Difference? Spotting vs Astro Scopes (2 Viewers)

[Paul Godolphin]

Please can anyone help with explaining the reasons why Spotting Scopes don’t work for Astronomy, and Astronomical Scopes are useless in daylight? Exactly what changes inside them make their characteristics so different?
I guess many of us will have looked through an astronomical telescope in the daytime, and been disgusted with the poor contrast, dark image and ugly widespread optical distortions. Compared to our birding scopes an astro scope appears like a cheap kid’s toy, the optics apparently of such grossly inferior quality, you’d think you were using a $10 item with plastic lenses! In comparison, a fine quality birding scope of the same dimensions is razor sharp, bright and crystal clear.
But later that night……..
When you test the same two scopes to look at stars, the opposite happens. The Astronomical telescope now allows easy viewing of the moon, planets and their moons, and details of the star systems. The images are well-defined and the contrast is pleasing, revealing all details within a suitable range of brightness. The spotting scopes also undergo a ‘reversal’ at night: The contrast becomes incredibly high, and the image is completely unusable. Viewing the moon is so bright at times that eye pain is experienced. The sky is deepest inky black, but planets and their moons and the stars are not visible in detail because they are so intensely bright that no detail can be seen. Around the edges bursts into jagged brilliant spikes and the moisture upon your eyeball scatters and flares the intensely concentrated brilliance focussed on one tiny spot. It’s like staring into a car’s halogen headlights at night, and trying to read the brand name on the glass, ie.it’s not possible!
Anyone explain this? I’ve tried numerous astro scopes and all the best birding models. The same applies to top-end binoculars. Can’t see a thing in the sky at night with superb Leicas and Swaros. Yet rubbishy $20 cheapo dim small-aperture gift-shop glasses work great. In daylight the tables are turned, of course. So what’s going on here?
Thanks in advance for your knowledge.
Paul

 

[erniehatt]

You must be using a reflector type scope ie. a Dobsonian. I use a refractor type scope, and have no problem with either. Ernie

 

[medinabrit]

Yesterday being kind of bored i took my pentax 100 pf ,A nikon 82 ed & a takahashi fs 60 & takahashi fs 78 out to compare .The taks are astro scopes .
To be perfectly honest they were all exellent whether it was birds ,distant utility pole electric insulators or at night jupitor & the moon etc.
Good optics are good anywhere in my opinion .
Of course the spotter have the waterproof advantage & the backward view in the astros is annoying for birding & general daytime use.
Brian.

 

[Matt_RTH]

A good Maksutov Cassegrain or refractor telescope can be an outstanding spotting scope.

I think the issues for spotters related to astro are:
* Diagonal introduces distortion that in terrestrial use are minimal with size of image, but critical for star sharpness (point of light).
* 45 degree diagonal takes away more light than a 90 degree diagonal.


Telescopes used as spotter:
* Good ones are very sharp due to astronomical application!
* A 45 degree prism undermines this sharpness but can still be outstanding!
* A 90 degree prism that just inverts image up/down is a popular application for terr use.
* Only short FL, fast aperture telescopes are really applicable for spotters. I wouldn't try to use a 127mm F9. So F6 and 80mm or smaller practical. Then there are Maksutov Cassegrains which are smaller mirror scopes with a folded lightpath design so they are small and light! To me, their focal lengths are too long to be practical for my use, though there are 300mm F5.6 models out there that I think may be a possibility.
* As mentioned earlier, a Newtonian or other mirror based scope would not work or would be impractical (like a Schmidt Cassegrain).
* Not weather proof!

Applicable to both:
* ED or APO is way better for both. See the moon in a scope with lots of CA and see what I mean.

IMHO, the biggest issue between spotting scopes and telescopes for terrestrial use is weight! An 80mm telescope is way heavier than a typical 80mm spotter! No problem if it is always within a few paces of the car, but for those of us who like to get some mileage on birding expeditions, lighter is much more enjoyable.

Fortunately, there are extremely reasonably priced telescopes out there great for spotting scope use. The William Optic and Astronomy Technologies.

