Newbie... Reflector / Refractor?

[jamespels]

Hi all,

I have decided that I want to spend about £400 on turning a childhood interest (too many years ago!) into a hobby.

Main area of interest is DSOs but I also want to be able to take a good look at the planets, our moon and so on. Initially I will be focusing on rebuilding my knowledge of the night sky and just looking at things; before long I know I will want to start taking pics of things to see more.

I am really not clear on the refractor / reflector debate at the moment. For my budget I can get what seem to be a reasonable 120mm refractor (SkyWatcher Evostar 120mm on EQ5 mount) or 200mm reflector (SW Explorer 200P on the same mount). Not sure which of these would be the better choice, if I am on the wrong route entirely or if I should be considering something a bit smaller (e.g. 100 / 150mm equivalents on EQ3-2) and keeping funds for accessories.

I am really not fussed with a goto mount but I do want something I can upgrade for motorised tracking when I stick a camera on it come summer (EQ3-2 and EQ5 both have single axis motors for about £80 - are they any good?).

Sorry this is a long first post, and thanks in advance!

J.

[nightfisher]

here is some pointers in the refractor/reflector debate

reflectors need collimating quite often fracs dont need hardly any tweaking

short focus fracts suffer cromatic abberation on bright objects short focus reflectors dont

[rowan46]

hello and welcome to the site, there have been a lot of questions about astrophotography lately. I think its because stargazing live said you stick a camera on trhe end of a scope and expose for 30 secs. Unfortunately its not quite as simple as that or we'd all do it. for deepspace astrophotography the first and most important thing you need is a mount it must be a german equatorial mount or a pier with a wedge. it must be capable of tracking very accurately or giuiding or both. it must be very steady and it must carry a fair bit of equipment whilst doing all this. imaging is expensive I have heard of people spending about £1500 to do imaging and thats on top of the equipment they already own and hence doing it on the cheap.

Having said that photos of the moon are possible and fun with a dslr on the end of a scope. pictures of the planets are possible with a webcam and free software and of course many of us just look using large scopes. if you really are aiming for imaging by summer you may need to up your budget. this book will tell you everything you need to know about deep space photography and perhaps save you dropping a bundle of money by getting the wqrong stuff Books - Making Every Photon Count - Steve Richards meanwhile the sort of money you are talking about will get you some serious kit for visual work and many imagers have 2 sets of equipment

[jamespels]

Thanks both!

nightfisher - I am quite happy to collimate every night if that's what it takes - I know there are compromises to be made and I would rather spend a bit of effort than unnecessary cash if that's the option. Not quite sure what you mean by short focus though?

rowan46 - yeah, I've hear the £000s estimates from several people! Accepting that I'm clearly not going to end up with a imaging setup for my current budget, I would like to be heading down the right path at least. I can use an existing DSLR and webcam but will probably want to upgrade to a dedicated CCD at some point; this means my real considerations for now (I think!) are mount and the scope itself. The scope is obviously largely a preference thing but I am not sure how to choose between the options I listed (or if there is something else entirely I should be looking at); the mount is a pure requirements consideration - it must be capable of steadily supporting the scope plus camera and have a half-decent motorised tracking mechanism. I'm not talking about something that will track perfectly for an hour or anything - that can come later if I continue that far - but I would like something that can reliably hold a DSO steady for five minutes or so. I don't know enough about mounts to be able to judge but the EQ5 seems like a better bet than the EQ3-2; I have no idea how accurate the SkyWatcher single / dual axis motor drives are so this may eliminate these mounts anyway.

Thanks again,

J.

[brantuk]

For 5mins+ exposures you'll probably need to look at a guiding setup. Two scopes, two cameras and a hefty EQ mount (probably HEQ6 minimum).

If it was just for observing I'd say a big aperture dob, but as it is I'd suggest a good appo with maybe an ST80 for guiding. Unfortunately this isn't within your budget.

You can make a good start though reasonably cheaply. An EQ-5 will hold a small appo or a 150P Newt quite comfortably, and with a webcam you can begin snapping the planets. An RA motor will keep the planets in view nicely for that.

