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dusty mirrors
member
Reged: 01/27/08
Posts: 20
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C-STAR! 525 POWER!! HUGE 2 1/2 INCH LENSES! ok, i know that this "telescope" isnt worth anything. it is rusty, the plastic is severely uv damaged, and i think it was left standing in the yard for several years. nevertheless i WILL repair it! if for no other reason than this...... i am now sitting on the couch watching a new remake of "invasion of the body snatchers" and i dont think that i have anything more to loose. SO.... upon scrubbing the objective like an old pot, i find the uncoated lenses in fairly good condition. the diagonal is dirty but doesnt seem to be damaged. i cleaned the objective cell, blacked the edges of the lenses and painted inside surfaces of the cell with krylon ultra flat black. it looks good. my question concerns the tube. inside of the tube is an aperture stop, about two thirds down from the objective. is this a required part? does it restrict the incoming light? if so then why is it there? should i knock it out of there? the focuser tube also has one inside. what the heck are these for?
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werewolf6977
Lord High Smasher
Reged: 12/15/03
Posts: 7444
Loc: Hanover, Ohio
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That may actually be a baffle, not an aperture stop. This is useful for better contrast.
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Pete
6" Apogee/LXD55 - "The Beast"
Starhopper 6" Dob - "Shiva"
Spaceprobe 130 EQ - "Spacey"
Bushnell Fatboy
The Abomination
Sun Pak Pro 7500 Platinum Edition
10X25 Bushnell Camo Roofies
7X35 Tasco Classic Plastic (good views though)
7X42 Tasco Rare Bird
10X50 Nikon Actions (Type 7)
15X70 Skymasters - "DroolMeisters"
One ratty old IBM 600E LapTop
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Protheus
Vaguely offended
Reged: 09/01/07
Posts: 4659
Loc: Illinois, US
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Quote:
C-STAR! 525 POWER!! HUGE 2 1/2 INCH LENSES! ok, i know that this "telescope" isnt worth anything. it is rusty, the plastic is severely uv damaged, and i think it was left standing in the yard for several years. nevertheless i WILL repair it! if for no other reason than this...... i am now sitting on the couch watching a new remake of "invasion of the body snatchers" and i dont think that i have anything more to loose. SO.... upon scrubbing the objective like an old pot, i find the uncoated lenses in fairly good condition. the diagonal is dirty but doesnt seem to be damaged. i cleaned the objective cell, blacked the edges of the lenses and painted inside surfaces of the cell with krylon ultra flat black. it looks good. my question concerns the tube. inside of the tube is an aperture stop, about two thirds down from the objective. is this a required part? does it restrict the incoming light? if so then why is it there? should i knock it out of there? the focuser tube also has one inside. what the heck are these for?
Hey Dusty, was it uncoated before you started scrubbing it, or just after? 
Pete's right about the baffle. Probably it's not an aperture stop at all, and it will improve your image if you keep it.
Chris
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"To tread the sharp edge of a sword;
to run on smooth-frozen ice,
one needs no footsteps to follow..."
"Well, people sometimes ask me 'how did you get involved in astronomy?' I said 'I got born, what's your problem?'" -- John Dobson
"In discussing the large-scale structure of the cosmos, astronomers sometimes say that space is curved, or that the universe is finite but unbounded. Whatever are they talking about?" -- Carl Sagan
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Jim Haley
sage
Reged: 07/04/07
Posts: 281
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Sometimes times there is a long aperture stop inside the tube. It reduces the effective aperture. I think they do that to reduce chromatic aberation or other problems with the outside portion of inexpensive lenses. Perhaps it just makes it a "longer" focal length (easier to focus, less aberations, easier on cheap eyepieces). I definitely would not remove it.
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Jim Haley
12.5" f6 Starsplitter Dob
Orion 8" XTi (with computerized object locator)
Orion 114EQ reflector
80mm f6 refractor
Edited by Jim Haley (09/02/08 02:12 PM)
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akemag
sage
Reged: 10/26/07
Posts: 442
Loc: Sweden
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Was that the version with Nicole Kidman, it was pretty good  Anyway, good thing there. I was hoping to find an old refractor in decent shape at some yard sale. But no luck so far.
Hope you get it working soon.
