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Improved ST80 Review

Posted by Patrick O'Neil   10/17/2007 00:00:AM

Improved ST80 Review
By: Patrick O’Neil

The following is a review of the Orion Short Tube f/5 Astronomy achromatic refractor which I improved upon.

My observing experience- I have observed for the past 11 years, mostly using “department store” 50mm and 60mm telescopes, which I made improvements on. I am currently a full-time student pursuing a degree in mathematics and physics. I have a good basic understanding of optics that I have learned on my own.

My location is Carlsbad, New Mexico USA. Light pollution is not a major problem here. The seeing and transparency are usually average. From my yard I can see stars of about 4.5 to 5th magnitude near the zenith on a clear Moonless night.

I currently own four telescopes:
· Celestron C80ED (FPL-53 doublet) f/7.5 APO Refractor
· Orion 4.5” Starblast Reflector
· Orion Apex 127 Maksutov-Cassegrain
· Orion ST80 Achromatic Refractor

Why a ST80?

I bought this telescope because I like to observe immediately and do not want to mess with collimation all the time. I am the type of person that believes my telescopes must be in “near perfect collimation” at all times. I believe that it’s not just aperture that counts, it’s also what you do with that light after it is gathered. I like to collimate an instrument once and then don’t mess with it anymore.

No long cool down times and transportable are the other two BIG reasons I chose this telescope. I like to view a wide range of objects every time I observe. I wanted a lightweight, simple to use and to improve on refractor.
I also especially enjoy wide field viewing of the Milky Way, but did not want to purchase Naglers to view it (too expensive right now). This telescope has a wide field of view that allows for easy finding of targets with just simple plossls (4°FOV with a 32mm plossl!). These are the reasons for my purchase.

The telescope and the stuff that came with it:

· Optical tube assembly
· 20mm Expanse
· 9mm Expanse
· 90° Mirror star diagonal, 1.25”
· 8x40 Finder scope
· Finder scope bracket with O-ring
· Dovetail tube ring mounting plate
· Tube Rings
· Tube ring mounting hardware screws
· Objective lens cap
· Soft carry case
· Hex key (5mm)


Objective lens: Achromatic doublet, air-spaced
Objective lens coatings: Fully multi-coated
Aperture: 80mm
Focal length: 400mm
Focuser: Rack-and-pinion, 1.25’, accepts camera T-ring
OTA length: 15”
Optical tube weight: 3lbs. 7oz.

Initial impressions:

I received my ST80-A on May 28, 2007. The OTA struck me as sturdy, yet lightweight and short. The build quality is surprisingly pretty good. The OTA was somewhat flocked and has a single knife-edge light baffle about midway down the tube. This version of the ST80 comes with a dew shield that is metal and the optics are fully multi-coated instead of just fully coated. IMO I doubt the latter improvement has much bearing in real world observing, but it is nice to know that Orion is improving the scope.

The focuser works well once the grease is replaced with something of a lighter weight. The plastic focusing knobs look cheap, but do their job. I ended up replacing mine with some metal wheels.

This is really a pretty darn good star diagonal, definitely not junk. I keep this one around and still use it with my scopes from time to time. I did upgrade to an Orion 1.25” dielectric 99% reflectivity diagonal (#8880) which Orion tells me has a accuracy of 1/10th light wave.

These were OK. Too much field curvature for me, though. I ended up selling them because the plössls I already had were sharper and showed fewer aberrations. The Expanses do give wide FOVs, but in this scope IMO basic good plössl beat them where sharpness and contrast are concerned.

Tube rings and hardware:
These do a good job and mounted up nicely to my EQ-1 mount.

Lens cap:
This cap has about a 43mm stop on the cap that can be removed. This turns the focal length from f/5 to f/9.3. I find this feature nice when casually viewing the Moon. The longer focal length significantly reduces the chromatic aberration and the 43mm of aperture do not blind you when the Moon is full.

Finder and bracket:
This mounts to the OTA very easily and quickly if you choose to use it. The 8x40 finder has good coatings and shows no reflections like a lot of cheaper finders I have used. This finder splits Albireo. Nice.

