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If you drift timed all of your eyepieces you will find that most if not all have a slightly different focal length to the stated focal length, irrespective of manufacturer. Similarly if you take 5 mirrors of a stated focal length (say 15"/f4.5) from the same mirror maker unless they are specified as required as a pair, they will all differ slightly somewhere between f4.4 and f4.6, depending on the mirror maker. My 14"/f4.5 Zambuto mirror is actually f4.43. Does it matter? Not 1 iota. Of course optics for the professional and research market are another matter and another price point.
Denkmeier are doing you a big favour by matching them and stating an accurate focal length.
Cheers
John B
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