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Skywatcher 190mm Maksutov-Newtonian Astrograph

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124 replies to this topic

#41
Whirlwind

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Hi all

Sorry to be a pain, but does anyone know what the back focus on this beastie would be? Hunted on the 'net but cant find any details, though my gogle skills might be lacking!

Thanks

Ian

#42
SteveL

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Can you explain what you mean by "what is the back focus?".

The OTA is designed to work as an imaging scope primarily, and the native focus point is designed to provide focus for CCD/DSLR/webcam/etc as it is. If you want to use it for visual, you have to use the extension tube supplied to get to focus for eyepieces.

#43
Whirlwind

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Hi

Sorry, I'll try and make myself a bit clearer, just not using the right terminology.... :oops: I currently image with an SXV-AO and associated OAG, filter wheel and Atk16hr, so the imaging train is quite lengthy. This is fine on an ED80 but not sure that I will be able to come to focus with such a long train with the 190MN. Eg say arbitrarily the image train is 100mm from the focuser and the 190MN comes to focus 80mm from focuser then with best will in the world I will never be able focus as the ccd will always be beyond the focus point? Is that any clearer?

Thanks

Ian

#44
SteveL

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Ah, I got that now... i`ll measure up when I get that first clear night with it, just so you know the imaging back focus distance.

#45
FLO

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SteveL has posted his first light report :D

The telescope certainly delivered on flat-field performance and even illumination:


CCD Inspector shows a VERY flat field from a raw full size FITs file.

Posted Image

Posted Image


Edited by FLO, 11 April 2009 - 06:06 PM.


#46
Psychobilly

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Wowser...thats flatter than a flat thing thats been flattened by a flat thing flattener !!!

#47
steppenwolf

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Ooooh, that is flat .........

#48
barkis

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Could I just verify that that flat sheet is representative of, in this case, lack of field curvature, a desirable condition of course.? How does the CCD Inspector evaluate this result.
In other words, what is it measuring in order to arrive at a graphical representation.?
Ta. :D
Ron.

#49
SteveL

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Its measuring the FWHM of the stars across the entire image, and displaying the changes in that across the image as a 2D surface map (for the top image), and a 3D map (for the lower smaller image)

I regularly use this to collimate my Hyperstar, as it also shows "lopsidedness" in the star sizes, but also shows just how well its coping with keeping the image flat across the chip. It also displays where it thinks the centre of the collimation point is, using the 2D/3D map it has generated, so you can adjust the collimation accoringly with the CCD in place.

#50
beamish

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Now that sounds very useful Steve.

#51
barkis

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Thanks for the explanation Steve.
I'm beginning to understand it.
Could a Newt 8" f5, perfectly figured, be capable of a similar result, without the aid of a coma corrector, or even with it.? It isn't 20 questions, honest. :D
Ron.

#52
gary1968

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Wowser...thats flatter than a flat thing thats been flattened by a flat thing flattener !!!




hahahaha, liked that one Billy, :-)

#53
FLO

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Could a Newt 8" f5, perfectly figured, be capable of a similar result, without the aid of a coma corrector


No, not without a coma corrector. If used with a coma corrector then it could deliver similar results, particularly if it has been designed with imaging in mind (has a larger than usual secondary for a wider field of illumination).

It isn't only the incredibly flat, wide, even field of illumination and 'built-in' coma correction that separates the Mak-Newt from regular Newtonians. The 190mm Mak Newt is a sealed tube so is less prone to tube currents. The tube is also made from 1.5mm steel so is less likely to flex and knife-edge internal baffles reduce internal reflections for increased contrast.

HTH

#54
barkis

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Thanks Steve.
I have not seen the weight of the OTA in print, at least I don't remember seeing it. SteveL had the unit side by side with his ED80 at Kielder, and stated indirectly, that the load was lighter than when his C11/ED80 Combo occupied the mount. He had three counterweights fitted to balance the SW & ED80. That means I would need another weight, unless two would cope with the SW OTA and a ZS66 scope. What say you sir.?
Ron. :D

#55
SteveL

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I believe the OTA weighs somewhere in the region of 22lbs, but that may well have been the weight of the Orion Optics (USA) version, which has to somewhere close.

#56
barkis

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Spot on Steve, just saw this this morning.
Ron.
http://www.telescope...roduct_id=09972

#57
FLO

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Another from SteveL, using the Skywatcher Explorer 190MN and Starlight Xpress MX25 :)

(Click on the image for the larger version).

Posted Image



Edited by FLO, 12 April 2009 - 01:18 AM.


#58
Starflyer

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That is a cracking image Steve, but when I saw that you'd posted in this thread I was rather hoping that you'd be announcing a price cut :)

Yes I really want one of these, and no I can't afford it (at the moment) :)


Ian

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#59
FLO

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There will be one in use at SGL-4 :)

#60
Starflyer

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I can't make it to SGL4 :)

Are you going to Salisbury and if so will you be bringing one along for us to drool over?

10" f/6.3 Newt / 10" f/4.8 Newt
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