Roger Samworth

Some solar scope calculations

I have wondered about the resolution I get with my solar scope, so here are some fag-packet calculations:

Telescope diffraction limit (in radians)= 1.22 X wavelength in cm/scope dia. in cm

Telescope diffraction limit (in arcseconds)= 206265 X 1.22 X wavelength in cm/scope dia. in cm

Ha light  wavelength = 6562 angstroms = 6562 X 10^-8 cm

Lunt LS35 THa is 3.5 cm dia

Diffraction limit = (206265 X 1.22 X 6562 X 10^-8)/3.5

= 4.7 seconds, or about 5

Solar diameter is around 30 arcminutes, or about 1800 arcseconds

In this image the distance between the 2 spots is around 0.135 X the solar diameter, or around 250 arcseconds

The lines or striations around spot 2620 at their thinnest, are around 1/50th of this distance, or around 5 arcseconds.

So. my Lunt LS35THa images could, in fact be diffraction limited!

The GONG cameras have an aperture of 2.8cm, so they are similar.

Conclusion, to get images like this one (


  1. Win lottery
  2. Buy Lunt LS152 THa
  3. Get bigger window-sill

Of course, a Quark fitted to a 80mm scope should be pretty good! (Andy)


Sunspot 2720

Sunspot 2720 has now appeared and seems to be developing quite rapidly.

“Spaceweather” says:

“New sunspot AR2720 is not only large, but also strange. Its magnetic polarity is reversed. The North and South ends of its enormous magnetic field are backwards compared to the norm for sunspots in the current solar cycle, decaying Solar Cycle 24. Could AR2720 be the first big sunspot of the next solar cycle, Solar Cycle 25, popping up now in the middle of solar minimum? Stay tuned for more information about this intriguing possibility after the current geomagnetic storm is over.”!

Yesterday’s prominence

Here is another stunning amateur image of the prominence I imaged yesterday:

This time from Florida, and again with expensive glassware (6″ f/8 refractor + Quark)

I console myself that again, it wouldn’t go on a window-sill and be at instant readiness (“The best telescope is the one you use the most”). Doesn’t stop me sighing deeply – – -!

C’mon you Quarkers – put up some competition!

Prominence processing comparison 14/08/2018

Having been seriously impressed with this image of the prominence the other day acquired with a Lunt LS152

Sunspot AR2718

I thought I would have another go at processing my window-sill image. I screwed down the alignment box size (in Registax 6) to 10 pixels and limited the processing to the prominence area. I then added a bit of Lucy-Richardson sharpening in GIMP. I think the extra aperture of the LS152 allows a much faster shutter speed, limiting the blur due to atmospheric wobble. The result is below.

Not as good as the LS152, of course.

There is also the small matter of a factor of 20-30 in the price of the optics of course – – – – Sigh!