Newbie questions re Newtonians

[KP82]

I've been using 4" triplet fracs for visual and some casual imaging for all my life. Recently I've been thinking about getting a larger aperture unit for better DSO visual (this will be for visual only as I'll stick to my frac for imaging). However 6" ed fracs are both too heavy and too expensive, so they are out of the question. And for big DSOs SCT/Mak with their narrow FOV have also been ruled out.

That leaves fast (f/5 - f/6) newts the only choice. Now I've never used a newt before except for looking through someone else's dob during star parties. I've heard newts require much more maintenance than fracs (the main reason I went for the fracs at the beginning). So my questions are how hard it is to keep the newts in collimation and whether I'd need a coma corrector (e.g. TV Parracor T2 and Baadar MPCC) for visual on a fast newt?

The newt I've been looking to get is the Orion Optics VX6 + 1/10 PV upgrade. Its light weight will make it fit perfectly on my existing Alt-az mount.  Anyone has experience with this scope?

[alanjgreen]

Hi KP82,

For visual, I would not go smaller than 8" if you want to see any decent DSO results. 6" is just too small for a visual reflector if you want to see faint targets.

I also would not focus on getting a reflector to fit on an existing mount as the best value you are going to get is a nice 8" dobsonian, if you want goto then budget for goto as well. Having to get (a) the mount then (b) the scope and fit the two together would not be my recommendation. Balancing a long reflector tube can be a challenge.

For me, rather than spend on an expensive small mirror, I would just get an 8" skywatcher collapsible (goto or not goto, the choice is yours). The benefits of an expensive 6" mirror over a chinese import will be pretty non-existent.

There are plenty of dobs available second hand if you want to save some money too. If you can push to a 10" then you will see further improvements in your visual observing!

What is your budget?

Do you plan to use goto?

Read up on "push-to" as an alternative to "goto". Push to just lets you use an "app" for targeting and you provide the muscle to move the scope. I use Nexus push-to with my dob and its great. If you get a Goto dob then the motors etc just add to the weight.

 

I would not worry about coma at f5 or f6, you will only need a Paracorr coma corrector if you get as fast as f4. You will need decent eyepieces though if you go for an f5.

 

As far as collimation goes then you just need to force yourself to learn how to do it. Either

(a) Just keep doing "star tests" whilst using the scope and if it aint broke then dont fix it.

(b) Buy a cheshire eyepiece & then during a rainy period, get setup inside and practice collimating the secondary & primary. Once you know what you are doing its easy. The more solid the scope then the less regular collimation it will need. If you get a truss design and keep building it and taking it apart then it will need regular collimation. Learn how to do a "star test".

(c) Buy Howie Glatter laser & Tublug and its all easy peasy from the start... Expensive kit but works like a dream.

 

Alan

[Cosmic Geoff]

I use a C8 SE SCT on a GoTo mount for looking at DSOs (galaxies) on the occasions when I am able to observe from a dark skies site.  In theory, the FOV is too narrow for viewing some larger objects and my 203mm Newtonian would serve better.  In practice, I have never been in a situation where a galaxy visibly overlapped the FOV of the SCT.  I have not taken the Newt to a dark skies site as it is less portable than the C8 SE.  When I tried to observe a few galaxies from home with the Newt I found it very difficult to find anything with it because of its lack of GoTo.  I had a nice view of M31 but could not find amything else.

[KP82]

While I do find it very convenient to find targets with the 4" triplet on my HEQ5 Pro, I don't mind trying to locate them manually. In fact I'm pretty good at searching out the galaxies/nebulae with my portable Bresser AR102xs RFT on a Alt-az mount. I just want a larger aperture that I can take with me to dark skies. A SkyWatcher 8 or 10 inch dob with its heavy brick like base is simply too cumbersome.

