Don't know what to do

[Rami7]

Hi all, I'm Rami, from Cairo Egypt. I want to buy a scope and after hours and hours online I think I've made up my mind and I'll go for an 8 inch reflector. Now, in Egypt ,they don't sell meades or celestrons or any other known scope brands, there's one manufacturer of telescopes , please find the link to his website http://www.egypt-telescope.net/price%20page.html

I'm afraid the quality will not be that great. What shall I do? Shall I try to build it ? Shall I get a known brand like meade or celestron from Dubai for example? What to do?

[Sandraj]

Hi and welcome, have you looked at Amazon uk to see if they will ship to you, I am sure I read a post where someone had one shipped to India.

[brantuk]

Hi Rami - I just had a look at that website and they do list Celestron and Meade scopes there - maybe they are an importer or distributor? I would pay them a visit and see what they have got in stock. If you can't find anything that matches your requirements, or they can't order stuff in for you - then it's a great excuse for a trip to Dubai.

[michael.h.f.wilkinson]

Welcome to SGL Rami,

Most likely, these telescopes are rebadged Chinese-made telescopes. The certainly look like many of the Synta, GSO, etc scopes and mounts. The simple equatorial mount listed is an EQ2 or clone, The goto mount is a Skywatcher EQ5. The latter could carry an 8" reflector, especially their 8" F=800 which is short, for visual. The top alt-az mount is the same as a GSO alt-az mount, and the bottom right is a Teleoptic giro mount. They need not be better or worse than similar offerings from Celestron or Skywatcher. If you can check them out an have a look through them you could get a better idea. If you like what you see, go for it. If you have the option to import, and it gives you more confidence in the product, that might be better for you. The eyepieces shown are fairly basic, but the Plossls should be OK for starters. If you get hooked in the hobby you can always upgrade them. If you go for the 8" F=800, I would avoid the 80° ones on offer, because an F/4 scope needs quality EPs, especially in the wide-angle and ultra-wide-angle range.

Hope this helps

[Rami7]

Wow, thank you all for your time. Michael you said I shouldn't go for 80 degrees? I don't know what that is? Could you please tell me what are the specifications of a good 8 inch reflector? Focal length should be around what ? And what is this degree thing?

Thank you so much.

[michael.h.f.wilkinson]

Wow, thank you all for your time. Michael you said I shouldn't go for 80 degrees? I don't know what that is? Could you please tell me what are the specifications of a good 8 inch reflector? Focal length should be around what ? And what is this degree thing?

Thank you so much.

The website lists a series of eyepieces with an 80 degree apparent field of view (AFOV: the apparent diameter of the circle you see through the telescope). The wider this is, the more difficult it is to correct all the optical problems.

Plossl eyepieces listed on the site are decent performers, with a 50 degree AFOV. At short focal lengths, they do become more difficult to use for people with glasses, because you need to put your eye close to the eyepiece in these designs.

I spotted an 8" F=800mm scope on the site which is similar (or identical) to the GSO 8" F/4 sold elsewhere. The focal length itself tells me nothing about the quality, it tells me more about the field of view. Typically for reflectors, shorter focal lengths are slightly worse for planets, because the little diagonal mirror at the front needs to be larger. They are better for wide field objects, however. At a longer focal length (F=1200 is common at 8", yielding a focal ratio (focal length divided by aperture) of F/6), the field of view become a bit narrower, and planetary performance a (tiny) bit better. At F=1600mm (F/8) the performance on planets is better still, at the expense of a smaller field of view, and very long tube length, which requires a sturdier mount. Scopes with low focal ratio (like the F/4) need to be collimated (i.e. the optics must be correctly aligned) with more precision than the F/8 telescope.

Another important difference is that the smaller the focal ratio the more difficult it is to correct for optical aberrations (errors) in the eyepiece. My F/10 Schmidt Cassegrain is quite tolerant for cheap eyepieces, but the kids' F/4.3 Newtonian is not.

Hope this helps

[wolfpaw]

The website lists a series of eyepieces with an 80 degree apparent field of view (AFOV: the apparent diameter of the circle you see through the telescope). The wider this is, the more difficult it is to correct all the optical problems.

Plossl eyepieces listed on the site are decent performers, with a 50 degree AFOV. At short focal lengths, they do become more difficult to use for people with glasses, because you need to put your eye close to the eyepiece in these designs.

