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L

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RE: Filters
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A rough test of telescope filters (Solar filter + Colour filters + Baader contrast filter + IR-cut filter) with a with a 80mm F6 achromatic refractor and Vesta pro webcam.†

The Sun, and Sunspots 11471, 11472 and 11469 used as targets. Weather and 'seeing' were variable so not a precise test.

Ed ~ Music created on an Amiga 1200.



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L

Posts: 131433
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Planetary Filters
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Using Planetary (Colour) Filters

With the response curves and transmissivity values I have calculated, I now have a better understanding of what exactly all these different filters are doing.† The blue filters remove greens and reds, the green filters remove blue and red, etc.† One obvious question, and one that luckily many other amateur astronomers have already figured out is:† what are all these colour filters good for?† The simple answer is to increase the contrast between different features when viewing planets through your telescope.
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L

Posts: 131433
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Filters
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A cheap way of buying coloured filters is to pickup small (25, 27, 28.5, 30 & 30.5mm etc) camcorder or vintage camera filters and simply drop them into a Barlow lens (with, or without, the 'magnifying' lens removed); the loose glass filter will be held securely by the eyepiece. The larger filters can be removed from their cells to fit into the Barlow tube. (See previous posts)

Vintage camera filters such as the Voigtlander 29mm push-fit types can be picked up relatively cheaply (i, myself, sometimes use a nice light yellow Voigtlander glass filter).

A †Step Down/Up Filter Ring Adapter could also be used (but getting one for the correct step may require getting two adaptors).†



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L

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Using Colour Filters With Telescopes



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L

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A money saving tip on eyepiece filters is that you can use normal photographic filters; just hold them in front of the eyepiece. Second-hand filters are only a few pounds - and are an excellent and quick way to test how the filters affect an image. In some observing situations this is actually preferable.
Using eyepieces with long eye relief would be advantageous using this method.
Those with rubber eye-shields, the filter can simply be rested precariously on top.
A slightly more permanent solution if you have a 2" drawtube is to attach a stepper ring to the Reducer (for those with 31.7mm eyepieces).† A 48mm filter will fit inside a 2" drawtube. Different filters can then be simply screwed onto the attached stepper ring (or an empty filter ring).
You can use superglue or blue tack etc, to attach the stepper ring.† 49mm filters are usually too large, but they can be disassembled and the filter simply stuck on the front.

Of course, those with a threaded 2" diagonal can normally directly use 48mm eyepieces.

It should be noted that suitable 31.7mm Barlow lens can loosely hold vintage 30 - 32mm glass filters, or modern-day camcorder filters. The filters can be simply slipped into the eyepiece holder, and held in place by the eyepiece. The lens of the Barlow can be removed to turn it in to a glorified filter tube, (though, removing the lens of the Barlow will affect the drawtube travel distance and focusing).

Ed ~ A mountain bike tyres inner tube can be cut down (and cleaned) to make excellant rubber eye-shields... (more on this, and fashion tips, in a future post)



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L

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How to make narrowband filter deep sky images with a DSLR and clip filter for astrophotography



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L

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How to make your own objective solar filter for binoculars, camera or telescope

Cut two equal sized rings of stiff cardboard. The inner diameter to be the same as the full aperture of the telescope-lens (or mirror), the outer diameter to be 10cm (~4") larger.
Cover one full face of each cardboard-ring with double sticky film or "Double-Tape". Cleanly cut any inner and outer excess of film, so that only the two cardboard faces are covered with sticky tape.
Stretch out a square piece of "Kleenex-Tissue" flat on a hard plane surface (a table) and secure the four corners of the tissue with clear adhesive tape. The tissue must be stretched out flat without ripples.
Cut a square piece of AstroSolar Film a little larger than the outer diameter of the stiff cardboard rings.
(For cutting put AstroSolar Film between two sheets of white paper. This "sandwich" with both sides paper and the film in between can easily be cut without producing cheases or fingerprints on the film.)
Gently place AstroSolar Film onto the flat Kleenex-tissue and secure the four corners with tape - but do not stretch it!
AstroSolar Film must not be put under stress tension to retain it's precision optical property.
Hold one cardboard ring with the sticky side down 10mm above the film and let it fall down onto the film, so that the ring touches the film all around at the same time..
Turn around the cardboard ring with the film covered side facing upward and lay it back onto the Kleenex. Stick the second cardboard ring against it. Now you have created a round film-holder with AstroSolar Film cleanly and securely fastened without creases and ripples - but most of all: without stressing the film!
Now put a 50mm (2") wide stripe of strong cardboard around the telescope dew cap or front end and tape the ends with double-tape. Repeate this procedure 3 times with double-tape between each layer to produce a stiff 50mm high cardboard cylinder to precisely fit onto your telescope.
At last glue the AstroSolar film holder onto the 50mm cylinder while the cylinder is still mounted onto the front end of your telescope

