My first scope - need Eyepiece and general scope advise
Hi,
I have now idea what I'm doing. I just bought my first scope which is an 8" Vue Eye 05413 EQ - I can't find any info on this scope using Google. I picked it up for $250 with a 25mm PL and a 6.4mm PL 1.25".
Does anyone know anything about this make/model of scope?
I need a 3x Barlow for moon and planet stuff and probably better quality lens with a wider view angle - possibly an adjustable lens - not to sure (would like something for deep field as well). The adjustable eyepiece mount/adapter screws off with a 40mm thread and I am wondering if I can change this to 2" or if I'm stuck with 1.25".
I have attached some photos - any advice would be appreciated.
Hi Nige, The scope looks to be the same one that National Geographic
stores sell. Being as most Chinese and Taiwanese focusers are made
in only a couple of factories, there is a chance that the Skywatcher focuser parts from their 8 and 10" Newts might enable you to use 2"
EPs.I would avoid 3X barlows, unless you are willing to fork out
for a high quality one. 2x ones are usually superior optically, and a 3x
would be useless with your 6.4mm EP anyway; The resultant magnification [about 380x if your scope is f4] would almost never be
useable with that scope. A great budget way of getting started is the
8-24mm 1.25" zoom EP sold by Seben on ebay for around $60. It's
great value for money, and used with or without a 2x barlow it gives
a great range of mags, and only requires very slight tweaks to the focus
as you zoom.
raymo
I'm thinking that since the focuser only measures 40mm at the threaded section I won't be able to get an adapter for 2" EP's and I will need to replace the whole focuser if I want to use 2" - is that correct?
Is there any substantial gain/advantage to 2" EP's over 1.25"? Would it be worth upgrading to 2"?
Quote:
Originally Posted by raymo
I would avoid 3X barlows, unless you are willing to fork out for a high quality one. 2x ones are usually superior optically, and a 3x would be useless with your 6.4mm EP anyway; The resultant magnification [about 380x if your scope is f4] would almost never be useable with that scope.
Since it is a 200mm aperture the practical mag should be 400x should it not? - or are you saying that it won't deliver this because its (mirrors I guess) low quality?
It has a FL of 750mm and with 6.4 EP gives me 117x and I thought a 3x barlow would be ideal giving me 350x (still within the practical limit of the scope of 400x) - why would this be unuseable with this scope? I went for a 8" scope so I could get a mag in the 300's.
* Barrel size is the limiting factor to the widest the apparent field of view can be for a given focal length. An example will best demonstrate this: the longest 1.25" EP that will give an AFOV of 68º is 24mm. In the 2" format this is 42mm. But, having such a fast scope (f/4), another factor comes into play, coma. It is a phenomenon that affects reflectors where the resulting light cone coming off the primary mirror is too stumpy for an eyepiece to handle, and the resulting aberration is seen as the stars along the edge of the field of view having little 'comet tails' that rediate out from center. This is not a flaw, but something that just is. Longer focal length eyepieces show this much more than shorter ones.
* 300x magnification is possible, optical quality allowing. Even 400X is not out of the question. But the one all limiting factor is the atmosphere. And it doesn't matter how good your gear is, the atmosphere will determine how high magnification can be used. Typical conditions allow 120X tops. Good conditions allow 250x. Exceptional conditions allow 400X.
* I too have Barlow lenses. Both 1.25" & 2". I never used the 1.25", & only once the 2" in the four years I've had it! Most folks you'll find prefer to use the appropriate short focal length EP over a Barlow. Barlows seem like a good idea, but in the end they just get in the way, & are another thing to drop in the dark. One thing few people actually realize too is thaya Barlow won't necessarily have the EP behave in the same way as neat. But, all the same, a Barlow is a good idea for your scope (just determine optical quality first before commiting more funds. Just be aware that EP/Barlow combos aren't a guarantee of an optical match with your fast Newtonian. You might want to borrow a mate's Barlow to see how it works in your scope with the eyepieces you have.
f4, or f/4, is the focal ratio of the telescope, in the same way of a camera lens. It is the ratio between the focal length divided by the diameter of the scope. A fast scope is one with a focal ratio of f/5 or less. A slow scope is one of f/6 or greater.
