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Adamsavage
2012-Jan-28, 02:29 AM
If you were to put a eye piece on Hubble, what would be the resulting maximum useful magnification ? Is there a way to do this math ? :confused:

glappkaeft
2012-Jan-28, 03:02 AM
The maximum useful magnification is usually defined as 2xApature in mm (which always results in an exit pupil of 0,5 mm) or 5000x. The minimum useful magnification depends on the exit pupil, but if we assume a 5 mm pupil, we get 500x

George
2012-Jan-28, 03:03 AM
The resolution limit of this amazing 2.4 m aperture telescope is about 0.05 arc seconds. The resolution limit of the eye is about 60 arcsec. So, I think if you had a way to get 1200x magnification you would match the telescope's resolution to the eye. I don't think exit pupil would be a problem (for max. mag.). [I missed the prior post]

Adamsavage
2012-Jan-28, 03:28 AM
The maximum useful magnification is usually defined as 2xApature in mm (which always results in an exit pupil of 0,5 mm) or 5000x. The minimum useful magnification depends on the exit pupil, but if we assume a 5 mm pupil, we get 500x

So with my 5 inch scope at F5 using a 10mm eyepiece I would be only seeing roughly 1% of what the Hubble is cable of seeing..That's just mind blowing..

glappkaeft
2012-Jan-28, 03:35 AM
So with my 5 inch scope at F5 using a 10mm eyepiece I would be only seeing roughly 1% of what the Hubble is cable of seeing..That's just mind blowing..

Yes but it gets worse since we observe through the atmosphere we are most of the time limited to 300x or less due to atmospheric seeing.

Shaula
2012-Jan-28, 09:33 AM
And Hubble can do tricks like integrating over time to pull out faint stuff that the eye just cannot do.

slang
2012-Jan-28, 11:53 AM
The news item about the Hubble Ultra Deep Field (http://hubblesite.org/newscenter/archive/releases/2009/31/) has some videos showing how far Hubble zooms in. If you were to look at that same patch of sky, with the same magnificiation, you wouldn't see the same. Hubble had to collect light for 48 hours to make the very faint background galaxies visible in this magnificent image (http://hubblesite.org/newscenter/archive/releases/2009/31/image/a/format/large_web/).

chornedsnorkack
2012-Jan-28, 12:56 PM
Yes, Hubble Space Telescope has 240 cm primary, whereas the Hooker Telescope on Mount Wilson has had 254 cm primary since 1917.

Which magnifications and eye pieces have proven useful on Hooker Telescope?

How is the seeing on Mount Wilson?

I hear that adaptive optics have been retrofitted on Hooker Telescope after 1992. Have these changed the useful magnification?

Romanus
2012-Jan-28, 04:08 PM
HST's focal length is about 57,600 mm, and magnification is the telescope's focal length divided by the focal length of the eyepiece. For a 40 mm eyepiece, this works out to 1440x, which is well within the limits of a telescope that size.

George
2012-Jan-29, 04:08 PM
If maintaining surface brightness is a criteria, then 400x is the limit. [6mm of entrance pupil/2400mm aperture = 400.]

Exceeding 400x will make nebulae and other extended objects fainter (per unit area) than is seen with the naked eye.

chornedsnorkack
2012-Feb-02, 05:21 PM
If maintaining surface brightness is a criteria, then 400x is the limit. [6mm of entrance pupil/2400mm aperture = 400.]

Exceeding 400x will make nebulae and other extended objects fainter (per unit area) than is seen with the naked eye.

In which case you will be needing a 144 mm focal length eyepiece.

Eye, unlike Hubble cameras, is slightly less sensitive to dim light at first, and then has much shorter period to integrate light over. An advantage of the eye is a wider dynamic luminosity range, right?

If Hubble were somehow integrated in a manned space station, what type of 144 mm eyepiece would you provide for naked eye observation?

How much difference would the absence of skyglow in heaven make for a naked eye observer? Are there any objects which naked eye observers aboard spaceships and stations easily see but naked eye observers on ground cannot?

What is the largest telescope that actually has been carried on manned spaceships or stations and used for naked eye viewing?

George
2012-Feb-03, 04:37 AM
In which case you will be needing a 144 mm focal length eyepiece. Good point. Would a 0.5 telecompressor with a 70 mm eyepiece do the trick?

My point above was to note that the surface brightness dimishes even with greater aperture. Your point adds to this significantly. Both are not intuitive, and most assume extended objects get brigher per unit area with greater aperture compared to what we seen with the naked eye.


