fetoma
Pooh-Bah
Reged: 09/26/06
Posts: 1094
Loc: NW Ohio
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Hi Group,
I'm not the best at understanding these reports. The wavefront error is measured at 555nm, is this the standard measurement in nm?
Also, the Strehl is at 92%. Isn't that a low number? I would expect it would be higher, but I'm not sure with the hybrid design of the scope.
Thanks! 
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Frank in NW Ohio
Vixen CF VC200L and R200SS
Meade SN-10
Celestron 9.25" SCT
Meade 8" f/6.3 SCT
Intes-Micro M73
Stellarvue 80/480 LOMO Triplet
Takahashi FS-60C
Celestron CGE
QHY8 and SXV-H16
www.jerseydevilastronomy.com
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dave b
Post Laureate
Reged: 05/10/05
Posts: 3535
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a strehl of .92 is good.
what you would want is to have your club test the mirror independently and see how far apart the two results are.
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dave bonandrini
30" f/5.2 Dobsonian
President of GCAC
Astromart Moderator
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walt r
Post Laureate
Reged: 02/13/07
Posts: 3463
Loc: Doylestown, PA
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The .92 strehl is the complete Mak-Cass optical assembly. So that is an excellent number considering the 30% CO.
I have the MK67 certificate with similar numbers. The scope, once properly cooled, gives very, very sharp images and almost perfect star tests.
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Walt
Obsession 18" f/4.45 #1370 AN/SC
MK67 Deluxe 6" f/12 Mak-Cass, Super Polaris GEM, JMI MicroMax DSC
DIY 60mm f/6 Achromat
Cookbook 245 CCD
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Mike I. Jones
Carpal Tunnel
Reged: 07/02/06
Posts: 1572
Loc: Fort Worth TX
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They may have measured it at 632.8nm in a He-Ne inteferometer, then scaled the test results to 555nm to give the peak photopic visual response performance (in daylight). At night with scotopic seeing the eye is more sensitive to cyan light at around 505nm, but 555nm is fine.
He gives the on-axis spot size as 4µm, but doesn't say whether what the CO is and whether this is monochromatic or across the F-C spectral range. The zero-CO DL Airy ring diameter is 2.44(0.55)(3)=4.026µm, so you're right at the theoretical disk size limit at 555nm. The ring is even a little smaller with central obstruction.
Agree with Dave - the Strehl of 0.92 at 555nm is plenty good visually for almost any night of average to good seeing and for any imaging use.
I think Dave meant test the system, not the mirror by itself.
If someone has an 8" or larger optical flat and a Bath or other interferometer, the scope could be tested in autocollimation, which doubles the wavefront error (WFE) at these low WFE levels. The resulting WFE would be divided by two and the Strehl calculated from that.
Sounds like a good'un!
Mike
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fetoma
Pooh-Bah
Reged: 09/26/06
Posts: 1094
Loc: NW Ohio
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These are the advertised specs:
Make: Intes Micro
Model: M73
Aperture: 180mm/7.1"
Focal ratio: f/3
Focal length: 540mm/21.3"
Lens: BK7
Coating: Broadband multi
Mirror: LK5(Pyrex)
Coating: 96%
CO: 80mm/45%
Optics: 1/7 wavefront ptv+
Tube: aluminum
Finish: white
Focus: zero image shift moving primary w/micro fine adjustment
Weight: complete-13.6kg/30lbs
Length: 530mm/20.9"
Diameter: 218mm/8.6"
Backfocus: 52mm to flange
Spot size on axis: 4 microns
No visual work will be done with this scope. It will strictly be an imaging scope.
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Frank in NW Ohio
Vixen CF VC200L and R200SS
Meade SN-10
Celestron 9.25" SCT
Meade 8" f/6.3 SCT
Intes-Micro M73
Stellarvue 80/480 LOMO Triplet
Takahashi FS-60C
Celestron CGE
QHY8 and SXV-H16
www.jerseydevilastronomy.com
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sixela
Postmaster
Reged: 12/23/04
Posts: 10855
Loc: Boechout, Belgium
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Quote:
At night with scotopic seeing the eye is more sensitive to cyan light at around 505nm,
But you can't see small detail with it (compared to what you can see with photopic vision, it's *really* blurry), so it still makes sense to use photopic vision as the yardstick.
