View Full Version here: : favourite magnification for solar viewing
06-04-2010, 01:50 PM
Dear solar observers,
Time for a new ep to use with my ed80/lunt 50mm Ha combo. I am currently using my 9mm Nagler which gives me 67x. This is quite thrilling, but I would like to go for a higher magnification. I'm thinking of a Radian to get good eye relief so those with glasses can enjoy the view, and it would be parfocal with my naglers. (my Vixen LVW 17mm is a bit tight on the infocus with this setup). My question is, what is the useful upper limit of magnification with solar viewing. Does viewing by day reduce the magnification that can be used? What magnification do people use the most?
Thanks in anticipation.
06-04-2010, 03:19 PM
I dont think you will have an issue with upper magnification limit from a contrast point of view but you will have more thermals in the air from nearby neat sources (eg. roofs, paths etc).
Note with the Radian you will be losing true field for the same magnification. eg. Your 9mm Nagler (12.4mm field stop diameter) will give 1.2deg at 67x and an 8mm Radian (8.3mm fsd) will give 0.8deg at 75x. A 6mm Radian (6.3mm fsd) will give 0.6deg at 100x and will just fit the full solar disk. A 5mm Nagler (7mm fsd) will give 0.67deg at 120x. Either will give a nice view of the Sun and any flares with a little room to spare. A 7mm Nagler (9.7mm fsd) will give 0.93deg at 86x and may be a good alternative.
The Radians are very comfortable eyepieces to use with their 20mm eye relief and if your prefer the longer eye relief then they are a good choice. Note if you want to see the full solar disk don't choose a size too close to the true size of the Sun (0.5deg). Even 0.6deg is a little close since it only takes a small misalignment of your mount and you are constantly nudging the telescope to keep the object centred. It is for this reason I prefer 0.7 to 0.8deg for full disk solar or lumar viewing.
07-04-2010, 09:13 AM
Thanks. I'm still unsure about how high a magnification is useful. I'm quite happy with my view of the whole disc with the 9mm Nagler, but I'm wondering how much mag I can use to pick out details. Do people find the view of individual prominences, sunspots, filaments etc improved by going higher than 67x and if so how high? Is the seeing more problematic than by night due to the extra heat in the atmosphere and on the filter? If, so, just how far can the power be usefully pushed. If the answer is that there is not much to be gained by going to higher magnification, that will be fine - I can rest content with my 9mm. It's just that constant question - could this be even better?
07-04-2010, 10:43 AM
Shortly after sunrise the layer of air near the ground starts to heat up and becomes bouyant (lighter than the air above it). Eventually a bubble lifts off, sucking in the warmed air around it and rising thousands of feet into the atmosphere - the rising column of air is called a 'thermal', and thermals can rise at a speed of thousands of feet per minute. This process accelerates through the morning causing maximum turbulence in the middle of the day, when the Sun is overhead and delivering the most energy to the ground. Thus the maximum magnification is less when the Sun is overhead due to the increased atmospheric turbulence. I like to use a Lunt zoom eyepiece to dial in the magnification allowed by the atmosphere at any given time.
Higher magnifications can be achieved at night due to the lack of solar heating of the ground. The Sun really chops up the lower few to several thousand feet of the atmosphere by day.
IME, you're not likely to use much more that 67x, but it all depends on your local conditions.
07-04-2010, 08:19 PM
Thanks Tony, that's what I was wondering. I will just relax, cool the eyepiece acquisition instinct and enjoy my wonderful equipment. Perhaps until it comes to a double stack filter...
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