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Large aperture Newt good for DSO imaging?


OzDave
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Hi,

I'm in the market for a new scope but I don't think I have enough experience to know which type would be best, although I do know what I want to use it for.

Basically I only use my scopes for imaging these days. Observing is something I only do rarely. I have a wide field scope in the Equinox 80, which is great for certain things and my other scope, the Mak 127 is really only useful for solar system objects, which don't interest me that much. I might sell it one day.

So, what I want is a scope that will be good for smaller DSOs such as globular clusters and planetary nebulae. I've seen images from others of various globs where the stars at the core are fairly resolved. I'd like something that could do that, but maybe I underestimate how big a scope is required for this?

I am leaning towards a large aperture Newt, like a SW Explorer 200PDS or maybe the 250PDS. But I'd need a coma corrector, which would be ok I guess.

Alternatives might be something like the MN190 Mak-Newt, or the Equinox 120 Refractor. Or perhaps I should wait for some of the new SW kit that is expected in 2011...but I'm not really know for being able to wait long...

I'm guessing the qualities that a suitable scope should have, would be long focal length to "zoom" in on the small DSOs, but then a large aperture to ensure the scope is fast enough for imaging.

I guess I'd be prepared to pay up to say £1500 for the OTA and I'm planning to also get an EQ6 or HEQ5 to go with it. However, cheaper is better for the OTA as long as the quality is there. e.g. Newts are cheaper, but are they as good as refractors or Mak-Newts in terms of image quality?

Do you think a Newt + Coma corrector would satisfy my needs, or should I be looking at Refractors and/or the Mak-Newt? Or maybe other types of Astrographs? Any suggestions much appreciated.

Regards,

David

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The Skywatcher 190 MN Is a superb Instrument for DSO Imaging.

Mounted on the EQ6 Pro mount, it has produced some exquisite images. Examples can be found in the Deep Sky Section under SteveL, TJ, and Deneb, Who's images are produced from unguided exposures. The ED80 and zs66 Apos have also been used to good effect on DSO's. There is plenty of other capable scopes to do the job, but others will give you their opinions too.

Ron.

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How have the ED80 or ZS66s been good for smaller DSOs with their short focal length? I already have an Equinox 80, and smaller targets such as globs or planetary nebulae just don't resolve that well in the wide field. Maybe that's my technique though.

I know the MN190 is excellent, but would I be able to resolve more detail with a larger aperture Newt? And would the images be as good?

David

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Apart from what Ron has commentated so far, the MN190 is very good at resolving fainter dso's especially when it comes to imaging, I was quite surprised just for 1hours with of data how much M33 was captured..

But also I would say even if you were to buy something like a 10" newt. you still can't compare it to a beast MN190. Also the MN190 has 5 internal baffles to eliminate internal reflections & further enhance contrast.. Yes the cool down time with an open tube is less then the MN190, but in the long run I you'll still be better off with the MN190 if your purely thinking about imaging... It's a true Astrograph

Also the introduction of the dual speed focusers on the scope are very good & well built - not the standard run of the mill dual speed focusers from SkyWatcher, they have a nice internal 50mm extension tube if your going to use the scope for an observing tool.

Just some thoughts from a MN190 Evangelist :icon_salut:

Nadeem

Edited by Deneb
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I have been using a 250px newt for DSO imaging for over six years and have found it excellent at getting up close and personal with DSO's.

I use a MPCC and have had to mod the focuser to achieve focus, the 250PDS has a shorter tube length with the secondary closer to the primary so this may not be an issue.

Here is a shot of ngc206 within M31 to give you an idea of the image scale at prime.

Have a look at my website for more work with the 250. Click me

Mike.

yfronto-albums-mike-deegan-s-yfronto-s-images-picture6890-ngc206-l-har-g-b2.jpg

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Having used a 120ED frac, 200mm F/4 Newt, 10"Schmidt Newt, and now a 190 Mak Newt I have to say, like Nadeem I really.. really like the 190MN.

The 120ED with the dedicated flattener is very nice to use but a bit slow photographically speaking compared to the 200 F/4 Newt, but this needs spot on collimation and I had troubles keeping all the imaging train in line, also the need to get a Coma corrector in the right position, but oh boy is it "fast".

The Schmidt again at F4 is very fast with reduced coma but it is very heavy, just too heavy and again had to be very accurately collimated.

