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D&G 5" f/20 - info wanted

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#1 The Ardent

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Posted 27 July 2013 - 04:33 PM

This is the D&G I bought from Camera Concepts at NEAF 2013.
5.375" clear aperture, approx. 117" long, so 5" f/20 is just a guess. Unknown history, unknown previous owner deceased. Written in lens cell is "Refigured D&G OBJ" and then some illegible words. I don't know if this is an original D&G or a refigured ATM lens. The cell and tube look just like my previous D&G.

The previous owner used Parallax rings with a strongly curved base, so I bought new rings to attach the 19" Losmandy dovetail.

I had the tube shortened and powdercoated by Binoscope Company. Looks brand new.
Just had first light (for me) last night, amazing optics. Sharp and color-free. :jump: I didn't have a lot of time so I just used the DM4 for testing.

If you know anything about this scope please share.

Thanks!!

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#2 terraclarke

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Posted 27 July 2013 - 04:51 PM

Interesting telescope. Looks like you either need a taller tripod or a shorter chair. ;)

#3 Awesomelenny

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Posted 27 July 2013 - 06:36 PM

I remember seeing this loooonng scope at NEAF! Wow! Should be virtually free of chromatic abberation with this long f/ratio. It's going to have to be some real planet killer! You will definitely want to make sure you collate this carefully in the beginning before you do anything. Use a 3rd magnitude star for that and you should get a really nice airey disk. Then enjoy this beauty. Wow I want to hear reports of performance!

#4 Awesomelenny

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Posted 27 July 2013 - 06:39 PM

Oh by the way did you have a dew shield with it? If not, get a short 12 to 14 inch piece of aluminum tubing from a local company or Hastings Irrigation.

#5 bremms

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Posted 27 July 2013 - 09:37 PM

That is Looooonnnggg. Very cool.. careful the moment arm of such beast will damage a mount.

#6 Chuck Hards

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Posted 28 July 2013 - 03:59 PM

I tried to commission a 5" f/20 doublet a couple of years ago, but the fabricator had to bow-out due to health issues. I have a 2" f/20 home-made refractor (unknown objective provenance) and have to agree, there just isn't a color issue at f/20.

That is an amazing telescope! I'm green with envy. (No Freud jokes, please.)

#7 starman876

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Posted 28 July 2013 - 05:57 PM

what kind of finder are you planning to use. I am sure it also needs to be a long focal length?

#8 The Ardent

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Posted 28 July 2013 - 06:20 PM

All I need is a Telrad. With a 35 Ultima 7 Sgr and the M8 are framed in the FOV, that about 36', close to the same size as the central Telrad ring.
Shopping list: Dewshield and longer saddle for the EQ mount.

I plan to have this scope set up for at least two public events at Crockett and Sky Meadows in the fall.

#9 bremms

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Posted 28 July 2013 - 06:46 PM

That baby needs a 55mm Plossl. Still a 2.75mm exit pupil!

#10 mustgobigger

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Posted 28 July 2013 - 08:12 PM

love those long FL refractors....your going to love it.
i have a couple myself. :bow:

#11 The Ardent

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Posted 28 July 2013 - 08:32 PM

I meant to ask this earlier:
What's the best way to measure focal length? Aim at the moon and use an index card to find the focus point? Or will a streetlight work as well?
Thanks!

#12 Mirzam

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Posted 28 July 2013 - 08:47 PM

You can use a streetlight or telephone pole but it needs to be far away--like about 500 yards at least. If you use an object that is too close the focal point will be shifted considerably.

JimC

#13 DAVIDG

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Posted 28 July 2013 - 08:53 PM

It depends how accurate you want the know the focal length. The Moon will give it to you directly. If you use a streetlight it needs to be a couple of miles away or you need to know the distance if it is close.
The lens equation is 1/f = 1/(d image) + 1/(d object) were "d image" is the distance from the lens to were the image is formed, "d object" is the distance to object your looking at, and f is the focal length of the lens. When the object is at infinity "1/(d object)" goes to zero so 1/f = 1/(d image) so your measuring the focal length directly.

