LS35THa 35mm f/11.4 solar refractor

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The Lunt LS35THa 35mm solar refractor puts serious Hydrogen-alpha solar viewing within the reach of virtually every astronomer. You can piggyback this lightweight (3 pound) solar scope on a larger existing telescope or mount it on a photo tripod or altazimuth mount to use as a quick grab and go scope for spur-of-the-moment observing at lunchtime or when on vacation. Because this Lunt scope is small and compact (only 16.35” long and 62mm in diameter at its widest), the LS35THa it is ideally suited to being mounted in pairs side by side for binocular viewing.

The H-alpha filter in the Lunt 35mm solar refractor shows you much more of the living Sun than ordinary glass or Mylar white light solar filters that only show you sunspots. With the economical Lunt LS35THa, you see the violent ever-changing tapestry of multiple prominences leaping off the edges of the solar disk, as well as sunspots and some surface detail.

The Lunt LS35THa is a fully multicoated 400mm focal length achromatic refractor with a 35mm clear aperture and an f/11.4 focal ratio. Its built-in Hydrogen-alpha solar filter is centered on the 6562.8 Ångstrom H-alpha solar emission line. The filter has a narrow <0.75 Ångstrom passband for high contrast. The two-part filter uses a permanently mounted 35mm etalon behind the objective, with a 4mm blocking filter for primarily visual use built into the standard equipment 1.25” star diagonal.

A tuning mechanism built into the system lets you tilt the etalon to center the passband precisely on the H-alpha line for maximum contrast. The tuning mechanism also lets you perform off-band observations of Doppler-shifted disk features to determine whether they are moving towards you or away from you.

The 4mm clear aperture of the H-alpha blocking filter in the star diagonal is matched to the focal length of the telescope and designed primarily for visual observing. It gives you a full disk image of the Sun at prime focus with almost any optional 1.25” eyepiece you might care to use. A typical 10mm Plössl, for example, will give you a magnification of 40x and a 1.25° actual field. This gives you plenty of dark sky background around the solar disk to show off the prominences. A 20mm 1.25” Plössl will give you a magnification of 20x and a little over a 2.5° field of view compared with the 0.5° diameter disk of the Sun, but will brighten the prominences. A 6mm Plössl will give you 67x magnification and about a 0.77° field, letting you get up close to the Sun, although the resulting very narrow 0.52mm exit pupil may start dimming the prominence detail more than you might like to see. 

If solar imaging is in your plans, consider the L35TPAK deluxe upgrade. In addition to adding a Sol Searcher finder, Vixen-style dovetail, and Lunt 10mm eyepiece to the basic scope, the L35TPAK upgrade changes the 4mm blocking filter to a 6mm aperture filter that is better suited for solar imaging.

The diagonal’s 1.25” eyepiece holder has a built-in helical focuser that makes focusing easy, even if you are observing in the dead of winter while wearing gloves or mittens. Simply rotate the eyepiece to focus it sharply on the solar image.

The Lunt LS35THa comes with a pair of mounting rings that have collimation screws so you can precisely line up the scope with the optical axis of any larger scope on which it might be piggybacked. The rings are attached to a mounting bar with a 1/4”-20 thread hole for mounting the scope directly on a photo tripod for a quick peek at the Sun. The bar also lets you mount the scope on a dovetail plate and piggyback it on a larger scope or install it on an altazimuth mount with slow motion controls for easier extended observing and tracking of the Sun. 

Most solar telescopes exhibit a “sweet spot” in their field of view where subtle prominences pop into clearer view and the larger prominences show more contrast and detail. Experimentally moving the Lunt LS35T/Ha around so that the Sun’s limb and prominences move to different parts of the field will soon reveal where your particular scope’s “sweet spot” is located.

Focal Length:
This is the length of the effective optical path of a telescopeor eyepiece (the distance from the main mirror or lens where the lightis gathered to the point where the prime focus image is formed). Focallength is typically expressed in millimeters.

