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Old 22-09-2009, 02:00 PM
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toryglen-boy (Duncan)
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Richtey Chretien Vs. Mak Newt

Howdy

Am using a 200mm F5 newtonian for imaging, and its ok, i need to use the MPCC, and it suffers from vignetting, but it has its advantages.

Last night i was asked the question i have waited nearly 10 months to hear

"What do you want for Christmas?"

so i am looking at a dedicated scope for imaging, and i am looking at either an 8" RC, or the equivelant Mak-Newt. Whats best for DSO's, and whats the pro's/cons of each?

i did google this, but i guess IIS member opinions are a factor in this to, so what do you think? they are both around the same size, and cost




ADDENDUM : I just called Andrews, about the Mak-Newt. They said they are not gonna get them in now, as they are overpriced, and there are far better scopes they have in stock for the money.

Last edited by toryglen-boy; 22-09-2009 at 02:32 PM.
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  #2  
Old 22-09-2009, 03:08 PM
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Satchmo (Mark)
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Mak- Newt would be my choice as it will have a wider field of view, faster F ratio, no spider vane diffraction, and has all spherical surfaces so would have smoother optical figure . I don't know about vignetting , I assume they have that covered. Sirius Optics carry them for AUD $2000 I think.

That being said I doubt you would see any significant improvement over the 8" F5 Newt with MPCC . Why not fit a larger secondary if that will help with the vignetting.
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Old 22-09-2009, 03:21 PM
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Quote:
Originally Posted by Satchmo View Post
Why not fit a larger secondary if that will help with the vignetting.
Thats an idea !
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Old 23-09-2009, 08:20 AM
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toryglen-boy (Duncan)
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Quote:
Originally Posted by Satchmo View Post
Mak- Newt would be my choice as it will have a wider field of view, faster F ratio, no spider vane diffraction, and has all spherical surfaces so would have smoother optical figure . I don't know about vignetting , I assume they have that covered. Sirius Optics carry them for AUD $2000 I think.

That being said I doubt you would see any significant improvement over the 8" F5 Newt with MPCC . Why not fit a larger secondary if that will help with the vignetting.
indeed, but i dont know about such things, would it make the vignetting vanish altogether with a larger secondary?

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Old 23-09-2009, 11:56 AM
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Hi Duncan.

Getting the itch...again...your worse than me mate. How many scopes is that weve seen you buy over the last year lol.

I thought, and I'm probably wrong, that coma and vignetting were both caused by the parabolic nature of the mirror/lense and the an RC design provides the flatest fied possible with todays (amature) scopes. Even though the RC has a parabolic mirror there is a corrector in there somewhere?

Thanks
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Old 23-09-2009, 12:22 PM
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Bang for buck I'd wait for the 10" GSO RC
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Old 23-09-2009, 12:32 PM
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toryglen-boy (Duncan)
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Quote:
Originally Posted by White Rabbit View Post
Hi Duncan.

Getting the itch...again...your worse than me mate. How many scopes is that weve seen you buy over the last year lol.

I thought, and I'm probably wrong, that coma and vignetting were both caused by the parabolic nature of the mirror/lense and the an RC design provides the flatest fied possible with todays (amature) scopes. Even though the RC has a parabolic mirror there is a corrector in there somewhere?

Thanks
i was led to belive it was the opposite mate, the nature of the optical train gave a flat image, and there where no "correctors" in there at all !!

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Old 23-09-2009, 12:51 PM
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dannat (Daniel)
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intes make a mak-newt -AEC are the dealer i think

bintel use to stock the meade mak newt, don't know if still available

the mak newt's are usually with short f/l & are heavy
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Old 23-09-2009, 08:22 PM
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Duncan the RC will deliver a larger illuminated field for your CCD as the secondary mirror is quite large (at the cost of contrast). Field curvature and is still present and can be corrected with a lens (flattener). RC scopes have hyperbolic mirrors which has kept them so expensive for so long as they are difficult to make well but they are coma free. As Peter Ward has shown APS size chips will not show much vignetting on the GSO scopes (from his cropped samples) without a flattener, it is more evident when you use the monster chips. I would not thumb my nose at a Mak Newt either as I have seen terrific pics from these scopes but as the secondary is smaller and I think there would be a greater amount of vignetting present. The Mak newt will be longer whilst the RC will be more compact (mount vibration). You also really need to consider the type of objects you want to image in respect to the different focal ratio's (F8 Vs F4?).

Mark


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i was led to belive it was the opposite mate, the nature of the optical train gave a flat image, and there where no "correctors" in there at all !!

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Old 23-09-2009, 09:00 PM
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An RC does not need a corrector for a flat field but it does "need" a flattener for field curvature to make the stars smaller at the corners.

How much it needs this perhaps depends on the model. The difference on an RCOS 12.5 inch I believe was marginal and not important.

That scope would evenly illuminate a STL11. RCs do not require correctors you may be thinking of corrected Dall Kirkhams which do and they are similar to an RC except I think its an ellipsoid primary mirror.
Planewave CDK and Orion Optics ODK are corrected Dall Kirkhams. So is the Ceravolo Astrograph. It seems to be the current popular design.

Greg.



Quote:
Originally Posted by White Rabbit View Post
Hi Duncan.

Getting the itch...again...your worse than me mate. How many scopes is that weve seen you buy over the last year lol.

I thought, and I'm probably wrong, that coma and vignetting were both caused by the parabolic nature of the mirror/lense and the an RC design provides the flatest fied possible with todays (amature) scopes. Even though the RC has a parabolic mirror there is a corrector in there somewhere?

Thanks
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Old 23-09-2009, 10:58 PM
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Quote:
Originally Posted by gregbradley View Post
An RC does not need a corrector for a flat field but it does "need" a flattener for field curvature to make the stars smaller at the corners.
Greg.

Its the same thing.. A corrector corrects for an error(s). A flattner is still a corrector, as it "Corrects" for field curvature.
But i think we get you meant.

Theo
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Old 27-09-2009, 08:49 PM
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not to divert your thread but the larger secondary can be explored more easily with a little ripper of a piece of software called Newt. http://www.dalekeller.net/ATM/newton...t/newtsoft.htm
Apologies if this was old news
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Old 29-09-2009, 03:20 PM
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In my experience 8 inch RC has a lot less vignetting than a 6" Mak-Newt

Quote:
Bang for buck I'd wait for the 10" GSO RC
Me too.
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