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Impact of Atmospheric Conditions on Spotting Scopes

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Old Wednesday 26th December 2018, 22:58   #1
Bsimmons
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Impact of Atmospheric Conditions on Spotting Scopes

I'm wondering if there are particular spotting scope designs that lend themselves to handling adverse atmospheric conditions better than others.

Perhaps a scenario will clarify what I'm trying to understand. I was watching wolves in Yellowstone at a distance of approximately one mile. After early morning sessions heat waves began to compromise my view substantially. Are there particular spotting scopes that handle this better amongst the Alpha brands? FWIW I was using a Kowa 883 with the 25-60x.

Thanks for all the knowledge you share. I'm new to posting here, but have really enjoyed learning more about optics.

Brian
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Old Wednesday 26th December 2018, 23:10   #2
Pileatus
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Originally Posted by Bsimmons View Post
I'm wondering if there are particular spotting scope designs that lend themselves to handling adverse atmospheric conditions better than others.

Perhaps a scenario will clarify what I'm trying to understand. I was watching wolves in Yellowstone at a distance of approximately one mile. After early morning sessions heat waves began to compromise my view substantially. Are there particular spotting scopes that handle this better amongst the Alpha brands? FWIW I was using a Kowa 883 with the 25-60x.

Thanks for all the knowledge you share. I'm new to posting here, but have really enjoyed learning more about optics.

Brian
Crank it down to 25X and enjoy the best view you can get given the circumstances. At the Jersey shore I can read everything printed on a distant buoy in early morning with my 883 or Nikon ED82. As the day progresses, detail not only degrades but often disappears in the shimmering heat.

When I first tested my Nikon ED82 (many years ago) I did so with a lot of heat shimmer. I was really disappointed by its performance until I did my research. Later, with good atmospheric conditions, everything became clear!
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Old Wednesday 26th December 2018, 23:12   #3
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Originally Posted by Bsimmons View Post
I'm wondering if there are particular spotting scope designs that lend themselves to handling adverse atmospheric conditions better than others.

Perhaps a scenario will clarify what I'm trying to understand. I was watching wolves in Yellowstone at a distance of approximately one mile. After early morning sessions heat waves began to compromise my view substantially. Are there particular spotting scopes that handle this better amongst the Alpha brands? FWIW I was using a Kowa 883 with the 25-60x.

Thanks for all the knowledge you share. I'm new to posting here, but have really enjoyed learning more about optics.

Brian
No, but using lower magnification might help a bit.
Actually in some conditions binoculars might be more useful.
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Old Wednesday 26th December 2018, 23:39   #4
henry link
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Low aberration scopes handle adverse atmospheric conditions better than higher aberration scopes. That's because aberrations and air turbulence have similar adverse effects on the Modular Transfer Function of a scope's objective lens. When they are both present the effects are additive, so the MTF is degraded more than it would be if only one of them was present.

Unfortunately there's no way to predict the aberration levels of individual scopes, even of the same model. A star test is the only way I know to separate the cherries from the lemons.

Last edited by henry link : Thursday 27th December 2018 at 02:29.
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Old Thursday 27th December 2018, 14:19   #5
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In reference to what Henry says above (#4) about optical aberrations compounding the effects of atmospheric turbulence in degrading the image of a telescope, I have used this in side-by-side comparisons to pick out cherries. I found it easy to tell which of two scopes was better in poor air with turbulence, but for this to work you need a known reference. Also, you need to do enough back-and-forth to make sure that differences are not due to changing conditions, as turbulence tends to be turbulent rather than stable and predictable.

Some fifteen years ago, I picked up a cherry Fieldscope 82 A this way, first checking resolution targets and an artificial star, and then doing the final selection process in turbulent air against a 78 A Fieldscope that had near-perfect optics. I highly recommend trying it.

Kimmo
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Old Thursday 27th December 2018, 14:25   #6
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And to answer Brian's question, I can only echo Pileatus: assuming you have a good sample of the Kowa 883, you already have what is one of the best scope designs and models for adverse atmospheric conditions. To know if your sample is a cherry or something else, you need to either star-test it or to compare it directly to other scopes. The risk of doing so is in potentially finding out that you don't have a cherry.

