I just finished solving an issue I was having with my Brunton Eterna ED 20-60x80 spotting scope --
Basically, I became dissatisfied with the dim view when zooming over 50x up to 60x. I don't use my scope for birding, but the solution I found would definitely benefit anyone birding from their home out to a great distance.
The Problem: brightness of view in scopes, and binoculars, is determined mostly by the exit pupil size. It is generally thought that exit pupil below 2, even in bright daylight, begins to degrade both resolution and color saturation. The brand of spotting scope doesn't change this... from Swarovski to Barka, ED glass or normal glass. Tiny exit pupils kill the quality of image.
Spotting scopes of 80mm objective lens fall below 2.0 exit pupil at 41x, assuming in best case it really is a full 80mm aperture.
Now, I use my ED spotting scope for viewing out to sea, and up the coastline, anywhere from 0.8 miles up to 30 miles, so I am always at 50-60x magnification. At those magnifications, the image, to me, even in bright daylight, is just too dim, washed out color, and slightly unsharp. This isn't because my scope is mid-level ED glass, but because of the tiny exit pupil at those magnifications/
Solution: so I could either go for an alpha glass spotting scope, which would improve the view somewhat, but it would be like chasing diminishing returns down the small exit pupil hole.
Instead, I realized I don't need light weight, water proofing, or extreme ruggedness for viewing long distance from my deck. So the inherently poor optics from high magnification through an 80mm aperture scope and tiny exit pupil are not necessary for me. I assume a lot of birders would like to view from their deck, or even long distance in the field set up in the same spot for hours.
After a lot of research on astronomy forums, I decided to get a 5" (127mm) Maksutov telescope. It weights 7 lbs, and is actually shorter than my Brunton scope at 12". By its design it is more rugged than any other telescope design, so it would rarely need to be collimated like most telescopes need. Some posters at a couple of astronomy forums say they have never had to collimate their Maksutov even after travelling and bumping it around. It arrived Monday. I have it mounted, as I did with the Brunton, on a Manfrotto tripod with a Manfrotto video head.
I have compared the views in low light, and bright light, through my new MAK and my existing Brunton. There is no comparison, even with the current entry level correct image 45* prism (which I will upgrade for $80) and my mid tier eyepieces. My premium eyepiece arrives Friday. At 50x up to 60x, the colors in the Brunton are very washed out, and with the MAK they are bright and pop. The resolution is superior with the MAK as well.
Here are the advantages with this particular scope:
- The optics are superior due to a large exit pupil. I have a 32mm eyepiece installed which gives me 52x magnification with 2.5 exit pupil. I also have an Explore Scientific 26mm eyepiece coming Friday, which gives me a 2.0 exit pupil and 64x magnification.
- The cost is far less than half that of mid-level ED scopes, and 10% the cost of an alpha class 80mm spotting scope.
The 127mm Maksutov OTA, whether that be Orion or Celestron, is about $385, and the upgraded eyepieces were $35 for the 32mm and $110 for the 26mm. Even the $15 included 25mm plossl provided superior images.
Disadvantage: I lose lightweight (8 lb. vs. 4.5lb.), waterproofing, and greater ruggedness. Those I didn't mind. The real loss is zooming, and usable views below 40x magnification. Telescope Zooms don't work because their magnification range yields exit pupil sizes mostly below 2 and down to under 1. So I can no longer zoom. But again, I don't view under 0.8 miles, so that doesn't bother me nearly as much as the poor high magnification image quality in the spotting scope.
So, for all you birders who don't need a lot of portability with your scope, you should consider a Maksutov telescope instead of, or to complement, a spotting scope. It gives superior optics vs. ANY 80mm spotting scope, and costs under $600.
Just thought you guys would want to know about this alternative, since I really didn't see much written about it while I was researching.
Basically, I became dissatisfied with the dim view when zooming over 50x up to 60x. I don't use my scope for birding, but the solution I found would definitely benefit anyone birding from their home out to a great distance.
The Problem: brightness of view in scopes, and binoculars, is determined mostly by the exit pupil size. It is generally thought that exit pupil below 2, even in bright daylight, begins to degrade both resolution and color saturation. The brand of spotting scope doesn't change this... from Swarovski to Barka, ED glass or normal glass. Tiny exit pupils kill the quality of image.
Spotting scopes of 80mm objective lens fall below 2.0 exit pupil at 41x, assuming in best case it really is a full 80mm aperture.
Now, I use my ED spotting scope for viewing out to sea, and up the coastline, anywhere from 0.8 miles up to 30 miles, so I am always at 50-60x magnification. At those magnifications, the image, to me, even in bright daylight, is just too dim, washed out color, and slightly unsharp. This isn't because my scope is mid-level ED glass, but because of the tiny exit pupil at those magnifications/
Solution: so I could either go for an alpha glass spotting scope, which would improve the view somewhat, but it would be like chasing diminishing returns down the small exit pupil hole.
Instead, I realized I don't need light weight, water proofing, or extreme ruggedness for viewing long distance from my deck. So the inherently poor optics from high magnification through an 80mm aperture scope and tiny exit pupil are not necessary for me. I assume a lot of birders would like to view from their deck, or even long distance in the field set up in the same spot for hours.
After a lot of research on astronomy forums, I decided to get a 5" (127mm) Maksutov telescope. It weights 7 lbs, and is actually shorter than my Brunton scope at 12". By its design it is more rugged than any other telescope design, so it would rarely need to be collimated like most telescopes need. Some posters at a couple of astronomy forums say they have never had to collimate their Maksutov even after travelling and bumping it around. It arrived Monday. I have it mounted, as I did with the Brunton, on a Manfrotto tripod with a Manfrotto video head.
I have compared the views in low light, and bright light, through my new MAK and my existing Brunton. There is no comparison, even with the current entry level correct image 45* prism (which I will upgrade for $80) and my mid tier eyepieces. My premium eyepiece arrives Friday. At 50x up to 60x, the colors in the Brunton are very washed out, and with the MAK they are bright and pop. The resolution is superior with the MAK as well.
Here are the advantages with this particular scope:
- The optics are superior due to a large exit pupil. I have a 32mm eyepiece installed which gives me 52x magnification with 2.5 exit pupil. I also have an Explore Scientific 26mm eyepiece coming Friday, which gives me a 2.0 exit pupil and 64x magnification.
- The cost is far less than half that of mid-level ED scopes, and 10% the cost of an alpha class 80mm spotting scope.
The 127mm Maksutov OTA, whether that be Orion or Celestron, is about $385, and the upgraded eyepieces were $35 for the 32mm and $110 for the 26mm. Even the $15 included 25mm plossl provided superior images.
Disadvantage: I lose lightweight (8 lb. vs. 4.5lb.), waterproofing, and greater ruggedness. Those I didn't mind. The real loss is zooming, and usable views below 40x magnification. Telescope Zooms don't work because their magnification range yields exit pupil sizes mostly below 2 and down to under 1. So I can no longer zoom. But again, I don't view under 0.8 miles, so that doesn't bother me nearly as much as the poor high magnification image quality in the spotting scope.
So, for all you birders who don't need a lot of portability with your scope, you should consider a Maksutov telescope instead of, or to complement, a spotting scope. It gives superior optics vs. ANY 80mm spotting scope, and costs under $600.
Just thought you guys would want to know about this alternative, since I really didn't see much written about it while I was researching.
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