Telescope Reviews: 36.4mm to 1.25" diagonal to 6" Dynascope

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strdst
Post Laureate

Reged: 03/23/08

Loc: Oregon Territory

36.4mm to 1.25" diagonal to 6" Dynascope
#5669998 - 02/09/13 12:22 AM Attachment (39 downloads)

I recently made the plunge. A Vixen adapter that would allow me to plug a 1.25" diagonal directly into some of my classic Japanese refractors. Very cool. Except I didn't have what I would consider a quality 1.25" diagonal... so...

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strdst
Post Laureate

Reged: 03/23/08

Loc: Oregon Territory

Re: Vixen 3720 36.4mm to 1.25" diagonal new

[Re: strdst]
#5670008 - 02/09/13 12:36 AM Attachment (36 downloads)

one evening I see this box with a few minutes to go before the auction ends. This is going to take a walk on the dark side to acquire. In 1966 I had a fantastic 3" Edmund refractor that I basically destroyed by clam shelling the objective. I've tried to make amends for that, I really have. The 1/2" and 1" eyepieces somehow wound up in the warming oven of the antique wood cook stove we put in the kitchen in 1977. I'm thinking the diagonal did as well. The finder scope? I think I sent the kids off to be pirates or something... I can't find it anywhere in the house... I'm thinking everything was cemented and melted or was lost in the woods. I don't know... except this looked familiar and with promise.

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strdst
Post Laureate

Reged: 03/23/08

Loc: Oregon Territory

Re: Vixen 3720 36.4mm to 1.25" diagonal new

[Re: strdst]
#5670023 - 02/09/13 12:57 AM Attachment (32 downloads)

It arrived, it is as advertised, in excellent condition in original box. There was this crazy good promotional from Paypal. Paypal pay later. Take $10 off the first purchase. Nothing like money off a pretty good deal already. In this case doing business with the
"tile guy" (dark side element) was pretty sweet. I'm feeling good that this was a find, not a pick-a-part find, but some new old stock. I like the diagonal and fondly remember it coming with my Edmund 3" refractor. I'm thinking a very nice classic connection to my current scopes that accept the adaptation. Here is the Vixen adapter and Edmund diagonal in a Lafayette Arcturus.

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Ducky62
professor emeritus

Reged: 10/31/10

Loc: The ATL

Re: Vixen 3720 36.4mm to 1.25" diagonal new

[Re: strdst]
#5670028 - 02/09/13 01:03 AM

Is there a prism or a mirror in there? Does it have the black paint inside that flakes off and falls on the diagonal when you slip fit an EP or Barlow in it?

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strdst
Post Laureate

Reged: 03/23/08

Loc: Oregon Territory

Re: Vixen 3720 36.4mm to 1.25" diagonal new

[Re: Ducky62]
#5670074 - 02/09/13 02:17 AM

Hmmm, yes prism, like back in the day... Mid 1960's and so far no flaky black paint, There was a few seconds tonight when the sky cleared and then... uncleared. Maybe tomorrow...

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strdst
Post Laureate

Reged: 03/23/08

Loc: Oregon Territory

Re: Vixen 3720 36.4mm to 1.25" diagonal new

[Re: strdst]
#5670087 - 02/09/13 02:52 AM Attachment (24 downloads)

But this post isn't entirely about diagonals. Some scopes don't use 'em. I try to avoid those but every now and again... I Cave. Well not exactly Cave but ... pictures at 11 or 3 or later tomorrow. I bought something that may require joining a Yahoo group

EP's that came with.

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mustgobigger
Post Laureate

Reged: 06/12/07

Loc: Michigan

Re: Vixen 3720 36.4mm to 1.25" diagonal new

[Re: strdst]
#5670204 - 02/09/13 06:48 AM

do those have the saturn logo on them.

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terraclarke
Pooh-Bah

Reged: 05/29/12

Loc: Over the river and thru the wo...

Re: Vixen 3720 36.4mm to 1.25" diagonal new

[Re: mustgobigger]
#5670557 - 02/09/13 11:30 AM

Nice find. I love good prism diagonals. I'll take one over a mirror any day on a long FL refractor.

