Trouble with the Barlows and Erecting Eyepiece - whats it for???

[BamBam]

Hello everyone again, we have followed your advice and taken the telescope out in the day to get use to start getting use to the finderscope and the telescope in general. We used the 20mm lens and had some success but when we tried the 2x Barlow Lens we couldn't see anything, what are we doing wrong?

Also there is a 1.5 x Erecting Eyepiece - what is it for? The instructions that came with the telescope could be written in chinese for all the help it has given!!!

Please note I say 'we' as the telescope belongs to my young daughter but I think my husband and I are catching the stargazer bug as well so we are all in this together!

I have suggested to my daughter that she makes a log of everything she sees when we finally get to stargazing proper - we are so praying for a clear night - what do you think?

Again many thanks for your warm welcome and advice given so far.

[DoctorD]

Hi

You need to use the x2 Barlow with a lens. It effectively doubles the magnification.

The 1.5x erecting prism will be used when using the scope for terrestrial objects to make the view the right way up. No need to use this for astronomy targets as it does not matter what way up these are.

Hope this helps

Paul

[BamBam]

Thank you DoctorD that makes sense about the erecting eyepiece was beginnining think we needed to get use to viewing the world upside down!

We did use the Barlow with the 20mm lens but we couldn't see anything and yes we did take the lens cap off (after the first try!!), do you thinkthe object was too close?

[John]

As Paul says, for astronomy use, the upside down view is the one to get used to as the erecting eyepiece will detract from the quality of the view.

Astro scopes generally won't focus on things closer than 50-100 feet away, sometimes further than that. Try using just the 20mm eyepiece to start with and then try the barlow with that eyepiece. You will need to re-focus with the barlow in use.

[Catweazel]

Hi BamBam, it is possible that you were too close to the object that you were trying to focus on, what distance was it? Also how far can you see into the distance from where you are? If possible, try something half a mile away. BTW, which scope are you using?

[BamBam]

Yes I think we were far too close (nowhere near half a mile away!) but at the moment we are trying to get use to scope in daylight so only operating out of our garden at the moment. The scope is a Sebens 700 x76. This is the first scope for our nine year old daughter and I have no idea whether it is good or not, we are total newbies to Astronomy. At first I was going to buy her a National Geographic one but that seemed too much like a toy so I went for the Sebens as it had reasonable reviews and the price was good for a 'training scope'.

[cantab]

With the Barlow the focus may be quite different to without. Or it could just be no good, the Barlows that come with cheap scopes often are poor.

Seben are infamous for making some truly awful scopes, but I believe yours isn't one of them. It looks like a typical 3 inch Newtonian, wobbly mount and bottom-end eyepieces but hopefully even Seben will have put half-decent mirrors in it.

[Catweazel]

Hi again,

I probably got carried away with half a mile, try something 100 - 200 yards away! I usually pick the furthest TV aerial that I can see from my garden.

Your scope is decent choice for beginning astronomy, it's f9 so should be fairly forgiving on eyepieces, and you will get good moon and reasonable planetary views with it. You will certainly get plenty of use out of it, and it usually only takes that one "wow" moment to get you hooked

[BinocularSky]

Sorry, but I'm going to be absolutely frank with you: the Barlows and erecting lenses provided with that telescope are of extremely poor quality (I know because one of my students has the same accessories with a different Seben scope); you will get better image quality without them.

[BamBam]

Thanks for all your responses, we will be back in the garden practising again tomorrow! Can feel a small shopping trip coming on for new eyepieces plus some warm winter jackets (my husband has just rolled his eyes!) but now I have found SGL I will be asking for advice.

[JamesM]

Well you have certainly come to the right place for advice as there is plenty of experience here for you to draw upon. Regarding eyepieces, I would recommend the BST brand as they are relatively inexpensive (£43-47 each) compared to some of the choices out there. It is certainly worth thinking towards the longer term with eyepieces as they generally out last various upgraded scope purchases that you might make in the future. You can take a closer look here at these eyepieces and in particular you need to look at the top middle box and the bottom left hand corner box with regards to the sizes available. Generally no matter what scope you have, the quality of our skies means that on average you cannot use more than around x180 magnification. Set against this figure is the theoretical maximum that an individual scope can magnify from the amount of light that it can collect. A general rule to calculate the scope's maximum magnification is take the aperture and multiply by 2 (76 x 2 = 152) so in your case you should only buy eyepieces that provide no more than x152 magnification. So what is the range of eyepiece sizes available for your scope? The answer can be found by dividing the scope's length (700mm) by the focal length of any given eyepiece ensuring that we don't exceed the total magnification available (x152). So taking the 20mm eyepiece that came with your scope, we can calculate that 700mm divided by 20mm gives us a magnification of x35 which is well within the limits of your scope. This size of eyepiece is very good in providing a wide view of the night sky and can be helpful in either locating objects such as planets, or it can help provide a wide enough view to contain the target object such as with the pleiades (...or seven sisters as its more popularly termed), being a constellation of very bright stars that are impressive to look at. Now if we want to take a closer look at a planet that we were able to locate with the 20mm then we will need a little more magnification. So we take the figure of 700mm and divide this time by say a 6mm eyepiece, then we can get a magnification of x116 which will get you a lot closer. If we then went further, say using a 5mm eyepiece which would generate magnification of x140, we might have a problem, because here we are getting close to the theoretical maximum of the scope and this where the quality of the mirror comes into play. The Sebens is a modestly priced scope and my guess would be that this level of magnification might be demanding too much from such an inexpensively produced mirror. Personally I would keep to the 6mm eyepiece as a maximum but clearly with the BST range in the lower left hand corner of the above link, there are many sizes in between those mentioned above that could be used. A good wide view in addition to a magnified view would certainly help you to enjoy the moon, planets, clusters and the brighter deep sky objects. Of course there are many other sizes available and purchasing a better quality 'barlow' lens can help extend separate eyepieces further but perhaps that might be food for thought later down the line.

I hope the above helps with your understanding but please come back to us with any questions.

Clear skies

James.

[Rik]

Hi all. Well after reading some of the comments on here I'm feeling gutted. I've just bought my little girl a national geo 22021 as shes fell in love with the stars but people saying they are pants. I was having trouble with using the barlows lens and e-eyepiece as i cant see nothing! It's only our first go so ill hopefully try again tomorrow if it's clear.

Edited December 29, 2019 by Rik

[joe aguiar]

forget about the erecting image the  makers of these scope just throw a lot items to make the scope look like it has a lot acessiors BUT most those items are low quality stuff.

AS the other guy above said its to look at daytime stuff altho most people who want to do that don't get reflecting scopes anyway.

The other reason the 20mm ep may be ok but not with the barlow cause those eps and barlow again are of the lowest quality being its a 20mm I have a very good felling its a h20 or also called a hygens which are not graet. The 20 will be ok if it came with a 12.5H that's so/so but the 4mmsr is just trash forget about that one.

you may want to get a decent plossl or super plossl and maybe a decent 2x doublet barlow for better views BUT fior now u can keep using the 20 and 12.5 if that's what they came from. Also take into consideration those eps have a field of view( how much space u see threw it) of like 22 to 25 degrees. A plossl will give  twice that of 50 degree noty to mention it will be much much better quality, and a super plossl will be 52 degree fov.

joejaguar