Matt

 

[Matt_RTH]

BTW, AFAIK on binoculars, the roof prism light path goes through more surfaces than porro prisms, which is why porros look better than roof binoculars (less surfaces = more light maintained). Worth noting that most spotters use porro prisms rather than roof.

 

[AlanFrench]

I had my ATS 65 HD out the other night and was watching Jupiter's moon Ganymede move into Jupiter's shadow. At 60x, the "birding scope" showed a reasonable amount of detail on Jupiter, and I easily saw Ganymede fade and vanish from view. The Moon is a treat through virtually any spotting scope, especially around first or last quarter.

My 90mm apochromatic "astronomy instrument" provides wonderfully detailed views of birds. It replaced my Questar 3.5", which I used for birds more than I used it for astronomy.

Clear skies, Alan

 

[Sout Fork]

Please can anyone help with explaining the reasons why Spotting Scopes don’t work for Astronomy, and Astronomical Scopes are useless in daylight? Exactly what changes inside them make their characteristics so different?

I must say I'm surprised at this. I have never seen any dramatic difference between the two types of scopes.

Optically, the only basic difference between the two is the built in prism in the spotter. While the prism does give you a correct image it also limits ultimate magnification more than an astro scope without a prism. Put a prism on an astro scope and you have the same problem.

Other than that I can't account for the big difference you seem to think you see between the two.

Of course all of the above assumes all else being equal. Astro scopes tend to have longer focal lengths and perhaps larger objectives but both are governed by the same laws of physics so far as I know.

SF

 

[Vectis Birder]

It’s like staring into a car’s halogen headlights at night, and trying to read the brand name on the glass, ie.it’s not possible!
Anyone explain this? I’ve tried numerous astro scopes and all the best birding models. The same applies to top-end binoculars. Can’t see a thing in the sky at night with superb Leicas and Swaros.

I'm an experienced visual astronomical observer and have never had problems with my Leicas when viewing the night sky.

 

[Paul Godolphin]

Guess it's me that's nuts!

Thanks for your replies, fellas.
I guess that none of you have ever experienced what I'm describing. Dunno why I can see this so clearly in so many different scopes, but none of you have ever had the problem?
I took my 20x60 and 30x80 spotting scopes to the observatory and compared them to astro scopes after your replies. Same problem. The astro scopes are 'gentle' and dim, with a nice subdued image, showing subtle hues and stripes on the face of Jupiter, and the surrounding skies dark bluey grey. (like the mild contrast in the foam on a cup of milky coffee). My spotters however, show jet black sky, and dazzling brilliance from the planet, so it just glares like a white laser, making it impossible to see any detail. (by comparison, like a cup of black ink with a bubble of white polystyrene floating on the surface). I put a neutral density filter across the eyepiece and wore sunglasses and then I could see the face of Jupiter, but the surrounding sky was then totally blacked-out.
Are you absolutely sure you can't see this?? The effect is so strong that I'm amazed nobody else can see it. It's as if somebody has turned the 'contrast knob' on the TV up from no.2 to no.9 when comparing an Astro scope to a spotter.
I'm quite prepared to accept that there must be something wrong with my eyes in view of all your comments, which are most appreciated and I thank you for replying.
cheers Paul (even more confused)

 

[Matt_RTH]

Is it possibly coma or ghosting? I haven't observed at high enough mag on a spotter to be able to try but I will give it a go next week on my PF-65ED (I like DSOs and prefer big Newts to little refractors).

Better question is what scopes are you using for the test? That would make the academic question more concrete.

I've only had planets be too bright in a large newtonian. Not looking at Venus by chance? That's actually a great planet to use as a test as it is very bright and will reveal ghosting and other problems very well.

Anyway, my money is on ghosts that won't focus in but I realize I do so at my own peril.

 

[Paul G Astronomer]

Brilliance

Sounds to me like that spotter scope is experiencing too much brightness. Try cutting out a piece of black construction paper to cover the main lense. and cut a 1" or even a 1/2" hole in it. Place that over the objective lens to reduce the amount of light that's coming from Jupiter. This will cut down on the glare and offer better contrast.

