Are collapsible dobsonian telescopes reliable?

[trickybilly]

Hello everyone,

Tomorrow I'll go to buy my telescope. It is a "collapsible" ("Flex Tube") dobsonian (200/1200), f/6, central obst.:46mm. I'm a bit scared of the collapsible structure (stability?)...should I be?

P.S. Do I need to buy a tool for telescope collimation? Some Youtube videos show a tool for that...

I'm glad to have found a forum interested in amateur astronomy, best wishes all :)

[Allan_L]

Welcome to IceInSpace :welcome:
General answer to your question is YES, they are stable and reliable.
But some are easier to use than others.
Which brand are you considering?
Where are you located?
Our general advice is to try to see some operating in the field before committing.
Did you check out the For Sale classifieds forum here on IceInSpace?

Collimation,
Although not essential, a collimation tool is highly recommended.
Again a variety is available and it is best to talk to users before committing.

I have had two Skywatcher collapsible DOBs (one is currently for sale in the classified section here) and I have been very happy with their performance and how easy they are to transport and set up.

Hope you enjoy your new hobby, and feel free to ask many questions on this forum.

[trickybilly]

200/1200 Dobson Skywatcher FLEX
I'm from Serbia.

What brand do you recommend? Since I will spend my whole month salary on the telescope I'd like to learn collimation without a tool for now...
Thank you. Few questions:
What additional costs may emerge? I have read that telescope oil... how important is it? This is a big investment for me, any good advice on maintenance that'd allow long product life would be appreciated.

Thank you for the warm welcome and answer :)

[Allan_L]

Collimation:
I believe the Glatter laser collimator (and tublug) are regarded as among the best, but are very expensive.
Additionally, some people say a Cheshire Collimator is more accurate but not so easy to use in the dark (as it does not include a laser). They are also much cheaper.

I use a cheaper Orion laser collimator and check the fine tuning with a Chesire.

The AstroBaby Collimation Guide is my bible.
http://www.astro-baby.com/collimation/astro%20babys%20collimation%20guide .htm

Other Expenses:
You can start observing straight away without any further costs, but eventually you may like some of the following accessories:
A shroud is considered important by many to eliminate stray light (and foreign objects) entering the tube.
Bobs Knobs collimation screws for the secondary mirror (to avoid the risk of dropping an Allen key onto the primary mirror in the dark while collimating it.
A Red Dot Finder. I find the supplied finder scope is very good once you have the scope pointed in the general direction, but a RDF will help you get it pointed in the general area quicker.
Right Angled Finder scope. (I think the new models come with this included, by mine came with a "Straight through" finder scope which can be a pain in the neck after a while.
Dew Amelioration I don't know if this is a problem where you are, but if the mirrors dew up (as they do here often) it can be an early end to your observing session. Dew heater for secondary and maybe a dew shield cap (home made or commercial) may be in order.
Observing chair Allows comfort at the eyepiece, and steadiness, all of which allow more detail to be observed.
Finder guides Most deep sky objects will need a guide to find them. You pick some up free from some sites, or buy a book on how to locate them.
Stellarium is a free planetarium computer program that is a fantastic help to finding your way around.
http://www.stellarium.org/

I am sure others will suggest anything I have forgotten.

Most of all, enjoy :thumbsup:

PS: I am not aware of any uses of "telescope oil" for a flex-dob.
Most important maintenance tips:
keep the tube cover on when not in use.
keep the base dry (particle board swells when exposed to too much moisture)
keep caps on eyepieces when not in use.

[rustigsmed]

Hi and welcome!

Yes nothing wrong with flex tubes at all! I have a Sky watcher flex tube, goto. will yours have the goto motor drive?

the first two things i would buy is the bob's knobs collimation screws for the secondary mirror and a collimation tool. they just make life so much easier.

all the best

russ

[AG Hybrid]

As useful as bob's knobs and a shroud is. I would suggest a decent laser collimator as the first accessory. Accurate collimation is more important then ease of collimation if you have to make the choice.
Also, check to make sure the laser collimator is collimated itself. There is a tutorial somewhere here on Iceinspace to explain how that's done.

[goober]

As long as you understand Dobs are essentially kits, that you need to nuture, cool, collimate frequently, modify, and tweak, you'll be fine. :)

[raymo]

My 10" Skywatcher has given me great service for 4 yrs, and I have
been amazed at how well it it holds it's collimation. I demonstrated
this to a sceptical friend by collapsing and extending it, [locking and unlocking the 3 screws each time] 12 times, and when I finished the
collimator's laser beam was still within the doughnut on the primary mirror.[ The collimator was of course removed during the demonstration].
The scope was visually useable with no obvious deterioration in image
quality straight after the demo.It Holds collimation much better
than my friends 12" truss Dob. It must be because the extension
mechanism is so solid.
raymo

[Screwdriverone]

I had a 12" collapsible Skywatcher Dob and it was surprisingly good at keeping collimation.

I have a laser collimation tool which is very easy to use and helps get it spot on (pun intended).

Multiple collapses and extensions dont seem to affect it at all.

Very convenient telescope, I wouldn't be worried at all.

cheers

Chris

[barx1963]

For an 8" f6, really a cap will get collimation very close. I think the Astro baby site talks about them and really all you need is an old film canister (if you can find one these days).
Lasers are great BUT can be misleading, I have seen a lot of scopes badly out of whack but the laser shows all is correct.