The longer the focallength, the higher the magnification and the narrower the field of viewwith any given eyepiece. The shorter the focal length, the lower themagnification and the wider the field of view with the same eyepiece.

Focal Ratio:
This is the ‘speed’ of a telescope’s optics, found by dividing the focal length by the aperture. The smaller the f/number, the lower the magnification, the wider the field, and the brighter the image with any given eyepiece or camera.

Fast f/4 to f/5 focal ratios are generally best for lower power wide field observing and deep space photography. Slow f/11 to f/15 focal ratios are usually better suited to higher power lunar, planetary, and binary star observing and high power photography. Medium f/6 to f/10 focal ratios work well with either.

An f/5 system can photograph a nebula or other faint extended deep space object in one-fourth the time of an f/10 system, but the image will be only one-half as large. Point sources, such as stars, are recorded based on the aperture, however, rather than the focal ratio – so that the larger the aperture, the fainter the star you can see or photograph, no matter what the focal ratio.

This is the ability of a telescope to separate closely-spaced binary stars into two distinct objects, measured in seconds of arc. One arc second equals 1/3600th of a degree and is about the width of a 25-cent coin at a distance of three miles! In essence, resolution is a measure of how much detail a telescope can reveal. The resolution values on our website are derived using the Dawes’ limit formula.

Dawes’ limit only applies to point sources of light (stars). Smaller separations can be resolved in extended objects, such as the planets. For example, Cassini’s Division in the rings of Saturn (0.5 arc seconds across), was discovered using a 2.5” telescope – which has a Dawes’ limit of 1.8 arc seconds!

The ability of a telescope to resolve to Dawes’ limit is usually much more affected by seeing conditions, by the difference in brightness between the binary star components, and by the observer’s visual acuity, than it is by the optical quality of the telescope.

3.31 arc seconds
This is the diameter of the light-gathering main mirror or objective lens of a telescope. In general, the larger the aperture, the better the resolution and the fainter the objects you can see.
Heaviest Single Component:
The weight of the heaviest component in this package.
3 lbs.
1 year
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1. Jay on 4/18/2013, said: AstronomicsAstronomicsAstronomicsAstronomicsAstronomics
This may be the most economical entry to H-a solar observing and gives views that gratify a newcomer or amaze first-time viewers at outreach. I think it's a good value since the next step up in H-a solar costs about twice as much. I've used white light filters for 9 years to show sunspot detail well and see other solar disk texture on good days. H-a views with the Lunt 35 basic package show a more detailed solar disk, with prominences and filaments changing over minutes to hours, adding some drama to longer term sunspot changes that are visible in white light.

The 35 is small enough it can ride on some driven scopes (like 6 - 8 inch SCT) in finder rings to add the L35 H-a view to the bigger scope's white light view.

The simple tilt-tuner is elegant solution that works well to dial in details on disk, edge or best compromise views.

A zoom eyepiece is a good way to match daytime seeing and balance image brightness with detail.
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Visual Accessories
Eyepieces (1)
7.2mm to 21.5mm zoom
by Lunt Solar Systems
Finderscopes (1)
Sol-Searcher Solar finder for TeleView and Lunt scopes
by TeleVue
  • Helical focuser
  • Dust cover
  • 1.25” star diagonal with integral 6mm blocking filter
  • Mounting rings and tripod block with 1/4"-20 thread mounting hole
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Lunt Solar Systems - LS35T/Ha 35mm f/11.4 solar refractor

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Lunt Solar Systems - LS35T/Ha 35mm f/11.4 solar refractor
 AstronomicsAstronomicsAstronomicsAstronomicsAstronomics (Average: 5.00 | Users: 1)  Only registered users can submit ratings - Register Here
Our Product #: L35T
Manufacturer Product #: LS35THa
Price: $598.00  FREE ground shipping - Click for more info
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This economical and lightweight Lunt 35mm solar telescope is ideal for grab-and-go solar observing or for mounting piggyback on a larger scope for detailed and constantly-changing Hydrogen-alpha views of explosive prominences leaping from the limb of the Sun, sunspots, and more . . .

. . . our 34th year