The main issue here for me anyway is apeture. The smaller the apeture the more intense a point source of light becomes. Thats most likely your issue, the lenses in a spotting scope use a faster focal ratio compared to that of a large apeture telescope.

My thought anyway...

 

[Paul G Astronomer]

Optics

Re; Read your original post. Basically it boils down to optics, focal ratio's, wave fronts and wave lengths of the lenses and mirrors.

Most telescopes of the reflector kind are figured to a 1/4 wave mirror (industry standard in most cases) a hand made mirror can be figured to a true 1/20th of a wave or higher, I have a mirror figured to 1/32 of a wave. The difference here for example is the 1/4 wave mirror will see Saturn basically as all one color with some banding on the surface and on a really good night split the rings. The 1/32 wave mirror will see banding, clouds and a highly defined cassini ring. Several Moons as well..were as the 1/4 wave will only Saturns largest Moon titan.

This is pretty much the same for Spotting scopes and Refracting telescopes. To really get the best optics you need to spend the high end cash it seems and even then!!!! You need to be careful. We've had fella's purchase 20K scopes and returned them due to bad optics...once refigured the views were fantastic. Day or Night.

It's a long topic and quite indepth. There are coating issues as well, types of optical glass that used and host of other reasons.

But you can get some great photos using scopes, it comes down to technigues, dark frames, timed exposures, stacking and processing.
Here's a link to a very good friend of mine and he's purchasing better and better gear all the time. You can tell by his photos from his first page of the album to his last page.

http://www.fvas.net/gallery/categories.php?cat_id=8&page=1

Anyway as I said it's a long story!! With regards to optics....why doesn't a 300 dollar lens on a camera see as good as the 9000 dollar lens?? Comes down to elements within the lenses...

Gad I best quit now or I'll end up writing a book....

This might help a bit: (dry reading tho)

http://www.fvas.net/victor/mirror.htm

or

http://www.fvas.net/victor/testing.htm

 

[Paul Godolphin]

Sounds to me like that spotter scope is experiencing too much brightness.

Thanks Paul, and the others. Yes, that's for sure. The image is way too bright to see anything. My sunglasses experiment proved that. But as you can see, my technical understanding is limited, and I can desribe what I'm seeing in very eloquent terms, but in common language only. Sorry for not being able to put a name to the phenomenon.
I regret that I don't know the models of Astro scopes that were used, except that some were Meade, and they varied in size from about 80mm to over a foot across the 'big' end, and that some appeared to be 'straight through' and others had eyepieces on the side. Some were the size of oil drums and had motor drives tracking the objects viewed. They belonged to amateurs and the city observatory. All good for stargazing though!
The spotters used for comparative tests were Bushnell 20x50 straight prismatic, Kowa 32x80 straight, Swarovski angled 40x80HD and Leica 30x77 APO Televid. Same result with all.
I'm happy to accept that the fault is with me, so please don't knock yourselves about any more trying to give the answer, as there obviously isn't one. On this occasion, I guess I'm saying that "everyone's out of step except me" again!! ha harr!
Thanks guys, let's close the book on this one.
All the best Paul

 

[Pileatus]

Please can anyone help with explaining the reasons why Spotting Scopes don’t work for Astronomy, and Astronomical Scopes are useless in daylight? Exactly what changes inside them make their characteristics so different?
I guess many of us will have looked through an astronomical telescope in the daytime, and been disgusted with the poor contrast, dark image and ugly widespread optical distortions. Compared to our birding scopes an astro scope appears like a cheap kid’s toy, the optics apparently of such grossly inferior quality, you’d think you were using a $10 item with plastic lenses! In comparison, a fine quality birding scope of the same dimensions is razor sharp, bright and crystal clear.
But later that night……..
When you test the same two scopes to look at stars, the opposite happens. The Astronomical telescope now allows easy viewing of the moon, planets and their moons, and details of the star systems. The images are well-defined and the contrast is pleasing, revealing all details within a suitable range of brightness. The spotting scopes also undergo a ‘reversal’ at night: The contrast becomes incredibly high, and the image is completely unusable. Viewing the moon is so bright at times that eye pain is experienced. The sky is deepest inky black, but planets and their moons and the stars are not visible in detail because they are so intensely bright that no detail can be seen. Around the edges bursts into jagged brilliant spikes and the moisture upon your eyeball scatters and flares the intensely concentrated brilliance focussed on one tiny spot. It’s like staring into a car’s halogen headlights at night, and trying to read the brand name on the glass, ie.it’s not possible!
Anyone explain this? I’ve tried numerous astro scopes and all the best birding models. The same applies to top-end binoculars. Can’t see a thing in the sky at night with superb Leicas and Swaros. Yet rubbishy $20 cheapo dim small-aperture gift-shop glasses work great. In daylight the tables are turned, of course. So what’s going on here?
Thanks in advance for your knowledge.
Paul

