primary mirror

Hello everyone,I just finished building my first dobsonian the other day minus the mirrors,spider,and focuser.I'm building a 6"and have my mount and tube ready.I was getting ready to order a kit which includes both mirrors,spider,1.25" focuser and eyepiece,also the finder scope for 229.00,I felt this to be a good deal.What I was wondering was do I get the f/5 or the f/8 primary.My tube is 48" sonotube 8" diamater.Both is same price but confused on which I should get.I put this all off till last because I really dont know a lot about it.I just got hooked on astronomy and wanted a bigger scope and to see how one works.I figured building it was cheaper and has been fun,now I'm staerting to get a little nervous because I dont want to do it wrong and waste the money,229.00 dollars is a lot of money at my house unless its being spent on my kids or wife-small joke.Any help in this area would be greatly appreciated.Thanks for all your past help on giving me direction on the teflon bearings.Darrell Hensley

My personal thinking would be to go with the 6 inch F8 mirror. There are a few reasons for this...

First, a 48 inch Long OTA is about ideal for a DOB. Dobs seem to go like this: 6 inch F8, 8 inch F6, and 10 inch F5. All are about 4 feet long, fit across the back seat of a car and provide a comfortable eyepiece height. The 30 inch focal length of the 6 inch F5 will put the eyepiece too close to the ground for most people so you will have to figure out a way to get it back up.

Second, optically a 6 inch F8 mirror is very forgiving, it will provide nice sharp views to the edge of the FoV with relatively simple eyepieces. It will be much easier to collimate as well. The advantage of the 6 inch F5 is the wider field of view...

So, put my money on the 6 inch F8...

Jon