Another One Bites The Dust- Aperture Fever Won.

[astro744]

Originally Posted by Suzy

6” Resolving Power: 0.74 Faintest Stellar Magnitude: 13.6
8” Resolving Power: 0.56 Faintest Stallar Magnitude: 14.2
10” Resolving Power: 0.56 Faintest Stellar Magnitude: 14.7

I think the 10" resolution should read 0.46.

Note the magnitude differences can also be expressed in differences in light grasp. Light grasp over human eye open to 7mm = area of primary mirror / area of pupil.

eg. for 150mm telescope light grasp = 150^2/7^2 = 459
eg. for 200mm telescope light grasp = 200^2/7^2 = 816
eg. for 250mm telescope light grasp = 250^2/7^2 = 1275
eg. for 300mm telescope light grasp = 300^2/7^2 = 1836
eg. for 400mm telescope light grasp = 400^2/7^2 = 3265

Like I said in my earlier post, you will notice a difference between the 6" and 8" but the difference will be more pronounced between a 6" and 10". Likewise for an 8", you would notice the jump to 10" but a better jump would be to 12".

See if you can look through a 6", 8" and 10" on the same night with your eyepieces at a star party and then make a decision. The 10" being f5 will benefit from a Paracorr if you find the coma objectionable; only you will know.

[Paddy (Patrick)]

Hi Suzy

Bigger mirror, less dew.

with a fan, your mirror will be cool in 30 min. less if with a very simple mod you direct air flow over front of mirror.

collimation will be easy - 5 min each time at most.

I know a 60 year old lady with a 10" tube dob. she has no problems moving it around in her Nissan Pulsar.

My Vixen LVW 17 was a delight in my 12" f5 dob. I don't know about the pentax, but I don't think you're likely to need a paracorr at f5. And you will probably find planets better in poor seeing with a big scope as you'll have better resolution and won't push the magnification so mucj to see things.

Again, if you choose an 8" you will be happy. But really i think the only issue in favour of small is manageability

[that_guy (Tony)]

Originally Posted by Suzy

Hi Tony,
I will be selling my 6".
As mentioned I've got a 6" and looked thru a 10", and you've had an 8". Say with the Jewel Box Cluster for example, what notable difference do you make between the 8" and the 10" performance on the gold star with these scopes?
Thanks,
Suzy.

I havent tried it out with the jewel box yet, but you can see the difference immediately in the core of omega cen. Also Eta Carinae, you can see far more detail and more light... I would sell my 8" for a 10" again if i had to!

[norm]

Hi Suzy,

I'll add to your dilemma.

F5 and premium eyepieces - I think you'll be fine. I have an F4.7 with a pentax 10mm XW - no issues.
Visual parracorr to reduce coma - to be honest you are most likely to get away with not having to purchase one. If it was faster say mine or lower, probably recommended.

Collimation - I don't think the size makes all that much difference. In terms of complexity, with the right tools, you can collimate in less than 2 minutes.

Cooling down - I don't think its that bigger issue, certainly when the weather gets warmer/summer months, maybe just pull the scope out 30mins earlier. I have a 14.5" and to be honest, I don't fuss over it too much - 30-45mins and she's right.

Dew - as people have mentioned, dew is always an issue. Main area imho is with the eyepieces and viewfinder (telrad etc).

Truss dobs - u can set these up in the dark no problems. I can set mine up jcompletely unassembled with a red torch in 10-12 mins. Once you have done it a few times, it becomes 2nd nature.

Understandably you want bang for your buck and your concerns are valid, but don't stress over it too much, things will fall into place.

So the decision? Go with a collapsible 10" Skywatcher or Lightbridge.

Good Luck with the decision.

Norm

[torana68 (Roger)]

this could go on for a while..... where's the other girls for some insight on dragging a 10 around?

[Liz]

Originally Posted by torana68

this could go on for a while..... where's the other girls for some insight on dragging a 10 around?

\\

I was the first to reply roger.

Think Suzy is being led down the aperture track with a grin on her face.
The 10" is a lot bigger than the 8", but as I said, the collapsible is lighter than the solid 10" dob. It is managable, and more so with your hubby on hand Suzy. I thought your mind was set on the 8", but if you are tempted by the 10", then check them out ans see how heavy they are. You dont have to carry them far ... house to car/car to house. Most places you set up are near/next to car. As in another reply, I use a trolly once set up = easy.

