DADOS Slit – Spectrograph

DADOS® - a slit spectrograph made by Baader

developed at the Max-Planck-Institute for Extraterrestrial Physics in Garching

The first draft of the DADOS®-slit spectrograph was based on our simple Blaze grating, which we had made for schools for more than 20 years. When we unveiled the prototype of the DADOS® some years ago, we listened closely to the following online-discussions, which lead to several large changes in the design of the product.

So, many ideas and critics from active spectroscopists were incorporated in the design of the DADOS®. We are very grateful for all feedback, because we are sure that the final product has become much better because of this.

DADOS® is designed for telescopes with about f/10 or slower. Faster apertures will cause some vignetting. The spectral resolution is not affected by this in any way.

DADOS Slit Spectrograph – scope of delivery

• DADOS Reflection Grating with 200 lines / mm, not visible, preinstalled in the DADOS
• 1¼" Stop Ring #1905131
• T-2 Change Ring #2453620 for installation at the eyepiece clamp
• T-2 Quick Changer #2456313, preinstalled at the Dados
• DADOS 1¼" Eyepiece 20 mm Kellner #1304120
• DADOS 1¼" Guiding Eyepiece 10 mm Kellner #1304110
• Slit Viewer Assembly (Guiding lens with M28.5-thread for 1¼" filters)
• Baader Focusing Eyepiece Holder 1¼" / T-2 #2458125
• Allen Wrench 1.3 mm and 1.5mm
• Gloves for replacing the grating
• Storage case and Manual

DADOS Reflection Grating

Nowadays, we use the following three reflection gratings (200 L/mm as standard, 900 L/mm and 1200 L/mm sold seperately) which are copies of special master gratings (they are no standard gratings from a catalogue!) - the Blaze angle of the gratings (as well as the optics, see below) is matched perfectly to the geometrical and optical properties of the DADOS®.

• #2458557 Reflection Grating with 200 lines/mm, cemented onto tilting grating holder
• #2458556 Reflection Grating with 900 lines/mm, cemented onto tilting grating holder
• #2458559 Reflection Grating with 1200 lines/mm, cemented onto tilting grating holder

The desired wavelength range can be set with a micrometer gauge. A sturdy T-2 connector for large CCD-cameras (e.g. SBIG) or several adaptations of eyepiece holders (as well a much larger "Backfokus") is included.

Other gratings with the common size of 25x25x6mm with more or less resolution can also be used with the DADOS®.

The efficiency of the DADOS® slit-spectrograph is at least 60% at  550 nm.

Properties of the specially designed gratings of the DADOS®

The slits

The second core element besides the gratings is the reflecting slit element with a precisely manufactured triple slit (with gap widths of 25/35/50µm). You can see all three slits at the same time and easily choose the right one for each object at a glance.

Because of the forward-reflecting slit element with razor-sharp, perfectly smooth edges and an additional, sophisticated optical system of tilted mirror and projection lenses, you can focus – just as with larger spectrographs – directly onto the image of the star with affordable, common CCD-guiding cameras or webcams (not inluded) or even with a guiding eyepiece and easily guide the telescope!

Guiding eyepieces

Two reasonably-priced 1¼" DADOS Kellner eyepieces with 10mm (#1304110) and 20mm (#1304120) focal length are included. They can be used for finding objects and for manual guiding without a guiding camera. A slit illumination (included in the scope of delivery) made of a dimmable red LED helps you to focus the guiding star and the slit itself. It illuminates the slit from the back towards the guiding camera/eyepiece, so that the LED's light will not reach the lens of the collimator.

Lens system

The collimator system in front of/behind the Blaze grating is made of an achromatic and a triplett system. These were specially designed for the best-possible resolution and are coated with the best available anti-reflection-coating. These are no standard lenses from a catalogue!

The collimator lens can be moved over a wide range with a 2" Helical focuser very precisely, so that (almost) all known CCD- and DSLR-cameras (as well as almost all standard eyepieces) can be focused.

Adaptation and Mounting

On the telescope side, the DADOS® has got a black 2" nosepiece. You can attach an optionally available Neon-calibration lamp (#245 8590 - not included) with 2"-adaper and 220V cable to it.

If you remove the nosepiece, you can use the standard 2" SC female thread inside of the front part of the DADOS® for a variety of other adaptations. We have several adapters for a sturdy connection using this thread, e.g. a 2"/T-2 reducer (# 295 8242) to attach the DADOS® directly to optics with the standard T-2 photographic thread (M42x0.75).

You can also the female 2" thread of the front cube to screw the DADOS® without the nosepiese directly at a Schmidt-Cassegrain-telescope. Use our 2" Locking-Ring (#245 8270) to fix the DADOS® in any orientation - this way, you can even mount it between the fork arms of many Schmidt-Cassegrain with an alt-az mount. Both guiding and imaging camera are mounted in a 90°-angle towards the DADOS® to keep it as compact as possible.

To mount the DADOS® on a telescope or attach other accessories, a clamp with 3/8" and 1/4" thread (#245 8593) and 38mm diameter is available.

The two-piece clamp has got a 3/8" thread at the bottom side (a 1/4"-thread is included) and a 1/4" thread on top.

You can use it to mount the DADOS® on a ball-head or a tangent assembly as secondary unit. You absolutely need it in a classroom to mount the DADOS® on an optical bench or for any setup without a telescope.

There are plenty adapters available for all kinds of guiding cameras a well as for almost all imaging CCD-cameras – just take a look at our Astro T-2® accessories.

DADOS features

This user-friendly slit spectrograph, which was designed especially for use in schools or universities and for amateur observers, offers all features of a professional spectrograph. Especially remarkable are the following features:

• Two diffent reflection gratings and a specially designed optical system deliver a high light efficiency
• micrometer gauge for precise adjusting of the grating
• in contrast to spectrographs without a slit, even large objects (nebulae, planets, comets) can be analyzed – just like in a professional observatory
• the spectral resolution (lambda/delta lambda ~ 500) makes a precise spectral classification of stars possible
• the complete visible and near infrared spectral range (350nm – 950nm) can be covered with a SBIG ST-7
• the slit is directly visible with an eyepiece or webcam, which makes it easy to center and guide a star
• the slit spectrograph can even be used at fast optics up to f/6.3, although a slight vignetting is visible at optics faster than ca. f/10
• fits at standard 2" focusers
• compact, can even be used if there is not much space
• the spectrum of brighter objects is directly visible in an eyepiece
• there are three slits side by side (25/35/50µm)
• the slits can be illuminated from the back with a red LED for easier focusing of a camera on the slit
• the spectra can be taken with web-, digital or CCD-cameras
• all cameras and eyepieces can be attached with our T-2® adapters

Spectra of NGC 6543 and M57, taken by OStR Dipl.-Phys. Peter Stinner, Kopernikus-Gymnasium, Wissen

Test images with SBIG ST-402 ME, white LED + green laser + neon-calibrationlamp