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Aperature Size In Light Polluted Urban Skies

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#1 mikes1212

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Posted 29 January 2004 - 07:42 PM

The following is part of a post taken from the Yahoo Group, Talking Telescopes.

the original post:
12" Dobsonian - With the size, weight and urban light conditions at my house I may have to lower my sights and go for a 10" Dob. The money I save could be put to use for buying a few good EPs.

I do have a friend that lives out towards the mountains and the
viewing conditions are FAR better than what I have here at my house. The 12 inch dob would work great out there.

I will be doing probably 85% of my veiwing here at my house. With
the light pollution of my urban skies, the 10 inch would probably give me better viewing.


the answer given:
Actually this is incorrect. Under light polluted urban skies, _more_ aperture will be better. The opposite is a myth fostered by people trying to sell small telescopes! I live in an inner suburb of a large city and use my 11" Dobsonian much more than any of my smaller telescopes, and often wish I had a larger scope. But on the question of size and weight, a 10" definitely has the edge.

I am interested in what the people here in this forum have to say about this?

-------
Michael
20X80 Oberwerk LW

#2 jack45

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Posted 29 January 2004 - 09:07 PM

Mike

I just did that very thing with my Orion XT10"f/4.7 comparing it to my Discovery 12.5"f/5. In front of my house were I do 80% of my viewing, two street light on the same side my 12.5" scope was. The light did mess with the viewing of my 12.5" scope more so than my 10" scope, why there could be lots of reason. In my mind as I look back on it all thing were not equal in which to do a comparsion. My 10" scope show a sharper, clearer, more detail image of Saturn than my 12.5" scope but the 12.5" scope show a much bigger image of Saturn.
on M42 the 10" scope did the same thing the "E" star was easy to see knowing already were too look but with the 12.5" scope I had to look real hard to see it also with the 12.5" scope there was more star seen in the back ground. In the back of were I live is a field, so I took both telescopes there no street light in the way. And the 12.5" scope blow the 10" scope away easy, a lot of detail in Saturn, the "E" star was real easy too see.
Then I try M51 with the 10" scope it was there but not like in the 12.5" scope much better view with the 12.5" scope.
The street light played a big part in the view of my 12.5" scope why the focuser is on the right side of the scope, as I raised my scope more light got in the tube. The 10" scope was on my left side Orions focuser is on the left side not as much light was able to enter the tube or the focuser "oh" I use a 17mm Nagler T/4 and 12mm T4 Nagler so that the EPs would not be a issue.
My 12.5" scope is only or less then one month old so I hadn't flocked the tube or focuser, the 10" scope had these thing done four months ago.
Why am I telling you all this, because more aperture is better but also do all the things needed to get all you can out of a large scope my comparsion was flawed badly. I'd go with the 12.5" scope, so those day "15%" of, were I could go too a dark site would be something to look forward too. I have a small car and I put the 12.5" scope with the mount in the car with me my trunk is not needed. And this scope is big. I also have a meade 16"f/4.5 I'm upgrading it, I just put a new focuser in looking at making it a split tube. Last one I have a 17.5"f/5 coming in Feb, I've been waiting on my scope from Discovery how long? 3 Aug 03. the invoice said shipping date was 3 Nov 03 no scope but thats a difference story. I bet you said that was a long $.02!

Clear Skies!

#3 Guest_**DONOTDELETE**_*

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Posted 29 January 2004 - 09:09 PM

That's true. The fact is, you NEED more aperture the more light there is to see DSO's. Plus, you have a bigger telescope to use at it's full potential in the country. Read this post in this forum: http://www.cloudynig...ubbthreads/show
flat.php?Cat=1,2,3,4,5,8,9,10&Board=reflectors&Number=46601&pa
ge=0&view=collapsed&sb=5&o=&fpart=1

I'd copy and paste that... ;)

#4 jrcrilly

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Posted 29 January 2004 - 09:44 PM

I'm no optical expert but now we're talking about an area where I do know something. My observatory is one block away from the city square and the light pollution is heartbreaking. I can report that I can ALWAYS see deeper as my aperture increases. Less aperture at a darker site would do better yet, but then more aperture at a darker site would beat that.

