Orion Optics 1/10 wave thoughts.....

[Doc]

I'm thinking off building myself a planetary dobsonian. I've been looking at the Orion Optics 150mm mirrors, this is what they say on their website..

With our continuous developments in optics we have now reached a position where we can offer with 100% reliability, optics which we believe are the best availabe anywhere in the world. Our Ultra range has Strehl values typically around 99% with RMS values of the order of 0.02PV. Coupled with a guaranteed PV wavefront error so small, it often is less than 1/10PV wavefront

My question is how much better would this 1/10 wavefront be then say a typical 1/4 wave mirror is it really worth that extra money?

The idea is to make the ultimate lunar/planetary/double star splitting scope and would the optics above combined with a F11 ratio be ideal?

[russ]

Those optics will make the basis of a really nice planetary scope. I had the f8 version back in 2007 and it was very nice indeed. Saturn showed plenty of detail, nice contrast made picking out the banding that much easier. My only doubt was the cheaper Skywatcher Skyliner 150PL appeared to do just as well. Perhaps my 150PL was an exceptional example but there was nothing to choose between them.

Had i not been in a situation where i need to sell, not buy, i would have bought the 150PL in the For Sale section for £100. That would have done me nicely as a planetary scope.

[Doc]

There must be a difference Russ between a skywatcher with a typical 1/4 wave 93% strehl figure and a OO 99% 1/10 wave figure, or why would they make these so called ultra spec mirrors.

There are so many factors at work here, the main being your own personal eyesight I persume.

Has anyone else looked through these 1/10 wave mirrors and has anything to add.

[dweller25]

I too have thought long and hard over this.

I concluded that if I lived under skies with excellent seeing then it would be worth the extra money for 1/10th wave optics.

But in the UK we don't have excellent seeing so 1/8th wave is fine.

This may help ....

http://stargazerslounge.com/equipment-reviews/68085-orion-optics-v-skywatcher.html

[Doc]

That made very interesting reading, how I missed that first time round I don't know.

I think the main problem here is light pollution, get a 1/10 wavefront under dark skies and it should or will perform better then a 1/4 wave mirror.

Still worth considering when OO will sell a 6" F11 primary and secondary for £289.

Could be a nice little project.

[Earl]

I have been looking at this myself to amuse myself while its dead at work.

From what I see the Premium optics are really only of benefit in the right conditions, so if your viewing location has great skies for at least 50% of your observing time, then a Premium setup Might be worth considering.

Thats my take on it anyhow.

[dweller25]

A 6" F/11 newt will perform very well on the planets, it will probably match a premium 5" APO.

Also worth considering is the OO 8" F/8 Newt which will probably match a 7" premium APO.

[johninderby]

It's not too difficult or time consuming to make a top quality 6" mirror, hence the price from OO isn't too bad. With this size mirror there's no point in going for anything less than the 1/10PV as the savings would be very small. BTW the OO 1/10PV rating actually means better than 1/10 so you would probably end up with something around 1/11PV.

One reason for going for the top optics is that you can push the magnification higher than you can with a regular mass produced set of optics. The reduced light scatter of the smoother mirror surface stops the image from softening as much as you increase the magnification.

Sounds like a great little project.

John

[Peter Drew]

A 1/10 wave set of optics should certainly show a performance benefit over a 1/4 wave set, as would a 1/8 wave example. A side by side test was conducted by Sky and Telescope some years ago, comparing 6" mirrors of 1/2 , 1/4, 1/8, 1/10 and 1/20 wave correction. The 1/2 wave was withdrawn as being too poor and also the 1/20 wave on the grounds that it didn't represent normal availability. The result was that all the viewers rated the 1/8 as obviously better than the 1/4 but only the most experienced could tell the difference between the 1/8 and 1/10. An additional factor with high quality mirrors is the focal ratio as long focal lengths will usuall have small secondaries. Although these optical sets are expensive relative to mass production items, when compared to APO refractors of similar aperture it's a cheap high performance option. This topic is one that interests me greatly, I am in the process of constructing a high optical quality 12" F8.5 Newtonian, and a 12" F20 Dall-Kirkham Cassegrain for side by side comparison with an existing 12" F20 classical Cassegrain and a very good 12"LX200.

[johninderby]

OO can make you up a set of 1/20PV optics if you wish, but in their words a normal observer would never be able to tell the difference between them and the 1/10PV optics. The 1/20PV are really only intended for specialised research instruments.

I wonder what the PV is on the ODK20 f/10 Infrared scopes that OO is building for the ESO?

John

[Moonshane]

This thread is great and finally makes my mind up in terms of premium refractor (eg Vixen Flourite 102) vs. premium newt anyway. I am going to buy either the 8" f8 or the 6" f11 dobsonian once I can save the cash! I may even sell my refractor to do so.

I thought about making one myself but felt that the cost of the additional parts if decent quality would cost about the same as buying the whole dob unit from OO.

John's projects sound amazing. I looked at (but not through) a Tak Mewlon 10" the other day - truly a thing of beauty.....(I think this is a Dall-Kirkham Cassegrain?)

[Doc]

I'm also waying up the cost factor, I e-mailed OO and they will supply a 150 F11 dob with 1/10PV fully built with rockerbox and cradle for £549.

A basic mirror set is £289.

[dweller25]

The 150mm F/11 OO Newt will have the same planetary performance as a TEC140 APO.

