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Optical Clarity of Spotting Scopes

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Old Tuesday 5th February 2019, 18:00   #1
Dantanamo
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Optical Clarity of Spotting Scopes

I'm struggling to find a spotting scope that rivals the clarity of what I see when looking through binoculars. Yes, I know that the two are apples vs oranges, yet I wasn't expecting image quality to be so different between the two optical instruments. I donít live near a store that offers higher-end spotting scopes that I could go in and try out.

To explain further, I recently decided to sell my old Bushnell 10-30x 50mm spotting scope in order to enhance a recent interest in birdwatching. As I originally bought the Bushnell scope back in the 1980ís, I realize that my 21 year-old exit pupils were clearly in better shape than they are today. Even back then, zooming the scope out to 30x produced some rather dark and soft images. So I sold the scope after doing some research and eventually decided to purchase (online) Kowaís Prominar TSN-664M scope with their 20-60x eyepiece. Frankly, I wasnít very happy with the results at anything beyond 30x magnification. The view appeared to not only darken, but suffer from an overall lack of clarity and contrast. In fact the viewing image reminded me of shooting photos with a lens completely stopped down to itís smallest aperture; the resultant degradation is either termed diffraction or diffusion (Iíve forgotten which). So, after reading numerous reviews I decided to try their wide 30x eyepiece instead.

I canít say that Iím very happy with the image quality now, either. I donít mean to pick on Kowa, but am I simply expecting too much from an optical system that is designed to view images at much higher magnifications/focal lengths than a ďstandardĒ 8x pair of binoculars? Yes, I own and use a pair of excellent Zeiss Victory SF 8x42 bins, but Iím not expecting this image quality in a 65mm spotting scope. Even my cheapo pair of Bushnell Legacy 8x42 bins have a superior overall image, versus what Iím seeing in the Kowaís eyepiece.

Incidentally, Iíve been viewing birds at the feeder behind our house, and focusing on any nearby details like the wood grain of a fence and/or tree branches, icicles, et cetera. Nothing has been backlit, and our days have been primarily overcast but not exclusively. Opinions are most welcome.
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Old Tuesday 5th February 2019, 18:19   #2
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You've clearly demonstrated the difference between the image of a fixed magnification alpha binocular against a very good spotting scope, using the top end of a zoom eyepiece. The spotter just wont deliver the same "clarity" that you experience with your Zeiss SF.
If you ever get the opportunity you may enjoy the view through a Kowa 883 / 884 series or its equivalent in Swarovski or Zeiss. A fixed x 30 Wide eyepiece would be almost perfect with a Swaro 80mm HD if you track one down.
P
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Old Tuesday 5th February 2019, 21:09   #3
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I’m surprised you’re disappointed with the 30x fixed eyepiece on the Kowa 663. I own that scope and think that combo gives excellent results. Perhaps your scope has some issues?
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Old Tuesday 5th February 2019, 22:11   #4
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Iím surprised youíre disappointed with the 30x fixed eyepiece on the Kowa 663. I own that scope and think that combo gives excellent results. Perhaps your scope has some issues?
Perhaps it does. I tend to get a headache after looking through the eyepiece for a minute or so, while focusing on different subjects.
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Old Wednesday 6th February 2019, 00:22   #5
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Perhaps it does. I tend to get a headache after looking through the eyepiece for a minute or so, while focusing on different subjects.
Thatís definitely not right. I spent hours looking through my scope with no eye strain whatsoever.

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Old Wednesday 6th February 2019, 07:03   #6
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Perhaps it does. I tend to get a headache after looking through the eyepiece for a minute or so, while focusing on different subjects.
This is definitely not right. When reviewing scopes I spend very long periods looking through them and I have never had eyestrain or headache yet. And the fact that you are not satisfied with the fixed magnification 30x eyepiece is also suspicious. Sounds like the scope has problems.

Lee
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Old Wednesday 6th February 2019, 14:59   #7
Binastro
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Dantanamo,

Sometimes problems with scopes may be actually eye issues.

Do you wear glasses, and have you had a recent full eye test?
Is the image the same with either eye?
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Old Wednesday 6th February 2019, 18:48   #8
Dantanamo
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Dantanamo,

Sometimes problems with scopes may be actually eye issues.

Do you wear glasses, and have you had a recent full eye test?
Is the image the same with either eye?
Yes, I have worn glasses for years (20/30 vision without them). My most recent eye test was 3 years ago (all was fine), so perhaps it's time I did something about that. The image is the same with both eyes.

I should add that a photographer, I haven't noticed any issues when looking through my camera's viewfinder. Same goes for using binoculars.

