Help me decide on my First Scope

[Nitin]

Firstly, Thank you so much for creating such a huge knowledge base here, for beginners (like me) to follow.
 
Here are 2 options that fit my budget (~10,000 Rs):
 
1. Sky Watcher 114/900 EQ1 (http://www.tejraj.com/reflectors-sk1149.html)
- Better eyepieces (super-plossl)
- Can verify this model on other sites. This confirms parabolic primary mirror.
 
2. Sky Watcher 127/900 EQ1 (http://www.tejraj.com/skywatcher-127eq.html)
- Comparatively large aperture 
- Kellner eyepieces (not good, but 3 of them)
- Can't verify this model on other sites. Mirror could be spherical.
- Tube length is 870 mm (< 900mm FL). Can this be Bird-Jones design ?
 
3. Anything else on http://www.tejraj.com thats within my budget.

Please advice.

[baggywrinkle]

Welcome to SGL.

Beware of those magnifications offered. A good rule of thumb is max mag under good seeing = 2 x apeture in mm.

So the max mag on the 127 would be around 250x not the 675 cliamed with the 3x barlow.

The lighter the OTA for these mounts the better, they are not over substantial so I would say the 114mm would be the better option.

I checked the Skywatcher website and could not see a 127mm reflector, 130 yes.

http://skywatcher.com/products.php?cat=4

[Schorhr]

I have a "Sky" 130/900, it was later sold as 125mm and afaik it has a spherical mirror. At around 120mm it will reach a Strehl of closely 0.8 IIRC, so  it still is a nice Budget telescope; the worst case would be to stop it down to 114mm and depending on the edges of the 114 probably it would Show a equal or better image.

The Main Problem is the eq1 Mount. Even on an eq2 or astro3 I find the 900mm tubes shake way too much, especially when magnifying higher.

If you can Get a (spherical) 114/900, 130/900 or a 130/650 (parabolized!) for a Good price, build a dobsonian Mount for it (€5, wood planks, laminate flooring, furniture glider pads, nut, bolt, screws...).

I see they also have diy kits and mirrors... Could be another option using plumbing pipe or similar

Or you save up for a 8" (200mm) dobsonian - or get a used one. That telescope will show a lot more if you aim for deep sky and could last you a life time ;-)

Sadly the 114/500 from national geographic probably is not so well suited (aperture ratio - will show some blur outside the center field of view with cheap eyepieces; Coma - longish stars in the outer field; only suited for higher magnifications if the mirror is not parabolized well; low but ideal to put on a table, a box, wall...) but the mount is stable and the telescope itself is very portable.

Any other shops there or used market?

[Nitin]

Welcome to SGL.

Beware of those magnifications offered. A good rule of thumb is max mag under good seeing = 2 x apeture in mm.

So the max mag on the 127 would be around 250x not the 675 cliamed with the 3x barlow.

The lighter the OTA for these mounts the better, they are not over substantial so I would say the 114mm would be the better option.

I checked the Skywatcher website and could not see a 127mm reflector, 130 yes.

http://skywatcher.com/products.php?cat=4

I will try to stabilize the mount with weights (sand bucket trick), EQ1 is all I can afford for now.

Coming back to mag, for 114 reflector, I can go up to 225x maybe. Will that be able to show me some faint image of Saturn/Jupiter ?

[Schorhr]

A 114mm telescope can Show you a small Saturn and if the conditions are good (if the planet higher up, clear air, good seeing) the Cassini division. Go check out http://stargazerslounge.com/topic/196278-what-can-i-expect-to-see/

The weak mount will make it very hard to keep Saturn centered at high magnification, lots of shaking is anoying and limits the amount you can see!

Consider building a dobsonian rockerbox, it's not difficult and more stable. http://www.ringohr.de/tmp6//rockerbox_einfach.jpg

http://www.ringohr.de/tmp6//dob_fachw9a_1b.png

Beware of cheap eyepieces such as 4mm Plössl, they have a narrow eye relief and difficult to view through. Plössl under 10mm in General.

Barlows reduce contrast further, at least Get an achromatic barlow If you choose that Route.

[Nitin]

I have a "Sky" 130/900, it was later sold as 125mm and afaik it has a spherical mirror. At around 120mm it will reach a Strehl of closely 0.8 IIRC, so  it still is a nice Budget telescope; the worst case would be to stop it down to 114mm and depending on the edges of the 114 probably it would Show a equal or better image.

The Main Problem is the eq1 Mount. Even on an eq2 or astro3 I find the 900mm tubes shake way too much, especially when magnifying higher.