The 200mm F/8 OO Newt will have the same planetary performance as a TEC180 APO.

Hows that for value for money.

[beamish]

The 150mm F/11 OO Newt will have the same planetary performance as a TEC140 APO.

The 200mm F/8 OO Newt will have the same planetary performance as a TEC180 APO.

Hows that for value for money.

That's quite a fuse you've lit !

Stand well back it's only a matter of time

[dweller25]

Even Roland Christen says Newts are the best planetary telescope .....

What is the Best Planetary Telescope - How To

BUT - I prefer to view from the back and see nice tight star images.

[ncjunk]

This thread is making me feel guilty for having an spx 8" f8 1/10 pv sat in my garage gathering dust! I really must use it.

[albedo0.39]

Nice project Mick. Seems like you have some good plans in mind with the improved optics from OO. I think for planetary you need a smaller secondary ratio compared to (say) the LB so wonder what you had in mind ?

having seen (but new viewed) a Takahashi Mewlon 12" with a much smaller obstruction, I can vouch for the attraction of a good planetray scope, but given the choice and unlimited funds, I'd ache for a decent Apo....

Tough choice !

[Moonshane]

on this point, would it be worth me buying an additional smaller secondary for my 12" f5 dob? would that improve the contrast and or planetary performance at all?

the reason I ask is that I had an estimate to refigure my mirror to 1/10 PV and recoat for £400 including return shipping and VAT etc.

might be an option for me and would prevent cries of 'what??? another scope????'

[russ]

Oh no this thread is awful, really bad! I had successfully talked myself out of a dedicated planetary scope, convinced myself the OO was no better than the SW and now i'm lusting after another OO 6" f8 newt.....you lot are terrible!!!!

[Doc]

Nice project Mick. Seems like you have some good plans in mind with the improved optics from OO. I think for planetary you need a smaller secondary ratio compared to (say) the LB so wonder what you had in mind ?

having seen (but new viewed) a Takahashi Mewlon 12" with a much smaller obstruction, I can vouch for the attraction of a good planetray scope, but given the choice and unlimited funds, I'd ache for a decent Apo....

Tough choice !

My 16" LB is fantastic at DSO's, it really does excell at finding this little elusive plantaries, but it sucks at planets and splitting binary stars.

I cannot afford a APO on an EQ6 so the plan is:

A OO 150 F11 mirror set with 1/10PV optics and a strehl of at least 99%. The secondary is only 1" so pretty unobstructive.

I'll source my own tube and mirror cell to fit. I'll then fit a good quality focuser and a curved spider so the diffraction spikes are smudged so it should improve the views.

As for the rockerbox I've had an idea using a thrust bearing and locking collar for altitude and transfer bearings for azimuth. Include a wixey on the OTA and a built in azimuth encoder on the base.

Then you have the ultimate planet killing scope.

[russ]

Sounds great Mick....good luck with it. Don't forget to keep an eye on the Buy'n'sell though. There's been a few OO 150 and 200 planet killers on there and they simply don't sell. I remember a 200 f8 1/10th PV dob that started at a high price but ended up down at £300....and still not selling. You could possibly save yourself some serious money.

[John]

This is a rather late addition to this thread (I've been away) so I hope it does not duplicate anything but this report by Ade Ashford may be of interest:

Orion Optics OD150L De-luxe

I very nearly bought an F/8 1/10 wave OO newt a couple of years back for this purpose and still fancy something along those lines. As Russ says, they go for a snip used compared to the new price.

[ollypenrice]

I've had a couple of OO 10th wave scopes here and they were impressive. I didn't spend ages at the EP with them or do any back to back. However, I don't agree that you need a great sky to see the difference for planetary observing because it is the ability to take magnification that matters.

I'm not going to bite over the TEC-Newt assertions which may be correct but personally I would never say 'will' give the same result as a TEC 140 or 180. I would go no further than to say 'should.' There is collimation to think of and the greater susceptibility of the Newt to tube currents. I recently described a watercooled one-20th wave temperature-controlled Newt on the forum and that was totally outstanding. Last night the TEC was in a world of its own, too, holding nearly 400x on the moon. The turbulence was slow moving enough to make the high power worthwhile, just.

But a slow, accurate Newt is a brilliant idea for planetary observing and should perform out of its skin if all the other factors, mostly thermal, are sorted. BTW, the watercooled Newt I described was painted black, not white, the builders asserting that getting rid of heat at night was more important than not absorbing it by day.

Are you thinking of curved secondary vanes to smear out any diff spikes? Might be worth it on the bright planets?

Olly

[johninderby]

I've had a couple of OO 10th wave scopes here and they were impressive. I didn't spend ages at the EP with them or do any back to back. However, I don't agree that you need a great sky to see the difference for planetary observing because it is the ability to take magnification that matters.

Olly

Absolutely!

It surprises me sometimes just how much magnification you can use with an OO 1/10PV mirror on lunar/planetary.

BTW on the subject of curved vane spiders a good one will cost about twice as much as a 4 vane straight one. Apparently they have to be set up just right to get the full advantage. Speak to OO about them as they can do them as an option.

John

[Moonshane]

right that's it. I'm selling some books. New Naturalists anyone??

definitely an 8" f8 1/10th HILUX PV OO dob. just need to find one.......

if it beats my refractor, may well even sell that too.