TheSkySearchers

Posted: **Fri Nov 22, 2019 4:16 am**

Are the objective lenses in the cheap refractors any good? Just thinking. As we know, the cheapo scopes sold in big box stores usually have terrible hardware: tripods, mounts, focusers, finders. But how is the front end glass? I have machine tools and can upgrade or make lots of hardware. It might be fun to chop up a cheapo refractor and make up a new focuser and mount for it. Craigslist is littered with such stuff some of which can be had for $20 or so. Keep in mind that this would be a project for fun, not to save money or time. But if the objective lenses are trash, then I'd not bother.

Posted: **Fri Nov 22, 2019 4:27 am**

Yes, most of budget refractors have reasonably good objectives.

Posted: **Fri Nov 22, 2019 4:37 am**

I think it is strictly a YMMV sort of thing. A lot can go wrong with glass and some of it might have to do with cutting corners poor QC etc.

One less expensive refractor that has IMO surprisingly good glass is the 120mm f8.33 refractor made by Synta and sold by Celestron and Meade. When I got mine it behaved badly but after I did collimation on it in my home shop it was a terrific performer. Used it in a Mars opposition (2003) and could clearly resolve the Tharsis region volcanos and Olympus Mons.

The Orion ST 80 is another one with good glass but needs mechanical upgrades. It's not available anymore but has been replaced by the CT80 which is cheaper in mechanical construction but still has (I think, someone correct me if I'm wrong) the same objective. Chromatic aberration will be an issue for high power use.

The Orion ST120 is another candidate.

BUT.... why not order a known good Fraunhofer achromatic doublet and just build around it?
http://www.istar-optical.com/achromatic.html

They have a good reputation for quality glass and you wouldn't be wasting the bathwater to save the baby. They also have lenses available with low dispersion glass.

Posted: **Fri Nov 22, 2019 4:59 am**

Most of the name brand objectives are reasonable and would be a fun place to start off learning how to make your own refractor.
Some objectives as nFA pointed out are better than others so keep your eyes open for a good one.

Posted: **Fri Nov 22, 2019 5:08 am**

Thanks, folks. While the Istar objectives look great, the fun is to make something out of a piece of junk. I think I'll keep an eye on the local thrift shops, which our town seems to have many of.

Clear skies....

Posted: **Fri Nov 22, 2019 8:24 am**

Even the cheap 60mm f12's have quite good optics, so you can probably pick up something that will give good views from the Thrift shop. If you make a nice tube, mount and focuser you could always upgrade the lens down the track. If you manage to find a 100mm or bigger scope to play with then you are golden with one of the iStar lenses as nFA suggests.

You never know what you might find: I picked up an old 4" f18 objective in a brass cell for $5. (I would love to find out its provenance as it seems to be a 19th century build: and I found a reference that John Herschel had a 4" scope that ended up here in South Australia and then disappeared into history!!!) When I put it in a 4" down-pipe and had a play it gave images of the planets that gave my Tak TSA 102 a run for its money in terms of sharpness! One of these days I might make a tube worthy of it, but my artist daughter has stolen it for use in her artwork as a camera obscura (it can project an image inside a room that just about fills a queen-size sheet!).

Have fun, and good luck!

- Dean

Posted: **Fri Nov 22, 2019 3:38 pm**

DeanD wrote: ↑Fri Nov 22, 2019 8:24 am
...

You never know what you might find: I picked up an old 4" f18 objective in a brass cell for $5. (I would love to find out its provenance as it seems to be a 19th century build: and I found a reference that John Herschel had a 4" scope that ended up here in South Australia and then disappeared into history!!!) When I put it in a 4" down-pipe and had a play it gave images of the planets that gave my Tak TSA 102 a run for its money in terms of sharpness! One of these days I might make a tube worthy of it, but my artist daughter has stolen it for use in her artwork as a camera obscura (it can project an image inside a room that just about fills a queen-size sheet!).

Have fun, and good luck!

- Dean

Oohh that sounds like fun!

Posted: **Fri Nov 22, 2019 7:15 pm**

notFritzArgelander wrote: ↑Fri Nov 22, 2019 4:37 am I think it is strictly a YMMV sort of thing. A lot can go wrong with glass and some of it might have to do with cutting corners poor QC etc.

