Newtonian for astrophotography

[doseri]

hi all

i am building my new setup , with new sky-watcher neq6 mount ,for that i would like to have new telescope for it , is Newtonian good for astrophotography, and limit with budget ,i was looking on the web and see this TS 8" F4 UNC Newtonian Carbon tube Telescope

see the link http://www.teleskop-express.de/shop/product_info.php/language/en/info/p5033_TS-UNC-200mm-f-4-Newton-Teleskop---Carbon-Tubus---optimierter-Fokus.html

like to have Your comments on it ,is it good for astro image and what about the prices for it

thanks

sam

[RikM]

A fast Newtonian telescope can be very good for Astrophotography but generally takes a great deal of effort to get it prepared and working properly. It is not an 'out of the box' option. If you have the time and skill to whip it into shape then it could be good but if you want good results with less effort then a short fast ED80 refractor would be my choice for a first imaging scope.

[Ouroboros]

Sorry ... What's the "great deal of effort required to get it repaired and working properly"?

I get my 200p onto the mount, attach the camera and away I go.

I suppose there's more time collimating every now and again, but that's all daytime work. It seems to me that a Newtonian is about as simple as it gets.

[Ouroboros]

By the way .... How does dewing up compare between a Newtonian and a refractor. I hardly ever have problems with the primary mirror dewing up because its down the bottom of a long tube. But I regularly get a dewed up finder scope - so assume the same must apply to a refractor. True or false?

[RikM]

A 200P is f5, so fairly forgiving in collimation errors, the f4 200mm Newtonians (like the TS Newt in the link) have a collimation window only about half that of an f5. So twice as difficult to get right.

Re dewing, I find that though the primaries are well protected, the secondaries dew up quite often. I have fitted dewshields and this does help. I have nice small heater bands on my refractor and finderguider so never have problems with those. I can't afford a secondary heater for my main imaging Newt and don't have the DIY skill to fit a couple of mossfets to the back of the mirror cell.

For my deep sky imaging I use 6" and 10" Newtonians, f5's for ease of use

[doseri]

A 200P is f5, so fairly forgiving in collimation errors, the f4 200mm Newtonians (like the TS Newt in the link) have a collimation window only about half that of an f5. So twice as difficult to get right.

Re dewing, I find that though the primaries are well protected, the secondaries dew up quite often. I have fitted dewshields and this does help. I have nice small heater bands on my refractor and finderguider so never have problems with those. I can't afford a secondary heater for my main imaging Newt and don't have the DIY skill to fit a couple of mossfets to the back of the mirror cell.

For my deep sky imaging I use 6" and 10" Newtonians, f5's for ease of use

Newtonians f5 is easy to collimation then f4

[ollypenrice]

Sorry ... What's the "great deal of effort required to get it repaired and working properly"?

I get my 200p onto the mount, attach the camera and away I go.

I suppose there's more time collimating every now and again, but that's all daytime work. It seems to me that a Newtonian is about as simple as it gets.

It depends on how right you want it and on how big your chip is etc. A Newtonian is not by any means as simple as it gets. A well made refractor is as simple as it gets but is generally far more expensive. Briefly, the problems associated with Newtonians, especially fast ones, are collimation, orthogonality, coma and frontal area presented to the wind. I'm not anti-Newtonian but if you go to a firm like Takahashi in search of a focal length around 500mm you find, in looking at ther prices, that they charge even more for a corrected Newtonian than they do for a quadruplet apo. This rather suggests that they don't think a Newtonian is as simple as it gets... In imaging fast Newtonians are, in my view, as complicated as it gets and that's why I don't use them. This is not to say that they can't be made to work, but I totally agree with RikM in his post above. Image with a Newtonian if you are up for it. Image with a fast Newtonian if you are really, really, up for it.

This image was taken in an F3.9 apo which has never been collimated from new and was simply taken outside, pointed at the sky, focussed and told to get on with it. I really don't think that can be compared with getting the best out of a reflector.

http://ollypenrice.smugmug.com/Other/Best-of-Les-Granges/i-R4v6bFN/0/X3/M42%20WIDE%202FLs-X3.jpg

Olly

[Earl]

A newt needs for more effort to get it right and constant tweaking, if your happy to do that great.

I picked a 250p with the intention of imaging, and almost every problem solved just presented a new one, I gave up in the end and went for a Refractors, and then it took a while to settle on the right one.

[Ouroboros]

I must be much less fussy than some. Or less discerning perhaps. I didn't collimate at all for the first 18 months of owning my Newtonian. Since getting a collimation laser, I check it and tweak it every now and again but never find the small errors found before corrections have made much difference.

I find coma an irritating feature of images taken with my 200p, but that's an inherent aberration of a parabolic mirror. I'm yet to get a clear sky to properly test my recently acquired coma corrector.

However what the coma shows me I think is that, since the axes of the aberated stars at the edge of the field all point nicely at the centre of my DSLR images, my telescope is pretty much well collimated. I can't really expect better than that can I, however much I tweak?