[JG777]

@KP82 I have the Orion Optics VX6 F5 and with 1/10 PV. It is my mid range grab n go scope and also my most used scope. I now use this more than the 9.25 Evo or my small refractors. The reason is it is a big enough aperture to see the main DSOs,  galaxies, etc, and especially wide clusters in glorious detail. It is so much more manageable than an 8 inch , yes an 8 gets you better views but the 6 is easier to take to dark skies, mount and move around. It cools down fast thanks to its size and having a cooling fan and thanks to the overall good quality of the fittings it holds collimation very well. I swapped out the secondary mirror phillips screws for proper knurled grip type screws which make tweaking the seconary easier  as can do it by hand rather than screwdriver. Usually on the night I pop a Baader laser in after cooldown and if any adjustment is needed its usually very small and done in seconds. This scope also far exceeded my expectations on planets and in all honesty gives the bigger SCT a run for its money for planets. There is a lot to like about an F5 6 inch for versatility and being accessible.

Alan picks up a very good point about balancing Newts on AZ mounts so the bigger and longer they are the more of an issue it is. My VX6 does not entirely balance properly on my AYOII, almost but not quite, however it does not make any difference in use as the AYO is such a quality unit, I also use a push to set up. Remember that being F5 and a shorter tube you can adjust it to as low to the tripod leg clearance as possible, something that may not be as effective witn a bigger longer 8 inch on AZ mount. This will depend on your mount type and how far out the mount bar protrudes. 

Also you wont need a coma corrector!

HTH.

 

[ollypenrice]

I like Newts for visual, partly because the need to reach perfect collimation and other fine tuning isn't there. What does nicely for the eye (or mine, at least) may not do nicely for the camera. I used a 20 inch F4 for 12 years without a coma corrector and none of our guests ever suggested I buy one. One or two were surprised that there wasn't one in the scope already, though.

Regarding choice of supplier I'd always be inclined to type their name into Google followed by 'customer service.'

Olly

[Stu]

The VX6 scopes do looks great, really compact and with a good set of optics they should give great results.

The only other suggestion I could give would be the MN190. I'm sure it would be too heavy for your requirements, but it does give almost apo like views in a 7.5" f5.3 scope. Weighs 10kg though so would need a serious mount.

[KP82]

3 hours ago, JG777 said:

@KP82 I have the Orion Optics VX6 F5 and with 1/10 PV. It is my mid range grab n go scope and also my most used scope. I now use this more than the 9.25 Evo or my small refractors. The reason is it is a big enough aperture to see the main DSOs,  galaxies, etc, and especially wide clusters in glorious detail. It is so much more manageable than an 8 inch , yes an 8 gets you better views but the 6 is easier to take to dark skies, mount and move around. It cools down fast thanks to its size and having a cooling fan and thanks to the overall good quality of the fittings it holds collimation very well. I swapped out the secondary mirror phillips screws for proper knurled grip type screws which make tweaking the seconary easier  as can do it by hand rather than screwdriver. Usually on the night I pop a Baader laser in after cooldown and if any adjustment is needed its usually very small and done in seconds. This scope also far exceeded my expectations on planets and in all honesty gives the bigger SCT a run for its money for planets. There is a lot to like about an F5 6 inch for versatility and being accessible.

Alan picks up a very good point about balancing Newts on AZ mounts so the bigger and longer they are the more of an issue it is. My VX6 does not entirely balance properly on my AYOII, almost but not quite, however it does not make any difference in use as the AYO is such a quality unit, I also use a push to set up. Remember that being F5 and a shorter tube you can adjust it to as low to the tripod leg clearance as possible, something that may not be as effective witn a bigger longer 8 inch on AZ mount. This will depend on your mount type and how far out the mount bar protrudes. 

Also you wont need a coma corrector!

HTH.

 

Thank you so much for sharing your personal experience. BTW that's a very neat setup you have there. I like it a lot. Your picture clearly illustrates my point: for visual a portable manageable setup that I enjoy using frequently is much more valueable tha cumbersome ones that feel like a chore to set up every time therefore rarely used despite larger apertures.

The Alt-AZ mount I currently have is a SkyWatcher AZ5 w/ 1.75" steel tripod. It's rated for up to 9kg payload. So I guess it would be adequate for the VX6. It certainly works very well with my 4" triplet which weighs about 5.2kg OTA only.

It's great to know that I don't need an expensive coma corrector for visual despite being a fairly fast scope. I'm still a little concerned about collimation. You said the fitting is pretty good at holding the collimation but you still need the put the laser collimator in the focuser before observing every time. Does that mean screwdrivers need to be carried around all the time assuming I don't replace the original screws with the thumb screws like you've done? Also every time you adjust the collimation, is it just the primary mirror or both?