One less expensive refractor that has IMO surprisingly good glass is the 120mm f8.33 refractor made by Synta and sold by Celestron and Meade. When I got mine it behaved badly but after I did collimation on it in my home shop it was a terrific performer. Used it in a Mars opposition (2003) and could clearly resolve the Tharsis region volcanos and Olympus Mons.

The Orion ST 80 is another one with good glass but needs mechanical upgrades. It's not available anymore but has been replaced by the CT80 which is cheaper in mechanical construction but still has (I think, someone correct me if I'm wrong) the same objective. Chromatic aberration will be an issue for high power use.

The Orion ST120 is another candidate.

BUT.... why not order a known good Fraunhofer achromatic doublet and just build around it?
http://www.istar-optical.com/achromatic.html

They have a good reputation for quality glass and you wouldn't be wasting the bathwater to save the baby. They also have lenses available with low dispersion glass.

would you need a second rear glass element ?

Posted: **Fri Nov 22, 2019 7:23 pm**

yobbo89 wrote: ↑Fri Nov 22, 2019 7:15 pm
notFritzArgelander wrote: ↑Fri Nov 22, 2019 4:37 am I think it is strictly a YMMV sort of thing. A lot can go wrong with glass and some of it might have to do with cutting corners poor QC etc.

One less expensive refractor that has IMO surprisingly good glass is the 120mm f8.33 refractor made by Synta and sold by Celestron and Meade. When I got mine it behaved badly but after I did collimation on it in my home shop it was a terrific performer. Used it in a Mars opposition (2003) and could clearly resolve the Tharsis region volcanos and Olympus Mons.

The Orion ST 80 is another one with good glass but needs mechanical upgrades. It's not available anymore but has been replaced by the CT80 which is cheaper in mechanical construction but still has (I think, someone correct me if I'm wrong) the same objective. Chromatic aberration will be an issue for high power use.

The Orion ST120 is another candidate.

BUT.... why not order a known good Fraunhofer achromatic doublet and just build around it?
http://www.istar-optical.com/achromatic.html

They have a good reputation for quality glass and you wouldn't be wasting the bathwater to save the baby. They also have lenses available with low dispersion glass.
would you need a second rear glass element ?

No. The iStar objectives are a complete doublet.

Posted: **Fri Nov 22, 2019 7:32 pm**

notFritzArgelander wrote: ↑Fri Nov 22, 2019 7:23 pm
yobbo89 wrote: ↑Fri Nov 22, 2019 7:15 pm
notFritzArgelander wrote: ↑Fri Nov 22, 2019 4:37 am I think it is strictly a YMMV sort of thing. A lot can go wrong with glass and some of it might have to do with cutting corners poor QC etc.

One less expensive refractor that has IMO surprisingly good glass is the 120mm f8.33 refractor made by Synta and sold by Celestron and Meade. When I got mine it behaved badly but after I did collimation on it in my home shop it was a terrific performer. Used it in a Mars opposition (2003) and could clearly resolve the Tharsis region volcanos and Olympus Mons.

The Orion ST 80 is another one with good glass but needs mechanical upgrades. It's not available anymore but has been replaced by the CT80 which is cheaper in mechanical construction but still has (I think, someone correct me if I'm wrong) the same objective. Chromatic aberration will be an issue for high power use.

The Orion ST120 is another candidate.

BUT.... why not order a known good Fraunhofer achromatic doublet and just build around it?
http://www.istar-optical.com/achromatic.html

They have a good reputation for quality glass and you wouldn't be wasting the bathwater to save the baby. They also have lenses available with low dispersion glass.
would you need a second rear glass element ?
No. The iStar objectives are a complete doublet.

wow! that makes for an easy diy project, sign me up!

Posted: **Fri Nov 22, 2019 7:36 pm**

yobbo89 wrote: ↑Fri Nov 22, 2019 7:32 pm
notFritzArgelander wrote: ↑Fri Nov 22, 2019 7:23 pm
yobbo89 wrote: ↑Fri Nov 22, 2019 7:15 pm

would you need a second rear glass element ?
No. The iStar objectives are a complete doublet.
wow! that makes for an easy diy project, sign me up!

I often find myself wishing my mechanical skills were better. :shrug:

Posted: **Fri Nov 22, 2019 7:38 pm**

gregl wrote: ↑Fri Nov 22, 2019 5:08 am Thanks, folks. While the Istar objectives look great, the fun is to make something out of a piece of junk. I think I'll keep an eye on the local thrift shops, which our town seems to have many of.

Clear skies....