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400mm f/4.46 self made Dobsonian on Tom Osypowski equatorial platform
Orion Starblast (114mm f/4 reflector, Alt/Az)
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HiggsBoson
Pooh-Bah
Reged: 02/21/07
Posts: 1118
Loc: Kal-li-fornia
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Be advised, the US National Bureau of Standards changed its name to the National Institute of Standards and Technology in 1988. The fact that this document uses a name that has been out of date for 21 years gives rise to a concern. It is unlikely that the NIST issues a calibration report for the measurement system in 2007 using their old name.
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Michael
ATM: 6" F/9 Newtonian Travel Scope
ATM: 12.5" F/4.5 Real Soon Now...
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GlennLeDrew
Pooh-Bah
Reged: 06/18/08
Posts: 1269
Loc: Ottawa, Ontario, Canada
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Frank,
Looks like a well made f/3 astrograph to me. And remember that such an optically fast system is really designed for deep sky work. If the axial resolution is indeed 0.7 arcsec, you'll probably rarely ever realize it in your images because in most locations seeing is not often at the sub-arcsecond level, and even less so during the full duration of those longer exposure times.
Moreover, the advertized 4 micron spot size will not be fully sampled by any current electronic detector I can think of, where something like a 2, or nearly 3, micron pixel size would be required.
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Home-made 11X50 right angle bino, 8.1 deg. FOV
Modified 26X100 bino, 3.5 deg. FOV
Home-made Mk II RA bino, using interchangeable objectives and eyepieces
My Gallery
Mediocre minds discuss people. Good minds discuss events. Great minds discuss ideas.
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mbellot
member
Reged: 08/21/09
Posts: 12
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Quote:
Be advised, the US National Bureau of Standards changed its name to the National Institute of Standards and Technology in 1988. The fact that this document uses a name that has been out of date for 21 years gives rise to a concern. It is unlikely that the NIST issues a calibration report for the measurement system in 2007 using their old name.
More likely that is a form letter/certificate that Mike Palermiti bought a ream of two decades ago and hasn't used up yet.
Its not issued by NIST, it simply states that the equipment he used to test the scope has been calibrated to USNBS (NIST) standards. Big difference.
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fetoma
Pooh-Bah
Reged: 09/26/06
Posts: 1094
Loc: NW Ohio
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Hi Glenn,
Are you saying that the scope specs are too good for this to be used from Earth? LOL!!! 
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Frank in NW Ohio
Vixen CF VC200L and R200SS
Meade SN-10
Celestron 9.25" SCT
Meade 8" f/6.3 SCT
Intes-Micro M73
Stellarvue 80/480 LOMO Triplet
Takahashi FS-60C
Celestron CGE
QHY8 and SXV-H16
www.jerseydevilastronomy.com
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fetoma
Pooh-Bah
Reged: 09/26/06
Posts: 1094
Loc: NW Ohio
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mbellot,
I believe Mike Palermiti is now out of the scope business. Mark Rieck at Teton Telescope is going to be the go-to guy for Intes-Micro in the USA.
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Frank in NW Ohio
Vixen CF VC200L and R200SS
Meade SN-10
Celestron 9.25" SCT
Meade 8" f/6.3 SCT
Intes-Micro M73
Stellarvue 80/480 LOMO Triplet
Takahashi FS-60C
Celestron CGE
QHY8 and SXV-H16
www.jerseydevilastronomy.com
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wh48gs
sage
Reged: 03/02/07
Posts: 458
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Quote:
Also, the Strehl is at 92%. Isn't that a low number? I would expect it would be higher, but I'm not sure with the hybrid design of the scope.
Those are specifications of a kind that don't tell you nothing specific. If they are for an extended range of wavelengths, that would imply chromatism correction bellow apo level. If it is for the optimized wavelength, it is sort of on the low side, but still can be considered good for such a fast system. The c.o. effect definitely hasn't been counted in - and it shouldn't, because Strehl indicates quality of the wavefront, which can be affected by c.o. only marginally - which is in this system almost certainly larger than D/3, thus degrading the normalized central difraction intensity to bellow 0.8 by itself. The combined intenity, a product of the two, is closer to 0.7. Even with a perfect Strehl, it would still be bellow 0.8, but that is rather usual with imaging systems.
Vla
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