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REFLECTORS FOR PLANETARY WORK

loron91423

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loron91423

loron91423

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Astronomer Alberto Montalvo taught me that there is such a thing. Several very important elements are required before a reflector can be considered for the study of the moon, planets, and the sun. (Remember however that no reflecting telescope will yield as good an image for lunar and planetary work as a refracting telescope does because of the optical design not because of certain design type or manufacturer or craftsman.) Refractors and reflectors are different telescopes because they are designed to do different tasks but a reflector can be made to perform well for lunar and planetary study. The first is the main element of a reflecting telescope for planetary work is the quality of the optics. (primary and secondary mirrors) and the optical design system it's self with respect to with respect to the aperture and f/ratio. The second main element to be employed within the system is that of a three vane curved spider to support the secondary mirror or diagonal. The vanes do not reduce diffraction spikes completely but make it much less noticeable by flushing the light to the inside walls of the telescope's tube assembly.

I saw examples of this system when viewing through the reflecting telescopes of astronomer Alberto Montalvo. He assembled a collection of reflectors that are some of the finest optical systems for use in lunar and planetary study. You may Google him to locate more information of him and the telescope designs that he used for his study of the moon and planets.

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philsail1

philsail1

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Thank you for that information on suitability of reflectors to view the Moon and Planets Loron. Would it be such that an f10 reflector will give better views than an f5?

Could an f5 reflector's view be significantly (and noticeably) improved by changing the four vane "spider" for a curved three vane assembly?

Also could an f5 reflector's views be significantly (and noticeably) improved by the use of very high quality eyepieces?

Would an f5 reflector's views be improved that much by employing the two improvements above?

I would think that most people would not want to spend a large sum of money trying to improve a standard (say Skywatcher) reflector if the viewing improvements were not going to be that noticeable.

Is it a case of "if you want the best views, you have to buy the best (optically constructed) telescope money can buy, or can standard "affordable" telescopes be improved (optically) by spending money on them!

Regards,

philsail1

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loron91423

loron91423

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Thank you for your comments on our thread. As to the f/number the visual brightness of an object depends on the telescope's aperture not f/ratio. In photography it is a much different matter then in astronomy. If one has a well made optical system in their reflector, the investment into a 3 vane system is well worth it.

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blinky

blinky

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Wait a minute! The curved spider vains do not 'flush the light to the inside walls of the telescope's tube assembly' Curved vanes create many small diffraction spikes just around the outside of the object. They actually create a lot of small spikes rather than 2 or 4 spikes as seen by normal spiders.

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Kaptain Klevtsov

Kaptain Klevtsov

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To answer Phil's questions:-

The f/10 'scope would be easier to collimate accurately and not as sensitive to collimation so the view would be slightly better. The f/10 would be easier on the eyepiece design so cheaper eyepieces could be used. The f/10 would have double the magnification for a given eyepiece so you could use longer focal length eyepieces for the same size image, giving more comfortable eye relief.

The curved vanes would get rid of the diffraction spikes and make the effects of the diffraction less noticeable.

For planets you don't need expensive eyepieces as you don't need a wide view.

Flocking and curved vanes are about all you can do to the f/5 for improving the views as far as I know.

Kaptain Klevtsov

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loron91423

loron91423

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ALBERTO MONTALVO He knew it all the time! "IT'S THE PLANETONIAN" Guess who? In late September 1990 turned in early reports of a large storm on Saturn? To find out read Sky&Telescope December 1990 page 591 and February 1991 page 144 :hello1:

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Whippy

Whippy

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ALBERTO MONTALVO He knew it all the time! "IT'S THE PLANETONIAN" Guess who? In late September 1990 turned in early reports of a large storm on Saturn? To find out read Sky&Telescope December 1990 page 591 and February 1991 page 144 :hello1:

And this has what to do with this thread?

Tony..

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SteveL

SteveL

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ALBERTO MONTALVO He knew it all the time! "IT'S THE PLANETONIAN" Guess who? In late September 1990 turned in early reports of a large storm on Saturn? To find out read Sky&Telescope December 1990 page 591 and February 1991 page 144 :hello1:

Maybe its just me, but I find your posts are becoming increasingly non-sensical, and do not appear to follow the usual and normal flow of forum posts and replies between members. If you intend to post the contents of your blogs and your various web sites on here, wouldnt it be better to just post the links to those sites (just the once - http://www.myspace.com/lutzobservatory and http://www.geocities.com/lutzobservatory/org.html ), and then involve yourself in a rational two way discussion with the members of the forum, rather than just stating information that wasnt really requested, seems a little dubious at times, and seems more like personal opinions?

Just my own thoughts...

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Sam

Sam

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ALBERTO MONTALVO He knew it all the time! "IT'S THE PLANETONIAN" Guess who? In late September 1990 turned in early reports of a large storm on Saturn? To find out read Sky&Telescope December 1990 page 591 and February 1991 page 144 :hello1:

Where did that come from? :?

:spam1:

:(:D:shocked:

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Ajohn

Ajohn

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This sort of thing has interested me for a long time. Finally went out and bought an early 5ins meade f9 ed apo. (A couple of years ago.) Most of my experience had been with an 8ins and 10ins SC and a 10ins newt before that. I still have the 10ins sc but haven't had it out for years. The apo settles down instantly and gives very fine views of all objects. The 10ins SC is a pain in the neck in comparison but would probably out perform it in some respects when it's collimated correctly and has more importantly settled down - it won't match the apo for contrast though. That's the draw back with reflectors. The central obstruction and spider vanes of any form cause undesirable diffraction effects. These lower contrast and effectively reduce visible detail in any object including nebulae. This is a fact pointed out in many of the older amateur astro books - it takes at least a 6ins newtonian to match the performance of a 4ins achromatic refractor. I and at least one other source reckon 8ins is a safer bet. That matches up with my experiences with a 10ins sc and a 5ins refractor. The sc has a huge central obstruction compared with the optimum 20% by diameter and no spider. Even 20% causes a marked change in diffraction effects. Like most things concerning telescopes it's a compromise. This all ties in with my 1st decent scope a 10ins F6.8 newtonian with a central obstruction a little over 20%. The person who bought it off me fitted it with an even smaller mirror sized and positioned so that the focal plain was only just available for eyepieces or a ccd camera.

I'm assuming that anyone reading this can apply all of that to using a reflector to studying the moon and planets. There are a couple of other factors. One is that a parabola only produces a perfect image of a point source exactly one axis and at infinity. Planets and the moon especially are not point sources. Not at infinity either but that effect isn't significant. The 2nd point is that off axis resolution drops of rapidly very rapidly on shorter focus mirrors. That can be somewhat problematic both visually and photographically. On film for instance one needs f20 in order to obtain the maximum resolution available from a 10ins scope. That's where cassegrainians come in but unfortunately these tend to have oversized 2ndry mirrors to avoid light baffling problems unless they are designed purely for planetary use.

Optical quality has already been mentioned. All I would add is that is much easier to obtain on longer focal length mirrors. Even more easier on refractors too. Putting it all together an 8ins f8 newtonian with a quality 1/10 wave mirror and a small central obstruction is probably the best lower cost way to go what ever it's used for especially if a larger 2ndry mirror is also available of photography and viewing certain nebulae. There is even an argument that states that there isn't any point in an average amateur owning a telescope any larger than that. :( It's not as daft as it sounds.

John

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