D2764A EEPROM + $100 Nikon Plan Apo 20x / 0.75 objective

[Bob-O-Rama]

So I got one of those $100 Nikon Plan Apo 20x/0.75 "NIKON Plan APO 20X / 0.75 DIC N2/ 0.17 WD 1.0" objectives. This is the first micro-photography I've done in ~30 years, let alone in my basement, so I ran into a lot of "noob" mistakes ( enumerated at the end ). The subject is a 1980's 64K EEPROM chip.

20x - kinda looks like a printed circuit board.



20x + 2x rear doubler = 40x - not a disaster, not great.



100% crop from another 40x - warts and all



A comparison of a 100% crop from the Nikon at 20x with the CF-4 at 5x scaled to match.



The whole die at about 5x via CF-4 objective.



Confessions:

1. I normally mount subjects in black modeling clay, and after final adjustments let it rest for 30 minutes or so. This is fine at say 6x. I was impatient and there was significant subject drift which blurred the images.
2. It was laundry day. The washing machine vibrations were being picked up by the rig.
3. The Infinity Photo-Optical K2 Distamax + NWE Objective was used as the tube lens. It is designed for this, however I forgot to set it to infinity focus. That should improve IQ. Next time.
4. The spacing between the objective and the tube lens is off by about 5mm
5. No cover glass. Does this actually matter?
6. I could tell just jogging it forward that the objective had such thin DoF that it was challenging to the 1 micron steps in the WeMacro.

I have to assume fixing any of these will help.

[Ichthyophthirius]

5. No cover glass. Does this actually matter?

Yes. At NA 0.70 it matters a lot. Actually, it looks quite good despite the lack of a coverglass.

It'll be interesting to see this with a cover glass and all that spherical aberration gone!



Regards, Ichty

[Olympusman]

It may be the difference between a macro setup and a microscope with axial illumination.

Mike

[Bob-O-Rama]

I think its a lot of both. The center of the image seems to suffer from the raking angle I am having to use to get it lit. ( I do not have a coaxial lighting setup, so its coming in from the sides as a severe angle. ) Anyway I have a lot of playing around. Cover slips and turning off the washing machine are high on the list, as is using the tube lens properly. I think its a tossup at this point. :-)

Here is a 100% crop at the center of the 30MP frame. Fugly. but honestly pretty typical of the diffraction you get with chips. Diffuse and head on lighting helps, but I can't do either of those easily. looking for suggestions.



Here is another - showing how the lighting makes a huge difference.

[Scarodactyl]

The cover slip (or equivalent) is absolutely essential for this objective. I am surprised your results are this good without it. It's a super amazing lens though, especially for the price!

[rjlittlefield]

3. The Infinity Photo-Optical K2 Distamax + NWE Objective was used as the tube lens. It is designed for this, however I forgot to set it to infinity focus. That should improve IQ.

This is not so clear. Considering the whole situation, it seems quite possible to me that you have inadvertently compensated for lack of cover glass, by focusing the K2 closer than infinity.

To explain...

It is important to have the tube lens focused at infinity when the objective is being used as intended.

But here (as I understand the situation) you've used an objective that was designed for cover slip, without one. That amounts to using a cover slip that is a lot too thin.

One of the classic methods for correcting spherical aberration due to cover slip errors with finite objectives is to lengthen the tube if the cover slip is too thin.

With an infinity objective, the same type of correction is made by focusing the tube lens closer than infinity. In both cases the objective is made to focus closer than it would with a nominal tube, and it's that shorter focus that introduces the correction.

I don't have any information available that would predict how much correction could be made this way.

But for future experiments where there may be cover slip errors, I would encourage you to adjust focus on the Distamax for best image quality, not for infinity focus.

--Rik

[Lou Jost]

I think I remember reading that coverslip aberrations usually can't be adequately corrected by short-focusing the tiube lens, because there is not enough focus throw to do the job.

The guys who make your Infinity tube lens also make one that does correct coverslip errors dynamically. Maybe you have one? If not, I think a coverslip is a cheaper option in this case. But if your objective is one of those unmarked versions, you'll have to do some research on this forum to figure out the correct thickness for your version.

[Adalbert]

Hello Bob,
Really nice!
I have bought such $100 lens too but its name is a little bit different: “NIKON Plan APO 20X / 0.75 DIC N2/ 0.17 WD 1.0”
Please check the NA 0.70 or 0.75
I haven’t started testing it yet but you have shown very promising results.
BTW, You should not install your setup on the washing machine :-)
BR, ADi

[Bob-O-Rama]

3. The Infinity Photo-Optical K2 Distamax + NWE Objective was used as the tube lens. It is designed for this, however I forgot to set it to infinity focus. That should improve IQ.

This is not so clear. Considering the whole situation, it seems quite possible to me that you have inadvertently compensated for lack of cover glass, by focusing the K2 closer than infinity.
--Rik

This occurred to me as well, as I've seen where the internal focus on the K-series was used to for reducing aberrations introduced by shooting through portholes in reaction chambers. This is sort of the same problem. Even if its not, there will no doubt be a "better" position for the focuser. I'll give it a try.

[Bob-O-Rama]

Hello Bob,
Really nice!
I have bought such $100 lens too but its name is a little bit different: “NIKON Plan APO 20X / 0.75 DIC N2/ 0.17 WD 1.0”
Please check the NA 0.70 or 0.75

Yeah, I had that wrong. Its the 0.75 one, and the description is identical to your. I edited my posts to reflect that. Thanks!

[ChrisR]

Did you by any chance measure the thickness of the quarz wndow on the chip - before you (I assume) belted it witha a chisel to reveal the chip?
I'm just musing. There were versions of inf/apo/20x/NA0.75 which were designed for thicker cover glass.
If it just happened to suit, then I think, from sketching rays, that the air gap between glass and chip wouldn't matter, but I'm not sure. Rik et al?

[Lou Jost]

In some optical diagrams of objectives designed to shoot through glass (like the Mitutoyo G Plan Apo), the glass plate is shown in the middle of the optical path, without showing measurements of the location, as if that didn't matter. See the drawings on Edmund Scientific:
https://www.edmundoptics.com/p/g-plan-a ... ive/29604/

Also I have not seen any difference between putting the glass on top of the subject or against the objective.

[rjlittlefield]

If it just happened to suit, then I think, from sketching rays, that the air gap between glass and chip wouldn't matter, but I'm not sure. Rik et al?

If the glass is perfectly flat, uniform, and perpendicular to the optical axis, then the air gap doesn't matter.

But note that for each point on the subject being imaged, the diameter of cover glass that is inside the entrance cone increases in direct proportion to its distance from the subject. This means that any variation in cover slip thickness is more likely to cause problems when the air gap is large.

--Rik