[rowan46]

there may be another way get yourself a pair of binoculars learn the skies and keep posting questions after 50 posts and a months membership you get access to the for sale board astronomers look after their gear and you may be able to pick up some bargains

[rowan46]

I forgot to add this is a lovely program to learn the stars with Stellarium

[nightfisher]

here is one suggestion, a skywatcher 127mm maksutov scope, they are short and lightweight but superb optics on an eq5 mount so you could use the dslr, but better still use a webcam to do lunar/planetary imaging, these scopes are long focus f11 or more so are not regarded as any proper use on dso`s, however i have seen some image`s done with even higher maks (f14) that are truly stunning, also if you want to do imaging starting with lunar/planets is a much easier and cheaper option, the 127 mak is a cracking lunar planet scope that should give some half decent views on dso`s, my 140 mak shows the neb in orion beautifully

[jamespels]

Hi rowan46 - thanks for this - will keep an eye on the "for sale" board... Will also take a look at the Stellarium s/w,

nightfisher - cheers for the advice - hadn't thought of a mak at all (didn't know what one was until yesterday!). Why is a slow scope considered poor for DSOs? Presumably, if you can keep it on target, it's just a case of a longer exposure? Or is the challenge keeping it on target?!

Cheers,

J.

[nightfisher]

i dont understand the science of it but short focal length is considered best for dso about f5, pricey little refractors like williams optics and 80mm ED scopes, if you use high focal length scopes on dso you end up with much longer exposure times............i think. But high focal lengths are better for planetary imaging

[themos]

DSOs tend to be quite "wide" objects, they take up a lot of sky, so you don't need much magnification for them. That translates to shorter focal length requirements than planets. That also means that it's easier keeping the scope dead on target, for photography. The downside is that they are faint so need a lot more exposure time than planets. Basically, planetary and DSO photography impose completely different constraints on optics and mount.

[rowan46]

as you said the challenge is keeping it on target it has a narrower field of view, higher magnification add this to the increased exposure time and you can see why people don't use them for imaging dso's, but on planets they are great instruments

[Astro_Baby]

I dont image but I think the reason for fast focal ratios is down to ecposure time. Faster the scope the faster exposure time can be. Big focal ratio means longer exposures, longer exposures means higher accuracy needed in the mount tracking which translates as bigger ££££££

There are some stunning pics done with long focal length scopes like the TAL 200K but I guess its harder and astroimaging is tough enough I imagine without adding complications.

[jamespels]

Heh, so now I have a third option and know I cannot possibly afford what I want to do!

I guess that's always the way unless you're Jonathon Ross!

One thing though seems apparent: I need to get the best mount I can that still leaves reasonable spends for the scope itself and avoid overloading it - this seem like a reasonable approach?

[jamespels]

Another thought, just how big (in real terms) is a 200mm newtonian and how fragile are they? Is this something I am going to be happy putting in the back of a car every weekend?

[mattski]

I had a similar challenge and ended up getting a refractor as I wanted low maintenance and there's something that appeals about them that the others don't quite have for some reason :-)

[themos]

Another thought, just how big (in real terms) is a 200mm newtonian and how fragile are they? Is this something I am going to be happy putting in the back of a car every weekend?

It will be fine.

[sixela]

Another thought, just how big (in real terms) is a 200mm newtonian and how fragile are they? Is this something I am going to be happy putting in the back of a car every weekend?

Newts are fairly robust. The good thing about having to collimate them is that even a dent in the tube won't bother you.

They do pick up some dust so you have to have the courage to remove the mirror from the cell once every year to give it a bath, but that really is no big deal.

Just to summarise:

"I'm mainly going to observe and I'll get a scope for photography later": 200mm Dob.

"I'll be wanting to image planets with a webcam and dip my toes into DSO photography, all with a limited budget": 150mm f/5 Newt on EQ5 with a good dual speed focuser (important for photography if you pick an f/5!) and a 5x Barlow eventually for webcam photography. Don't be tempted to get a smaller mount or larger scope on the EQ5.

If you want an EQ3-2 mount, pick the scope below or an f/5 130mm Newt, and make sure it has the newer steel tubular legs tripod.

"If I take up astrophotography it'll be planetary with a webcam, and I want something extra portable": 127mm Mak on EQ3-2 or EQ5 (or obviously the original Vixen GP).

The advantage of an EQ5-class mount is that you will still be able to mount an 80mm ED doublet refractor on it as well if you later fancy wide field DSO photography.

You can also try to squeeze a clearance/sale ED 80mm refractor on an EQ5 in the budget, but that's clearly skewed towards photography of DSOs only and compromises observing a lot (at least if it's your only scope, though it's a perfect complement to another larger scope that you'd buy later).

