In the past, for white light solar observing, I've normally used my 6" F/8 Newtonian. To get away from the thermal and portability issues of this set up, I've been considering using my 50mm 10x - 30x spotting scope.
My question is would a 50mm scope operating at 30x be sufficant to use for daily sun spot counts?
Thanks in advance.
You'd be in good company with the smaller scope, Wolf used a 37 mm scope for his observations. However, it may be difficult to see these solar minimum sunspots that are now A type and very small.
Perhaps give it try and compare the results with both scopes?
I use a 102 mm APO f/8 with a 10 mm ocular to give me 80x. I think I remember reading a number of years ago that this was the prefered magnification and, therefore, this is what I've used. Is that true?
I think most would agree that 80 x is a little high, but still OK. The issue is whether you might be counting pores rather than sunspots with high magnification. Here's a good reason for the smaller aperture (not too small) scopes and lower magnification:
I was able to do a comparison between the 30X50mm spotting scope and my 6" Newtonian operating at 50X. In both scopes the recent active region 2755 was not visible with the 50mm being limited by magnification and the 6" by seeing. As expected the seeing was much better in the 50mm.
I was able to do a star test on the 50mm and (keep in mind I'm not an expert) the optics appeared to be okay with the shadow of the amici prism only visible in the out of focus image. Though not a good test target, within the limits of a 50mm, it did do a good job resolving fine detail on the moon.
In summary, having a very portable scope, that's easy to move to avoid trees, roof tops, and for taking quick looks through holes in the clouds makes me lean towards the 50mm.
This brings me back to my original question: Is 30X enough magnification for useful sunspot observations?
I looked in the solar database and I find only one other person with a magnification of 30 x. All other observers (using the direct method) have greater magnification. So, I would say it's a little weak on that end.
So many different telescopes and ways of observing the sun, I'm not sure what is the best magnification. I think there is concern in the solar community that folks are not counting pores with too much magnification.
The AAVSO and SILSO create k- factors for each observer after you've made over 100 observations with you telescope. These are based on the idea that after 100 observations you will or should be consistent in knowing how to count sunspots, and what to look for with size of group (and to not split the groups), and estimating the number of spots in each group, etc. for the total Wolf number.
So, just pick the best (easiest) scope for your self and be as consitent as you can, once the new cycle 25 begins, and many groups and sunspots can be counted, you'll get a k - factor and just stick with your telescope.
Greetings Steve. I'm writing to you my feedback as well. When i first began sun observations i used an eight inch dobsonian but i had terrible thermal and seeing issues especially on hot days. I switched to a 70/700 mm refractor which made things really better but with two cons. The major one, i can not see very small spots and second i have a little trouble moving it. I am now thinking of switching again for a 114/500 dobsonian which is small in size,giving me the opportunity to put it into the box and move but i am thinking of thermal issues as well.Now at winter there not hot days but i won't have any problem and later at summer i may have that kind of problem. As far as magnification is concerned,i found that 70-80x is the best for me to observe. All the observations i make is with direct method.
One more thing. Rodney,wil i have any issues with that k-factor if i switch now my telescope? I have been observing for 5 to 6 months now,making approximately 70 observations so far. Thank you very much!
I would not worry about your k-factor during this solar minimum. I think it is more important to choose the best telescope for your observations. When cycle 25 begins then we will need to look at everyone's k factor and it would be best to be consistent for 100 obsverations with the telescope you find works the best.