3X Barlow lens
It is a precision multi-lens all-glass
optical system, just as an eyepiece is, and can actually
improve the performance of many eyepieces.
However, the Barlow lens that cheap department-store or
toy-store telescopes are terrible: uncoated lenses, shiny
on the inside, the chrome part of the eyepiece also
chrome inside! Also, the entire tube was shiny black
plastic. Completely useless.
We can not change the lens, however we can remove all the
shimmer hence lens edges, the tube and internal field
stops can be blackened to reduce internal reflections and
- Unscrew the barlow
lens and use sandpaper on the inside (both
sides). Make circular (like threading) movements
or random, but never strait lines (from top to
bottom). Be very careful that you do not thouch
- spray or paint the
inside flat mat black. Do not forget the chrome
part on the inside too!
- Next, we need a baffle to reduce the
glare even further. Unscrew the both parts of the
Barlow and you'll see a little rim.
That's the place we will
put our baffle. I used a plastic ring and drilled
a hole in the center of 10 mm. Paint it flat
black on both sides and glue it against the rim.
- Re-fit the Barlow.
Homemade: Make a 2X Barlow lens
out of a 3X Barlow
A 3X Barlow is way to much for those cheap
department-store telescopes. Building our own 2X Barlow
lens and reducing the default magnification of a 3X
Barlow is rather simple and will make it more useful
(less blur, more contrast, shorter length and so easier
to use on refractors). It will provide sharper images.
Prior to the type of lens used the magnification of a
Barlow lens mainly depends on the distance of that lens
to the eyepiece. So, to modify the Barlow is easy:
- You need to do the
same modification as stated above to remove the
- We don't need the
top part of the Barlow lens (where you put the
eyepiece), but do not throw it away! Further in
the text we will see how to use that part as a
0.96 inch eyepiece converter for a 1.25"
telescope focuser. We gonna use the bottom part
(where the lens is fitted).
- Next, we need a
baffle to reduce the glare even further. Lens
edges and internal field stops are blackened to
reduce internal reflections and improve contrast.
You can make the baffle out of whatever you have
around that fits the inside of the Barlow (+/-
...mm). I made the baffle out of a tiny piece of
5/8" PVC pipe and some double-sided adhesive
tape. Saw about 5 mm of the 5/8" pvc tube.
Then stick the tape in two layers on top of each
other on the pvc-tube. Remove the adhesive around
the baffle (else it will be virtual impossible to
get it 1/3 inside the bottom part of the Barlow
Now paint the baffle mat black.
- The outside of the
bottom part of the Barlow lens is threaded. Ideal
to screw our eyepiece holder onto it. So we need
some PVC tube that nearly fits the thread with an
inside diameter of 0.96" to fit the
eyepiece. These are the measurements of the
- Finished "shorty" modify
Improve old 0.96"
There are many ways to improve the original
eyepieces without buying new ones or replacing the
focuser to allow fitting 1,25" eyepieces (Plösll
are real good for their money).
Most 0.96" eyepieces that came with those cheap
department-store or toy-store telescopes are terrible:
shiny on the inside, the chrome part of the eyepiece also
chrome inside, often plastic lenses etc.!
First and easiest thing we can do is to remove all
internal reflections inside the eyepieces themself and
(if needed) clean the lenses as well (read about it here). None of those eyepieces I saw had any
baffling or are even lacking flat black mat paint! Shiny
black plastic isn't all that dark! Just keep it in the
light, straight or under an angle, and you will clearly
see the reflections. Any reflections are loss of light
and can cause ghosting and glimmer. So get some matt
black paint and paint the inside of the eyepiece (be
careful not to touch the lenses!). The contrast will
improve and reduce ghosting and glimmer. It will greatly
improve observer comfort by minimising glare and
providing sharper images.
0.96" eyepiece with the lenses removed
to clean and to paint everything flat mat black. To clean
the lens of your eyepiece you need to take care of a few
things which you can read all about it here.
Homemade 25mm eyepiece out of
an old camera
I had an old (defective)
analog film camera from where I removed the lens pieces.
There was a wide angle lens combination (8mm-22mm) fully
coated in it. Ideal to make myself a wide view 25mm
eyepiece for my SkyWatcher telescope.
Get yourself a plastic 35mm film canister (black
with gray lid and one with the black lid).
