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Equipment Discussions >> Eyepieces

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Sarkikos
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Reged: 12/18/07

Loc: Nyctophobia, Maryland, USA
Re: Another RKE 28mm Question new [Re: Starman1]
      #5720539 - 03/08/13 01:25 PM

Don,

Quote:

3) Light transmission and concentration of that light (see the spot diagrams for the design) are what is going to improve the brightness and contrast on DSOs, along with good polish on the lenses, strict adherence to the design parameters, and the long laundry list of other factors that improve what we call "contrast".




Perhaps counterintuitively, reducing light transmission can also increase "contrast." Isn't this why some planet observers use ND filters for bright planets and the Moon, besides reducing the perceived brighntness? I don't use ND filters for planets, but the theory is at least that reducing the overall brightness will enhance the perceived contrast. The same sort of function may be taking place in simpler coatings for observers of DSO. Some observers have said that eyepieces with simpler coatings - such as Brandons, RKE and Sirius Plossls - bring out structure in bright nebulae and bright galaxies, making them appear more "contrasty."

Mike


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Sarkikos
Postmaster
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Reged: 12/18/07

Loc: Nyctophobia, Maryland, USA
Re: Another RKE 28mm Question new [Re: Starman1]
      #5720568 - 03/08/13 01:37 PM

Don,

Quote:

4) Seeing colors in stars is a matter of improving transmission through the eyepiece. Flattening the curve of the spectrum of transmission may or may not improve the visibility of colors in stars. Accenting the colors at the spectral position of peak sensitivity of the color-seeing cones in the eye might, though. Ironically, a non-flat spectrum might enhance colors more than a flat spectrum.




I have noticed that sometimes the color in stars seems more saturated if I defocus the star image a little. I've done this often for newbies so they can see the colors easier. Maybe something similar is happening for eyepieces with simpler coatings to make the stars seem more colorful. Of course, I don't mean that the stars are not as sharp, but that they are in some way more colorful. I know that many Brandon and RKE enthusiasts have said that stars seem more colorful and striking when viewed through these eyepieces.

Mike


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Starman1
Vendor (EyepiecesEtc.com)
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Reged: 06/24/03

Loc: Los Angeles
Re: Another RKE 28mm Question new [Re: Sarkikos]
      #5720819 - 03/08/13 04:39 PM

Activating the cones in the eye requires intensity of image. Larger apertures will bring out colors as will superior light transmission in a scope, higher Strehl ratio, more transparent atmosphere, superior polish on the lenses in the eyepiece, stronger contrast with the background, and so forth.

If people comment about that with Brandons or RKEs, it is likely because the eyepiece lenses may have superior polish, or higher transmissions, or cleaner eyepieces or simply what I like to refer to as the "it's new" phenomenon.

When I was in the bicycle business, and learned about frame design (and actually designed some), I learned about what makes a particular bicycle handle one way or the other and how to design in the handling characteristics I preferred. I noticed that people test-riding bikes didn't always prefer the design with the best handling, and I investigated why. In talking with a lot of sales people, I discovered that people invariably attributed better handling characteristics to whatever was newer, i.e. that the newest tires put on their bikes handled better, that the newer frame had superior handling, that the newer crankset performed better. And the reason was because it was different than what they had before. Difference was equated with Better.

I think the same thing occurs with eyepieces. People read a lot of praise for a specific brand or model, they buy one of them, and they discover for themselves that "the reviews were right". It's a case of "it's new, and different than what I had before, so it's obviously better", whether that's true or not. Six months later, the honeymoon is over, the product is just what it is and it may not be better, so it goes on sale or gets replaced with something different and, different is better.

Now obviously this isn't always true. Some people actually evaluate the eyepiece without any judgment-clouding preconceptions. But I'm not sure it is the majority of comments or reviews. In my experience, small number of lens eyepieces don't correct very well at the edge of the field, so typically, only the center is very sharp. Is that the characteristic of a planetary eyepiece? Or is having a larger number of lenses and a well-corrected, anastigmatic, outer field more desirable? Obviously light loss isn't an issue with planets, so one would think superior correction over the field would matter more than lens count.

