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Which scope would you pick?


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Hi. I currently have a Skywatcher 200pds for imaging on an HEQ5 mount, but was thinking about moving away from Newts to a nice refractor, my main reason being the wide field possibilities for deep sky photography and also image stability. I haven't progressed to guiding yet so need something that lets enough photons in over a short period of time.

I'm toying between http://www.firstlightoptics.com/pro-series/skywatcher-evostar-100ed-ds-pro-outfit.html or http://www.firstlightoptics.com/evostar/skywatcher-evostar-120-ota.html

I'm guessing the Pro has better optics, but I'm struggling to see what it has over the Evostar and its bigger aperture.

HELP!!!!!

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The skywatcher pro series are ED's whereas the evostar are achromats.

The pro series will show hardly any CA (chromatic abberation, a blue/purple airy disk around planets and bright stars).

For imaging you ideally need to be using an ED, with imaging it is not about aperture as much as it is about the speed of the scope. The 80mm would be the better option for imaging as it is a faster scope but you will also be needing a flattener/focal reducer.

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The skywatcher pro series are ED's whereas the evostar are achromats.

The pro series will show hardly any CA (chromatic abberation, a blue/purple airy disk around planets and bright stars).

For imaging you ideally need to be using an ED, with imaging it is not about aperture as much as it is about the speed of the scope. The 80mm would be the better option for imaging as it is a faster scope but you will also be needing a flattener/focal reducer.

Exactly this :D

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If you're not guiding you'll want something even faster really... in the same price bracket if it were me I'd be looking at something like this .. http://www.firstlightoptics.com/william-optics/william-optics-zenithstar-zs71-ed-2013.html with the reducer gets you down to F4.72.

To be honest you're going to want to guide though..

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I totally agree that a good ED 80mm APO is a good choice in imaging! However I disagree on that HEQ-5 mount is going to struggle on tracking! I have a 80mm ED Lunt APO refractor with a 50mm Guidescope where my QHY5 and QHY8L CCD are fitted to the scope, all of this is mounted on a EQ-5 mount and to be honest with you it works a dream!

With a HEQ-5 mount it's going work much better than my EQ-5, So you don't need bigger mount, if you're going to fit an 80mm ED refractor. However on the 8" Newt yes a NEQ-6 is needed! Other than that choice is yours mate! :wink:

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Aah, good response, so if I was only viewing then keep the big newt, if only imaging then use the ED? Now I see why this damn obsession gets expensive! Throw on a guidescope and camera and good grief it adds up!

What sort of viewing would I expect with the 80 compared with the 200 newt?

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Hi I agree with a lot of these posts, I have an HEQ5 and a Skywatcher ED80. I have only as yet imaged unguided, however the results were far better than I expected. This goes to show that even just tracking the HEQ5 is pretty good especially with the ED80. I am looking forward to guiding with an ST102 scope and the 80.

Dave

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The thing is about imaging! It's all about the F-ratio, quicker that F ratio the more light photons can be collected! Now you get 80mm ED refractors as low as F6 but combine with 0.8x focal reducer and you're hitting F5. collecting more light, however apeuture is not really needed for astro-photography!

I'm lucky to own an ED refractor and 8" Quattro Reflector, however I would choose the Quattro every time with it's ultra fast optics of F4 and with added apeuture does help a little. The tiny 80 ED lunt is really my travel imaging scope which does give superb images but there is no high demand for a heavy duty mount instead and carrying all that extra weight, also with the 80 ED apo being small it's quick to set up as well and no hassle with collimation issues but collimation is dead easy to do so it really never bothers me!

I be honest with you I would keep the 8" reflector, you can make perform better with images, if you invest in Coma corrector than you'll have much better images. So if you been getting great images from your reflector, than save your money mate.

ED refractors are great if you want a portable imaging scope but you'll still need to buy a focal reducer and field flattner to get around F5 ratio which costs around £200 for it, And then you'll spend around £500 to £700 for good ED refractor! The reflector is good perfomer and getting a Skywatcher Coma corrector costing around £150 is probraly you're best investment! It's upto you mate bit of hassle of setting up the reflector but more apeture and faster optics than an ED refractor anyway, or pay a lot of money for scope which you'll need more more money to get it down to fast F5 though faster and easier set-ups and no collimation issues!! There's so many choices to choose from??? :cheesy:

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Treat me as a thickie - why is aperture not so important with a refractor? Surely with a diameter of only 80mm its going to let in a tiny amount of light compared with my 8" newt?

