confused and need help choosing telescope

[angelus316]

Hi,i need help in choosing one of the following for terrestrial as well as sky viewing

celestron firstscope 90EQ 90mm x 1000mm refractor or

AOE maksutov cassegrain 105mm x 1400 mm

thanks in advance for the help

[74tuc]

If I were choosing one of these 'scopes I would choose the AOE Maksutov because it is a physically smaller 'scope - both these 'scopes are intended for astronomy and will perform poorly in the terrestrial setting.

Both of these 'scopes have a "longish" focal length and will support magnifications upto about x180 which means the mount and tripod must be quite stable. The "firstscope", being a refractor (longer and more bulky) needs a better mount than the Maksutov and the mounts in both these 'scopes look like they have the same capability. The Mak would be easier to use.

The the long focal length (F# 13) of the Mak' means that it will be a high magnification 'scope with the Firstscope being not far behind. For terrestrial viewing a magnification of about x10 to x30 is a useable range and neither of these 'scopes will do this. Heat haze limits greatly the useable magnifications and the refractor will show a great deal of colour fringing at high mags.

I looked at AOE's web site and noticed that AOE 100mm Mak appears to have a more tobust mount than the 90mm. Perhape you may want to consider the 100mm if the price is right!!

Regards,

Jerry,

[angelus316]

hi,Jerry.
thanks for looking into it for me,yes i forgot to put in the details for everyone so here goes-

1- celestron firstscope 90EQ
OPTICAL DESIGN Refractor
APERTURE 90 mm (3.54 in)
FOCAL LENGTH 1000 mm (39.37 in)
FOCAL RATIO 11.11
FINDERSCOPE StarPointer
MOUNT Equatorial, w/Quick release
EYEPIECE 1 20 mm (0.79 in)
EYEPIECE 2 10 mm (0.39 in)
STAR DIAGONAL 1.25 Erect Image
ACCESSORY TRAY Round, Thread-in
TUBE RING One piece w/quick-release
PIGGY BACK ADAPTER Yes
TRIPOD QE1
HIGHEST USEFUL MAGNIFICATION 213 x
LIMITING STELLAR MAGNITUDE 12.3
RESOLUTION 1.54 arc seconds
RESOLVING POWER1.29 arc seconds
PHOTOGRAPHIC RESOLUTION 180 line/mm
LIGHT GATHERING POWER 165 x
ANGULAR FIELD OF VIEW 0.8 °
LINEAR FIELD OF VIEW 42 ft (12.8 m)
OPTICAL COATINGS Multi-Coated



2 - AOE 105m

Optical design

Maksutov Cassegrain

Aperture, mm

105

Focal length, mm

1400

Focal ratio

F=14

Resolving power

1.2"

Limiting magnitude

12.5m

Magnification, max

250x

Finderscope

8x21 Erect image

Mount and tripod

EQ2 German-Equatorial, adjustable aluminium field tripod

[ving (David)]

of the 2 i'd go the mak for extra aperture and it'll be more conpact for easier transport. the mounts for both of these arent very stable tho.

but i tell ya what, whats your budget? maybe we can hunt down something even better

[74tuc]

Re: What will I see?

1. More stars than you can "shake a stick at".

But seriously a 4" 'scope will show you quite a bit:

- All messier objects (visible from here) - the guy who first catalogued these only had a 1/2" 'scope.

- Some of the brighter galaxies (eg. NGC 253)
- Some of the brighter nebulae (eg. M41)
- Star clusters (eg. 47 Tuc - Omega Centauri may be a little too large to see all of it) - Collinder star clusters are interesting (eg. "Tuft of the Dog's Tail")
- Have some fun splitting double stars
- Have a go at comets

2. Planets:
(Best observed with a cheap WebCam and Registax)

- Need high magnification - can be disappointing.

1. Mercury - Worth a look to say youv'e seen it.
2. Venus - Bland and featureless but it displays phases like the moon.
3. Earth - very boring.
4. Mars - good target but moving away from us at a great rate of knots.
5. Jupiter - Excellent - don't know about the not so great red spot.
6. Saturn - Excellent - But get in before its rings look edge on!
7. Neptune - Looks like a bright dot.
8. Uranus - Looks like a dot.
9. Pluto (demoted) - Forget it!! (Mag 14)

3. Moon - Keep you occupied for a long long time.

A couple of tips:

Join the Astronomical Association of South Australia - Great bunch of people, excellent advice and superb facilities.

If you buy the Mak ask Raf to replace the finder with a good "Red dot finder" - IMHO Red dot finders are the best thing since sliced bread.

Coffee time.

Regards,

Jerry.
Get a Planisphere and a star chart program (eg. Starcalc ... freeware)

[angelus316]

hi i can get the celestron for 310 and the mak for 315.
my budget including postage is about 370

[ving (David)]

i wonder if thats almost enough for a 150mm dob...

yup, over at www.andrewscom.com.au you can get a 150mm dobsonian reflector for $349 plus postage. 150mm of aperture will stomp all over 105mm

the scope is a guan sheng gs580. go have a look and see if you like it
dont be put off by the mount, dobs are way easier to operate than an eqatorial mount for beginners

[acropolite (Phil)]

Difficuly call, seeing the object is to use the scope for both terrestrial and astro viewing. I would be looking at something with a shorter focal length. As Jerry said on hot days 20-30 magnification will be about all that is useable and with a focal length of 1400mm the mak is not suitable. Something around the 600mm focal length will perform both tasks but Ving's suggestion is the go, a 6 inch dob is a very useful aperture and you will see and enjoy your astro viewing much more. Lee Andrews usually packages a cheap set of Binoculars free with each Scope, I would suggest that you negotiate to pay just a little extra and get a pair of 10x50 binoculars for your terrestrial viewing requirements.

[angelus316]

i just want to say thanx to everyone who replied.
i have e-mail lee andrews about the dobs and if it fails i'll go for the mak.
just one question though, how much better would i view planets with the 6 inch dobs compared to the 105mm mak.
thanks again for all the help guys and gals.

[acropolite (Phil)]

how much better would i view planets with the 6 inch dobs compared to the 105mm mak.

The difference on faint objects would be significant, I have an 80mm refractor and an 200mm SCT, the jewel box cluster in the 80mm looks sparse and almost lifeless, in the 20mm its colourful and full of stars. The 150mm dob will have approximately double the light gathering capacity of the 105mm Mak.

[iceman (Mike)]

The dob isn't for terrestrial use - just be aware of that. Things will be upside down!

So as Phil said, get a pair of binos for your bird-watching etc.