Kimmo
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Old Thursday 27th December 2018, 16:32   #7
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In reference to what Henry says above (#4) about optical aberrations compounding the effects of atmospheric turbulence in degrading the image of a telescope, I have used this in side-by-side comparisons to pick out cherries. I found it easy to tell which of two scopes was better in poor air with turbulence, but for this to work you need a known reference. Also, you need to do enough back-and-forth to make sure that differences are not due to changing conditions, as turbulence tends to be turbulent rather than stable and predictable.
Been there, done that. I did this comparison between the four 60mm Nikon ED Fieldscopes we have in the family (2 x ED II, 1 x ED IIA, 1 x ED IIIA) some years ago. Worked quite nicely, although the differences were fairly small, probably because the Nikon Fieldscopes, even the tiny ED50, have remarkably little sample variation compared to some other brands in my experience.

I did a star test a few days to check the results I had got, and it basically confirmed my initial the results: One scope was slightly better than all the others, two were nearly the same, and one was slightly worse than the others.

Today I sometimes use this method to check quickly whether a scope is a lemon or a cherry, using my own EDIIIA as a reference.

BTW: Kimmo, nice to see you posting here again!

Hermann
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Old Thursday 27th December 2018, 17:24   #8
Binastro
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Hi Brian,
Basically, one has to choose and learn when the best atmospheric conditions are present.
If the Seeing is awful, not a lot can be done, except to reduce magnification.

In my experience long focal length astro refractors handle poor conditions better than short focal length spotting scopes.
Also the tube material and design is critical.

Small aperture scopes are usually less affected, so it might help to reduce an 88mm aperture to say 65mm with a mask.
A large front iris would be interesting.

The Mirador 30x-120x70 Maksutov spotting scope handles poor Seeing well.

Observing height and target height above the ground are important, but I suppose these occur in Yellowstone.

I find that observing from indoors through window glass helps a lot.
The boundary layer of air outside the window does not impede much, but there should be no indoor heating.
But this will not be possible in Yellowstone.
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Old Thursday 27th December 2018, 17:24   #9
Bsimmons
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Thanks for the feedback. This is really helpful. So it sounds like one of the best ways to test how well a given scope will perform is to star test it. I've read about that process a little bit, but I have a couple questions:

1. Do I need the magnification to be compounded somehow for this to be effective? If so, what's the easiest way to accomplish this?

2. I live in the northwest United States, so finding a cloudless night is not always straightforward. Do I need an artificial star? Any recommendations on this front?

Thanks again!
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Old Thursday 27th December 2018, 18:13   #10
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Hi Brian,
Basically, one has to choose and learn when the best atmospheric conditions are present.
If the Seeing is awful, not a lot can be done, except to reduce magnification.

Small aperture scopes are usually less affected, so it might help to reduce an 88mm aperture to say 65mm with a mask.
A large front iris would be interesting.
I guess it's the most significant single measure you can do. If possible choose early mornings and late evenings for long distance observation.

Large scopes with high magnification, let's say 30x and up, even at it's lowest setting, seems like a real misfit for difficult conditions then, as I seldom see people applying masks to their scopes...

Last edited by Vespobuteo : Thursday 27th December 2018 at 18:22.
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Old Thursday 27th December 2018, 19:05   #11
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Like Vespobuteo said: try a the binocular-way. Take a good bino with high mag (10x ore more) with you, look through one side and then through both tubes, if you have bad seeing conditions. If you can see better with both eyes (with focus to the bad seeing, heat waves etc.), you can then try a good big-bino, which is portable and has the mag you need (e.g. APM 70ED).

While I'm stargazing, using a binoviewer or better a big-bino (e.g. APM 100), there is obvious better performance using both eyes (with the 'whole optical neuronal capacity' of your brain), than watching mono.

