Atmospheric limitations (1 Viewer)

[OPTIC_NUT]

It's been years since I took the spotter out. I've been more into binoculars.
Recently, however, I am looking into greater distances and birds.

I took the 20x/40x 60mm Swift spotter out to a hill nearby where you
can see field edges, ponds, woods, and development, and Boston 22 miles
away. The weather was a little windy, 50 degrees F but raising under a
strong sun.

I expected Boston to be a blur, given a little haze and a lot of distance.
When I looked at a development 2 miles away, however, there was a lot
of shimmer and blur. Going from 20x to 40x just increased the appearance
of the wiggling. Fixing on a large pond with a few houses 1/2 mile away,
I got a better view, but the mullions on the windows, for example, were
doing quite a "snake dance". When a gust blew through a thick pine
grove halfway along the sight line, the distortion got pretty bad for
a minute. Maybe this was a blob of heat from the sun-warmed trees...
...not sure. It might have been the wind. I could have recognized a
familiar face on the lawn at 20x or 40x, I think, at good moments,
but I don't think even the 40x could yield more detail at the distance.

Was I seeing something rare or common?
I have a friend looking to follow wind surfers at 1/2 to 1 mile out.
If terrestrial shimmer is worse than astronomical, is looking out
over the ocean even worse? Wind surfing happens in windy places, after all.

I'm thinking....40x can get me more detail at 100 to 300 yards,
but the atmosphere scuttles power past 20x at longer ranges. Are there
rules or thumb on this? I'm a bit surprised....maybe it was a 'bad' day.

 

[Alexis Powell]

For a variety of reasons, thermal effects among them, I rarely find powers above 30x useful for birding. But stability of the air is highly variable, and there are certainly times when it is possible to see very far clearly. On bad days, going to a hill top to look down to distant birds is often a good strategy because it minimizes how much near ground/water air (which is often the most unstable) you have to see through. Effects of wind vary, but a constant wind is often a good thing because it sweeps away/quickly mixes warm pockets or prevents them from forming in the first place.

--AP

 

[henry link]

I agree with Alexis about elevation. Sometimes just a few feet can help.

I frequently use 90-92 mm scopes for long range birding at high magnifications, typically between 60x and 80x, sometimes 100x or more. A state of near equilibrium between air and surface temperature is the key. On many days there is a window of equilibrium as the temperature rises in the morning and another in the afternoon as it falls. Cloudy days tend to have more stable air than sunny days. It's also true that the image in good optics is less disturbed by air turbulence because the MTF drops more when the effects of optical aberrations are added to the effects of turbulence.

 

[OPTIC_NUT]

Constant wind, thermal equilibrium, mixing.....
I'm thinking overcast days with a damp low cloud deck might be good on the North Shore
or the Cape. Right now the sea is really cold so there aren't many days without a lot
of turbulence and mixing. He can't get much height, unless they are off the
tall bluffs on the elbow of the Cape. I did see better once...it was Ospreys 1/2 mile
away, spiraling up. They were high and I was low. Maybe the same effect, rays
cutting through the air layers instead of riding them parallel.

A 90mm Mak might be nice to start him on, but it would be a shame if the conditions
were not good very often. I was thinking starting with a smaller fixed power scope
would let him get the feel before taking the plunge.

I've used the 20||40 x 60 Swift on mountains before...it's incredible how different
the view is, even at just 3400 feet. The bird view goes many miles and the stars
are really steady.

 

[Rui_Caratão]

Usually these incredible days taken place during winter and you recognise them with your eyesight, seeing further than on most days. I usually like the afternoon better and from 4pm forward the image betters untill the lack of light diminuishes your resolution

I will attach 2 images taken from a Zeiss 85 at 60x and 168x from one of those days...

 

[OPTIC_NUT]

Fascinating.
The air looks excellent, although you can see the effects.
Past 1 mile, you see less "live wiggle" and more averaging "blur",
just averaged wiggle.

I should get some more observations. Just 1/2 to 1 mile, in my case.

Seems I've posted at a good time...with people showing their photos.

My personal most-used site is a bluff 30 feet over a pond. I need to take
the spotter out more for experience. The wind-surfer guy will have a tough time,
I think, from 6 ft over the sand.

 

[Cosme]

pollution plays a role too. in my country house im able too see way further

so after a heavy rain, its the best; clean the air, cold the temperature, cold the ground ... etc etc

rui, you got a zeiss??? :t::clap:

 

[Rui_Caratão]

I borrow one from a friend sometimes ...

