Observing the Sun with an optical instrument is extremely dangerous. The concentrated energy from the Sun damages the human eye or a camera. Therefore, there is a wide range of filters available that reduce the light from the Sun. Generally, any telescope with a closed tube (i.e. not a truss-tube) can be converted into a solar telescope.
Filters can be distinguished between those that are mounted in front of the telescope lens and those that are attached to the front of the eyepiece. The former is especially safe, because dangerous radiation does not enter the telescope at all.
Another distinction is whether the filter simply reduces the light, or whether it allow only certain spectral lines to pass through. The first variant is also called a white light filter. These filters preserve the natural view of the Sun and enable the photosphere with its sunspots to be observed. The second variant is usually seen in H-Alpha filters. These allow only a certain wavelength of hydrogen atoms to pass through, and show the structures of the Sun's chromosphere.

Baader
Sun filter foil AstroSolar® ECO-size OD 5.0 140x155mm
$ 26.90

Baader
Sun filter foil 20 x 29 cm
$ 33.90

Omegon
solar filter, 60-80mm
$ 19.90

Astroprints
Solar Filters ZWO Seestar S50
$ 35.90

Omegon
solar filter, 130mm
$ 24.90

Baader
AstroSolar Photo Film OD 3.8
$ 39.90

Omegon
solar filter, 150mm (6'')
$ 59.00

Omegon
solar filter, 90mm
$ 24.90

Omegon
solar filter, 114mm
$ 24.90

Explore Scientific
Solarix solar filter foil with DIN A4 and ND5 cutout sheets
$ 33.90

Unistellar
Solar Filters Smart eQuinox/eVscope
$ 292.00

Omegon
173mm-193mm solar filter
$ 89.00

Omegon
138mm-153mm solar filter
$ 69.00

Vaonis
Solar Filters VESPERA
$ 210.00

DayStar
Combo QUARK H-Alpha solar filter, for chromosphere
$ 1,800.00

euro EMC
SF100 size 6: 129mm to 157mm AstroSolar
$ 95.00

Artesky
Solar Filters 95mm
$ 65.00

Lunt Solar Systems
1.25" Herschel wedge with ND3.0 filter LS1.25HW
$ 269.00

Lunt Solar Systems
Filters Double-Stack Filter DSII for Solar telescopes LS80MT & LS100MT
$ 4,330.00

euro EMC
SF100 size 4: 83mm to 105mm AstroSolar
$ 67.00

euro EMC
SF100 Size 5: 103mm to 131mm AstroSolar
$ 82.00

Unistellar
Solar Filters Odyssey/Odyssey Pro
$ 234.00

euro EMC
SF100 size 7 for 155mm to 189mm AstroSolar
$ 113.00

Artesky
Solar Filters 115mm
$ 81.00

Explore Scientific
Sun Catcher solar filter for 229-254mm (9"-10") SCs
RRP:
$ 71.00
Our price:
$ 35.90

Lunt Solar Systems
Filters Double-Stack Filter DSII for Solar telescope LS130MT Ha
$ 6,800.00

Explore Scientific
Sun Catcher solar filter for 80-102mm telescopes
$ 32.90

TS Optics
Solar Prism with Polarizing and Narrowband Filter 1,25"
$ 187.00

DayStar
QUARK H-alpha filter, prominences
$ 1,800.00

Meade
Filters Glass Solar Filter 1200
$ 444.00

euro EMC
Solar Filters SF100 size 10: 269mm to 327mm Thousand Oaks
$ 177.00

DayStar
Filters 0.5Å H-alpha Quantum PE filter
$ 30,600.00

euro EMC
Solar Filters SF100 size 9: 215mm to 273mm Thousand Oaks
$ 155.00

Baader
AstroSolar solar filter for ASBF 100mm binoculars
$ 78.00

Lunt Solar Systems
Filters B3400 Blocking-Filter in 2" extension tube
$ 4,100.00