MG
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Old Wednesday 2nd January 2019, 23:08   #12
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Originally Posted by kabsetz View Post
And to answer Brian's question, I can only echo Pileatus: assuming you have a good sample of the Kowa 883, you already have what is one of the best scope designs and models for adverse atmospheric conditions. To know if your sample is a cherry or something else, you need to either star-test it or to compare it directly to other scopes. The risk of doing so is in potentially finding out that you don't have a cherry.

Kimmo
Kimmo:

Thanks for the post, it seems the variance may be significant in spotting
scopes, among all budgets and mfrs.

I have a question for all, can a scope that is a bit off, be sent in for service to the mfr., and can they be tuned for the best view ?

I suppose the eyepiece can be at fault also.

I have not seen this question brought up before.

Binocular are often sent in for collimation issues, I have experience.

Jerry
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Old Thursday 3rd January 2019, 11:35   #13
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Jerry,
It depends on the technician doing the work and how much time is given to get the best results.
I would think that Swarovski and Zeiss usually work to high standards at their headquarters.
So do military optics makers.

But the original billion dollar Hubble optics were faulty. It is supposed that if it failed to be launched properly, nobody would have known. A simple test was all that was needed to see the mistake.

There are so many things that could be slightly or more than slightly wrong with consumer optics.
The lens elements and prisms could be, and are not made to perfect standards. The optical figure, smoothness and wedge vary.
The glass could have striations.
The lens elements may not be exactly centred.

High quality movie lenses costing $10,000 to $100,000 are made to very high standards, but even here faults occur.

Someone like Horace Dall would refigure optics routinely to give best results where top performance was needed.
Often to much higher standards than the original maker.

I had a Vivitar zoom lens, which was well regarded, but testing showed it to be faulty.
I sent it back to Vivitar with test slides and they took three examples. tested them on their very good optical bench and sent me the best one as a replacement. It was very good.

Few peope actually know if their optics are actually good or not.

Nowadays there are probably very few top optical technicians. Maybe a few hundred worldwide.
However, testing equipment is probably good and the manufacturer can just find a good example to replace a poor one.
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Old Thursday 3rd January 2019, 12:42   #14
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In my experience, if one lists exactly what is wrong with an optical instrument, maybe backed up by photos, then the work will be given to a senior competent technician.

With lower priced optics, a replacement will be given, which may be better than the faulty one if one is lucky.

I have had cases where a new optic is sent and I have been told to keep the one that I say is faulty. The maker says that the faulty one will just be thrown away.

Also, sometimes, where offers are made, saying give us your old item, and there is a good reduction on a new one, one will be told to keep the old one. Sometimes they actually want the old one, sometimes not.

With faulty optics, nowadays I usually cannot be bothered with the hassle of returning it etc. and just write it off as a loss.
There are much more important things in life than optics.
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Old Friday 4th January 2019, 17:11   #15
richard866945
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observing through window glass

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Originally Posted by Binastro View Post
I find that observing from indoors through window glass helps a lot.
The boundary layer of air outside the window does not impede much, but there should be no indoor heating.
But this will not be possible in Yellowstone.
That is surprising!
I serviced a telescope last winter and got a call from the owner a week later saying the image had deteriorated, badly.
When I visited him, he was viewing through a closed window and the glass was wrecking the image. When the window was opened, he could see a spider on its web at the bottom of a long garden. Since then I have always advised customers to avoid looking through glass.
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Old Friday 4th January 2019, 22:03   #16
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Hi Richard,

My kitchen double glazing is fine at 120x with a good 100mm scope, O.K. at 190x also, viewing birds on chimney pots at 124 metres. At a horizontal angle of 30 degrees. At least terrestrially on a bright day.
For planetary observations about 100x is the limit for the south facing window.

The other windows are not so good, but absolutely fine with binoculars up to 30x and beautiful with a PST H alpha telescope at 80x. Only 40mm aperture scope. Usually used at 32x. With good Seeing the resolution is amazing, so long as Sun is at around 20 degree elevation early morning or late afternoon.
Resolution deteriorates at above 30 degree elevation.

