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DAVIDG
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Re: Jaegers objective new [Re: Napersky]
      #4764503 - 08/23/11 02:28 PM

Before you spend the money on AR coatings I highly recommend that you bench test your lens or have someone like D&G test it for you. What you think might be a coating issues could actually be a figure issue. My 4" Jaegers lens tested poorly and it was coated. See the pictures I posted in this thread. MgF2 coating are more expensive then metal ones and you'll need to have at least two if not all four surfaces coated. The cost will be a few hundred dollars. Once the coating are applied they can not be chemically removed so if the issues turns out to be a figuring problem then they will need to polished off, adding to the refiguring costs plus the cost of having them applied again.

- Dave


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Napersky
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Re: Jaegers objective new [Re: DAVIDG]
      #4764638 - 08/23/11 03:43 PM

David,

Absolutely, In fact I have asked a friend if he might build a Stellafane Tester and Stand for me. If he will I will be bench testing in the near future.

Mark


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Napersky
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Jaegers OG specifications new [Re: Napersky]
      #4764642 - 08/23/11 03:46 PM

Does anyone know the specifications of the OG from Jaegers on the 6":

Type of Crown
Type of Flint
thickness
radii of the curves


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dawsonian2000
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Re: Jaegers objective new [Re: Sean Cunneen]
      #4764936 - 08/23/11 06:37 PM

Quote:

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.

Sean




Wow, Sean! It just so happens that after reading your previous message, I was thinking about coatings too. Yes, I want to get mine coated too. I will do some research and report back. Look forward to seeing what you will find out as well.

Mel


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dawsonian2000
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Re: Jaegers objective new [Re: DAVIDG]
      #4764960 - 08/23/11 06:50 PM

Good point, Dave. But, I wonder how much D&G would charge for their testing. I guess I will just have to give them a call.

Mel


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Sean Cunneen
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Re: Jaegers objective new [Re: dawsonian2000]
      #4765400 - 08/23/11 11:29 PM

I did some calling around and Majestic Coatings in NJ will do MGF2 coatings on all 4 surfaces for $150, $125 if he can do 2 objective(4 lenses) at once. So I have to find a coating-buddy. Majestic does D&G's lenses...

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dan_h
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Re: Jaegers objective new [Re: Sean Cunneen]
      #4765927 - 08/24/11 10:17 AM

I am pleasantly surprised. That's really quite reasonable.

dan


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DAVIDG
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Re: Jaegers objective new [Re: dan_h]
      #4765961 - 08/24/11 10:30 AM

Quote:

I am pleasantly surprised. That's really quite reasonable.

dan




That is quite resonable. A good friend made a 6" lens awhile back and was quoted by another compnay around $600 to have all four surface MgF2 coated.
One thing to also keep in mind is that the glass is heated to have the coating applied so there is always a minor risk of something happening. For modern glass this isn't usually a problem but for vintage glass there are a number of cases that resulted in either breakage or the figuring being changed. I know of one first hand and luckly the objective was able to be refiguring.

- Dave


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Napersky
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Re: Jaegers objective new [Re: Sean Cunneen]
      #4766030 - 08/24/11 11:00 AM

Sean,

I am waiting for a friend to see if he will build me some test equipment so that i can Ronchi bench test my Jaeger's 6". I am following David G.s advice to have it tested before committing to coatings. If after Ronchi bench testing it shows littler or no spherical abberation then I will be your partner on the mgf2 coatings.

If the lens is good without refiguring I definitely will be getting them coated!!!!

Mark


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Gene7
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Re: Jaegers objective new [Re: Napersky]
      #4766167 - 08/24/11 12:09 PM

Just be sure you adjust the spacing of the elements for the best performance. Gene

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Sean Cunneen
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Re: Jaegers objective new [Re: Gene7]
      #4766294 - 08/24/11 01:04 PM

During coating the elements are heated to 500 deg. Scary, but not crazy. If there was a bubble or chips in the glass I wouldn't be so cavalier but I have a good feeling about this.

There are a couple of variables I should have looked at and if it is clear tonight I will revisit...

First I neglected to mount my dew shield which let in some stray light, I am in the city.

Second: surplus shed used 1/2" pieces of masking tape as spacer material which intrude into the lens by 1/4" to 3/8". This certainly could have played a part in flares. I'll play with the simple things first before I worry about figure...

One question; With a good star test, sharp focus at high powers and good planetary surface detail visible, could a bad figure still be an option? I can't see it. Bad eyepieces I have had tend to muddle details, not be sharper in-spite-of...