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strdst
Post Laureate

Reged: 03/23/08

Loc: Oregon Territory

Re: Vixen 3720 36.4mm to 1.25" diagonal new

[Re: mustgobigger]
#5670881 - 02/09/13 02:53 PM

Quote:

do those have the saturn logo on them.

As in a set of five Galoc's?

No.

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Ducky62
professor emeritus

Reged: 10/31/10

Loc: The ATL

Re: Vixen 3720 36.4mm to 1.25" diagonal new

[Re: strdst]
#5670938 - 02/09/13 03:49 PM

Did you get a Criterion Dynascope?

Needs

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strdst
Post Laureate

Reged: 03/23/08

Loc: Oregon Territory

Re: Vixen 3720 36.4mm to 1.25" diagonal new

[Re: terraclarke]
#5670959 - 02/09/13 04:03 PM

Quote:

Nice find. I love good prism diagonals. I'll take one over a mirror any day on a long FL refractor.

Me too. I have so many .965 diagonals of substance, but till now nothing but a lightweight hybrid to hold 1.25" eyepieces.

Just handling this diagonal brought back a nearly 50 year old memory of using my Edmund 3" refractor to observe (in an averted vision sort of way) M-57. Not what I expected... no central star, and no crazy colors. Disappointed I trained the scope on e Lyrae. It must have been the most calm atmosphere ever in SoCal. Perfect airy discs, the slightest scintillation in the diffraction rings. I probably spent 3/4 of an hour just falling through space that night.

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strdst
Post Laureate

Reged: 03/23/08

Loc: Oregon Territory

Re: Vixen 3720 36.4mm to 1.25" diagonal new

[Re: Ducky62]
#5670976 - 02/09/13 04:13 PM

Quote:

Did you get a Criterion Dynascope?

Needs

Wow, you are good!

And I wasted my morning taking photos to present the reverse strip tease... You know a declination axis lock knob here, a feather boa there. Oh well now I'm released to do real stuff like going to the dump to recycle and mop the floor, do a few loads of wash... Thanks Ducky

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strdst
Post Laureate

Reged: 03/23/08

Loc: Oregon Territory

Re: Vixen 3720 36.4mm to 1.25" diagonal new

[Re: strdst]
#5670997 - 02/09/13 04:31 PM Attachment (18 downloads)

Gotta love 1957 Bakelite... Ducky you are soooo in trouble!

I can only imagine what this would be worth had it been a Chevy Bel Aire in like condition.

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strdst
Post Laureate

Reged: 03/23/08

Loc: Oregon Territory

Re: Vixen 3720 36.4mm to 1.25" diagonal new

[Re: strdst]
#5671003 - 02/09/13 04:32 PM Attachment (13 downloads)

And those not Galocs...

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strdst
Post Laureate

Reged: 03/23/08

Loc: Oregon Territory

Re: Vixen 3720 36.4mm to 1.25" diagonal new

[Re: strdst]
#5671040 - 02/09/13 05:08 PM Attachment (13 downloads)

Tripod... yeah hardwood tripod legs... Not what you usually find under a 6" newtonian.

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Ducky62
professor emeritus

Reged: 10/31/10

Loc: The ATL

Re: Vixen 3720 36.4mm to 1.25" diagonal new

[Re: strdst]
#5671050 - 02/09/13 05:14 PM

It was the EPs and the reference to a Yahoo Group that gave it away

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strdst
Post Laureate

Reged: 03/23/08

Loc: Oregon Territory

Re: Vixen 3720 36.4mm to 1.25" diagonal new

[Re: Ducky62]
#5671141 - 02/09/13 06:06 PM Attachment (12 downloads)

You ARE good!

The experience in the Yahoo group is so... OK what I'm going to say is... the experience here on CN with photos and linking so easily done it makes for a fantastic, so rich of an experience. The Dynascope group is so different, and perhaps I haven't learned how to use the site yet. Over there it is like writing a Western Union Telegram back in the day. stop. I could use their help but I am not sure I can communicate without

anymore. stop.