From talking to owners of Skywatchers Flex Dobs, they are a really well made product.

Hope to hear some reports about how you get on.

Malcolm

[trickybilly]

Thank you for all the answers.

Bought said telescope, tried it out tonight. Problems:
1) Can't find a single star. I have found the moon once, it just plain brightness, cannot see any details on it from the brightness. (no lunar filter). Other than that: blackness everywhere.
2) Is this setup good -eyepiece holder-eyepiece adaptor-eyepiece (picture)
3) I have found a metal tool which is not mentioned in the manual (picture)
http://imageshack.com/a/img21/4333/ao61.jpg
Additional info:
1) Finderscope works 100% (moons and stars)
2) The secondary mirror sends the picture to me since I have removed the eyepiece holder/adaptor/eyepiece setup and looked directly into the telescope - saw the moon and the stars reflected from the secondary mirror. But when I put the pictured things on the telescope I cannot see anything.
3) Assembled according to: http://www.youtube.com/watch?v=Rcz0oLjiyHI (no info on optical setup). Read the manual.
4) No collimation after unboxing. The salesperson told me that this telescope won't need collimating for while.

Clouds came after 30 mins of observing... Hope for clear skies for my next attempt :)

[OzStarGazer]

Can you check if it is collimated yourself?

[omegacrux]

That metal tool is what holds your 1.25 ep , remove the 2in barrel at the back and fit the stepped 1.25 into the focuser , that tube on the back of the 1.25 is fitted when using 2in ep's

David

[Allan_L]

Yes, I agree with David.
Seem like almost everyone who buys one of these falls for that trap.
You have the 2" eyepiece holder AND the 1.25" eyepiece holder both loaded.

This makes your eyepiece too far away from the focus point.

Remove the 2" adapter.

Use the eyepiece with the higher number (probably 20mm or 25mm) for first sighting (it has less magnification and is easier to centre on stuff).

Then switch to the smaller number (probably 10mm or 12mm) for closer detail. Note that too much magnification will present a fuzzy view unless atmospheric seeing conditions are good.

Enjoy.

[Screwdriverone]

Yep, Allan and David have it spot on, remove the large barrel at the left of your photo and simply put the 1.25" adapter in the focuser, slot in the eyepiece and you are good to go.

Chris

[trickybilly]

I had a wonderful time observing the moon with the 25 and 10 mm eyepieces, thanks to your advice. A few remaining questions:
1)"That metal tool is what holds your 1.25" I cannot seem to find where to insert the metal thing...or figure out how to use it.
2) Is it safe to move the telescope by the two tension handles? (just a few meters to take it outside.). When should I use the handle on the front base board?

[Allan_L]

Q1
That metal tool is an Allen Key.
It has nothing to do with the eyepiece, and is only for maintenance.
I presume it is the allen key for adjusting the secondary mirror, when collimating. Don't try this until it needs collimation. (dropping the allen key down onto the primary mirror would be bad)

If you see Astro-baby's collimation guide, (link provided in my earlier post) you will see where the allen key can be used in altering the secondary mirror tilt by adjusting the three hex head bolts on the top of the secondary holder stalk (in Step 3).

Q2
Yes it is safe to move the telescope in total by using the tension handles (preferrably only short distances).
When moving longer distances, remove the scope from the mount and move separately.
The handle can be used to pick up the mount (like a briefcase) when the telescope is not attached.

Glad you enjoyed your first night out with it.
Keep it up.
And keep asking questions :thumbsup:

[raymo]

One rider on carrying the complete scope with the tensioning handles;
it's fine to do that, but make sure that you tighten them moderately;
if left loose the threaded part of the handle can bend. It is also fine to
carry the tube assy by one of the three tubes when the scope is extended ready for use, as long as the three locking screws are tightened.
raymo

[trickybilly]

Jupiter and it's moons were beautiful. But:
If I place Jupiter to the upmost part of my "viewing circle" it escapes at the bottom in just 5-10 seconds. I need to constantly hold (or gently push upward) with my hand the front part of the tube OR hold/gently push downward the back part otherwise the image escapes in just seconds. The tension handles and the 3 slider locking screws are tight. I understand that the image moves due to planetary movement, but is it ok that I need to hold the tube or else it disappears in 5 seconds (10 mm eyepiece)? Suggestions?

[Allan_L]

Yes it is OK to hold the tube.
Or one of the two knobs may be easier.

The rotation of the Earth, when you see the effects of it like this (under high magnification) it is an eye-opener isn't it!

That sounds pretty close to normal.

If you start to use heavy eyepieces, you may then need to add some weight to the base to help balance it out. Some people use magnet blocks.
I personally like to balance the scope before use, so that I can have the tension handles loose enough to keep nudging the scope easily and smoothly, to keep objects within the field of view.

It becomes second nature after a while.

[Screwdriverone]

The reason Jupiter moves so fast out of the field of view is not Jupiter's motion, but the Earth's motion.

We are whizzing around so fast that at high power you will struggle to keep the planet in the FOV for long, this is normal.

If your seeing conditions are good, then less power (higher numbered eyepiece) will keep it in view for longer and the image will be a little clearer, but you will probably not see as much detail.

One reason tracking and goto dobsonians are good value, they "hold" and track the object using sidereal (Earth rotation) motors to keep the sky synchronised to the movement of the Earth.

"Nudge, Nudge, Nudge" is the order of the day for any manual dobsonian user unfortunately.

Cheers

Chris