We will be using the 35mm film canister with the
gray lid as the eyepiece holder
and the top of a second 35mm film canister with
black top to use as a cover from where the lens
will peep through.
We'll also need a
piece of metal tube that fits inside the film
canister. This will make it strong enough (of
course you can use any other PVC tubing that fits
- Paint the inside of
the cansiter and the metal tube black or flock
- Glue the metal tube
inside the film cansiter.
- Cut the bottom of
the film canister (the one that had the gray lid
Cut or drill a hole in the cover of the cover of
the black covered 35mm canister so it will fit
the smallest part of the film camera lens.
We mount the lenses
in a way that the smaller part of "peeps
through" the back film canister hole.
Make a eyepiece out of
- I had a cheap 10$
binocular which I had no use for...except...to
experiment with the pieces for homemade
This 12x25 binocular has achromatic lenses,
coated eyepiece lenses and two erecting prisms.
- So lets make an
10mm eyepiece from thbinocular eyepiece
Tip: you can even keep the erecting prism if you
want upright images. The roof prism design
employs silvered surfaces that reduce light
transmission by 12% to 15%. The prism does create
light loss and some less contrast.
- The binocular with the
eyepiece removed which also clearly shows the
- The old 35mm film
canister comes in place (again). To give it more
strength I used some metal pipe that fits snuggly
inside. "Luckely" the binocular
eyepiece fits the cansister perfectly. You can
also modify the eyepiece to be used in those old
0.96 eyepiece telescopes too. Much better then
the cheap plastic lenses that they often sell
together with those cheap department store
Make an erecting eyepiece out
of the prism of a binocular
- The prisms of this
(same) binocular are ideal for making a
rectifying eyepiece (puts everything right side
up, like a diagonal).
We need a 1,25 " diameter PVC tube and a
piece of tube that has an inside diameter of
1,25mm (those connection pieces plumbers use to
connect two pieces of tube together).
The smaller part fits into the focusser and holds
the prism. The larger tub fits over the smaller
one and allows your eyepieces to be inserted.
- First sand the
inside of the two tubes and paint it matt black
(or flock it)
- This explains clearly how the
erecting eyepiece is mounted and constructed from
two tubes of PVC and the prism of the binocular.
- Tip: the prism
could also be used in your finder if you want an upright
the roof prism used here
A Schmidt-Pechan prism is a type of optical prism
used to rotate an image by 180°. They are
commonly used in binoculars as an image erecting
The prism consists of two glass prisms separated
by an air-gap. Multiple total internal
reflections of the light cause a vertical
flipping of the image; a "roof" section
of the second prism also flips the image
laterally, together causing a 180° rotation of
the image. The image's handedness is not changed.
Compared to the double-Porro prism or Abbe-Koenig
designs, the Schmidt-Pechan is much more compact.
However, the large number of reflections and
glass/air transitions of the light make the prism
more lossy than the other designs. Some of the
surfaces must be optically coated for efficient
internal reflection, since the light is incident
at an angle less than the critical angle.
Homemade 1.25" to
0.96" eyepiece adapter
Remember that old
0.96" Barlow we modified?
And the top part we didn't need? Well, we need it now to
make ourself a homemade 0.96" to 1.25" eyepiece
adapter. This will allow you to use your old lenses,
barlow and diagonal with your telescope.
Saw the Barlow top to
about 28mm in length (not critical)
You will need to file it
down a bit to fit inside your telescope's 1 1/4"
eyepiece holder (+/- 31mm), and voila, a 0.96inch
If you do not know what
collimation is then please read this first. In short: Collimating a telescope
is lining up its optical components (lenses, mirrors,
prisms, eyepieces) in their proper positions.
If you have a cheshire collimation piece then you can
skip this...but this is a cheap alternative...not as
good, but still...
- if your scope has 1,25" eyepieces: out of a
plastic 35mm film canister (black with gray lid). Drill
or punch a small pinhole (+/- 4mm) in the exact center of
the lid and cut off the bottom of the canister. Replace
- if your scope has 0,96" eyepieces: use an
protection lid that came with your scope (like one of
your diagonal or the one used to protect the eyepiece
holder). This is of transparent material. Drill or punch
a small pinhole (+/- 4mm) in the exact center of the lid.
Draw a diagonal with a thin black permanent marker.
This device will keep your eye centered of the focuser
tube. The next thing to improve things:
More to follow, so
please visit again soon.