Hi Rob
I’ll try to answer your question by explaining my set up and how I use these filters, so here we go:
• I use the standard Baader Solar Film (visual and astrophotography) when I am imaging with the LPI at prime focus and with the PowerMate x2.5 Barlow.
• I use the Baader Solar Film 3.8 (astrophotography only) when I plug in the PowerMate x5 Barlow.
With my 4” f9 refractor, here are some examples of the LPI exposure settings:
Baader Solar Film (visual)
• Prime Focus: exposure 0.002 secs
• PowerMate x2.5 Barlow: exposure 0.008 secs
• PowerMate x5 Barlow: exposure 0.032 secs
Baader Solar Film 3.8 (astrophotography)
• PowerMate x5 Barlow: exposure 0.001 secs
Basically, the standard Baader Solar Film is fine for prime focus, the x2.5 Barlow and when the seeing is good, sometimes even the x5 Barlow.
To use the x5 Barlow I need to fit the Baader Solar Film 3.8 although I first focus through the visual film as the Baader Solar Film 3.8 (astrophotography) comes with a warning to not use it visually.
Notes on LPI and image stacking:
1. At prime focus I can usually always use the LPI “in-camera” track and stack function to stack around 10 to 20 images to improve the final result.
2. Using the x2.5 Barlow I can only use the LPI “in-camera” track and stack function when the seeing is above average, otherwise the final result is smeared due to combining individual images that do not quite register due to the shearing between each frame.
3. I have never been able to use the LPI “in-camera” track and stack function with the x5 Barlow, even with exposures as short as 0.001 secs, as the sun spot image shears and ripples so much on the display. In fact, parts of the image are in focus whilst other parts are blurred due to the variations in seeing at such high magnification, even across such a small field of view.
4. I purchased the Baader Solar Film 3.8 (astrophotography) from Claude Voarino at Astronomy and Electronics Centre at
http://www.astronomy-electronics-centre.com.au/ and from memory it cost me around $50 for an A4 size sheet.
Hope that helps.
Dennis