8" F6 1/10 wave V's 10" F4.8 1/6 wave

[John]

I'm weighing up the pros and cons of moving from my current 10" F/4.8 Orion Optics Europa Deluxe which has a 1/6th wave and Hilux coatings to an 8" F/6 OO SPX with 1/10th wave optics.

I suppose I'm tempted by the idea of really excellent optics (assuming OO's assessments of their products optical accuracy are reliable) in a reasonably lightweight and portable package. While I enjoy DSO observing, my viewing location lends itself more to planetary / lunar / binaries due to some light pollution, surrounding houses and trees.

I owned a Skywatcher 8" F6 dobsonian for a while and really enjoyed it's relatively trouble free and consistent performance so I'm hoping that the OO SPX 8" F/6 would offer this to even higher levels.

I'm also wondering if the increased optical quality would, at least to some extent, outweigh the aperture reduction, at least on the sorts of objects I spend most of my time observing ?.

Has anyone any thoughts to help my deliberations ?.

Thanks

[johninderby]

I used to have an OO 8" f/8 dob with the 1/10PV mirror, and on lunar / planetary it would out do a standard 12" dob (Meade, Skywatcher etc). I wouldn't imagine that there would be that much difference between the OO 8" f/6 1/10PV and your OO 10" f/4.8 1/6PV on lunar / planetary.

Here's another thought. Get the dob version with the same specs as the SPX, as there's not much difference in price, and then you could use it as a dob or EQ mounted.

John

[dweller25]

I have an excel program that calculates effective planetary performance for different apertures and secondary obstructions, but not surface accuracy of the mirror.

The three scopes plus the 10" F6.3 version mentioned above in terms of planetary contrast effective aperture rate as :-

8" F/6 - 176mm

8" F/8 - 187mm

10" F/4.8 - 228mm

10" F6.3 - 230mm

So on the face of it the smaller aperture will not be as good as your current scope, although the better mirror will reduce the difference a little.

I currently use a Skywatcher 8" F/6 on an EQ mount which I am VERY pleased with, in fact I cannot believe how well it performs.

I have been pondering for a long time about upgrading to either an OO 8" or 10" with the 1/10th wave optics and will be very interested to see what you do and what results you get.

If the view is the priority I think you will find it difficult to meaningfully improve upon your 10" with 1/6th wave optics.

If your finding the 10" too big then the 8" F/6 with 1/10th wave will be a winner but with slightly reduced planetary detail.

[ollypenrice]

If you are really keen on planetary might you not even consider a still slower Newt, which would have to be bespoke - eg a David Lukehurst? The Americans have one or two long focal length planetary Newtonians on the market from the specialists, I think.

Olly

[johninderby]

Some useful calculations, but the one additional factor that needs to be taken into account is the ability of the better optics with their smoother finish, and hence less light sctter, to accept higher magnifications. If only there were some way to effectively quantify this.

I did mount my 8" f/8 on an HEQ5, and it was fine for visual use. Short mounting pillar needed though to keep the eyepiece at a convenient height. I really liked the 8", but upgraded to a 14" with 1/10PV and a StellarCAT drive, great for visual use and actually easier and quicker to set up than the 8" on the HEQ5.

John

[neil phillips]

Rather than a 8" f6 spx i would get a 10" Europa f6.3 with 1/10th optics, a friend put a fan in the Europa which helped a lot, the closed back design is not good, as the mirror will never ever completly rid itself of thermal waves down one edge of the primary, but using a fan in this system does get the thermal problem minimized to the point were great lunar and planetary imaging is possible. My 10" Europa really is in a class of its own, when i fit a spx cell and open up the back, the performance will most likely equal a large refractor. And im not kidding, we are talking large razor sharp optics here. A 1/10th pv f6.3 10" Europa will almost certainly out perform a 8" SPX, My 10" Europa will often go sharper than my 12 " 1/12TH PV F6. SPX

Being affected less by thermal issues even though it still has a closed back

Poor seeing also just gets eaten up by this scope, often i can produce a good result even in poor seeing. Those who have followed my work will know im not mistaken here.