If this Dynascope is anywhere near what was advertised in 1957 I'm stoked...1/20 wave optics. One owner and I got to meet him. Retired pediatrician, the most awesome 70 year old! Physically fit, sharp of mind, firm on the selling price. Well 2 out of 3 ain't so bad.

nice endcaps, dust caps.

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gelkin
scholastic sledgehammer

Reged: 09/22/10

Loc: Western, MD.

Re: Vixen 3720 36.4mm to 1.25" diagonal new

[Re: strdst]
#5671344 - 02/09/13 08:03 PM Attachment (11 downloads)

Oh no Kieth. You are going to run both sides of the fence now. A switch hitter?

Those old Criterions are very cool.

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strdst
Post Laureate

Reged: 03/23/08

Loc: Oregon Territory

Re: Vixen 3720 36.4mm to 1.25" diagonal new

[Re: gelkin]
#5671445 - 02/09/13 09:21 PM Attachment (15 downloads)

Gerald...HI!

Yes, but two counterweights shy of yours. It was only an hour drive away. As much as I miss the anticipation of the UPS guy, the strapping tape and packing peanuts all over the place, this guy is HEAVY (compared to my RV-6)! Glad I could look/buy/and haul on the same day and save the shipping costs. A few years ago I "won" a maybe 1980's RV-6 on eBay for $160. Afterword the seller apologetically re-thunk the shipping at $180. I could have bailed on the transaction then but wanted to try it out, so I paid up. I gotta say these scopes with the mirrors are pretty amazing. Kinda ugly but still optically amazing

The afternoon I chose to go see/buy/haul this telescope was on a Monday. I had been sick over the weekend with a respiratory flu and while feeling somewhat better chose to take a rare sick day from work. By the time I made contact with the seller it was getting late... and cold. The OTA only fit in my car if I removed the roof. Honda Del Sol's are great in the summer, but...a mid 30's drive home only extended the sore throat for a week. Small price to pay.

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strdst
Post Laureate

Reged: 03/23/08

Loc: Oregon Territory

Re: Vixen 3720 36.4mm to 1.25" diagonal new

[Re: strdst]
#5672750 - 02/10/13 05:43 PM Attachment (12 downloads)

Playing with the new Criterion today. The focuser rough draw tube was totally stuck within the focuser. I remembered to not have the scope standing on end, mirror down, as I took the pressure off of the rack and pinion gear just in case the brass tubes fell through, which they did. Although the OTA was on its side I got lucky and it just missed the secondary mirror. Lots of liquid wrench and steel wool has got things sliding snugly again.

The seller included a Goodwin Resolving Power Lens with the telescope. Perhaps more interesting than the Barlow itself is the eight pages of typewritten instructions than it was rolled up in.

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Ducky62
professor emeritus

Reged: 10/31/10

Loc: The ATL

Re: Vixen 3720 36.4mm to 1.25" diagonal new

[Re: strdst]
#5672948 - 02/10/13 07:47 PM

8 pages of instructions for a Barlow? What could it possibly say? You ought to scan and send the file to Robert Provin.

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strdst
Post Laureate

Reged: 03/23/08

Loc: Oregon Territory

Re: 36.4mm to 1.25" diagonal to 6" Dynascope new

[Re: Ducky62]
#5673153 - 02/10/13 09:59 PM

Quote:

8 pages of instructions for a Barlow? What could it possibly say?

Oh pretty much everything!

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strdst
Post Laureate

Reged: 03/23/08

Loc: Oregon Territory

Re: 36.4mm to 1.25" diagonal to 6" Dynascope new

[Re: strdst]
#5673206 - 02/10/13 10:30 PM Attachment (12 downloads)

I took ol' Dyna up to the lake today for an outing. Had the weather been better a picnic would have been nice... Here are a few more pictures...Being a refractor kinda guy I'm still puzzled where Dyna's good side might be. lol.

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strdst
Post Laureate

Reged: 03/23/08

Loc: Oregon Territory

Re: 36.4mm to 1.25" diagonal to 6" Dynascope new

[Re: strdst]
#5673227 - 02/10/13 10:43 PM Attachment (8 downloads)

OK, lake is a stretch this time of year. A flood control dam thoroughly drawn down ready for the next wet weather event. Next June through September it will be full of water and boats again. First and only time I observed Mercury was from up here on the dam face. And the Leonid shower in 2000 or 2001 was absolutely crazy up here with a horizon to horizon view.