If you can Get a (spherical) 114/900, 130/900 or a 130/650 (parabolized!) for a Good price, build a dobsonian Mount for it (€5, wood planks, laminate flooring, furniture glider pads, nut, bolt, screws...).

I see they also have diy kits and mirrors... Could be another option using plumbing pipe or similar

Or you save up for a 8" (200mm) dobsonian - or get a used one. That telescope will show a lot more if you aim for deep sky and could last you a life time ;-)

Sadly the 114/500 from national geographic probably is not so well suited (aperture ratio - will show some blur outside the center field of view with cheap eyepieces; Coma - longish stars in the outer field; only suited for higher magnifications if the mirror is not parabolized well; low but ideal to put on a table, a box, wall...) but the mount is stable and the telescope itself is very portable.

Any other shops there or used market?

No used market, and other retailers selling this same 114/900 telescope at ~12,500.

Major problem with this retailer is trust. Many reviewers have complained that they received mirrors with scratches/damages and are not addressing returns.

That is why I am going for the items they are re-selling, not manufacturing.

114/900 has a parabolic mirror, and I can try stabilize the mount with weight. Later if time permits, can build a Dobs mount too.

[Schorhr]

Never trust advertisement promises

AFAIK most 76 700 and 114 900 do not need a parabolic mirror and are still difraction limited due to the long focal length. Cheap 130/650 and bird Jones designs have problems due to the fact that most entry level scopes out there are not parabolized. Bird Jones are much shorter then their focal length, if the tube is just slightly shorter, that's due to the setup of a newtonian (secondary mirror redirecting optical path sideways).

too bad that there are no other vendors there.

I checked shipping from Germany, would not be too cheap (starting at around 40€ to ship 6kg) but perhaps teleskop-express can make you a good offer?

A Heritage 130p would be over your budget but still affordable. Or you can ask the sellers here @ eBay, there are companies selling 125/900 without mount at 59€ or another sells a 114/900 on eq1 @75€ but shipping probably ruins the cheaper price.

I have calculated intl. Shipping for a smaller 76mm dobsonian before, but I guess that would be to small for you

Perhaps ask your local shop if they can order a 130p?

[Nitin]

Thanks a lot Marcus (Schorhr) and baggywrinkle for your suggestions. I think I am going the Do-It-Yourself way with the rockerbox design shared above.

Here is the link for new question on (150-F/??)

http://stargazerslounge.com/topic/221365-building-my-first-telescope/#entry2380104

[Schorhr]

 Good luck The above design is for smaller telescopes, 130/900 worked fine though, so I guess a 6" version could work. It's the cheapest solution as I have to build 8 or so. If you need further info, let me know. I also posted in your new thread.

How much for the 150mm mirror?

Did you ask the local vendors if they can source a 130/650 (Heritage, Explorer 130p?)?

[Nitin]

Marcus, The Explorer 130 is ~33K here.

I believe the duty here in India is ~35% on the (purchase price + shipping cost + Insurance). And then retailer will add some profit on final number.

Anyways, I am following your post (that sketch for dob on new post) and some more online resources.

The mirror costs around 6.5K. overall cost may go ~12K but it will be more fun...

Its monsoon season here, cloudless nights are atleast 2 months away. Ample time to finalize, start and then finish the work.

[Schorhr]

Yes, a DIY project can be fun, but be aware that a DIY telescope as first telescope is a complex task, even if you use hardware piping and such :-)

I have built mine as cheaply as I could and as easy as possible  (to build it with students) using

-24x48mm wood / roof battens
-laminate flooring scraps
-felt glider pads
-M6 or M8 bolt, washers, nut
-pipe socket plug 100/110mm or (stable/grooved cans) -> Larger for a 6"
-3.5x45mm (drywall) self-drilling, fine-thread screws
http://ringohr.de/tmp6/76dob1b_1.jpg

The screws are a great time saver: No wood splitting, no pre-drilling the wood.
http://www.globalsources.com/gsol/I/Self-drilling-screw/p/sm/1078094761.htm#1078094761

At ebay they where really cheap, in the hardware store they cost a lot more.

If you care here are sketches of my prototype, but be aware that this is all for the 76/700 or   114-130/900

http://ringohr.de/tmp6/dob_sch.png http://ringohr.de/tmp6/dob_sch3.png

http://ringohr.de/tmp6/dob_sch2.png

http://www.ringohr.de/tmp6//dob_fachw9a_1.png

http://www.ringohr.de/tmp6/dob_fachw9a_1b2.png

http://www.ringohr.de/tmp6//v4___222tubes.png

http://www.ringohr.de/tmp6//v4_76-700-newDesign.png

http://www.ringohr.de/tmp6//dob_fachw3test-pl.png

Base size and height must be changed for a larger telescope of course.

