I'm considering buying an 80 mm refractor, but I noticed that they come in both short and long tubes. What are the advantages and disadvantages of having more or less focal length, specifically for astronomical observing?
go grab yourself a 3m long tube. you will notice that theres less light and a greater effect of zooming in then go and grab your 1 meter long pipe and youll notice theres a bit more light and a wider view.
The other thing is that a ST is alot more portable than a LT, then theres the question of what are you using it for and what are you future intentions. If you are going for observational usage why are you going a 80mm refractor?
Post up a bit more detail and we can help you from there.
In achromatic models, shorter focal lengths produce more chromatic aberration than a longer focal length in any given aperture. Longer focal lengths may also produce sharper images due to reduced chromatic aberration; and because long focal length optics are easier to make, there's a reduced likelyhood of imperfections. For this reason Long focal lengths are better for lunar and planetary targets.
Short F/L achromatic refractors are more designed towards wide-field deep sky viewing and are not particularly suited to planets.
The reason why I ask is that I think a refractor will be better suited for my needs. It will be more portable so I can take it away and I'll be able to use it on the balcony or roof. Generally, it will get me outside more, which is something I find that I don't get to do enough.
So I'm actually downgrading from a 10" Dob (shocking, isn't it!)
Short vs. Long Tube Refractors
