Observing notes - Ealing 4-26-2007 Lunar visual
Don Colton wrote,
I question whether you will get diffraction effects based on aperture on the moon at 560X with the Ealing. . . . . You may, also, be getting deterioration of the image due to the quality of the eyepiece. I have found some eyepieces perform very poorly at high power.
Good point. I do have low-end eyepieces and did not try my one 20mm Nagler. The specific lunar test for diffraction deterioration that I use are fine rilles - like Rima Gay-Lussac (Rukl 31) mentioned in the prior post. At lower magnification, the rille was crisp. At extreme power, parts of the rille visible at lower power, appeared broken and merged with the surrounding terrain. This visual effect held even during periods of calm - thus ruling out atmospheric turbulence as a cause. My understanding is that this is an effect of the diffraction waves overlapping each other at extreme mag. But the low-end eyepiece probably is the right cause. - Kurt _______________________________________________ Sent via CSolutions - http://www.csolutions.net
Unfortunately the Naglers do not do that well at high power because of the number of elements. I have found that good plossls, the Takahashi and the monocentric are the best performers. I have a 4.8 Nageler, a 4 mm Takahashi and the 6 mm TMB previously noted. Both the Takahashi and the TMB are better for fine detail than the Nagler but they have narrow fields of view. The collimation of the Ealing may also be a factor but so also may be the atmosphere. Even though the seeing may appear calm, at high power the detail may not be there. I have seen a significant difference in the image quality at Wolf Creek on a good night versus lower elevations. One night at Wolf Creek we split Beta Delphinus at the time .5" with an 18 inch Starmaster (with tracking) at 900x. I normally can not use more than 300-400x without the stars "smearing" in Sandy with the same scope. -----Original Message----- From: utah-astronomy-bounces+djcolton=piol.com@mailman.xmission.com [mailto:utah-astronomy-bounces+djcolton=piol.com@mailman.xmission.com] On Behalf Of Kurt Fisher Sent: Friday, April 27, 2007 1:29 PM To: utah-astronomy@mailman.xmission.com Subject: [Utah-astronomy] Observing notes - Ealing 4-26-2007 Lunar visual Don Colton wrote,
I question whether you will get diffraction effects based on aperture on the moon at 560X with the Ealing. . . . . You may, also, be getting deterioration of the image due to the quality of the eyepiece. I have found some eyepieces perform very poorly at high power.
Good point. I do have low-end eyepieces and did not try my one 20mm Nagler. The specific lunar test for diffraction deterioration that I use are fine rilles - like Rima Gay-Lussac (Rukl 31) mentioned in the prior post. At lower magnification, the rille was crisp. At extreme power, parts of the rille visible at lower power, appeared broken and merged with the surrounding terrain. This visual effect held even during periods of calm - thus ruling out atmospheric turbulence as a cause. My understanding is that this is an effect of the diffraction waves overlapping each other at extreme mag. But the low-end eyepiece probably is the right cause. - Kurt _______________________________________________ Sent via CSolutions - http://www.csolutions.net _______________________________________________ Utah-Astronomy mailing list Utah-Astronomy@mailman.xmission.com http://mailman.xmission.com/cgi-bin/mailman/listinfo/utah-astronomy Visit the Photo Gallery: http://www.utahastronomy.com
Based on my experience, Don is 100% correct- every Nagler I've used has been "soft" near the center of the field. Even my mid-priced orthos do better than Naglers as far as definition goes. This isn't noticed at low powers; at high powers typically used for plantary observation and close double-stars, wide-field isn't needed. The Ealing can sometimes have troublesome tube currents for the first few hours of observation. It takes that big primary a while to cool down. But this is usually easily identified as separate from diffraction limitations. On 4/27/07, Don J. Colton <djcolton@piol.com> wrote:
Unfortunately the Naglers do not do that well at high power because of the number of elements. I have found that good plossls, the Takahashi and the monocentric are the best performers.