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strdst
Post Laureate

Reged: 03/23/08

Loc: Oregon Territory

Re: 36.4mm to 1.25" diagonal to 6" Dynascope new

[Re: strdst]
#5673230 - 02/10/13 10:45 PM Attachment (10 downloads)

Some detail...

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strdst
Post Laureate

Reged: 03/23/08

Loc: Oregon Territory

Re: 36.4mm to 1.25" diagonal to 6" Dynascope new

[Re: strdst]
#5673236 - 02/10/13 10:47 PM Attachment (7 downloads)

and smaller detail...

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strdst
Post Laureate

Reged: 03/23/08

Loc: Oregon Territory

Re: 36.4mm to 1.25" diagonal to 6" Dynascope new

[Re: strdst]
#5673254 - 02/10/13 10:57 PM Attachment (11 downloads)

And a question. I had the owner/seller hold my Maglite to the mirror end as I looked for light coming through the coating. He mentioned that there was a part attached that if removed would allow for better air circulation in the OTA. So much for the mirror test. My question is this... can I undo this piece without messing up the mirror collimation? I'm pretty intimidated by the collimation process.

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actionhac
Post Laureate

Reged: 08/09/08

Loc: WA

Re: 36.4mm to 1.25" diagonal to 6" Dynascope new

[Re: strdst]
#5673461 - 02/11/13 03:46 AM Attachment (6 downloads)

That's very nice Keith. That is pure 1950's.
I wonder if the previous owner meant removing the chrome cap in the center for better air circulation.
I'm still experimenting with newt thermal management. Sometimes I can't decide if I should allow air to move through the tube or not, or just seal it off behind the primary. You can try it both ways. I'd say generally its better to let air move through the tube, sometimes forcing it with a fan. Especially to cool the tube and mirror to ambient.
Here's some info. Scroll down the page for collimation, collimation tools and tube currents, thermal management:
http://www.garyseronik.com/?q=taxonomy/term/3
Some more:
http://www.fpi-protostar.com/bgreer/index.htm

This is a cell similar to the Criterion. I don't know why Criterion went to all the trouble to blank off the free area with that black wrinkle plate. And the chrome plug must be for allowing some air movement, but why so little.
Obviously Criterion had different thoughts on airflow with the Dynascope and I wonder if a owners manual might shed some light.

Edited by actionhac (02/11/13 11:02 AM)

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Grava T
Pooh-Bah

Reged: 06/18/08

Loc: Quebec, Canada

Re: 36.4mm to 1.25" diagonal to 6" Dynascope new

[Re: actionhac]
#5673557 - 02/11/13 07:13 AM

Beautiful newt Keith. For a refractor guy, as least you got the eyepiece in the right position.

Nice observing spot!

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actionhac
Post Laureate

Reged: 08/09/08

Loc: WA

Re: 36.4mm to 1.25" diagonal to 6" Dynascope new

[Re: Grava T]
#5673970 - 02/11/13 12:29 PM

Here is a 1958 sales brochure from Robert's site:
http://geogdata.csun.edu/~voltaire/classics/criterion/dyna1960.pdf
In the brochure it states:
"Mirror is housed in a ventilated cell".
And this statement:
Ventilation has been carefully computed to allow least thermal interference".

A description of the picture Rear of the Dynascope calls the chrome plug a "ventilation plug".
An owners manual may explain when and why you would "pull the plug" and also if you can remove the black wrinkle painted plate for a open tube end.

Robert

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strdst
Post Laureate

Reged: 03/23/08

Loc: Oregon Territory

Re: 36.4mm to 1.25" diagonal to 6" Dynascope new

[Re: Grava T]
#5674801 - 02/11/13 09:05 PM

Quote:

Beautiful newt Keith. For a refractor guy, as least you got the eyepiece in the right position. Nice observing spot!

Thanks Michael. It's the "fully rotating tube assembly". Makes keeping the eyepiece well placed, a snap.

