Skywatcher Mercury 705, what next?!

[Absolutebeginner]

So, last Christmas (on the advice received from this site, for which many thanks), I bought my son a Skywatcher Mercury 705. And, it's excellent!

But I now have a couple more questions:

1. Should I get a Moon filter (which I assume cuts down the light reflected from the Moon) for general observation, unless I intend to use the telescope only when there is almost no moonlight. And if the answer is 'yes', can anyone recommend one that will (a) fit and (b) not break the bank; and

2. I think the magnifying lens is +10, which I have to say, was a tad disappointing in terms of 'detail what you can actually see' when we used it to look at Venus and Mars (yes, I know that sounds like a bit of an 80s pop cliche). So, question 2 is, should we buy a stronger magnifying lens and, if the answer is 'yes', what strength and what might one recommend?

As ever, whilst I appreciate all and any advice, if we can keep it simple and 'non-techie' it would be really useful (as I'm a bit uncomprehending, astronomywise. As you can tell...).

Many thanks in advance.

Andrew

 

[Putaendo Patrick]

A Moon filter is only used when observing the Moon, i.e. it doesn't help to cut down the effect of the Moon's reflected light on the sky as a whole. Some people find the Moon uncomfortably bright especially when it is near full, however others seem much less affected. Next time you observe the Moon put a sunglasses lens over the eyepiece. If it makes a significant difference to you, buy a basic Moon filter, they cost about 10 pounds or less, and for general observation there isn't a great benefit to spending more.

If you bought the Mercury 705 new it probably came with two eyepieces (magnifying lenses) marked 10 and 25. The actual magnification these give depends in the focal length of your telescope - 500mm in the case of the Mercury, so you are in fact getting x50 with the 10mm EP and x20 with the 25mm EP.

To achieve better views of the planets you could certainly increase the magnification, although the relatively short focal length and small aperture mean there is a limit. A reasonably inexpensive 5mm Plossl design eyepiece would double the magnification to x100. These EPs can be found for 20 to 30 pounds new, and perhaps half that second-hand.

[Peter Drew]

As Patrick intimates, the numbers on the eyepieces for astronomy refer to the focal length of the eyepieces. The magnification is derived by dividing the focal length of the telescope by that of the eyepiece. In my opinion, entry level telescopes such as the Mercury are ideal for getting used to operating a telescope, I wouldn't recommend spending much to "upgrade" it, I would rather save the money towards buying a larger telescope as the better progression with the interest. A 150mm or 200mm aperture Dobsonian is usually advised and each would be a relatively low cost major improvement to your current experience. A secondhand purchase makes an even better approach.                  

[happy-kat]

Given how few clear skies are keep it cheap when observing the Moon use your sunglasses if you find out too bright.

NEVER look at the sun.

This will give you more budget for the eyepiece. You won't I don't think see any detail on Mars or Venus but a slightly higher powered eye piece might show a bit more on the Moon. You don't mention budget for that eyepiece.

[Astro Imp]

I don't usually disagree with Patrick's thoughts but I must point out that a 5mm Plossl will have very short eye relief. This is the distance from rear lens to where the image is formed and where you need to place your eye. For a 5mm Plossl this will be about 3.5/4mm which a lot of users will find uncomfortable.

[glynnlondon]

Agree with advice above if the interest in the hobby is progressing with your boy then the next step would be to upgrade the scope and sell the mercury on. That's how all of us started ?.

You can get as advised a higher mag ep in the planetary range of 7 - 8 mm which you can keep if you upgrade the scope and will be noticeable on lunar observing with what you have.

If he's outgrown the 70 starter scope I would rather put the cash towards a larger aperture scope. It's a bit of a bummer that Jupiter and Saturn are so badly placed at the moment but a lot of people have got a scope like an 8 inch dob which has the reputation of being in the goldilocks zone for an all rounder ( as scopes go )

[Putaendo Patrick]

 

1 hour ago, Astro Imp said:

I don't usually disagree with Patrick's thoughts but I must point out that a 5mm Plossl will have very short eye relief. This is the distance from rear lens to where the image is formed and where you need to place your eye. For a 5mm Plossl this will be about 3.5/4mm which a lot of users will find uncomfortable.

I fully agree with Astro Imp on the problem of short eye relief on higher power Plossls. However, at this stage of the game, it is certainly the most economic option. Eye relief aside, the Plossl design is an excellent performer and these, made or at least sold by most of the major brands, are quite common second-hand. Not so many years ago, most amateur astronomers (especially me!) would have died to get their hands on a Plossl . Recently in the classified section of the forum, someone was selling a 6mm Celestron Plossl for 16 pounds, postage included - I reckon if you're on a tight budget, it doesn't get much better than that!

If eye relief is a problem, I would recommend a 5mm BST Explorer (also branded as Starguider and Paradigm): http://www.365astronomy.com/5mm-BST-Explorer-ED-Eyepiece.html  But these cost getting on for 50 pounds new and don't come up second-hand so often.

 

[Ben the Ignorant]

Don't know why they are overlooked but Explore Scientific has very affordable 1.25", 5-lens, 70° eyepieces in 20mm, 15mm and 10mm.

[happy-kat]

I would also think the BST Explorer would be a good option because I think they are ED glass which would I think give as good view as possible with a refractor like the Mercury which will show chromatic aberation on very bright objects. CA is the blue/purple fringing on bright objects like planets and the Moon you can't magic it away but a decent eyepeice I think will help your general viewing.

[ronin]

Think this is going to be a bit difficult. Reason I say this is that the scope is a Skywatcher Mercury 705 and although it sounds as if it has done well in getting used getting even 1 BST Starguider is a cost of £49. Which to me seems as if it would be a significant proportion of the scope cost. Which for whatever reason I am always a bit reluctant to suggest.

Is there any intention to get a bigger/better scope? If so then comes the question = What?  

As mentioned a plossl would or should do well but the eye relief is small and so likely uncomfortable.

The eyepiece(s) you have will be fairly basic, one is a 10mm, and the 10mm's are notorious for their general poor performance. No eyepiece for you will show Venus or Mars. Mars is too small and Venus is cloud covered so all you get is a fuzzy ball or cresent. If the focal length is 500mm for the scope then with the 10mm you get 50x magnification (Scope focal length/Eyepiece focal length). OK for Jupiter but that is about its limit.

A 5mm BST is a good eyepiece and will be a significant improvement, if the cost is acceptable. If it is get one. Will add that maybe a 8mm BST is better giving 62x - not really a big jump however.

There are not really many alternatives. One possible thought is an eyepiece called (I think) Skywatcher LER. I know of them as I have a 20mm version. Not as good as the BST, but they have reasonable eye relief (LER = Long Eye Relief). I think they are still a relatively simple 3 piece eyepiece design actually. Owing to the "simplicity" they should not be expensive. Slight problem may be finding a source for them.

Occasionally the BST's appear on the used market, but it means you have to wait then you have to be the person that gets them.