[jamespels]

Hi sixela,

very succint - thanks!

Can you clarify something for me please? A quick google tells me that a dual speed focuser essentially allows quick "approximate" focusing as well as very fine focusing for camera work - is this correct? It looks from FTO's site like these are an upgrade path for SkyWatcher Explorer - again, is this correct or am I missing something?

[Astro_Baby]

A 200 newtonian is around 240 mm wide including the tube rings and around 900mm long assuming its a 1000mm focal length.

Mine runs in at around 11kg but its been modded to have some extras so its a bit heavier than one from the factory.

They do travel ok with reasonable care, mine has a nylon padded bag it rides around in but on an EQ mount they can be quite heavy.

To give you an idea of bulk and weight here's what I carry.....

SW 200P in bag....around 250x1000mm and weighs in bag about 14kg

HEQ5 mount head in bag......about 400x400x70 and weighg of approx 10kg

HEQ 5 tripod legs........about 1000x70mm when folded, weight approx 7kg

Counterweights (x3)........altogether 150x150 and 15kg weight

Eyepiece case.......aluminium flight case, size of large attache case

Accessories case.....same as above

Powertank.........size of laptop bag and weights about 1kg

You can see you neec a bit more than just the scope, there are ALWAYS extra bags to carry.

That lt will fit in the back of a Toyota Aygo with room to spare but I almost never use this scope anymofe because of its weight and bulk. Last year it was probably used less than half a dozen times.

[Zakalwe]

Have a look at AstroBaby's excellent website

Link

[JamesM]

I would to suggest that you buy the mount WITH the motors attached, as it will work out cheaper than buying afterwards and the effort to attach them etc.

Sadly, as soon as astrophotography is mentioned, the needs for and demands made upon kit are dramatically skewed and is why I reinforce the recommendation made earlier that you buy Steve Richard's "Making Every Photon Count." It will lay out in front of you exactly what you need and why so that you are fully aware of what the possible costs are further down the road - imaging is very addictive!!

There's no rush, the stars aren't going anywhere and its important that you get it right for you.

Clear skies

James

[jamespels]

Thanks for all the advice, folks...

James - technically speaking, the stars are all off somewhere, just VERY slowly... Maybe one of them will even go pop when I'm recording in just the right place...

Back in the land of reality, I am going to put long exposure imaging on hold for a while. After a long chat with Steve at FLO (thanks Steve!), I have pretty much settled on a SW 150P (maybe DS) on an EQ5. It'll cost more in the long run but planned / possible future upgrade path is along the lines of 1) dual axis motors, 2) second scope (short refractor), 3) double mounting arm (or whatever you call it!), 4) CCD camera or similar, 5) guidance system & goto upgrade for EQ5. Of course, by the time I've got round to that there will be 101 other things on the wish-list and I am bound to get diverted with "essential" eye pieces and other bits and bobs but at least I am getting kit to set me off in the right direction, I think.

[cotterless45]

Aye, you'll not go far wrong with a Sw150p. Ditch the supplied lenses and get some decent replacements.

It's worth getting a Telrad finder, it's easy to find things using the Telrad charts.

[sixela]

Hi sixela,

very succint - thanks!

Can you clarify something for me please? A quick google tells me that a dual speed focuser essentially allows quick "approximate" focusing as well as very fine focusing for camera work - is this correct? It looks from FTO's site like these are an upgrade path for SkyWatcher Explorer - again, is this correct or am I missing something?

That's correct. a dual speed focuser has an extra fine focus knob with 1:6 to 1:10 reduction (usually with a Vernier reducer, i.e. a planetary gear with a ball bearing). IIRC, the cheaper Skywatcher Newts don't have a dual speed focuser but the Blackline series have. Of course, you can always just use the normal focuser and upgrade it afterwards to something even better than the Skywatcher dual speed (Moonlite focusers are very popular for this but cost quite a bit, and there are also e.g. the Baader Steeltrack and the even cheaper GSO dual speed focuser), but aftermarket dual speed focusers aren't that cheap.

It's more important for planetary imaging with a webcam, but you can also get a helical focusing 2"-1.25" adapter and keep the original focuser.

One thing to watch out for is to have a scope where the focal plane can be placed far enough from the tube, because DSLR sensors are a lot further from the focuser than eyepiece focal planes. Just ask FLO.