 

[mooreorless]

I had my Orion 100ED on the back porch yesterday evening, about 7PM and later. I used 12.5 mm eyepiece at 72x and conditions were very good. I am sure I could of identified someone I knew up at the overlook 2.8 miles away. The view through this scope was much better than this picture I took with the scope, in fact no comparison. By the time I thought to use the 9mm eyepiece the light levels were lower and I couldn't say that 100x was better. I think 80x-90x would of worked. There were no vehicles until it was getting dark and I could make out what looked like a couple of Yellow Labs that these people left out to do their business, they were towards the left more behind trees and once in a while go past the trees. At this point the light levers were low and I was using a 32mm[28x] eyepiece and moved up some to identify the dogs better. The view started rolling later from the air currents.BTW there was no CA that I could see at all, even at 100x.
http://www.birdforum.net/attachment.php?attachmentid=489665&d=1396102930

 

[mooreorless]

I left the Uni-Star Basic heavy tripod set up on the back porch and have been looking off and on all day. The same area 2.8 miles away on the overlook. There is some shimmer and quite a bit at times, I have went back and forth between different eyepieces and I can still use the 72x one some of the time. There was a truck that went through and I could tell it was a Ford right away, it never stopped. As far as birds go, I could tell they were Black Vultures. Same 100ED. I just caught a glimpse of a truck going through. Turns out they parked where I could not see the vehicle and walked up to this clearing. There were 4 people 3 fellows and a young lady. The one fellow was either bald or very short haircut. I could make out their faces somewhat, did not know them. I was going to up the power to 112x but they left. There are not many birds around up there, just vultures flying around.72x was usable for this.

It is 84°F [digital thermometer] on my back porch, this porch has a roof over it. If you look at this picture of a verizon sub station 210 yds. away, I can read the lettering on the small orange and gray stamp all the way to the right with this scope right now. 72x and 100x Danger High Voltage[Orange part] gray part smaller print [Suitable for use as service maintenance equipment ] I am not using an image erect diagonal, so everything is backwards.

http://www.birdforum.net/attachment.php?attachmentid=311060&d=1299118025

 

[dannat]

well done steve,

i agree with cosme about the rain -seems to clear up the air to a extent -i live in the country but work at an Obs. in a big city - the viewing is chalk/cheese the clean country air easily supports more mag.

what are the optics in the swift like? 60mm isnt much aperture for 2 miles

 

[mooreorless]

Thanks Dannat!

I just tried this same scope and setup outside today 4PM Eastern Daylight Savings time and up to about 5PM.It is 88-90°F outside. I looked at the "overlook"[same distance] area and could see the green round area on the one tree with either the 72x and 36x, using the 32mm eyepiece [28x] I could still see the green "spot", but it was harder to see. The mountain has a somewhat blue tint to it of course. The same Verizon substation decal[210 yds. I could read it up to my 5mm eyepiece 180x. I was able to watch the Black Vultures flying around just below the top mountain.

I just tried the power line 5 miles away and I thought there were some big birds sitting on the top. The one flew away, so yes they are Vultures. Here is a picture of what I am talking about. The conditions are a lot worse then when I took that picture through the 100ED P-Focus. I hope this helps some. I measured the distance with Google Earth a good while ago, not exact of course.

I just watched one of the buzzards land on the lower part. There are two "ears" that stick up and just below that there is what looks like a bridge, the birds are on what would be a "road" of a regular bridge. I found the 20mm[45x] and 25 mm[36x] eyepieces worked pretty decent at this distance and conditions
http://www.birdforum.net/attachment.php?attachmentid=367184&d=1327917578

I will have to try my Nikon 60ED Fieldscope some time comparing, not really fair. I wish I had the 82 Fieldscope.

 

[gulf1263]

Used both the Questar 3.5 and 7 for observation and surveillance under all kinds of conditions.
We discovered that we got shimmer off of snow fields and ice fields when the sun came up, haze also was a problem.
Haze over lakes, blurred views on sunny days, etc, high mags and large objective didn't help, you just saw more "crap" in the air.
Best time was in the morning and evening it seemed.
Some of the new optronics can use algorithims(?) to improve the view.
Conventional optics can be limited in what they can make out at distance.
Maybe Kimo has some insight into the problem.
Art

 

[mooreorless]

I tried the Nikon 60mm ED Fieldscope, I found in every instance the 100ED had a better image in these conditions, 86°F, close to same power what ever. I watched a crow trying to open a wild garlic bulb out in my one cornfield, it gave up. This is just what I found this evening 6-7PM. 72x was usable sometimes at the long distance and shorter distance most of the time, unless looking across a road.

 

[OPTIC_NUT]

Beautiful stuff, mooreorless!

