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  #1  
Old 13-04-2017, 09:39 PM
AussieBill (Bill)
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Aiming a small telescope ? Any tips

Hello,

I have problems aiming my 76 / 350 National Geographic Dobson telescope.

Particularly on objects high in the sky, I try to look along the edge of the tube to "line it up" on the target and then I still have to do some random wobbling around looking for the target. Am using 20mm eyepiece - I have a 20mm and a 4mm and a 2x Barlow.

Any hints or previous threads I can look at, or is it simply practice ?

I know that some people have used these small 76/350 dobsons as spotting scopes on their bigger scopes so they must be able to aim them fairly easily.

Bill
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Old 14-04-2017, 01:34 AM
Wavytone
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Well ...

Those scopes are so small I'd pick it up, tuck it under one arm and use like binoculars and sweep the sky to find things. With practice you'll get the hang of it.

The old mechanical solution was an equatorial mount with setting circles, on the basis you knew how to accurately align it with the South Pole and set the ra circle to read correctly. From there you find the position of objects from an atlas and dial them up, if you get it right. Few manage to do it this way. It's a fair challenge and impossible for some.

The optical options are:
- a simple sight consisting of a small ring at the top of the OTA and a dot or dimple at the back, line your eye up on these;
- finderscope, possibly a 90 degree one;
- red dot finder,
- telrad or similar.

Electronic solutions:
- encoders and software working as "push to"
- GOTO mount.
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Old 14-04-2017, 02:15 PM
N1 (Mirko)
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Hi Bill, I had one of these for a while.
The answer is practice.
The second option could be as simple as "iron sights" , bluetacked onto the tube. That will be accurate enough for finding stuff. I saw one made out of lego, bloody brilliant.
The 20mm is too short for pleasing, steady views as a handheld monocular. Mine worked OK that way with a 32mm Plössl.
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Old 14-04-2017, 02:27 PM
N1 (Mirko)
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Hi Bill, I had one of these for a while.
The answer is practice.
The second option could be as simple as "iron sights" , bluetacked onto the tube. That will be accurate enough for finding stuff. I saw one made out of lego, bloody brilliant.
The 20mm is too short for pleasing, steady views as a handheld monocular. Mine worked OK that way with a 32mm Plössl.
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Old 14-04-2017, 03:59 PM
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dannat (Daniel)
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buy a cheap red dot finder off ebay & stick or screwit on
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Old 14-04-2017, 10:36 PM
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barx1963 (Malcolm)
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If you really want to use it, if you have a camera tripod, remove the tube from the dobsonian mount and see if you can rig up a way to mount on a tripod. Then get a red dot finder and that will help a lot.
I bought the version o this that was being sold as a "solar" scope a while back and it is tripod mounted and is sort of useable. The dobsonian mountings are simply too lightweight to be effective.
If have used mine to get quite a few objects, but I have the advantage of having done a lot of star hopping over the years.

Malcolm
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Old 15-04-2017, 12:21 PM
AussieBill (Bill)
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Thganks for all the suggestions

I had no idea that red dot finders might be so cheap so for $10 Aus. thats worth a try.

Tucking it under my arm sounds interesting and will also have a go with the camera tripod - should be able to mackle something together.

Bill
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Old 18-04-2017, 06:38 AM
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sil (Steve)
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Before dodging up a tripod mount turn the whole thing over and you might find the existing mount has a threaded hole already to mount to a camera tripod a similiar tabletop dob I have has this feature. Aiming is problematic and a red dot finder could work but since you cant lock the position of the scope its not a usable solution I dont feel. You'll just keep bumping it all out of position and using a red dot finder to put a target in the eyepiece is difficult enough on a good setup anyway without some hunting around.

Perhaps you're expecting too much for the cheapest entry level scope. You really should get yourself a star map (pocket book or app) and learn how to navigate the stars or "star hop" which is still a skill you need with a large computerised telescope. Astronomy is not a 30 second hobby, takes time and patience.
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Old 22-04-2017, 02:05 AM
AEAJR (Ed)
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I don't know that scope but something like a RDF can help a lot. But you can even tape on a small tube, maybe a roll from the bathroom as a first approximation. Tape it on and get it aligned so that when you have something centered in the eyepiece it is centered in the tube. Remember you align the finder to the scope, not the other way around.


Daytime Activity

Spend time during the day getting the finder aligned with the scope. Read the manual. Use a distant target. 100 feet is way too close. 1/2 KM away minimum. I like to use phone or power poles and target in on the cross arm.

How to align a finder scope
https://www.youtube.com/watch?v=r3zGgrY7sK8



Test the scope with each eyepiece. Focus on distant things. Get used to the fact that the image is inverted. Figure out how to move around with that reversed image. Do this during the day.

Find a branch or a bird or something that has lots of detail. Use your target tube/RDF/Finder scope, then low power then high power to see how much detail you can get. If you have a barlow, use it to get closer.

Notice how well the image is in the center vs. the edge. There may be some loss of sharpness at the edge. A little, or only the outer 10% is fine. If you start to lose significant sharpness during the day any more than that then there might be a collimation issue or some other issue. A lot depends on the type of eyepieces you are using.


(Eyepiece Designs - This is the one I turn to when I am trying to understand or explain the differences between the various designs.
http://www.chuckhawks.com/common_eyepiece_designs.htm)


Take note of the difference in field of view between your eyepieces.

