What magnitude can I see with 76mm reflector?

gmeredith (Graham) · #1 15-12-2008, 11:11 AM

Hi there, a noob question - I have a 76mm Tasco reflector with a 2x Barlow, and 6mm and 20mm eyepieces. People mention an object for viewing being magnitude 9, for example. I understand the meaning of magnitudes regarding stars etc, but I was wanting to know what I could use my particular scope to see, regarding deep sky objects, so that if someone or a catalogue mentions that such and such a star or nebula is x magnitude, then will I be able to see it using my scope? What is my telescope's useful magnitude viewing limit?

Cheers, Graham

bmitchell82 (Brendan) · #2 15-12-2008, 11:18 AM

he he he. well you stated yourself what your limit was

it was Tasco. you should be able to get upto mags 9 or 10 im guessing but it also depends on light pollution and the sort.

gmeredith (Graham) · #3 15-12-2008, 11:52 AM

Yes, even greater limit is my budget hehe!

Ok, then that gives me a bit of a start. I want to start using charts and catalogs, and so at least I know what is in my viewing ability when they state some info about an object.

One day when my bank account grows up, its going to be a 12" skywatcher. It's great that I got such a cheap intro into astronomy with my Tasco for $10, though. All my experiences have been good ones so far. But I can see a time when I'm going to want more, and more, and MORE! I'd like to get into photography - I can see myself heading down that track eventually. The Tasco will get me some good experience with that, too, for when I eventually get the 12".

Cheers, Graham

bmitchell82 (Brendan) · #4 15-12-2008, 11:56 AM

well for $10 you cant say no.

i got given a $100 dick smith special, i have never got a good view out of it yet. though it made my want a big 10" SW

youll get there just hang on and everything will be fine!

Smirnoff · #5 15-12-2008, 12:03 PM

I'd say about mag 10.5-11 would be the limit for a 76mm.

Coen · #6 15-12-2008, 12:13 PM

I get, on a good night, down to 11.8 with a 70mm refractor (slightly different to the 76mm reflector) - suspect down to 10.5 is probably more workable though. That applies to stellar magnitudes not the magnitudes of non-stellar objects which are often a different kind of animal due to their often extended nature (magnitudes quote are integrated over the object's area - classic is Helix nebula as an example, magnitude 6.5ish but spread over a large area = interesting to find).

Do not know the focal length of your telescope but suspect the 6mm eyepiece will not be all that useful most nights.

bmitchell82 (Brendan) · #7 15-12-2008, 01:12 PM

thats why i suggested mag 9-10 because of the scope, it will be nothing special, as well as not having high transmission objectives and light pollution in hobart (not that theres all that much). Ide pick then 10 as your maximum useful limiting mag. but even at this you wont be able to dicern too much.

gmeredith (Graham) · #8 15-12-2008, 01:39 PM

The focal length is 600mm, and I think its an f/5 from memory (at work at the moment, don't have it at hand). I get a pretty good view of the Great Nebula in Orion, and can see a couple of the stars or the bright patches in it, if that gives you any reference point. That's with the Barlow and 20mm eyepiece. Interesting in that the 20mm and barlow together seem to give around the same magnification as the 6mm eyepiece by itself, but give a discernable improvement in clarity compared to the 6mm.

cheers, Graham

Smirnoff · #9 15-12-2008, 01:47 PM

if the F/L is 600mm, then your Focal ratio will be around F/7.9 (600 divide 76).

Did your 6mm eyepiece come with the scope? If so, it might be one of those notorious cheap Ramsden or Hygens designs, which are practically useless at these short focal lengths. To find out , look for the letters "H" or "SR" on the barrel. In your scope it gives 100x, which should be easily handled by a 76mm, but if the eyepiece is what I think it is, it's more suited to a job as a paperweight. The 20mm+barlow combo is atleast usable and gives a lower mag (60x) which yields a clearer image. However, I suspect that the 20mm eyepiece is again a Ramsden or Hygens (if it came with the scope) and the Barlows that come with these Tascos are cheap plastic jobs which are borderline useless.

gmeredith (Graham) · #10 15-12-2008, 02:07 PM

Ahh, just found the focal length in a photo of it. It's an F/8, you're correct. Yes, the 6mm came with it, as did the barlow. I'll look this evening as to the markings on the eyepieces, but I suspect you're right. **EDIT** did a google search, found it in this thread:

http://www.cloudynights.com/ubbthrea...l/fpart/1/vc/1

- specifically on p2 of that thread, down the bottom of the page.

They are Huygens. Back in the 1980's when this scope was made, I think it was only $99 new, so that would be about right. The 20mm is quite good though (at least to my untrained eye), even with the barlow, its mainly the 6mm that is not so good. Good enough for me, but I can tell that if I compared it to some really good eyepieces I would never look through them again. That's what worrie$$$$ me

Cheers, graham

Smirnoff · #11 15-12-2008, 08:24 PM

The 6mm Hygens is a classic example of the notoriously bad high power eyepieces that come with these tasco refractors. No point even trying to use it. I'm assuming the barlow is also more or less a plastic toy, as is also often the case when thrown in with these scopes.

If the focuser only accepts 0.965" barrel diameters, I suggest grab a hybrid 0.965" to 1.25" diagnal and a pair of decent plossl eyepieces and a 2x barlow. The GSO plossls will work well in your scope and aren't expensive. They are however infinitely better than those Hygens paperweights

Cheers

Ian Robinson · #12 16-12-2008, 01:04 AM

76mm scope , you are able to see 11.5-12 mag stars, take 2-3 mags off that for fuzzies , irrespective of the type of telescope and eyepiece providing the sky is clear , moonless, your eyes work and are dark adapted. Hope that answers your question.
I can see 12 mag, maybe 12.3 with my 20x80 binoculars , no reason why you should not be able to match that.

Suggest you keep the magnification used under 2x the size of the scope in mm for best viewing , more magnification will add nothing wrt resolving fine details and will only spread the light out over a larger image.

Gotta start somewhere and for those thumbing their noses , not everyone can afford to splash out and buy an "decen" scope (even as a dob) or some quality eyepieces and a good barlow straight off.

gmeredith (Graham) · #13 16-12-2008, 09:04 AM

Thanks everyone for your advice! Now to start looking. I wish I could get a decent view for a bit - the weather has been cloudy for nearly 2 weeks straight

and I'm hanging out to see the Andromeda galaxy.

I think that I'll put all my money into saving up for the 12" SW in the new year, rather than buy new optics for the 76mm. I'm likely to use the little one for photography anyway, and it has a T-piece, so I won't need the eyepieces for it in that instance. Then I can put my money away for better EP's for the 12" later after I've gotten used to it.

Cheers, graham