Jump to content


Photo

Kson 2" O-III Filter Review

  • Please log in to reply
5 replies to this topic

#1 Olivier Biot

Olivier Biot

    Amused

  • *****
  • Posts: 24946
  • Joined: 25 Apr 2005
  • Loc: 51°N (Belgium)

Posted 25 November 2011 - 04:10 PM

Kson 2" O-III Filter Review

By Bobby Irvin.

#2 David Knisely

David Knisely

    Hubble

  • *****
  • Posts: 15540
  • Joined: 19 Apr 2004
  • Loc: southeastern Nebraska

Posted 26 November 2011 - 02:37 AM

The reviewer wrote:

All observations were done using the 10 inch Newtonian. My understanding is that you need at least 6inches of aperture to provide enough light gathering power to use an O-III filter. I haven’t tried it in my 4 inch Refractor for that reason.


This is a myth. What you need for the OIII is a larger exit pupil (7 mm to 3 mm, or 3.6x per inch of aperture to 8.5x per inch of aperture) and not necessarily a lot of aperture. Using a little too high a power with these filters can dilute the nebulosity to the point where the benefit of the filters is more difficult to see. I have used the Lumicon OIII in apertures from 50mm on up. I have stuck my 2" OIII filter in the front of my 9x50 finderscope to see both sides of the Veil at the same time. One of my favorite views of the North America Nebula is in my 100mm f/6 refractor at 15x and 25x using the OIII filter. With larger aperture, more objects will come into range that a good OIII filter will be able to help with, but that does not mean that it cannot be used successfully in telescopes smaller than six to eight inches.

My first use of the filter was on M57, the Ring Nebula in Lyra. This was done at a dark site South of Barstow in California. M57 was bright and easily viewed at a variety of magnifications without any filter. The addition of the O III filter did not improve the view and appeared, in fact, to detract somewhat since it darkened the field. M57 is a planetary nebula so this may account for the poorer performance.


M57 does not necessarily require an OIII filter when viewed from a dark sky site, but it does help, especially when trying to catch fainter detail like the outer "lace doily" shell around the main ring. An OIII filter is a nebula filter and *is supposed to darken the field*, as what happens to the stars is not important. It is letting through the two Oxygen III nebular emission lines and blocking everything else to make the nebular features easier to see. In fact, the OIII filter is often the "filter of choice" for observing planetary nebulae. One trick the more experienced observers use to locate tiny planetary nebulae in rich star fields is to "blink" them by passing the OIII filter between the eye and the eyepiece. The stars all dim, but the planetary nebula remains undimmed, standing out like a sore thumb. Also, there are some planetary nebulae which are only easily seen well with an OIII filter, so one finds seasoned observers reaching for their OIII when hunting a new nebular object a lot of the time. Under skyglow, the OIII often becomes the filter of choice on many nebulae and not just planetaries. Clear skies to you.

#3 mwtse

mwtse

    Sputnik

  • -----
  • Posts: 29
  • Joined: 03 Jun 2011

Posted 26 November 2011 - 08:41 AM

I have Kson O-III, Kson UHC and a DGM NPB.

First of all, the plastic case come with the DGM is even poorer than the Kson brand. It is make of fragile clear plastic that cannot survive through the shipping. And all these three filters fit nicely with my TeleVue 2" eyepieces.

On the other hand, the performance of the two Kson are not very satisfying, that's the reason why I finally purchase the DGM. The transmission of the Kson UHC is lower than DGM, and the O-III is even poorer. I use them on a 8" f/6 with 57X, but the view is very dim when the UHC is used. The O-III is even dimmer. Moreover, the brighter stars look pure green through this two Kson filters. On the other hand, the DGM give brighter view and more nature colours.

The bottom line is that the Kson can bring out more details in nebula like M57. In my light polluted site, M57 is difficult to notice for a novice, but adding a Kson make it stand out. I got the Kson filters dead cheap (about half the price of Irvin, so it is not too bad.

#4 Jim Rosenstock

Jim Rosenstock

    Fly Me to the Moon

  • *****
  • Posts: 6590
  • Joined: 14 Jul 2005
  • Loc: MD, south of the DC Nebula

Posted 26 November 2011 - 11:06 AM

...all these three filters fit nicely with my TeleVue 2" eyepieces.

On the other hand, the performance of the two Kson are not very satisfying.... .The bottom line is that the Kson can bring out more details in nebula like M57. In my light polluted site, M57 is difficult to notice for a novice, but adding a Kson make it stand out. I got the Kson filters dead cheap (about half the price of Irvin, so it is not too bad.


But why put cheap, disappointing filters on your nice 2" TeleVue eyepieces? Why add a weak link? :question:

(Actually, to be further contrarian, IMO nebula filters do you a lot more good at a dark site....oh, they help a little under light-polluted skies, but I think it's best to save the faint stuff for the darkest skies anyway....)

You will keep--and use--a good nebula filter for the rest of your observing life. Go ahead and get a good one....the price per use will go down rapidly, I promise!

Cheers,

Jim

#5 mwtse

mwtse

    Sputnik

  • -----
  • Posts: 29
  • Joined: 03 Jun 2011

Posted 29 November 2011 - 06:03 AM

[

But why put cheap, disappointing filters on your nice 2" TeleVue eyepieces? Why add a weak link? :question:

(Actually, to be further contrarian, IMO nebula filters do you a lot more good at a dark site....oh, they help a little under light-polluted skies, but I think it's best to save the faint stuff for the darkest skies anyway....)

You will keep--and use--a good nebula filter for the rest of your observing life. Go ahead and get a good one....the price per use will go down rapidly, I promise!

Cheers,

Jim


So I have bought and was using a premium filter to replace the Ksons, now the weakest link should be my eye.

#6 bob irvin

bob irvin

    Mariner 2

  • -----
  • Posts: 265
  • Joined: 22 Mar 2011
  • Loc: Greater Los Angeles, CA

Posted 05 December 2011 - 03:20 PM

I got the Kson filters dead cheap (about half the price of Irvin, so it is not too bad.


wow..... now I"m bummed that I paid too much for a mediocre filter. :bawling:

bob






Cloudy Nights LLC
Cloudy Nights Sponsor: Astronomics