Simply put; for viewing a big aperture is best because the exposure is short (the blink of an eye). With AP the small aperture is compensated for by longer exposures. A 600 second exposure gathers quite a bit of light! The 80mm will give a wider FOV than the 200pds so will give you a better choice of targets for a given camera (generally).

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I may have this wrong of course as I am no imager but surely the OP already has a fast scope? the 200p is f5 and (I think) the 80mm ED recommended is f5 so they have the same focal ratio. the 'problem' with the current scope is the mount I expect. the difference is focal length and aperture (which is not relevant to a large extent for DSO imaging if the mount is adequate for the OTA).

I doubt that imaging is any different to observing in that you will need different scopes of different focal lengths to allow different objects to be imaged effectively. it's about matching the image scale with the chip on the camera and matching both with the size and brightness of the object imaged.

where resolution does matter (and therefore aperture) with imaging is with planetary and lunar.

the above is as I say just what I have gleaned from other posts and I think it's accurate but hopefully others will confirm.

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Neither aperture on its own nor focal length on its own have any bearing on the light intensity arriving at the chip. The intensity of light is governed by the focal ratio, the focal length divided by the aperture. I know this is counter intuitive but it's true. An F5 scope is about twice as fast as an F7. That is alarming, no? An hour at F5 needs two hours at F7, yet at first glance there doesn't seem to be that much difference between the numbers. (In digital imaging the pixel size is important too but let's stick to the optics.)

If you want to image at all seriously then I would go for the HEQ5 and an autoguider. Simple as that. You can do taster-imaging with less, certainly, but you cannot get your optics or camera to perform to their limits with less. That is quite certain.

The 200P should be capable of giving good images and it's fast. It will need a coma corrector and good collimation. I like refractors (up until such apertures as they become impracticable) simply because they are easier and need no adjusting. Certainly there are lots of targets for short focal lengths and, indeed, this is my own favourite form of imaging. I use a small refractor with a FL of 328 or 450mm. It absolutely must be an apo, though, and have a flat field (usually from a flattener-reducer.) If you really don't want to guide you want both a very short focal length and a very fast F ratio. The short FL is the more critical.

Olly

http://ollypenrice.smugmug.com/Other/Best-of-Les-Granges/22435624_WLMPTM#!i=2277139556&k=FGgG233

Edited by ollypenrice
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It can be best to guide reflectors with off axis guiders since these won't err if the mirror moves slightly. They'll also tax yur mount significantly less. However they are a bit more of a faff to set up. Lots of people guide with the QHY5 and free PHD software.

Olly

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You're making a good choice by sticking to the reflector, You be spending so much more on a ED 80 I reckon you'll be disapointed! I would opt for a good QHY5v guide scope and you'll need an adaptor which will screw in the guide camera and then able to screw the camera into your existing Skywatcher finderscope. Then use PHD Guiding which is a freeware software which the easiest guiding program I've used and it works 100% for me! Top class program without a doubt!! I'll send a PM over to you mate for details!

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The only connections you'll need is a cable for the ST-4 port which will connect to the camera and the HEQ-5 mount ST-4 port, And then you'll need a USB cable which will connect the camera to the laptop! that's it. If you use the Finder guider as your autoguiding it will be fine on HEQ-5 mount for weight issues, However if you're seeking to fit a 80mm guide scope, you'll need a guide bracket to fit on to the scope, with that you're adding an extra 4kg on the mount, which means you'll need to upgrade to a NEQ-6 mount! That's why I'll go for the finder guider set-up, it's fiddly at first but once it's set up right it works wonders mate! This probraly the best upgrade route there is mate! I use this method on my 80mm ED lunt and 9x50 finder guider on my EQ-5 which runs like a dream!

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i just made a webcam guider out of the 9x50 (deliverd with the ED80) and a ps3 eye. (-> cost: 3 hours of work, trial and error)

first "guiding"-sessions at home were promising...

...now i´m waiting for clear skies...

so you don´t need an "expensive" guding cam with a big scope...for learning an first tries the guiding scope should be sufficient...

...i hope so, if not my work was for nothing :grin:

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The OAG can not be fitted on to finder, This OAG can only be fitted on to the main telescope, it can take some considerable time to set it up right, and you'll extension tubes to get the spacing correct. For me I use the guidescope always!!! Some people might disagree with me, but I find it the easiest method for autoguiding!

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