What reduces chromatic aberration?

[25585]

Have a Paracorr for my dob's to make viewing better, but what is best to reduce chromatic aberration in my F5 TV Genesis?

[Galen Gilmore]

I have heard that a green filter will reduce CA, not sure if that is true or not.

[Guest Tuomo]

http://www.baader-planetarium.com/en/baader-fringe-killer-filter.html

[cloudsweeper]

Stop down the aperture and it's gone - OK for bright objects.

Doug.

[John]

Baader Semi-Apo filter might help. Or the Fringe Killer as linked to by Tuomo above.

Stopping the scope down will work because it makes the optics slower, albeit smaller in aperture.

A #8 light yellow filter is supposed to reduce CA as well.

[Moonshane]

I don't like changing the colour of something to remove colour. Seems nonsensical to me.

I'd simply accept the limitations of the scope on 'inappropriate' objects and enjoy it's strengths on 'appropriate objects.

[Alien 13]

The minute you put any glass (even a TV) in the imaging train you will get CA, apart from a camera of course...

Alan

[John]

11 minutes ago, Moonshane said:

I don't like changing the colour of something to remove colour. Seems nonsensical to me.

I'd simply accept the limitations of the scope on 'inappropriate' objects and enjoy it's strengths on 'appropriate objects.

Having tried filters I tend to agree Shane. The chromacor was the only device that I found really promising but they won't work well with the Genesis, assuming that you could ever find one that is.

 

[Ben the Ignorant]

2 hours ago, Galen Gilmore said:

I have heard that a green filter will reduce CA, not sure if that is true or not.

That is true (I tried), but it dims and colors everything. All color filters reduce chromatic blur (I tried), by the way, at the expense of natural color balance. They also sharpen everything (I tried) because there are no longer several colors spread over an approximate focus.

[Ben the Ignorant]

1 hour ago, cloudsweeper said:

Stop down the aperture and it's gone - OK for bright objects.

Doug.

Yes. Just 5mm less can reduce the problem drastically with some semi-apo scopes, but I'm not sure of the effect on that first generation f/5 Genesis. Try 7 or 8mm if 10mm are too much for a particular scope. Most of the CA comes from the outer edge of lenses.

[Ben the Ignorant]

On ‎05‎/‎10‎/‎2017 at 21:10, John said:

A #8 light yellow filter is supposed to reduce CA as well.

It does, and doesn't alter the overall color nearly as badly as a green filter does. I compared six colors, the only that you could forget inside the focuser after a while is the light yellow #8 filter, the eye gets used to the moderate change pretty easily.

[Ben the Ignorant]

1 hour ago, Moonshane said:

I'd simply accept the limitations of the scope on 'inappropriate' objects and enjoy it's strengths on 'appropriate objects.

Looks like the right attitude when putting the eye at an achromat or an old semi-apo.

[25585]

I will try a yellow filter. Have some from photography to see the effect before buying. 

 

[Louis D]

Here's a photo comparison someone did of the various fringe killer filters in an achromat.  I can't find the original post.  The Baader contrast booster filter actually looks the best to my eyes.

[25585]

1 hour ago, Louis D said:

Here's a photo comparison someone did of the various fringe killer filters in an achromat.  I can't find the original post.  The Baader contrast booster filter actually looks the best to my eyes.

Ooh. And a 2 inch as well! Could be more glass to buy!

[Stu]

When I had my Genesis, I did not like the CA so just enjoyed what it did best, which is very flat, widefield views of the Milky Way, large open clusters and large Nebulae like the Veil and NAN. With a 31mm Nagler there is not much to touch it, somewhere around a 5 degree field, sharp to the edge because of the petzval element which means there is little or no field curvature.

[Paz]

Where im looking at anything bright enough to make ca a problem the first thing i try is stopping down the aperture, and then filters if need be but Im not a big filter user.