[ZeroID (Brent)]

Re the size/weight issue which seems to be the big bugbear here. Remember an 8" f6 is the same length as a 10" f5 ( give or take a few mm) and only 50 mm more (2") in diameter. So height to eyepiece etc is not a problem and especially if it's collapsible it takes up very little more room in a vehicle. And that 2" extra diameter is mostly empty space anyway !! It's just a bigger hole.. heheheh
This is my reason for opting to go 10" over the 8".

I'd suggest doing the Astrofest Test before deciding. Look at the options. Good luck.

[Suzy]

Originally Posted by ZeroID

Re the size/weight issue which seems to be the big bugbear here. Remember an 8" f6 is the same length as a 10" f5 ( give or take a few mm) and only 50 mm more (2") in diameter. So height to eyepiece etc is not a problem and especially if it's collapsible it takes up very little more room in a vehicle. And that 2" extra diameter is mostly empty space anyway !! It's just a bigger hole.. heheheh
This is my reason for opting to go 10" over the 8".

I'd suggest doing the Astrofest Test before deciding. Look at the options. Good luck.

I like you're thought process Brent You are right, portability concerns are my issue. I know I can handle an 8, and I have tried a 10" and have no probs using it. To me, it's really not that big at all. Just the moving it around issue, but as others have said, I can use a trolley and i will be happy to do that. My concerns now mostly lay within the list of points I detailed- the maintenance issues. I'm after ease and portability basically. I don't want it to be a hassle to get my scope out and then not use it much. I worry about that. I use my 6" all the time (weather permitting) as it stands now.

[Steffen]

Originally Posted by astroron

6” Resolving Power: 0.74 Faintest Stellar Magnitude: 13.6
8” Resolving Power: 0.56 Faintest Stallar Magnitude: 14.2
10” Resolving Power: 0.56 Faintest Stellar Magnitude: 14.7

From what I see, I see a whole magnitude difference between the 6 and an 8 (that’s 2 and a half times brighter, right?), but not even a mag. Difference between the 8 and the 10.

To me this reads like 0.6mag between 6" and 8", and 0.5mag between 8" and 10". i.e. a more or less linear progression.

What matters less once you get to 6" and larger is the resolution. Under *most* circumstances the difference in resolving power won't matter much - how many times do you get 0.5 arcsec or better seeing?

You will see more of the fainter details not because of better resolution but because the image will be brighter, and a full extra magnitude between 6" and 10" is nothing to sneeze at. More light gathering power can also mean the difference between colour and monochrome.

When I was young an astro veteran told me not to waste money by increasing aperture in increments. Double it or don't bother, he said. If you have a 6" and crave more aperture go for a 12". If you have an 8" go for a 16". I believe there is some truth to this, because frankly, I haven't seen all that much difference between 8" and 10" Dobs (of which you'll see plenty at observing nights and star parties) apart from a somewhat brighter sky background and ever so slightly longer spiral arms.

Comparing an 8" with a 16" - or Alex' 17.5" - is a different story altogether. The other night at Katoomba the Blue Planetary was obviously and unmistakably blue through the 17.5" but white in 8" and 10" scopes. To my old eyes anyway.

I believe all it comes down to is handling/portability and price. Get the biggest Dob you can handle, transport and afford. If price is the only hurdle then I'd suggest saving up a bit longer rather than going from a 6" to an 8".

Now, going big most of the time also means going fast. Faster optics show their aberrations far more readily than slower ones. This means, among other things, greater care has to be taken when figuring the mirror, mirror disfiguration during cool-down will be more apparent, collimation is more critical and hence will need to be done more often, eyepieces need to be selected more carefully (i.e. from closer to the top shelf).

This means increased cost (scope and eyepieces) and less convenience (longer cool-down). The need for collimation shouldn't hold you back. After spending all this money I'd feel bad about not taking 5 minutes after every car trip to bring the scope into top collimation and therefore top performance.

Just my 2 cents.

Cheers
Steffen.

[Suzy]

Thankyou Steffen for taking the time to write such an informative and helpful post. You have given me some really good information to think over. You have covered everything very well.

Thanks also by the way for the mention of the Blue Planetary - it was on my list of targets to see and I sure would have been expecting to look for something blue. I will still search for it, but I think I'll find it easier now that I have a better idea on what to expect to see.

Thankyou everyone else for your input and help so far as well. I appreciate the time you are all taking to help me.

[charsiubau]

I can't handle my husband's 10 inch solid tube dob even with a trolley.