Sean


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DAVIDG
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Re: Jaegers objective new [Re: Sean Cunneen]
      #4766500 - 08/24/11 02:22 PM

Sean,
I've tested many many optics over the years, many of which have been stated to have very high wave rating of better then 1/10 wave and made by big name companies and the owners have stated that they "star test" very well. Yet many when bench tested fall far short of the claims. Most are in the range of 1/2 to 1/4 wave at best. The Jaegers lens I purchased and posted pictures of it being tested is a typical example. Wolfgang Rohr has an excellent German site in which he tests many telescopes. The results are very revealing to their actual quality. http://www.astro-foren.de/forum.php I believe Mark (Napersky) visited with Wolfgang last Summer and saw his workshop and testing equipment in action.
The other thing is that if you test the lens before coating you can compare the results to after coating to be sure nothing has changed from the heating of the elements.
Third, Surplus Shed is guessing at the spacer thickness with using masking tape. You'll be guessing as well by using different materials and thickness and also fighting with seeing conditions to determine if the correction is better or worse then before. If you bench test it you can see the effects of the spacers thickness and tune them for the best overall correction quickly and easily.
I just restored a 3" 1940's Tinsley refractor that many people said the images were excellent, yet when I bench tested the lens it was BACKWARDS in the cell.

- Dave


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dawsonian2000
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Re: Jaegers objective new [Re: Sean Cunneen]
      #4767325 - 08/24/11 08:58 PM

Hey Sean,

In my research, I also found Majestic Coatings; contacted them and was able to work out the same deal on having two objectives MgF2 coated on all surfaces for $250.00. I expected more. I guess a bit of research can reveal much. Jeff responded so quickly that I did not hesitate on the deal. Hope you can find someone to go in with you too. Being that they also coat D&G's achromats, I figure they must do good work. If I hear of anyone else wanting to get their objective coated, I will point them in your direction to hop in on your deal.


Mel


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dawsonian2000
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Re: Jaegers objective new [Re: Sean Cunneen]
      #4767371 - 08/24/11 09:31 PM

Hey Sean,

Sounds to me your lens is working fine and that the addition of the coatings will help significantly. The difference in light transmission with coatings as compared to not having them is quite a bit. Approximately 92% without and 98% with. I guess the ultimate test is what is seen with your eyes through the scope. And it sounds like your visual test went well. As for testing, I have seen a number of lens providers with figure test results as bad as those generated by Dave. Just check the test results of some of the achromats iStar sells. Another company is Barride; and others. For several of their doublets, the Ronchi tests look ronchy too (no pun intended). Not to say testing is not a good idea. I truly think it is.


I plan on removing the masking tape and replacing them with aluminum tabs.


Mel


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Sean Cunneen
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Re: Jaegers objective new [Re: dawsonian2000]
      #4768022 - 08/25/11 08:38 AM

Oh yes Mel, I see those Istar test results just about every clear night . I am thinking of trading in my 6"dia test report for an 8.5"dia test result this winter!

Barride optics has a bunch of bad optics floating around and has refused to make good with their customers, not such a good plan...

According to Jeff at Majestic, each surface coated increases transmission by 1.4%.


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Alan French
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Re: Jaegers objective new [Re: Sean Cunneen]
      #4768059 - 08/25/11 09:13 AM

Quote:

(in part)

According to Jeff at Majestic, each surface coated increases transmission by 1.4%.




Are you sure you have that right? Uncoated glass reflects 4% of the light, so the total transmission for four surfaces would be 85% (0.96^4).

Adding a MgF2 coating reduces the reflected light to 1.5%, increasing the total transmission to 94%, for a 9% gain in light transmission.

If I owned a well-performing uncoated lens, I would not chance sending it out for recoating.

Clear skies, Alan


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Napersky
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Re: Jaegers objective new [Re: Alan French]
      #4768277 - 08/25/11 11:02 AM

Mel,

Great news that Majestic Coatings does coatings for D&G.
I heard from one of the classics guys and in 4-5 weeks he will attempt to build me a Stellafane tester with Mirror test stand! Hurray!

Next step is I will be working on getting my Interferometer working. It's not a Bath but a Zygo.. It works but it needs to be set-up...adjusted etc. I bought it from England just to test my telescopes.

Mark


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martym
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Re: Jaegers objective [Re: Napersky]
      #4768379 - 08/25/11 12:03 PM

You know I'm wondering why all this posting about coating the J6/15? Mine came both elements MgF all sides, did no one elses?

marty


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dawsonian2000
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Re: Jaegers objective [Re: Napersky]
      #4768447 - 08/25/11 12:32 PM

Hey Mark,

I'll be look forward to reading your results from your Zygo test once you receive your test equipment.

Mel


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mikey cee
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Re: Jaegers objective [Re: Alan French]
      #4768524 - 08/25/11 12:55 PM

Quote:



If I owned a well-performing uncoated lens, I would not chance sending it out for recoating.

Clear skies, Alan


That's what R.E. Brandt told me in 1979. I never considered the risk of having it done on my own. Maybe this is one reason for D&G's not offering any outside coating services anymore. Also could be a contributing factor to their ever growing delivery times. Too many ruined objectives that needed refiguring then a second chance at the coaters. The coaters are never going to admit that but they'll never give you a 100% guarantee either. Mike

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