The 190MN is just a joy to use, no other bits of glass to correct the image, pretty fast at F/5.3, easy to collimate and with a good dew strap stays clear of condensation.

I would however like to try one of the new SW 10" carbon fibre F/4 newts at some point, very fast and, hopefully, good at keeping the imaging train in line.

My several 1000's worth!

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Arrgh...I almost wish I'd never asked now! I think I may be more confused!

Nadeem, I know the MN190 is a fantastic scope and I know that you and others have produced some terrific images with it.

But looking at Mike's website gallery, it seems that a larger Newt is also pretty capable. All the images I saw there look like the sort of thing I want to be able (one day) to produce. The image of M13 has a pretty well defined core, which is what I was referring to in my original post.

Is the MN190 able to resolve M13 as well? I think I remember seeing a pretty nice globular from someone with an MN190, but was a while ago now and I can't remember.

How much difference would the extra aperture that the 250P has over the MN190 make? Skywatcher claims something like 44% extra light gathering power over a 200mm scope, which I guess would allow a longer focal length for the same speed of scope and hence more resolving power.

How much do the internal baffles of the MN190 improve contrast?

Not sure how to break the tie on this one...I don't live near any astronomers, let alone people that would have these scopes.

Anyone else want to weigh in an opinion on this? Is there anybody with experience of both types of scope for imaging?

Nadeem, do you think that the MN190 would be able to produce images like Mike is showing on his site? I'm not talking so much about quality as I'm certain that in the right hands both scopes produce excellent results. I guess I'm talking about resolution of detail, contrast, field of view/scale, flatness/coma effects etc.

David

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That's excellent information Pete. The MN190 does sound, by all accounts, an excellent piece of kit. Having compared it to your other scopes, it seems that collimation is a hassle on the Newts. Can you comment on your experiences imaging with the 10" Schmidt-Newt? Collimation and weight issues aside, was there anything positive to be said about that, compared to the MN190?

I have to admit, I like the "look" of the MN190, not that that is an important factor at all, and I also like the fact that it's physically smaller than a larger scope (I know that's kinda obvious, but I don't want things to be too unwieldy).

The fact that it is billed as an Astrograph is also a plus.

I think what I would be worried about if I got an MN190 is whether I'd get significantly better results with say a 10" Newt on the same target. Maybe it would be possible to get a more resolved image, but for that I'd have to trade off a bit of contrast, and extra hassle for collimation etc. Does that sound like how it would be?

David

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...it seems that collimation is a hassle on the Newts...

I'd have to add support to Yfronto's comments about the SW250. They are also a LOT more affordable than the MN190, although I see that's not a problem with your budget.

As for collimation, I've just acquired a brand-new SW250P DS which I intend for imaging and visual use, and straight out of the box it took me just a few minutes to collimate. and most of that time was sorting out the secondary, which should be a one-off. The new model has knobs for collimating rather than screws (are they what's known as Bob's knobs?) and I was amazed how easy it was to collimate using them. 'tis a lovely scope.

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My M13 here http://stargazerslounge.com/imaging-deep-sky/113302-yet-another-m13-sorry.html

Regarding the SN10, David, I think with the right mount and a coma corrector and a good focuser to replace the toytown one that comes with it I would say it is a highly underated scope so long as it is well collimated and can be picked up cheaply secondhand, the weight was the main issue for me, although I must add that on some bright subjects eg M45 you get ghosts (mine looked like space ships) near all the bright stars.

Sure a Newt is cheaper than the MN but you do need a good Coma Corrector.

But the F/4 CF newt out next year looks interesting but at what price?

I just love the MN!

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Nadeem, do you think that the MN190 would be able to produce images like Mike is showing on his site? I'm not talking so much about quality as I'm certain that in the right hands both scopes produce excellent results. I guess I'm talking about resolution of detail, contrast, field of view/scale, flatness/coma effects etc.

David

Tell you the truth, I don't think at all, I know it would produce images like Mike has on his site or maybe better depending what gear is used with it ( & no offence to Mike) especially when guiding, also the MN190 is also good at being used with barlows.

Nadeem.

Edited by Deneb
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Ah yeah, that was an image I'd been looking for today, but somehow missed. I remember seeing it and thinking WOW!

I think I'm edging towards an MN190. Not that I don't think a Newt would be good, but I think on balance, a proper astrograph might suit me better. The slightly shorter focal length will make it easier to guide, and I think it's fast enough at f/5.something.

