Purchasing Decision for Eyepieces/Barlows

[ace2029]

Good morning to all!

I'm new to astronomy and have just purchased the Skywatcher 130P EQ2 and a 2x Achromatic Barlow.

I want to check that my calculations are correct as I don't want to spend money on an incorrect piece of equipment.

According to the manufacturer's information, the highest practical power of the scope is 260x.

Focal length is 650mm.

Therefore, a 5mm eyepiece with a 2x Barlow will therefore be a 2.5mm eyepiece effectively.

650mm / 2.5 = 260

So to achieve maximum magnification I would only need a 5mm eyepiece in combination with the 2x Barlow.  Is this correct?

Can you go beyond 260x?  What happens to image quality/clarity if you do?

Many thanks indeed!

Andy

[TiTanecd]

For DSO 260x is plenty and a 5mm will work well for that. 

Good nights means you can use that higher magnification. Poorer nights lower magnification is better.

As you increase magnification you reduce the amount of light and also increase the negative atmospheric effects (in this case 260x more). So on clear nights can you achieve very high magnifications.

Saying that the moon can take alot of magnification even pushing your limit. I've seen the moon at 400x on perfect nights.

[ronin]

I would expect that you will get about 180x maybe 200x from the scope, not 260x.

The magnification claims have slowly increased over time, and even  increased for the same unchanged scope.

One scope I have claims some simply insane magnification, it is a nice little 70mm achro and works well to 70x and maybe 100x, the manual says 240x :eek: . Which is about 3.5x diameter. In reality it will get to about 1.5x diameter, on a good day with a following wind. It works much better at 1x diameter.

[Alfian]

Its very easy to get caught up in high magnifications when you start out after all isn't that what telescopes are about? Well no, not primarily - mostly its about light gathering.  When I first started, not so long ago it seems, I bought a reasonable quality 3x Barlow to pump up the magnification, without losing the eye relief of my 9mm EP. That Barlow has not been out of its box in over a year!

In practice I think you will find that a lot of observation will be done sub 100x  and a useful max to aim at given seeing conditions would be 180  - 200 tops. My most used/best buy EP is a 15mm Vixen NPL.

[D4N]

You will generally want to push for maximum magnification on lunar and planetary targets. A lot of DSO's are huge and using high magnification will cause you to end up looking right past it.

If you don't have a motor drive for your EQ2 you will also find that targets disappear out of the field of view very quickly at high magnification.

I have a 130P and feel a 4mm EP was the maximum it would take and on most occasions I would be better off with a 6mm EP. You might be able to push it further with high quality eyepieces but it starts to get a bit silly when the eyepiece costs far more than the OTA

It will also depend greatly on the seeing.

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[rwilkey]

For DSO's you need low power (30-50x), for Moon and planets higher power is good (150x or thereabouts).  Don't get hung up on getting ultra high power, that is not what astronomy and telescopes are about. 

[ace2029]

Thanks for the advice everyone - I can see I nearly fell into the trap of "more power!!".  Glad I posted this on here - I'll focus (no pun intended) on getting good quality eyepieces at low to medium power.

[nicoscy]

Generally speaking:

It has a 1.25" focuser so the eyepieces that will provide the widest FOV are the 32mm Plossl and the 24mm 68 degree eyepieces. Only difference between the two is that the 32mm will provide a larger exit pupil thus sending more light into the eye, but you will feel as if you are looking through a "narrower" window than the 24mm.

I would pair the 24mm with a 16mm and a 4mm eyepiece and use the barlow to get 24mm / 16mm / 12mm / 8mm / 4mm and 2mm.

Yes, at the 2mm setting resolution will not increase, just the image scale but even this is usable on a decent night for the moon

I got into lunar viewing myself this year and I find that you can easily push magnification past normal limits on most evenings. Don't be afraid to seek high magnification on the moon.

I would recommend the Explore Scientific series of eyepieces as the best value for money eyepieces around. The 24mm ES 68 degrees and the 16mm 68 degrees are very high quality eyepieces for the money.

I would also recommend the 4mm Televue Radian if you can score one from the classifieds (I did just that) as pre-owned it comes at a reasonable price, offers high eye relief which is always a concern at high magnifications and has a generous 60 degrees AFOV.

I am sure there are many other eyepieces to consider, but I would recommend good eyepieces if budget allows as scopes come and go, but a good choice of eyepieces will be with you for a long time.