Of course you can use boards or such, any type of wood you can souce cheaply or free.

I like cheap DIY, and you would be amazed how low budget you can go ( http://www.ringohr.de/tmp6/YesWeCAN004.jpg , hehe)

But be aware that there are so many bits and things you will have to construct, that you may end up with more then saving for the pre-build dobsonian.

Teflon gliders and ebony star / kitchen counter plate would work much better...

Or google for pipe mount if you want a more stationary set up.

Regarding the telescope tube I have posted a link to a german board with lots of images on how it could be done. 

Focuser-> A lamp screw focuser or a film can slider can work

I was unable to find a english page, but the images on the german forum may give you the idea. 

http://www.astrotreff.de/topic.asp?ARCHIVE=true&TOPIC_ID=88004

http://www.astrotreff.de/topic.asp?ARCHIVE=true&TOPIC_ID=35835

Else you could source a cheap toy telescope and use it for parts.

Finder scope->Seben finder costs 8€ or so, but you could construct a iron sight, get a gun finder scope from china for 3€, or build one out of $1 reading glasses and a magnifying glass even.

Mirror cell

I've read about people using bubble wrap. :-) Or silicone glue dots. The mirror must sit in the mirror cell without tension and the mirror must be adjustable.

Secondary mirror

I have had the idea of modding a $2 tripod ball camera mount, but there are other possibilities there...  

Is the secondary mirror included in the kit at the site you have posted?

The tax and duty is high, wow.

If you want to experiment a bit, you may be able to source a astromedia telescope kit with a 70mm mirror for €15-20, it's a fun cardboard kit but you can build it with hard tubes too, and evaluate if it's the right choice to make one DIY. 

[Nitin]

Your scope looks awesome. Better in existing form compared to sketch of the design update.

For mount and other calculations, I am following this link http://www.scopemaking.net/dobson/dobson.htm

It has same PVC socket/cap on teflon gliders for Alt-Bearing.

But for Azimuth, I am considering cheap rotating cake stand (like this http://www.wilton.com/store/images/site_images/415-900_m.jpg)

My father gets them custom built for his bakery, they have bearings. Can change rotation smoothness and has locking mechanism. supports ~10KG

This is the retailer site for purchasing the parts http://www.astroviewtelescope.com/

AVM series is the mirror, buying 150 fl 1200 from that list.

AVMC is mirror cell, not buying this. Building from above scopemaking tutorial.

AVDE is elliptic secondary, buying 32 mm from that.

AVSPD is spider holder for secondary. buying curved one for 200mm tube. The one shown in scopemaking tutorial looks dangerous where the spider can fall on primary.

Focuser (simple & Advanced) I am not sure. Planning to visit him next month and see the quality.

Finder 6x25 is the cheapest I can find anywhere. Can't be worse than a red-dot finder. I am short sighted, can't use red-dot one.

EPs and barlow, will have to search some more on those.

[Schorhr]

I have no idea how stable that cake plate is, but I have seen smaller scopes on TV turn tables. Didn't work for me, too weak.

Also, gliding solutions have proofed to work well, as the initial force needs to be high on some bearing solutions thus making it difficult to move the telescope smoothly at high magnifications. But some dobsonians are even sold with bearings, so it can work. The big bonus of friction/gliders is that it is dirt cheap and easy to build.

The build / instructions look good, my design is much simpler and for smaller OTA :-) But you know, whatever you have lying around is the best material :-)

Personally a red dot finder is better, but if you observe without glasses, a finder scope might work better (if it is adjustable to compensate).

But at the beginning you could just build a tube to aim. Or get a cheap toy binocular at the dolar store for parts.

A lamp socket focuser is easy and works for 1.25" eyepieces. Of course 2" eyepieces are great as they can show a larger field with 30-40mm eyepieces, but those would probanly be over your budget unless you buy a kit such as surplusshed (USA) offers.

I am sure you can find some cheap eyepieces, else let me know!

The Seben are dirt cheap, work well, and international shipping under 1 kg is very afforadble over here. Plus I am sure you have some sort of tax free value there too? OR ask the telescope shop if they have cheap used eyepieces, perhaps even telescopes with dents or broken parts, you may be able to source a mirror cheap this way.

what does the 6" mirror cost now?

I wish you the best of luck with your project!