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caheaton
super member
Reged: 05/26/09
Posts: 138
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Hello, I'm contemplating the purchase of an ETX80 or ETX90 and am undecided on which to purchase. I intend to use it for both visual observing and casual imaging (afocal attached to lens, probably with either an Olympus SP565 or Canon SD1100...the former is fairly heavy at 10 ounces, the latter very compact and light). I understand the limitations of both scopes in regards to aperture, chromatic aberration (ETX80), etc. I currently have an old Tasco 4.25" and even it seems too much to lug about, hence my desire for compact. Price is also an important factor. My basic questions are this: will both these scopes handle the weight of the cameras (perhaps I will add some weight at the top of the tube to balance) and most importantly...which will provide the brigther image for my camera..the 80 with its lower F ratio or the 90 with its greater aperture and better optics?
Craig
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Arthur Dent
Galactic Hitch-Hiker
Reged: 10/23/08
Posts: 1150
Loc: South Yorkshire, UK
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Hi there Craig!
Welcome to Cloudy Nights and the ETX forum in particular.
Well, my first response would be to say "aperture is king" so go for the '90 if your budget can stretch (or even a 125 if you look at the second-hand market).
However, you ask about an ETX for imaging.
The mount that the ETX has (an Altitude / Azimuth or Alt-Az) is NOT really suitable for imaging - unless you are looking to image the Moon and the brighter planets.
The Alt-Az mount is only really suitable for SHORT exposures. Anything longer than about 30 seconds will introduce "field rotation", and the only way around this is to polar align the telescope and drive the telescope in only one direction (Right Ascension). The Meade field tripod has a built-in wedge to facilitate this.
If you plan on taking images of Deep Sky Objects (or DSO's for short), then an Alt-Az mount is not really suitable for this purpose. The gearing inside the ETX mount is also really not up to the job.
To get great astroimages, then a stable equitorial mount (known as a GEM) IS A MUST. These are polar aligned and have more expensive (and precise) metal worm gearing.
Cheap scopes with a stable mount will out-perform more expensive scopes on poor mounts.
You also need to think about WHAT is doing the imaging. Most folks think that a DSLR is the way to go, but many people use webcams (often suitably modified for long exposures) and then stack many, many images using suitable software to improve the S/N ratio.
You can, of course, get decent images of the Moon and brighter planets using a digital compact camera but again, several frames that have been stacked, along with suitable "flats" (that is all over white frames) and "darks" (that is all over black frames) will improve matters dramatically
Art
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If I like it, the wife says that we can't afford it!
=======================================================
Meade ETX105 (a nice "Grab & Go" scope) & Celestron NexStar 6SE with Bob's Knobs.
Various EP's from 6mm to 26mm, a 2x Barlow, 2" diagonal and 7Ah PowerTank.
MRF and Antares 8x50 RACI finder scope - both for the 6SE's OTA, whilst the ETX gets a plain RDF.
Canon EOS 400D DSLR (un-modded) and SPC900 webcam. Finally climbing the AP Learning Curve!
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caheaton
super member
Reged: 05/26/09
Posts: 138
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Thanks for the quick reply, Art. That agrees with my research...but for fairly short exposures (under 30 seconds), the tracking appears to be adequate. That's why I'm concerned about image brightness.
Also, you stole my avatar! In other forums to which I subscribe, I've always used good old Charlie Brown. Looks like I'll have to find a different one for this forum. :-)
Craig
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Arthur Dent
Galactic Hitch-Hiker
Reged: 10/23/08
Posts: 1150
Loc: South Yorkshire, UK
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No problem Craig
I use Charlie Brown as an avatar because when I look in the mirror, I see CB staring back!
BTW, are you aware of the Mighty ETX Website - run by Mike Weasner?
Link here.
As far as the weight issue goes, the ETX mount will handle a DSLR attached to the rear camera port.
I'll post a photo for you of my ETX with Canon 400D DSLR attached.
Art
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If I like it, the wife says that we can't afford it!
=======================================================
Meade ETX105 (a nice "Grab & Go" scope) & Celestron NexStar 6SE with Bob's Knobs.
Various EP's from 6mm to 26mm, a 2x Barlow, 2" diagonal and 7Ah PowerTank.
MRF and Antares 8x50 RACI finder scope - both for the 6SE's OTA, whilst the ETX gets a plain RDF.
Canon EOS 400D DSLR (un-modded) and SPC900 webcam. Finally climbing the AP Learning Curve!
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Arthur Dent
Galactic Hitch-Hiker
Reged: 10/23/08
Posts: 1150
Loc: South Yorkshire, UK
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Here you go Craig.