Last edited by Dantanamo : Wednesday 6th February 2019 at 18:58. Reason: Needed to add details
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Old Wednesday 6th February 2019, 20:03   #9
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I was thinking that with a smaller exit pupil, an eye problem may show up that doesn't with a larger exit pupil.
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Old Thursday 7th February 2019, 19:39   #10
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I was thinking that with a smaller exit pupil, an eye problem may show up that doesn't with a larger exit pupil.
Maybe, although with the usual bane of the hobby astronomer it's the other way round - it starts to show its ugly face with larger exit pupils.

Again, a star test might help to identify problems...

Joachim

Last edited by jring : Thursday 7th February 2019 at 19:43.
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Old Tuesday 12th February 2019, 10:15   #11
richard866945
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headache

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Originally Posted by Dantanamo View Post
Perhaps it does. I tend to get a headache after looking through the eyepiece for a minute or so, while focusing on different subjects.
With a binocular, a headache or any eyestrain is definitely an indication of mis-alignment.
I have not heard of this problem with a telescope but I have seen a number of scopes with one slightly loose / dislodged prism and that does affect the image.
In general, the higher power of a telescope will require good viewing conditions.
Slight heat shimmer or a bit of mist will not be noticeable in an 8x42 binocular but will affect the image through a scope.
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Old Sunday 24th March 2019, 23:49   #12
DunninLA
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I think you are learning that spotting scopes have unacceptably small exit pupils for some people, and I am one such person.

Your binoculars are giving you 5.25 exit pupil. Your kowa scope at 30x is giving you 2.2. Think about how much darker that is than 5.25, and from only one eye to boot!

Some eyes need more light than others to perceive a contrasty, detailed and color saturated image. I know that is my case because I had Lasik surgery in 1996. at that point in the SOTA, a slightly diminished perceived brightness was one of the side effects.

I sold my spotting scope because I used it at 50-60x magnification, at which settings my exit pupil was below 2.0, and down to 1.33. Like your observation, images were dark, lacking color, and lacking detail. And you only get the benefit of one eye.

You might consider a 95x spotting scope aperture, and spend most of your observing at 25x magnification, to give you an exit pupil of 3.8. Even then you wouldn't be getting the 5.25 exit pupil of your binoculars.

Or do what I did and get a 127mm MAK scope... 12" long, 7 lbs, and certainly a much better image than I was getting (because of exit pupil size) at 50x magnification from my 80mm ED spotting scope, which I sold. Many people would agree that 80mm objective spotting scopes lose their effectiveness above 40x magnification. And of course proportionately, 65mm spotting scopes above 32x. But clearly for you, and me, those magnifications are far too much to receive a satisfactory image.

Last edited by DunninLA : Monday 25th March 2019 at 00:05.
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Old Monday 25th March 2019, 04:41   #13
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OP --

Assuming you want to stick with a spotting scope, you will want a very large aperture.

Check out the very affordable https://www.celestron.com/products/r...spotting-scope

With 100mm ED objective lens, you could use the lower range of the 22-67 zoom, and get an exit pupil of over 4.0. The quality of glass and prism will not be the same as the Kowa, but glass quality isn't your problem... small exit pupil is, and this scope solves that problem.

With the M2, you can use telescope 1.25" eyepieces instead of the zoom. You could buy an inexpensive telescope eyepiece of fixed 25mm, say the Celestron Xcel for $65 which given the 540 focal length of Celestron M2 scope would give you 21.6x magnification and about 3.8 exit pupil. Or a 32mm eyepiece like the Celestron Omni for $35 which would give you about 17x magnification and therefore an exit pupil of about 5.5, which is more than you're getting from your Zeiss bins, so the image will be bright. Another $65 eyepiece like the Meade HD60 18mm for $75 would give you 30x and 3.3 exit pupil. Or buy all three eyepieces and learn where each is appropriate for what you're viewing that day.

Last edited by DunninLA : Monday 25th March 2019 at 04:51.
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Old Monday 25th March 2019, 10:42   #14
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Actually, in daytime use the eye pupil is likely to be 2mm to 4mm not 5.25mm.
It is only in poor light that 5.25mm will be reached and older folk may be limited to that.
Young eyes open to 7mm to 9mm at night, although those with 9mm eyes have very poor resolution.

My eyes still open to perhaps 5.5mm.

I still have no problem using a 0.5mm exit pupil with one eye and about 0.3mm with the other.
The Skywatcher 90mm Maksutov was fine for me at 190x, but 125x was the best power.
When young I had no problem with 0.25mm exit pupils.

We are all different.
If someone needs larger exit pupils that is fine.