Being able to use powermates on the MN190 would be a bonus. Does that work on Newts, or do they run out of focus travel?

I think all the images I've seen from the posts are great, way better than I have ever achieved with my kit so far, and I thank everyone for their input so far.

David

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The extra aperture does bring resolution to Mike's images which I doubt my large refractor or the MN could match. The laws of physics are there for a reason! But I also think that Mike knows a thing or two and if I bought a big Newt I wouldn't be expecting to get it out of the box and do as well. Or nearly as well. With the MN and, even more so, the refractors, I think they just get on with it on their own.

On Newts there is another thing to consider. Only strong tubes and strong focussers will carry heavy CCD cameras and filtewheels successfully. Light DSLRs are not a problem but CCD is very different.

Olly

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On Newts there is another thing to consider. Only strong tubes and strong focussers will carry heavy CCD cameras and filtewheels successfully. Light DSLRs are not a problem but CCD is very different.

Olly

How heavy is a CCD?

The 1000D is 450 grams.

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The extra aperture does bring resolution to Mike's images which I doubt my large refractor or the MN could match. The laws of physics are there for a reason! But I also think that Mike knows a thing or two and if I bought a big Newt I wouldn't be expecting to get it out of the box and do as well. Or nearly as well. With the MN and, even more so, the refractors, I think they just get on with it on their own.

On Newts there is another thing to consider. Only strong tubes and strong focussers will carry heavy CCD cameras and filtewheels successfully. Light DSLRs are not a problem but CCD is very different.

Olly

Who said anything about Mike not knowing "a thing or two" ?, im sure the chap knows plenty, im sure he could teach me & others plenty !

What I have expressed here are just opinions of my experiences & what I think what the MN190 is capable of (using one - why not), sometimes my opinions may come over harsh, but certainly not mean't to offend.

Another aspect what Olly has commentated on about focusers when using ccd cameras, take into account you would have to change the focuser to something like eg. a moonlite & their not cheap :o

Nadeem.

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Nadeem, I intended no reference to your comments in making mine about Mike's expertise. None at all. Rather I was suggesting that the Newt needs more thinking about and more expertise than the scopes you and I use. (Indeed, that's why I use the ones I do!)

Not only does the Newt need a strong focusser, it needs a strong enough tube on which to mount it, or the heavy CCD gear will still pull itself away from orthogonality.

I'd like to know where Mike orientates the camera and focusser in order to maintain dynamic balance in the system, balance in all possible positions of the scope. I haven't cracked this one myself. One possibility, though awkward, is to put focusser axis parallel with the counterweight bar and the camera on the mount side. (ie in front of the mount. This would, of course, be no good for viual use.)

Mike?

Olly

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I'd like to know where Mike orientates the camera and focusser in order to maintain dynamic balance in the system, balance in all possible positions of the scope. I haven't cracked this one myself. One possibility, though awkward, is to put focusser axis parallel with the counterweight bar and the camera on the mount side. (ie in front of the mount. This would, of course, be no good for viual use.)

Mike?

Olly

Thats the same orientation I use, put the focusser axis parallel with the counterweight bar.. It works quite well.. especially when your not guiding.. :o btw no offence taken..

Nadeem.

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I'd like to know where Mike orientates the camera and focusser in order to maintain dynamic balance in the system, balance in all possible positions of the scope. I haven't cracked this one myself. One possibility, though awkward, is to put focusser axis parallel with the counterweight bar and the camera on the mount side. (ie in front of the mount. This would, of course, be no good for viual use.)

Mike?

Olly

I have the camera in line with the scope mounting and counterweight bar.

Mike.

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Thanks Nadeem. I'm interested that you use this orientation because I rather feared the idea might be seen as barmy. I'll give it a go.

Olly

Surely nothing is barmy if it produces good results. Who could have predicted that webcams would be so popular for planetary imaging!? Now that's barmy :o

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Thats the same orientation I use, put the focusser axis parallel with the counterweight bar.. It works quite well.. especially when your not guiding.. :o btw no offence taken..

Nadeem.

I do the same with a slight out of line twist so as to get an inbalance in DEC with the OTA pointing straight up. Having the Camera/filter wheel "inboard" saves quite a lot on the counterweight needed.

I also agree with Ollys point on tube strength, I have noted flexture in my F4 Newt around the focuser hence my possible interest in CF tubes.

The MN tube is robust - and heavy, I am sure the baffles help in keeping the tube rigid.

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