I wouldn't worry about attaching a digital compact like the Canon SD1100 (IXUS 80). The mount would probably also handle the Olympus SP565.
Art
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If I like it, the wife says that we can't afford it!
=======================================================
Meade ETX105 (a nice "Grab & Go" scope) & Celestron NexStar 6SE with Bob's Knobs.
Various EP's from 6mm to 26mm, a 2x Barlow, 2" diagonal and 7Ah PowerTank.
MRF and Antares 8x50 RACI finder scope - both for the 6SE's OTA, whilst the ETX gets a plain RDF.
Canon EOS 400D DSLR (un-modded) and SPC900 webcam. Finally climbing the AP Learning Curve!
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rmollise
Post Laureate
Reged: 07/06/07
Posts: 4491
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Quote:
Hi there Craig!
The mount that the ETX has (an Altitude / Azimuth or Alt-Az) is NOT really suitable for imaging - unless you are looking to image the Moon and the brighter planets.
While I certainly wouldn't recommend an ETX for long exposure imaging, people have gotten some nice results. More to the point, the mount CAN BE SET UP IN EQUATORIAL mode. The tripod used on the MCT ETXes includes a built-in wedge which can be used to polar align the scope.
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Uncle Rod
Rod's New Book:
Choosing and Using a New CAT
Available now!
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jgraham
Postmaster
Reged: 12/02/04
Posts: 6695
Loc: Dayton, Ohio
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The ETX-80 will certainly be more forgiving because of it's shorter focal length and wider field of view, but the 90 is such a nice scope I think it would be worth the extra effort. If you were only interested in wide field imaging with light visual observing I might consider the 80, but for a more balanced mix of visual and imaging I'd consider the 90. I think you'll find the 90 is particularly well suited for lunar and planetary imaging where the targets are bright, they'll take full advantage of the 90's excellent optics, and the tracking issue isn't as important.
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-John
================================================
Homebuilt scopes from 4.25-16.5"
Meade LXD75-N6/SN6/SC8, DSX-90, ETX-60BB, ETX-125PE, DS-2130
Orion StarBlast, BinoViewers, Coronado PST
Rebel XT/XTi, DSI Pro (I, II, & III), DSI, LPI, Electronic Eyepiece, Phillips SPC900NC
Tasco 60mm Refractors
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Domerman
What have I done?
Reged: 07/21/07
Posts: 942
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ETX 80 and 90 are completely different scopes (80 being a short wide field refractor and 90 being a long focal length mak-cass). ETX 80 would be much easier for wide field imaging and be more forgiving with tracking error given the focal length, however, alot of CA will be apparent in the image. The etx 90 will require very long exposures given the f/13.8 f-ratio for DSO imaging and really it is not very possible for a complete beginner to obtain a nice image of a DSO with this scope. Also, a large DSLR will likely not be fully illuminated by the small secondary of the scope, thus leading to significant vignetting. I'm sure planetary imaging would be suitable for the ETX 90, but you would need to buy a modded webcam because a DSLR would likely not suffice.
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~Steve
My Astro-Photo Blog: http://absurduniverse.blogspot.com/
Mounts
BUSTED CGEM w/Dual ADM Vixen/Losmady Saddle and ADM SBS
Scopes
Astronomy Technologies 6" f/9 Ritchey-Chrétien
Orion 80ED w/MoonLite Focuser
Orion ST80 (Guide Scope)
Cameras
QHY8 w/IDAS LPS filter
DSI-C (Auto-Guider)
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caheaton
super member
Reged: 05/26/09
Posts: 138
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Thank you to all for the advice...I decided to go ahead and order the ETX-80 anyway...the more I thought about it, the more I realized that visual use will be what I do most (better then 90%), and that I would really like a scope that I could bring with me when I travel. This scope fills that niche. Later, I'll acquire a larger scope to replace my old Tasco. (Leaning towards a 10" Dobs, but don't tell my wife. :-) ). Thanks again...
Craig
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AlexDJ30
sage
Reged: 09/02/08
Posts: 267
Loc: Monterrey, Mexico
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If your wife knows you enter cloudynights she already read that of the 10 dob idea...she said thats OK , you can buy one but she wants to remodel a new backyard for your house!
hahaha LOL
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Equipment:
- ETX 125 AT
- C6 ASGT
- WO 66mm SD
- 2.5X ED Barlow, 8-24mm Zoom Eyepice
- Canon EOS Rebel XSi
- Celestron Nextimagen
- Orion Starshoot CCD cam
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