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strdst
Post Laureate

Reged: 03/23/08

Loc: Oregon Territory

Re: 36.4mm to 1.25" diagonal to 6" Dynascope new

[Re: actionhac]
#5674823 - 02/11/13 09:18 PM

Robert, thanks.

So just the chrome round you think. I was anticipating removing everything down to the aluminum cell like other scopes look. The plug makes more sense, maybe not in a faster thermal equilibrium way but it looks nice.

You didn't mention Trixie in the Barlow photo. I found her in the park. Might be one of Glowy's old buds

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actionhac
Post Laureate

Reged: 08/09/08

Loc: WA

Re: 36.4mm to 1.25" diagonal to 6" Dynascope new

[Re: strdst]
#5675130 - 02/12/13 01:25 AM Attachment (8 downloads)

I think you may have a good idea Keith removing the whole plate with plug so its like the RV-6.
Still I wonder why Criterion went to all that trouble to fill in the back of the cell and only having a small port with a removable plug. They obviously were on to something we are not familiar with.
I would start by trying out the removable plug. With it removed and in place under various conditions. In focus and defocused stars should help tell you if the mirror is not equalized or if tube currents are the problem or atmospheric seeing is spoiling the view, if you do have any problems.
Its tough trying to figure out which of all the possibles is causing the problem. Once you know where the problem is coming from and can correct it then the newt is fabulous. I have a long ways to go although I'm better then I was.

I did see Trixie she's darling. Does she have the powers to glow, looks like she might. Here Glowy's being silly again as usual:

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tim53
Postmaster

Reged: 12/17/04

Loc: Highland Park, CA

Re: 36.4mm to 1.25" diagonal to 6" Dynascope new

[Re: actionhac]
#5675548 - 02/12/13 10:29 AM Attachment (7 downloads)

Me? I've got Rodney to certify my scopes:

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rguasto
professor emeritus

Reged: 11/18/10

Loc: Long Island, NY

Re: 36.4mm to 1.25" diagonal to 6" Dynascope new

[Re: strdst]
#5675570 - 02/12/13 10:44 AM

I added a fan to the rear of my 8" dynascope. Works extremely well and stays on all the time with no vibration detectable during observing. It's and 80mm USB fan with an 80mm to 60mm (reducer) blowing onto rear primary.
Pictures are in classic scope photo gallery. Also posted in yahoo group under "8" deluxe dob"

http://www.cloudynights.com/photopost/data/508/159290resize1-thumb.JPG

http://www.cloudynights.com/photopost/showphoto.php?photo=23091&password=...

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strdst
Post Laureate

Reged: 03/23/08

Loc: Oregon Territory

Re: 36.4mm to 1.25" diagonal to 6" Dynascope new

[Re: rguasto]
#5688207 - 02/19/13 02:04 AM Attachment (4 downloads)

I actually got two good observing nights last week. One ended in dew/ice accumulating pretty quickly. The other in fog off the river in the backyard. But the air was still and I had some nice targets long enough to appreciate...

The Vixen adapter to use my new "old" Edmund 1.25" diagonal is fantastic! And the Dynascope even being out of collimation was very impressive. I know the previous/only owner never touched the adjustments. He was quite proud of that

I just want to get a bit of advice before anything goes south. The three secondary mirror collimating screws are reluctant to turn. They seem to be brass (soft) and I don't want to bugger them up right off. I'm wondering if removing the spider (?) (what is this style secondary holder called?) from the tube is wise while loosening things up. And what do you loosen first and second and third. Here are a few pics. This guy is pretty cool!

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strdst
Post Laureate

Reged: 03/23/08

Loc: Oregon Territory

Re: 36.4mm to 1.25" diagonal to 6" Dynascope new

[Re: strdst]
#5688210 - 02/19/13 02:08 AM Attachment (4 downloads)

I don't have a laser collimator, but a neighbor gave me this to use...

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strdst
Post Laureate

Reged: 03/23/08

Loc: Oregon Territory

Re: 36.4mm to 1.25" diagonal to 6" Dynascope new

[Re: strdst]
#5688213 - 02/19/13 02:10 AM Attachment (4 downloads)

And this is what I see looking through that tiny hole...

