4" refractors vs 6" reflector on planets

[michael.h.f.wilkinson]

On a more serious note, one thing which did not come up in the discussion is the quality of the EPs. When checking out a bog-standard newt, with bog-standard plossls, you cannot blame every difference you see compared to a TEC APO with Nagleror Ethos EP on the objective. I found that sticking a Vixen LV into the focuser of the Konus 4.5" I have as wide field kit, completely transformed the scope, when compared to the Huygens and MA EPs usually supplied with it.

[great_bear]

now you scare me if I pay a lot of (for me nevertheless) money and risk getting a bad mirror?

Well, you could always upgrade to an Orion Optics Newtonian, and then you can choose exactly the quality of mirror you want.

[Astro_Baby]

But then you'll have no guarantees the rest of it will work

Hides behind sofa

[Brinders]

The difference between Newt owners and SCT owners is that most Newt owners at least realise that their scope is supposed to be collimated by the user. Few SCT users bother to even try.

That's a pretty broad generalisation! I check the collimation on my SCT every time I use it both prior to observing and during the session. I can honestly say I have only had to collimate it the once when it first arrived. My TAL newtonian needs collimation at each session. But the SCT lives outside and moves a few feet at most from its Keter plastic cabinet in the garden, while the TAL lives indoors and has to be moved through a couple of doorways and garden gates before it eventually gets set up in the garden.

Brinders

[michael.h.f.wilkinson]

I agree with Brinders. Maybe it is because I built a Newtonian before, but I am well aware of collimation issues, and check mine regularly. I do find the C8 is very solid, and I have not had fiddle with collimation much after I took delivery of it.

I do not know how other SCT owners fare, but I feel you really need to jar the optics badly for a well collimated SCT to need recollimation.

[Rob]

I cannot agree when comparing the SCT. I've had 2 C8's one ok, and one very soft. And I collimate my scopes to an inch of there lives, and will offten collimate 2/3 times a night with my newt.

Problem is we are all buying mass produced scopes, some are good, some are poor, some are superb!. this goes for Newts, SCT's and refractors.

The only way to be sure on quality is to go for certificated optics or make your own.

Try not to worry so much on which will be the best, just enjoy what you have to work with.

Rob

[KaStern_Former_Member]

Hi Bombassa,

Whats this? Bad mirrors?

How common is this?

I was looking for a larger 'production line' newton for next year but now you scare me if I pay a lot of (for me nevertheless) money and risk getting a bad mirror?

Noone could tell you how common this is because noone has tested a large number

of these 130mm f/5 mirrors.

In the thread I the member BerndGaehrken presented some pictures to point out

that his 130mm f/5 sample was a very good sample. Later on the mirror has been tested too by Mr Kafalis and the result was mixed. It too had a relatively steep step

in the surface, but towards o edge that mirrors was better than the first sample.

No Strehl ratio was calculated. From what Stathis Kafalis wrote it seems to be likely

that this mirror fails to be diffraction limited too.

If you are planning to buy a newt primarily for planetary viewing I propose to buy

a long focal length one. Fpr example a 150/1200mm Newt.

If you plan to observe most of the time deep sky objects you will use lower magnifications

most of the time and mirror quality will be less important than fpr planetary viewing

(but be not un-important!) .

Maybe the vendor or the manufacturer quarantee specs for the mirror?

If so you could return a bad mirror.

cheers, Karsten