8" newtonian vs. 12" newtonian (on dob mount)

[Andrew*]

HI Jamie,

You're more than welcome - glad you got there in the end. I compressed it a bit so it wasn't so clear - sorry!

You have it exactly right - 60' (arcminutes) = 1° (degree), and 60" (arcseconds) = 1'. Of course, arc seconds are tiny, but necessary for amateurs to measure the separation of double stars for example. For all normal deep sky observations, arcminutes or degrees suffice.

As for the 8" query, well I firmly believe that an 8" newtonian is an excellent compromise for most astronomers. It is not too large or heavy for any adult of standard build, doesn't require too large a mount, is easy to maneuvre and offers great views. If you go for a dobsonian mounted telescope, though, a 12" is also very accessible.

Good to have some more international members - welcome again!

Andrew

[russ]

Russ, "btw i had the 10mm series 1 Speers and it was cracking, a real gem of a find. Not sure what the series 2 adds over the series 1."

Now I'm not sure where you're located but I assume it's not Canada. Cracking must be slang denoting something good, rather than the literal sense of the word, right?

-I'm in northern Alberta if anyone cares to know...

Sorry, cracking means great eyepiece. What about 'real gem'.....is that not a Canadian recognised term? I must remember not to use that sort of stuff. :oops:

Russ

[jamieren]

Yeah, it was actually the "gem" line that tipped me off initially. Just saw M81 & M82 this weekend for the first time. Had to search a bit with the 32mm eyepiece (couldn't pick them out with the 8x50 finderscope or my trusty 7x50 binocs!) and there they were. Nice, but this really has me looking forward to seeing them thru the 12" this weekend (God willing!). On that note, do you have any suggestions for a wide angle lens? I was looking on All-star's website and checking out a few of the teleview panoptic eyepieces but man, 250 bucks is a lot of cash for a beginner (and that's the cheapest one!). I'm supposing something with a wide afov is preferable for cutting down on time finding those dim DSOs. I was thinking maybe a 2" barrel to max out on the potential for a wide fov. A the moment I have (but it'll go back with the 8" when I trade it) a 32mm 1.25" and I understand the greatest potential for such an eyepiece is 50*.

Your opinion, guys?

[russ]

The main problem you have with the 2" widefield eyepiece is the demands a fast newtonian will put on it. A cheap 2" eyepiece will be horrible. Basically only the centre portion of the field will be focused. Some don't have a problem with this and are just happy with the widefield. But this is where those megabucks eyepieces really payback your investment.

I've owned TV Panoptics, Naglers and Pentax XL's, all really showed their worth. Their benefit is marginal in a slower f6+ scope but in an f5 or faster they are worth every penny (dollar).

Have a look into finding a Burgess Paragon. They are almost as good as the TV and Pentax but considerably cheaper. And they should be a little cheaper in Canada.

Also consider that Speers Waller. The 10mm is a bargain for $79 and the best eyepiece you'll get for that money. Also checkout the 17.2mm version for $119. Both have huge 82 degree AFOV and are perfect dobsonian eyepieces. They get rave reviews.

Russ

[acey]

Hi jamieren - you already have the absolutely most important item for doing deep-sky astronomy, which is dark skies.

Sounds like you've already talked yourself round to 12 inch which would be a great choice but to give my own thoughts, I've been using an 8 inch from dark sites for a number of years, and I'm forever telling myself I should upgrade to a 12 inch (and this autumn I think I finally will) but the reason I haven't yet is there's just so much you can see with an 8 inch, and as you realise, it's a great size in terms of portability.

There are, as you note, cooldown issues with larger aperture, though on deep-sky that's not quite so crucial. Similarly a larger aperture (and probably shorter f-ratio) means a smaller margin of error in collimation - again, it's not the most important thing for the deep-sky fan, but it's worth remembering. My 8-inch happily survives a bumpy car-ride into the countryside and I never even bother to collimate once I get there (which is sheer laziness) but I don't really need to. With a 12 inch you probably would - the mirror is so much heavier.

I'm glad I started with the 8 inch. You seem a little underwhelmed with views so far and that's natural - my first view of M31 was disappointing. Now I look at 12th-mag galaxies and find my jaw dropping. As Herschel said, seeing is an art that has to be learned. For me, the 8 inch has been a great way to learn. I've viewed all the Messiers, all the Caldwells above my horizon, and I'm several hundred into Herschel's catalogue (which runs to 2,500 items - all viewable with an 8-inch).

As I said, the most important thing is dark skies - but second most important (or equally important) is learning how to make the most of every photon your scope delivers. A great book for me in this respect was O'Meara's "The Messier Objects". As he puts it, your eye has to be like a long-exposure camera, building up an image over time. No scope is going to do that for you.

Only eyepieces I use are TeleVue Plossls - I find that two are enough for most observations (the 20mm and 8mm). I have a Barlow that I never use with the dob (though it has some use with a small refractor I own). A Lumicon UHC filter is great for viewing faint emission nebulae (though not necessary for bright ones).

After skies and eyes in order of importance, I put a good star map (such as SkyAtlas). The field edition (white stars on black background, thick paper) is ideal. Mine is covered in mud but still fully functional. It has never crashed...

The 8 or 12 choice is down to you but think of the portability issue - if it ain't fun to move then it won't get used. You can always upgrade later. You might find you never need to. And if you really can't make your mind up, you could always go for a 10 inch...

Andrew