Posts Made By: Ed Blankenship

Well, that is wonderful !!!

AND ID is relatively close to where I live near Portland, OR !!!!!

I'll have to go and check it out this summer !!!

Thanks for posting Rod !!!

Hi Rod & All,

First let me say thanks for the good reference article on filters. I agree that this article is a good one to sort out the sometimes confusing "Marketing Spin" that manufacturers barrage us with to try and sway us to their products instead of their competitors. All filters are a compromise because the can only "throw away light" to possibly improve the contrast of the image.

Second, let me thank Rod for a very nice and well balanced review of the Broadband filters he tried in his situation. Good job !!! I especially liked the comments about the "Moon glow" and agree with Rod that any moon in the sky is bad for DSOs when viewing unfiltered, not just first quarter or more gibous. I also appreciate Rod's comments about trying the interaction of eyepiece focal length, exit pupil, etc. with the different filters he tried. The interaction is important to explore.

Third, after trying a number of filters from my back yard (which is on the edge of the Portland, Oregon "sky glow") I have concluded the following: (1) Broadband (LPR type) Filters in a 10 inch SCT give very nice results that work almost as well as the 100 mile drive to really dark skies with my 8 inch SCT. I've been pleased in the contrast improvement of M1, M42, M43, M51, M57, M81, M101, etc. (2) Narrow band filters (for me) boil down to a UHC does everything an O-III AND a H-Beta does for me, so after careful comparison with all three (LUMICON Brand filters)I sold two of the filters here and kept the UHC for use in my 8 inch SCT. (3) If I had the 10 inch SCT available to me again (or larger reflector even more so), I'd spend more time viewing from my backyard with filters, but with 8 inch SCT AND smaller scopes, I'm better off driving to dark skies than trying to make the filters work at (or closer to) home. (5) Both Narrowband & Broadband filters are very helpful to me when doing outreach to people who are newer to astronomy (example is an O-III or UHC can really make M57 "pop").

Best Regards,

Ed Blankenship

Hi Bill,

First, Happy New Year (well, another 100 minutes or so for me) !!!

Second, I'm going to try and get Tom Dey or one of the refractor gurus to reply to your question, but first, I'll take a stab at a quick answer for you.

The "Fluorite ca filter" probably doesn't exist. The reason is that the ca you are asking about (in inexpensive doublet refractors) is introduced by the choice to use only two lenses: Usually Crown Glass and Flint Glass which have differing "dispersion" properties that aren't exactly complementary. The goal is to "inexpensively" make Red & Blue light focus at the same focal plane and have Green light focus at a very similar plane. The problem is that other colors (farther away from Green than Red or Blue = mainly Violet) don't focus close enough to be well corrected. There are a number of filters that you can explore to deal with the violet, but I digress . . .

The fluorite lense you refer to is an alternative glass that has "ED = Extra-low Dispersion", so that it gives less of this false color, but at a "price", since the Fluorite Glass is more rare and more expensive that what it replaces in the "two lense system" that is chosen because of the low cost. ED glass doublets work very well, but sometimes it is actually less expensive to a a third lense aka Triplet scopes.

The better way to go is to use one (or two or more) additional lense(s) to correct more things (like ca and flatness of field and spherical aberation, etc.) and bring a better color balance to the focal plane. The four lense Petval system uses four lenses so that more of the ca is taken care of compared to the two lense system, but is more expensive (You get what you pay for).

Your quote:

"The chromacor was a sub aperture corrector to address chromatic aberration common in refractors.
It was very effective for visual use at eliminating the unfocused purple.
It has been out of production for years."

as you say.

The cleverness of the chromacor (from the Ukraine, I believe) was that it corrected for (some or most) of the ca, if you carefully matched which chromcor you choose to go with "your" doublet, you could additionally address some or all of the SA = spherical aberation as well. The additional cleverness was that one could use the chromacor on a big (6 or even 8 inch), inexpensive doublet without any modification (by just inserting it in the 2 inch focusser at the "small end" of the refractor). Really a nice solution !!! Too bad they are getting hard to find !!!

Ed

P.S. Hey Tom, care to elaborate ??? Anybody else want to jump in ???

Hi Michael, Tom & All,

I'm going to guess that you are trying to use this camera in a relatively fast refractor, right ?