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actionhac
Post Laureate

Reged: 08/09/08

Loc: WA

Re: 36.4mm to 1.25" diagonal to 6" Dynascope new

[Re: strdst]
#5688683 - 02/19/13 11:17 AM

Keith if what your camera is seeing through the hole is the same as what your eye is seeing try just grabbing hold of the spider and give it a slight turn to centralize things.
I don't remember the Criterion holder but the 3 brass screws are all pushing against the diagonal holder if I remember correctly so if you loosen one a hair all 3 should loosen slightly but this will change collimation. It may also be possible to slacken off the center stud to relieve pressure on the 3 screws. I wish I had one in front of me, I can't remember how it works.
Try moving the spider first before touching the 3 screws.
The spider is attached to the tube with one screw, rotate the spider on that pivotal screw and see if the primary is centered in the diagonal when looking through the small hole in the cap.
You don't need a laser. The cap with a hole is fine at f8 focal ratio. I think the Dynascope may be f8.5.
As a final touch up defocus a star like Polaris and see if the rings are concentric.
Polaris is good because it doesn't move.
Don't defocus too far, just 3 or 4 rings and work through from low to high powers.
I use one of these:
http://www.scopestuff.com/ss_coll2.htm

Robert

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strdst
Post Laureate

Reged: 03/23/08

Loc: Oregon Territory

Re: 36.4mm to 1.25" diagonal to 6" Dynascope new

[Re: actionhac]
#5690126 - 02/20/13 02:17 AM

Thanks Robert,

I got home late tonight. Cloudy and cold. I'll start with the Twist as you recommend. Nearly same vintage after all

If the twist doesn't collimate the secondary, maybe the Jerk will. I hope I don't need to
escalate to the Funky Chicken....Not a pretty sight

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rguasto
professor emeritus

Reged: 11/18/10

Loc: Long Island, NY

Re: 36.4mm to 1.25" diagonal to 6" Dynascope new

[Re: strdst]
#5690315 - 02/20/13 07:55 AM

That collimation cap is all you need. That F8 scope will have a large "sweet spot" somewhere around a centimeter. Don't even think about a laser in that focuser - it will seat differently every time you insert it and each time it will be way off. To adjust the tilt of the secondary you must loosen the center nut, then adjust the 3 screws. Start by loosening the screws so you don't strip the slotted heads
-Rob

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strdst
Post Laureate

Reged: 03/23/08

Loc: Oregon Territory

Re: 36.4mm to 1.25" diagonal to 6" Dynascope new

[Re: rguasto]
#5704676 - 02/28/13 01:55 AM Attachment (8 downloads)

Had some time to make adjustments of the secondary. The sky offered some sucker holes last night, the view of Jupiter was quick but not conclusive. Too much turbulence even for a 60mm refractor that I know can do so much better. Sometimes I just really hate the weather where I've chosen to live Waaaaughhhh!

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strdst
Post Laureate

Reged: 03/23/08

Loc: Oregon Territory

Re: 36.4mm to 1.25" diagonal to 6" Dynascope new

[Re: strdst]
#5725119 - 03/11/13 02:10 AM

I got a few opportunities to view Jupiter. The image seemed sharp, not very contrasty, and quite a bit of spurious light. I shined a maglight through the backside and it looked like M-13 through a really big scope. Do I need to recoat? Will it tame the spurious light?

Post Extras:

Joe Cepleur
Pooh-Bah

Reged: 03/18/10

Loc: Dark North Woods

Re: 36.4mm to 1.25" diagonal to 6" Dynascope new

[Re: strdst]
#5725466 - 03/11/13 09:51 AM

Great scope! The perfect seductress for a now former refractor guy. Love the round spider. Neat ventilation plug.

The cap over the mirror end of the tube may or may not effect air flow appreciably, but it does reinforce the edges of the fifty-year-old tube. Maybe desirable to leave it in place.

I recognized the view from ActionHac's yard even before reading his name. Guess I've been on the forum for a while!

