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martym
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Reged: 02/15/10

Re: Jaegers objective new [Re: dawsonian2000]
      #4725244 - 08/01/11 05:53 PM

Mel,

Are you concerned about CA on the system at f/10?
Have you considered a folded f/15?

marty


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dawsonian2000
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Reged: 07/26/06

Loc: Riverview, FL, USA
Re: Jaegers objective new [Re: martym]
      #4727177 - 08/02/11 07:55 PM

Quote:

Mel,

Are you concerned about CA on the system at f/10?
Have you considered a folded f/15?

marty




I am not too concerned with CA in the 6" f/10. Despite the shorter focal ratio as compared to the f/15, I believe the aperture alone should be a counter measure to help reduce CA when using higher magnification. But, as we seasoned refractors builders know so well, other factors such as a bad figure, misalignment, improper spacing of elements can introduce more CA than a triangular prism.

You know, my first choice was the f/15, but I did not have a place to store it. The f/10 is a more tamed beast to handle; at home or taking it for a ride to remote sites. A folded f/15 would work, but it also introduces more alignment anomalies to contend with.


Mel


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tim53
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Loc: Highland Park, CA
Re: Jaegers objective new [Re: dawsonian2000]
      #4728324 - 08/03/11 02:16 PM Attachment (87 downloads)

I wish I'd folded my f/15. It's so long that I haven't used it since I got back from CSPAMP-II (that was 2009!):

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tim53
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Re: Jaegers objective new [Re: tim53]
      #4728330 - 08/03/11 02:20 PM

And the blue thingy is a 6" f/5 built about 20 years ago by a late friend of mine from JPL, Dick Zanteson. It's a beautiful piece of workmanship and a joy to use.

"In real life", I was planning on putting weights on either side of the main tube of the f/15 to get the eyepiece closer to the saddle, but I haven't done so yet.

-Tim.


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tim53
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Re: Jaegers objective new [Re: tim53]
      #4728341 - 08/03/11 02:24 PM Attachment (131 downloads)

Here's my 6" f/10 Jaegers on my EM-10 mount (a bit of Chinese underkill, but not too bad).

The tube is rougher than it looks, as I made it from scrap maple flooring and only had a finishing sander to approximate "round" on my bench.

This scope is a very nice visual instrument, even on the planets, but there's too much false color for color imaging of planets that aren't Mars, even with a Baader contrast booster filter in place. Green monochrome planetary is good, though, as is prime focus DSO color.

-Tim.

Edited by tim53 (08/03/11 02:25 PM)


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martym
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Reged: 02/15/10

Re: Jaegers objective new [Re: tim53]
      #4729042 - 08/03/11 10:36 PM

If anyone is interested in buying mirrors to fold the optical path Nova is selling some zerodur 1/20 wave 20/10 scratch-dig surplus flats cheap. I think that most were made for laser labs. The link: http://www.nova-optical.com/Flat%20Mirrors.htm

Mine was marked for Lawrence Livermore National Laboratory and serialized.

marty


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Gene7
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Reged: 06/10/10

Loc: Mid Ohio, USA
Re: Jaegers objective new [Re: martym]
      #4729484 - 08/04/11 07:37 AM

Do not know why above material from Nove was presented. You cannot fold a scope image with a 2 inch or smaller mirror nor can you pay $1,000 for it. Gene

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Mirzam
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Re: Jaegers objective new [Re: Gene7]
      #4729531 - 08/04/11 08:34 AM

Well, it depends on what you are folding and how you fold it. They show a 3" flat for $200, which seems pretty reasonable in comparison to secondary mirror prices from various vendors.

This would be adequate to fold a 6-inch objective if you use a "4" design.

JimC


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martym
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Reged: 02/15/10

Re: Jaegers objective new [Re: Mirzam]
      #4729646 - 08/04/11 10:08 AM

I'm kind of confused about the reply to the Nova posting. I checked the link and it shows flats up to 10" in diameter and a 4" for $300, so the link is valid and a 6" f/15 can be folded almost in half with a 4" flat and a 2" eliptical diagonal or a 3" round flat instead of an eliptical diagonal.
You can get both flats for $500. and fold that f/15 tube down to about 4 feet long. That's what I've got for my f/15.

marty

Edited by martym (08/04/11 02:16 PM)


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Gene7
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Reged: 06/10/10

Loc: Mid Ohio, USA
Re: Jaegers objective new [Re: martym]
      #4730312 - 08/04/11 05:31 PM

I have plans to "Z" fold my 1200mm x f/9.5 x 127mm Shed Achro, with collimation mount. Have a 1/4 wave 4 x 4 inch mirror, hope that is good enough. Plan to test it at 45 deg. in front of my ED 80mm OTA. I understand a mirror used at near 90 deg. angle need not be as good as one used at a more flat 45 deg.

You people graphing or calculating the needed mirror size do not forget to consider the field stop size in the planned eyepiece. With a large stop the folding mirrors need to be bigger.

It is also my observation that the closer a mirror is to the eyepiece or observer the less accurate it needs to be. My smaller mirror I believe is 1/10 wave. Will be able to use a low sturdy pod with a Gimble mount on the light weight 1/8 inch ply box. Camera for digiscoping will have a rack on top with a Crawmach focuser through a Hyperion eyepiece. Any comments please. Gene

note; I plan to keep my box at 20 inches long, 7 inches wide, by perhaps 14 inches high with the camera rack on top.

