Chromatism correction

[alcofribas]

Hello

Is there a way to reduce the chromatism of a fast achro, say 150mm F/6, with a simple system, 2-3 standard lenses, located around the focus ? The goal is not to be as performant as more complicated (and costly!) systems such as the Chromacorr, but to reduce the chromatism by 20-30%.

[Watcher3]

ISTAR was at one time working on their version of a chromacore. I forget the name they were going to use. I believe it was supposed to be between 2 and 3 hundred dollars, and better than a chromacore, (somehow adjustable instead of different models being chosen depending on individual lens correction). I don't know what became of it.

I know Ales is very busy right now, but if I, or someone else has to contact him for other business, that may be worth asking about.

[gord]

I believe it was going to be called the RAYCORR. And it may still be a possibility at least based on what Ales had said.

The issue they ran into was some incorrect information on glass specifications from a supplier, which affected the design that they had come up with. Without the proper glass, the design wouldn't work. So I think they were looking for other options and/or an updated design. At least that's what I recall.

I would love to have something like that to be able to get more out of a standard achro. Big difference in price between even the amazing prices that IStar has for the apo's and an achro+corrector.

Clear skies,

-Gord

[Watcher3]

Now that you wright it down, I remember it like I just read about it yesterday. I guess my memory is starting to go. Memories aren't as solid as they used to be. Thanks for putting some factual information in place of my vague recollections,Gord!

[intesmicro]

Hello, I also chromatism on my Istar 150/1500. It's not too annoying in my opinion. I plan to take one or more filters, especially the brand Baader.
See here for a discussion on a German website:
www.astro-foren.de/showthread.php?t=5719&page=2
The Baader Contrast Booster seems the best, but it gives a yellow cast to the image. I'll be testing this filter soon.
Jef

[astrosean]

With an achromat, you will always be stuck with CA of some kind. Correctors like Chromacorrs or "tri-space" designs are limited to longer focal length scopes, Chromacor was designed for f/8 scopes. Vixen advertised their petzval scopes as having 50% more color correction than an achromat however they are limited to powers of 150x or so before the get mushy(or so I've heard). If no color is what you want, then either long focus or APO is the way to go...

[intesmicro]

Hello, I am making images of the Sun, Moon and Jupiter. The chromastisme is visible, but I find it too embarrassing.
The images are here: astrosurf.com/jiaifer/page150essaisimagerie.htm
Sincerely, JF

[borispider]

Nice pics intesmicro. You see the YouTube movie I posted here:istarscopeclub.proboards.com/index.cgi?board=achros&action=display&thread=8

[gord]

Jef, excellent images! I especially like the solar ones. How much of the detail shown in those images that are processed, do you see in the eyepiece? And that was with a Herschel wedge, correct?

On you Jupiter image, the larger one, that is the same view I have in terms of false color seen. It is noticeable, but I find that after observing for a while I no longer really pay attention to it.

Clear skies,
-Gord

[intesmicro]

Hello and thank you Gord and Borispider.
In visual, the Sun is very good, granulation is visible. Note that I had no filter for this experiment. Yes, I use a Herschel prism.
Other solar images, made with other instruments are here:
astrosurf.com/jiaifer/pagederniereimageloupebis.htm
The film on the Moon is excellent Gord!
Regards, Jef

[borispider]

Wow. Very Nice solar pics, intesmicro.

[intesmicro]

Good evening, I did some testing with 150/1500 with filters to reduce the chromatic aberration.
astrosurf.com/jiaifer/materiel/essaisfiltres
Here is a slideshow to get an idea of the result.
Sincerely,
Jef
Happy New Year to you!

[jimcurry]

Dec 16, 2010 16:23:53 GMT -5 astrosean said:

Vixen advertised their petzval scopes as having 50% more color correction than an achromat however they are limited to powers of 150x or so before the get mushy(or so I've heard). ..

Sean:
I have the Vixen 140 NA petzval. If the seeing permits my scope is good to 40x/dia. I had it out one night on Jupiter and it took around 250 before the image started breaking down. Mushy at 150x isn't accurate. I routinely take it to 160x while galaxy hunting.

Jim

[glenm]

Dec 13, 2010 10:11:27 GMT -5 alcofribas said:

Hello

Is there a way to reduce the chromatism of a fast achro, say 150mm F/6, with a simple system, 2-3 standard lenses, located around the focus ? The goal is not to be as performant as more complicated (and costly!) systems such as the Chromacorr, but to reduce the chromatism by 20-30%.

Jim,

I do believe Ales has finished a visual corrector for CA. I think Ales will update the information on this product soon.

Regards.
Glen.

[mikey cee]

Dec 14, 2010 12:17:07 GMT -5 intesmicro said:

Hello, I also chromatism on my Istar 150/1500. It's not too annoying in my opinion. I plan to take one or more filters, especially the brand Baader.
See here for a discussion on a German website:
www.astro-foren.de/showthread.php?t=5719&page=2
The Baader Contrast Booster seems the best, but it gives a yellow cast to the image. I'll be testing this filter soon.
Jef

I have both the Contrast Booster and the Semi-Apo in my filter wheel. Clear view is between them. The CB isn't worth the powder to blow it to hell. It's just about the same as a #8 filter. I hate yellow anythings. The SA filter is just the ticket. It cuts out most of the CA....not all but most! Guess what? That's right folks, a nice neutral color. It does dim down the image but everything is a tradeoff. My 8" f/13.3 gives a brite enough image that it's just about right. 8-)Mike