Sounds like I now have a 5mm nagler for sale Bob Moore Commerce CRG - Salt Lake City office 175 East 400 South, Suite 700 Salt Lake City, Utah 84111 Direct: 801-303-5418 Main: 801-322-2000 Fax: 801-322-2040 BMoore@commercecrg.com www.commercecrg.com -----Original Message----- From: utah-astronomy-bounces+bmoore=commercecrg.com@mailman.xmission.com [mailto:utah-astronomy-bounces+bmoore=commercecrg.com@mailman.xmission.c om] On Behalf Of Chuck Hards Sent: Friday, April 27, 2007 11:32 PM To: Utah Astronomy Subject: Re: [Utah-astronomy] Observing notes - Ealing 4-26-2007 Lunar visual Based on my experience, Don is 100% correct- every Nagler I've used has been "soft" near the center of the field. Even my mid-priced orthos do better than Naglers as far as definition goes. This isn't noticed at low powers; at high powers typically used for plantary observation and close double-stars, wide-field isn't needed. The Ealing can sometimes have troublesome tube currents for the first few hours of observation. It takes that big primary a while to cool down. But this is usually easily identified as separate from diffraction limitations. On 4/27/07, Don J. Colton <djcolton@piol.com> wrote:
Unfortunately the Naglers do not do that well at high power because of the number of elements. I have found that good plossls, the Takahashi and the monocentric are the best performers.
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Not at all, Bob, keep the Nagler. Sometimes you want high power with a wide field but top resolution isn't necessarily a criterion. Or if using a smaller scope with a short FL, even a 5mm eyepiece may not yeild an especially high power- yet you retain the wide field with the Nagler. TeleVue recognized the softness of the Nagler series, and better resolution was the motivation behind the Panoptic line. While a successful marketing strategy by uncle Al, a super-wide-field isn't the Holy Grail of eyepiece traits. Resolution will always be the top criterion of eyepiece (telescope) performance. A super-wide-field is usually an aesthetic concern, for most observing. Don's advice to go with better plossls (and I'll insert better orthos as well) is sound, for sharpest resolution. Keep the number of air-to-glass interfaces as low as possible, minimize total number of elements. With longer focal-ratio scopes, simple eyepieces can give incredibly sharp views. Remember that much of the purpose of all those lenses in super-wide-field eyepieces is to compensate for shortcomings inherent in low f-ratio Dobsonian primaries. My 3 cents. On 4/28/07, Bob Moore <BMoore@commercecrg.com> wrote:
Sounds like I now have a 5mm nagler for sale
Bob Moore Commerce CRG - Salt Lake City office 175 East 400 South, Suite 700 Salt Lake City, Utah 84111 Direct: 801-303-5418 Main: 801-322-2000 Fax: 801-322-2040 BMoore@commercecrg.com www.commercecrg.com
-----Original Message-----
From: utah-astronomy-bounces+bmoore=commercecrg.com@mailman.xmission.com [mailto:utah-astronomy-bounces+bmoore=commercecrg.com@mailman.xmission.c om] On Behalf Of Chuck Hards Sent: Friday, April 27, 2007 11:32 PM To: Utah Astronomy Subject: Re: [Utah-astronomy] Observing notes - Ealing 4-26-2007 Lunar visual
Based on my experience, Don is 100% correct- every Nagler I've used has been "soft" near the center of the field. Even my mid-priced orthos do better than Naglers as far as definition goes. This isn't noticed at low powers; at high powers typically used for plantary observation and close double-stars, wide-field isn't needed.
The Ealing can sometimes have troublesome tube currents for the first few hours of observation. It takes that big primary a while to cool down. But this is usually easily identified as separate from diffraction limitations.
On 4/27/07, Don J. Colton <djcolton@piol.com> wrote:
Unfortunately the Naglers do not do that well at high power because of the number of elements. I have found that good plossls, the Takahashi and the monocentric are the best performers.
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For anyone who has not yet signed up, we are attempting to get a final count of the participants for the Bryce Canyon Astronomy Festival in the next few weeks. If you would like to participate and bring a scope you can get free camping and admission to the Park. Please email me at djcolton@piol.com or dcoltonsprint@earthlink.net if you would like to participate. I need the following information: 1. Nights participating 2. Scope you are bringing 3. Vehicle license number and make. 4. If you want free camping. Clear Skies Don
participants (4)
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Bob Moore -
Chuck Hards -
Don J. Colton -
Kurt Fisher