Your scope is close enough to f/4, which is a very fast ratio.
Barrel size is the limiting factor to the widest the apparent field of view can be for a given focal length. An example will best demonstrate this: the longest 1.25" EP that will give an AFOV of 68º is 24mm. In the 2" format this is 42mm.
ok - how are you working this out exactly? when you say barrel size are you referring to the diameter of the EP or the scope?
Quote:
Originally Posted by mental4astro
But, having such a fast scope (f/4), another factor comes into play, coma. It is a phenomenon that affects reflectors where the resulting light cone coming off the primary mirror is too stumpy for an eyepiece to handle, and the resulting aberration is seen as the stars along the edge of the field of view having little 'comet tails' that rediate out from center. This is not a flaw, but something that just is. Longer focal length eyepieces show this much more than shorter ones.
I think I understand this thanks to your excellent explanation - your saying that coma is a result of the geometry i.e. the shorter the scope the larger the angle of curvature towards the outer regions of the primary mirror.
Quote:
Originally Posted by mental4astro
* 300x magnification is possible, optical quality allowing. Even 400X is not out of the question. But the one all limiting factor is the atmosphere. And it doesn't matter how good your gear is, the atmosphere will determine how high magnification can be used. Typical conditions allow 120X tops. Good conditions allow 250x. Exceptional conditions allow 400X.
I too have Barlow lenses. Both 1.25" & 2". I never used the 1.25", & only once the 2" in the four years I've had it! Most folks you'll find prefer to use the appropriate short focal length EP over a Barlow.
I can appreciate the effect of the atmosphere but I think I should be able to see more than what I can. I don't seem to be able to see much at all, when I use my PL 6.4 EP I can only see the surface of the moon and not quite as good as an old $15 60mm Tasco refractor we bought for the kids - using a 3x barlow and a H12.5 EP.
If most folks don't use a barlow what can they actually see - can you see Jupiter? I can't and I expected to see Jupiter and a couple of it's moons on a good day. I tried looking a Venus also but can't see more than a slightly enlarged star. This is disappointing, is it the quality of my EP? What can I expect to see with say a good quality PL 8mm EP and no barlow? The mag factor just seems too low to me.
Quote:
Originally Posted by mental4astro
But, all the same, a Barlow is a good idea for your scope (just determine optical quality first before commiting more funds.
I agree completely - I am happy to spend a little money on a better quality EP and a barlow but how do I determine the optical quality of the mirrors in the scope?
Is it better to upgrade to a 2" focuser and EP as opossed to 1.25"? If so I would be happy to upgrade the focuser to 2" providing the scopes mirrors are going to preform. I don't want to spend the money on 1.25" gear and then find out that I should have bought 2" gear.
Should I ditch this F/4 scope and get a 1m 8" so its not such a fast scope - or would this not make much difference? No point spending money on EP's and focuser if the scope is not going to preform - better to change the scope now if I need to.
Most likely the mount will be the bottle neck. Does not look sturdy enough for an 8" Newt. Inexpensive GSO Plossls & 2x barlow would help you out in the EP department... but that mount is going to be a source of frustration me thinks.
Hi Nige, Your H12.5mm EP is an old design, and won't do your scope any favours, but, your scope should knock the socks off a cheap 60mm
refractor with just about any EP, so something has to be wrong, either
with the scope, or your efforts with the scope.
Firstly, if Venus is a slightly enlarged star something is very wrong.
Have you checked that the scope is at least reasonably collimated?
If it is really badly collimated, nothing will look good.
I don't understand what you mean when you say you couldn't see
Jupiter; did you mean that you couldn't locate it, or that the view was
as bad as Venus.
Don't worry about using your high power EPs like the 6.4mm until
you have got the scope up and running properly.
