s'cuse me, would ya mind if i picked ya brains a bit?

[majortom (Andy)]

g'day all, after browsing, it appears i've landed in the right place. the generosity of both time and assistance in the astronomical society is truly inspiring and welcoming. anyhow; after aquiring a small refractor a bit over a month ago, the predictable occured. so the first thing i did was some web based research. the next thing i did was to find a reputable astro gear retailer and bombarded the poor bloke with a ton of questions, salivated over his immaculately presented gear, and tried out half of his binocular display. the next thing i did was walked out with a few new eyepieces, a pair 7x50 bino's, a planisphere, some filters and astronomy aus. 2009/2010. he gave me 2009 free even after all i'd put him through. anyway, to cut a very long story short, i'm stuck. the next inevitable chapter in my story involves the unavoidable scope upgrade. although i'm only new to astronomy, over the last few weeks i have learned alot. so my new object of desire? thats where i hope some of you guys might be able to help. i have pretty much settled on a big(ish)gso dob. but for reasons of convenience am torn between a 10 or 12. now what i was hoping for is some unbiased first hand experience, ie; advice from those that have been fortunate enough to look through both scopes side by side (although opinions are also welcome). for i'm keen to know if the extra 2" are worth the backache and portability restrictions, for some one like myself with little experience. apologies for the longwinded intro, but would really appreciate your time and experienced advice. regards; andy.

[norm]

Welcome Andy to the forum.

The 10" is on the limit IMO in terms of portability and lugging it in and out of a car - thats if your planning to cart it around to dark skies. Its not so much the weight being the issue, its the fact that they are somewhat cumbersome to handle.

The 12" (solid tube) doesn't lend itself to portability and is more geared for someone who can 'wheel' it out of say a garage/shed on a trolley and start viewing after collimation.

I can't remember the % difference between a 10 and 12, someone will need to enlighten you and I on that (I can't remember the formula).

If I had to choose, I'd go a 12", but a collapsible type, something like the Lightbridge, Skywatcher or maybe Orion Intelliscope (albeit the last one is expensive). This gives you the portability and extra 2".

One of the most valuable accessories you can get for your scope is an ArgoNavis. At approx $1200 (argo + encoder kit), its not cheap, but it can take your viewing experience and enjoyment to another level - and literally exponentially.

I'll also throw in the saying ' the best scope is the one you will use the most'.

Cheers, Norm

[seanliddelow (Sean)]

Transporting a collapisble 12" isnt a problem but a trolley brought fom bunnings and some hockey straps will make your life a lot easier. The 12" dob I brought comes with a 2" eyepiece adapter (Theres nothing better then the LMC and the Milky Way with a big low powered eyepiece on the 12") .

[mental4astro (Alexander)]

The 2" larger diameter in the 12" gives a 44% larger area than that of a 10".

10" or 12"? IMO, a 10" dob is probably the largest that will comfortably accomodate someone sitting in a chair while viewing at zenith (directly overhead) without straining- that is the main feature that dictated my choice of a 10". It is the most common form of seating- don't discount this!

A properlly constructed observing chair should overcome this. But you will need to have one and not all novices can balance and view at the same time (novice meaning general public with no experience).

Solid tube: 10"

Collapsible tube: 12", Just like Norm.

[majortom (Andy)]

thanks heaps for your time guys. some good advice, the collapsable dob thing i havn't really looked into just because they appear a little more expensive, and i am looking at my fist real scope (+ i am still working on the wife). and the argo i really like the idea of, but as you said norm it's not cheap (actually more than the sopes i've been eying off. the 2" eyepiece thing is a must have from what i've seen, sean. i looked at a 40mm instore and i could imagine that to look through one would be almost like climbing in there. and that tip about a chair & 10" is bloody good advice, alex . and something i'm sure wouldn't have occured to me until my neck started to ache. and on that point, a 10" might be more family friendly too. is that what you have found alex? noting your reference to wife, kids,scope, happy. i like that. if you added beer to the list it would just about paint the picture of a perfect life.

[mental4astro (Alexander)]

Originally Posted by majortom

if you added beer to the list it would just about paint the picture of a perfect life.

I would have added it, but the allowed space in the avatar ran out!

Comfort for the family was not my finding. More my own comfort as it is me at the EP for hours. Their viewing time is minimal in comparison. Might seem selfish, but it is me who is crazy enough to insist on becomeing mozzie fodder, .

There is a characteristic of eyepieces that you should keep in mind when trying to decide on one. 'Exit pupil' is the size of the image formed by the eyepiece as light leaves it. The longer the focal length of the EP, the larger the exit pupil. The consequence of a too big exit pupil is that it will illuminate the iris and not fall entirely within the pupil. This is the same as reducing the apeture of you telescope. The area of the view will be larger, but the image will not be as bright as it can be. You will be just robbing yourself of the precious light our telescopes collect.

Another consequence of this in a reflector is that the shadow of the secondary mirror begins to become obvious.

A fellow IIS'er, Wavytone, gave me a rule of thumd to give the maximum eyepiece focal length for a reflector:

6mm X f/ratio of scope = max eyepiece focal length.

As an example, should your scope be an 8" f/6 reflector, the longest focal length would be 6mm X f/6 = 36mm.

You could use a 40mm eyepiece at a stretch, but...

The way to get around this with eyepieces is using those with large 'field of view'. This is expressed as the XX degrees, refering to the apparent angular view size the eyepiece provides. There are other consequences to very large FOVs coupled with fast f/ratios. This has been addressed in another thread. I can chase it down if you like.

If money is a limiting factor, mate, a 10" is a very big scope. Once apeture fever hits, you won't even remember your debate over the 12".

[norm]

I'm with Mental here. If the money wont stretch for a 12" a 10" is a great scope and size just about right. You definitely wont be disappointed.

Cheers Norm

[el_draco (Rom)]

Gotta remember, how much does a "little bit more expensive" compare with 44% more light coming down the tube? Its a good arguement to use if the price is 10% more for example... (works for me every time!).
Portability is an issue but don't make it the only issue. I've built/used 10" and 12" scopes and I'd take the 12" if you can move it relatively easily.

[Paddy (Patrick)]

Hi Andy, this is a question that generates so many different responses! I found my 12" GSO solid tube dob ideal for wheeling out of the shed on a trolley, not too hard but not particularly easy to load into the back of a Camry wagon with not a lot of room to spare and I was glad that I only did this once in a blue moon as I mostly observe at home. In previous posts, I've warned people with Hyundai hatches that the two might not be a good mix, but they ended up with big scope in little car and were happy ( http://www.iceinspace.com.au/forum/s...ad.php?t=36260 ). What strikes me in this is that the difference a bigger aperture makes to observing experiece is always surprisingly small. When I was comparing my 12" to 16" scopes prior to upgrading (a 78% increase in aperture) I was not blown away by the difference. there is a difference in the detail observable, but its not like you see twice as much. Similarly when I compared the views in my scope to those in Tim Nott's 22" (a 90% increase) we both agreed that there was a difference, but not earth shattering. Mainly a bit more detail on faint DSOs.

I reckon 12" scopes are great, but not that much greater than 10" and if you have any doubts aabout how much you'll use a scope due to portability, 10" is a good choice. Truss dobs are also a good option - they will save space, but you will still have a reasonably heavy primary to lift. I am pretty ocnfident that you will have a good time with either.

And, as always, I think it well worth getting along to a club night or star party to have a look at/through 10" & 12" scopes before you buy one.