After reading many discussions on the Meade vs Celestron SCT focal reducers, and the confusion about what backfocus spacing is required, I decided to run a simple test (see pictures below).
At the bottom is a Celestron f/6.3 reducer/corrector; in the middle is its Meade counterpart, also labeled as an f/6.3 reducer/corrector; and at the top is the Meade f/3.3 reducer. The bright point at right is the rising Sun, good for the infamous “firestarter” method of focal length measurement. Hey, it was a simple setup, and I hadn’t made coffee yet.
It’s immediately apparent that this particular Meade f/6.3 unit is not the same as the Celestron. The Celestron is right at specs, with a ~230 mm focal length. The Meade f/3.3 also clocks in close enough to specs, with an ~80 mm focal length. But this Meade f/6.3 unit being tested shows a focal length of just ~130mm. That places it at around 0.4 reduction! (All you optics PhDs will have to run the math for me – no coffee, remember?)
Many observers have noted that sometime around 2005 to 2010 Meade’s f/6.3 reducers seemed short. Some have called it a defect; others have speculated that Meade wanted to provide clearance for fork-mounted SCTs to swing vertical. I find this second explanation farfetched.
But it also doesn’t seem like a defect to me. I’ve used this exact Meade “f/6.3” unit for many years with great results – big flat fields, nice stars to the edge of a KAI-2020 sensor through a C-11, good enough for some ambitious DSO mosaics. It’s a fine lens – just a much shorter-than-labeled focal length. By far.
If you own one of these “short” babies, I’d keep it. It’s a great compromise between the regular f/6.3 and the scary short f/3.3 that’s only good for very small sensors. But always ask before buying one online, and use the numbers here to determine which version you’re being sold.
Did Meade and their Chinese manufacturer get their signals crossed? I’d think that the extra curvatures in a 130 mm unit would be harder to figure. Maybe someone out there has the inside scoop on what happened.