Incidentally, the true aperture of the 127mm Skymax is about 120mm. This is because Maksutov Cassegrains need oversize primaries with a diameter larger than the front corrector.
It seems that these Chinese? Maksutovs quote the primary size not the true aperture.
I don't know what the Russians do, but their well known 500mm f/8 mirror lens is 63mm aperture, whereas Nikon, Minolta and Canon 500mm f/8 mirror lenses are much larger.
The strange thing is that the 500mm f/8 Minolta mirror lens for MD manual focus is smaller than the Minolta and Sony Autofocus 500mm f/8. I have both.
The Russians are quoting the geometrical f number, but the T number is probably T/10, because of the light loss due to the secondary and transmission losses.
The Japanese top quality makes correct for the central obstruction light loss but not transmission losses.
Some Korean and other mirror lenses are undersize.

I am not sure what the size of the 3.5 inch/89mm Questar primary is.
My Custom 6 inch Maksutovs probably have oversize primaries.

My 12 inch Maksutov had a 12 inch corrector, but 12.5 to 13 inch primary.
When the corrector broke in half on the makers work bench I was left with no telescope, but insisted I get one, and the primary was used to make the 12.5 inch f/3.5 f/14.6 windowed thin edge primary Dall Kirkham. It took three years to make. It is possibly slightly over 12.5 inches, but the optical window was I think 12.5 inches aperture.

With an erector prism the 127mm Skymax, if it is 1500mm focal length for astro work with no diagonal, may be 1600mm with a star diagonal and maybe 1650mm with an erector prism.
This could be measured.
The 32mm eyepiece may not be 32mm, as eyepieces often are not the marked focal length. Often they are 5% out, sometimes more.

This doesn't really matter.
What matters is how the magnification suits and if the observation is satisfactory.

B.

Last edited by Binastro : Monday 25th March 2019 at 10:50.
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Old Monday 25th March 2019, 20:01   #15
DunninLA
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Skymax, if it is 1500mm focal length for astro work with no diagonal, may be 1600mm with a star diagonal and maybe 1650mm with an erector prism.
\
What matters is how the magnification suits and if the observation is satisfactory.

B.
Agreed. I have been using 1650 as the in-use focal length of my Mak when calculating EP.

Regarding what magnification suits... for whatever reason, the 52x I am getting from the $40 Celestron Omni 32mm 50* plossl eyepiece gives me a superior image in my Mak to the 64x $120 26mm 62* Explore Scientific eyepiece I will be posting back to the store. The ability to resolve detail at both 900 yards (the closest thing I tend to view) and 1.8 miles (the usual beach/rocks/street corners I look at) is a tie between the two eyepieces, as is the edge detail and focus. However, the 32mm is brighter, has more saturated colors, has a cooler color tone, and is just more "pleasing". I was surprised I could not read smaller letters on signs with the 64x vs. the 52x magnification. I believe it has to do not with my Mak, but with atmospheric limitations to "usable" magnification. I believe that by further magnifying heat waves and atmospheric particles, the 64x has met its match. I have reached (for atmospheric conditions this month anyway) the highest optimal daytime magnificaiton with 52x, of at least somewhere between 52 and 64. I also don't know if I were to try a 40mm eyepiece, whether I would actually be able to resolve smaller letters at 2 miles than I do with the 32mm, but I am going to try at some point.

Last edited by DunninLA : Monday 25th March 2019 at 20:05.
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Old Monday 25th March 2019, 20:23   #16
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It is always that trying things out is best.

The Seeing conditions are likely to change not only monthly, but hourly or less through the day.
The other thing is tube currents, usually O.K. in sealed optics, tube colour and tube material.
Direct sunshine on the tube or shielded. Shielded is better.
Usually refractors do better here than mirror scopes.
Long refractors better than short refractors.

I said that if I was younger I would set up my 12.5 inch Dall Kirkham, but then realised that neighbours might consider this over the top looking at a beach.
I think that up to a 6 inch refractor or 180mm Maksutov would be considered fair at 1 mile.
An 8 inch Dall Kirkham, possibly O.K.

Another point is that a big scope might need a pillar mount going through any wooden decking into the ground underneath.
The decking may impart vibration or movement.

My best eyepiece is an old 8mm RKE, three element eyepiece.
Naglers are good, but don't resolve better.
Plossls and orthoscopics can be very good.

B.
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Old Tuesday 26th March 2019, 12:12   #17
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I’ve got very nice views with a 66mm Astro APO refractor and ultrawide Astro eyepiece, 30x fixed magnification. I have used a zoom, but it’s a compromise. In reasonable daylight 30x is fine, can push to about 50x but then will start to dim off. I recently decided I wanted a binocular view and spotting scope powers and so bought a set of 70mm APM Astro APO binoculars. 4kg, so not for long hikes, but when observing from a hide they provide a very wide and detailed intimate view. After using them a while, my Nikon 8x30E2 feel like a narrow field, fuzzy edged let down.
Have a look though the posts on this forum, decide what size, weight, cost fits your needs, but spotting scopes are more than capable of giving some pretty amazing results.

Peter
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Old Tuesday 26th March 2019, 16:02   #18
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I was thinking about the best scope for viewing at 2 miles, and thought a 10 inch refractor would be good.