When I added a Paracorr, it obviously added additional lenses and lost a little light. Yet, in Paracorr/no Paracorr tests, it was obvious I was seeing fainter stars with the Paracorr. Tightness of focus and concentration of the light into smaller spots was obviously the reason, yet what I saw was counter-intuitive. My very best view of Jupiter, ever, was through a stack containing 18 lenses (PowerMate, Paracorr, 8mm Ethos). And better, that great image held across at least 90% of the field as I watched the planet drift. With more color than I'd ever seen (bluish tones on the limb darkening, gray-green projections, ocher-colored EQ bands, salmon colored GRS, gray-green polar shading, beige, yellow, ivory, and cream colors in the bright bands, and pure white in some storms). Was it the stack of lenses, or simply magnificent seeing conditions? I credit the latter. And, perhaps, really well-polished optics.

It also points out that some eyepieces with poor correction everywhere except in the center aren't really good eyepieces overall, and that doesn't seem to relate to lens count in the eyepieces, except maybe inversely (witness the number of people praising the Delos as a "planetary" eyepiece).

By the way, your technique of slightly defocusing a star to see color more easily is often used by photographers, where in a tightly focused, long-duration shot is stacked with a much shorter one that is slightly defocused. This makes the colored stars appear more strongly colored.
Here is an example: Orion


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Sarkikos
Postmaster
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Reged: 12/18/07

Loc: Nyctophobia, Maryland, USA
Re: Another RKE 28mm Question new [Re: Starman1]
      #5720937 - 03/08/13 06:03 PM

Don,

Quote:

I think the same thing occurs with eyepieces. People read a lot of praise for a specific brand or model, they buy one of them, and they discover for themselves that "the reviews were right". It's a case of "it's new, and different than what I had before, so it's obviously better", whether that's true or not. Six months later, the honeymoon is over, the product is just what it is and it may not be better, so it goes on sale or gets replaced with something different and, different is better.

Now obviously this isn't always true. Some people actually evaluate the eyepiece without any judgment-clouding preconceptions. But I'm not sure it is the majority of comments or reviews.




Good reviews might influence me to try or even buy an eyepiece, but they won't make me keep one. I'm no fanboy. I don't have brand loyalty or product nostalgia, and I try not to succumb to argument from authority. If an eyepiece doesn't perform well for me in my telescopes, out it goes ... eventually. I do like to give it a fighting chance.

Mike


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Brett Carlson
sage


Reged: 12/12/11

Loc: Rochester, NY
Re: Another RKE 28mm Question new [Re: Sarkikos]
      #5721247 - 03/08/13 09:21 PM

Interesting thread....I have two RKE's that I bought with a pair of scopes I bought together. One is a 28mm and a 21.5mm. I'm thinking that one or the other came with the Astroscan. Does anyone know what eyepieces came with the Astroscan?

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GOLGO13
Carpal Tunnel


Reged: 11/05/05

Loc: St. Louis area
Re: Another RKE 28mm Question new [Re: bcuddihee]
      #5721320 - 03/08/13 10:24 PM

I liked the 28mm RKE so much I bought two more of them when I saw a good deal on them. I guess I wanted a backup and one I can through in a telescope case for travel.

All three of mine seem to be just fine.


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bremms
Carpal Tunnel
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Reged: 08/31/12

Loc: SC
Re: Another RKE 28mm Question new [Re: GOLGO13]
      #5721762 - 03/09/13 08:23 AM

Seen Astroscans with both 28 and 21.5. The 21.5 makes more since at F4 a 28mm is a full 7mm exit pupil. That is a bit too large for most people. A 21.5 gives about 5.5mm EP.

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BillB9430
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Reged: 12/02/06

Loc: Illinois
Re: Another RKE 28mm Question new [Re: Brett Carlson]
      #5721860 - 03/09/13 09:24 AM

The Astroscan currently comes with 28 mm and 15 mm FL eyepieces. I think they are Plossls, not RKEs, though, since they claim a 50 degree Afov. The current primary mirror is 105/445 mm. Older models came with RKEs.

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