Hey Apo, you ever seen one like this? (B&L Phase lens with no phase ring?)

[BramHuntingNematodes]

I can't find a trace of the phase ring. Was it removed? Can it be buffed out?

[PeteM]

Could be due to its age? You've heard the saying: "It's just a phase - he'll/she'll grow out of it."

OK - no idea. Phil might know - for some low power objectives the phase ring is at the back aperture of the objective and can be removed. Don't know if the B&L you have is like this.

[apochronaut]

There were some phase objectives from AO called B-Minus, in an L, M and H version. Most date from the 50's but one persisted into the 70's as an infinity corrected objective.The ring in the phase plate is imperceptible to the eye and the phase effect a little more towards BF with more particulate detail. Very small details show up as though in dark phase but broadcast against an almost BF background. I wondered initially if B & L did something like that but you think it would be designated . There is always the possibility of it being a prototype or experimental objective. No doubt, they played around with competetive systems but might not necessarily have made a specifically engraved barrel.
I have not had one of those older Flat Field 10X phase objectives in my hand, just a more recent planachromat. I have one of the 20X Flat Field phase objectives , however.
The phase plate on both is at the very rear of the objective, so it would not be hard to remove it and get a good BF objective out of it.
You didn't get it from treasure trove did you?

[BramHuntingNematodes]

Naw I bought it from a guy. Came from university surplus, so the tampering explanation makes much more sense than the exotic experimental prototype explanation, unfortunately. Breaks my heart a little, but I already have two BF flat field lenses in fine shape and I don't need another one. Guess I'll have to return it but still have the 20 planachromat phase which is something of a miracle.

[BramHuntingNematodes]

Hey now that you mention it though I looked it up and the 47.5 apo I got from the auctions was from the treasure trove. It works a treat.

[apochronaut]

Hey now that you mention it though I looked it up and the 47.5 apo I got from the auctions was from the treasure trove. It works a treat.

The O.D of the ring on the 10X planachromat is right about 5.8mm . The I.D. , just over 4mm , if you wanted to try to make one to fit an objective. It seems to be deposited right on the upper surface of a flat optical disc that is not present in any of the non phase planachromats. The upper surface of the disc sits ~3 1/2mm above the upper surface of the back lens.
The disc is 12mm across, set into the back of the objective with a threaded setting ring above a brass shim or spacer. It functions as a diaphragm, with 8mm of clear glass visible inside it's mounting structure in the centre of which is the 5.8mm-4+mm phase ring.

As phase rings go , it is quite narrow and only a partial block. Bright light shines through it. Something like the thin silver foil adherent to plastic that is found on the inside of certain food packaging might be a start. I suspect that it is a bit transparent, if peeled off the plastic.
There are these punches available. https://www.ebay.com/itm/1-30mm-Eyelets ... ect=mobile

[BramHuntingNematodes]

Thanks for the advice. I discussed our findings with the the guy and he found a phase plate inside a non-phase lens in the same pile of surplus and will send it. Maybe it's the right one or maybe not. Never can tell with these academic types.

I may try some experimentation also. I tried punches in the past but the are difficult to maintain concentricity with and also create a lot of deformation on the outside. A combination of punches and a die cutter may work. A full custom die cutting solution would be ideal, or perhaps a small automated cutting plotter for flexibility. I am intending to experiment with my turntable cutter at slower rpm with higher torque and cutting lubricant as I have had some good results so far with it.

The biggest problem I have had so far is that the phase shifting film creates a ludicrous amount of internal reflection, so the amplitude and AR modifying components are more crucial than I first thought. I was looking into dielectric film used in car window tinting, but I would also want to measure its phase retarding properties as well.

[Rossf]

Have you checked with centring telescope? I only ask cos the 10x Pv phase from Leitz has the ring right at the edge at the front-no light gap at all-you only really see it as the light ring moves past it when adjusting the heine condenser-it a very thin phase ring also-could it be that?
Regards Ross

[BramHuntingNematodes]

Oh yes, definitely looked at it from every angle it was quite a mystery however the phase plate was found inside another lens where it didn't belong. It arrives in the mail a bit later. I speculated that so.eone was trying to fit a more conventional lens with the plate to work on a non flat field b&l stand, as these flat field lenses are stand specific unlike most fixed tube length lenses.

[microb]

Thanks for the advice. I discussed our findings with the the guy and he found a phase plate inside a non-phase lens in the same pile of surplus and will send it. Maybe it's the right one or maybe not. Never can tell with these academic types.

Can you post a picture of that? I had thought the ring was attached to one of the lenses and not removable. Unless I'm misunderstanding here.

[BramHuntingNematodes]

In a stunning turn of events this nice mounted phase plate does not fit at all!

[apochronaut]

That ring doesn't look to me like it is for any flat field or planachromat objective but it is close. It could be from the last generation of 160 objectives. The 10X and 20X rings are very close in size and ring width.
That one has a spacer attached to replace the rear spacer the non phase objective would probably have had riding against the rear diaphragm. I think you will find that the rear retainer/diaphragm on your flat field objective sets against the rear lens bezel and drives the entire lens pack down, only stopped by the relative position of the front shroud; a mechanism in that parfocalizing system I posted about, recently. If you remove the rear diaphragm, that phase ring might thread in as a replacement( if it is B & L and if they kept the same thread...many companies do). You will probably have to cut the spacer off which isn't needed anyway, in order for the depth to equal the depth of the existing rear diaphragm. Looks doable.

[BramHuntingNematodes]

You will probably have to cut the spacer off which isn't needed anyway, in order for the depth to equal the depth of the existing rear diaphragm. Looks doable.

Phew gonna take some nerve.

[BramHuntingNematodes]

While messing around with this in the meantime I have managed to acquire the planachromat 10x and 40x phase lenses originally for the Balplan. Can confirm a) they look great on the ff Dynazoom and b) the phase rings match the sizes of the diaphragms in the older Dynoptic condenser. The difference between the flat field 40x phase and the planachromat 40x phase is quite subtle, but in a side-by-side the planachromat has better contrast and better color. This is a pretty good system to use in tandem with the old dynoptic fitted with apos for brightfield.