Solar With Baader Continuum - 100mm Apo v 120mm Achro

[Mr Spock]

Well, this was a surprise. I've just been doing some solar with the Tak and decided to try the old 120mm achro. With the Baader Continuum filter and similar magnifications (7mm Nirvana in the Tak, 10mm Nirvana in the achro) I was able to do a direct comparison between the two. 

The 120mm consistently showed more detail. It was sharp and sunspots looked black. Detail in spots was easier to pick out and more tiny spots were seen. Granulation and faculae were also easy to see. This wouldn't be repeated on planets due to CA from the achro, but for solar with that narrow band green filter it's a winner.

[ONIKKINEN]

With regards to CA, i use the new version of the Baader solar continuum filter on Jupiter and the Moon (not for Saturn, too faint) with my 90mm f/5.5 Long perng semiachromat. Makes it a very faint disk but i find it makes the bands really pop out and i see more than with no filter or a Baader fringe killer. Really it has become my go-to filter for Jupiter observing with the 90mm. Try it out some night? Might be surprised by the improvement in contrast with your 120mm achro.

[Mr Spock]

I'm not sure I'd want the planets or moon looking green. I'll stick to the apo for those 

[Gonariu]

I look at the sun almost every day with an achromatic 80/400 bought used in May 2020 (the Konus Vista 80) and I must say that, by placing a glass solar filter at full aperture, a W58 green filter at the eyepiece and using X80, I have beautiful visions of our star; the W58 filter usually improves the image a lot for me.

Edited October 15, 2023 by Gonariu

[John]

I think our eyes are most sensitive to green light (wavelength 530-550nm). Optical guru's say that optics for visual use should be tested in that wavelength. I believe the continuum filter transmits 540nm which makes sense. Probably a good filter to use for star testing as well.

 

 

[Stu]

2 hours ago, Mr Spock said:

Well, this was a surprise. I've just been doing some solar with the Tak and decided to try the old 120mm achro. With the Baader Continuum filter and similar magnifications (7mm Nirvana in the Tak, 10mm Nirvana in the achro) I was able to do a direct comparison between the two. 

The 120mm consistently showed more detail. It was sharp and sunspots looked black. Detail in spots was easier to pick out and more tiny spots were seen. Granulation and faculae were also easy to see. This wouldn't be repeated on planets due to CA from the achro, but for solar with that narrow band green filter it's a winner.

I think if it’s a reasonably well corrected, longer focal length scope then that’s possibly to be expected. It’s the SA in the f5 scopes which kills off the fine detail.

[Mr Spock]

25 minutes ago, Stu said:

It’s the SA in the f5 scopes which kills off the fine detail.

I had an 80mm f5 from the same stable (Helios). It was dire at any kind of magnification and acceptable at only very low power. The 120mm / 1000mm I have is highly corrected for SA; remove the red and blue and it's not unreasonable for it to be very sharp. It can be quite detailed on the moon if you can ignore the purple haze over everything.

[Mr Spock]

I suppose I should have removed the continuum and put an ND on to see what it was like in white light. A bit fuzzy I suspect.

[John]

This test report on the Baader Continuum filter is interesting. It finds that the filter is much more effective when used with achromats than it is with apochromats:

Test Report: Baader Solar Continuum Filter revisited – now with 7,5nm FWHM / Baader Planetarium Blog Posts (baader-planetarium.com)

 

 

 

Edited October 15, 2023 by John

[Stu]

15 hours ago, John said:

This test report on the Baader Continuum filter is interesting. It finds that the filter is much more effective when used with achromats than it is with apochromats:

Test Report: Baader Solar Continuum Filter revisited – now with 7,5nm FWHM / Baader Planetarium Blog Posts (baader-planetarium.com)

 

 

 

That makes sense John. I still find it a benefit with an apo though.

[Mr Spock]

1 hour ago, Stu said:

That makes sense John. I still find it a benefit with an apo though.

Yes, they do make a noticeable difference.

[Mr Spock]

I've been doing some reading to see if I can determine what is happening. My best guess from the info I've seen is an achromat is best corrected at around 540-550nm which coincides with the narrow band of the continuum; out side that the achromat has little correction.

The apo has a 'close enough' correction from 400nm to 900nm and therefore gives a colour free and sharp image in white light which the achromat cannot.

[John]

Those DPAC tests that they discuss on CN tell some interesting stories about correction in differing wavelengths of light.