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Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: May/17/2007 at 18:12
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Optics GrassHopper
Optics GrassHopper

Joined: February/06/2007
Status: Offline
Points: 6


Has anybody  used an astronomical telescope sometime?

I think that I need one to see the impacts at 700, 800 meters, or more.

Could you tell me any advise??

Thank you very much


Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: May/17/2007 at 18:21
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Optics Master
Optics Master

Joined: November/27/2004
Location: United States
Status: Offline
Points: 1436

True astronomical scopes (most of them CAT scopes) don't see a lot of field use because their design results in an inverted and turned around image that, while completely unnoticed when looking at the stars, would be a real challenge for field use.


Some astronomical/CAT scopes do have special eyepieces that correct the image to a "right side up" configuration and and are sometimes seen among birders who like the ability these scopes possess to successfully and effectively utilize ultra-high magnifications (100x+.)   The downside is that quality astronomical/CAT scopes are very expensive, very large, and/or tend to be far more fragile than traditional prismatic spotting scopes - which limits their field worthiness.







Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: June/10/2007 at 19:54
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Optics GrassHopper
Optics GrassHopper

Joined: January/14/2007
Status: Offline
Points: 66

Spotting scopes by design need to portable, being portable implies some amount of rougher handling, but being portable also put limits on image resolution and/or magnification. Astronomical telescopes are designed to provide good images for the aperture, typically over a range of magnification exceeding that found in spotting scopes, but they'll be larger and more fragile. Both need to contend with seeing conditions, so you'll probably be best off with less than say a 5in aperture, where 4in might be nominal for higher maginfication terrestial viewing. A decent 4in achromat should be over f12 or so, which makes it bulky (4x12 = 48 inches long, even longer is better for less color fringing), while a shorter 4in ED will be a lot more money. Orion has a 4in ED tube assembly for about $900, other companies offer some for 3x to 4x that price.


The 80mm ED tube assemblies can be found for half that, Orion has one as do others, and they might be the best value for trying higher magnification during daytime viewing. You can get good 'diagonals' which correct the up/down viewing, and while ones that also correct left/right you do loose image quality. Plossl eyepieces are fine and can be had starting at probably $50 each. You'll also need a tripod, sturdier is better, one with decent adjustments. Anyway, see below one review of the Orion 80mm ED. They mention that it similar to the shorter Meade 90mm ETX, which is another option, but you'll need to do your own reviews.


I have a 'junk' 50mm telescope that someone gave me, and after some adjustments and such I've used it at 120x while watching shadows from it's moons move across Jupiter. I also have a 'junk' 60mm lens that someone gave me that tests very well, which is a future project. 



Alex, who is more experienced with optics, helped me put my new toy through its paces. A few weeks after I loaned it to him for testing I called to see when I could fetch it back. He replied “What 80 ED?” I took that as a good sign.

Yes, Alex did reluctantly surrender it after I had the chance to compare views with his excellent Meade ETX90 (3.5” Maksutov-Cassegrain). In mid November, a near full Moon and Mars were available and we took advantage of decent seeing to judge the 80 ED’s optics. The Meade has slightly more aperture, but is limited by a central obstruction. Both scopes gave very similar color-free views of the Moon. If there was a color difference it might have been due to our eyepieces, but I did not see any. I did sense a slightly crisper and brighter edge to the 80 ED which is not unexpected due to its clear aperture.

The 80 ED took a good bit of magnification.  Convention dictates that an 80mm diameter objective should perform its best up to 160x.  However, we saw very little drop-off in image quality at 200x (3mm Radian). Indeed, we pushed it to 240x (5mm-8mm Speers Waler at 5mm with 2x Ultima barlow) and the views were still sharp.

Mars was a modest 13.5 arc seconds in diameter by this time, yet its rusty color and tiny polar cap were distinct at 150x in the 80 ED. I also noticed some slight coloring around Mars (red on one side and blue on the other). I have also noticed this on Venus in subsequent testing. It might be a collimation and/or cool down issue, or it might be the scope’s optics.  Strangely, it does not appear in my lunar observations. This phenomenon causes me to wonder whether to classify this scope as an apo or “semi-apo”. I’ve not yet decided.

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