Peak 2 Valley in the U.S.A. offer 10 inch f/12s in achromat and Apo versions.
11 feet long.
268 pounds weight (122 kg).
Price from $41,000 for achromat.
Price from $99,000 for Apochromat..

I actually think that my friend in the U.K. would make a superb one for less.

Then there is the mount.

So, sell the Bentley or Rolls and get a 10 inch refractor.

There may well be old observatory refractors that would cost a lot less.

Horace Dall refigured a 10 inch Merz refractor objective.
He said that it wasn't very good, but I'm sure it was much better when he returned it.

Jim Hysom made the 12 inch new objective for the Northumberland refractor, but I don't know how much he charged.

The Harvard public observatory refractor in Boston is a 9.5 inch f/12, but it only had a low power eyepiece when I viewed Jupiter. So I don't know how good it is.

B.
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Old Tuesday 26th March 2019, 16:51   #19
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APM offer to make refractors upto 12” if your wallet and proposed mount can cope with it. Seeing effects will limit the performance, unless you could add adaptive optics (as the professional telescopes do, but I don’t see this as practical in the daytime.... maybe “lucky imaging” could help get the best results.

Peter
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Old Tuesday 26th March 2019, 19:37   #20
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Yes, Peter, there are problems with daytime viewing through a horizontal air mass.

For a large scope in the daytime, it is probably the location and weather that determines how well one can see at distances of miles.

For most, large refractors are out because of cost.

I have had brilliant views with the 6 inch Maksutov at 5 miles across the sea.

Horace Dall got fine photos at 17 miles, and Wall tested his 30 inch refractor optics at 10 miles from his upstairs windows.

The rather competitive prices for the Skywatcher 120ED and 150ED refractors are attractive.
I am not sure that the Esprit triplets would do better terrestrially as they may have more thermal problems, but it would be nice to try them.

B.
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Old Sunday 14th April 2019, 18:37   #21
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Binastro, I enjoyed reading your post as an Englishman pointing to the U.S. for large refractors. Meanwhile our local observatory went to the England to get one!

http://www.custerobservatory.org/equip.html
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Old Sunday 14th April 2019, 22:11   #22
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HI Dd61999,
That is a very nice collection of instruments at your observatory.

What are the last three.
The Ross 7x21. Maybe 21 inch or 530mm f/7 lens?
I don't recognise this. I had several 6 element Ross Xpres WA EMI (Extra Marginal Illumination) 20 inch f/6.3 lenses. They covered 7x5 inch very well and at a push 10x8. They were soft coated internally c. 1955. I sent one to Australia. I don't know if it is still in use.
I had a Ross 24 inch f/5.6? telephoto, but this wouldn't cover 10x8. It went to a photographer doing theatre work using a Pentacon 6.

What are the last two SCTs?
Is 8 inch the aperture or the focal length?

The largest refractor I have is a shortish 135mm aperture, but it isn't good having zonal problems and bad ghosting.

B.

Last edited by Binastro : Sunday 14th April 2019 at 22:15.
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Old Monday 15th April 2019, 01:01   #23
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HI Dd61999,
That is a very nice collection of instruments at your observatory.

What are the last three.
The Ross 7x21. Maybe 21 inch or 530mm f/7 lens?
I don't recognise this. I had several 6 element Ross Xpres WA EMI (Extra Marginal Illumination) 20 inch f/6.3 lenses. They covered 7x5 inch very well and at a push 10x8. They were soft coated internally c. 1955. I sent one to Australia. I don't know if it is still in use.
I had a Ross 24 inch f/5.6? telephoto, but this wouldn't cover 10x8. It went to a photographer doing theatre work using a Pentacon 6.

What are the last two SCTs?
Is 8 inch the aperture or the focal length?

The largest refractor I have is a shortish 135mm aperture, but it isn't good having zonal problems and bad ghosting.

B.
Good questions, I am just a casual visitor at the observatory. I knew the large refractor was from the U.K. So when I saw your comments, I went to the webpage to get more info and realized there are even more telescopes I havenít looked through.

I had no idea they had a 10Ē binoculars telescope, which I would love to look through. Iíll have to go back soon and be more attentive to their other equipment on hand. Although from memory I believe the SCT were 8 inch in aperture. They had some big SCT's but not sure if they belong to the observatory or if the telescopes belonged to the locals
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Old Monday 15th April 2019, 17:39   #24
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Hi,

not sure if the original poster still reads this or still has the scope in question, but a 664 definitely should be sharp up to 60x with the zoom (unless you got the old 80s style zoom with the rubber eyecup - that one is awful), let alone at 30x.

If you still have the scope please do a star test and take an image of what you see - one can see all kinds of optical problems from that and can then ask Kowa to fix it.

Joachim
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