Baldwin Astronomical Optics

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Large Aperture Fast Focal Ratio Telescopes [LAFFRTs] are awesome. You get to see the universe with the light grasp of large telescopes while standing on the ground most of the time. No need for a tall ladder which can lead to a terrible fall.

The center of action for LAFFRTs is the large, fast mirror. Lots of folks don’t want to make large, fast mirrors because they are challenging. Foucault and Ronchi analysis can leave ambiguity and this is discovered in star testing. A bad time to find out the mirror is wrongly figured is when it’s already in your scope. A more critical analysis is needed with these mirrors.

That’s why the Slit Image Test analysis is performed in our shop. By the time the mirror is done and star tested, it’s spot-on figured. Our mirrors don’t go to you until this highly precise test shows it to have a peak to valley wave-front error less than 1/10 wave [l = 550 nm], an RMS error less than 1/26 wave, and a Strehl computation of more than 94%. Furthermore, the mirror must pass our smoothness criteria, lack of visible astigmatism, no detectable turned or rolled edge, no zoniness or micro-ripple, and a star test examination, usually done with a 3.5mm eyepiece and 2x Barlow. We then ship the mirror to be aluminized with 96% to 98% reflectivity. We’re hoping the word “premium” is running through your head right now.

When you get your mirror from us it will have a process checklist so you can see the details in which we require in our production, a variety of test analysis sheets, knife-edge images at varying radii of curvature, ronchigrams, a slit image, an internal stress polarization photograph, and a promise that you will be satisfied. If your mirror does not meet the above requirements we’ll rework it. We hold ourselves to this high quality so errors won’t happen, but we will promise to take care of any errors we make holding to these above specifications. In order to observe through your high-precision mirror with exceptional views, we also recommend a more serious cell than most ATMers make. An example would be the one offered by JP Astrocraft. This no-nonsense support deters the stresses that can totally eliminate the fine figure of mirrors causing some individuals to think there is something wrong with the optics when in fact the structure holding them is the culprit. With thickness aspect ratios in the twenty range, cell support to critical. Besides, if you’re going to obtain premium optics, a premium coma-corrector, and premium eyepieces, why would you drop the ball at the structure support system?

Focal ratios as fast as f/3 are available. Paraboloids [for Newtonians], hyperboloids, ellipsoids and spheres are all available. Keep in mind that LAFFRTs require coma correctors to ensure the entire field of view is coma free. Coma is a naturally occurring optical issue with fast paraboloidal mirrors used by Newtonian telescopes. We recommend the Starlight/TeleVue SIPS unit. That enables you to have a smooth, high quality focuser with the coma-corrector already in place. This also allows you to have a coma-corrector that does not need to be adjusted between eyepieces. Using this or a similar unit will allow you to make best use of any large aperture fast focal ratio mirror.

Mirrors are polished on the back for smooth, slippery sliding against your flotation cell.

We are also observers and enthusiasts, and we know how important these mirrors are to you and your fellow observers. This amateur enthusiasm keeps us honest, accurate, and end-user friendly. You will not be disappointed, and you will show off your telescope views and proudly share them with all your astro-buddies.

Clear Skies!

Jeff Baldwin