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## Planning to buy a first telescope?

 Quote by Drakkith 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

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 Quote by davenn 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?

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 Quote by Drakkith For AP sure, but for visual use, if the magnification through the eyepiece is the same between two scopes, nothing is different, correct?
personal experience tells me that I can see a difference, say M42, the Orion Nebula

maybe will have to have both scopes outside together again one nite
just to confirm or deny my long held beliefs haha

D
 Recognitions: Gold Member Science Advisor 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

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 Quote by davenn 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
That doesn't make sense to me man. At the same magnification the object should appear exactly the same brightness in both scopes. The difference in FOV would only be because of the eyepiece design. And I'm not sure what additional light you are referring to. An F/4 newt and an F/8 newt with equal objectives have exactly the same light gathering ability. You just need to use different eyepieces to get the same magnification on each one.

 Quote by davenn 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
Thanks for the response. To answer your question, I don't find the goto scopes necessary or fun. I like doing my own star finding and am not interested in astrophotography. Since I doubt there is anyway to upgrade my little refractor to make it up to snuff with a 10 or 12 inch dob (?) I felt might as well get a bigger scope. I'm also considering getting a Smith Cassegrain of some sort any suggestions are welcome. My budget is 700 dollars or less. I will be using the scope for looking at mainly the planets and galaxies.
 Recognitions: Gold Member Science Advisor You mite get a new 6" schmitt-cass for up to that price, maybe an 8" but I doubt it have a good look through scope sales sites, a non-goto 8" may well be affordable you should/mite be able to get a good respectable condition second hand one for ~$700 my 9.25" goto schmitt-cass was$3300 My 10" dobo was $600 look, if you are not worried about astrophotography, just stick with a good decent sized dobo either of those 2 above would do you well for a few years, till "aperture fever" starts to bite hard ;) haha cheers 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. Recognitions: Gold Member  Quote by BH Wiz I found these on amazon "Celestron UpClose Porro Series 10-30 x 50 Zoom Binoculars"...Are they good?  Quote by Storm89 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.  Quote by Drakkith 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. Of course. That's the rule of thumb I've gone by on most occasions. From what I can see the two are somewhat similar, but the difference is in the stand, which I understand is quite important. I'm actually asking cause my birthday is right around the corner and I've been meaning to put a telescope on my wish list and these are around the price I could probably sum up if most of my family gathered round. I doubt they will, but you can always live in the hope, can't you? I can't find much else than Bresser Galaxia 114/900 or Bresser Pollux 150/1400 (but without a 3x Barlow) or Bresser Lyra 70/900 at that price range. The National Geographic one is a little cheaper, but the stand appears somewhat worse.  Recognitions: Gold Member Another good rule of thumb is that you can buy base-level optics from a well-respected manufacturer and probably get superior quality. I bought my basic Nikon 50x7s from L.L. Bean, and they are wonderful. High-end manufacturers can let their quality-control and good materials permeate their whole line without busting the bank. Buying optics from some line that sources their gear from various manufacturers in China offers you no such advantages. Good luck!  Recognitions: Gold Member Science Advisor 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  Recognitions: Gold Member Science Advisor You will be better off sending the mirror out and getting it recoated. After sitting around that long the coating will almost certainly need professional help. Optic wave labs, for example, [http://www.opticwavelabs.com/coating.php] will strip and recoat a 6 inch primary for around$50, and the secondary for \$30 [perhaps less]. That is not a bad deal.
 Recognitions: Gold Member Science Advisor thanks, chronos - that'll be the plan. old jim
 I just bought my first telescope, finally settled on the Orion XT8 after originally considering a Celestron 90EQ refractor or 130EQ Newtonian. Figured I might as well get something that will last me a while from the get-go instead of wasting money on lower end scopes. Anyway, what are some good eyepieces to consider getting? I believe the XT8 only comes with one 25 mm piece, so I think I'd like to get a 6-10mm piece for planetary viewing. Also, should I get one of those laser collimators, or will I be able to get by without one?

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 Quote by jim hardy 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
Personally, I won't do business with Cary at Optic Wave Labs. Too risky. He hasn't taken any of my money but he has wasted a lot of my time. Search Cloudy Nights for the many tales of woe... and just as many happy endings. If you've already jumped in then good luck!

I think you'll need it.

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