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View Full Version : 6" versus 10" Dobsonian



naios
2006-Mar-17, 12:02 PM
Let's say theoretically that I wanted to move up from a 6" to a 10" Dobsonian. I am out in the suburbs and right now there are no star parties going on, so unfortunately I am not able to get the opportunity to see for myself.

What kind of difference would I see between the various DSO's, etc. It's bothering me now that I didn't spend a couple more bucks at the beginning instead of now where I've spent money on eyepieces. I know going to 10" that size and weight starts to become a factor, however I think I'd be able to manage.

Also, remarkable how many objects went streaking through my view yesterday night. Wondering if they were meteorites, satellites or little green aliens :D

aurora
2006-Mar-17, 03:35 PM
If the objects were points of light that moved quickly through the eyepiece, those were satellites. If the object was a streak of light, that was a meteorite. I've seen both through my scope, but many more satellites than meteorites.

There is a definite observable difference between a 6 and a 10 inch scope. Deep space objects will be somewhat brighter, somewhat more detail will be observable on extended objects, and a few of the dimmer objects will be observable in the 10 inch while a 6 inch would show them only with difficulty.

It's hard to describe the difference in words. I believe some of the vendor web sites post doctored pictures which are supposed to depict the difference.

JohnW
2006-Mar-17, 04:48 PM
I believe some of the vendor web sites post doctored pictures which are supposed to depict the difference.
Scroll about a third of the way down this page (http://www.belmontnc.4dw.net/Beginners.htm) for an example. These are drawings, not photographs, so are pretty close to what you'd see at the eyepiece.

redshifter
2006-Mar-17, 06:02 PM
I upgraded from an 8" to a 10" and there was a significant difference in what I could see. Objects that I couldn't see in the 8" I could see in the 10" and objects that I could see in both scopes had noticably more detail in the 10" (planets looked about the same though, but they are very bright compared to most DSO's). Considering that an 8" mirror gathers something like 75% more light than a 6" and a 10" gathers something like 50% more light than an 8", the difference between a 6" and a 10" is significant.

naios
2006-Mar-17, 06:08 PM
I appreciate your help. Now, I just have to save up my pennies...

Dave Mitsky
2006-Mar-17, 07:56 PM
There's another aperture range eyepiece simulation at http://www.globaldialog.com/~obsessiontscp/m13page.html

It would be helpful if the magnification of the views was specified. The drawing for the 8-inch seems a bit pessimistic.

Dave Mitsky

aurora
2006-Mar-17, 09:40 PM
There's another aperture range eyepiece simulation at http://www.globaldialog.com/~obsessiontscp/m13page.html

It would be helpful if the magnification of the views was specified. The drawing for the 8-inch seems a bit pessimistic.

Dave Mitsky

Yes, their 8 inch image seems to me like what I would see in my 80mm refractor.

Grey
2006-Mar-17, 09:47 PM
Yes, their 8 inch image seems to me like what I would see in my 80mm refractor.Well, of course they're trying to sell you a 30 inch scope. :)

JohnW
2006-Mar-17, 09:49 PM
There's another aperture range eyepiece simulation at http://www.globaldialog.com/~obsessiontscp/m13page.html

It would be helpful if the magnification of the views was specified. The drawing for the 8-inch seems a bit pessimistic.

Dave Mitsky
It looks like they're increasing magnifications as aperture increases, which seems unnecessarily confusing.

redshifter
2006-Mar-17, 11:57 PM
Their 15" view seems pretty close to what I see with my 10"

cjl
2006-Mar-18, 03:25 AM
Our 10" RCX400 gives views between their 15" and 18" as far as quality/number of stars. It overall looks like their views (at least at the smaller sizes) are more towards the pessimistic.

Dave Mitsky
2006-Mar-18, 05:02 AM
It looks like they're increasing magnifications as aperture increases, which seems unnecessarily confusing.

I don't believe that's the case. More stars are seen, as one would expect, due to the increased aperture.

Dave Mitsky

Fr. Wayne
2006-Mar-19, 08:25 AM
Doesn't the 10" increase dramatically one's ability to separate double stars? I think so.

aurora
2006-Mar-19, 04:23 PM
Doesn't the 10" increase dramatically one's ability to separate double stars? I think so.

Sort of indirectly, since it allows one to observe at higher magnifications.

Splitting double stars wants good quality optics, and good seeing conditions.

Larger scopes that gather more light are better, given good optics. But smaller scopes with excellent optics can be very good for splitting doubles.

Kaptain K
2006-Mar-20, 08:38 AM
The maximum resolution of a scope is directly proportional to the diameter of the objective lens or mirror. Twice the diameter = twice the resolution (all else being equal). So a 10 inch scope can resolve stars that are 6/10 the seperation of the best a 6 inch scope can do.

JohnW
2006-Mar-20, 04:42 PM
I don't believe that's the case. More stars are seen, as one would expect, due to the increased aperture.

Dave Mitsky
No, they're increasing magnifications. Watch that pair of stars at 10 o'clock as it moves to the edge of the field, then falls off the 30" view.

Edited to add: I think what they might be doing is showing the view through different scopes with the same eyepiece. If someone is willing to lend me six Obsessions for a few months, I'll check.

Dave Mitsky
2006-Mar-21, 09:30 PM
You're right. I never looked at that page very closely before. IMO, a set of images at a fixed magnification should also be included.

Dave Mitsky

Fr. Wayne
2006-Mar-22, 04:02 AM
I love my 25mm eyepiece with a very light green filter for "boldly going where no man has gone before." (giggle.)