Achromatic abberation..

[paul mc c]

Hello all, I am using a 102ed doublet that a believe is fpl 51 glass and want to know would there be much of a difference with a similar scope with FPL 53 glass.

I have added pic for example.

[Ags]

I find an Astronomik L3 filter helps. A very nice picture by the way!

[happy-kat]

Sharpcap has a function for chromatic aberration in the latest release I've found effective when I've tried it on a few of my images.

[PeterC65]

I can't see any CA in the image you posted. I don't get any better with my 72mm FPL53 refractor.

I agree with @Ags that a UV / IR cut filter greatly improves colour rendition but it looks like you may already be using one from the image you posted.

The SharpCap CA function creates and artificial green layer from the red and blue I believe, which may well reduce CA but to me it feels like I would be throwing away some of the data.

 

[Steve Ward]

7 minutes ago, PeterC65 said:

I can't see any CA in the image you posted. 

Really .... ?

 

[paul mc c]

4 minutes ago, Steve Ward said:

Really .... ?

 

That's what I see.....

[alacant]

Hi

I don't think a change of glass will make much difference, but a triplet may.

Ideas. Use a:

• focus mask to get you close to focus, then remove it. Use live view to move away from that focus point until the blue halo is reduced.
• reflector
• #8 and correct the colour cast afterwards

Or just mask and reduce it:

[Rob]

I'm planning to do some light imaging with my ED102 fpl-51 soon also. I had planned on using a Badder semi-apo filter along with my L-pro to see what results I get. 

[Ags]

1 hour ago, PeterC65 said:

I agree with @Ags that a UV / IR cut filter greatly improves colour rendition but it looks like you may already be using one from the image you posted.

The Atronomik L3 cuts a little far blue in addition to UV, so it can improve blue halos at the cost of a little richness of color.

[vlaiv]

You can also reduce CA fairly easily (and cheaply) by using aperture mask.

That will trade off some imaging time for reduction in CA, but results can be rather impressive. I'd start with 80mm mask - maybe do a comparison session when the moon is out and you won't be imaging otherwise - find a bright hot star, that way you won't need much exposure time to reveal CA and compare with / without mask results. Even better - make several masks and compare them all - like 90mm , 80mm, 75mm

 

[Ags]

33 minutes ago, vlaiv said:

You can also reduce CA fairly easily (and cheaply) by using aperture mask.

That will trade off some imaging time for reduction in CA, but results can be rather impressive. I'd start with 80mm mask - maybe do a comparison session when the moon is out and you won't be imaging otherwise - find a bright hot star, that way you won't need much exposure time to reveal CA and compare with / without mask results. Even better - make several masks and compare them all - like 90mm , 80mm, 75mm

 

An aperture mask will also have the benefit of making the field seem slightly flatter as it will increase depth of focus. Not that I see any field curvature issues in this image.

Edited March 11 by Ags