Barlow x2 lens

[weetooner]

Hi folks, have just got my 1st scope, sky-watcher mercury 705, and was wondering if it is worth my while buying a barlow x2 lens? It came with 10mm & 25mm eyepieces, can anyone tell me what kind of difference am I likely to see if I use a barlow?.

Also I would like to use it for some terrestrial viewing and was wondering instead of using the 90 degree diagonal can I get a straight through lens (if there is such a thing) or can I just remove the diagonal and put in one of the eyepieces that came with it?

Cheers.

[brantuk]

A 2x barlow will give you 100x magnification with the supplied 10mm eyepiece. This should be ok some of the time (very clear and transparent seeing) but bear in mind the highest practical power for the instrument is only 140x - so you're getting pretty close to that. I wouldn't push it more than 100x - and I'd expect some colour fringing even at that. Most scopes in UK conditions rarely work well at much over 80% of the stated highest practical power. Hth

[Tonys]

I've just purchased a 705 too and mine came with a 45 degree prism diagonal, which is intended to give an upright image and is what you need for terrestrial viewing. If the image you are seeing with your diagonal is upside down it is a mirror diagonal which is best for stargazing, as the mirror shouldn't introduce as many aberrations as a prism and light transmittance should be better. The eyepiece can be fitted without a diagonal, but the image will be upside down and possibly may not achieve focus. The 705 is great value at present. I got mine from FLO, really for the AZ 3 mount that came with it. If the 705 performs anything like the bigger Skywatcher refractors (allowing for it's size and focal ratio) I think you will be well pleased with it.

[RichieP]

If you just use your eyepiece in your refractor directly, the image will be rotated 180° I.e. up becomes down and left becomes right.

With your Mirror diagonal in place, the image will be the right way up but still flipped left to right.

As mentioned above you can get correct image prism diagonals that get everything the right way around. These can be 45° or 90°. (Note that not all prism diagonals are correct image, some just act like mirror diagonals)

The use of correct image prisms is ideally suited for daytime terrestrial observing. They use multiple prisms which degrade the image slightly.

Skywatcher do a fairly decent 45° correct image diagonal which I would recommend.

Richard

Sent from my GT-I9305 using Tapatalk

[Tonys]

Weetooner - pay no attention to what I said about the mirror diagonal as RichieP is absolutely right ie the image with this is upright but reversed left right. (I tend to view through the diagonal orientated sideways to rather than above the scope which confuses things eg me ). Thanks RichieP for putting things right and sorry for the confusion.

[Reeny]

I can recommend the 2.5x Multi element Revelation barlow for £32 to get you going.

Expect the magnification to be an actual 2.1x (not 2.5) and you should get some good results.

http://www.telescopehouse.com/acatalog/Revelation_Astro_2_5x_Barlow_Lens-1.html

[Alfian]

I'd second the the Rev. Barlow - bit of a hidden gem - much better than the price suggests.

[Alien 13]

I've just purchased a 705 too and mine came with a 45 degree prism diagonal, which is intended to give an upright image and is what you need for terrestrial viewing. If the image you are seeing with your diagonal is upside down it is a mirror diagonal which is best for stargazing, as the mirror shouldn't introduce as many aberrations as a prism and light transmittance should be better. The eyepiece can be fitted without a diagonal, but the image will be upside down and possibly may not achieve focus. The 705 is great value at present. I got mine from FLO, really for the AZ 3 mount that came with it. If the 705 performs anything like the bigger Skywatcher refractors (allowing for it's size and focal ratio) I think you will be well pleased with it.

The 705 with AZ 3 package has to be the bargain of the year a proper scope with a decent tripod for the price of a supermarket toy..