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bremms
scholastic sledgehammer

Reged: 08/31/12

Loc: SC

Re: 36.4mm to 1.25" diagonal to 6" Dynascope new

[Re: Joe Cepleur]
#5725568 - 03/11/13 10:50 AM

It should have very good contrast at F8 with a small diagonal.
If its the original coating. it's going to not give great images. I have a few really nice mirrors in my storage area. I'm planning on some nice reflector biulds in the next few months.

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actionhac
Post Laureate

Reged: 08/09/08

Loc: WA

Re: 36.4mm to 1.25" diagonal to 6" Dynascope new

[Re: bremms]
#5725699 - 03/11/13 12:05 PM Attachment (7 downloads)

I just did the same with my RV-6 mirror.
I haven't viewed with this mirror yet.
I don't know much about this subject, but looking at my picture below I'd say the rather spotty unevenness of the aluminum coating is probably erosion.
I would imagine when the aluminum was originally deposited it was much more uniform and probably the aluminum molecules were nice and evenly distributed.
Now with this erosion and the hills and valleys in the coating we will see a loss of contrast and some scattering of the light.

Post Extras:

Bill Griffith
sage

Reged: 08/12/09

Loc: Ca.

Re: 36.4mm to 1.25" diagonal to 6" Dynascope new

[Re: actionhac]
#5725788 - 03/11/13 12:49 PM

Robert,

Does your mirror need recoating? Sure looks like it.
Loss of contrast probably. Not so sure if scattering is a function though. I don't think the non coated surface sends photons on a different path. My understanding is that the figure has not changed.
Reflectness is actually higher with thin coatings.

Many mirrors with higher reflectness will show a flashlight image through the backside. A visual glance tells our brain something is wrong with what we see. Yours is pretty thin though!

Bare aluminum coating is on average about 1000 to 1500 angstroms which I believe amounts to .1 micron. 25 microns to .001 of an inch.

Coatings do not effect a figure of a mirror or lense if done close to correct.

Bill

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bremms
scholastic sledgehammer

Reged: 08/31/12

Loc: SC

Re: 36.4mm to 1.25" diagonal to 6" Dynascope new

[Re: Bill Griffith]
#5725816 - 03/11/13 01:04 PM

I did some experiments with coatings in an independent lab study in college. Reflectivity was pretty constant above 1/4 wavelength thick ~1500 angstroms. Below 1000 it did start to fall off and below about 700 was the knee of the curve. We went up to about 4000 angstroms and there was no easily measurable change from about 1200-4000 angstroms.

Yes that is an eroded coating. A few pinholes is normal but that coating is not good and will cause scattering.and you should be able to see a bulb filament through the coating.

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bremms
scholastic sledgehammer

Reged: 08/31/12

Loc: SC

Re: 36.4mm to 1.25" diagonal to 6" Dynascope new

[Re: bremms]
#5725837 - 03/11/13 01:14 PM

I just found my data from the thin film experiments. The coatings were flat in response down to about 700 angstroms then gently tailed off the "knee" was more like 400 angstroms.
Better to check something you did nearly 30 years ago than rely on memory. Thicker coatings are going to be more uneven due to the vaporization techniques and are to be avoided.
Bob hit the nail on the head with this one.

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Bill Griffith
sage

Reged: 08/12/09

Loc: Ca.

Re: 36.4mm to 1.25" diagonal to 6" Dynascope new

[Re: bremms]
#5725995 - 03/11/13 02:37 PM

Mea Culpa

My apologies Robert I didn't mean to imply you were wrong. Just asking the professionals out there lurking

Thanks Marc for getting the rusty gears turning in the right direction.

I had completely forgot about introducing the index of refraction! That would scatter visable wavelengths.

Although I was under the impression that a 1/4 wave step would need to be 10 times the amount of a 1500 A deposition.

The reflectness not reflectivity measurements I have acquired are from a Carey 5000 and hyperspectral cameras.

Bill

Edited by Bill Griffith (03/11/13 02:45 PM)

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bremms
scholastic sledgehammer

Reged: 08/31/12

Loc: SC

Re: 36.4mm to 1.25" diagonal to 6" Dynascope new

[Re: Bill Griffith]
#5726166 - 03/11/13 03:47 PM

1/4 wave is about 1500 angstroms. 5500 angstroms is about the center of the visual spectrum. Which is 550 nanometers. Mixing the two can be confusing. Angstrom is 10-10 and Nanometer is 10-9. I always try to use nM.