Move from one target to another and get used to finding and refocusing.



Finding and tracking during the day

A very very high jet is perfect. A bird will be too fast.

Use your finder scope to get that Jet in the FOV. Now, using the longer FL, higher number, eyepiece try to pick it up in the eyepiece. You might have to lead it a bit to account for moving from the finder to the eyepiece. Let it fly into the FOV. This will also test how well your finder and your eyepiece are aligned.

Now track that jet with the low power eyepiece. How much detail can you see? How long does it stay in view?

Now do the same with the high power, shorter FL eyepiece. Note it will be a little harder to keep it centered as the FOV is now much smaller. Stars and planets move slower than that jet so they will be easier to track.



All of this will be valuable training for the night time. These are the same skills you will need but they will feel easier during the day. When it is dark you will already be used to doing these things.
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Old 04-05-2017, 06:29 PM
AussieBill (Bill)
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Red dot finder arrived - TERRIFIC !!

Hey,

The RDF arrived - a $10 cheapie - what a terrific gadget .............. whoever invented that deserves a beer. Set it up on some small bushes approx 1klm away. Have not tried tracking jets yet.

Yes I do need to grow some starhopping skills - only doing big easy ones right now - used Scorpio to find Saturn last night .............. only Mars left out of the easy planets now.

Wasn't able to recognise Aquarius at all last night but was able to hop up from Jupiter and saw some flashes in the approximate area of the expected meteors.

So Scorpio and Orion and Southern Cross and False Cross are all easy enough but I reckon some of those other patterns are very difficult to see. Will keep trying.

........ and thanks again for all the advice. The RDF is great.

Bill
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Old 05-05-2017, 03:10 AM
astro744
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Quote:
Originally Posted by AussieBill View Post
Hey,

The RDF arrived - a $10 cheapie - what a terrific gadget .............. whoever invented that deserves a beer. Set it up on some small bushes approx 1klm away. Have not tried tracking jets yet.

Yes I do need to grow some starhopping skills - only doing big easy ones right now - used Scorpio to find Saturn last night .............. only Mars left out of the easy planets now.

Wasn't able to recognise Aquarius at all last night but was able to hop up from Jupiter and saw some flashes in the approximate area of the expected meteors.

So Scorpio and Orion and Southern Cross and False Cross are all easy enough but I reckon some of those other patterns are very difficult to see. Will keep trying.

........ and thanks again for all the advice. The RDF is great.

Bill
Yes RDFs are great! Whether they are a simple red dot, Telrad, Starbeam or other they are a valuable tool for pointing your telescope.

You mention Aquarius but it is rising in the east well before dawn before Venus which is in the early morning sky at the moment. Jupiter is in the evening sky in the east near a bright star called Spica which is in Virgo. By the way it's Scorpius not Scorpio, the latter used by astrologers.

Scorpius can be used to get to Saturn which is just over the border in Sagittarius at the present time. In fact Saturn is near the Lagoon and Trifid nebulae at present. These are located in the 'steam' coming out of the 'spout' of the 'teapot' which is often used to describe the constellation of Sagittarius. Eastward of Sagittarius is Capricornus (not Capricorn) and then Aquarius. I always see Capricornus as a big Star Trek insignia.

Get yourself a good star chart like any Tirion's offering or Stellarium for PC (free) or app (small charge) and you will soon learn the sky and how it changes throughout the night and throughout the year. Note every star rises about four minutes earlier each day so in a month that's two hours earlier. What is rising at 2am now will be rising at midnight in a month and 8pm in three months from now. You can observe almost the entire year's worth of sky on a long winter night except for the part the Sun is in and the twilight band either side of the Sun.

Enjoy you 'scope and have fun navigating and star hopping!
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  #12  
Old 11-05-2017, 04:30 AM
AEAJR (Ed)
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Quote:
Originally Posted by AussieBill View Post
Hey,

The RDF arrived - a $10 cheapie - what a terrific gadget .............. whoever invented that deserves a beer. Set it up on some small bushes approx 1klm away. Have not tried tracking jets yet.

Yes I do need to grow some starhopping skills - only doing big easy ones right now - used Scorpio to find Saturn last night .............. only Mars left out of the easy planets now.

Wasn't able to recognize Aquarius at all last night but was able to hop up from Jupiter and saw some flashes in the approximate area of the expected meteors.

So Scorpio and Orion and Southern Cross and False Cross are all easy enough but I reckon some of those other patterns are very difficult to see. Will keep trying.

........ and thanks again for all the advice. The RDF is great.

Bill
STAR HOPPING

Star hopping 101 – Video play list
https://www.youtube.com/view_play_li...B0AD5D29A76981

Star hopping guide
http://www.nightskyinfo.com/star-hopping/

Star Hopping Tutorial
http://astrobob.areavoices.com/2013/...ed-from-stars/
http://www.daviddarling.info/encyclo...Andromeda.html

FINDER CHARTS – Star Hopping guides and log pages
Various lists
http://astronomylogs.com/pages/chart...r%20Charts.pdf
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  #13  
Old 22-05-2017, 12:33 PM
AussieBill (Bill)
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Thanks Ed

Appreciate the links Ed, Thankyou.

Will have a look tonight - been busy on non-astronomy boring stuff lately and havent logged in for a while.

Bill
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