Mike Jones article.qxd:Layout 1 - Astronomy Technology Today
Mike Jones article.qxd:Layout 1 - Astronomy Technology Today Mike Jones article.qxd:Layout 1 - Astronomy Technology Today
BAFFLE OPTIMIZATION FOR CASSEGRAIN TELESCOPESTable 3. Optimized baffle design prescription for fastCassegrain example.Table 2. Example of the numerical convergence of the baffle optimizationalgorithm.shadow. This difference in obscurationsdiminishes for slower primaries andsmaller image formats.MakingBaffle TubesBaffling is usuallybuilt fromthin, stiff sheetmetal, but can alsobe made from thincarbon fiber laminatelayups. Theinterior and exteriorsurface shouldideally be dead flatblack with nosheen or luster visibleeven down tonear-graze angle.The surfaces canbe sandblasted orglass bead peenedto roughen themetal surface, and a very flat black paintapplied, such as Krylon Ultra-Flat Black,Aeroglaze Z306 6 , or a high-temperatureblack paint for barbeque grills, exhaustmanifolds, etc. The paint is lightly appliedin thin multiple coats to avoid shiny, reflectivepooling of the paint binder.Baffles can be cylindrical and thuseasy to make. However, at near-graze angleseven the blackest, most diffuse surfacescan become specular (mirror-like),and graze-angle stray light can reflect specularlyfrom interior and exterior surfaces,partially defeating the benefit of the baffling.Conical baffles can be used ratherthan cylindrical baffles, with the taper anglesdesigned to minimize visibility as seenfrom both mirrors and at focus. Puristsmay even add additional baffle stops insidethe tapered primary mirror baffle,similar to baffling a refractor, to furthertrap stray light.ConclusionI have posted CassDesign2 (CD2),which implements the algorithm de-Mark Rieck, Ownerwww.tetontelescope.com(208)403-4339COME SEE THE VIEWFROM THE TOP!2nd AnnualMakNewt Madness Sale!FREE SHIPPING plus FREE DEWSHIELD• If you've always wanted apo refractorperformance, but couldn't afford the price,Intes Micro MakNewts are the answer for you• Custom machining or tailor the accessoriesyou want with our Teton MakNewt options• Tailoring exactly the right scope for your needs is our specialty• Unparalleled service both before and after the sale58 Astronomy TECHNOLOGY TODAY
BAFFLE OPTIMIZATION FOR CASSEGRAIN TELESCOPESscribed here, in the Files section of theYahoo group “Astronomy TechnologyToday.” Regarding any licensing issues, Isimply certify that CassDesign2 is beingmade available to the public totally free ofcharge, with no fees or sharewaredonation requests, but with no liability tome. Download it, play with it, use it for areal system you build, and please reportany errors you encounter on theYahoo ATT group site. I have a real dayjob in optics; CD2 is strictly for fun.Enjoy!Bibliography:1. Jones, M.I., “Stray Light Revealed”,Astronomy Technology Today, Oct.2007, Issue 5, pp. 26-27.2. Young, A.T., “Design of CassegrainLight Shields”, Applied Optics, Vol. 6,No. 6, June, 1967, pp. 1063-1067.3. Prescott, R., “Cassegrainian Baffle Design”,Applied Optics, Vol. 7, No. 3,March 1968, pp. 479-481.Figure 9. Optimal baffling for the system in Figure 7.4. Hales, W.L., “Optimum CassegrainBaffle Systems”, Applied Optics, Vol. 31,No. 25, September, 1992, pp. 5341-5344.5. ZEMAX® is an optical design softwareproduct of the ZEMAX DevelopmentCorporation, 3001 112th AvenueNE, Suite 202, Bellevue, WA 98004-8017 USA, www.zemax.com.6. Aeroglaze Z306 black absorptivepolyurethane is available from the LordCorporation, 2000 West GrandviewBlvd., P.O. Box 10038, Erie, PA 16514-0038, 814/868-3611 ext. 3277,www.lordfulfillment.com.Astronomy TECHNOLOGY TODAY 59
- Page 1 and 2: Don’t Miss A Single Issue!www.ast
- Page 3 and 4: Baffle Optimizationfor CassegrainTe
- Page 5 and 6: BAFFLE OPTIMIZATION FOR CASSEGRAIN
- Page 7 and 8: BAFFLE OPTIMIZATION FOR CASSEGRAIN
- Page 9: BAFFLE OPTIMIZATION FOR CASSEGRAIN
BAFFLE OPTIMIZATION FOR CASSEGRAIN TELESCOPESTable 3. Optimized baffle design prescription for fastCassegrain example.Table 2. Example of the numerical convergence of the baffle optimizationalgorithm.shadow. This difference in obscurationsdiminishes for slower primaries andsmaller image formats.MakingBaffle TubesBaffling is usuallybuilt fromthin, stiff sheetmetal, but can alsobe made from thincarbon fiber laminatelayups. Theinterior and exteriorsurface shouldideally be dead flatblack with nosheen or luster visibleeven down tonear-graze angle.The surfaces canbe sandblasted orglass bead peenedto roughen themetal surface, and a very flat black paintapplied, such as Krylon Ultra-Flat Black,Aeroglaze Z306 6 , or a high-temperatureblack paint for barbeque grills, exhaustmanifolds, etc. The paint is lightly appliedin thin multiple coats to avoid shiny, reflectivepooling of the paint binder.Baffles can be cylindrical and thuseasy to make. However, at near-graze angleseven the blackest, most diffuse surfacescan become specular (mirror-like),and graze-angle stray light can reflect specularlyfrom interior and exterior surfaces,partially defeating the benefit of the baffling.Conical baffles can be used ratherthan cylindrical baffles, with the taper anglesdesigned to minimize visibility as seenfrom both mirrors and at focus. Puristsmay even add additional baffle stops insidethe tapered primary mirror baffle,similar to baffling a refractor, to furthertrap stray light.ConclusionI have posted CassDesign2 (CD2),which implements the algorithm de-Mark Rieck, Ownerwww.tetontelescope.com(208)403-4339COME SEE THE VIEWFROM THE TOP!2nd AnnualMakNewt Madness Sale!FREE SHIPPING plus FREE DEWSHIELD• If you've always wanted apo refractorperformance, but couldn't afford the price,Intes Micro MakNewts are the answer for you• Custom machining or tailor the accessoriesyou want with our Teton MakNewt options• Tailoring exactly the right scope for your needs is our specialty• Unparalleled service both before and after the sale58 <strong>Astronomy</strong> TECHNOLOGY TODAY
Change language