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#51
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best of Hubble images
Nicholas O. Lindan wrote:
"Paul Furman" "Focal reducers are positive lenses which do two things ..." The only similar thing I've heard of is A close-up lens. It reduces the lens focal length, but the lens stays in the same spot Does it reduce the focal length? If I focus a 'bare' lens at closest distance, then put a closeup lens on the end I have to crank it to infinity to get back in focus (and move in closer). For a simple lens design, cranking to infinity actually *increases* the focal length. so the new reduced focal length lens is now focused pretty close. It increases the aperture - the new lens is faster - but as it is extended for close up the bellows correction (close-up correction) compensates and the effective f-stop is the original lens f-stop. If you put a close-up lens on a view camera, where you can rack the lens closer to the film, you get a usable shorter lens. There are negative "anti-close-up lenses(?)" used with view cameras to increase focal length. Not used much anymore. |
#52
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best of Hubble images
Paul Furman wrote:
Nicholas O. Lindan wrote: "Paul Furman" "Focal reducers are positive lenses which do two things ..." The only similar thing I've heard of is A close-up lens. It reduces the lens focal length, but the lens stays in the same spot Does it reduce the focal length? If I focus a 'bare' lens at closest distance, then put a closeup lens on the end I have to crank it to infinity to get back in focus (and move in closer). For a simple lens design, cranking to infinity actually *increases* the focal length. Oh, sorry, I had that backwards. You are right. so the new reduced focal length lens is now focused pretty close. It increases the aperture - the new lens is faster - but as it is extended for close up the bellows correction (close-up correction) compensates and the effective f-stop is the original lens f-stop. If you put a close-up lens on a view camera, where you can rack the lens closer to the film, you get a usable shorter lens. There are negative "anti-close-up lenses(?)" used with view cameras to increase focal length. Not used much anymore. |
#53
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best of Hubble images
[A complimentary Cc of this posting was sent to
Robert Sneddon ], who wrote in article : Those defects bite into its light grasp and resolution. A new Hubble would have a perfect mirror day one resulting in better science day two. The problems with the solar cells are known and would be fixed in the new design etc. etc. LOL! Have not you forgot they said it about the Hubble I too? :-( Yours, Ilya |
#54
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best of Hubble images
In message , Ilya Zakharevich
writes [A complimentary Cc of this posting was sent to Robert Sneddon ], who wrote in article bc0BFEVc4MyHFw1H@nosp am.demon.co.uk: A new Hubble would have a perfect mirror day one resulting in better science day two. The problems with the solar cells are known and would be fixed in the new design etc. etc. LOL! Have not you forgot they said it about the Hubble I too? :-( They didn't say that about the Hubble which was a very experimental satellite in more ways than one. The mirror wasn't tested properly, in part to save money. This was a Bad Idea. The problems with the solar cell panels (the largest ever deployed on a scientific satellite up to that time) were actually foreseen, in fact. Sadly for the Hubble designers, the people who knew there were going to be problems with the panels were the people who had designed similar panels for the American Keyhole spy satellites and they had to keep their mouths shut for security reasons. -- To reply, my gmail address is nojay1 Robert Sneddon |
#55
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best of Hubble images
[A complimentary Cc of this posting was sent to
Robert Sneddon ], who wrote in article : A new Hubble would have a perfect mirror day one resulting in better science day two. The problems with the solar cells are known and would be fixed in the new design etc. etc. LOL! Have not you forgot they said it about the Hubble I too? :-( They didn't say that about the Hubble which was a very experimental satellite in more ways than one. Yes, they did. [It was less than 40 years ago. Is your memory that short? ;-] The mirror wasn't tested properly, in part to save money. This was a Bad Idea. The problems with the solar cell panels (the largest ever deployed on a scientific satellite up to that time) were actually foreseen, in fact. Sadly for the Hubble designers, the people who knew there were going to be problems with the panels were the people who had designed similar panels for the American Keyhole spy satellites and they had to keep their mouths shut for security reasons. I do not follow: are you implying this won't happen to Hubble II ?! Yours, Ilya |
#56
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best of Hubble images
In message , Ilya Zakharevich
writes ], who wrote in article ff1wV0HZQbyHFwFH@nosp am.demon.co.uk: The mirror wasn't tested properly, in part to save money. This was a Bad Idea. The problems with the solar cell panels (the largest ever deployed on a scientific satellite up to that time) were actually foreseen, in fact. Sadly for the Hubble designers, the people who knew there were going to be problems with the panels were the people who had designed similar panels for the American Keyhole spy satellites and they had to keep their mouths shut for security reasons. I do not follow: are you implying this won't happen to Hubble II ?! The mirror of a Hubble II *will* be tested properly and the solar cell panel design will not have the vibration and deployment problems the Hubble I did. Those are some of the lessons learned from the first version. Of course it's entirely possible a Hubble II will have other problems as it's likely to be experimental in other ways. -- To reply, my gmail address is nojay1 Robert Sneddon |
#57
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best of Hubble images
[A complimentary Cc of this posting was sent to
Robert Sneddon ], who wrote in article : The mirror wasn't tested properly, in part to save money. This was a Bad Idea. The problems with the solar cell panels (the largest ever deployed on a scientific satellite up to that time) were actually foreseen, in fact. Sadly for the Hubble designers, the people who knew there were going to be problems with the panels were the people who had designed similar panels for the American Keyhole spy satellites and they had to keep their mouths shut for security reasons. I do not follow: are you implying this won't happen to Hubble II ?! The mirror of a Hubble II *will* be tested properly and the solar cell panel design will not have the vibration and deployment problems the Hubble I did. Those are some of the lessons learned from the first version. Of course it's entirely possible a Hubble II will have other problems as it's likely to be experimental in other ways. Of course; this WAS my point. There are 3 factors to consider: a) lessons learned and accumulated in the published literature; b) availability of people to chat with who learned the "previous lessons"; c) degree of "experimentality" of the platform. So if one could launch the exact replica of Hubble I, AND one could collect all the people on Hubble I team together, it would have been a perfect mission. But it is NOT POSSIBLE to collect all these people together; and, IMO, "b" is much more important than "a"! AFAIK, the space programs are practically dead now (except for Chinese? - do not know anything about them). My estimates are that "b" has almost disappeared. So even the exact replica would have a lot of possibilities to go havoc. [And, speaking of "a", I've heard a rumor that (what was available of) blueprints of Saturn V are lost. (AFAIK, some late-moments additions were never reflected in blueprints, just in people's memory.)] Hope this helps, Ilya |
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