[laser_jock99]

hi all

i am building my new setup , with new sky-watcher neq6 mount ,for that i would like to have new telescope for it , is Newtonian good for astrophotography, and limit with budget ,i was looking on the web and see this TS 8" F4 UNC Newtonian Carbon tube Telescope

see the link http://www.teleskop-...erter-Fokus.html

like to have Your comments on it ,is it good for astro image and what about the prices for it

thanks

sam

This scope is much cheaper and does exactly the same thing image wise (probably has identical optics)

http://www.teleskop-express.de/shop/product_info.php/info/p52_TS-GSO-8--F4-Newtonian-Telescope---optical-tube-assembly.html

A quick search of the web finds plenty of images taken with this scope (bear in mind they may be by experienced imagers) but will give you an idea of what is possible.

The UNC scope has a nice focuser but the carbon tube won't add a lot to the functionality. Collimation is not rocket science and nothing to be afraid of. You will need to get a good coma corrector for imaging (add say another 150 Euros?).

It is true a small refractor is easier to set up and handle- but find me an 8" F4 TRUE APO refractor for under 600 Euros? These fast Newtonians do offer significant 'bang for you buck' even though they do require more effort to master.

The plain truth is though that no single scope can do everything- if you take up the hobby seriously you will end up owning several telescopes. An 80mm apo refractor should also be in your 'collection'.

[doseri]

This scope is much cheaper and does exactly the same thing image wise (probably has identical optics)

http://www.teleskop-...e-assembly.html

A quick search of the web finds plenty of images taken with this scope (bear in mind they may be by experienced imagers) but will give you an idea of what is possible.

The UNC scope has a nice focuser but the carbon tube won't add a lot to the functionality. Collimation is not rocket science and nothing to be afraid of. You will need to get a good coma corrector for imaging (add say another 150 Euros?).

It is true a small refractor is easier to set up and handle- but find me an 8" F4 TRUE APO refractor for under 600 Euros? These fast Newtonians do offer significant 'bang for you buck' even though they do require more effort to master.

The plain truth is though that no single scope can do everything- if you take up the hobby seriously you will end up owning several telescopes. An 80mm apo refractor should also be in your 'collection'.

thank you laser_jock99 and for all members

can you Recommends more Newtonians for me

thanks

[ollypenrice]

This scope is much cheaper and does exactly the same thing image wise (probably has identical optics)

http://www.teleskop-...e-assembly.html

A quick search of the web finds plenty of images taken with this scope (bear in mind they may be by experienced imagers) but will give you an idea of what is possible.

The UNC scope has a nice focuser but the carbon tube won't add a lot to the functionality. Collimation is not rocket science and nothing to be afraid of. You will need to get a good coma corrector for imaging (add say another 150 Euros?).

It is true a small refractor is easier to set up and handle- but find me an 8" F4 TRUE APO refractor for under 600 Euros? These fast Newtonians do offer significant 'bang for you buck' even though they do require more effort to master.

The plain truth is though that no single scope can do everything- if you take up the hobby seriously you will end up owning several telescopes. An 80mm apo refractor should also be in your 'collection'.

I don't believe it's true that the carbon tube won't affect functionality. I've tried a variant of the cheaper scope and it was awful. The metal tube was not capable of holding the focuser at right angles to the light path. Using a coma corrector added so much extra length that the leverage introduced fatal sag into the system. The stiffer carbon tube should solve that problem. Also the focal plane at F4 is shallow so having no expansion in the OTA ought to help maintain focus. Mechanically the cheap scope was also wanting and indeed one of our guests was startled to discover that all the baffles had fallen off his example and onto his primary mirror.

Although I don't know this to be so I suspect that the more expensive TS scope will use the same optics in a more viable mechanical passage. The cheaper scope looked too good to be true and judging by the ones I've seen this proved to be so. The same optics in a decent structure, though, do have real potential.

Olly

[laser_jock99]

I don't believe it's true that the carbon tube won't affect functionality. I've tried a variant of the cheaper scope and it was awful. The metal tube was not capable of holding the focuser at right angles to the light path. Using a coma corrector added so much extra length that the leverage introduced fatal sag into the system. The stiffer carbon tube should solve that problem. Also the focal plane at F4 is shallow so having no expansion in the OTA ought to help maintain focus. Mechanically the cheap scope was also wanting and indeed one of our guests was startled to discover that all the baffles had fallen off his example and onto his primary mirror.

Although I don't know this to be so I suspect that the more expensive TS scope will use the same optics in a more viable mechanical passage. The cheaper scope looked too good to be true and judging by the ones I've seen this proved to be so. The same optics in a decent structure, though, do have real potential.

Olly

The cheaper scope will almost certainly ship with a weaker Skywatcher/Vixen type dovetail bar that is probably too short to support the scope fully. Rather than pay the extra 400 euros for the carbon tube why not get a 400mm Lossmandy style dovetail bar fitted? Bolt on a decent top bar (the one you'll mount the guidescope on) to the tube rings and you won't see too much flex. Not rocket science.....