Soft carry case:
This is nice to have to put the OTA and accessories in. I find this especially useful when going to a dark site to observe, very handy.

Modified Orion ST80 f/5:
Below are the modifications that I have made to the telescope.

· OTA inside textured with AT LEAST 5 layers of flat black spray paint.
· Objective lens edges darkened.
· Objective lens custom hand figured.
· Focuser grease cleaned and replaced with lightweight lubricant.
· Focuser metal wheels (replace plastic one) added.
· Dew Shield flocked with AT LEAST 5 layers of flat black spray paint.
· Orion #8880 dielectric star diagonal.
· Custom collimation of OTA.

After all this work and improvements here is what can now be seen with the ST80-A

Moon and planet performance with improved ST80-A:

The full Moon can be viewed with NO chromatic aberration with a 32mm (12.5x) and a 26mm (17x) plossl. A 17mm plossl begins to show a thin colorful ring around the lunar limb, but the images are still very sharp. At 40x with a 10mm plössl CA becomes apparent; however, at around 133x on up the CA seems to vanish substantially. Perhaps due to the Barlow extending the focal ratio?
CA does appear on the lunar limb, but it does not “bleed” in craters or detail. In fact the Moon is portrayed nicely against a dark background at low power and even more so at around 133x on up. I find powers between 80x to 133x reveal the most detail on the Moon with this telescope. I have run the telescope up to 170x on a few occasions. The image holds, but no additional detail could be seen.

At 80x and above I have seen several moon shadow transits, both poles, the GRS many times, and the main cloud banding.

At 80x and above I see darkening on the planet. The planet shows a nice disc.

Open Star Clusters, Associations, and Asterisms with improved ST80-A:

This is the area that this ST80 reigns king. I get a 4° FOV with just a plain old 4-element 32mm plössl. How many telescopes can do that without breaking the bank?

Pleiades Asterism:
On a dark night the stars of M45 do in fact appear like “diamonds on velvet.” This is just an amazing, breathtaking view with a 17mm plössl.

The Double Cluster:
NGC 884 and NGC 869 reveal many colorful stars and appear in the same FOV with a 17mm plössl (23.5x).

Persei Association:
Mirfak and multitudes of colorful jewels are present in the same FOV with a 32 (12.5x) or 26mm (17x) plössl. One could spend hours on this association of stars with this telescope.

Stock 2:
Is a magnificent sight in this scope with either a 26mm or 17mm plössl.

Shows many stars with a 17mm plössl. The object fits nicely in the same FOV.

Coathanger Asterism:
Looks like what it is called with a 17mm plössl.

A 17mm plössl works wonders in this simple setup on clusters like M6, M7, NGC 6231, and Cr 316. Wow, these objects are just awesome! Be careful to not fall out of your chair when you see them in this wide-field telescope. The view is that good.

Deep Sky Performance

OK, everyone knows that a 80mm telescope is just a 80mm telescope. So, what can you possibly see with that? Well, if your telescope has excellent contrast, is properly collimated, uses a good diagonal, and a simple eyepiece design—well, then a lot can be seen for a telescope of this size.

Globulars, Nebulas, and Galaxies:

This globular shows only the brighter outer most stars being resolved at power of 80x and up. The entire object is bright.

Resolves many stars at 80x w/ direct vision.
Looks good in this telescope because it is a bright and “loose” globular. A power of 80x on up to around 133x reveals many stars with direct vision with more to be seen using averted vision.

Begins to show stars at 80x with direct and averted vision. Any power over 133x dims the view too much IMO. On a good clear dark night a wealth of detail does present itself with this object.

NGC 6144:
Is also visible and fairly bright in this telescope at 40x using a 10mm plössl. This globular is closer to Antares than M4.

Orion Nebula:
M42 shows the trapezium at only 23.5x with a 17mm plössl. A 6mm Expanse at 67x makes the “wings” pop into view with lots of nebulosity seen.

Shows the “dumbbell” shape nicely with a 6mm Expanse.