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strdst
Post Laureate

Reged: 03/23/08

Loc: Oregon Territory

Re: 36.4mm to 1.25" diagonal to 6" Dynascope new

[Re: bremms]
#5729302 - 03/12/13 11:08 PM

Ok Robert is a reflector kinda guy although his inner refractor kinda guy burns bright. Robert is conflicted, which makes him totally awesome here. Robert knows when a mirror ain't up to potential and knows a great achromat when he sees through one. Me... I know when I'm sockless looking through a refractor but reflectors puzzle me.
So far this beautiful Criterion 6" comes in second to my standard grab and run, a HOC.Monolux 4380 60x910 refractor Goodwill scope. Certainly the Criterion is brighter, but both scopes are comparable for image sharpness at similar magnifications. If the haze of light around bright objects (Jupiter) indicates a recoat of the mirror or mirrors is necessary, where should I send it? The scope was born in 1957 and has never been touched. At that time Criterion was promising 1/20 wave optics IIRC.
I certainly don't want to recoat if it is unnecessary. Don't even want to remove the mirror if it is unnecessary. I'm a cheap refractor kinda guy. These fussy mirrors scare me!

So should I consider a recoat in order to minimize the stray light or keep working on collimation instead?

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strdst
Post Laureate

Reged: 03/23/08

Loc: Oregon Territory

Re: 36.4mm to 1.25" diagonal to 6" Dynascope new

[Re: strdst]
#5729379 - 03/12/13 11:40 PM

BTW,

Trying to post on a phone totally sucks. Which hopefully explains a few things I missed or messed up in the previous post. Sorry.

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actionhac
Post Laureate

Reged: 08/09/08

Loc: WA

Re: 36.4mm to 1.25" diagonal to 6" Dynascope new

[Re: strdst]
#5729467 - 03/13/13 12:43 AM Attachment (3 downloads)

I'm not so sure about the flashlight coating test, I think it may be overly critical shinning a flashlight at any lens or mirror its going to look horrible.
I put my sheer no-nonsense mirror back in the tube and it really looks good through the eyepiece. So I did the flashlight coating test on a brand new mirror and it looks like *BLEEP* too!
How clean is your mirror Keith, a really dirty mirror can scatter light. Nice thing about your Dynascope is you can take out the screws holding the cell in the tube and if you mark the cell and tube and put it back with the marks in the same place it shouldn't affect collimation.
I'd forgot just how good the Criterion's are. If your mirror isn't worse than mine your scope should perform beautifully. I know it will need to be working very well though to please a refractor guy!
OK here's another shot of mine:

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strdst
Post Laureate

Reged: 03/23/08

Loc: Oregon Territory

Re: 36.4mm to 1.25" diagonal to 6" Dynascope new

[Re: actionhac]
#5729521 - 03/13/13 01:30 AM

I think mine looks about like your last post... 55yrs into it ,never a recoat. This scope for its size is pretty heavy. To replicate a view through a fantastic 60 m isn't enough to keep it around. I've heard a few recently bad recoater stories. If I send it away to.who?

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actionhac
Post Laureate

Reged: 08/09/08

Loc: WA

Re: 36.4mm to 1.25" diagonal to 6" Dynascope new

[Re: strdst]
#5729543 - 03/13/13 01:40 AM

I don't know who to recommend Keith. I thought I would send one here:
http://www.nova-optical.com/
I have a Nova mirror in my dob and the coatings have held up very well for ten years old exposed in a open truss that lives out in my shop year round next to the lawn mower and the rototiller.

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dgreyson
sage

Reged: 11/06/12

Loc: South Carolina

Re: 36.4mm to 1.25" diagonal to 6" Dynascope new

[Re: actionhac]
#5731048 - 03/13/13 08:21 PM

I had my 10 inch recoated by nova and was very pleased with their service several years ago. Havent delt with them recently but was planning on sending my 12 inch later this summer.

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