Review - Meade Bahtinov Focusing Mask, 12"
Posted: 20 December 2019
Bahtinov Focusing Mask, 12"
I recently received some Deep Sky Object astrophotography filters (SII, H-Alpha, and OIII). During my initial focus tests with my existing Bahtinov Mask I discovered that I could not easily focus on faint stars when using the filters. I suspected that was due to the small openings in the Mask. Meade just released some Bahtinov Masks that have full aperture coverage and work with all 8" ($23), 10" ($30), and 12" ($40) telescopes. I decided to purchase one for my 12" LX600 telescope in the hope that the full aperture coverage would give brighter images of focus stars.
The 12" Mask comes in a large thin box with a single sheet of instructions, as seen at the right. There are three small Pegs which are attached to the Mask to hold it inplace on the telescope tube. The Attachment Pegs have a soft rubber covering to protect the telescope and a corrector plate. However it will be a good idea to confirm the Lock Nut is fully tightened before placing the Mask on the telescope.
The mask fits 12" apertures telescopes with just the Pegs attached. Three L-brackets are included so the mask will fit slightly larger tubes, up to about 14" diameter. The photo below shows a Peg and an optional L-bracket.
The Mask is made from plastic. After I removed the Mask from its plastic bag I placed the Mask on a carpet. Static electricity caused a lot of carpet fuzz to adhere to the Mask surface. I was able to mostly remove the fuzz using a vacuum cleaner.
I placed the Meade Bahtinov Focusing Mask (without the L-brackets) on my 12" LX600 telescope. After adjusting the positions of each of the Pegs I was able to get a good fit on the aperture end of the telescope.
As with all focusing masks, it is necessary to aim the telescope at a bright star (or other bright point source) and adjust the diffraction pattern by turning the telescope focus knob so that the center spike is centered between the outer two spikes. An out-of-focus image with the Meade mask is shown on the left and an in-focus image on the right. (Images have been cropped from the full frame.)
So was the focus star brighter with the Meade Bahtinov Focusing Mask versus my other mask when using a filter? I used an H-Alpha filter and took these images; the Meade Mask is on the left and the other mask on the right.
The Meade mask shows the spikes much longer than the other mask, making focusing on the DSLR Live View screen much easier.
The Meade Bahtinov Focusing Mask performed as expected to accurately achieve a precise focus. Being plastic it is lightweight and so will not cause any movement of the telescope when attached. And it provides a bright and clear diffraction image that is usable with faint stars or filters. If you need a focusing mask the Meade Mask is an excellent choice.
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