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Looking into a eagle nest at 3,200 feet away. Indoor glassing options (1 Viewer)

billb9430

Well-known member
Hello Eaglejonny,
May as well turn the "firehose" on full, so long as you've asked the question about image erectors for telescopes. Lots of alternatives here to consider:
1. The simplest "image erector" if you happen to choose a Newtonian (sometimes called Dobsonian because of its mount) reflecting telescope is simply to aim the big tube horizontal (or in your case, slightly downhill) at the nest and stand with your back to the nest as you view and look "down" into the eyepiece projecting from the top side of the scope tube. Obviously you cannot stand in front of the scope, since that would block the light. It is pretty easy to stand a little to one side and get a nice, erect and correct right-and-left image view. I have a friend who uses a 10" diameter scope like this to watch grizzly bears.
2. If you use a refractor astro scope "straight through" the image will be upside down, so you need to somehow invert the image so up-down is correct and MAY also want to revert the image, correcting so right and left are properly oriented. A commercially available 1.25" or 2" aperture "diagonal" mirror or prism will accomplish the "invert" function and is the most cost effective way to go with a refractor. The eagle in the scope image will be facing the opposite way, left and right, but will be upright. Some folks do not mind this, others do. Right angle diagonals simply slip into the scope focuser tube and the eyepiece used is then inserted into the diagonal to view at right angles.
3. if you want a fully "correct" image with a refractor, there are several good options, but none are particularly simple or cheap.
a. A straight-through (with offset) Porro prism cluster can be purchased that will fit in a 1.25" focuser tube and hold the eyepiece for "correct viewing". This is a good solution, but requires the telescope to have a long travel focuser to allow enough "in" travel to accommodate the optical path length of the Porro prism pair cluster to reach infinity focus with your eyepiece. I've made scopes that use this prism scheme with a surplus 7 x 50 binocular Porro prism cluster ($15 or so) built within the homemade main scope tube. There is also a Porro Type 2 prism that does the same thing, but is arranged differently for easier use in a homemade spotting scope. See this archived thread from Cloudy Nights site for a 2" diameter Porro Type 2 prism cemented up using two Porro-Abbe prisms. This type can also be cemented up from 4 identical common right angle prisms. https://www.cloudynights.com/topic/185367-surplus-shed-127700mm-rftspotter/#entry2391788
Many commercial spotters use Porro prisms with the two prism sets separated so that moving the prisms apart and together changes focus..
b. Sometimes, the Porro prism erecting system is followed by a "half penta prism" that serves to change the viewing angle to 45˚. Pentax PF spotters use this scheme. It works well, but cuts into edge of field illumination for close viewing distances.
c. A separate 45˚ prism can slip into the refractor focuser and give a fully corrected image. These are Schmidt prisms and are in the category of "roof prism" design. The "roof" is simply a right angle reflective portion of the back of the prism where light on the left is reflected right and right to left by total internal reflection. Schmidt prisms are sometimes incorrectly called Amici prisms.
d. An Amici prism is a right angle roof prism that again gives a fully corrected image, but is viewable by looking at 90˚ from the telescope axis. The Amici prism is commercially available in both 1.25" and 2" focal tube diameters and can slip into the telescope focuser tube and will hold different eyepieces for viewing. Like the Porro prism cluster and Schmidt prism, the Amici prism requires more "in" focuser travel than straight through "inverted" viewing, but needs less "in" travel than the insertable Porro or Schmidt prism erectors.
e. The Schmidt-Pechan prism is common in roof prism binoculars and some other prism types are occasionally utilized (Leitz Trinovid), but those are rarely seen in refractor erecting systems.

Hope this at least gives you a starting point in your research as to what optics are usable for your eagle viewing. Your nest should provide fascinating views.
 

Binastro

Well-known member
Re post #1.

If the distance is 3200 ft horizontally and 300 ft vertically then the slant distance is less than 3220ft.
0.6 miles and just under 1000m or 1km.

From my experience optimising the observing conditions, i.e. temperature equal inside and outside the building and choosing the best observing conditions is far more important than any degradation from an upright image prism so long as the prism is of good quality.

Becoming a weather observer is important.

My world class astrophotographer friends follow the jetstream speeds just above their location.
If it is 100 mph plus they don't bother to open their observatories.
Even at 50mph it affects the results.
Apparently they can follow the jetstream in real time.
Jetstream speeds can reach 300mph I think.

I don't do this. I just see how steady the air is and go from experience.