Edited by Gene7 (08/06/11 05:47 PM)


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Mirzam
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Re: Jaegers objective new [Re: Gene7]
      #4730389 - 08/04/11 06:27 PM

It's good that you plan to test your flat mirror. As far as near-90-degree reflection angles mitigating the need for surface accuracy I don't see why this should be the case. The added error at the wavefront is 2x the surface error at each reflection it seems to me.

JimC


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Gene7
scholastic sledgehammer


Reged: 06/10/10

Loc: Mid Ohio, USA
Re: Jaegers objective new [Re: Mirzam]
      #4730885 - 08/05/11 12:06 AM

Did not mean to indicate that a near 90 deg. reflection mitigates the surface accuracy, it is just that low angles makes the situation worse. Information from Antares:
http://www.antaresoptics.com/SecAdvantages.html

If an image enters and leaves at a 45 degree angle (total reflection 90 deg) the error is 1.414 (square root of 2) worse than if near a 90 deg. reflection.

Antares seems to have there stuff scattered and you cannot get to it all from one link. But wow, I hate to pay for their 1/15 wave mirror when I can get a 1/10 wave for a fraction of that cost! They say the secondary should be twice the accuracy of the primary. Gene


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martym
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Reged: 02/15/10

Re: Jaegers objective new [Re: Gene7]
      #4732070 - 08/05/11 04:52 PM

The late Optical Engineer Ernie Pfannenschmidt wrote an article in March 2001 Sky & Telescope describing a folded refractor. In the article are diagrams and text with a lot of useful info.

marty


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Napersky
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Reged: 01/27/10

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Re: Jaegers objective new [Re: martym]
      #4762434 - 08/22/11 01:57 PM

I just ordered the 6" F15. I couldn't pass it up.
I will just have to push myself with making a Ronchi tester but there is no-way I would get one buit in 10-days.

Mark


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dawsonian2000
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Re: Jaegers objective new [Re: Napersky]
      #4763278 - 08/22/11 10:17 PM

Congratulations on the purchase of your Jaegers 6" f/15, Mark! I hope it will turn out well once its construction is complete. I know Surplus Shed says the lenses are tested for correctness before they leave their facility, but you never can tell unless you try it in a completed telescope, or test it prior with a Ronchi tester. I would like to build a Ronchi tester too so I can test all of my refractors.

I have the f/10 and I am starting to collect the parts to get my project on the road. I have the tube and the cell (original Jaegers cell). But, I am considering having a collimation cell made for it.

Mel


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Sean Cunneen
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Reged: 08/01/07

Loc: Blue Island Illinois
Re: Jaegers objective new [Re: dawsonian2000]
      #4763345 - 08/22/11 11:04 PM

I mounted my 6" f15 objective mounted in it's jaeger's cell in my homebuilt OTA tonight and took it out for a dry run. Compared to my modern Istar multi-coated objective star points were a bit dimmer. Star points were very sharp and the optic star tested very nicely. Through a green filter the star test was perfectly symmetrical on both sides of focus. The diffraction rings were even, round and uniform. I was pleasantly surprised! Off axis viewing caused a bit of a reflection, I believe due to the lack of coatings however viewing on axis was fine. I had a partial split of the double-double at 100x and a clean split at both ends at about 160x.

I think Surplus Shed did an excellent job matching up my objective, I expected worse. If all the other lenses are like mine I think folks will be very pleased with their purchases!


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plyscope
Pooh-Bah


Reged: 11/23/06

Loc: Perth, West Australia
Re: Jaegers objective new [Re: Sean Cunneen]
      #4763556 - 08/23/11 12:58 AM

Stop it Sean, you're tempting me to buy another lens.

Andy


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dawsonian2000
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Re: Jaegers objective [Re: Sean Cunneen]
      #4764035 - 08/23/11 10:31 AM

Sean,

Great news on the performance of the Jaegers 6" f/15! I figured without coatings there will be some light transmission degradation, but with all of the conjecture about these achromats I was getting a bit apprehensive. I feel more confident my f/10 will be a great performing once I have constructed it; despite the lack of coatings.

Mel


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Sean Cunneen
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Re: Jaegers objective [Re: dawsonian2000]
      #4764147 - 08/23/11 11:24 AM

Late last night around 1am Jupiter finally popped into view. The lack of coatings was really evident as there was a lot of glare and haze. On axis views were good but off axis views left a lot to be desired. Detail on the planet was very good but the strong light from Jupiter overwhelmed the view. The planet's limb washed away in a haze.

The objective took magnification very well, better than my Istar but when comparing the crystal clear Istar images, modern coatings win. I am calling around today to see how expensive a MGF2 coating would be. If others are interested, let me know and I'll tell you what I find out.

As for the OP's original question: Stick with newer glass unless you are ready for a labor of love. This objective shows a lot of promise but it looks as though $425 is just the beginning!

Sean


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Napersky
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Re: Jaegers objective [Re: Sean Cunneen]
      #4764458 - 08/23/11 02:06 PM

Sean,

I was just going to post about getting these coated. You can count me in on the coating thing when you call around. I believe that is the way to go. Once coated the Jaegers should perform great. Have you tested for spherical aberation w your ronchi yet?


Mel, I believe that Jon Siple wrote an article in the Rosette about the Jaegers F10 some years back. I am going to look for it next.

I hope to have a Ronchi tester made for me soon....


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