I started with an 80 mm refractor. My second scope was an Orion XT8 Intelliscope. This is a PushTo model where the computer helps you find your targets but you have to move the scope as there are no motors. However it can be used manually like any other Dob too. About $700
So I would give a very positive review of an Orion XT8.
I now have an Apertura AD12 (Zhumell Z12, Orion Skyline 12) and am very pleased with this one too. The 8" and 10" are similar, just a bit smaller. I think the Apertura/Zhumell/Skyline package offers a nicer set of of accesories than the XT8 for about $50 more.
Compare Aperture - 3" vs 6" vs 8" vs. 10"
To compare them from an aperture, square the aperture to get the ratio of the areas. Let's include your current scope.
9 to 36 to 64 to 100.
A 6" provides 4X or a 400% increase in light gathering over your 3". That is HUGE! The increase to a 6" will dramatically change what you can see and how much mag you can apply to the image.
An 8" provides 177% of the light gathering of a 6". Or you can say it gathers 1.77 times as much light as a 6". That is substantial and will be noticeable. It is about a 7X increase over your 3". Gigantic.
A 10" provides 277% of the light gathering of a 6" or 2.77 times. That is big! And it gives you 11X the light gathering of your 3".
A 10" provides 156% of the light gathering of an 8", or you could say it gathers 56% more. That is substantial, but not as big as the difference between the 6 and the 8.
That is how you compare the aperture increase. Figure about a 15% increase in the maximum magnification you will be able to use as you go up each size. The more light you gather the more mag you can apply up to the limit the atmosphere the sky imposes.
To help put this into perspective, My 12" gathers about 2.25X as much light as my 8" so it provides a brighter image in all cases. When using the 12", I can typically apply about 40X to 70X more mag on any given object on most nights and have a similar quality of image. For example, my 8" would often top out around 180 to 200X on planets. In the 12" I can typically hit 220 to 270X on the same night, depending on transparency and seeing.
Naturally that is not always important as some things look better at lower mags. But on the Moon and Planets, splitting tight double stars, that extra mag comes in handy.
Now you look to moving them. About 35 pounds, 45 pounds and 60 pounds, depending on the brand. Each can be mored in two pieces. I chose the 45 pound 8" because I knew it would be easily within my comfort zone to move. I originally thought I would be storing it in the house.
If you store it at ground level in a garage or a dry shed, you can put any of them on a cart. If you live in a third floor walk up I would lean toward the 6" as that you can probably carry in one trip. The 8" might be challenging for 3 floors and the 10" will likely require two trips.
Remember, after you move the scope, you will need a chair and your accesories so that is at least one more trip.
My 8" ended up being kept at ground level where I kept it on a cart in the garage My 12" lives in the garage on a hand truck so they are all easy for me to move and store. But if they were stored in the house, weight would be a significant factor.
At age 18 you may be fit and strong and feel weight is of no concern, but it is. The more trips it takes, the more time it takes to move and set-up, the less likely you will be bothered to use it. A 6" that is easy to move so it gets used often is better than a 10" that is too much bother.
If you want to put it in the car, where will if fit. If you have an SUV, any of them will fit nicely. If you have a smart car things will be tight. My 8" fit nicely in the back of my Ford Escape with 1/2 the back seat down. A 10" would have fit just as easily.
Focal Ratio and Eyepieces
Typically the 6" is about F8, 8" about F6 and the 10" about F5.
The lower the focal ratio the more challenging it is for eyepieces to provide a clean image across the entire field. That is the reason for the earlier comment that the 10" will require more expensive eyepieces. In my opinion, equire is a strong term in this case, but the point is valid.
If you are using Plossls, I think you will be fine with all of them. But if you want to get a wider field of view then you will want eyepices with wider than the Plossl's typical 50 degree AFOV. Less expensive ones will look good in the 6", OK in the 8. In the 10" you will get more noticeable edge distortion with cheaper wide AFOV eyepieces.
Better eyepieces will benefit all of them, but in the 10" the difference will be more noticeable.
The 6" and 8" fit in your budget. The 10" will put it at the limit, or take you a little over depending on the package you select.
Orion, Apertura, Zhumell, Sky Watcher, Meade are all good brands of Dobsonian telescopes. But my leaning would be to the Apertura and I would suggest Highpoint Scientific. However, if you have a local store that you can work with, go with them for the personal service and support, if they offer that.
Hope that helped.
Edited by aeajr, 13 October 2019 - 09:31 AM.