Jump to content

Stargazers Lounge Uses Cookies

Like most websites, SGL uses cookies in order to deliver a secure, personalised service, to provide social media functions and to analyse our traffic. Continued use of SGL indicates your acceptance of our cookie policy.

sgl_imaging_challenge_banner_beauty_night_skies.thumb.jpg.2711ade15e31d01524e7dc52d15c4217.jpg

Recommended Posts

Good afternoon all, 

Ive made a lil nest egg for my next scope, having had a refractor I am now looking at a reflector.

I was looking at the Celestone Omni series or the skywatcher explorer range, or even a lightbridge. I notice alot of the focal lengths wont really help me get to that higher magnification without sacrificing eye relife. 

Alot of the high end scopes I see have a long focal length like 2000+ but only appear to be about 500-1000mm long. How are they achiving this? 

I know the apature is more important but if im honest anything would be a step up from what I currently have :'D

This would give me the magnification I want but the price isnt exaclty ideal. My budget is £400-£600.

Edited by Mattwaters

Share this post


Link to post
Share on other sites

Cats like a Maksutov or Schmidt Cassegrain have lenses and mirrors. Light comes in, bounces of primary at back of tube, goes back up and hits another mirror on the inside of the objective lens and then goes back down and out through a hole in the middle of the primary at the bottom. My Mak 127 has a focal length of 1500mm but it's only about 35cm long (and I love it!)

  • Like 2

Share this post


Link to post
Share on other sites

Irrespective of the word I assume you are looking at a reflector. Guess "not" should be "now".

Except for a couple of the smaller reflectors 114, 127 and maybe a 130 the focal length and the tube length match. The tube length is about 80% to 90% of the focal length as the secondary mirror deflects the path out to one side.

If you are talking SCT/Mak then for ease just consider them as folded. The mirror shapes add in complexity but folded is the simplest way to consider them. So yes they are a lot shorter. Equally they are not usually called a "reflector" in the strict sense.

If it is a reflector you want as in Newtonian then do check the focal length against the tube length as some have a built in barlow in the focuser. Problem is the implimentation is poor and so the scope delivers poor performance.

Eye relief is where you put you eye and is a function of the eye piece, again do you mean exit pupil ? Exit pupil is a function of the eyepiece and the magnification and if you want high magnification the the exit pupil is small:

Exit pupil = Eyepiece Field/Magnification:  Solution is nice expensive eyepieces of wide FoV as in 82 or 100 degrees or a small exit pupil.

If you meant eye relief then buy BST Starguider with 16 tp 19mm eye relief. Others will have different eye relief vut be careful of 1 mm difference as the eye relief can be measueed from 2 places and those 2 places are 1 or 2mm difference. Some have 20mm eye relief - think Delos might. The eye relief of a plossl is about 2/3 of the eye piece focal length so they vary.

So which reflector draws your attention.

Edited by ronin

Share this post


Link to post
Share on other sites
3 minutes ago, ronin said:

Exit pupil = Eyepiece Field/Magnification:  Solution is nice expensive eyepieces of wide FoV as in 82 or 100 degrees or a small exit pupil.

Apparent field of view has no effect on exit pupil. The equation should be

Exit pupil = Aperture/Magnification 

 

With regards to the OP, a dobsonian mounted Newtonian will get you the most aperture for your money. You can get quite a substantial manual dob for £600. However, if you want/need goto then the cost of such a mount will leave less money available for the optics. 

  • Like 1

Share this post


Link to post
Share on other sites

Thank you, Im enjoying finding my targets manually so I would prefer my money to be spent on optics rather than goto mounts. I will have a look about and let you know what I find.

Share this post


Link to post
Share on other sites

What mount do you currently  have would help

A bang for your buck would be a 10" dob £429 from flo or cheaper 2nd hand

Edited by Frank the Troll
  • Like 1

Share this post


Link to post
Share on other sites
7 minutes ago, Frank the Troll said:

What mount do you currently  have would help

A bang for your buck would be a 10" dob £429 from flo or cheaper 2nd hand

I have an Equatorial CG-3 that came with my astro master... so nothing special and would be looking to replace as well :/

Share this post


Link to post
Share on other sites

From your stated requirements and budget I would think a 8" - 10" Dobsonian would tick a lot of boxes. Magnification upper levels can be achieved with a Barlow which will preserve or even increase the eye relief.   :icon_biggrin:

  • Like 1

Share this post


Link to post
Share on other sites
9 minutes ago, Mattwaters said:

Thinking this would be better than the Omni or Explorer Series. 

Thoughts?

 

A dob base is great for visual astronomy. The only thing to consider would be of you want the flex tube version you linked to or the solid tube version, or possibly an 8" if you think the weight might be an issue. 

Share this post


Link to post
Share on other sites

If you went 2nd hand, you could get an 8 or 10" on an eq5 goto, on your budget, worth a thought

All my kit is 2nd hand bits and pieces, works just as well as new stuff

 

 

 

Edited by Frank the Troll

Share this post


Link to post
Share on other sites
4 minutes ago, Frank the Troll said:

If you went 2nd hand, you could get an 8 or 10" on an eq5 goto, on your budget, worth a thought

All my kit is 2nd hand bits and pieces, works just as well as new stuff

 

 

 

Cheers, Ive seen there is a good second hand market out there so will keep an eye out, Ive got time anyway. Afew more targets this year but for next year I want a good scope to see Mars!