You should get stunning views of the moon with an 8" Newt, but it seems that the scope is not coming to focus, so being that you got it
second hand, maybe a focuser extension tube is missing.
Try focusing on something in the distance during the day and see if
you get a sharp view. If not, note whether it is because the focuser
won't rack far enough out. If that is the case, wind the focuser fully out, loosen the EP and slide it out further whilst looking through it.
If it focuses then you need an approptiate length extension tube.
Try this first, and we'll take it from there.
raymo
Just for the record I am using the H12.5 EP with the 60mm refractor not the 8" newt. The tasco gear is 3/4" so the are not interchangeable between the two scopes without an adaptor - which I don't have. I am using a 6.5mm (its actually 6.5mm not 6.4) and a 25mm plossl that came with the 8" newt.
The collimation does look reasonable, it is off slightly in one direction but it seems to be centred pretty well. The guy I bought it from said he had it set up perfect so don't mess with it. It could have moved in transport though.
I can locate Jupiter, its not quite as bad a Venus in that it looks like more than just a star but only just. It appears as a very small round object < 1mm in diameter but has no definition with my 6.5mm EP. Its only the fact that its not a pin point star and is slightly roundish that I realise its Jupiter.
I just tried looking at something in the distance during the day and I can't really focus on it. its not because of the travel in the focuser as I can run through the point of focus with more travel in the mechanism at my disposal in both directions. It is because when I try to focus on the object it just doesn't become completely clear at the point of focus and then goes out of focus again as I move through that point. I tried both EP's and the 25mm gives better focus than the 6.5 EP - the 6.5 is terribly blurry.
It seems to me like the EP's are not preforming. I pulled the 6.5 apart and checked lens configuration and cleaned it - made no diff, still the same.
Most likely the mount will be the bottle neck. Does not look sturdy enough for an 8" Newt. Inexpensive GSO Plossls & 2x barlow would help you out in the EP department... but that mount is going to be a source of frustration me thinks.
You could be right on both counts. I need to sort out the optics before the mount - but I was wondering about it.
You raised some interesting points in your post after mine. I'll answer these first in turn.
1, I am only talking about the diameter of the eyepiece barrel that fits into the focuser. It's something like looking into two straws same length, but one larger diameter than the other. The smaller straw with the smaller diameter will show a narrower field of view. Another example might help. We'll take the larger AFOV of 80deg. In the 1.25" eyepiece format, the longest focal length that will allow for an 80deg AFOV is 16mm. In the 2" format, this is around 31mm. You'll notice that the maximum focal length is getting smaller as the AFOV increases - that's because a straw will only show you so much of the sky.
2, Your reasoning of the "geometry" is correct, coupled with the refracting properties of the glass in the eyepiece. Different eyepiece designs handle things better than others. Into the eyepiece/scope equation there is also the complication of optical matching between the scope and the eyepiece. The focal plan of a scope is not a flat one, it can be concave or convex depending on the scope design. Newtonians are concave, Schmidt Cassegrains and Maksutovs are convex, refractors convex too. As a result, different eyepieces can then introduce different aberrations to the image depending on whether than can handle the shape of the focal plane the scope produces.
3 & 4, This one is going to hurt... . After reading your posts, I'm beginning to suspect you have a dud primary mirror. I am familiar with the scope you have, and sadly very few of them have a good primary. This is more the reason why as you increase the magnification the image is degrading even more. The eyepieces you have may be 'cheap', but they will still give a reasonable image. The image will not improve with better eyepieces. The tell-tale sign is the poor image with the 25mm eyepiece, and the even worse image with the 6.5mm. I saw this too when I tested one of these same scopes a few years back. An f/4 mirror is a difficult shape to produce correctly. Sadly the company who makes these just doesn't get it, and just pumps out these junk paper weights. Sorry.
