Hi

Check this homemade telescope website:


http://www.geocities.com/telescope1999/14-5inch.html

Could a 14.5 inch telescope really look at the planet Mars at 575X?

He also saw the moon at 750X.

Thanks

Yep. what matters is partially the mirror and focal length but the eyepiece is more important. A large mirror gets you good resolution. A good eyepiece gets the magnification. If you had a decent Plossl and Barlow lens combined with a large mirror, the effects could be stunning.

As the man says, he goes for planetary astronomy. Magnification is the key.

If you are doing deep sky work then this would not be optimal. You'd need a better f-stop and not so high power magnification. To me, this is where schmidt-cassegrains and CCD's win. If only I had one.

Maximum magnification per inch of objective is 50x.
1"mirror= 50X magnification
2"mirror=100Xmagnification.
3"mirror=150Xmagnification.
But,This cannot continue.

The truth is that the maximum useable magnification for large telescopes is 300x.
The limit of 300x is because the atmosphere does not allow for any more.

You can use a highpower eyepiece and use 300- 400-500- magnification, but the image will be distorted and useless.



My Astro Photos Link (http://www.users.tpg.com.au/area52/astro/deepspace.jpg)

Which goes to show that I'm not a good observational astronomer. Time to re-read my book on optics :)

Re. " ... because the atmosphere does not allow for any more."

Even with adaptive optics?

I know that it's beyond the amature's purse, but as compensation, checking
NOAA forecasts of atmospheric turbulence can help. Can it not?

Take care :(

http://users.tpg.com.au/area52/me.jpg
300x is the limit for use with normal telescope and eyepieces.


Now adaptive optics, they are another story.
They will compesate for atmospheric turbulents, and magnification will be far greater then 300x.
Their price tag will also be out of this world.

Adaptive Optics:
To appreciate the daunting task faced by designers of adaptive optics systems, one should understand that an initially plane wavefront travelling 20 km through the turbulent atmosphere accumulates, across the diameter of a large telescope, phase errors of a few micrometers. These have to be sensed with a minimum number of photons and corrected to about 1/50 of a micrometer every millisecond or so. Another complication is that, for short integration times, the field of view over which the atmospheric wavefront distortions and hence the images are correlated, the isoplanatic angle, is very small (only a few arc second for visible wavelengths).

Because of the high bandwidth and the small field to which correction can generally be applied, adaptive optics uses a small deformable mirror with a diameter of 8 to 20 cm located behind the focus of the telescope at or near an image of the pupil. In some current projects, the possibility of using a large deformable secondary mirror is being developed. The choice of the number of (usually piezoelectric) actuators is a tradeoff between degree of correction, use of faint reference sources (see below) and available budget. For instance, a near-perfect correction for an observation done in visible light (0.6 /265m) with an 8-m telescope would require ~ 6400 actuators, whereas a similar performance at 2 /265m needs only 250 actuators.

A large number of actuators requires a similarly large number of subapertures in the wavefront sensor, which means that for correction in the visible, the reference star should be ~ 25 times brighter than to correct in the infrared. Most current astronomical systems are designed to provide diffraction-limited images in the near-infrared (1 to 2 /265m) with the capability for partial correction in the visible. However, some military systems for satellite observations in the USA do provide full correction in the visible on at least 1-m class telescopes.

Two main methods are used to measure the degraded wavefront, the Shack-Hartmann device, which measured the slope of the wavefront from the positions of the images of the reference star given by each subpupil, and curvature sensing, where the intensities measured in strongly defocused images provided directly give the local curvatures of the wavefront. Correction in the Shack-Hartmann device is made with individual piezoelectric actuators. Correction in a curvature sensing system is accomplished with a bimorph adaptive mirror, made of two bonded piezoelectric plates. With both methods, wavefront sensing is done on a reference star, or even on the observed object itself if it is bright enough and has sufficiently sharp light gradients. The measurement can be performed in the visible for observation in the infrared, or in the infrared itself (1 to 2 /265m), if e.g. the reference star is too faint in the visible.