I spotted an 8" F=800mm scope on the site which is similar (or identical) to the GSO 8" F/4 sold elsewhere. The focal length itself tells me nothing about the quality, it tells me more about the field of view. Typically for reflectors, shorter focal lengths are slightly worse for planets, because the little diagonal mirror at the front needs to be larger. They are better for wide field objects, however. At a longer focal length (F=1200 is common at 8", yielding a focal ratio (focal length divided by aperture) of F/6), the field of view become a bit narrower, and planetary performance a (tiny) bit better. At F=1600mm (F/8) the performance on planets is better still, at the expense of a smaller field of view, and very long tube length, which requires a sturdier mount. Scopes with low focal ratio (like the F/4) need to be collimated (i.e. the optics must be correctly aligned) with more precision than the F/8 telescope.

Another important difference is that the smaller the focal ratio the more difficult it is to correct for optical aberrations (errors) in the eyepiece. My F/10 Schmidt Cassegrain is quite tolerant for cheap eyepieces, but the kids' F/4.3 Newtonian is not.

Hope this helps

And it goes without saying that a focal ratio of f/4 will be very hard on eyepieces and will almost certainly require a coma corrector if Rami isn't to experience some serious aberration.

He'd be better off trying get an 8'' f/6 (200/1200) telescope and forget the ones with short focal ratios, especially something as low as f/4.

(And welcome to SGL Rami!)

[Rami7]

I would like to thank you all for welcoming me into your community it feels good ! And Michael, I can't thank you enough for your time and effort and the detailed replies. Now, what I understood is that I should look for a 200 - 1200 mm reflector and I shouldn't even consider anything under 1000mm focal length. I do wear glasses so thanks for the valuable advice. Please feel free to suggest any other type of telescope as I'm open to anything. I'm a bit concerned about the corrections and alignments you mentioned !

The point is I'm open to anything, my main aim is to get the best possible resolution with let's say maximum 500/600$.

So if I'm going in the wrong direction by choosing the 200mm reflector please tell me.

If I don't hear from you then I'll proceed with the plan as it is!

[michael.h.f.wilkinson]

If you go for a 8" F/6 (f=1200mm) scope, you should perhaps consider buying one on a Dobsonian mount. This is the cheapest option, and the ones from Skywatcher are very popular as a first scope. You cannot go wrong with them. They usualy come with 25mm and 10mm eyepieces. The 25mm is generally OK, but the 10mm is difficult for those who need to keep on their glasses when observing. This is necessary only if you have some form of astigmatism (like the cylindrical astigmatism I have). If your glasses have simple positive or negative lenses you can take them off while observing, and correct for your eyesight just by refocusing. If you want to replace your 10mm by something suitable for people who observe with glasses I suggest you try the different "planetary" eyepieces. These have long eye relief (long distance between EP and optimal position of the eye). Teleskop-Service has a series referred to has HR-planetary, others are sold as TMB Planetary clones.  A 10 and 6mm would complement the 25mm nicely. The 6mm would give 200x which is very good for planets, the 10 is a good intermediate one for many deep sky object at 120x, and the 25x covers wider objects nicely (48x), just over 1 degree of the sky).

[AlexB67]

Not that there is anything wrong with the short focal length telescopes , you just may find that the view on the outer edges through an eyepiece are not as good as near the centre and this will be noticeable, and as already said with cheaper eyepieces this will be even more pronounced problem. Also the 203mm aperture scopes on that site at f/4 the optics become more difficult to align accurately and stay in alignment ( collimation ), so you need to buy a good collimator, not too expensive, but it can be done.

Ideally I would look around for one of the chinese made telescopes in your price range like the 1200/203 f/5.9 skywatcher Dobsonian if you want to start with visual observing and have look around if that is an option as something you can buy, like this one as sold in the UK

 http://www.firstlightoptics.com/dobsonians/skywatcher-skyliner-200p-dobsonian.html

I had a god look at the site and you could always ask them, they seem to have a customer service. It does seem slightly strange  why they are selling that specific selection of reflector telescopes to me as the only option.  I would say they are not ideal starter models with those specifications.

edit: Oops Michael already said much of it and beat me to it.

[AlexB67]

and welcome to SGL  by the way

[Qualia]

Rami, apart from the good advice above, it may be a good idea to contact one of the star gazing groups in Egpyt. They may be able to offer you some advice on what to do, where to purchase and you may even get a chance to go along and have a peek through their own gear. I know it is comercially run but these guys might be able to help: Space Tours. The reviews about them seem very positive, so they're probably going to be a group of sound gentlemen who more than likely will give a helping pointer.