I have to say...I have taken out the spotter more lately, and I haven't seen as much distortion as I
saw that day. I've also been following eagles that rise over the highway cloverleafs, and I suspect
looking up or having sight-lines away from the ground helps a lot.
I'm not so down on atmospherics now, just need to learn how to predict them.

Gulf1263, do you have photos with a high megapixel count?
One scheme I use in haze is to downsample 20MP(in my case) to 1.5MP
(~28% size scale) with Lanczos filtering (this is in Irfanview, a freebie), re-add saturation,
re-add contrast (10-20%), and sharpen once. The result is about a full screen of pixels
but with better contrast and recognizable detail. Haze messes with everything
but you usually have pixels to throw at it. If you can tolerate some yellowing
haze filters really do a lot. And haze filters are real-time, of course.

 

[OPTIC_NUT]

well done steve,

i agree with cosme about the rain -seems to clear up the air to a extent -i live in the country but work at an Obs. in a big city - the viewing is chalk/cheese the clean country air easily supports more mag.

what are the optics in the swift like? 60mm isnt much aperture for 2 miles

Interesting thing about rain: it's a heat exchanger...really evens out the
temperatures. Of course, it scrubs haze out too.

True, it's low for 2 miles. Testing at close range, it's magic
for resolution, though. It does well at 1/2 mile and 1 mile.
They claimed some kind of special 3-element
achromat. They don't call it APO.
The eyepieces are ordinary orthoscopic. It's f/6.5.
I was pondering a Celestron C90 with a binocular splitter in the future.
(give the optic cortex some duplicate signals to work on).
Then again, the C90 might be a really narrow view.

 

[OPTIC_NUT]

I should say 1/2-1 mile, to its' 40power limit, really. That's all.
Now that I've taken out a regular 70mm f/12 with decent eyepieces...and run a booster
(6x16 monocular) on my 20-power turret setting (120x boosted),
there is no comparison with the detail the 70mm/f/12 shows at 70 or 150 power.
I suppose saying a scope is good at a certain distance should be paired with a power
or a physical dimension..

A spotter that gets beyond maybe 60x is going to be quite pricey regardless of aperature.
So much sherical and chromatic trouble to get past. That goes away with f/8 APO or f/12.
Of course, the width of the view is greater for the spotter at lower powers, but they all
have a narrow view at 100x anyway. Even 70 degrees apparent (nice EP) is 0.7 degrees fov at 100x.

I followed an eagle finally today with the f/12. I actually kept up fine when it was 400---600 meters away,
at 80x. So one strategy could be a spotter under 300m, an alt-az astro over 300m. The astro is longer,
but it's actually lighter. When I feel rich I'll get a nice 80mm f/8 APO. Meanwhile, I can get $100 eyepieces
for my $150 telescope and re-use the value later.

 

[mooreorless]

ON,
If I understand this right you bought a 70mm F12 Astro scope on an alt-az mount.

 

[OPTIC_NUT]

Yes.
A "my first scope" clunker, with glare suppression and binoc. eyepiece enhancements.
(matte black plastic roll liner, small and large binoc eyepieces set into 1.25" holders)

I was testing the concepts:

---that a high f-ratio removes most spherical and chromatic aberration compared to a short barreled spotter
---that a power of 60-120 will give decent detail with that barrel
---(and the really big question that I can successfully track an eagle at high tangential speed with a f/12
(alt-az) ..at 500m, that is.

All these points met with success, but I had to:
---line the tubes inside with a matte-black finish (radically improved the contrast) and
---use a 'Plossl-plus' or a Kellner eyepiece from scrapped binoculars.
This was another radical improvement. The beginner eyepieces are narrow field and darker.
Eyepiece salvaged from a 10x25 has a shorter fl than one from a wide-field 7x35 pair..

It went more successfully than I thought it would. The atmosphere was excellent and I got good views
of eagles at around 500m+ (on the move) and jets at 5-20 miles (the Logan 5pm push).
The whole thing was very light. I hiked a hill 25 miles from Boston, MA carrying with one hand.


Now, I could use:
---a sturdier tripod, but not much heavier.
---a shorter barrel of course (but not heavier! This was very light.)
---a super eye-piece I can re-use on good telescope

Next scope: maybe an F/8 psuedo-APO ED?


http://www.telescope.com/catalog/product.jsp?productId=9895&gclid=CJuf_MzPs78CFQsYMgod81IA0g
(Orion's "almost APO" ED scope).

 

[henry link]

FPL-53 is the glass equivalent of Fluorite with an Abbe# of about 95. Assuming an optimum mating element, an f/7.5 FPL-53 doublet, like the Orion ED80, would be a real APO with considerably better color correction than a conventional f/12 achromat. The problem, as always, will be getting a really good one.