The stability of the air depends heavily on location.
Some places are good, some aren't.

The best conditions occur when the land, sea and air are at the same temperature.
Ideally about 60F or 16C.
Although at high locations such as Pic Du Midi it is I think colder. These top Seeing conditions occur at night.

Regards,
B.
 

Binastro

Well-known member
Hi John,
If your location is at 5,000ft plus elevation and has fairly steady temperatures, then your location may be good for distance observations.

Regards,
B.
 
Hi John,
If your location is at 5,000ft plus elevation and has fairly steady temperatures, then your location may be good for distance observations.

Regards,
B.
Sad to say I am at about 1,000 ft. Does the denser air at this elevation effect Astro scopes more than bino's or spotting scopes at this elevation?

Thanks so much huge help!!! I was considering the Swarvo BTX but don't think the magnification would suit me.
 

jring

Well-known member
Sad to say I am at about 1,000 ft. Does the denser air at this elevation effect Astro scopes more than bino's or spotting scopes at this elevation?

Thanks so much huge help!!! I was considering the Swarvo BTX but don't think the magnification would suit me.

Physics is the same for all telescopes. The aperture has an effect to how strongly an instrument is affected by bad seeing - larger aperture gives a higher probability that seeing will affect the image. So use the smallest instrument that will properly support your intended magnification (which tends to be a refractor due to no central obstruction).

Binos are a different thing as you have two telescopes and thus two chances to get a clear image and the brain will use the good parts of each... but at a price... a pair of APM 120mm ED bins will be in the same price range as a BTX 95. And of course the added complexity that they can be knocked out of alignment and needs proper IPD setting if you want to observe with more than one person.

Joachim
 
Hi.

If you use it indoors with open windows, the temperature indoors and outdoors has to be equal, otherwise terrible images due to temperature variation, tube currents etc.

So maybe a dedicated room with correct temperature.

I have only one double glazed good window, the kitchen window, which takes 120x to 180x with 100mm scopes and maybe 120mm.
I used a bathroom with no heating and opened the window for an hour before observing at night.
With an anorak and scarf over my face, to stop body heat.
At 4.7 miles I resolved one arc second markings on a large clock tower, maybe 80ft up.
My viewing 30ft above ground.
Magnification 250x and very steady on many nights at 3 a.m.

During the day such high powers are not possible.
But 100x should be O.K. sometimes with an open window temperature stabilised.and 180x with very good bits of double glazing.

In your situation I would go for a good 120mm ED refractor.
If using through double glazing the larger the scope the less magnification the window glass can take.
Numerous astro eyepieces are available, wide angle or normal.

You need either a 90 degree good mirror diagonal for best views or an upright vision prism.
But these prisms degrade the image, although I don't find this too bad, whereas others here feel they aren't so good.

I used a Porroprism device, but most are roof prisms I think nowadays.

Regards,
B.
Wow being able see a second hand move at 4.7 miles that sound crazy. heck maybe I could see a baby eagle blink at 3,200 feet :) I am looking at some 120mm ED refractors and I am still a bit confused on what eyepiece I need to get to see it as a correct view, I am kind of guessing but am thinking I need one with a roof prism correct? Thanks so much, I am really hoping they use this nest site, and the birds I am seeing are not a resident pair looking for interlopers.
 

Binastro

Well-known member
Hi John,

The eyepiece gives the magnification.
The focal length of the objective divided by the focal length of the eyepiece gives the magnification.

The prism gives the upright image.

But the 120mm ED refractors seem to provide a 90 degree mirror included that gives an upright image but laterally reversed, i.e. left to right.
So one looks down into the scope.
This means a lower tripod.

The ED refractors probably have two basic eyepieces included and maybe a Barlow doubling lens.

Basically, with a 120mm ED refractor one can use magnifications from 25x to 250x.
The highest powers are for astro use in good Seeing conditions.

Others here have more knowledge of current eyepieces than I do.

Regards,
B.
 

pianoman

duck and diver, bobolink and weaver
Another vote for an astro scope here. Your circumstances are particular - a nest at a fixed spot, so you won't need rapid focus or easy portability.
 

jring

Well-known member
Hi,

I have a Skywatcher 120 ED, an assortment of EPs and a highrise building at about 1km distance visible from my balcony. I guess in the next few days I will have one with overcast skies and good seeing during lunch break... will check what is possible.

In general magnification = focal length of the telescope / focal length of the eyepiece. The usual 120mm ED doublets have 900mm focal length.