[wolfpaw]

Not that there is anything wrong with the short focal length telescopes , you just may find that the view on the outer edges through an eyepiece are not as good as near the centre and this will be noticeable, and as already said with cheaper eyepieces this will be even more pronounced problem. Also the 203mm aperture scopes on that site at f/4 the optics become more difficult to align accurately and stay in alignment ( collimation ), so you need to buy a good collimator, not too expensive, but it can be done.

Ideally I would look around for one of the chinese made telescopes in your price range like the 1200/203 f/5.9 skywatcher Dobsonian if you want to start with visual observing and have look around if that is an option as something you can buy, like this one as sold in the UK

 http://www.firstlightoptics.com/dobsonians/skywatcher-skyliner-200p-dobsonian.html

I had a god look at the site and you could always ask them, they seem to have a customer service. It does seem slightly strange  why they are selling that specific selection of reflector telescopes to me as the only option.  I would say they are not ideal starter models with those specifications.

edit: Oops Michael already said much of it and beat me to it.

Sorry Alex, but I thought we'd put this 'edge of field' nonsense to bed in the other thread where it was decided that aberration across over half of the field of view in a fast Newtonian was entirely normal and to be expected. I apologise for keep banging on about it but people buying anything below f/5 should be told what they can expect to see and not be fobbed off with stuff about 'edge of field' aberration when the truth is somewhat different.

Rami - if you want a largish Newtonian reflector try and get an 8'' f/6 200/1200 Dobsonian telescope. Anything larger will become a money pit.

[Rami7]

Thank you all, another thing ! The images on YouTube surprisingly show the 6 inch reflector's pics sharper than the 8inch in general. Is that possible? When I put it together with what you said earlier about the focal length it does make sense actually! In that case would a 6 inch reflector be the better choice for me or did I get it wrong?

Qualia, thanks for the advice I've tried contacting the manufacturer in Egypt but they gave me very short and not at all helpful replies. They seem to be unprofessional and not trustworthy, while here I found very experienced people and quite helpful. However I'll try to contact someone else in Egypt for a practical advice as where to buy the scope but was hoping to get decided on what to buy first.

Thank you again, hope I'm not being a pain with all the questions !

Rami

[Rami7]

Ok , I understand now the 8inch is in fact much better, I've just had a look at the link with the skywatcher as advised

[michael.h.f.wilkinson]

Sorry Alex, but I thought we'd put this 'edge of field' nonsense to bed in the other thread where it was decided that aberration across over half of the field of view in a fast Newtonian was entirely normal and to be expected. I apologise for keep banging on about it but people buying anything below f/5 should be told what they can expect to see and not be fobbed off with stuff about 'edge of field' aberration when the truth is somewhat different.

Rami - if you want a largish Newtonian reflector try and get an 8'' f/6 200/1200 Dobsonian telescope. Anything larger will become a money pit.

A Newtonian at any focal ratio has coma which is to be expected. As so often it gets worse in scopes with lower F-ratio (as most aberrations do). This is an optical aberration affecting the edge of the FOV more than anything. The astigmatism introduced by will exacerbate the problem at the edges of the field of view. A coma corrector (mentioned above) can sort the coma out, but not the astigmatism produced by cheaper EPs in scopes of F/5 or below. Astigmatism depends much more steeply on the angle of incidence of rays than coma does, and will therefore affect the edge of the field of view more than any other part. There is of course a steady increase of aberrations from the centre to the edge, but the edge is affected most.

[wolfpaw]

A Newtonian at any focal ratio has coma which is to be expected. As so often it gets worse in scopes with lower F-ratio (as most aberrations do). This is an optical aberration affecting the edge of the FOV more than anything. The astigmatism introduced by will exacerbate the problem at the edges of the field of view. A coma corrector (mentioned above) can sort the coma out, but not the astigmatism produced by cheaper EPs in scopes of F/5 or below. Astigmatism depends much more steeply on the angle of incidence of rays than coma does, and will therefore affect the edge of the field of view more than any other part. There is of course a steady increase of aberrations from the centre to the edge, but the edge is affected most.

I wouldn't call 50% of the field of view the 'edge' but I suppose we all have our different definitions.

[AlexB67]

To be fair, you can't generalise with 50% either, the amount of visible coma in a narrow FOV eyepiece will be noticeably less.  A decent quality TV plossl  with 50 degree FOV or a vixen with long eye relief would still work well in scopes in the f4.5 - f5 range to a degree of satisfaction for many, without having to break the bank and not splash out on a coma corrector and get too annoyed by the amount of coma for visual use, Depends how you look at it, is the glass half full or half empty for what you get in return for what you spend I'd say. 