I actually went for a different but more expensive solution - a 9.25 inch Celestron on a cg5 equatorial mount which I can carry and assemble myself with no help from anybody. The optical tube, the mount/tripod and the counterweights come in at 10 kg each. The downside is that it takes more time to get up and running than a dob. The upside is it has tracking and goto. I bought it for these two reasons: the biggest aperture I could manage alone and the tracking. That said, our most used scope is actually our Televue 85 mm refractor because of its supreme portability.

My main advice to you is, whatever you decide, before you buy the telescope, make sure you see it in the flesh and lift it yourself. And take a tape measure - things don't look as big in the shop as they do in the car or at home.

Good luck

[charsiubau]

I think 8 inches (dob or SCT) is the perfect compromise between portability and reasonable aperture. You can travel with an 8 inch and still have lots of room for other things or people in the car. I know of at least two females in our club who have 8 inch dobs. The difference over a 6 inch will obviously not be as great as with a 10 inch but it will still be significant.

However I would look at the 10 inch truss dobs before deciding. The Meade 10 inch lightbridge in particular looks quite small (compared to the GSO solid tube 10 inch) on the shop floor. On the Meade website it says the primary mirror housing is 30 lb, the mount 27 lb, the secondary housing 6 lb and the trusses 2 lb. You may be able to manage the weight of these components, but it will take longer to set up than a solid tube dob.

[Suzy]

Thankyou, Liz & Charsiubau, It's great to get a females point of view - you'll have been very helpful.

[The3rdKind (John)]

Gidday Suzy Q,

Long time since I communicated wif ya .
I've got the local park here now with keyed access along the driveway and keys to the toot as well. Some of us are going up on Sunday night (20th June) for a gawk festival. Get your eyballs over this side of town and have a gander thru mine again if you like.

One of the guys here has got a 12" Skywatcher collapsible (spellcheck) DOB and your not getting much more (eg Sombrero is very faint but visible from this location). The difference is he can pack it into his liddle rice burner with room left over and also the manouverability of the set-up is just beautifull. It is featherlight.

I'm out there very night with my 10" but am now wishin' hopin' cryin' prayin' to get my hands on some Meade S4000 super or Ultra wide angles. I say this because my 10" is ab fab but trying to manouver it on the mount is jerky and its easy to apply certain pressure and overshoot the object (especially high power barlowed down). If it was smoother and less clunky it would be a joy to use. Hence I'm going for the wider FOV.

BUT, I have ordered a ball bearing mettalic (spellcheck) ring which sits on the base of the mount to smooth this a great deal but I still have the Alt Az to deal with.

In your case, I'd give 12" very serious consideration as the collapsible dobs have superb movement at the mount.

Hope this helps Suzy, Hope you and yours are well, and hope to see you at our new site.

[M54 (Molly)]

Hi Suzy,

I know a woman who has a 10" solid tube dob and she says that she can lift it in and out of her car boot ok.
I think she collimates it each time it is used, at least after a ride in the car.
She uses it on a regular basis at the local astro clubs dark sky site.

I have a 5inch dob and plan to keep using it for quite some time yet, but when I do finally upgrade I'll be going through what you're going through now. And I'm terrible at making decisions!

So this thread is providing me with much interesting reading which I'll be filing away for the future.

Good luck with your decision.

[Starkler (Geoff)]

Originally Posted by floyd_2

Suzy,
if you can manage it, I would recommend upgrading to a 10" rather than an 8". An 8" seems like too much of an incremental upgrade. Go for the maximum aperture that you can handle / afford.

I recommend buying a 12" flextube and be done with it, as you're eventually going to end up there anyway
Once that no longer satisfies you can talk about aperture fever

[Suzy]

Originally Posted by Starkler

I recommend buying a 12" flextube and be done with it, as you're eventually going to end up there anyway
Once that no longer satisfies you can talk about aperture fever

Not so long ago I read an article from a very wise man.... he explained how appeture fever starts. Every time he upsized, he could see a new feint fuzzy and just had to, had to, see it, so he would get bigger apperture, and then he would spot something new that was feint with this new and bigger apperture, and then the process gets repeated over and over again.

Knowing this evil & self destructive journey now, I can quite happily look at a feint object and say "I don't really give a rats", I will just simply imagine/pretend/exagerrate about what it is. 10" is as high as I will ever want to go with this in mind.
See.. there is a cure for aperture fever after all - it's called "just don't go there" pill!

That all being said Geoff, I will race anyone to the front of the line to have a look thru your scope. Though then the fever will start up and I will have to search for this post to get my sanity back. Hey, I never said there was a complete cure!