Share this post


Link to post
Share on other sites
7 minutes ago, Mattwaters said:

 I want a good scope to see Mars!

Mars will be disappointing what ever scope, you might see a ruddy brown reddish disk and thats it, or if lucky, a hint of polar cap

Now Jupiter and Saturn, that's a whole different story

 

Edited by Frank the Troll
  • Like 1

Share this post


Link to post
Share on other sites

@Mattwaters  just a few questions which may help give a better idea as to what to recommend.

1 hour ago, Mattwaters said:

I notice alot of the focal lengths wont really help me get to that higher magnification without sacrificing eye relief

I know the apature is more important but if im honest anything would be a step up from what I currently have :'D

This would give me the magnification I want but the price isnt exaclty ideal

1) what is your current scope and mount. ?

2) what eyepieces do you have ?

3) are you comfortable with collimating scopes and is the one you currently own collimated ?

4) you say higher magnification and you have one in mind, what would that be ?

5) what do you expect to gain from that magnification ?

6) do you want a tracking or manual mount and if a manual mount how good are you tracking objects at high magnifications ??

7) what night sky objects do you want to observe in particular ?

8) do you have easy access to a garden as scopes get big in more ways than aperture ?

Edited by spaceboy

Share this post


Link to post
Share on other sites

I have a Skyliner 200P and I like it, so I'd expect the 250PX would also be pretty good. You'll need to get some black cloth to put around the open section of the tube.

In the UK the poor seeing often means that you don't get any more detail from using magnifications above 200-300x, so that, rather than your scope's aperture, will limit the magnification you can use. With a Dob higher magnifications can also be inconvenient as the objects cross the field of view rather quickly so you have to move the telescope tube a lot. But if you want something with tracking/goto you will have to shell out more money or buy a smaller scope.

As far as Mars goes, in order to see detail you need to catch it close to opposition when it's at its closest to Earth. There's an opposition roughly every two years. Some oppositions are closer (and therefore better) than others - the one next year is very close but extremely low from the UK. The 2020 opposition will also be fairly close, but higher in the sky, and that should be the best opportunity to see detail in the next ~20 years: Mars's disc will appear larger than Saturn's. Most of the time Mars is unfortunately just a tiny red dot.

Share this post


Link to post
Share on other sites
2 hours ago, harrym said:

In the UK the poor seeing often means that you don't get any more detail from using magnifications above 200-300x, so that, rather than your scope's aperture, will limit the magnification you can use.

Even at equivalent magnification, the larger aperture dob will often show more detail in moments of steadier seeing.  It will also excel at faint objects.

The OP should definitely check the used market for 10" dobs.  They come up fairly often here in the states.  It can always be resold for about the same amount, so nothing lost trying it.

Share this post


Link to post
Share on other sites
13 hours ago, Mattwaters said:

Thinking this would be better than the Omni or Explorer Series. 

Thoughts?

Screenshot_20170903-182846.png

Screenshot_20170903-182900.png

im selling one of these if your interested, open to offers

Share this post


Link to post
Share on other sites

If planets are a major target for you, you might wish to look for a scope with a longer focal-length than a Dobson-mounted (or other Newtonian reflector) Newtonian can supply. Such as the already described CAT (catadioptric) telescope - with a folded light-path using both lenses and mirrors.

But one thing is certain - no one telescope will do everything really well. Each type of telescope excels at one type of object. Or maybe two. Which is why you see many of us have several different types of telescopes - such as in my signature.

Dave

Edited by Dave In Vermont
syn.

Share this post


Link to post
Share on other sites

There is a Goto 250P flextube on a Dob mount just like in those pictures going for good cash in the SGL classifieds at the moment - I wish it had been for sale when I got my 200P

Share this post


Link to post
Share on other sites

Hello , If 400-600 is what you wanna spend on an optical tube and you want higher magnifications , you must sacrifice field of view . Maybe you might go for a Cestron C5 or C6 , or a 5 ich MAK cassigrain . They give you more magnification as well they would be abale to be used with your current mount and they are a pretty small package compared to a relfectpr or longer refractor . The schmidt cassigrain has tons of add ons and you can add a reducer corrector to it to give you in effect two scopes in one a f/6.3 scope with it on the scope and the off the scope a f/10 scope you can do alot with this set up and is good for imaging as well . with the reducer corrector on it  at f/6.3 its good for wider field flatter views  of view nebula, open star clusters ect .... at f/10 you can do higher magnification planets , globulars , and double stars really the schmidt cass. Is a really all around good to great performer at alot fo things and its a small package and good for your mount optical tubes can be purchased used for a lower price I owned a C5 and I used it as my primary instrument for 10 years did alot with it as well but sct,s are a comprimise scope it does alot fo things in the good range but not great . A refractor even a low end refractor will out resolve an SCT a larger relfector is brighter and i fel will out resove and SCT as wel as long as its collominated well . so think about it an SCT might be the way to go longer narrower focal ratios, reducer corrector turns any sct into a wider scope and they are light weight and can sit on smaller mounts such as yours best of luck . 

Share this post


Link to post
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.

Guest
Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.


  • Recently Browsing   0 members

    No registered users viewing this page.

×
×
  • Create New...

Important Information

By using this site, you agree to our Terms of Use.