Eyepieces don't have prisms, an Amici prism (a kind of roof prism) might be used instead of a mirror diagonal to get an upright and side correct image vs the upright but left-right flipped image of the mirror diagonal.

But the only one which I would try to use at the intended magnifications of up to 200x would be the Baader 2" Amici with Zeiss optics... and that is 600€...

Joachim
 
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Hi,

I have a Skywatcher 120 ED, an assortment of EPs and a highrise building at about 1km distance visible from my balcony. I guess in the next few days I will have one with overcast skies and good seeing during lunch break... will check what is possible.

In general magnification = focal length of the telescope / focal length of the eyepiece. The usual 120mm ED doublets have 900mm focal length.

Eyepieces don't have prisms, an Amici prism (a kind of roof prism) might be used instead of a mirror diagonal to get an upright and side correct image vs the upright but left-right flipped image of the mirror diagonal.

But the only one which I would try to use at the intended magnifications of up to 200x would be the Baader 2" Amici with Zeiss optics... and that is 600€...

Joachim
Thanks I guess if these eagles really do nest here I can imagine years and years of looking into this nest so I would love to do it right the first time. I really would like to see the image in the scope right side up and right to left correct as well. It will just seem so much more natural. So for example would I buy a EVO Star 120mm refractor and then buy the Baader 2" Amici with Zeiss optics? I really appreciate your time and help on this! John Let me know what you see on the overcast days ahead. Wonder if you could read a dollar bill that far away.
 

Binastro

Well-known member
Under the best conditions at night at 3215ft distance with perfect lighting I would expect details 1/5 inch to be seen with a very good 120mm refractor.

However, during the day, even under very good conditions I think that details 1/2 inch might be visible.

The direction of the light is important preferably behind the observer.

A dollar bill might be recognised, but I am not sure how big the letters are.
I have a dollar bill somewhere.

An important consideration for a 120mm ED refractor is the mount.
Here a good altazimuth mount is probably best.
Also the floor should be firm if used indoors.

Regards,
B.
 

Binastro

Well-known member
Looking at a one dollar bill, I think that at night at 3a.m. in ideal conditions, perfectly lit, the large 1 on the front and ONE on the reverse might be seen.

Probably not in the daytime, although I am not sure.

Knowing what is written is much easier than trying to read unknown text.

B.
 
Under the best conditions at night at 3215ft distance with perfect lighting I would expect details 1/5 inch to be seen with a very good 120mm refractor.

However, during the day, even under very good conditions I think that details 1/2 inch might be visible.

The direction of the light is important preferably behind the observer.

A dollar bill might be recognised, but I am not sure how big the letters are.
I have a dollar bill somewhere.

An important consideration for a 120mm ED refractor is the mount.
Here a good altazimuth mount is probably best.
Also the floor should be firm if used indoors.

Regards,
B.
The lighting will be absolutely perfect in the morning till noon, I look into the nest almost directly west from my house. I have been reading about mounts quite a bit and am learning how important they are. I can literally screw my mount right to the floor if I have to. And I have access under the floor to beef up the flooring, subflooring, and framing if need be. Whatever I get it will not shake or move :) I can see this leading to more star gazing. I live out in the country with little light pollution.
 

jring

Well-known member
Hi,

I would really save the money for the Amici prism - since the nest is stationary, you will not really notice that the image is mirrored on the vertical axis.
Rather get a sturdy alt-azimuth mount and tripod - or a column if you really want to mount it to the floor.

PS: I can see adult black kites blink easily in good light with my 77mm scope and 52x at 550ft... chicks probably too but they tend to be hidden in the nest or the foliage most of the time...

Joachim
 

Binastro

Well-known member
I don't know if looking down at a 95 degree angle is O.K. or not.

The slant angle is depressed at just over 5 degrees, i.e. 300/3200 or approx 1/11th of a radian (57.3 degrees).

My PST telescope has a 90 degree view, but the Sun is usually at about 20 degrees elevation, so I am looking at 70 degrees down.
I find no problem with this, but I limit observation to a few minutes of time only.

Regards,
B.
 

dannat

Well-known member
long refractors are big cumbersome & need serious mounts, a maksutov w reflectix to insulate is much easier, i have a 120mm meade & 127mm mak, mak is much quicker to setup & mount, high power is easy w cheapish astro pieces, atmospheric conditions will play a part as you’ll likely need to be around 100x mag, not all areas in daytime can handle this. couple of yrs ago i had my 100mm mak against some alpha spotters, looking at a grizzly feeding nearly 1 mike away, they topped out at 60x, my mak gave better views at 90x, at 1/5 the price
 

Binastro

Well-known member
Hi Dannat,

Yes, I like and use Maksutovs.
I have several from 60mm to 150mm true aperture.

