Bigger Dob allow greater mags on planets?

[Benboy]

Hi guys,

I have a 6" dob and am considering my next scope - possibly a 10 or 12" truss tube dob.

What I want to know is does having more aperture actually allow me to push the magnification levels higher on planetary viewing. I know that people say that you can roughly x50 the size of your aperture(in inches) to get the maximum usable amount your telescope can handle magnifying . In my case it would be 300x. Then of course you have to take into consideration the "seeing" conditions at the time which means you only really get to use the scope at its max on exceptional nights. So most times I'd have to drop mine down to between 150-200x to get a reasonably crisp image on planets.

So just because I increase to say a 10 or 12" Dob which can supposedly handle 500-600x magnification, does that actually mean I would practically be able to use a higher mags on planets than I can on my 6" or am I still going to be limited to around 150-200x because of the seeing conditions or other factors regardless of the scope size? If so is there any advantage of having a larger scope for planetary viewing?

Cheers for any input :)

Ben

[Paddy]

Hi Ben,

You will not often get your scope to mags beyond 300X but certainly it is sometimes possible. I occasionally get to push my scope to 600X. Bigger dobs do have better resolving power - I can't remember the formula but I think the increase is directly proportional to the aperture. It does make a difference for resolving detail on Jupiter and Mars in my experience.

The biggest impact is however collecting light for DSOs.Going from 6" to 10-12" will make a big difference to your observing.

[cookie8]

Hi Ben
Bigger scope in aperture means better light collecting ability means brighter objests. When you zoom up a planet ,however bright it appears to the naked eye, it becomes dim. When its dim you can't make out the details ( imagine readind small text under dim light). So in terms of seeing subtle details of planets yes the larger the better because with the same mag the image is brighter.

[ballaratdragons]

It's not always a matter of bigger is better, but anyway, these links may help you understand it a bit better :thumbsup:

http://outreach.atnf.csiro.au/education/senior/astrophysics/resolution_sensitivity.html

http://www.universetoday.com/19433/telescope-resolution/

[Benboy]

Thanks guys.

What I'm really wanting to get at is - in general usage will I be able to up my mags a bit without losing crispness of image by having a larger aperture scope? Or will I still in general be using around 200x mag.

Edit:Ken - Hadn't seen your post when I posted this, will have a read thanks!

[ballaratdragons]

To try keep the answer simple for you Ben,
upping the apature will allow you to see a magnified object brighter.

You can look at the same object in a 6" and 12" at the same magnification (say 300x), but the 12" will see it brighter but not necessarily clearer.

The advantage is light gathering power.

12" will allow you to magnify more and still have a bright object, until the 'seeing' takes over.
And every scope also has a limiting resolution.
Otherwise we would be able to magnify 1000x or more.

[Stu Ward]

Just remember though, the higher the magnification the quicker the object moves across the FOV
A manual dob will require a lot of careful nudging at High Mag

Stu

[Suzy]

Hi Ben, I'll speak from my own experience going from a 6" to a 10". :)

Jupiter in a 6":
In a 10mm: Both the NEQ & SEQ red bands could be made out, the planet was small, and the red spot was faint and just visible.
Barlowed to 5mm: bit larger, image not as detailed/sharp (and the red actually looked redder through a 10mm).

Saturn in a 6":
By the time Saturn came around later in the year, I worked out that a 7mm hit the sweet spot better on planets. Barlowing a 15mm wide angle ep down to 7mm, the planet was mostly always beautiful and sharp. The black Cassini division could easily be made out, and the black ring closest to the planet (the D ring) surprisingly could always be made out (even by my hubby and daughter).
In a 4mm, I once saw the faint shadings of the bands on Saturn. It appeared very large and filled up the entire field of view of a standard Celestron 4mm plossel. Constantly nudging the dob proved too much work while trying to see detail with such a tiny field of view- it was incredibly frustrating.

The biggest difference I noted for planetary viewing on both a 6" and 10" was that I could see planets almost all of the time successfully on a 6", whereas a 10", even with a 10mm ep, I had trouble getting "great" (not fantastic) views on a regular basis. Yes, there was definitely more resolution using a 10", but the viewing times had definitely decreased. I soon came to learn first hand what others have said, that larger apertures tend to magnify poor seeing conditions. In my opinion though, I would rather see a planet which gives me some detail to chew on for say 5 times for that season, than having a planet I can see all the time with little detail.

