How to paint black lens edges?
Vincent
I would like to make the work you can see here:
I have the same binoculars, but I wander what would be the best
material to paint the lens edges: it must adhere and be opaque.
Once a friend of mine told me of a paint made of "Indian ink" or
"China black" (I don't know exactly how to put in English the Italian
"Nero di China"), Vinavil and water. I made, it, but lost the bottle
and don't remember the proportions.
Maybe the paints used my modelists can do it, but I remember they
"smell".
Any suggestions?
Many thanks.
--
Stars shine like eyes
Joseph Gwinn
Vincent <vinc...@gmail.com> wrote:
> Hi all,
> I would like to make the work you can see here:
>
> http://tinyurl.com/276qua
>
> I have the same binoculars, but I wander what would be the best
> material to paint the lens edges: it must adhere and be opaque.
And not flake off after a few years.
> Once a friend of mine told me of a paint made of "Indian ink" or
> "China black" (I don't know exactly how to put in English the Italian
> "Nero di China"), Vinavil and water. I made, it, but lost the bottle
> and don't remember the proportions.
In English, "Indian ink" is called "India Ink", and is water based.
China Black appears to be the traditional Chinese calligraphic ink,
which is similar to India Ink.
Water based inks are likely to flake off of glass.
> Maybe the paints used my modelists can do it, but I remember they
> "smell".
Any good grade of solvent-based glossy black enamel paint ought to work.
If the refractive index of the resin into which the soot is dispersed is
close to that of glass, the absorption of light will be profound. Avoid
water-based coatings.
Joe Gwinn
Adam Norton
"Joseph Gwinn" <joeg...@comcast.net> wrote in message
news:joegwinn-657F9A...@comcast.dca.giganews.com...(snip)
> In English, "Indian ink" is called "India Ink", and is water based.
>
> China Black appears to be the traditional Chinese calligraphic ink,
> which is similar to India Ink.
>
> Water based inks are likely to flake off of glass.
> > Joe Gwinn
I have actually used India ink before with decent results. India ink has a
binder of either shellac or gum arabic so it does not easily rub off or
flake. The index match is not quite as good as some lacquers though. It is
also quite dillute, so a thick coating of liquid is needed to create a thin
coating of pigment.
Another quick and dirty method is to use an indellible black Sharpie marker.
--
Adam Norton
Norton Engineered Optics
Optical design and systems engineering for Silicon Valley and beyond.
www.nortonoptics.com
(Remove antispam feature before replying)
Joseph Gwinn
"Adam Norton" <AnortonR...@ix.netcom.com> wrote:
> "Joseph Gwinn" <joeg...@comcast.net> wrote in message
> news:joegwinn-657F9A...@comcast.dca.giganews.com...
> > In article <Xns99DE7C74538F7...@193.43.96.1>,
> > Vincent <vinc...@gmail.com> wrote:
> >
> (snip)
> > In English, "Indian ink" is called "India Ink", and is water based.
> >
> > China Black appears to be the traditional Chinese calligraphic ink,
> > which is similar to India Ink.
> >
> > Water based inks are likely to flake off of glass.
> (snip)
>
> > > Joe Gwinn
>
> I have actually used India ink before with decent results. India ink has a
> binder of either shellac or gum arabic so it does not easily rub off or
> flake.
Yes, but the adhesion to glass isn't really that good, compared to a
lacquer or oil-based enamel. If one is going to go to the trouble to
blacken the edges, one might as well use something that is sure to work,
and to last, so I would prefer paint or lacquer over ink.
> The index match is not quite as good as some lacquers though. It [ink] is
> also quite dilute, so a thick coating of liquid is needed to create a thin
> coating of pigment.
>
> Another quick and dirty method is to use an indelible black Sharpie marker.
I use these markers a lot, but note that the black fades over time and
light exposure as the black dye bleaches. I found this out when marking
fluorescent lamps with installation dates, so I could track service
lifetimes. Carbon blacks will not fade, so for lamp marking I went to
india ink.
