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AlvinP

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    First Major Beginner's Upgrade

    in Getting Started Equipment Help and Advice

    Posted

    So; these are the models im currently looking into:

    Refractors 

    Reflectors - (i understand they all require constant collimations to keep focused and sharp)

     

    Thanks

    First Major Beginner's Upgrade

    in Getting Started Equipment Help and Advice

    Posted

    1 hour ago, NigeB said:

    Hi Alvin,

    That's a short question but the answer is perhaps a little longer...

    It's true that the central obstruction reduces the effective aperture, though there are other things in play that could have a bigger impact on performance.

    The amount of obstruction varies by telescope design, but ~30% reduction in area is fairly typical for a reflector. So in the case of the examples you give, a 90mm refractor has an area of pi*(90/2)^2=6362 square mm of unobstructed aperture , whereas the 114mm reflector has an aperture area of pi*(114/2)^2 = 10,207 square mm, but a 30% obstruction means that you only get 70% of that area - so that's 7144 square mm. It's still 12% more collecting area than the 90mm refractor, but all other things being equal I doubt you would see much difference (but read on...)

    There are a couple of other points to bear in mind. There may be a little bit more "loss" in the reflecting design than the refractor (mirror reflectivity tends to be a little lower than lens transmission), and that further narrows the gap between the refractor and reflector examples you chose if we're just considering how much light they collect.

    However there  are other considerations. The angular resolution of the telescope goes as the diameter of the aperture as well, and in principle the 114mm reflector offers improved resolution over the refractor. The central obstruction does have some practical effect on that as well, but if the optical quality of the two telescopes is equal, and the reflector is well collimated, then the advantage is certainly real.

    My view is that based on the points above, then what the view through the eyepiece looks like (or the image, if you're using a camera) will be determined more by parameters such as the focal length of the telescope assuming that the optical quality of the two is comparable. And if the focal length is similar, then I would expect the views to be similar - again assuming optical quality is comparable in the two systems. If the reflector has a "spider" holding the secondary mirror, then it will produce diffraction spikes in the image, which the refractor won't do. Some people like the spikes, some don't - it's a personal choice, but the kind of thing that might persuade you to go with one over the other.

    So while I would not disagree with the statement you quote as a broad guideline, there are always other factors to consider, particularly when the two options are as closely matched as the ones you suggested.

    If there are specific models you're looking at, post the model numbers here - you'll get lots of advice from SGL members considering the specific details of the telescopes along with user experiences, and that is probably more useful in helping you to reach a decision.

    Best Regards


    Nigel

     

    Thanks! this is really good

    First Major Beginner's Upgrade

    in Getting Started Equipment Help and Advice

    Posted

    Thanks for the replies; another thing i read on a website was: "A key advantage of the refractor is that there is no central obstruction. The secondary mirror of the reflector blocks some of the light coming into the tube which reduces the effective aperture. In telescopes with 5” or less aperture the refractor is typically considered to have about a 1-inch advantage. This means that a 5” reflector and a 4” refractor would be considered about equal in light gathering ability, a key measure of the power of a telescope."

    How accurate is this? would this mean that a 90mm Refractor would perform similar/close than a 114mm Reflector? Or is this based on older designs and has been reduced in newer models?

    Hello

    in Welcome

    Posted

    I have been browsing these forums for a couple of months non stop and just today decided to sign in with Facebook and make a post.

    I got a 70x400mm cheap scope, but im looking forward to all the amazing stuff ill learn on these forums!

     

    • Like 1

    First Major Beginner's Upgrade

    in Getting Started Equipment Help and Advice

    Posted · Edited by AlvinP

    Hello,

    I've been on these forums a couple of times for the last 2 weeks and ive found amazing advice, on telescopes, mounts and eyepiece. Besides reading countless of information on the internet about various equipments; pros and cons; and i got some queries about how to upgrade my setup.

    My original purchase was a 15x70 Celestron Binoculars last year, and boy ive seen amazing things with it, specially globular clusters, Jupiter and Saturn and the Orion's Nebula; for me these were amazing; i still use them given how easy it is to look at the sky with them and how bright and full everything looks.  A couple of months ago i got a 70x400mm Gskyer Telescope with an AZ mount (The cheap 99$ one that Amazon is displaying on all its adds for the last two months)  it came with a 25mm and a 10mm eyepieces as well as a x3 barlows (which i didnt even count as part of my scope as it is too bad quality and i havent managed a single decent view with it).

    Currently My Celestron Binoculars (x15) seem better for visualizing the sky than the 25mm eyepiece (x16) (things seem a very bit dimmer). And since the Barlow is a "no go", the 10mm (x40) eyepiece is what i really use, it has decent zoom and detailed views , it is my go to eyepiece most of the nights.

