mechanical and Optical length) for 45mm systems

Thanks!

[apochronaut]

The parfocality variances of older objectives can result from various causes. Firstly, if an objective has ever been disassembled or repaired and the exact components that originated in it are not put back in, the parfocality can change slightly. Older objectives also could vary slightly due to glass batch variance and the internal shimming required in order to bring spherical aberration within tolerance.
As time has wandered on , the tolerances of raw materials have tightened, as have manufacturing practices, so the consistency of objective manufacture has improved to the point of being quite a bit more exact.

In talking about parfocal lengths, probably the term nominal should be used because small variances will always be there

Also, different eras have resulted in different design goals. Spencer and B & L at one time both offered tube length and parfical options. B & L had both 8 1/2" and 160mm tube lengths offered for the same objectives. I have two virtually identical Spencer 10X .30 apochromats, with the exceptional detail of both having 160mm tube lengths but varying in parfocal length from 34mm parfocal to about 40mm or more likely 1 9/16".
F. Koristka , oddly, used inch measurements for some of their production?

[patta]

In talking about parfocal lengths, probably the term nominal should be used because small variances will always be there

two virtually identical Spencer 10X .30 apochromats, with the exceptional detail of both having 160mm tube lengths but varying in parfocal length from 34mm parfocal to about 40mm or more likely 1 9/16".
F. Koristka , oddly, used inch measurements for some of their production?

Yes, I would stick to the "nominal" lenghts, and the list will never be really complete...
The Spencer 1 9/16" will have its special place... but I would continue to call them "AO Spencer", Reichert after 1985.

The Koristka, it is weird; very old, from a time when the UK was dictating standards in microscopy (RMS...).
My Koristka objective here is called 1/12" (focal length I presume) but the specified working distance is: 1mm Edit: no is not 1mm! It is written IMM as "immersion"; working distance is definitely shorter, like... 1/64".
Tube length, no idea, they were mostly making the objective only, to be mounted on other's stands.

The Koristka 1/12' measured at 36,8 mm
one 10× PZO "single piece barrel" measured at 34,7mm

[MicroBob]

Hi Patta,
Zeiss West was a result of the outcome of WW 2. Before the end of the war Zeiss had the Winkel Zeiss plant in Göttingen, working independently from the plant in Jena. I think they used 39mm objective parfocality, it should be in the Mikrofibel.

Leitz objective, tube length and intermediate image placement has changed in steps and for using older eyepieces on 160mm tubes you might add 8mm spacer rings to your list.

I'm into 3D printing too but haven't tried to print threads so far. How are your results and what layer height fo you use?

Bob

[patta]

Hi Patta,
Zeiss West was a result of the outcome of WW 2. Before the end of the war Zeiss had the Winkel Zeiss plant in Göttingen, working independently from the plant in Jena. I think they used 39mm objective parfocality, it should be in the Mikrofibel.

Leitz objective, tube length and intermediate image placement has changed in steps and for using older eyepieces on 160mm tubes you might add 8mm spacer rings to your list.

I'm into 3D printing too but haven't tried to print threads so far. How are your results and what layer height fo you use?
Bob

The 39mm from Zeiss Winkel is new, i'll check the Mikrofibel for tube lenghts.

The 8mm spacer is the one online already: it is the workbench used to test the 3D printing. You can give it a try.

Printed threads come out pretty well; the RMS of the objectives is quite fine (0.7mm pitch.) and I had to make several trials to find the right thread geometry and tolerances.
I use 0,1mm as layer height, the smallest my printer gives. Even the M12x 0.5mm screw of board lenses comes out functional.
I tried many times to cut fine threads on metal with the lathe, but that's delicate, I never succeeded, so printing, it is easier and seems to work.

Giorgio

[patta]

This list will never be complete, but I'm getting more or less satisfied.

I've added 45mm and some modern infinity system.
The table is now share on google Drive, you can edit it
https://docs.google.com/spreadsheets/d/ ... sp=sharing

Giorgio

[patta]

I more or less give up in this quest, I have enough data already. Big holes on Nikon and Olympus though.
It is incredible how many different systems have been developed!
Attached a static .pdf table of the results so far.

[apochronaut]

Hey ! You left out the Bausch & Lomb Little Gem not to mention the Tasco 750X Zoom Scout !

[EYE C U]

finally received a set of 160 objectives to finish off a zeiss scope for the grand kids..they are marked 160 but don't focus...they need to be closer than the table reaches....think tomorrow i'll slip a spacer under the table..the condenser is built in the table so should be ok...

[patta]

I left out thousands of stands! The B&L little gem, I refuse to put it in until one comes in my hands, as it seems to not even have a defined parfocal distance, since the objective is modular

[EYE C U]

WORKED FINE...3 SKATEBOARD WHEEL SPACERS INSTALLED AND ALL IS WELL...OFF TO THE GRANDKIDS IT GOES....FOR THE 28 BUCKS THEY ARE PRETTY NICE..CLEAR AND FOCUS WELL..(NOW)

IMG_8321.jpg (95.9 KiB) Viewed 6483 times

IMG_8320.jpg (55.62 KiB) Viewed 6483 times

[BramHuntingNematodes]

Yeah had a similar time adapting some old B&L objectives to an equally old Zeiss scope. Everything works well now!

[patta]

....FOR THE 28 BUCKS THEY ARE PRETTY NICE..CLEAR AND FOCUS WELL..(NOW)

Nice solution! By rising the stage, you avoided objective extenders and got perfect conjugate distance!
I see, you purchased chinese "185" objectives, that have 35mm parfocal length - while the Zeiss stand was expecting 45mm objectives.
The chinese "195" should be 45mm (didn't try myself though).

[EYE C U]

I WENT BY THE 160...DIDN'T KNOW ...ALL MINE ARE ZEISS SO NEVER HAD AN ISSUE..

[patta]

I've just published also a RMS to M25 adapter, 15,04mm long, for everybody's to print.
It makes possible to fit 45mm RMS DIN objective onto modern (CFI) Nikon stands.
More RMS-RMS to come.