Planning to buy a first telescope?

Dave, other than the obvious effect the focal length has on magnification and eyepiece choice, why would the faster scope give brighter views? Or is that all you meant?

for the same reason a low f stop gives more light through a camera lens

f2 more light ( brighter image) than f5, than f10 than f22 etc

this is a function of the mirror, lens itself

this really becomes a benefit when doing astro photography cuz for a f5 you dont need to do the same much longer exposure time that you would need to do with a f10


Dave

For AP sure, but for visual use, if the magnification through the eyepiece is the same between two scopes, nothing is different, correct?

I think part of the thing is... even at the same magnification,
the f5 system is going to give a wider FOV which even on its own
is letting more light through

D

not really

the scope he bought some time ago was a 90mm (f10) refractor
I had to go searching through this thread to discover for myself lol




Both these 2 scopes being decided between will make awesome "light buckets" :)
10 - 12 inch at ~ f5 or so will be quite fast optics compared to the refractor and
nebulae etc will appear so much brighter

CowedbyWisdom .... I can assume by your trend in choices of scopes that you are not really interested in goto ability or motorised tracking for astrophotography use ?

either of these 2 dobo's will make great viewing of the skies .... see if you can find some independant/unbiased reviews of both of them .... ie. not reviews that may be posted on the sales page sites

I own a 10inch f5 dobo, solid not truss tube, if you got the truss tube one, you would need the shroud to wrap around it to keep ambient light out
I also own a Celestron C9.25, 9.25inch f10,
each has its uses the f5 is a light bucket, but lower magnification
fast optics like f5's can suffer from a little spherical and chromatic aboration but this is normally only visible around the outter edges of the field of view and under higher magnifications. They are great for wider field objects, globular and open clusters, diffuse nebulae etc

The f10 scope offers much higher useable magnification and get great for small bright objects
planetary nebulae, galaxies, planets etc

Both those scopes say max useable mag of ~ 500x. I suspect that would be really pushing it and a bit of sales hype, In practice I would suggest that ~ 200 - 300x would be closer to the truth before the aborations spoken of earlier become quite obvious
Thats from personal experience with several fast scopes over the years

Dave

I found these on amazon "Celestron UpClose Porro Series 10-30 x 50 Zoom Binoculars"...Are they good?

Wondering. How good are the National Geographic Telescopes? Specifically NATIONAL GEOGRAPHIC 114/900MM AZ. Say compared to the Bresser Galaxia 114/900.

A good rule of thumb is "the more you spend, the better they will be".
Obviously it's not always that simple, but generally it works out that way in my opinion. I'd look for similar products and see what the price range is for them. If yours is at the bottom of the bucket, it's probably not too good.

not to hijack - but seems not worth a separate thread.

Is it possible to clean a telescope mirror?

About 30 years ago i bought Dad a 6" Meade mirror out of Sky&Telescope magazine.
We built a simple newtonian with a redwood twelve sided tube. Local astronomy club deemed it "handsome" which Dad enjoyed tremendously.

It has now sat for fifteen years since his death and is quite dusty.

Is this something an amateur can do, or should i mail it someplace?

Suggestions welcome -

old jim