Best Filter for Chromatic Aberration - Baader 495 Longpass or Baader Fringe Killer

[TangoCharlie]

Greetings!

 

I just purchased an Explore Scientific AR152 Achromatic Refractor.  I wanted to ask which filter works best for Chromatic Aberration?  The Baader 495 Longpass or the Baader Fringe Killer?  Thanks so much.  I will be doing observing first but later in time I will get into imaging.

 

T C

[Bobby1970]

I have a semi-apo filter and use it in my ST80 and ST120. It doesn't completely get rid of CA but it does improve matters to a point where the CA doesn't bother me anyway. I picked it up second hand, not sure i would want to spend the cash on a new one.

[alacant]

Hi. Congratulations on your purchase. I have the ar152s. For imaging, a wratten #8 stacked with a uv/ir cut works great with a modified dslr. I'm sure the #8 would work well for visual too and save you the extra which is charged for what are after all just yellow filters. HTH.

Edit: Here's a before and after...

 

[John]

All these CA reducing filters seem to add a tint (usually yellow) to the image. The Baader Semi-Apo is favoured by some:

 

 

[Louis D]

Here's a recent post of mine on another thread related to fringe killer filters.

[spaceboy]

I had an AR127L with which I used a Baader semi apo filter. It worked fine but there was never any delusion that I was using anything other than an achromatic refractor. I assume if your intension is imaging your AR152 is the faster f/5 so will show even more CA than the slower AR127L.

For visual I have yet to find a filter that cleans up CA as well as the Baader SA filter. I will point out though that I have always found my eye sort of gets used to CA and you don't tend to notice it unless you look for it. I liken it to looking at the Eskimo nebula in that you loose the halo of nebulosity if you stare at the center star long enough.

Other filters will reduce the purple halo but introduce a far more noticeable yellow cast to the views. Due to this, in the case of imaging I doubt there is any better resolve than to go with mono only snaps of the night sky. I'm aware there are some software that remove halos to some degree but as for filters a camera sensor is always going to be more sensitive than the eye and so require a great deal of post processing to result in a worth color image.

[alacant]

6 hours ago, spaceboy said:

AR152 is the faster f/5 so will show even more CA

The ar152 f5 is a 4 element Petval with a f10 objective. It shows little chromatic aberration. I believe the OP is referring to the ES ar152 f6.5. HTH.

[John]

The best method to control CA that I ever used was a Chromacor. They were designed for F/8 objectives though and cost rather a lot (as well as being rather hard to find)

 

[mikeDnight]

Personally I wouldn't use a CA filter as the always seem to add a false hue to the view. Ive always found the natural view to be preferable in short achromats despite the visible CA. The only way to limit CA or get rid of it all together in a short refractor is to go down the ED or Apo route. 

Mike

[mikeDnight]

15 minutes ago, John said:

The best method to control CA that I ever used was a Chromacor. They were designed for F/8 objectives though and cost rather a lot (as well as being rather hard to find)

 

I've never used a Chromacor John. Are they still available, and wouldn't the cost of buying one push the overall price well into the ED apo price range?

Mike 

[John]

9 minutes ago, mikeDnight said:

I've never used a Chromacor John. Are they still available, and wouldn't the cost of buying one push the overall price well into the ED apo price range?

Mike 

I've owned 3 of the things Mike and managed to get them at rather good prices. Their usual prices are much higher though and you can buy a used ED120 for around the same price. I used them with 6" achromats though and I've not seen many sub £1K 6" ED doublets around

While the Chromacor's did a great job on CA and SA correction (rather than filtering it) they were finicky to install not particularly compatible with the ultra-wide eyepieces that I like to use so in the end I decided to move to ED doublets.

I learned quite a bit about chinese achromats while playing around with them though

[spaceboy]

2 hours ago, alacant said:

The ar152 f5 is a 4 element Petval with a f10 objective. It shows little chromatic aberration. I believe the OP is referring to the ES ar152 f6.5. HTH.

TBH I think ES, Bresser, Meade AR refractors are basically all the same scope other than brand tags and maybe colour and trimmings. 

Thanks for the info on the ar152 f/5 though as I wasn't aware of that and is handy to know.

[nightfisher]

When i asked about CA filters i was told it was a bad idea

[TangoCharlie]

Thanks for responding.  Yes I am referring to the AR152 f6.5 scope by Explore Scientific.  

TC

[Dave In Vermont]

I have a Baader Fringe-Killer, APO-Filter, and another one whose name escapes me at the moment. And they are all a trade-off: Remove the 'blue.' Add the 'yellow.'

They are merrily collecting dust in my case. I simply don't get bothered by a touch of blue around bright objects.

Dave

[TangoCharlie]

On 4/27/2017 at 13:05, alacant said:

Hi. Congratulations on your purchase. I have the ar152s. For imaging, a wratten #8 stacked with a uv/ir cut works great with a modified dslr. I'm sure the #8 would work well for visual too and save you the extra which is charged for what are after all just yellow filters. HTH.

Edit: Here's a before and after...

 

i had an experienced astronomer of 40 years suggest for CA the following filter: neutral density minus violet filter?