The “doughnut” shape is easily seen without a filter on a Moonless night. This telescope also reveals the nearby 13th magnitude star with slight averted vision and high power.

This spiral galaxy shows its core readily with a 6mm Expanse. Other than that, not much else is apparent, but hey - you can see it.

M51 and NGC 5195:
Can see the cores of these galaxies with direct vision and with averted vision more structure is observable. The two cores appear connected using a 6mm Expanse.

M81 and M82:
Are of course visible. A 6mm Expanse reveals their galactic structures (spiral and edge-on). More detail is visible at 80x and up depending on the night.

Easily fits in the same FOV along with M32 and M110 when viewed at low powers. A dust lane is visible with averted vision using a 6mm Expanse on a dark night.
Takes magnification well and shows a bright core. This galaxy reminds me of some globulars with its appearance.

M110 (NGC205):
Is a dimmer galaxy that orbits the Andromeda Galaxy. This shows well with a 6mm Expanse and even reveals its shape.

Shows up well using a 17mm plössl or 6mm Expanse. I have not tried to push the magnification on this galaxy, so I don’t know if it would help seeing more detail.

Double Stars:

Epsilon Lyrae (Double-Double):
These stars split using a 6mm Expanse at 67x. Clearly elongates at 40x using a 10mm plössl.

Beta Lyrae:
Looks good at 12.5x with a 32mm plössl.

This double looks good at any power.

Splits at 80x using a 10mm plössl and 2x Barlow. Looks better at 133x or 170x with a 6mm Expanse and 2x Barlow or a 4.7mm Meade and 2x Barlow. Primary shows yellow/orange. Companion shows a light blue.

This star elongates clearly at 133x and 170x. This telescope could probably split this star on a steady night.

Delta Hercules:
This star shows well at 133x with the dim companion showing blue with direct vision. The primary is a bright orange/yellow.

Presents itself well in this telescope. Had one of the best views of this star when using this telescope at 1:30 in the morning. I viewed it at 170x. The primary appears Orange/yellow, and the companion appears deep sea blue in color.

Have split this star with only 23.5x in this telescope, but I prefer a power of about 40x to 80x. Primary is a creamy white. The companion is a dim blue.

Eta Cassiopeia:
Same powers as Polaris. Primary looks yellow/orange. Companion looks orange/red in this telescope.

Alula Australis:
This star splits at 170x in this telescope. I use the 4.7mm Meade UWA and a 2x Barlow. At this power to my eye they look a yellow/greenish color.

Delta Cygni:
The ST80 splits this star at 170x. The primary appears a whitish shade at this power. The companion appears as a dim purplish dot fading in and out of the first diffraction ring of the primary.

What I have learned:

1. A Moon filter “kills” CA on the Moon, no matter what phase.
2. I can see everything with the stock star diagonal that I can see with the 1/10th wave dielectric diagonal; however, the views look sharper and have more contrast with the dielectric.
3. A good quality 17mm plössl works awesome with this telescope on open clusters and give a 2.2° FOV.
4. A good quality 32mm plössl gives a 4° FOV.
5. A 6mm Expanse does well on most DSOs.
6. A Barlow of good quality is needed to fully enjoy this telescope.

What I use with my ST80-A:

· 32mm Orion Highlight Plössl
· 26mm Orion Highlight Plössl
· 17mm Orion Highlight Plössl
· 10mm Orion Highlight Plössl
· 6mm Orion Expanse
· 4.7mm Meade 4000series UWA
· 2x Orion Barlow Shorty Plus (3-element)
· Orion Moon filter
· Celestron UHC filter
· Stock 1.25” diagonal
· Orion 1/10th wave 99% dielectric diagonal


Quick, Easy, No Frequent Collimation, No Long Cool Down Times. Did I Mention Wide Fields of View?

CA on the Moon without filter, Not A Light Bucket.


I hope that you liked this review and found it informative. Even with out all the mods this telescope performs well, especially for the price. Clear Skies and Dark Nights.

Click here for more about this subject. -Ed.