Read more (PDF)



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L

Posts: 131433
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Solar Filter
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Baader AstroSolar Safety Film

Baader Planetarium is proud to present a new safety film for solar observation. It is made for the construction of high-quality objective-filters for observing the sun with telescopes, binoculars, camera or video-lenses. This foil is CE-tested and reduces the intensity of sunlight by 99.999% (neutral density 5.0).
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AstroSolar is essentially free from pinholes, since - other than with even the most expensive glass filters - it is coated on both sides, so that the chance of two pinholes overlapping each other is extremely faint. Pinholes do appear, but to 1 out of 10000 only in optical density 2.5! Baader AstroSolar safety film has been approved for eye safety by the National Bureau of Standards in Germany, the PTB. Unlike any other Solar Filter on the market, AstroSolar is CE-tested according to EG-Norm 89/686 and EN 169/92 ( notified body 0196). All processes connected to this product have been thoroughly tested.

Price: £15.00

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L

Posts: 131433
Date:
Filters
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Object

Features

†Filter

Mercury

Planet/Sky Contrast

#23A Light Red

Features

#25 Red
#29 Deep Red

Venus

Clouds

#38A Deep Blue
#47 † Violet
#58 † Green

Planet/Sky Contrast

#25 Red
#29 Deep Red

Terminator

#25 Red
#29 Deep Red

Moon

Detail

#56 Light Green

Feature Contrast

#8 † †Light Yellow
#12 † Yellow
#15 † Deep Yellow
#80A Blue

Low Contrast Features

#82A Light Blue

Glare Reduction

ND13 Neutral Density

Mars

Clouds

#15 † Deep Yellow

Maria

#8 †† Light Yellow
#15 †Deep Yellow
#11† Yellow-Green
#21 †Orange
#23A Light Red
#25 † Red
#29 † Deep Red

Blue-Green Areas

#12† Yellow
#23A Light Red

Dust Storms

#38A Deep Blue
#56 † Light Green

Polar Caps

#15 Deep Yellow
#25 Red
#29 Deep Red
#32†Magenta
#47 Violet
#56 Light Green
#58 Green

Low Contrast Features

#82A Light Blue

Jupiter

Clouds

#11 Yellow-Green

Belts

#8 †† Light Yellow
#15† Deep Yellow
#21† Orange
#23A Light Red
#25 † Red
#29 † Deep Red
#32 ††Magenta††
#38A Deep Blue
#56 † Light Green
#80A Blue

Rilles

#80A Blue

Festoons

#80A Blue

Atmosphere

#56 † Light Green

Red-Orange Features

#12 †† Yellow

Orange-Red Zonal

#8 † †† Light Yellow

Red/Blue Contrast

#11 †† Yellow-Green

Blue/Light Contrast

#25 †† Red

Great Red Spot

#38A† Deep Blue
#80A† Blue

Galilean Moon Transits

#25 Red
#29 Deep Red

Red/Blue/Light Contrast

#56 Light Green
#58 Green

Polar Regions

#21 † Orange
#23A Light Red

Disc

#38A Deep Blue

Low Contrast Features

#82A Light Blue

Saturn

Clouds

#11 Yellow-Green
#12 Yellow
#25 Red
#29 Deep Red

Belts

#15† Deep Yellow
#21† Orange
#23A Light Red
#38A Deep Blue
#58 † Green
#80A Blue

Polar regions

#21† Orange
#23A Light Red
#58† Green
#80A Blue

Rings

#32†Magenta
#47 Violet

Cassini Division

#11 Yellow-Green

Red/Blue Contrast

#11 Yellow-Green

Red/Orange Features

#12 Yellow

Low Contrast Features

#82A Light Blue

Uranus

Dusky detail

#8 † Light Yellow
#15 Deep Yellow

Neptune

Dusky detail

#8 † Light Yellow
#15 Deep Yellow

Double Stars

Bright Primary

ND13 Neutral Density

Sun

Solar Filters

Astronomical filter sizes:

28.5 x 0.6 mm to fit standard 31.75mm Eyepieces



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L

Posts: 131433
Date:
Wratten #82A Light Blue
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Wratten #82A Light Blue (73% transmission) works well with Jupiter, Mars, Saturn and the Moon.

Features this pale blue filter enhances:

Moon: Low-Contrast Features
Mars: Low-Contrast Features
Jupiter: Low-Contrast Features
Saturn: Low-Contrast Features

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