Can a Barlow or low power eyepiece be used as a Finder?

[Nova Load]

I've been struggling to find things with the Finder on the Celestron Astromaster 130EQ and was wondering if anyone has tried using a Barlow lens or a low powered eyepiece instead of a Finder scope?

Thanks.

[John]

The barlow lens is used together with an eyepiece and has the effect of increasing the magnification that the eyepiece gives by the factor specified on the barlow, eg: 2x, 3x etc. So it's not going to be any use as a finder. 

A really low powered eyepiece can help but this will show you a very small patch of sky so you would still need a simple finder, either an optical one or the red dot type to get the scope pointing at the right general patch of sky.

Perhaps you current finder can be adjusted to work better for you ?. Making sure it is accurately aligned with the main scope is vital if the finder is going to work properly.

[joehay_yorkshire]

Alligning the red dot you have should be the best thing - just point it at a building a few miles away and adjust until the red dot is on that, and the building is in the centre of the fov through your eyepiece. start with low power then build it up, then the alignment can be improved at night on jupiter. Failing this, replacing the finder with a telrad or a proper finder scope for £30 to £50 should help - though a well aligned red dot would be better, then just put that £50 pounds or so on to nice eyepieces or a solar filter or something ;-) 

[cantab]

Over in this thread about the same scope: http://stargazerslounge.com/topic/206494-widest-15-eyepiece/ it's mentioned the widest true field possible is about 2.5 degrees. That's not wide enough for a finder in my opinion, I'd want at least twice that.

[acey]

I use the 50mm finder on my 12" scope to get me to a naked-eye star I can identify on my map, then I use a low power eyepiece (32mm plossl) in the main scope and star-hop to my target. 19th century visual astronomers often used a low power "finding eyepiece" on observatory telescopes (e.g. the 72 inch Leviathan). But the technique is only useful if you have a map of sufficient detail so that you can match the view in the eyepiece with the picture on the map (this is true for finding in general), and you need to be able to get pretty close to your target to begin with. I use Great Atlas Of the Sky, which plots stars to mag 12 at a scale of 35mm per degree.

In general you would probably be better with a low-power finder. If you have trouble seeing any stars through it then it may be that your sky is too light polluted. You could try investing in a decent 30 or 50mm finder, or use half of an old pair of binoculars. Make sure your finder is properly aligned with the main scope: use a distant streetlight or the star Polaris (both of which won't move) and adjust the finder so that a star centred in it will also be centred in your highest power eyepiece. Some people prefer Telrads etc - I don't but it's something else you could try.

In the past I tried mounting an 80mm short-tube refractor with star-diagonal on my dob as a finder, but I quickly discovered the flaw: the scope gave a left-right reversed view (because of the mirror diagonal) making map-reading a nightmare.

A common difficulty in using finders is not knowing how to match directions in the eyepiece with directions on the map. Star patterns should be enough to solve this but if not then bear in mind that stars always enter the field of view at east (left on a map) and leave at west (right on a map). If you see lots of stars in the finder it can be confusing, but with some practice you can get used to mentally filtering out the fainter ones, and match the brighter ones with the map. When beginning a star-hop make absolutely sure that you've got the right star, and that you've turned your map the right way. Look at the pattern around the star, on the map and in the finder, and be sure they're matching. Then proceed in short hops, confirming the identity of stars in the same way as you go along. If you have a decent map (e.g. S&T Pocket Atlas) then this technique should get you close enough to your target so that it will be visible in the main scope at low power. If your map is highly accurate then you will be able to get the target at the centre of a high-power eyepiece - better than many GoTo users manage.

To summarise: using a finder is basically about using a map, so make sure you have a good map.

[Astro Imp]

More great advice from acey.

I would make one point, a lot of newcomers don't use a finder or red dot finder correctly. What do I mean? Don't squint through the finder/red dot device using one eye. The correct way is to keep both eyes open and move the scope until the image you see through the finder is superimposed on the image you see with the other eye. This obviously doesn't apply to right angle finders.

HTH,  good luck.

[John]

More great advice from acey.

I would make one point, a lot of newcomers don't use a finder or red dot finder correctly. What do I mean? Don't squint through the finder/red dot device using one eye. The correct way is to keep both eyes open and move the scope until the image you see through the finder is superimposed on the image you see with the other eye. This obviously doesn't apply to right angle finders.

HTH,  good luck.

This is good advice. There is a knack to using these things and it's worth persevering with for a bit. I find the trick is to look past the RDF screen and focus on the starry sky rather than the screen. The red dot / circle / whatever should then appear projected against the stars while the actual finder screen is out of focus. You sometimes need to move your head around a bit to find the spot where the dot etc is clearly visible against the sky.

[kaybee]

I'd also recommend spending a little time aligning the RDF.

Then, as Alan says, keep both eyes open when using it.  If it's aligned correctly you should find that once the dot is sat over a star you'll also find that star is centred in the Eyepiece.