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

[jamieren]

I'm gathering info for a purchase. Just got the 8" last week and I see the 12 is on sale now. I've talked to the shop & they've agreed to give me full credit to put toward the 12 if I so choose. I also have an opportunity to go try it first (though it's 3 hours away). Here's what the choice boils down to:

1. Are the views going to be THAT much better in the 12?

2. How much grief can I expect to go through with cooldown?

3. Portability issues. I'm sure 80 lbs worth of scope is a challenge, but when compared to the brighter more refined views it should be more than worth it, right?

4. Travel. I don't have to go far to see dark skies (I live in a town pop. 4200) and own a minivan. With a scope 6ft long I should be able to fit it in the back without problems...

If anyone has experience with this comparison or similar issues, by all means post them here!

[peeceeTal2M]

Go for the 12" i'm sure you'll not regret it and you will have far better views through it than with an 8" especially if you can get to a dark site away from lights.

Phill

[John]

I would probably go for the 12 inch as well as the additional aperture will provide noticably better views (although an 8 inch is no slouch of course ).

I'm not sure which brand of scope you are talking about here but if it's Skywatcher then there is a big difference in size / portabilty between the 8 and 12 inch scopes which can affect how often the scope gets used for some people.

John

[jamieren]

I'm not sure which brand of scope you are talking about here but if it's Skywatcher then there is a big difference in size / portabilty between the 8 and 12 inch scopes which can affect how often the scope gets used for some people.

John

Actually it's an Antares 12". Thanks a lot for the advice guys. Does anyone have info regarding the other issues ie. cooldown, how a 12" will fit in a van?

[russ]

Not sure what f ratio the Antares is but the Orion Optics 12" f4 went across the back seat of a Honda Accord. But i guess yours will be f5 - f5.3 which adds another 300-450mm onto the length. Shouldn't be a problem for a van. Unless it's a Sooty wagon.

Russ

[jamieren]

Mine's gonna be 1500 mm so I guess that makes it close to an f5. In foresight I guess I could just go take some simple measurements...

[John]

Mine's gonna be 1500 mm so I guess that makes it close to an f5. In foresight I guess I could just go take some simple measurements...

Do keep some of your budget for eyepieces as well. F/5 scopes are quite fussy with regard to the quality of eyepieces and the ones that come bundled are not usually that great.

John

[jamieren]

"Do keep some of your budget for eyepieces as well. F/5 scopes are quite fussy with regard to the quality of eyepieces and the ones that come bundled are not usually that great."

That was going to be the topic of my next post, but perhaps I'll just discuss it here. From my understanding the best eyepieces are either plossl or nagler. The plossls performing well throughout the whole range of magnifications and the nagler being exceptionally suited to low & medium ranges. I've seen naglers for $600 or more (each!) and plossls for as little as $50. The plossls are much closer to my price range and are very popular I understand. I did get 3 of these with my 8" (which I suppose are low grade) and they seem to perform satisfactorily.

I think I'll be doing a mixture of viewing, but primarily deep space and stars. Secondary to that would be planet viewing. One of my main focuses is to get some of those stars in under high magnification. I'm also guessing that deep space objects are difficult to view with high mag. as they are typically dim?

Thus far without any outside input I was planning to stay with plossl for now, and perhaps spend $50 - $100. I would really like to focus on high mag, but I've heard it can be disappointing when seeing conditions are substandard and you end up with eyepieces that go largely unused as a result. This would be a real bummer if I would spend $100 on a 6mm and rarely use it. With my current setup the 12.5mm gets the most use, I'd like to use the 6mm more but it just doesn't focus as well in most cases. The times the image is stable it's quite an improvement, though. Thus, maybe I could cut the balance and get say, a 10mm. That would give me 150x mag and it could be used enough to be enjoyed (?)

The other dilemma I have is about 2" eyepieces. I have a hard time understanding how the make any real difference if we compare apples to apples. That is to say a 12mm of both sizes will have 12mm of lens to view through (next to your eye) right? I understand about eye relief, especially at higher magnifications. It's not very comfortable to plant your eye on the glass when trying to see at 200x, so is this where a 2" would be most advantageous? Do the 2" in practice always give a wider field of view? ..And is it usable - does this make potential for distortion around the edge of the view? How about whether you can physically take it all in, do you need to be constantly repositioning your eye to see all of what's coming through it?

I have an opportunity to try out a few from my "local" shop when I go to check out the 12" dob I'm considering in a couple weeks. Any suggestions would be appreciated on what I should look for.

P.S. and please guys, I really don't want to hear "you get what you pay for", it's only going to get me into a lot of trouble with the wife listening to that talk!

[russ]

Not all Plossl's are created equal. I found the Meade 4000 very disappointing except the Japanese made 12.4mm and 26mm. But you'll do well to find one of those. The whole range is produced in China now and can only be described as budget fodder. Better to search out a TeleVue Plossl or one of the Celestron Ultima, Orion Ultrascopic, Antares Elite, Parks Gold offerings. They have superior build, polishing and coatings.

And there are alternatives to the Plossl without the need for a Nagler (just yet).