[Starkler (Geoff)]

Originally Posted by Suzy

Not so long ago I read an article from a very wise man.... he explained how appeture fever starts. Every time he upsized, he could see a new feint fuzzy and just had to, had to, see it, so he would get bigger apperture, and then he would spot something new that was feint with this new and bigger apperture, and then the process gets repeated over and over again.

Yes theres that and it all comes down to how big an effort in time, money and effort you want to put into this past time and its always subjective and personal.

I started with an 8, upgraded to a 10, bought a couple of smaller scopes and then got the 15. A 6,8,10, or 12inch can be moved around and transported in a car by one person. My 15 wont fit in a sedan and has to go in a trailer. I think I could quite happily downgrade to a 12 and sell everything else just to save the transportation hassle. I really think a 12 hits a sweet spot of being the maximum easily transportable size and the minimum size worth looking through for dso's. After using a 15, a 10" wouldnt satisfy me but a 12 might.

Aperture always wins but only if its not too big and cumbersome to move and use. If you could move the scope from its storage place to its viewing place with a trolley without negotiating stairs etc I recommend the 12.

If you have to carry it around up stairs and around obstacles then an 8 might be tops.

That all being said Geoff, I will race anyone to the front of the line to have a look thru your scope. Though then the fever will start up and I will have to search for this post to get my sanity back. Hey, I never said there was a complete cure!

If you were at the last Snake Valley camp you would noticed my scope looking very lonely and unloved due to Tims 22" being nearby. What amazing views! I need a bigger scope now

[mic_m (Michael)]

Hi Suzy,

There is a misunderstanding on this thread about the weight of the collapsible SW dobs vs the solid tube versions; more specifically people have attributed the weights inversely. It is actually the solid tube SW that weighs less than the collapsible SW. The tube weight of the 8” collapsible is 11kg and the tube weight of the 8” solid tube is 7.98kg. The 10” the collapsible weights 15kg while the 10” solid tube weighs 12.42kg. It is worth noting that the optical tube of the 8 and 10” solid tube dobs are both about 1200mm long, which is the same as the collapsible dobs tube length when it is extended, however, the tube length of the 8”and 10” collapsible dobs can both be reduced to about 800mm. The bases are the same weight and the same dimensions for the solid tube and collapsible dobs in each size range, so that is not a factor of differentiation between collapsible or solid tube scopes but rather between 8”and 10” aperture.

The above tells you two things; if weight is the issue, not bulk, then the solid tube SW dobs are preferable. However, if it is bulk (more specifically OTA length) rather than weight that is your concern the collapsible SW dobs may be a better option given that the size of their optical tube can be reduced for transport or storage. However, given the difference in height is marginal when collapsed for the 8”-10” versions I don’t think there is any great advantage in going with a collapsible dobsonian. While the collapsible is not really any more complex or more difficult to set up there is the issue of obtaining an effective light shroud. This can be expensive and difficult to fit for the three strut design as the collapsable dob is not a true truss telescope where the truss structure supports the shroud and keeps it away from the light path.

Also, you should note that the original white tube versions of the collapsible dobs have their UTA knobs (the handle above the lower strut and below the focuser on the side of the UTA facing the LTA) in a slightly different location to the black tube versions. More specifically the black tube version have the knob moved down towards the lower strut away from the focuser. The holes cut in the Astrozap shroud for these knobs are cut for the black tube versions, not the white tube versions. So if you end up getting the collapsible version of the telescope and are planning to buy a shroud from Astrozap be sure to get one with a black tube.

As has been noted, while all other things being equal a larger scope will show you more, you have to consider the ease of use, if a telescope is too bulky or too heavy for you to easily move than there is really no point in buying it. If you can manage a 10” go with that, but if a 10” is too much of a hassle to move easily go with the 8” (8” is a decent sized scope and it will show an improvement over your 6”). But only you can determine what you are comfortable with using and transporting.

Good luck with your decision,

Michael.

[Liz]

Originally Posted by mic_m

Hi Suzy,

There is a misunderstanding on this thread about the weight of the collapsible SW dobs vs the solid tube versions; more specifically people have attributed the weights inversely. It is actually the solid tube SW that weighs less than the collapsible SW. The tube weight of the 8” collapsible is 11kg and the tube weight of the 8” solid tube is 7.98kg. The 10” the collapsible weights 15kg while the 10” solid tube weighs 12.42kg.
Michael.

Well, blow me down ... thank you Michael ... think I just presumed it was the other way round.