5 & 6, If you do end up changing to a better 8" scope, it should actually come with a 2" focuser, which will also have a 1.25" adapter with it. This then deals with the question of eyepiece barrel size. A slower scope will give a final image with less coma, for sure, though this is just one aberration of many, and I don't consider it a major one. If you do go for a new scope, brands like GSO, Bintel (a rebranded GSO), Skywatcher and Saxon are really good mass produced instruments. These brands have got the hang on what a good mirror needs, and have done really well to have come up with a mass production technique that makes damn good mirrors, fast and slow.
You mentioned collimation in your previous post. Collimation and the need to tweak it in a Newtonian go hand-in-hand. There are just too many moving parts that will shift ever so slightly when you transport a scope. The process sounds daunting, but it is not. It's just re-aligning the optics, a simple process that takes a little to get one's head around, but then becomes second nature. I have three Newtonians at home, and every time I set one up, I just go through the 1min go-over routine, and it's done for the night. Simple and the reward for this do-it-yourself tweak is excellent, .
Would you consider a dobsonian mount rather than an equatorial mount? Reason I say this is a dobsonian mount is much easier so set up an use than an equatorial - it is nothing more than a 'gun turret' arrangement, up and down and swing around. If you are concerned with having trouble in finding objects in the sky, don't be. With charts and the scope's finder scope this isn't a problem (the low tech end, which is all I do even after 30 years in astro). Then there are amazing smart phone apps that allow the phone to become a deep sky object finder where you sit the phone on the scope and use the phone to guide you to the object you are after.
Hi again Nige. On reflection[pun intended], I think there is something
going on here that Mental and I are missing.
Firstly, I don't think that a mirror that was so bad that Venus looked
like a bloated star would ever leave the factory; or If it somehow did,
the buyer would have returned it as unuseable.
I truly don't wish to be patronising, but are you absolutely sure that
you were looking at Venus and Jupiter? You state that Jupiter is very
small through your 6.5mm EP. about a mm. That is impossible at the
approx. 120x that a 6.5mm gives. Even at that modest mag it would be
quite large, and even with a poor mirror it's 4 brightest moons would
be readily visible.Pulling EPs apart is usually a no no, and if you separated
the lenses, you possibly stuffed the EP, as each lens has a proper
rotational position relative to its neighbour, in quality EPs at least. Firstly, I suggest you borrow
a known good EP of any focal length, in order to narrow down the
problem to either the scope or the EPs.
raymo
Well, I pulled the mirrors out and cleaned them. Put them back in an recollimated them as best I could without a laser collimator. Everything is a lot clearer now but I still have poor results from these eyepieces. They do look like cheap EP's.
The moon is a lot cleaner with the 25mm but my 6.5mm is crap (still the same as it was before I cleaned it) - really blury. I double checked that what I am looking at is in fact Venus and Jupiter and I sure I am locating them correctly. I still have the same results - I can see Jupiter better than Venus but it is still very small - now that I have cleaned the mirror I can see 4 moons around Jupiter but they are extremely small little dots of light.
I am keen to borrow a good eyepiece to have a look through for testing purposes and also a laser collimator so I can align the mirrors properly.Trouble is I don't know anyone. Is there someone in the community around Brisbane southside that could help me out? Or perhaps a club meeting I could go along to in my area?
I also keep a film canister collimation tool in my kit as I find it is excellent for dealing with the secondary mirror. A laser is fine (I have one too), but lasers won't give you the optimal position for the secondary. Some people, the film canister tool is the only collimation tool they have.
Eyepiece wise, if you don't get a reply in this thread, you can ask in the General Chat forum for help with this. I'm sure there will be plenty of IIS members in Brissie way willing to help. They will also have a lasrr collimation tool as well if you would like to try one.
I agree with Alex, no need to use a laser on these scopes, a film canister is the simple way to get it close enough.
You want to be very careful cleaning optical surfaces, easy to do more harm than good. Mirrors should only be cleaned if they really need it. There is an article here with some ideas on the procedure http://www.iceinspace.com.au/63-345-0-0-1-0.html
When you put the mirror back, make sure you don't tighten the clamps, they should be sitting just above the mirror surface, to tight and even a small mirror can distort.