Get the 10" 1/10TH PV F6.3 it will blow your mind

[brianb]

I'm also wondering if the increased optical quality would, at least to some extent, outweigh the aperture reduction, at least on the sorts of objects I spend most of my time observing ?.

IMO the extra aperture will trump anything else ... especially for imaging.

Great optics aren't everything, you need the support package to make them work properly - robust mount, well ventilated mirror cells, insulated tube ... f ratio is a secondary matter given that you are competent to collimate the thing.

[ollypenrice]

Neil, you might well be very interested in a telescope made by Ralf Ottow. It is a 12.5 inch Newt with watercooled primary. The watercooling is not all that complicated, a second glass disc on the back of the primary separated by glass blocks and silicone, with a spiral maze inside to promote even circulation. Water goes in (or out) in the middle and the opposite at the edge. Coolant is 0.75 litres of iced water run by an aquarium pump for about ten minutes to get the mirror about 2 deg below ambient. Then it is removed. The effect is staggering.

Olly

[brianb]

get the mirror about 2 deg below ambient. Then it is removed. The effect is staggering.

It certainly would be here: the mirror would be covered in condensation!

[Rob]

I had a the SPX200 F6 and on planets it was indeed the best scope I ever owned!. I so regret selling it

[johninderby]

There's an Orion Optics CT10 Ultra f4.8 1/10PV carbon fibre OTA up for sale on Astrobuysell....only £1,700.00

http://www.astrobuysell.com/uk/propview.php?view=33941

John

[John]

Thanks for the very interesting contributions folks. Lots to think about and clearly not a decision to be rushed into.

If I made a change it would only be for performance reasons as I find the 10" F/4.8 Europa OTA very managable for a 10". In fact, on my alt-az mount it's probably the nearest to a 10" "grab and go" that you can get.

Any further viewpoints welcomed

Thanks again !.

[neil phillips]

The subject of F number is a bit of thorny one, i have no direct evidence of what i belive, and is based purely on guess work from what i generally see in the imaging arena.

Its true that there certainly is great planetary work being done by guys using faster f4.5 scopes at say 10"

But most often the great work is coming from the larger 16" 18" f4.5 scopes in america.

I think the reason being is, as the scopes size increases so does the focal length, and the f number starts to become slightly misleading.

As a example i have a 10" f6.3 at 1600 mm focal length but also a lower f number f6 12" Scope with 1800 mm focal length. the work i have seen with the Orion f4.8 doesnt generally seem to reach the dizzy heights i have achieved with my f6.3 and by others like George tousardis

Maybe theres a certain limit at which a focal length should be before your job starts to get increasingly more difficult. And this might be one reason why i have not really seen a lot of consistent 10" f4.8 orion optics planetary work. the images are often at a much lower scale. though nice that they are of course

Now the subject of collimation, at f4.8 collimation may also need to be a bit more precise than the f6.3 counterpart. at times when my collimation may not have been as great as what it should have been ive still managed to get a nice sharp high power shot. I suspect under those circumstances with the f4.8 i may not have done so well, with probably a slightly smaller scale and probably more fuzz to boot. This not what you want trust me.

No matter how good you are, collimation errors can often creep into using a newtonian over a lengthy period of time, ( it certainly did with me ) So unless your great at collimation and can keep it that way for long periods of time.

personally i feel the f6.3 will most often outperform the f4.8 version Especially if your learning collimation over time the way i started.

I collimate both the secondary and primary ( tweak ) in the feild each and every time i image, so this notion that once done everything is fine, from my experiance is just plain wrong. John H also collimates like this in the feild everytime he images with hes 14" spx.

Ive read its easier to make a great optic at a higher f number. But with testing the way it is, Not sure if that would still be relevant or not ?

Either way you pays your money you takes your choice. I would strongly urge you to get a 10" 1/10th pv f6.3 either a europa with a modded fan or a spx. great as the 8" is its a little limiting. in time you will want that extra size.

I may at some point sell my 12" CUSTOM f6 1/12th pv spx 300 but not sure about that yet ive just toyed with the idea images on the planetary section

Olly ive seen this mentioned before does it work better in dry climates perhaps ? just refering to what Brian said

[John]

Thanks for the further thoughts Neil.