The double glazing is 1970s float glass uncoated and simple. I did not change it when advised to do so for more modern glass.
Heating must be off, and definitely better images than outside at medium magnifications during the day.

It depends on the actual glass. Some old windows are poor even with unaided eyes.
I note that modern double glazing is awful on reflection giving terribly distorted images, but in transmission maybe O.K. with binoculars.
With any window there are sweet spots where the resolution is better.
However, one must always beware of ghost images.
I once 'discovered' a faint diffuse comet with a 12x50 binocular. I had to make a round trip of ten miles to get my 20x80 binocular. I eventually realised it was a ghost image of Jupiter way off axis.

My previous 1960s plate glass single pane window was fine with any binocular, but I opened the window for 3 a.m. observations terrestrially over houses and parkland at 4.7 miles using a fine 120mm refractor. Resolution around 1 arcsecond on good nights. Magnification 250x.
It needed about 1 to 2 hours with the window open and I dressed carefully with an anorak to avoid my body heat affecting the view.
Ideally at 15C/16C or 60F ground and air temperature.

Viewing Mars in Horace Dall's attic high up on a hill in Luton with his 8 inch superb Maksutov at 400x was just mind blowing. If I hadn't seen it with my own eyes I wouldn't believe it. As good as my 12.5 inch Dall Kirkham outside.
This was through his selected and probably worked single plate glass window.
His 108mm f/30 Camera obscura was also world class, corrected for 4 colours.

Wall tested his 30 inch apertures optics at ten miles from I think his bathroom.

So it depends on the glass.

My friend, and I hope he doesn't mind my mentioning this, just bought a wall clock for about 6. He discarded the clock and uses the glass front window and its mount on his 8 inch Newtonian. He reports excellent star images at 150x with no sign of astigmatism etc. He will report further.

The optical window of my 12.5 inch Dall Kirkham, though, cost more than the main mirror.

Last edited by Binastro : Friday 4th January 2019 at 22:24.
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Old Saturday 5th January 2019, 14:19   #17
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note the comments on the human factor

http://bulletin.accurateshooter.com/...t-is-possible/

Mirage is a constant problem. About all you can do is dial the power back.
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Old Saturday 5th January 2019, 16:49   #18
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When I have the energy I'll list the factors that I have found regarding image quality.

Opening a window during the daytime for scope observations maybe O.K. when the temperature inside and outside is similar.

Astronomers, however, soon learn that opening the window at night usually results in a boiling view.
The is because hot air is rushing through the window aperture to the cold air outside. This is also funneled as the aperture is smaller than the room.
Observing outside is much better.

During spring and autumn if there is no heating on, and if the inside and outside temperatures are the same, and the window is open for a long time then the view is good if one keeps body warmth away.

Basically, there are two choices with viewing from inside.
Is the degradation in the image worse because of atmospheric effects or,
Is the deterioration due to a closed window worse.

If the window quality is good then often closed windows is the better choice.

With regard to my friend's use of the snug fit clock window and housing on his 8 inch aperture Newtonian, although he reports pin point stars at 150x and no astigmatism and no ghost images, a resolution test is also needed.
He may have been lucky to get good clock window glass.
He says that looking through it at a big angle showed no adverse effects.
In my experience seeing faint planetary detail is a far more demanding test than a star test.
Also planetary detail is a more severe test than seeing detail terrestrially during the daytime.

Over the last week the pressure has been high, 1042 to 1045 hPa, possibly a bit higher.
Another friend reports easily seeing two pylons or masts on the Isle of Wight over 40 miles away from the south coast. The transparency was unusually good although it was grey and cloudy.
He used a small spotting scope.

I also noted strange weather with 1044 hPa and rain showers.
I think that people feel better with high pressure and worse with low pressure.