The control system is generally a specialized computer that calculates from the wavefront-sensor measurements the commands sent to the actuators of the deformable mirror. The calculation must be done fast (within 0.5 to 1 ms), otherwise the state of the atmosphere may have changed rendering the wavefront correction inaccurate. The required computing power needed can exceed several hundred million operations for each set of commands sent to a 250-actuator deformable mirror. As in active optics systems, zonal or modal control methods are used. In zonal control, each zone or segment of the mirror is controlled independently by wavefront signals that are measured for the subaperture corresponding to that zone. In modal control, the wavefront is expressed as the linear combination of modes that best fit the atmospheric perturbations.

AO Operation is strongly affected by the size of the isoplanatic angle, usually ~ 20" at 2 /265m, but only ~ 5" at 0.6 /265m. It is generally NOT possible to find a sufficiently bright reference star close enough to an arbitrary astronomical object. Conditions are much better in the infrared than in the visible since atmospheric turbulence (and especially its high spatial frequencies) has, for a given AO correction, a weaker effect on longer wavelengths. The spatial and temporal sampling of the disturbed wavefront can therefore be reduced, which in turn permits the use of fainter reference stars. Coupled with the larger isoplanetic angle in the IR, this gives a much better outlook for AO correction than in the visible.

Nevertheless, even for observations at 2.2 µm, the sky coverage achievable by this technique (equal to the probability of finding a suitable reference star in the isoplanatic patch around the chosen target) is only of the order of 0.5 to 1%. It is therefore quite normal that most scientific applications of AO so far have been on objects which naturally provide their reference object like solar system small bodies, stellar environments, stellar clusters and a few very bright Seyfert nuclei.

At this time, a number of team or general purposes astronomical AO systems are routinely working on 4-m class or larger telescopes: (COME-ON)ADONIS, the first general purpose AO system, on the ESO-La Silla 3.6 m telescope; (UH-AO)Hokupa'a, the IfA-UH curvature system pioneer, observing at Mauna Kea and on the 8-m Gemini-North telescope; PUEO installed on the 3.6-m CFHT telescope (Mauna Kea); ADOPT on the 100" Hooker telescope (Mount Wilson), ALFA on the Calar Alto 3.5-m telescope, the first to use "routinely" a laser guide star (LGS) projector; the LLNL AO system at the 3.5-m Shane telescope (Lick Observatory), currently with a Natural Guide star only, but soon featuring an LGS; the first AO system on a very large telescope, viz. the Keck II AO facility at Mauna Kea. Many more are under construction or installation, including NAOS and SINFONI for the ESO VLT.

JAMMER :bugeye:

Puh-leez credit a source for your information (http://www.eso.org/projects/aot/introduction.html). No one will think less of you for finding it and referencing it, we appreciate the effort it takes you to locate the information in the first place.

And, since I missed your arrival on
the 14th, Welcome to Sci Forums!

Peace.

I friend of mine is an amateur astronomer also, and has built a number of telescopes.

http://www.ladyandtramp.com/scope.htm

Peace.

You can look at the planets at high power without adaptive optics. I have looked through scopes and have seen nice views at 600X and higher. Nice crisp images.

300X is not the maximum power for large telescopes (10 inches or larger). Go to a any "star" party, look through a big homemade scope and see for yourself.

What kills images is poor optics, poor collamination and more importantly poor seeing.

The website that started this thread also has links on sites on helping you determine the seeing conditions:

http://www.geocities.com/telescope1999/14-5inch.html

Steve

Welcome to sciforums, SteveR!

Just wanted to add:
The source for the info about the 300xmag. came from a book.
The book was titled something like"How to build your own Telescope"
So, the 300x thingy, I guess is reliable.
Sure, you could see whatever at 600x,and your eyes probably couldn't see the mineute errors at that magnification.
Weather your eyes are upto seeing the errors or not,thats up to the individual.
Most comercial scopes are ground to to +-1/8 wave error.
That means it can be out by a 1/4 of a wave.
So, you'll allready have errors at low magnification.

Somehow, I don't think you'll see many large scopes ground to 1/20 wave and use high power 8 element eyepieces , to compare errors with.
They don't grind them to 1/20 wave for nothing.
I totally agrea with SteveR, when he quotes"What kills images is poor optics, poor collamination and more importantly poor seeing."
Wellcome SteveR.
LASER :bugeye:Link to this Source (http://www.sciforums.com/t6403/s/thread.html)