matt
Vendor (Scopemania)
Reged: 07/28/03
Posts: 10991
Loc: Chaville, France
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Tom T made a review once of the William Optics Megrez II, a (better than semi) semi-apo with an ED Triplet. I don't need to explain why I'm asking  , but has there been another Megrez II which was still advertised as a semi-apo but without an ED element?
(I know there was a doublet, achro Megrez "I")
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riverpoet
sage
Reged: 11/03/03
Posts: 255
Loc: Slovenia, Europe
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There are 3 versions:
- Megrez II SD ("semi-apo)
- Megrez II ED Triplet APO
- Megrez Flourite APO
The one you're asking about is Megrez II SD, which is an improved version of Megrez I - basically a very good achromat.
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Ignacio R.
member
Reged: 02/24/05
Posts: 78
Loc: 25°39'N 100°20'W 2,100 ft
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The semi-apo class is difficult to define.
For some people the Megrez 80 ED ( triplet with ED element ) is a Semi-Apo and the Megrez fluorite is the "real apo".
Some others, including myself, think that the Megrez 80 SD is also a semi-apo. It is not a clasical achromat because of two reasons:
1) is not a typical crown and flint doublet. One of the two elements is made of a special glass, not a BK7.
2) The secondary spectrum is 50%-60% less than in a typical f/6 achromat.
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Ignacio R.
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LX-10 SC 200mm
ETX-125mm MC
WO Megrez II 80mm Fluorite Doublet
Nikon D40, OM-1, OM-2s
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gripweed44
Pooh-Bah
Reged: 02/12/05
Posts: 1019
Loc: PDX
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PICTURE? SD OR ED
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John
Omega Centauri is the finest Globular I have seen with my own eyes.
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Anonymous
Unregistered
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SD
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matt
Vendor (Scopemania)
Reged: 07/28/03
Posts: 10991
Loc: Chaville, France
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OK, so what I saw was probably an SD.
Ignacio, you say secondary spectrum is 50% smaller than a typical f/6 achromat, is it by your own experience or a report you read? How intrusive is chromatic aberration on it?
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Matt
CI700 mount with various scopes on top.
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Ignacio R.
member
Reged: 02/24/05
Posts: 78
Loc: 25°39'N 100°20'W 2,100 ft
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I have compared to f/8 and f/9 achromats and the color is the same or better. I have not compared directly to a f/6 achromat. There are several reports of people who has done this test. Somebody defines the color as three times better than an achromat, some others say 50%. There is a reference of someone describing the color as in a 80mm f/11.5 BK7/F2 achromat. Has Anybody in the forum done this comparison?
Do not expect a colorless view of Jupiter, the moon or bright stars. There is some color but is not filling the eyepiece! It can be reduced with a good minus violet filter. For wide angle views there is no problem.
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Ignacio R.
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LX-10 SC 200mm
ETX-125mm MC
WO Megrez II 80mm Fluorite Doublet
Nikon D40, OM-1, OM-2s
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