Author Topic: Looking for a 10" F8 mirror  (Read 500 times)

reapriavoland

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Looking for a 10" F8 mirror
« on: December 24, 2017, 03:25:48 PM »
Hi,

Now I'm retired I have the time to build a 10" F8 OTA to your best planetary images realistically possible.

I have a 1/16th wave two" Clave' apartment for it.

How ever no one seems to sell such mirrors.

I'm in the UK and Orion Optics UK are supposed now able to create good mirrors.

Is this my best option?

Cheers.  Andrew.



Anton Yardley

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Re: Looking for a 10" F8 mirror
« Reply #1 on: December 24, 2017, 06:04:45 PM »
<p>Hi Andrew
</p>

I've a complete depth 10" f/8 premium mirror but you're not having that.
The maker of my mirror suggested I purchase a thinner one to aid thermal cooling.
Orion[UK] mirrors banks are thinner.  However, do they perform 'specials' to purchase?

10" f/8 makes for a fairly long OTA.  2m / 6'6" long even with a very low profile focuser on a 30cm/12" tube.
That will require a hefty equatorial mount for fast damping.
I discovered even my Fullerscope's MkIV didn't cope very well with the very long moment arm.

Manoj Jensen

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Re: Looking for a 10" F8 mirror
« Reply #2 on: December 29, 2017, 05:10:25 AM »
I hope you can find it. I think that will make a Great scope. I'm in the central use and for a few years, used a 12 1/2" f/8 on a homemade English yoke mount, no drive, no deep sky photos. Miss that scope.

tioteyclasbeat

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Re: Looking for a 10" F8 mirror
« Reply #3 on: December 31, 2017, 09:08:50 PM »
Andy,

You have hope.

Go to the classic telescope forum on CN where they have Alika Herring mirrors here and there. As you probably know Herring, besides being a true master optician was also the fabricator of those long focus newt optics, (CAVE).

That's honestly your best bet. Also run an ad on CN for WANTED
: 10" F8.There you go.

Pete

Tommy Evans

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Re: Looking for a 10" F8 mirror
« Reply #4 on: January 01, 2018, 11:32:32 PM »
Royce Optics make 10" f/8 mirrors, both standards and conicals, for very reasonable prices.

http://www.rfroyce.c...nd_mirrors.htmClear skies!
Thomas, Denmark

tranardefa

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Re: Looking for a 10" F8 mirror
« Reply #5 on: January 03, 2018, 04:23:18 PM »
I won't try and talk you out of the 10" f/8 (I have a 10" f/8 mirror stashed for a future scope myself), but must point out a couple things for you to think about.

First item is that a 10" f/6 will do the job for imaging and visual too. The reason that we like the f/8s is that they have a larger coma free field which is nice for visual lower power use. At higher (planetary range) magnifications the coma free field (of the f/6) will be across most of the field of view.

Second item is that I love every thing Clave, but that secondary is too big for a planetary optimized 10" f/8 scope. Assuming a 12 OTA diameter and 3" of outside the tube focal plane extension you could get away with a 1.3" diagonal with very careful attention to mechanical alignment and collimation. A 1.5" gives you plenty of wiggle room and is the max size you should consider. Even on an f/6 scope we are talking a 1.7" diagonal.

+1 for Rusted's comments about a thinner primary. I'd shoot for a 1" - 1.25" thickness. Will help you immensely with temperature changes to your environment.

good luck with your project.

twenuvtentu

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Re: Looking for a 10" F8 mirror
« Reply #6 on: January 03, 2018, 04:52:26 PM »
The Royce 10"f8 mentioned above was a really nice performer in a friends dob.Currently it is being reincarnated in a new 'old classic' by Dobby (tom Dobbins). Tom got a hold of the last mount that schaffer built (never finished) and has been hard at work building a scope of yesteryear looks and quality. Anyway The Royce delivered fine images on steady evenings and superior images on a less than good night compared to a tak12"(never stablized) set up beside it.

tiogeroligh

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Re: Looking for a 10" F8 mirror
« Reply #7 on: January 04, 2018, 07:02:20 PM »
Quote
Hi Andrew

I have a full thickness 10" f/8 premium mirror but you're not having that.
The maker of my mirror suggested I buy a thinner one to aid thermal cooling.
Orion[UK] mirrors banks are thinner. But do they do 'specials' to order?

