Jump to content


Advice for first light/second light

Recommended Posts

hey everyone , i only got to play for a brief hour first time i tested my new scope!, now finally it's another clear night here:)

i just did the collimation (it seemed actually straight forward !)

I am wondering what i should try to look at tonight?, the moon is there , so it's not really ''dark'', im wondering @ what magnitude i can still look


Dobson 300p

eyepieces 10mm, 25mm, 26mm, 9.6mm

3* barlow

2'' 32mm panaview

moonfilter ( i got no other filters unfortunately..)

atm im in the backyard and can only view higher objects like the moon/saturn , but m42 for example is 2 low, i will be viewing between 11pm and 3 am or so ( gmt+1 it's currently 10:38)

any advise would be greatly appreciated!, for example could i see the sombrero galaxy when the moon is out?, there is not alot of light pollution here, but some, and as mentioned before i don't have any other filters then a moon filter!

thanks alot in advance for the advice

Link to comment
Share on other sites

I guess it depends on which direction you're facing and how clear your views arw - have you got stellarium on your computer? - It's a great for planning an evenings viewing for objects in your line of sight

Good luck - let us know how you get on

Link to comment
Share on other sites

yes i have stellarium!, but i wonder which is visable with the moon shining

it's fairly clear tonight!, i watched the moon a bit and got some good views, only @ 450* mag it started to get a bit poor, this could be due to the skie not being clear enough, or the 3* barlow not being the highest quality

Link to comment
Share on other sites

Hello Apoplexia,

450x is, as has been said, really quite beyond the limit in most situations. Light pollution, air stability, telescope aperture, collimation (for reflectors) and optical accuracy of lenses and mirrors all affect your ability to magnify a target.

The general rule of thumb is that 300-350x is about the most you can expect from any scope at sea-level. The higher you go (Hubble Space Telescope, anyone!?), the clearer and darker the sky, and the steadier air you have - the more you can do, but often the steadiness of the atmosphere (we call that seeing) will limit you to no more than 350x no matter where you are, what your scope is like, or how nifty your eyepiece are.

Understand that resolution, that is - your ability to see and separate out fine detail - is mathematically a function of the aperture of the scope. However, magnification requires light, and generally speaking, you trade brightness for magnification. The magnification with the best resolution possible is usually somewhere around double your aperture number, so: 2 x apperture in mm = Max magnification/resolution. You can often go higher to 3-4x the mm aperture of your scope, but you don't get any more detail from the images, and the view can become so dim, that fainter objects just disappear into the background.

To give you a more concrete example, let's take a 150mm reflector of average quality (something you might purchase in a telescope shop, for instance.)

Best possible resolution would be at appx: 300x

The image becomes so dim you start losing much of the fainter details if you go past 450x.

It won't hurt anything to push the magnification (neither you or your equipment will suffer in any way!), you can even get crazy and try to double up your barlow lenses and stuff. :) Try it on the Moon some night and see how much you can do - there's plenty of light there... if it only weren't for the darn air! :(

I hope that helps,


Link to comment
Share on other sites

There is always the possibility of looking at double stars, and in fact any star remains unaffected by light pollution be it from the moon or man made. So objects like the Double Cluster in Perseus, Albireo which is the 'beak' bit at the end of Cygnus the swan, Pleiades in Taurus are some examples and of course Saturn which at this moment, is always worth a look everytime your at the eyepiece. One aspect of observing that the brightness of the moon gives thought to, at that is the need to plan ahead what you would like to see under these circumstances. I have lost count of the number of times a clear sky has also been met with the sight of a rather bright full moon. I usually go out with some kind of list be it new items or familiar ones and projects like observing double stars can give structure to an evening's viewing that adds to the sense of achievement and general fun.

Clear skies


Link to comment
Share on other sites

heya, it's a skywatcher 300p, so i think 600 is the max then?, but i understand now 450 is not suitable in most situations, i saw more detail of saturn @ 180 then @ 450 mag, i could see 1 moon really clear btw:), it was not really dark because of the moon and there is some light pollution ( maybe i should just wreck the 1 street light that is close haha:P or put a cover on it;) )

watched the moon through a 32 mm 2'' eyepiece and OMG that was stunning!

im thinking of buying a 4 times powermate from tele vue for 2'' , so that the 32 mm could be used as a 8mm, to view saturn/jupiter and the moon ( any other things i could use that for), still learning alot here:P

i had alot of trouble trying to find a galaxy... it probably had to do with the moon being quite bright and me being unfamiliar with the sky, i might try to look for m31 tomorrow if the sky is clear, its just past 2 am now and i think i will call it a night ( it's quite moisty)

btw is it the difference between reflector and refractor that the moon looks brighter through my etx 80 then the 300p?, i didnt have to use a moonfilter witht he 300p..

Edited by ApOpLeXiA
Link to comment
Share on other sites

The 600x is a theoretical max only. In practice 250x - 300x will be the most that will be useful due to our seeing conditions. I've found 180x - 220x shows the best detail on Saturn over the past month or two - this is with scopes up to 10" in aperture.

Any light in the sky whether man-made or moonlight, washes out galaxies and nebulae almost totally - even the brightest ones. I don't bother with deep sky viewing when the moon is in the sky to be honest.

The easiest galaxies to find (when conditions allow) are M81 and M82 in Ursa Major - with a low power eyepiece (eg: 32mm) you can get them both in the same field of view.

But do wait for dark skies to start hunting galaxies - it will be a pretty frustrating experience otherwise, even with a 12" scope.

Link to comment
Share on other sites

Most has been said above. A couple of other tips:

A setting circle can be added to the base of your dob and a magnetic "Wixey" angle guage. Then you can read co-ordinates from Stellarium or Cartes du Ciel for accurate pointing of the scope. All for under £30 it's surprisingly effective.

To dim the moon replace the tube cap on the end of the main tube and remove the small off center cap - makes it much more comfortable viewing the moon.

M81/M82 are easy enough. You'll get them both in a wide angle eye piece. They are a good example of a "face on" and "edge on" galaxies - known as "Bodes" galaxy and "the Cigar" galaxy.

Also try for the Leo Triplet (three galaxies in fov). Choose a moonless night and expect to see mostly smudges with a little bit of shape. Ensure your eyes are dark adapted for 20 mins first or drape a dark cloth over your head and eyepiece when viewing :)

Edited by brantuk
Link to comment
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now

  • Recently Browsing   0 members

    • No registered users viewing this page.
  • Create New...

Important Information

We have placed cookies on your device to help make this website better. You can adjust your cookie settings, otherwise we'll assume you're okay to continue. By using this site, you agree to our Terms of Use.