What to ask?

[jet486]

Earlier I placed a question in relation to buying a 12" Dob. Now not wishing to appear a complete novice/idiot what should I need to know and more importantly what should I ask the salesman at Bintel before purchase? Please help.Cheers

[raymo]

If you have any interest at all in doing photography with your Dob,
ask the salesman if you can take shots at prime focus with the scope
he's trying to sell you. Many Dobs will not come to prime focus.[Skywatcher ones do]. Some buyers have been caught out by this, not
interested in photography at the time of purchase, but change their minds later, only to find that their scope is not suitable.
raymo

[Steffen]

The good thing about the salesmen at Bintel is that they are fellow amateur astronomers and will not pull the wool over your eyes. You can go in there unprepared and ask any questions that pop into your head

Cheers
Steffen.

[Allan_L (Allan)]

Originally Posted by Steffen

The good thing about the salesmen at Bintel is that they are fellow amateur astronomers and will not pull the wool over your eyes. You can go in there unprepared and ask any questions that pop into your head

Or even ask them, "Are there any questions I should be asking you...?"
That always gets them thinking !

I agree they are super helpful, and are considerate of us newbies.

[brian nordstrom (As avatar)]

Yes they are very good , dont be shy as the old saying goes like this ,, 'The only dumb question is the un-asked one'. Just DONT !! ask about 'ASTROLOGY' !! LOL . Brian.

[Renato1 (Renato)]

Reading the responses to this thread, leads me to ask a question, because I haven't kept up with things.

If one buys a 12' dob which can be used for prime focus photography, doesn't that mean that for the same focal length, the primary mirror has to be closer to the focuser, which in turn would mean that the secondary mirror has to be bigger, resulting in less contrast from that dob when viewing planets?

I figure that there would have to be a trade -off somewhere, or manufacturers would have been making dobs that could be used for photography years ago.
Cheers,
Renato

[julianh72 (Julian)]

Originally Posted by Renato1

If one buys a 12' dob ...

A 12-foot Dob - wow!

As Crocodile Dundee would say:
"That's not a telescope - THIS is a telescope!"

[Camelopardalis (Dunk)]

Also ask yourself how it feels to use... and how comfortable you are standing at it. You're going to spend a lot of the time at the eyepiece to get the most from it, you need to be at ease

[jet486]

Having no dealings with Bintel before, it appears that they have a very good understanding what people want and share the same interest in Astronomy. I didn't want to go and purchase my dob without some "before knowledge".

[Varangian (John)]

Originally Posted by jet486

Earlier I placed a question in relation to buying a 12" Dob. Now not wishing to appear a complete novice/idiot what should I need to know and more importantly what should I ask the salesman at Bintel before purchase? Please help.Cheers

Have them show you as much as they can about collimating the scope. What knobs do what and the sequence of events. No amount of internet browsing can ever replace an experienced person showing you how it is done face to face.

This will be the single most important thing you will have to do with your 12" Dobsonian after purchase and it is required relatively frequently.

[jet486]

Thanks John. I've read that I should have Bob's Knobs added and also different collimation tools.Firstly what are "Bob's Knobs" and what tool would you suggest for collimation a 12" dob?

[rrussell1962]

Ask about getting a Telrad, invaluable. Think about asking about getting Bob's knobs for both the primary and secondary mirrors. The set for the primary has stronger springs and the sets for both mirrors can be adjusted without tools, you will want to be able to do this eventually, so why not do it from the word go. If you are not confident swapping the collimation screws over yourself it may be worth asking if they will do it before delivery. I used one of those 12 inch dobs for a few years - with a great deal of pleasure, they are great out of the box but after a while I found myself thinking "what would make life a lot easier is...." Also ask if you can have a go at taking the OTA off the display model and lifting the OTA and base around the store, that will give you a good idea of how far you want to be moving the telescope and where would be a good place to store it.

[rrussell1962]

Apologies, should also have added a laser collimator is probably the easiest thing to use. Also be careful adjusting the secondary, the plastic can split if you over tighten the collimation screws, or possibly I am just clumsy. I ended up supergluing a machine washer in the back of the secondary holder to avoid stuffing t up a second time.

[Varangian (John)]

Originally Posted by jet486

Thanks John. I've read that I should have Bob's Knobs added and also different collimation tools.Firstly what are "Bob's Knobs" and what tool would you suggest for collimation a 12" dob?

http://www.bobsknobs.com/Newt/Newt.html

They are literally knobs that help streamline collimation and they can be applied to both the primary mirror and secondary mirror. At the back of the 12" GSO (Bintel) OTA (the tube) you will see 6 finger knobs that are used to collimate (adjust) the primary mirror. Bobs Knobs effectively replace these knobs with hardier more user friendly knobs. More importantly than the knobs however are the springs which are fitted on the thread of the knobs. These springs are really under-sized on the 12" GSO Dobsonian. You can also order heavier springs from Bob to replace the weak factory springs. Bob's springs help keep your primary mirror on the dobsonian better collimated as they are more rigid and not as susceptible to movement.

You can also replace the existing screws on the secondary mirror which I believe will be three screws with Philips Head screw driver fittings with three Bob's knobs which allow you to adjust the secondary mirror setting with your fingers (as opposed to have to put a screw driver there!)

I've attached a link to the site. I changed the primary knobs, secondary screws and primary springs on my Bintel Dob and it holds collimation so much better than it did with the factory knobs / springs. This means I don't have to collimate much or when I do it is usually just a little tweak.

The Bintel Dobsonian is a GSO brand so you'll need knobs/screws for a GSO telescope if you choose to buy them.

Hope this makes sense?

Cheers, John.

[CanberraChris (Chris)]

http://i.imgur.com/2UHILox.jpg

I am wondering what is the best resource for complete beginners, who only have a manual telescope mount. No GPS, no electrics. To find things in the sky.

[Logieberra (Logan)]

Originally Posted by CanberraChris

http://i.imgur.com/2UHILox.jpg

I am wondering what is the best resource for complete beginners, who only have a manual telescope mount. No GPS, no electrics. To find things in the sky.

Chris, if you're a smartphone kinda guy - you can't go wrong with SkySafari. Version 4 is the latest (beware the 'pro' version with all the bells and whistles, which you probably don't even need).

[Pinwheel (Doug)]

Being the owner of a Bintel BT-302-b 12" dob, you must be fit to own one. This is a 37.5kg outfit & the OTA is 20kg alone, You will move it about in 2 pieces & in the dark sometimes too. IT IS VERY BIG & HEAVY, It's like moving a hot water heater about!

Bintel are great people to deal with too BTW.

[raymo]

In answer to Renato's question, yes the secondary does have to be a little
larger, but the difference is minute, and the difference in contrast is
virtually undetectable. It still has a smaller central obstruction than
SCTs or Maks have, and my 150mm Mak has great contrast. I don't
think you'll see any lack of contrast in Jo's[ nebulosity] fine efforts.
A lot is made of this subject within the astro community, but it is really
only significant to the few people that want or need the absolute best,
often at great expense.If you get the chance, compare the view through
a Newt that will come to prime focus and one that won't. You'll be hard put to see a difference, assuming that both scopes have similar quality optics.
raymo