Hello all.,,according to an article I read about E.P. magnification.,. the human eye can not detect a difference of less then 1.4X,.,In other words.,.,if your E.P. gives you 50Xmag.,,.your next E.P. should give you at least 70Xmag.,. 50x1.4=70.,,.,70x1.4=98.,.,and so on.,.,So if you start with your lowest power mag. and multiply it by 1.4x.,.,,then divide the mag. by your focal length.,,you get the mm of your next practical E.P..,.,,So if your F.L. is 1200mm.,.,your E.P. is 40mm .,your mag will be 30x.,.,30x1.4=42.,.,1200/42=28.5.,.,so for you to be able to see a difference .,.,your next E.P. should be around 28mm.,.,.the article I read said give or take 10 percent,.,Many scopes come with a 10+25mmE.P..,and you think that if you get a barlow you double your E.P. selection.,.,but in all practical purposes the 25 makes a 12.5mm and the 10 makes a 5mm..,the view in the 12.5 will not be noticably different then the 10mm.,.,and the 5mm will make a noticeable difference but will only be useable under the best of conditions.,.,,Soooo.,.,a 16-18mm might be your best choice for your next E.P. to fill the gap.,., a 32-35mm to get less mag. .,.,or a 5-7mm for more.,.,I hope this helps in your choices.,.,O+O