In the end each to their own what they find acceptable or not.  If in doubt, as Qualia said contact some of these people, if there is some club or facility to go to  to look through some scopes that is often recommended and would be a good move if Rami has any doubt .   I agree though I'd think twice about buying a scope at f/4 though in that price range and aperture. For the bigger scopes where height becomes an issue and there is no option, but not in the range Rami is thinking about buying.

Rami, Good luck with the purchase   

[Rami7]

Thank you wolf paw and thank you Alex!

[RikM]

I wouldn't call 50% of the field of view the 'edge' but I suppose we all have our different definitions.

This depends very much on the focal length and apparent field of view of the eyepiece. Yes, at 28mm and 68° in my 254/1200 I can see noticeable coma over the outer 30%+ but it doesn't bother that much and at 10mm and 70° aFOV it is not noticeable at all.

Any way you look at it, a 200/1200 Skyliner (or similar) Dobsonian represents very good value for money.

[Rami7]

Please check this out and if possible give me your feedback ,I've found a storming Dubai where I can ask someone to buy it and ship it to me .. Tell me which one would be best for me or if they are of any good, Michael I've tried to pick one similar to the one you've showed me but this one is possible to get as the UK website won't ship to Egypt.

1- http://dubaitelescope.com/index.php?main_page=product_info&cPath=146_156&products_id=40

2- http://dubaitelescope.com/index.php?main_page=product_info&products_id=175

Thank you again,

Rami

[AlexB67]

Further to Rick's point, the nice thing about the 8 inch 1200/203 Dobsonian is that lot of  eyepieces  in the sort of  50 pounds range UK money and above will work well in it, show less pronounced eyepiece aberrations like astigmatism, and visible coma will be reduced quite a bit, even the lower wider angle eyepieces mag eyepieces with 60 - 70 degrees will work well without seeing too much coma. 

If you want to get a bit of insight into how all this works out here is a nice nontechnical overview of what you may expect to see.

http://www.umich.edu/~lowbrows/reflections/2007/dscobel.27.html

[AlexB67]

Please check this out and if possible give me your feedback ,I've found a storming Dubai where I can ask someone to buy it and ship it to me .. Tell me which one would be best for me or if they are of any good, Michael I've tried to pick one similar to the one you've showed me but this one is possible to get as the UK website won't ship to Egypt.

1- http://dubaitelescope.com/index.php?main_page=product_info&cPath=146_156&products_id=40

2- http://dubaitelescope.com/index.php?main_page=product_info&products_id=175

Thank you again,

Rami

Yes, they are the models we mentioned. Whether you want to go for a collapsible model or not is your choice, handy for transport. I love mine as it fits in a car more easily.  Both of these scopes in fact carry the same optics, the rest is some details about the mount and other build differences, but their performance will be on par.

[wolfpaw]

To be fair, you can't generalise with 50% either, the amount of visible coma in a narrow FOV eyepiece will be noticeably less.  A decent quality TV plossl  with 50 degree FOV or a vixen with long eye relief would still work well in scopes in the f4.5 - f5 range to a degree of satisfaction for many, without having to break the bank and not splash out on a coma corrector and get too annoyed by the amount of coma for visual use, Depends how you look at it, is the glass half full or half empty for what you get in return for what you spend I'd say. 

In the end each to their own what they find acceptable or not.  If in doubt, as Qualia said contact some of these people, if there is some club or facility to go to  to look through some scopes that is often recommended and would be a good move if Rami has any doubt .   I agree though I'd think twice about buying a scope at f/4 though in that price range and aperture. For the bigger scopes where height becomes an issue and there is no option, but not in the range Rami is thinking about buying.

Rami, Good luck with the purchase   

Perhaps so, but many people get a 10'' f/4.7 Newtonian for DSOs and to find DSOs it helps to have a wide-angle eyepiece around 24mm or 28mm (or whatever). What a shame then when those same wide-angle eyepieces only have around 50% clarity within the field of view because of the coma in the f/4.7. Sort of contradicts the reasons for having both the wide-angle eyepiece and the telescope itself.

[Rami7]

Ok so to avoid that coma problem should I go for the 150mm / 1200mm dos then instead of the 200mm / 1200mm ? Or will I miss on a lot and regret not going for the bigger aperture?