With Jupiter it is really low ATM and not very easy to observe. Even in my 20" the other night at about 2am it was a very more view with the atmosphere boiling away at low latitude. Neverteless you should be able to make out a disc and the 4 Galileas moons.
Thanks guys a film canister is a great idea - I will get hold of one and do this.
I actually adjusted my secondary mirror with the primary removed so I was looking straight out the barrel of the scope casing. I adjusted it so as to centre it about the scope casing by eye as per diagram B in the link Mental provided.
I watched a couple youtube video's and when I cleaned the mirror I did pretty much what is described in the link Malcolm provided. I used a ring binder reinforcement ring to mark the centre of the mirror as it didn't have anything marking the centre. I used some baking paper and a compass to make a template and placed it pretty accurately in the middle.
Thanks for the tip about the mirror clamps - I was wondering about this when I was doing them up. When I took the mirror out they were really tight so I did the same when I reassembled it. I think I will take it back out and loosen them off - no need for them to be this tight and it is probably distorting the mirror. What kind of effects will be evident with a distorted mirror?
I had to laugh at the two camps of mirror cleaning - the guy I bought the scope from is definitely in camp A and I am definitively in camp B LOL.
Thanks for the tip on the General chat forum Alex, I will ask for some help with borrowing an EP there.
Nige, I've found that the Kodak canisters best fit a 1.25" focuser.
What will an overtight held mirror image look like? The mirror will focus, but the image will be a little soft (particularly at high power), and when you defocus the image, the "doughnut" shade that appears on stars will look elongated or grossly distorted, rather than a nice evenly round shape.
I've got the exact same model under the Precision brand. It takes 1.25" EP and a Digital Camera adapter screws straight on the 2" thread. I also noticed yours is missing the Star motion tracker unit & it looked like the tube cradle assembly is reversed. See my photo.
I know this baby inside out, Needs a little fine tuning but its a good newt to start with.
I also think your expecting NASA quality images, You must be realistic. Try looking at M-42 with your 25mm EP and you will see something special. I have 40mm, 30mm, 20mm, 15mm, 10mm, 6.5mm, 4mm 1.25" Plossi EP's I bought the whole set on Ebay, once you sort out the collimation get some other size EP's things will become clearer...Pun also intended.
I really don't use my 10mm, 6.5mm & 4mm ep's it's just to hard to define anything, I prefer wide field views of Stars & Nebula's rather than the local planets. I did see Jupiter the other night & It was poor seeing due to bushfires polluting the night sky, however I still saw Jupiter as a colourless sphere & 5 moons. I have also viewed Venus as a white ball (no detail), I doubt any one would disagree that Venus is a disappointment to view thru any telescope.
I've got the exact same model under the Precision brand. It takes 1.25" EP and a Digital Camera adapter screws straight on the 2" thread.
Awesome, your the man! I was beginning to think I bought a one off dud.
I noticed a 55mm thread (approximately) on the focuser which I didn't notice when I posted the picture of the 40mm thread. Is this able to accept an adapter for 2" Ep's?
I have no motion tracker - is this readily available?
I will reverse the cradle mounts - thank you.
I might be expecting unrealistic image quality - I don't know what to expect. From what I have read I should get good results from an 8" scope. Considering the quality of scope that Galileo had at his disposal in 1610 I would expect the image quality of a modern 8" inch scope would blow my socks off! Maybe not but I'm still hopeful.
. After reading your posts, I'm beginning to suspect you have a dud primary mirror. I am familiar with the scope you have, and sadly very few of them have a good primary. This is more the reason why as you increase the magnification the image is degrading even more. The eyepieces you have may be 'cheap', but they will still give a reasonable image. The image will not improve with better eyepieces. The tell-tale sign is the poor image with the 25mm eyepiece, and the even worse image with the 6.5mm. I saw this too when I tested one of these same scopes a few years back. An f/4 mirror is a difficult shape to produce correctly. Sadly the company who makes these just doesn't get it, and just pumps out these junk paper weights. Sorry.
.
