Question regarding wide angle eyepieces and also a laser pointer!

[IC1101]

Hey guys,

I'm a little unsure of how to read the different kinds of eyepieces out there. I see a lot of things mention 68 degrees, and I also see anywhere from 15mm to 30mm...

Could someone please explain this to me (or even suggest a great eyepiece to use?) so that I can make a decision on what to get next?

Also, what's the deal with getting lasers? I can't seem to find an online store that sells them and I'm assuming there would be some kind of legality involved due to the nature of the product?

[barx1963]

IC
Couple of good questions there.
Firstly with laser pointers. In most states green laser pointers are classified as restricted weapons unless they are 1mw or less. As a result they can be hard to source. Before buying one make sure you understand the rules where you live.
Eyepieces can be very confusing. There are a number of numbers used to describe and eyepiece but the 2 main ones are focal length, which is usually in millimeters and Apparent Field of View (AFOV) usually in degrees.
Focal length determines the power of the eyepiece or how much the eyepiece in combination with a scope "magnifies" and object. If your scope has a 1500mm focal length and you put a 25mm eyepiece in it, you get 1500/25 = 60x so that combo magnifies an object 60x. Obviously if you use the same eyepiece with a scope of 800mm focal length you get 800/25 = 32x. So an eyepiece of shorter focal length will make objects appear bigger.
AFOV is the apparent size of the field of view when viewing using an eyepiece. Most plossls will have a 50deg AFOV. Other common sizes are 68deg, 82deg or 100deg. Usually the wider the AFOV the more expensive the eyepiece. Note if you have a 25mm plossl and a 25mm 100deg eyepiece objects will still appear the same size, just the field they sit in is much larger. Some observers prefer a large field as it enables you to see more surrounding stars and it feels more "natural". Others prefer a narrow field.
Other numbers you may see associated with eyepieces are "eye relief" usually expressed in mm, which is the distance your eye needs to be away from the eyepiece to see a focused view, barrel size, usually either 1.25" or 2" (though sometimes 0.965" or very rarely 2.5" or 3") which is the diameter of the barrell that is inserted into the focuser, and lastly "field stop diameter" usually expressed in mm, that is the size of the circle inside the eyepiece that defined the edge of the field of view.

Hope this helps!!

Malcolm

[raymo]

Hi IC1101, Every state has different rules regarding the max. power,
and who can own them. Regarding astronomical use, I think all states
require you to be a member of an astronomical club or society. Some
states require formal permission to own one, others don't. The rules
are in the process of being tightened in some states, due to the number
of incidents involving aircraft.
Regarding eyepieces, firstly, the mm figure [4mm, 10mm, 36mm, etc]
is the focal length of the eyepiece; the lower the number, the higher
the magnification it will give with any given scope. The mag. is the
result of dividing the focal length of the scope by the focal length of
the eyepiece. 1000mm focal length scope divided by 10mm
eyepiece =100x mag. 1200mm scope with 4mm eyepiece =300x mag.
The degrees figure is the field of view the eyepiece gives. Certain
eyepieces suit certain types of scopes better than others. Eyepiece field
of view varies from about 40degrees to an extreme 100 degrees.
The type and focal length of the eyepieces you choose will depend
on what scope you have, what you like to view most, and how deep
your pockets are.
raymo

[Merlin66]

Re Lasers.
In Victoria any hand held laser over 1mW requires a Police Clearance and Authority to use. It costs about $180 for the 2 year Licence.

[Wavytone]

IC,

Suggest you find an astro club and talk to some members about lasers - ideally during an observing night - before wasting your money to buy one.

While they are useful to point out objects in the sky to a group of people e.g. during a public night with a large group of onlookers, as a finder device for more serious use with a telescope they are not such a good idea.

In particular using a star party you will rarely find anyone with a telescope using them because there are better finders available - starting with the red-dot finders, TelRad, or even old-school 8 x 50 finderscope. All beat lasers hands-down IMHO.

And those with a scope properly set up with encoders (or GOTO) and integrated with SkyFi and an iPad or Android running "Sky Safari pro" (or similar) quite simply do not need pointers at all.

Many here have made the mistake of buying a laser, only to find it lies unused in the box most nights.

[Redshift13]

Re: laser pointers, there's plenty of choice on eBay - I got mine (<1mw) for $8, delivered to my door. It exactly does the job I wanted it to, enabling me to point out constellations, planets, etc. to folks on public viewing nights.

[raymo]

Are you a legal user/owner Rohan? the fines are hefty.
raymo

[Redshift13]

Hi Raymo,

For lasers with <1wm output (as mine is) they are not classed as a prohibited weapon, so no legal restriction on owning it.

Cheers,
Rohan

[Renato1]

Thanks for that info, I've just bought two.

The best usage I've found for laser pointers is to have a few people present with binoculars, then aim at a bright Deep Sky Object, and tell them to follow the laser with their binoculars to the object.

They love it.
Regards,
Renato

[raymo]

Sorry for jumping in, I didn't notice that yours was< 1mw.
Lasers on ebay have been known to be falsely labelled to avoid
various countries' restrictions. Might be interesting to compare
yours with another one of known higher power.
raymo

[Redshift13]

No probs. :thumbsup:

I certainly don't cconsider my laser to be high powered - probably lucky to reach 0.5mw! :rofl:but, yes, it would be interesting to compare with another of known power