- Dave

#14 The Ardent

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Posted 01 August 2013 - 06:29 PM

In my quest for a dew cap I called Astrozap since Ive used a couple of their nice flexible dew shields. No metal ones in my size. D&G did not return phone calls or emails. I thought AP might have some extra dew shields lying around, but again nothing in the right size. I wanted something finished, powdercoated, and meant for a refractor.

After a little searching and advice from some of you I found this:

http://hastingsirrigation.com/node/19

They support telescopes! The shipping seems a little high, but I don't think they can make a living selling to hobbyists. If they're willing to help a non-commercial client I'll pay the fees. The rolling service looks interesting.

#15 mikey cee

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Posted 01 August 2013 - 07:56 PM

Andy Beirow has always been helpful when I've called. ;) Mike

#16 BigC

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Posted 01 August 2013 - 09:02 PM

It occurs to me that a really big brother version of the crank-up camera tripod might be good.Leave the mast low for low angle,and crank it up for the zenith!Might need the viewing chair on rollers as the geometry changes. :)

#17 The Ardent

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Posted 13 August 2013 - 04:47 PM

The Hastings pipe arrived today. Subtract the time for mailing my order and shipping the package UPS, was a two-day turnaround. Arrived in good shape. The rolled end looks and feels great. No burrs or sharp edges on the cut end. Only complaint, there is some machine oil inside the tube. I have a machinist friend who can help with fitting to the lens cell. Then some primer and paint, or powdercoat.

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#18 The Ardent

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Posted 26 August 2013 - 10:36 AM

Friday was the first decent night in two months. Set up the scope to test balance. Forgot the pier extension so tripod was only 50" high.
The scope rode well. Balance was easy to achieve and maintain.
We were able to view a number of doubles and DSO's: Nu Sco, Beta Sco, Izar, M8, M20, M22 and several others. Star images were sharp with no aberrations.
No finderscope. "Gunsighting" with a Brandon 48mm put most targets in the FOV right away.

Photo by Mr Catapoman.

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#19 Mirzam

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Posted 26 August 2013 - 01:56 PM

I know that this is sacrilage, but I would seriously think about folding the lightpath in half (at least).

JimC

#20 Dr Morbius

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Posted 26 August 2013 - 02:05 PM

60 power with a 48mm Brandon......Heaven!!!! ..........and yes, folding the lightpath is sacrilagious, impious, and sinful. Please don't do it.

#21 The Ardent

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Posted 26 August 2013 - 04:03 PM

I will not have this scope's body severed in twain. You have my solemn obligation.
I didn't notice any excessive or objectionable vibration.

This refractor is for special occasions and public events, in other words, fun. :jump:

#22 plyscope

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Posted 26 August 2013 - 04:51 PM

Sure looks like a fun and cool telescope.

I've recently made a 5" f15 with D & G lens. Still not had a lot of time to use it but it has certainly been fun so far. A lot easier to manage than my 6" f15, though that is fun too despite the size and weight.

#23 rwiederrich

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Posted 26 August 2013 - 05:47 PM

Now you need to do something about that pier..so you can get that EP out of the dirt....when viewing at zenith or anywhere close by.
Rob

#24 The Ardent

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Posted 16 December 2013 - 02:48 PM

Sorry to dig up this old thread, but the original dewshield arrived today. It was believed lost when I bought the scope in April. My irrigation pipe idea is shelved for now. With the dewshield attached, the scope is beautiful and complete.

I believe this scope was a guidescope for a much larger refractor, possible a similar setup to the one for sale
in California. Discussed here on CN post #5884694 and here

I have seen a few giant refractors with the really long guidescopes.
My scope came from a setup based on the north shore of Long Island. I'm still looking for the origin of the lens, and the unusual sapphire coating.

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#25 The Ardent

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Posted 16 December 2013 - 02:57 PM

Here is a pic of the objective showing a reflection of a white ruler.
Ive had the scope out several times for public outreach, and the optics are excellent. No false color or distortions. Was able to binoview the moon last time out.

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