80mm acromat, f5.0, home built alt-az mount
The Orion ST-80 is a typical, low cost, scope manufactured by Synta in China. It is the same optical tube as the Celestron Wide Field 80 and is also marketed by a couple other companies.
Hey, itís my camping scope, let the moose knock it over. However, it does have fairly good optics and is a lot of fun for slowly scanning large areas of the sky. Besides, no matter what other equipment you have, you need something you can grab and look at an object NOW. Rarely have to allow any cool down time.
Optically, these scopes are remarkably good. They don't compare to a premium scope, but for a low cost, quick look, scope I donít think they can be beat. Images are fairly sharp. Being a fast (f 5.0, f/l 400mm) scope there is the expected violet fringe on bright objects, however, a good quality eyepiece helps. I have the Orion Minus Violet filter and it works wonders. Really bright stars still have a small halo, and everything has a color cast due to removing the violet/blue spectrums, but it is amazing.
There are several improvements to the earlier scopes that can be made - Orion recently released an upgraded version, hopefully these issues have been addressed:
1. Lose the provided erect image, 45 degree, diagonal. Can we say lousy? The one I got is barely usable for daytime use, let alone astronomy. Buy a decent 90 degree diagonal, I got Orionís premium mirror diagonal, which is very good.
2. The low cost eyepieces are marginal. If you have better eyepieces Ė use them. Otherwise, put a couple of decent eyepieces on your Christmas list.
3. Numerous internal improvements are also required:
As delivered, there is a definite spike in the stars. (All ST-80s Iíve seen suffer from this)
Cause Ė the screws in the focuser rack protrude into the light path.
Cure Ė grind them down flush with the inside of the focuser tube.
Cause Ė all the screws inside the optical tube are shiny. The inside of the focuser casting is shiny. Internal exposed draw tube and rack areas are chrome Ė super shiny!
Cure Ė flat black paint and a brush. Remove the screws holding the focuser assembly on.† Disassemble the focuser. Paint all non-painted areas, including the screws sticking into the optical tube, and the outside of the focuser draw tube. While things are apart, clean the glop they call grease out of the focuser. Lubricate with lightweight grease, I prefer lithium, it works well in the cold and doesnít melt out on warm days. Reassemble the scope and look in the front. See anything shiny? If so, take it back apart and go fix it.
Cause Ė poor manufacturing process, they get grease all over them!
Cure Ė slide off the dew shield, unscrew the retaining ring on the front of the objective cell (work over a soft surface) and remove the lenses. Pay attention to how they come out! If the two lenses stick together use a soft tool, such as a toothpick, carefully, on the edge to pop them apart. There are three small metal spacers around the edge to maintain the space between the lenses, donít lose them. Clean the glass per your favorite method Ė I prefer to let them soak in warm water with a LITTLE dish soap for a while. If they are really grimy, you may need to GENTLY wipe them with some clean tissues while under water, AFTER the chunks have soaked loose. Rinse with distilled water and allow to air dry. A black marker can be used to blacken the edges. There is considerable debate as to if this is any benefit on an objective lens, however, since you have it out, go ahead and do it. No harm, no foul. A little grease on the metal spacers will keep them in place between the lenses Ė be careful, a little bit can go a long ways here. Reinstall the glass in the cell and loosely tighten the retaining ring.
What the heck, why is everything really distorted???
Cause - you didn't assemble the front cell correctly. Don't feel bad, I've done this too.
Cure - Neither of the two pieces of glass are symmetrical. Look closely and reassemble them like the exaggerated drawing here.
Collimation is all screwed up
Cause Ė Duh! You just took it all apart, what did you expect?
Cure Ė Align it! Do not ever crank the objective retaining ring down tight! If your stars are triangle shaped, loosen the ring. Itís okay for the lens to have a slight rattle. Loosen the screws holding the focus assembly and wiggle back and forth until you get better star images. Tighten the screws. Loosen the screws holding the objective cell. Same thing, wiggle until better, then tighten. Go back and forth until you are happy with the image. It only takes a couple iterations and about 10 minutes. If you have any collimation tools go ahead and use them, but this scope is so short itís a breeze to do it the old fashioned way.
After completing the above modifications, my ST-80 is no longer the dog it was. The sky is now deep, dark and black, instead of a vague milky haze. Stars focus to a pinpoint. Planets actually do have some detail. It still isnít an APO, but itís closer than before. I have a Televue TV-60is and it blows the ST-80 away, however the ST-80 still gets a lot of use for wide field scanning when the Televue is tied up imaging.
And just to prove you can image with this scope : M-8 taken Jul 2005 from a very dark site.
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