10" f/8 makes for a rather long OTA. 2m / 6'6" long even with a low profile focuser on a 30cm/12" tube.
That will need a hefty equatorial mount for fast damping.
I found even my Fullerscope's MkIV didn't cope very well with the long moment arm.

Hi,

Orion do offer several quality options.

Commercial mirrors seem to have the same focal length:
6" F9

8" F8

10" F6.4

Or nominally those. Possibly due to having one curve generator for blanks.
Or because the geometry of reasonable secondaries works out OK.

Asking for a different sagitta may cost a bit more.

I agree with a thinner mirror with a fan.

I compared a 6" F5 Celestron(Vixen), a Fullerscopes 10" F6.4 and a 16" F5(with 70mm flat so about 13") one night.
The 6" despite living by a storage heater cooled down in 1.5 hours. The 10" took 5 hours and the 16" was still streaming off heat when I gave up. The 10" was best on Jupiter but a 6.5" off axis mask on the 16" was better on Saturn, a lower contrast challenge.

I have left the 10" in an observatory at my old house for my son and and grandson.
Its on a MK4. And damps out in under 2 seconds. You can focus with a steady image.
After a lot of mechanical tuning.

With first light on Saturn with new coatings and Clave' eyepiece it was as good as the first Voyager images (800x600).

Frank Hourigan who made a 1" plate 14" F4 for my club said the optical quality came about 5th in terms of image quality. WIth a 28mm Pretoria I saw plenty of detail on Mars with his mirror.

Certainly Orion could make a good F6.4 for me.
And I have a second MK4 at my new home and a chunky AWR UK made go to system I picked up at the BAA Winchester week last year. Just some of the 'junk' the club I was with said I had bought.
And a Fullerscopes 12" mirror tube with rings for the MK4 so I can have some space for thermals to roll up the tube out of the light path.

Cheers. Andrew.

monsresiwor

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Re: Looking for a 10" F8 mirror
« Reply #8 on: January 08, 2018, 02:00:39 AM »
Quote
I hope you can find it. I think that will make a Great scope. I'm in the central use and for a few years, used a 12 1/2" f/8 on a homemade English yoke mount, no drive, no deep sky photos. Miss that scope.

Hi,

There are two options. Get a configuration I know works on a MK4 mount or do an un-driven mount like yours. The advantage of un-driven is that it could be made to break down for transport to a nearby dark sky site my friend has got permission to use.

Cheers. Andrew.

ridafimist

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Re: Looking for a 10" F8 mirror
« Reply #9 on: January 08, 2018, 11:10:19 PM »
Quote
Andy,

You have hope.

Go to the classic telescope forum on CN where they have Alika Herring mirrors here and there. As you probably know Herring, besides being a true master optician was also the fabricator of those long focus newt optics, (CAVE).

That's honestly your best bet. Also run an ad on CN for WANTED
: 10" F8.There you go.

Pete

Hi,

Worth a look.

Cheers. Andrew.

Richard Washington

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Re: Looking for a 10" F8 mirror
« Reply #10 on: January 09, 2018, 11:15:21 PM »
Quote
Royce Optics make 10" f/8 mirrors, both standards and conicals, for very reasonable prices.

http://www.rfroyce.c...nd_mirrors.htmClear skies!
Thomas, Denmark

Hi,

I will look into that when back in the UK.

I mounted the 14" mirror on some Rover car body damping foam on a piece of 18mm birch plywood without issues.

The simple mounting of the conical mirror appeals to me.

Cheers. Andrew.

Patrick Zhu

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Re: Looking for a 10" F8 mirror
« Reply #11 on: January 10, 2018, 11:30:27 PM »
Quote
I won't try and talk you out of the 10" f/8 (I have a 10" f/8 mirror stashed for a future scope myself), but must point out a couple things for you to think about.