[ollypenrice]

The cheaper scope will almost certainly ship with a weaker Skywatcher/Vixen type dovetail bar that is probably too short to support the scope fully. Rather than pay the extra 400 euros for the carbon tube why not get a 400mm Lossmandy style dovetail bar fitted? Bolt on a decent top bar (the one you'll mount the guidescope on) to the tube rings and you won't see too much flex. Not rocket science.....

Not rocket science but not relevant to the problem, I don't think. The focuser on the cheap 200/800 bolts, naturally enough, to the tube. This tube flexes in the immediate vicinity of the focuser so I don't think tube rings will stabilize it, nor do I think using a Losmandy dovetail will change matters. The key problem is that the coma corrector, which is clearly essential, causes the camera to hang at a prodigious distance from the tube. As soon as I saw this I knew it was doomed. My CCD rigs are not by any means as heavy as some (Atik 4000s with manual filter wheels) and yet there was never a hope in hell of the chip remaining orthogonal at the end of such a long lever, and it didn't. One side was in focus, the other wasn't.

The forums would be full of images from these scope if they worked effectively, but they're not. One owner I know (the one whose baffles clattered down onto the primary) has constructed an all new scope assembly for the optics. This is an old story with GSO scopes. Several individuals and companies are busy putting the GSO Ritchey Chrétien optics into more serious scope assemblies.

So I'm all for TS being honest and putting the optics in a better made assembly. I'd think they were even more honest if they withdrew the cheap version because I don't consider it to be of serviceable quality, myself.

That's a personal opinion, I realize, but it's a considered one based on trying to use the scope and on talking to a couple of those who've tried it.

Olly

[laser_jock99]

This tube flexes in the immediate vicinity of the focuser so I don't think tube rings will stabilize it, nor do I think using a Losmandy dovetail will change matters. Olly

Not a problem I have encountered (my imaging rig is lightweight (DSLR + short coma corrector)) but something I will take advice on. Again it could be beefed up if necessary but we shouldn't really be needing adding tube strengthing plates to scopes- this out the realms of begginers!

I might buy the 8" F4 cheap version and give it a go - just for the hell of it! I'd be interested to try these at my dark sky site (my permanent pier is too tall for the 12").

[ollypenrice]

Not a problem I have encountered (my imaging rig is lightweight (DSLR + short coma corrector)) but something I will take advice on. Again it could be beefed up if necessary but we shouldn't really be needing adding tube strengthing plates to scopes- this out the realms of begginers!

I might buy the 8" F4 cheap version and give it a go - just for the hell of it! I'd be interested to try these at my dark sky site (my permanent pier is too tall for the 12").

Why not the Quattro, which is more convincing?

Olly

[laser_jock99]

Why not the Quattro, which is more convincing?

Olly

Given what you said about local tube flex I'm wondering if there is any difference between the various offerings in terms of steel thickness on the tubes? The SW Quatro has a different paint scheme and the Revelation has no internal baffles (at least not mentioned in the blurb). I think a few phone calls & e-mails are required before I slap some cash down.

[kirkster501]

Hi, I have been looking at a Newtonian too for imaging for more aperture than my 80ED on DSO's I might get a 200P and flog it later if I cant get on with it. I have never used a Newt before. I read bad things about the 250P being too unwieldy? I am not experienced enough to buy a quattro just yet i don't think.

Steve

[Earl]

Hi, I have been looking at a Newtonian too for imaging for more aperture than my 80ED on DSO's I might get a 200P and flog it later if I cant get on with it. I have never used a Newt before. I read bad things about the 250P being too unwieldy? I am not experienced enough to buy a quattro just yet i don't think.

Steve

I thought exactly the same and made the purchase only to sell it on as its big and needs lots of tweaks to get it up to where it needs to be. People do get good results and fair play to them! but ill not be going that path again for imaging.

[kirkster501]

Thanks for sharing your experiences Earl. Interesting. And not the first time I have heard this tale...

Steve

[RikM]

Most of my images have been with the little 150P. I find it much more manageable than the larger Newts. With its smaller lighter mirror it cools faster, and holds collimation better. With the shorter tube you can also see down a Cheshire okay and reach the primary adjusters at the same time, so no hopping back and forth. Doesn't catch the wind so much either compared to the bigger models. f5 is still pretty fast for light gathering and 750mm focal length is right in the middle, so gives a good image scale on loads of the brighter targets. I haven't changed the focuser so still the stock SW single speed C but I only have light camera (SXV-H9 + manual filter wheel) and it seems to cope okay. I am generally happy with the results I get given the effort I put in, but there is still plenty of room for improvement.

I do also use a 250PX for extra focal length on planetary nebs, and I like the tight stars it gives but it is a big old lump. I also plan to use it for planetary imaging but I tend to get side tracked by looking through it