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Home > Articles > Other Articles > Equipment/Optics > Lightholder 16" F/4.6

Lightholder 16" F/4.6
By Ralph Ford - 2/23/2007

I recently purchased a 16” F/4.6 mirror from John Lightholder. I wanted a 16” mirror and John had two completed mirrors in stock when I called. I found John to be friendly and knowledgeable. The purchasing experience was simple and straightforward. The mirror was sent to the coater and was at my door in a few weeks.

I was skeptical about the stated quality of the mirror, but felt that if it was only close to the stated quality I would have a very good mirror. The numbers as quoted by John were as follows: Strehl ratio: .999, Wavefront P-V error: 1/33, Wavefront RMS: 1/90, RTA: .278.

It took another month or so to get the scope assembled and ready for testing. I live about five miles south of the Los Angeles airport, my limiting magnitude is about 3 on good nights. By necessity my testing was limited to bright stars and the moon and planets. After allowing cool down time, I turned to a bright star. I inserted a 133 line Ronchi grating. Beautiful straight lines greeted my eye, so far, so good. Next I used a 10.5mm Plossl for a general impression. In one word, Wow. Inside and outside of focus images were identical, I began to think that John’s numbers were correct. I used a 5mm Plossl for more critical examination. Again, the images were identical inside and outside of focus. Let me say that I have over twenty-five years in the hobby, I have looked through hundreds of telescopes. I know how to do a star test. This mirror passed with flying colors. No edge issues, no astigmatism, for all practical purposes, perfect.

The seeing was good and Saturn was in the west just below the zenith. It was truly unbelievable. I pushed the power up to 700 with no breakdown in the image. For the first time, I am pretty sure I saw the Encke gap. My previous telescope was a 12.5” mirror from Pegasus, it was also excellent, but this 16” mirror simply blew it away.

I can’t recommend Lightholder Optics highly enough. The service and delivery time were excellent. The mirror is indeed excellent. Is it 1/33 wave? I don’t know, I do know that is appears to be perfect by my testing methods. I have not sent it out to be tested by interferometer or any other method. I think too much emphasis is placed on lab testing and not on field testing. A completed telescope’s performance depends on collimation and all of the other components in the optical train, as well a thermal equilibrium. Do I recommend Lightholder Optics? Without hesitation. Will you get what you pay for? Without doubt.

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