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Celestron Omni XLT 120
10" GSO DOB
Bresser Skylux 70mm
5mm Ortho
6.5mm, 25mm, 32mm Plossl
3.6mm, 10mm, 25mm MA
20mm Erfle
4mm, 10mm, 12mm, 18mm RK20mm Kellner
8mm, 20mm Huygens
1.5-2x Barlow
Orange, Green, Variable Polarizing Moon filter
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Protheus
Vaguely offended
Reged: 09/01/07
Posts: 4659
Loc: Illinois, US
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Quote:
Sometimes times there is a long aperture stop inside the tube. It reduces the effective aperture. I think they do that to reduce chromatic aberation or other problems with the outside portion or inexpensive lenses. Perhaps it just makes it a "longer" focal length (easier to focus, less aberations, easier on cheap eyepieces). I definitely would not remove it.
Hey Jim,
The effect is the same either way. A 40mm f/15 is 600mm long. A 60mm f/10 (also 600mm long) can be stopped down to 40mm and function perfectly well as a 40mm f/15. Whether it's done to avoid defects in the lens, or to make cheap eyepieces work better, the total set of incidental changes are more or less the same.
Still the fact remains that most refractors have light baffles, and not many of them have aperture stops, so it's more likely than not to be the former. There's a simple test you can perform to check which it is. If you can find the focal point of the lens (center, back however far the focal length is behind it), you can just put your eye there. If you see the edges of the lens, it's no aperture stop.
Chris
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"To tread the sharp edge of a sword;
to run on smooth-frozen ice,
one needs no footsteps to follow..."
"Well, people sometimes ask me 'how did you get involved in astronomy?' I said 'I got born, what's your problem?'" -- John Dobson
"In discussing the large-scale structure of the cosmos, astronomers sometimes say that space is curved, or that the universe is finite but unbounded. Whatever are they talking about?" -- Carl Sagan
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dusty mirrors
member
Reged: 01/27/08
Posts: 20
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update! i took the advise and left the baffle. i painted inside the tube with krylon ultra black. after soaking all of the screws in acid to remove the rust, and painting all the plastic parts with the special plastic bonding paint to repair the uv checkering it was ready to go back together.
i set up on the moon for the first test. holy cow! thats a great image! what the heck? i am stunned! "well it is the moon" i thought, "its not hard to get a great view of that". i turned it onto jupiter and the detail was there too! i saw the polar zones and two dark bands. everything was sharp and clear! this is a 60mm, 700mm fl CHEAP, CHEAP AS CAN BE, abused and left in the yard to die of exposure telescope. i am stunned at the quality of the view. now i am inclined to buy a small refractor. i didnt know that they could be so good. i would get a higher quality one of course, but i think that i am inspired by this p.o.s. scope. after an adjustment to the tripod i am giving this one to the kids. i will look around for a refractor for myself.
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Siderea
Astronomess
Reged: 11/21/05
Posts: 1652
Loc: Novato
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Hi Dusty
On those cheap 60mm, the objectives commonly give a great view with a good eyepiece.
Economy and quality suffer in all other areas first, tube, focuser, mounts tripods and eyepices.
So you fixed the bad parts and got yourself a winner.
A couch-ATMer?
LOL
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Clear skies and pumpkin pies!
lc Carol
60mm Telescope Club
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stefanj
Pooh-Bah
Reged: 11/15/07
Posts: 1350
Loc: Western New York State
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I am constantly amazed at what my cheap-o Meade 70AZ gives. The views are stunning- despite all the problems with the mount, focuser, finder.
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Life is a circus- and I'm stuck in the FREAK TENT
If these are blue- it means the moon is full!
Meade ETX 90RA w/ tripod
Meade AZ 70
Meade DS 2130 AT
Zhumell 10" Dob
Zhumell Plossel EP and Filter set
Simmons 10x50 Binoculars
GLPx6
LPI
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Protheus
Vaguely offended
Reged: 09/01/07
Posts: 4659
Loc: Illinois, US
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Quote:
CHEAP, CHEAP AS CAN BE, abused and left in the yard to die of exposure telescope. i am stunned at the quality of the view. now i am inclined to buy a small refractor.
Ahh, yep, as Carol said, the optics are often quite impressive. My wife is now the proud owner of an AT66ED, on the other hand, and that is a whole new level of "you can do that with a 66mm scope!?"
Have fun with it.
Chris
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"To tread the sharp edge of a sword;
to run on smooth-frozen ice,
one needs no footsteps to follow..."
"Well, people sometimes ask me 'how did you get involved in astronomy?' I said 'I got born, what's your problem?'" -- John Dobson
"In discussing the large-scale structure of the cosmos, astronomers sometimes say that space is curved, or that the universe is finite but unbounded. Whatever are they talking about?" -- Carl Sagan
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