There are solvent-based india inks intended for use on mylar drafting
film that will stick to ground glass and many plastics (except teflon,
polyethylene, polypropylene, and probably nylon).
What I would suggest is Krylon #1602 Ultra-flat black (a carbon-loaded
spray lacquer) or the like. The slow-drying oil-based outdoor enamels
are best, if one doesn't mind waiting a day or two for the paint to dry.
Joe Gwinn
Helpful person
There are many diverse opinions regarding blackening lenses. My
opinion (and I feel pretty strongly about it) is that in general
lenses should never be blackened. The problem with all blackened
edges is that the "inks" that work (to some extent) tend to flake. In
addition, the blackening that is thick enough to work adds thickness
to the lens diameter, often resulting in the lens not seating properly
in its mount.
Other options that can be used are:
1. Knife edge stops placed strategically within the lens.
2. Rifling the lens barrel (helps a little bit).
3. Depositing thin black chrome as a stop on lenses and at the
interface of cemented doublets. (This gives a nice knife edge.)
4. Bonding index matching black material on the troublesome surfaces
(not easy with lenses).
The improvements shown in your link (if not faked) are probably due to
extremely poor initial design
Richard J Kinch
> What I would suggest is Krylon #1602 Ultra-flat black (a carbon-loaded
> spray lacquer) or the like.
I second this. Spray a little in a cup and brush it on.
However, if you're using cemented lenses like achromats, take care your
paint doesn't solve the cement.
Adam Norton
"Helpful person" <rrl...@yahoo.com> wrote in message
news:1194269158....@k79g2000hse.googlegroups.com...(snip)
>
> There are many diverse opinions regarding blackening lenses. My
> opinion (and I feel pretty strongly about it) is that in general
> lenses should never be blackened. The problem with all blackened
> edges is that the "inks" that work (to some extent) tend to flake. In
> addition, the blackening that is thick enough to work adds thickness
> to the lens diameter, often resulting in the lens not seating properly
> in its mount.
>
> Other options that can be used are:
>
> 1. Knife edge stops placed strategically within the lens.
> 2. Rifling the lens barrel (helps a little bit).
> 3. Depositing thin black chrome as a stop on lenses and at the
> interface of cemented doublets. (This gives a nice knife edge.)
> 4. Bonding index matching black material on the troublesome surfaces
> (not easy with lenses).
>
> The improvements shown in your link (if not faked) are probably due to
> extremely poor initial design
>
Regarding baffles and stops and lens clear apertures, I heartily agree that
these are very important and too often are not designed very well. I think
this is due to engineers who have gained most of their optics experience
working with lasers where the lenses just have to be slightly larger than
the beam and the AR coatings are very good.
I agree that a well-designed eyepiece should not need the edge blackening
shown in the original poster's example.
That said, there are times when edge blackening is useful. One case is where
the reflection from a steeply curved surface falls on the inside of the lens
edge. It is a trade-off with the disadvantages you listed above. I heard a
rumor once that Zeiss actually used an array of black lacquer formulas index
matched to different glass types.
I have often thought polishing the edge of a lens might be something to try
since specularly reflected stray light is often easier to block than
scattered stray light. It also overcomes the disadvantages of the black
lacquer. Have you ever experimented with this?
Helpful person
wrote:
> I have often thought polishing the edge of a lens might be something to try
> since specularly reflected stray light is often easier to block than
> scattered stray light. It also overcomes the disadvantages of the black
> lacquer. Have you ever experimented with this?
>
> --
> Adam Norton
>
optics) this could be a very successful strategy. In general, I
prefer a scattering edge. This often results in a combination of TIR
inside the lens and angles that are easily absorbed by stops.
Charles Manoras
Joseph Gwinn
"Charles Manoras" <inc...@cette.adresse> wrote:
The black in nail polish comes from a dye, and so the color will fade in
a year or two. Carbon is forever black.
Joe Gwinn