small bubbles on the rear lens

[Adalbert]

Hello everybody,
Does anybody know, what are the small bubbles (not the scratch in the middle) on the rear lens of the microscope objective?

BR,ADi

[ray_parkhurst]

The bubbles look like they are associated with the "scratch", which looks to me like chemical damage. I'd bet there was a splatter of something long ago that damaged the coatings. Do the bubbles appear elsewhere on the lens, or just around the scratch?

[Adalbert]

Hello Ray,
The bubbles appear on the whole rear lens.
If it is a damaged coating, should I remove it?
BTW, I’m not really sure that they are on the surface of the lens.
BR, ADi

[ray_parkhurst]

Do you have a pic of the whole area of the lens surface? The bubbles are probably just small pits in the coating. Like any damage, unless they are very extensive they will likely just reduce the contrast slightly. For sure it's better to leave them alone and not try to remove them, as you may do more harm than good.

[Macrero]

What objective is that? Are you sure the bubbles are on the coating of the rear element and not in between of a doublet in the rear lens group?

Be that as it may, don't try to remove it, you're just going to make things worse.

I had a Mitty 20 with similar spotting (the small spots around the big one), but they were in a doublet in the front group, a weird case of separation/delamination. Objective did more than acceptably well, though.

Best,

- Macrero

[Adalbert]

Hi Ray,
Thank you for the hint!
I haven’t tried to remove the bubbles up to now. I only have taken some photographs of them :-)
BR, ADi

[Adalbert]

Hi Macrero,
Yes, it is the same lens you have mentioned :-)

I have just taken some photographs of the “bubbles” via the front lens.

- looked at that by the eyes you see something like that:


- focused the camera on the “bubbles” then you can see following crosses:


BR, ADi

[Macrero]

Well, that's indeed weird. Insteed of bubbles, that looks more like a tiny chips and scratches. But the "spotting" (or some of it) seems to be inside the optics.

I am afraid you can't do much/anything about it. How's the objective performance?

Best,

- Macrero

[Adalbert]

Hello Macrero,

I am afraid you can't do much/anything about it

You are probably right

Up to now I have taken only two photographs by the usage of this lens:





But I should use the different motives for the checking of the lens (as white paper with a black raster).

BR, ADi

[Macrero]

Adi,

those looks really good. If you bought the objective recently and the flaws were not described, send it back for a refund and get a clean one. If you were aware of the flaws and you got the objective for cheap, forget about the bubbles, scratches or whatever that is and use it to take some nice photos as those you shared Unless you are going to do exhibits at MoMA, in that case it may be worth it to buy a new one

Best,

- Macrero

[Adalbert]

Hi Macrero,
No, the seller has used this lens very seldom and hasn’t known the flaws.
Up to now I haven’t had any problem with my bargains :-)
First I would like to check this lens as I can.
So, I have just printed a raster (by a color laser printer) and stacked it.

BTW, I’ll create a new thread for this issue.
BR, ADi

[Pau]

- focused the camera on the “bubbles” then you can see following crosses:

I've seen this kind of patterns, not in lenses but in old microscope slides. They seem crystals more than scratches, in fact in my old slides case I think that this is due to crystallization of the mountant, could be the same with the cement between glass elements in your case?

[Adalbert]

Hello Pau,
Yes it could be the damaged cementing between the lenses inside of the objective
BR, ADi