For now I'm going to stay with my 10" F/4.8 but concentrate on getting the collimation spot on, upgrading the primary mirror cell and introducing some active cooling.

Some tactical flocking and an upper tube light shield will also be on the agenda.

I'm still interested in a slower newtonian in the long run though - a 12" F/6 1/12th pv sounds like a dream !.

[johninderby]

Orion Optics does a 16" f/6 mirror so it would be possible to special order a 16" f/6 1/10PV SPX .

Just a thought.......I'll go away now.

John

[John]

Orion Optics does a 16" f/6 mirror so it would be possible to special order a 16" f/6 1/10PV SPX .

Just a thought.......I'll go away now.

John

I saw a custom OO 16" F/5 (?) on an EQ mount at the Widescreen Centre in London a couple of months ago

I'd need to budget for a divorce as well I think .......

[neil phillips]

A 16" f6 would be frighteningly big, not sure a eq6 would be up to that, my 12" f6 is pretty pushing it, i know some have used 14" f5.3

though

Really would be a permanent obs project that. i move my 12" f6 in and out of the house. but its not fun lol. took me a while to get used to it. Now i mount it by myself, no help needed.

mounting a 16 " f6 would be frightening, probably a two man job, unless your a body builder ER WORLD CHAMPION, A well collimated 16" f6 would be interesting to say the least

[johninderby]

A 16" f/6 in a permanent obs......hmmmm. All you'd need is one of these to mount it on.

10 Micron GM4000 QCI

150Kg max load (125Kg for AP)

Now where's that winning lottery ticket ?

John

PS

Liittle bit bigger than an EQ6 isn't it !

[brianb]

All you'd need is one of these to mount it on.

I want one. And an elephant to carry it for me.

[nitram100]

For now I'm going to stay with my 10" F/4.8 but concentrate on getting the collimation spot on, upgrading the primary mirror cell and introducing some active cooling.

I would highly recommend adding some fans to the rear cell, i did it a while back and it drastically improved planetary performance on my OO 10" F4.8.

I have yet to try flocking the scope, but it is on my list of projects!

Here is an image of my rear cell just as i was finishing up the modification. I used 3 x 60mm fans and it cools down the scope in about 15 minutes. Before using the fans, i had a hard time seeing the GRS and Cassini, now they are easy

[John]

I would highly recommend adding some fans to the rear cell, i did it a while back and it drastically improved planetary performance on my OO 10" F4.8.

I have yet to try flocking the scope, but it is on my list of projects!

Here is an image of my rear cell just as i was finishing up the modification. I used 3 x 60mm fans and it cools down the scope in about 15 minutes. Before using the fans, i had a hard time seeing the GRS and Cassini, now they are easy

Thats a very neat job

Did you have that circular metal disk at the back of the mirror cell on yours ? - the collimation bolts go through it and the springs are sandwiched beween it and the mirror cell.

I was wondering if that disk needs to be retained and, if so, I guess that would need to have ventilation holes cut in it as well

[dweller25]

I would agree 100% with Nitram. Adding cooling fans will give you a big improvement in planetary views.

[nitram100]

I did have that big metal circular disc that you are referring to, but didn't have to cut any ventilation holes in it as i placed the fans in a position that allowed the airflow to bypass it..if that makes sense?

Hard to explain but this guy shows it perfectly!

K3's Astronomy Home Page

I have the exact same cell as him, so it was easy to follow.

Also, if i hold the dust cover about 3/4 the way over the front end of the tube i can really feel the air being thrown out, it gives really good airflow.

[johninderby]

Have you considered asking OO for a quote to regrind and polish your existing mirror up to 1/10PV?

To buy a new 1/10PV mirror and secondary from OO would be £670.00, so having yours redone would be a bit cheaper.

John

[brianb]

having yours redone would be a bit cheaper.

I honestly think the saving would be minimal - probably wiped out by the carriage back to the factory. To refigure the mirror means redoing all the polishing as well as replacing the coatings, that's where the time (read: money) goes - the raw material cost is insignificant.