The Sears 6210 and 6209 (oldies) (1 Viewer)

I was low on binocs in the 8x40(or 8x42) size,
so I picked up and cleaned (is was OK inside)
the 8x40 Sears Model 6210...
it's a moderate-width model with a near-perfect flat field..very nice, good color.
Extremely solid. Make by the mysterious "JB65"..no company in the JTI list.

So when I saw the 7x35 Model 6209, also JB65, I picked that up.
It was a 2 -hour cleaning and repair..and one side doesn't slide right.
Ugh. But I can tell the field. It is very good. However, there are much
bigger quantities of precision-flat-field 7x35s in the past (from Japan)
than 8x40s, so you'd be better off looking for a "featherweight"
(under many brands) or "featherlight" or the Zephyrs or a Triton 748.
So...look for one of those in good condition instead of a 6209 that looks
like it's been in a fight.

And...I'm keeping the 6210. It's small for a 40mm, although
it really does measure 40mm. Sort of a slightly bigger version of the
compact Tower 7x35 Featherweights.

I just salvaged the 6209s, opening eyepieces for
cleaning and blackening. The design is
Kellner-plus-parabolic-flat, just like Swift Triton 748s....aha!
Beautiful field in the
70mmx400mm (f/5.7) and the 70mmx700mm (f/10) telescope. 22mm fl.

It's amazing what the one aspheric face does for the field edges.
Depending on the element spacing, you can go to 60-deg apparent or 50-deg-precision/flat.

Optic Nut,

I was thinking of doing some blackening myself on some vintage bins. Just wondering what kind of advice you could give in that regard or a thread you could point me to. I'm interested in increasing lowlight performance. Seems as if some of the vintage bins I have looked at could use some on the internals. Maybe I'm wrong, seems like that would be easy to do at the factory. I'm just a novice at this kind of stuff though.

The achromatic doublet is about the only place where the
concentration and thickness make it a high-value job.

Half of the doublets have a shiny fired rim finish, so you need to
lightly grind the rim on ~#400 emery paper to get a ground glass finish.
Then it's just a matter of using a black Sharpie marker. Paint will usually
spoil the fit. I mark two patches, dry a few minutes, and hold by the black
parts and mark the un-done parts.

I know...most are not done, and many even have leftover balsam from
the gluing. Must be a labor cost issue.

Just cleaning an otherwise clear-looking EP can do magic to the contrast.
The blackening is just icing on the cake. Make sure you have an optical spanner
to work the rings (the 'two screwdrivers on two booms' tool).

It can be hard to put the lenses back in without fussing and jamming,
but I've found carefully piling together the elements and spacer rings
on top of a screwdriver 'spin knob' and raising them into the cell body
elevator-style (or lowering it onto them) gets rid of a lot of fuss.

For the contrast-obsessed, adding little hoods to the objectives is helpful.
There are many schemes for making hoods. I spray black emery cloth
with a little flat-black paint and wrap strips of it. Regular black abrasive
picks up some sheen at low angles, the carbide crystal faces.
A little flat black paint snuffs out that sheen... just a tad of the paint, not much..

When you say the achromatic doublet, is this the lense in the eyepiece that is the thicker one that looks like 2 lenses together. I had a Jason clipper apart, it had 3 lenses( 3 element?). The middle lense was thicker and looked like 2 lenses attached. I'm guessing this is it, and that you lightly sand the outside circumference, and Mark that black?

Thanks much.

Right../

Actually, each bit of glass is an element, so the EP from the Jason Clipper would be
"4 elements in 3 groups". You have an eye element, central achromat, and a field lens.
Yes...unless the rim is already frosted, you can just rotate it on the emery paper and mark it black.
The improvement is especially good for that eyepiece type, which was simply called
a "widefield eyepiece". Getting rid of scattering in the middle of the cell is awesome.
You have a pretty wide light cone hitting it.

I have 2 salvaged EPs from a cracked-arm pair, not sure if it was Clipper.
Sure enough: 4 elements, 3 groups, blackened central achro.
20mm fl. Put into a Travelscope 70, the field opens out and flattens. Excellent view.