Some brands to look for include Towa. Made in Japan is a good thing in inexpensive used refractors.

Posted: **Fri Nov 22, 2019 8:13 pm**

Hello Gregl,

you can find on the eBay or at the old photography shops the close-up lenses. Some of them are precisely made cemented doublets with AR multicoatings, I have a few from Canon and Hoya (55mm dia, 67mm dia), and have paid just peanuts.
They are miles ahead in quality if compared to what you find today in the small telescopes of similar aperture. Their typical focus is F=500mm and shorter.

Another choice is to take the Cook triplets from the overhead projectors. Their typical aperture is around 100mm, the speed is fast, like F/4, but you can stretch them with a 2" Barlow.

Happy doing,
JG

Posted: **Fri Nov 22, 2019 10:17 pm**

I know you are looking to re-condition something, but there is also another source. Surplus Shed, https://www.surplusshed.com/category/Objective_Lenses . They have sizes up to 153mm / 6". I got a 90mm f/10 for a travel scope, 69.00 US. They have air spaced glass down to 50mm. One thing though, the non-Wollensak lenses may be assembled wrong, in the cell backwards or the wrong curve facing the flint. That was mine. I also adjusted the spacing for best performance. Even with all that, the prices are to die for. The Wollensak 127mm I want to build a scope around is 249.00 US. And many times they have sales of 30% - 40% off. They are also typically out of anything above 100mm, but sign up for their newsletter and when they anticipate them being in stock you can pre-order them, many times at a discount. Their 70 or 80mm glass may be just the ticket. They also have some 1 1/4" refractor tailpieces, too. One last thing, stay with the higher f/ratios with smaller lenses, I don't think the 90mm f/5.5 will perform as well as the f/10, for example.

Posted: **Fri Nov 22, 2019 10:29 pm**

Hi Greg,
I can vouch for the old Towa glass. I have a cemented doublet 60mm that came from a Tasco 55VTE; it was like a spyglass with a click-stop focuser. I bought it and a few other old scopes at a garage sale for $10.

Image001.png

Sometime later I found a Celestron 60mm for $25 at a swap shop. I already have a few good classic 60mm's, but this one had a 1.25" focuser. I discover that if I took the Towa objective from the Tasco 55VTE and used it with a "normal" focuser, it made for a nice little f/7 60mm (420mm length); the 'Towatron'

IMG1.jpg

For a total of $35 and some time with a hacksaw and a drill, it's a fun little wide field scope. Even if it's only an achro it takes some OK pics:

Moon_Venus_2018_07_15.jpg

IMG3.jpg

Racoon_01.jpg

I'm always on the lookout for stuff like this. The iStars look tempting...

Posted: **Fri Nov 22, 2019 10:37 pm**

Thanks, Fatkitty. Boy, you folks are giving me all sorts of great ideas.

j.gardavsky wrote: ↑Fri Nov 22, 2019 8:13 pm Hello Gregl,

you can find on the eBay or at the old photography shops the close-up lenses. Some of them are precisely made cemented doublets with AR multicoatings, I have a few from Canon and Hoya (55mm dia, 67mm dia), and have paid just peanuts.
They are miles ahead in quality if compared to what you find today in the small telescopes of similar aperture. Their typical focus is F=500mm and shorter.

...

Happy doing,
JG

Hi JG:
Are you referring to the c.u. lenses that screw onto a prime lens like a filter? When I was a photographer I had the usual +1 to +3 c.u. lenses and a 55 mm macro lens but I've never seen one that was a doublet. Perhaps I've missed something there.

Posted: **Sat Nov 23, 2019 5:24 pm**

[quote Hi JG:
Are you referring to the c.u. lenses that screw onto a prime lens like a filter? When I was a photographer I had the usual +1 to +3 c.u. lenses and a 55 mm macro lens but I've never seen one that was a doublet. Perhaps I've missed something there.
[/quote]

Yes, they have the photographic filter threads, and the test of they are not a singlet, but an achromatic doublet is done when passing the beam of a green laser pointer.
With Heliopan, you can get the 2 element achromatic cloce-up lens up to 82mm,
http://www.angelfire.com/ca/erker/closeups.html

It is the skill of doing business to get these lenses for 10 bucks, like I've got mine,

JG

Posted: **Sat Nov 23, 2019 5:29 pm**

Thanks, JG .

TheSkySearchers

Cheap refractor glass any good?

Cheap refractor glass any good?

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