http://www.willbell.com/handbook/hand2.htm

 

[raymondjohn]

Dear John

Excuse my ignorance, but would this book be as usefull for someone living in the southern hemishere?

raymondjohn

 

[Pileatus]

Dear John

Excuse my ignorance, but would this book be as usefull for someone living in the southern hemishere?

raymondjohn

Sorry, it's written from a Northern Hemisphere perspective.
John

 

[DRodrigues]

image erectors

A good Maksutov Cassegrain or refractor telescope can be an outstanding spotting scope.

* A 45 degree prism undermines this sharpness but can still be outstanding!
* A 90 degree prism that just inverts image up/down is a popular application for terr use.

Matt,
I do cr-birding and have a Celestron C5 (probably from 1996...) that I don't use since never found a image erector that results in good focus over 70x, William Optics included... Did you ever tested one of good quality at higher than 70x? Questar seem to have a good image erector but it increases the power by 1.6x and only can be used in their telescopes. Did any one tested the image erector from Siebert Optics http://www.siebertoptics.com/SiebertOptics-correctionprisms.html ?
By the way, the C5 was collimated (I went to the importer to try to solve the question and he verified that) and I'm used to use 126x on terrestrial cr-birding (see it at cr-telescopes at http://pt-ducks.naturlink.pt/ ).
David

 

[Matt_RTH]

David,

CR birding... Color Ring birding? That's a new one for me. Sounds very challenging.

If I was in the same boat, I would consider one of the 80mm ED scopes with one of the available 90 degree 1/10 wave 99% dielectrics. But really, my atmospheric conditions here rarely let me go above 50-60x. The scope isn't the limiting factor for me.

You might check with the forums at astromart.com which are more telescope oriented. Those who use the Tele Vue 85, Ranger, Pronto, etc, might have some suggestions. I'm sure they are here, too.

I decided very fast that telescope birding (as opposed to using a spotting scope) was not for me as I don't need the extra weight. I even selected a 65mm over an 80mm scope for the weight savings.

 

[henry link]

David,

Have you tried the Baader Amici prism shown here? http://www.alpineastro.com/Star_Diagonals/Star_Diagonals.htm

It's quite expensive and I don't have any personal experience with it, but it has received some high praise from people who have been dissappointed by the 45 degree Schmidt roof prisms, including the William Optics. Frankly I'm skeptical since it's also is a roof prism and there's no mention of phase coating. The Siebert prism looks like it's probably a Schmidt-Pechan roof prism installed in an eyepiece barrel. At $32 I don't think it's likely to be phase coated or made well enough for high magnification.

Henry

 

[DRodrigues]

Matt,
Yes cr-birding is what you describe and I do it with ducks (have a look at http://pt-ducks.naturlink.pt/ - as research work) and other species (mainly flamingos and Spoonbills - more for fun).
The problem of star diagonals for cr-birding is that you the codes reversed, which is not very practical although there are people using these. Another practical problem is that I do lots of hide and down-hill cr-birding, so angled scopes aren't practical, 90º diagonals are even worst and the 60º of Televue also isn't a solution.

Henry,
I previously contacted Baader that told me that I will not be satisfied with any image rector they know... I don't know which prism the extendable Swaroskys and Optolyths have, but these seem to work, however aren't in the market...

David