Plossl's can feel very constrained these days with their narrow(ish) apparent field of view (AFOV). After using a Superwide or Ultrawide eyepiece i find the plossl very restricting.

You could consider the Baader Hyperion with a 68degree AFOV. They work quite well with f5 scopes. And Orion in the US do an identical version called the Stratus. They do cost a little more but worth it i feel for the view you get. Remember, the wider the field the less often you'll have to nudge the dob back into position.

Although i slammed the Meade 4000, i would recommend the Meade 5000 Plossl. It probably just classes as a Superwide (60degree AFOV). Compared to the 4000 it has a larger field, better coatings and superior build.

There are other Superwide eyepieces (GSO Superview, William Optics SWAN) but these are best avoided for an f5 scope.

If you really want to push the boat out, then TeleVue Nagler and Panoptics are beautiful. Although my personal fav eyepieces are the Pentax XL and XW. These are all something for another time though.

Russ

[John]

I agree with the points that Russ makes in his post.

I have opted to go for Naglers with my Dobsonian / Alt-Azimuth mounted scopes because the extra large, sharp field of view means that objects are observable for longer between "nudges". They do cost though .....

The Hyperions are very nice eyepieces and another that I have tried is the TS Planetary HR ones which are available on E.bay from Telescope Services (based in Germany but excellent service) and I think from Astronomica here in the UK (though their web site seems to be down at the moment). The planetary HR's go for £50 or a little less each and offer good eye relief and a sharp 60 degree field of view - even in short FL scopes. They are only available in the shorter focal lengths though (9mm is the longest).

That said, you can still have a lot of fun with some ordinary plossls now and get a feel for the scope while you develop your funding and business case to your wife for some more exotic ones .....

With my 8 inch dobsonian in my UK back yard I find I can use 170x-220x frequently and even 300x plus on really good nights - "nudging" really becomes a fine art at that sort of magnification though !.

John

[Doc]

Aperture rules.....

Also you will for ever be saying to yourself "what if".

As for eyepieces the baader Hyperions are excellent for the money they cost.

[Andrew*]

Hi Jamie (if that is your name?) and welcome!

You seem to have some knowledge of kit, so apologies if this is already familiar, but I think many of your eyepiece questions can be answered by this thread: http://stargazerslounge.com/index.php/topic,27003.0.html

As for choice - I give another vote for the Baader Hyperions, which come in at £78.50 each and I think you might get 10% off that. It might be a little over the budget you imagined, but you will love them, and a good set of eyepieces will outlast many scope upgrades. I think 3 eyepieces and a barlow will be necessary to cover your needs. If you don't quite want to go for them, a plossl set offers super value.

Which scope are you going to go for, by the way?

HTH

Andrew

[jamieren]

Due in part to some of the opinions and knowledge gleaned in this post I'm heavily leaning toward the 12". I already own the 8" and I have been reasoning with myself in such a manner "I'll likely have this scope for a long time, so I might as well invest in a good one now." I'm also pretty sure I checked out the thread you listed (it talks about several different series' of eyepieces) but I'm finding a lot of the info (including what I find in the book Skywatch) goes over my head. Not that it is too technical; I understand the idea of greater field of view in theory, but my lack of observing experience causes it to miss me in practicality. Something that confuses me is this talk of "60 degree FOV etc." In reality we're talking about 1* worth of the sky right? I know my finderscope has approx. 5* in view and I'm sure no 10mm eyepiece has anywhere near that.

Tell you what, guys. Why don't you take a look at the website www.all-startelescope.com and give your recommendations on what I should focus on. When I do go to check out the selection I will know which eyepieces to request some time with. Also would yous mind to tell me what you think of the pricing? Being new to the sport I think it would be easy for me to get hosed.

Thanks,

Jamie

[russ]

Just looking quickly on that site and there is one stand out mega bargain in the eyepiece range. The Antares Speers-Waller eyepieces for $79.....OMG!! Forget the Hyperion, you want a Speers. 82 degree AFOV, same as the Nagler and Meade Ultra Wide. Gets rave reviews and I had a 10mm Speers earlier this year but was forced to sell it to raise funds for other things. Never regretted selling something so badly. I used it in an Orion Optics f5 newtonian and it was sharp across 90% of it's 82 degree AFOV. That's near Nagler 'space walk' performance for budget money. The Speers used to cost £179 not so long ago. And it is vastly superior to the Hyperion IMHO. Wouldn't even give the Hyperion a second look if i had the chance of a Speers again.

Russ

[russ]

This link may help explain how the Apparent Field of View works and used to calculate the actual field of view:

http://en.wikipedia.org/wiki/Eyepiece#Field_of_view

Russ

[John]

.... I have been reasoning with myself in such a manner "I'll likely have this scope for a long time, so I might as well invest in a good one now."....

I can completely understand why you feel like that but the funny thing is that I've found that, in practice, scopes tend come and go but a good set of eyepieces lasts a long time.