If Hubble were somehow integrated in a manned space station, what type of 144 mm eyepiece would you provide for naked eye observation? With the telecompressor, would there not be some nice objects to observe?

ngc3314
2012-Feb-03, 04:49 AM
What is the largest telescope that actually has been carried on manned spaceships or stations and used for naked eye viewing?

I read one astronaut's story of observing with a 125mm Celestron, blacking out as much of the cabin as possible; I think they did this session during an "extra" day in orbit mandated by poor weather at the landing site. The sky isn't as much darker from LEO as one might imagine compared to a good dark site on the ground; nearly half of the ground-based sky brightness in the visible band comes from zodiacal light plus starlight scattered from interstellar grains (both highly dependent on location in the sky - data from Pioneer 10 did the first really complete separation of the two, IIRC).

Solon
2012-Feb-03, 07:49 PM
I read one astronaut's story of observing with a 125mm Celestron,

Can you provide more info on that? I can find very little on astronomy from the ISS, Shuttle, or other missions.
The Shuttle did do the Astro 1&2 missions, nothing at visible wavelengths though
16262
Ultraviolet shots are available through
http://archive.stsci.edu/uit/uitcat.html

Hornblower
2012-Feb-04, 02:29 AM
If maintaining surface brightness is a criteria, then 400x is the limit. [6mm of entrance pupil/2400mm aperture = 400.]

Exceeding 400x will make nebulae and other extended objects fainter (per unit area) than is seen with the naked eye.

That is true, but increasing the magnification of faint fuzzies (clusters, galaxies or nebulae) does not necessarily give an inferior view. Sometimes a small faint fuzzy can be seen more easily at higher magnification in spite of the reduced surface brightness because more of your retina is brought into play, enabling complex neural image processing that teases out the faint stuff.

Edited to add following reference.

http://www.visualdeepsky.org/chat/msg00783.html

chornedsnorkack
2012-Feb-04, 08:57 AM
That is true, but increasing the magnification of faint fuzzies (clusters, galaxies or nebulae) does not necessarily give an inferior view. Sometimes a small faint fuzzy can be seen more easily at higher magnification in spite of the reduced surface brightness because more of your retina is brought into play, enabling complex neural image processing that teases out the faint stuff.

Edited to add following reference.

http://www.visualdeepsky.org/chat/msg00783.html

Does it mean that an extended source of certain size is easier to see than a point source, or a smaller extended source, of the same integrated luminosity?

glappkaeft
2012-Feb-04, 09:53 AM
Does it mean that an extended source of certain size is easier to see than a point source, or a smaller extended source, of the same integrated luminosity?

Generally no. The Andromeda galaxy and mu And has similar maginitude and I can't think of any curcumstances where where that would be true. The phenomena Hornblower is taking about requires a extended object and depends on many factors (the light sensitivity curve of your eye, the flux of specific parts of the object, sky background flux, etc.). If you increase magnification you might see a dimmer object with more detail, a dimmer object with less detail, you might no longer see it at all or any and all combinations in different parts of the object.

Hornblower
2012-Feb-04, 01:25 PM
Generally no. The Andromeda galaxy and mu And has similar maginitude and I can't think of any curcumstances where where that would be true. The phenomena Hornblower is taking about requires a extended object and depends on many factors (the light sensitivity curve of your eye, the flux of specific parts of the object, sky background flux, etc.). If you increase magnification you might see a dimmer object with more detail, a dimmer object with less detail, you might no longer see it at all or any and all combinations in different parts of the object.

The phenomenon I mentioned previously depends on darkening the surrounding sky along with the reduction in the object's surface brightness when the magnification in a telescope is increased. The contrast is unchanged. This is not the same condition as having a large and a small fuzzy of the same total magnitude side by side in the same background brightness.

On a night when I could see M13 with averted vision but not direct, I could see stars of the same magnitude with direct vision.

George
2012-Feb-04, 05:01 PM
That is true, but increasing the magnification of faint fuzzies (clusters, galaxies or nebulae) does not necessarily give an inferior view. Sometimes a small faint fuzzy can be seen more easily at higher magnification in spite of the reduced surface brightness because more of your retina is brought into play, enabling complex neural image processing that teases out the faint stuff.

Edited to add following reference.

http://www.visualdeepsky.org/chat/msg00783.html
Yes, that is important.

I recall wanting to buy Clark's book, but it was too expensive a few years ago. He has a web page that is very informative on this topic...here (http://www.clarkvision.com/visastro/omva1/index.html).