First item is that a 10" f/6 will do the job for imaging and visual too. The reason that we like the f/8s is that they have a larger coma free field which is nice for visual lower power use. At higher (planetary range) magnifications the coma free field (of the f/6) will be across most of the field of view.

Second item is that I love every thing Clave, but that secondary is too big for a planetary optimized 10" f/8 scope. Assuming a 12 OTA diameter and 3" of outside the tube focal plane extension you could get away with a 1.3" diagonal with very careful attention to mechanical alignment and collimation. A 1.5" gives you plenty of wiggle room and is the max size you should consider. Even on an f/6 scope we are talking a 1.7" diagonal.

+1 for Rusted's comments about a thinner primary. I'd shoot for a 1" - 1.25" thickness. Will help you immensely with temperature changes to your environment.

good luck with your project.

Hi,

Well one option is to go for a 10" F5.

If a post I found recently is true my long doublet Clave' 2X Barlow is optimised to correct coma at F5. In conjunction with a Clave'? Also the Clave' Plossls are designed not to have lateral colour at F5. Clearly my 8mm Clave' is better than my 9mm Nagler in this regard. I was recommended the Nagler for average nights in Birmingham and on better ones acts as an intermediate finder for the Clave'.

APM? posted tests on various eyepiece brands coatings and the Claves' had the better throughput. Mine are 1985 vintage and Beacon Hill got Clave' to supply new SS barrels threaded for filters, which came free. So an extra component is not a problem. I just want a 10mm to make up a good range from 25mm down to 3mm with the Barlow. Some people are bothered with reflections off the back surface.

Nagler say to put Parracorrs before or after Barlows depending on the barrel size. I have never had a satisfactory reply as to whether a Barlow affects a Coma Corrector. So is Naglers advice based on it not making a difference?

Cheers. Andrew.

Michael Shen

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Re: Looking for a 10" F8 mirror
« Reply #12 on: January 11, 2018, 03:26:05 AM »
Quote
I won't try and talk you out of the 10" f/8 (I have a 10" f/8 mirror stashed for a future scope myself), but must point out a couple things for you to think about.

First item is that a 10" f/6 will do the job for imaging and visual too. The reason that we like the f/8s is that they have a larger coma free field which is nice for visual lower power use. At higher (planetary range) magnifications the coma free field (of the f/6) will be across most of the field of view.

Second item is that I love every thing Clave, but that secondary is too big for a planetary optimized 10" f/8 scope. Assuming a 12 OTA diameter and 3" of outside the tube focal plane extension you could get away with a 1.3" diagonal with very careful attention to mechanical alignment and collimation. A 1.5" gives you plenty of wiggle room and is the max size you should consider. Even on an f/6 scope we are talking a 1.7" diagonal.

+1 for Rusted's comments about a thinner primary. I'd shoot for a 1" - 1.25" thickness. Will help you immensely with temperature changes to your environment.

good luck with your project.

Hi,

Where can I get a good quality small secondary from, as they are hard to make anyway?

Cheers. Andrew.

Jeremy Kelley

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Re: Looking for a 10" F8 mirror
« Reply #13 on: January 11, 2018, 11:32:15 PM »
Antares Optics seems to be the best source for commercial secondaries, some of the custom mirror makers like Mike Lockwood also make and sell them. I just bought a secondary from Antares that came with an IF report stating 1/30 wave on the wavefront. Expensive but only 1/10 the price of the primary so it's worth it to me for peace of mind. They sell them according to accuracy, and price accordingly, all come with IF reports FWIW.

Just my take on your mirror idea, after spending a long time thinking about the ultimate planet scope for myself, my 10" f8 evolved into a 12.5" f/6 with a thin quartz primary. Living in the western US the temperature tends to drop rapidly after sunset and cooing mirrors becomes the biggest problem for planetary seeing. I've got a mirror on order, hopefully will be done late summer. No matter how perfect a mirror is if it's 2" thick it's not going to work for me here.

afelfillia

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Re: Looking for a 10" F8 mirror
« Reply #14 on: January 13, 2018, 06:09:06 AM »
No it's 1/30th wave on SURFACE error. Flats are (should) always spec'd on surface error. If one wasn't, I would buy somewhere else.
M.