That may be just me though

John

[jamieren]

Thanks for all the pointers guys. I will definitely check out the Speers-Waler eyepiece you mentioned, Rus. I'm assuming you're speaking of the 10mm. I notice there's series 1 and 2, does anyone know if there's a significant difference in performance? The price is 50% greater for the series 2... Also would yous recommend 2" eyepieces for medium mag. viewing, say a 20mm? Or would I be just as well to stick with the 1.25"?

On another note, I had a chance to take the 8" to a site out of town last night & I must admit I was a little disappointed. Don't get me wrong, I still enjoyed the discoveries.. I took in the double cluster near Cassiopiea, another cluster within the northern cross, and an arc of stars in the same area. So far unfortunately nebulas have evaded me (I looked in vain for the North America nebula near Deneb). It still has been far from the "breathtaking" views some speak of. Are they exaggerating, or is it my lack of ability to bring to bear the real goods into the scope? I know not to expect book quality views (damn those books, sometimes I wish those Hubble photos didn't exist!) but surely there's more than just groups of light points with no color.

[russ]

It's hard to describe what to expect. It's funny when i started i only expected to see the moon in detail and possibly track down the planets. I had no idea galaxies, clusters and nebula where even on the cards.

The moon was obviously mind blowing for the first time. And Saturn was gobsmacking, just never expected it. Jupiter almost as good. But what really did it for me was getting a star chart book from the library and finding M31. I couldn't believe it....another galaxy and i could see it from my own (parents) back garden. It was a smudge but i had the same feeling of excitement as seeing Saturn for the first time. The whole experience was better than i expected it to be. And all that was with a 50mm Tasco refractor believe it or not.

But then that was 1983 and information for a beginner (especially in the UK) was non-existent.

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.

Russ

[GazOC]

The North American is a pig to see without a filter, don't assume just because they are on the maps and show as large expanses of gas that you'll be able to see them as such. You're better of asking (or search) for a beginners list of easy to locate objects IMHO.

[russ]

I've never seen the North American despite my best efforts. Damn good sky needed for that.

[John]

I've never seen the North American despite my best efforts. Damn good sky needed for that.

You are not alone there Russ - I suspect I have probably detected parts of it visually but was actually looking "straight though it" so to speak.

My favourite at the moment is M27 - The Dumbbell in Vulpecula - looks really nice in my 8 inch - can't see any colour in it though.

John

[russ]

My favourite at the moment is M27 - The Dumbbell in Vulpecula - looks really nice in my 8 inch - can't see any colour in it though.

Totally agree John. M27 is a wonderful object and one the Skymax responds well too. The 150 showed a nice shape to M27, really pleased. And the good thing about M27 is you can hop a short distance to M56 and M57. Taking in Albireo on route. Great area of the sky!!!!

Russ

[jamieren]

How about the 2" eyepieces? Any helpful hints there, guys?

[Andrew*]

Jamie,

Most eyepieces come in a 1.25" barrel and this is fine for most focal lengths. However, when you get to low power eyepieces that view a very wide area of sky, the rim of the barrel restricts the view. 2" barrels are necessary to allow an unrestricted wide view. Eyepieces wider (i.e. with a longer f/l and wider apparent field) than 20mm with a 82* field, or 24mm with a 68* field or 32mm with a 50* field will always use a 2" barrel.

Incidentally, while the above three eyepieces all produce a different magnification with the same scope, they will all show the same size area of sky.

Earlier you were confused about the apparent field of view (AFOV) and true FOV of an eyepiece. Okay. An eyepiece with a very small AFOV will be like looking through a keyhole in a door. But if you used an eyepiece with the same magnification, objects will appear to be the same distance apart, but you will see a lot more of it, like looking through a porthole.

Your eyes can see around 68* of view. Eyepieces range from about 35* (keyholish and restrictive, but okay if you are looking at small objects like planets) to 100* (absolutely mind-blowing - the spacewalk experience! You feel like you're surrounded by stars). A standard plossl offers 50-52*.

But that's only the AFOV, which the eyepiece specifies. The actual size of the area of sky you are looking at is called the True FOV and is calculated by dividing the eyepiece AFOV by the magnification. So a 10mm eyepiece with 50* AFOV in a scope with a f/l of 1000mm (100x) is:

50/100 = 0.5 degrees or 30' (arcminutes)

HTH

Andrew

[jamieren]

But that's only the AFOV, which the eyepiece specifies. The actual size of the area of sky you are looking at is called the True FOV and is calculated by dividing the eyepiece AFOV by the magnification. So a 10mm eyepiece with 50* AFOV in a scope with a f/l of 1000mm (100x) is:

50/100 = 0.5 degrees or 30' (arcminutes)

It took me a couple of minutes to realize exactly what you were doing with the formula, but now I understand. This is going to rank right up there as one of the most useful bits of information I've been given next to measuring degrees in the sky by using your hands! Thanks a bunch.

I'm reasoning that there are 60 arcminutes in a degree, and it is the next smaller measurement, right? (') is the official symbol to signify arcminutes?

I've also noticed that quite a few of you veteran astronomers are packing 8" newts. Is this mainly because they are so much easier to pack up & go? Why wouldn't you all invest in something larger for the brighter views?

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...