[KP82]

2 hours ago, Stu said:

The VX6 scopes do looks great, really compact and with a good set of optics they should give great results.

The only other suggestion I could give would be the MN190. I'm sure it would be too heavy for your requirements, but it does give almost apo like views in a 7.5" f5.3 scope. Weighs 10kg though so would need a serious mount.

I thought good quality newtonians (e.g. 1/10 PV mirror) are natural APOs.

Yeah that MN190 is a little on the heavy side (weighs quite a bit more than even the VX8). It would definitely be a no-go for my Alt-AZ. And if I have to put it on my HEQ5 Pro, then it wouldn't be very portable to take with me to dark skies. But thanks anyway.

[Stu]

3 minutes ago, KP82 said:

I thought good quality newtonians (e.g. 1/10 PV mirror) are natural APOs.

Yes, thats true enough, but I think the Mak Newt has other advantages in terms of being free from coma, with a flat field and also has no diffraction spikes.

I reckon the VX6 is a great option though.

[JG777]

Your AZ5 will be fine as the scope weighs about the same as your refractor. More good news is that an encoder kit is available for your mount if you fancy a push to set up.

See here http://astrograph.net/epages/www_astrograph_net.sf/e

I found collimation with the VX easier to do than on SW scopes partly due to the minimal slop in the VX focusser, it is a good quality focusser much  better than standard SW and good enough to use a laser with. Having said that a collimation cap and a Cheshire device also provide very accurate collimation and in my VX6 all three devices agree on the result. 

Collimation is not that bad once you get the hang of it, there are a lot of guides on the net and some can be quite confusing.  Astro Baby did a very good one and this is a good guide as well. http://garyseronik.com/a-beginners-guide-to-collimation/ dont get bogged down its worth the effort.  

Once you are collimated it is only really small tweaks required, I sometimes do it before a journey out and always a quick check after set up and 10 minutes cooling from the fan. I find the check outdoors after a bit of cooldown to be most accurate, also the scope is now mounted and any tube flex can be accounted for. In reality for the secondary and primary we are talking about 30 seconds work , more often than not its a minor tweak for the primary, on occasion though you may need to adjust the secondary but not often. You will need  a small Phillips head screwdriver for the secondary screws and keep the scope horizontal in case you drop the screwdriver! Its easy to reach the back of the scope whilst viewing the front or viewing through a cheshire due to the short tube length. The adjusters on the primary are quite smooth in operation as well.

The bigger danger is the threat your 4 inch refractor might feel! I sold my 100 SWED PRO as the VX6 was just the more compelling choice for grab n go. Never regretted it either, even though it was optically great the VX just hauled in more DSO due to the extra aperture. Just as easy to pack in the car and maintenance is pretty low.  Mirrors have been out once for cleaning in the 2.5 years I have had it. 

Not sure if you belong to an astro society, if so someone there could help with collimation basics,  but its not particulary difficult , tuning a guitar is probably harder, dont let that one thing put you off . 

 

[KP82]

Thank you once again.

It's good to know there is an encoder unit for my mount. That website you listed is currently down for maintenance but I'll certainly take a look at it later.

I've read the collimation guide on Astro Baby. The secondary collimation seems a bit overwhelming for a frac user like me. The primary seems pretty straightforward similar to aligning a finderscope. I guess I'd eventually get used to it.

You made a good point about whether it's worth keeping the 4" frac once I get the VX6. I might dedicate the frac for imaging only and re-organise my eyepieces around the focal length of the newt. Or I could try taking pictures with the newt and see if its results would make the frac obsolete. The problem is that I might need to spend as much as the scope itself for a coma corrector. Also I don't know whether the 1/10 PV mirror would give me the same crispy/contrasty views on the Moon and planets (I do like to look at them when they are high in the sky. It's just DSOs take more of my observation time) like the 4" triplet APO.

I called up OOUK today and was told the current waiting time is about 3 weeks, so if I want the scope before Xmas I'd have to make up my mind this week.