Jupiter in a 10":
This is now the next Jupiter season to my notes above and have since purchased a premium eye piece, being a Pentax XW.

In a Pentax XW10mm: The planet is now slightly bigger. I honestly don't know if it has anything to do with the size of the apperture or whether the fact that Jupiter is actually closer to us this time around. Some input from others, size vs aperture would also be a help to me as well.
The planet was definitely brighter, the red bands were striking.
I could easily make out little cloud formations and the narrower red bands both in the north and south. The ripples of blue/grey clouds were jaw dropping as they were sharp and detailed.
Interestingly, when I threw on the 6.7mm Meade 5000 (it was a night of relatively good seeing that this focal length should have handled nicely), however, the ep made Jupiter very bright, washed it out and very little detail was discernible. I then changed to a Celestron 4mm which gave me much better contrast and resolution compared to the Meade.

Case in point: a good quality ep will show you a lot more.
There are factors which will dictate how well you see a planet: aperture/quality of eye pieces/ seeing conditions/ how well your eyes are trained at teasing out detail (the more you do the more you'll see).

I can't comment on a view through my 15mm barlowed down to 7mm (as I'd used on Saturn), as this ep is now rendered useless on my scope due to the fast ratio of the 10' dob- it gave me fuzzy images, and sea gulls every time I used it. Perhaps seeing conditions played a part too, I don't know, I just know I could never use it - on anything really.

Ben, for a much detailed explanation, have a look at the link I have supplied below which is my first Observation Report (posted) using my 10" dob. giving some comparisons from my 6" to the 10". In particular read about the sections on Jupiter and the Orion Nebula.
Please note that within this report I made reference to having problems with a 6mm TMB. I put down the performance that night to poor seeing conditions, however this actually proved not to be the case in my future sessions using the TMB. Since the report was done, I had many attempts trying to use it and did comparisons with other ep's, the TMB just would not come into focus on my dob, so it was rendered useless. Though others here have used it to great success and satisfaction. At the time of the report I thought that perhaps the seeing played a part on it's performance, but it wasn't to be the case.
http://www.iceinspace.com.au/forum/showthread.php?t=67200

I have come to understand why making notes of observations is so important. It is interesting watching my progression on discerning detail on objects past to present as my eyes improve.
A quick little story...
When I was looking through Ron's (astroron) 16" scope (monster much?! :lol:) he lined up NGC 104 (47 Tuc) for me. He told me to have a look and tell him what I could see. :rolleyes: Not knowing what to look at :screwy:, I nervously starting looking so my answer would be correct :help:. With confidence and a smile of satisfaction on my face, I responded back with "there's a break in the core". Phew, correct answer- was I relieved..:D. If he'd asked me that same question 12 months I ago I would have said, "yes yes I see a shiny bright ball" :P:lol: Ron is a great teacher. He did right by getting me to work it out for myself rather than telling me, with his guidance, pushing my new and slowly acquired observing skills.

Observation Reports are also very handy to check on things - my post here is probably a good example as I had to refer back to them.
You should join us in the Observing Forum and try your hand at reporting, we would love to have you there!

I hope my my post has been of some help to you. ;) :)

Blimey, I've just done a preview post to what I've written, and for pete's sake, I do waffle on don't I?! :face:
My wrists now ache :help: If I don't post anymore today, it's your fault Ben. :P:lol:

[kitsuna]

Absolutely true. Trying to watch Saturn in a 10in dob with 240x mag is a pain. It just dances across the FOV. I could pick out more detail at 96x because it was easier to track.

[Suzy]

What's more fun :rolleyes: is putting a high mag. orthoscopic ep in with an eye hole the size of a pin head as the entire planet fills up the fov. That's work as the tiniest movement of the planet you have to nudge the dob. :eyepop:Have to say, amazing detail though- if you can see it for long enough! :P :lol:

[astroron]

Using High Mag on Saturn at 300xmag is good fun as it is like watching a UFO zooming through your eyepiece:eyepop::lol::lol:

[overlord]

YES u can certainly use higher mag for a larger scope, BUT....

U need to have GOTO or tracking to use with a dob if you want to start pushing the magnification. Don't bother with 600x. Don't even bother with more than 200x unless u have tracking. i don't bother with more than 100x cos the sky moves too fast for my widdle brain. :eyepop:

[Suzy]

Widefield eyepieces will fix that :P :D:D
I have time to yawn, stretch and file my nails. :lol:
And I tried not to say "premium" in case I came across as ep snob. :question::P