Michael Broder said:

I have an STL-11000 camera with a defective CCD Chip. All the corners are light. I got the camera like that. I found a replacement 11002 chip that I would like to install myself. Has anyone out there pulled one of these cameras apart. Aside from getting dust on the Chip is there anything else I should be concerned with?

Thanks,
Michael

Could it possibly be out-of-focus light in the corners due to a curved focal plane ??? I'd expect if it were vignetting, you would have dark corners, right imaging guys ???

Ed

Bill Barrett said:

. . . eliminating the unfocused purple . . . fluorite filter or an alternative to the standard minus violet filter. Thank you, Bill

Hi again Bill,

Here's a good reference or jumping off point for "an alternative to the standard minus violet filter" that can be found in the "Members" section tab. I don't exactly agree on all the points and conclusions, but most of what is said is a very good write-up:

https://www.astromart.com/articles/article.asp?article_id=922

Cheers,

Ed

Nice image that I haven't seen before !!! Thanks for posting Rod

Hello Carter, Tom & All,

Carter, you ask a good question: A Deep, Thoughtful question. Tom's answer was good. Here, I'll try to also give you a good, thoughtful answer from my experience as well.

I am an Electro-Magnetic Compatability (EMC) Engineer who works in a Test Laboratory where measurements are made to determine if a computer accessory makes too much interference to be sold. My lab measures frequencies between 30 MHz and 2500 MHz in a room that is sealed off (think Faraday cage) from the outside world where Television and Radio signals from legitimate broadcasting stations would interfere with the sensitive measurements of the computer accessory we are tasked to measure. Additionally, we want only signals to get from the product under test to the measurement antenna either directly or via a reflection off of the reflective floor, but not from a reflection off the ceiling or the four walls of the Faraday cage so the walls and ceiling are treated with expensive RF absorbent material. What we have is effectively a Lloyd's Mirror Interferometer (but usually called a "Semi-Anechoic Room" or "Absorber-Lined Chamber") and this Interferometer is large enough to walk around in because the separation from product to antenna is 10 meters !!! Additionally, we have two antennas that are separated from each other by 36 Degrees, so the interior of the chamber is wider than eight meters and taller than 6 meters.

Now, when I measure the interference (which is measured in decibells relative to a Micro-Volt-per-meter), I have to search to receive antenna from 1 to 4 meters in height above the metal, conductive floor (a mirror) to find where the direct and reflected waves add (constructively) and not cancel (destructively). The signals that are low frequency (ie. low energy photons) are spread out and cover all of that 1-4 meters. The higher frequency signals look like they are more "localized" because they have more distinct peaks and nulls, as I raise and lower the mast which holds and positions the receive antenna from 1 to 4 meters.

What I would point out to you is that the spatial orientation of the E-M wave is frequency dependent (ie. Wavelength dependent), which implies that the photons involved have a certain "color" or energy content (in my case Micro-electron Volt). If I were working with light frequencies (Tera Hertz) like optical scientists and engineers work with, the wavelengths would be Nano-Meters or Angstroms and the energies would be higher Electron-Volt levels, but the concept of wavelength and frequency implying energy of the photons is really important.

I also struggle to wrap my brain around the concept of the photon and its "path" from source to destination. I agree with Tom: Richard Feynman was a very smart guy who essentially said that "Photons like to be every-where and every-when" in space-time. I have a four year degree in Physics and about 40 years in High-Tech Engineering. I don't completely understand the answer to your question either. I do know that the energy that a particular photon carries is part of the answer you seek: Low energy photons spread out much more than higher energy photons. I can see this in my measurements, trust me.

Best regards,

Ed

Hi All,

This thread was very interesting to me, so thanks to all who contributed. I don't disagree with the conclusions about a C5 on a fork or a C6 on the larger end. I wonder if a de-forked Meade ETX-125 might fit the bill and put the extra money toward a better mount ? I've been told that the money spent on a better mount up front pays dividends later.

Cheers,

Ed

Originally Posted by Andy Sedlacek

There's a guy, or was, that used to attend TMSP with a huge D&G 8-inch f/12 refractor on one of those exact mounts...But he had painted it yellow and green, as it was the theme for his John Deere telescope!

I also saw this guy's Green & Yellow "monster" and it was very impressive to a newbe !!!!

Nice mount for a 6 inch f8 "yard cannon" since it makes the OTA look small !!!

Ed

Originally Posted by john raymond

Yes

WOW, John, that is really an awesome setup !!!