Last edited by Binastro : Saturday 5th January 2019 at 16:55.
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Old Sunday 6th January 2019, 00:38   #19
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note the comments on the human factor

http://bulletin.accurateshooter.com/...t-is-possible/

Mirage is a constant problem. About all you can do is dial the power back.
If my calculations are right, those 7 mm bullet holes (1/14 lp/mm) at 1000 yds would require a resolution of around 3 arcseconds, which should be well within the capabilities of the 100 mm Pentax scope. Those with good eyesight should also be able to detect these at 63x magnification.
However, I think the author's assumption that the contact lens was responsible for the image degradation is wrong. He most probably has astigmatism in that eye, which most contact lenses do not correct.

@ Binastro
David,
I suppose that if you were to move your reflecting scopes outside you would probably experience more image degradation, until they had cooled down, than through a window.
I'm not fearful enough to put protective filters on my spotting scopes, but I think that misgivings about image quality are unfounded. I once read a test of UV filters, in which 8 or 10 of the better ones stacked together caused little degradation.
Double glazing though is going to involve a light loss of around 15% and, depending on temperatures and air pressure, is going to cause curvature in the panes, which might result in ghosting.

John
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Old Sunday 6th January 2019, 08:13   #20
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Hi,

regarding the correct magnification for star testing the rule of thumb is to use an eyepiece with the scopes focal ratio in millimeters. For common spotting scopes with around 500mm focal length at around f6, this means 80-100x, so just use the highest mag setting of your zoom.

You can build your own artificial star by putting some aluminum foil on a glass surface and make a very little hole with a pin or needle.

Tape in front of led flashlight and observe from 30m or so.

A very thorough treatment of the star test can be found on

https://www.telescope-optics.net/sta..._telescope.htm.

For a spotting scopes one should use the unobstructed images for reference.

Joachim

Last edited by jring : Sunday 6th January 2019 at 08:18.
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Old Sunday 6th January 2019, 17:22   #21
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An interesting story of a New Zealand telescope maker, possibly Graham Loftus, was told to me.

A New Zealand professional observatory had a large telescope installed, maybe 24 inch or larger and charged the public for viewing.

Possibly Graham Loftus did not think that the public should be charged for viewing the heavens.
So in a couple of days he made a slightly larger mirror and diagonal. He used possibly 3 oil drums welded together to make the tube.
In a few days the completed telescope was put in a nearby car park and free viewing was given.
The amateur telescope was better than the professional one as the optics were made for cooling temperatures rather than for a fixed temperature.

The professional observatory did not like this free viewing and competition, but couldn't prevent it and decided in their wisdom to give free viewing to the public.

Graham Loftus made about 20 telescopes from 20 inch to 36 inch aperture.
In general they were corrected for cooling temperatures.
I think he was a friend of the maker and rider of the 'World's fastest Indian' Burt Munro.
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Old Sunday 6th January 2019, 17:47   #22
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For some reason my server does not allow me to read the shooter reference.

But in my head.
7mm holes at 1000 yds or 914m?
7mm at 914,000 mm.
1 part in 130,500.
206,000 divided by 130,000 is about 1.6 arc seconds.

I could see black sunspots with a penumbral diameter of 38 arc seconds with unaided eyes with 20/15 vision or 34 arcseconds with my head braced against a lamp post.
Persons with excellent vision see 20 arsceconds sunspots with unaided eyes and an optimal safe filter. Penumbral sunspots need to be slightly larger than black transits such as Mercury or Venus.
This assumes absolutely optimum brightness of the Sun using safe filters.

In other words black spots on a white background are visible at smaller sizes than people assume.
But this assumes a black spot on a white background.
If there is not enough contrast a bullet hole cannot be seen even close up.
At 1000 yards one would need very good transparency and Seeing conditions.

I think that with excellent conditions only 30x would reveal 7mm bullet holes at 1000 yds for 20/15 vision.
But observing near ground level, I doubt that really excellent views are normally possible.

My friend who saw the masts on the Isle of Wight, maybe using his 65mm Acuter spotting scope.
I think his observing height was 230ft. He said that the sea horizon was very sharp and clear. This would be 19 miles away in normal conditions.
So at 45 miles to the masts, He would see objects at 400 feet above sea level or higher on the Isle of Wight.

Last edited by Binastro : Sunday 6th January 2019 at 18:02.
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