    However from reading all around, ive read that most of the stuff that come with the Telescope (aside from the scope itself) are actually really bad quality, specially no name brands without even webpage, so if i were to maximise my telescope i should update some of those items.
    -Recently i ordered a new Start diagonal to replace to default one (ive heard on Refractors its usually the weakest link next to eyepieces) as well as an economic x2 Barlow lens

    Keep in mind i recognize my 70mm cheap telescope will not suddendly become the Hubble Telescope, and that it doesnt matter how hard i push it, in the end such a low scope will be bound to hit its limit pretty fast, thats why i avoid 70$+ eyepieces and barlows for now.

    I expect to keep using this telescope for a good couple of months; at least until around August, when Jupiter and Saturn are more in the night sky, rather than morning.

    Now, im very satisfied with my current telescope; while the phone mount is garbage and the phone weight and the sound of my heartbeats pretty much shake the telescope out of position, as well as how cheap the mount is; it still gets the job done for seeing interesting stuff in the sky and i have managed to do some AP for some of the globular clusters, bunch of 1-2s images (with the wrong lens), not the best, not even good pictures; but decent overall for my equipment. I am currently interested in stargazing in general and some minor AP (as i dont have a camera, currently an Iphone 7s with the mount) Buuut im interested in borrowing a camera for the low sky photos without a telescope.

    I do most 97% of my Skywatching on my backyard, i live in a small country, there is some light pollution, but i can see the pleiades and the orion's nebula core on the naked eye most nights (so i guess its not that contaminated lol)
    Now; currently i like finding stuff by myself and show it to the other people around me who cant be bothered to find the moon in the sky, so setting up, finding and seeing stuff is part of what i like. 

    With all the above in mind..... Id like to plan ahead for my next purchases.

    First, im thinking a x3 barlow lens (to replace the original crappy one) and a 15mm lens (to have a bit better view than the 10mm, but less spread than the 25mm) in two or three months (with this id be able to check if my new eyepiece outperforms my default ones, but given the quality of the scope, i dont expect this to be noticeable).

    And Afterwards id love to get a new Scope, but im not quite sure what i want... and i would like some advice and help in choosing my next Scope upgrade.

    -I entered with and im liking the refractors; however i dont wanna spend 300-400$ on another refractor that is 20-30% better for triple the price
    -Ive heard really long focal lenght might bring some distortions; and also make the scope much bulkier, annnd most importantly i know that magnification is not everything; so a 1000mm long tube would prob bring too much magnifications for me to use properly on my backyard skies. So i think id settle for a maximum of 600-700mm.

    -Originally i was againts Newtonians in general, those inverted views scared me, i have a hard time of my own with my finderscope. Then i found out that Reflectors are the name of efficiency as they have more value per aperture than refractors; and as someone once mentioned "There is not really up and down in space, you will get used to it" annnd its true... save for references on the ground, like buildings, trees and mountains to help you locate where you are in the sky; once you are on it, you dont need right ups and downs.

    -I did see some 90mm Orion's Refractors as well as 90-102 Celestron Astromaster Refractors (these are 350-400$)

    -Im thinking a 130mm reflector is what im looking for; i think the 130mm aperture is a nice upgrade for my 70mm, and will keep me occupied for quite a long time; ive read about Orion SpaceProbe 130EQ and Celestron Astromaster 130EQ (ive also read, Power Seekers and Astromaster's are made out of pretty much garbage lol) Ive read that the main issue is the constant collimation required for them; but ive also read its something that can be learned and once you get used to it; its a pretty easy thing to do to keep getting amazing views.

    -Ive also seen people recommending  6-8'' Dobsonians; i know the deal with them; if anything i could aim for a 6'' one i found a litter under 300$ ive read they are amazing values for their aperture

    So, TL;DR: I have a 70x400mm Telescope, im new to stargazing, im really amazed and excited by what im seeing with my current scope, but would like an stable upgrade before the end of the year that will last me a year or two. I am interesteted both in regular and deep sky stargazing and astrophotography;  im not currently interested in an motorized mount; could deal with a regular Equatorial mount. But overall i am looking for  more aperture (100-150mm) to have clearer views; than focal lenght for zoom.

    Im also open to the fact that at one point i might have to get a scope for stargazing and another for AP; but would like an upgrade that could help me all around for both while i get initiated.

    ------------------------------------------------------------------

    Sorrry for the Huuuuuuuuge post, i was very excited while writing it; please let me know what you think and if there's anything else you'd want me to add to help understand my situation, thanks in advance!

     

     

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