But they vary in quality.
My Skywatcher 127mm isn't that good at 100x plus.
Also the true aperture is about 118mm.

My 150mm f/10 custom Maksutov was used at 95x terrestrially for years.

The 150mm f/15 could easily take 200x plus but was used for astro viewing.
If used outside they can take a long time to cool.

I think the 180mm Skywatcher Maksutov may have a fan for cooling?
I am not sure of the true aperture. Perhaps 165mm?

What is Reflectix?

I suggested the 120mm ED as refractors are usually trouble free.
I would suggest either a 150mm or 180mm Skywatcher Mak as an alternative.

Some old Maksutovs can have mirror tarnish problems, but not usually for twenty or thirty years.
It depends on the climate. Humid or not.
Some are O.K. after 50 years.

I suppose an ED refractor also has a weak element if moisture got in.
Old normal glass refractors are usually good for 100 years.

But yes, a Maksutov Cassegrain would be a sensible alternative to a 120mm ED refractor.

My 317mm Dall Kirkham would make light work of an eagles nest at 3200ft.
But is a serious scope.

The Celestron 9.25 inch SCT is optimised for quality and a Celestron C14 would be fairly spectacular at 3200ft.

Regards,
B.
 
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Binastro

Well-known member
Thinking about it further.

If money isn't an issue then I think the 120mm ED refractor is better for a person new to high magnification scopes.

The Maksutovs probably vary more in quality.
They suffer from cooling problems in large sizes.
I think the 180 Skymax may have a 32% central obstruction. If so it is large.
The price difference between a Skymax 180 and a 120mm ED is not that great.
Refractors are less trouble.

My 120mm standard glass refractors probably had an edge on the 150mm Maksutovs on most occasions.
I used the Maksutovs more because they were more compact.

A good altazimuth mount for a 120mm ED refractor does not have to be that large.
The scopes are not particularly large.

In a fixed indoor location the extra length of the 120 ED refractor and the mount are not a problem.
Also if taken out for astronomy they don't have severe cooling problems.
Probably ten to fifteen minutes is fine for the 120 ED refractor compared to perhaps 40 minutes to one hour for a 180mm Maksutov.

Regards,
B.
 

jring

Well-known member
Hi,

after two days of rain and fog, today it's sunny at 5 degree centigrade. So i put my 120ED on the balcony and observed the antenna jungle on top of a high-rise building which is 1km from my balcony as per google maps.

I used the Baader zoom with the fitting 2.25x Barlow, which on my ED120/900 results into 84-250x. At 250x the image was quite dark (to be expected with an exit pupil of a bit less than 0.5mm) and the image was barely usable - quite soft and seeing was well visible - as were the floaters in my eye...
The 70 deg afov of the Baader zoom at its high magnification end of 8mm focal length results into a true field of almost 5m radius at 250x. Consequently the magpie which helpfully rested on one antenna did not look really huge.
Also my wooden surveyor tripod did show its limits on the tiled concrete floor - even steps nearby were visible as little shakes and using the focus drive meant waiting 2 or 3s for the oscillations to stop...

One click down at the 12mm setting or 170x, the image started to get ok (except for some seeing due to the sun) but the magpie looked even more tiny than at 250x... don't dream of seeing it blink...
Floaters were still visible and the tripod still was a bit shaky.

So my advice would be - observe at 300m or so and the view will be brilliant ;-)

At 1km, you will be able to see the birds in the nest, but don't expect a close-up view where you can see details of the plumage pattern or the bird blinking...

Joachim
 

Binastro

Well-known member
Thanks Joachim.

How long does it take for the 120ED to cool to 5C?

Is your 120ED a particularly god example?

Did the Crayford focuser need adjustment?
Ed Ting has a video of the 100ED.

Would an adult eagle be big enough for a good view?

Would a 150ED do better?

Your eyepiece sounds ideal.

Regards,
B.
 
ZEISS. Discover the fascinating world of birds, and win a birding trip to Columbia
ZEISS. Discover the fascinating world of birds, and win a birding trip to Columbia
ZEISS. Discover the fascinating world of birds, and win a birding trip to Columbia

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