#5 summitlake

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Posted 30 January 2004 - 12:13 AM

I understand John's response and it seems consistent to me. Would the folks at Kitt Peak, or Mauna Loa, or Palomar hold out for a rule of thumb about whether 8" or 10" is some kind of absolute theoretical max for low-contrast skies? Looking at the boundary conditions, the 3" AC Gilbert and the 200" Hale, I have read that the Hale guys can ply their trade at high noon.

I'm not making fun of anybody. I have read of so many large aperture issues about viewing in poor conditions that I wish I understood them all better.

#6 mikes1212

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Posted 30 January 2004 - 06:46 AM

Thanks everyone for setting things straight.

Adam, I read the entire thread that you sent me the link to.

I don't know why, but after reading a few of the post here in the CloudyNight forums and some of the ones in the Yahoo groups, I was really under the impression that smaller optics was the was to go if you had to deal with light polluted skies.

The city (Washington D.C.) is to the east/front of my house. I will be doing my viewing to the west/back of my house.

Conclusion:
Smaller optics may give you slightly sharper views in urban skies, but the larger optics will beat the pants off of the smaller optics when you are done with your views in the darker skies.

Initially a 10 inch Dob would be a good fit for me, however after a few months of viewing at home and in the country I would probably be wishing that I had purchased the 12 Dob instead.

I hope an opportunity will be available to try a 12 inch Dob to compare with a 10 inch Dob. I want to see if I can handle moving the 12 incher, and place it up and onto it's mount. If I can, than I'm in business! I will be an owner of one very soon!

Thanks again everyone!


#7 Blair

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Posted 30 January 2004 - 07:33 AM

It sounds like the average seeing conditions and what is your key interest decides more of what size scope to have (oh, and how strong is your back).


#8 mikes1212

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Posted 30 January 2004 - 10:58 AM

I'm basically open minded about my viewing interest, from planetary to DSOs. I would like to view as much as possible. I do have an interest in astrophography, but That will have to wait.

Now my back is a different story. My lower back is in OK shape, but my upper back (cervical spine) is not.
My wife and daughter who will also be sharing this hobby, have all promised me that they will be very helpful with the scope that I choose. I do hope so, regardless of the size of the scope.

I can build a platform with wheels, and get a hand truck to help with transportation of the OTA and base.

#9 Relativist

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Posted 01 February 2004 - 05:04 AM

Yes, if you can afford it, and can handle the size get the bigger scope. I am getting a 10" because of my budget and the size of a 12" dob.(non-truss). Ideally, If my finances were there, I'd get a 14" tscope. One thing I'm doing for sure when I get my scope is flocking the inside of the tube, that and a bafel will help alot with stray light/light pollution. GL.

......Curtis

#10 mikes1212

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Posted 01 February 2004 - 09:47 AM

I was over at a fellow club member's house last night and he let me put together his Orion 10" Dob. I picked up the tube expecting it to be fairly heavy, and to my surprise it was not bad at all.

I'm not too sure of the exact weight on the tube, but I would guess around 30 lbs. Craig (who often answers post here in this forum) did have a leather strap handle on his tube. The handle made it easy to pick the tube up and steady it to place into the mount. The tube on the Hardin 12" will weigh close to 20 lbs. more. But I think I can handle it without too much strain.

After last night’s views of Saturn and the Orion Nebula, I'm hooked! I can just imagine how nice the views will be with a 12" Dob. If I had the finances available, I'd get a 14" scope too :p

I could possibly afford the Discovery 12.5" PDHQ, but the tube weighs 61 lbs! I think that weight is over my limit. The optics is probably better in the Discovery, but the weight difference and the time it would take Discovery to deliver the scope are the main factors in my decision.

Next thing I have to focus on will be accessories. First off is a good eyepiece or two. I have my eye set on a Tele Vie 2.5 Power mate, but I'm not sure how well this EP will work with the Hardin 12" scope? It's expensive too!


#11 Relativist

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Posted 01 February 2004 - 04:28 PM

Dude the teleview powermate isn't an eyepiece, it's a barlow type device. Did you see this review:

http://members.roger...mentor12dob.htm

Also the PDHQ was reviewed in S&T late last year, I'd check that out also. With the 8" dob I'm lugging around now I do not pick the whole thing up, but move it with a folding dolly (a cheap luggage type, not the expensive super thin one). If you look at the review you'll notice that he doesn't man-handle the OTA when moving it to/from his car. If you can afford the 12.5" PDHQ I'd call OPT, they have one on their showroom floor, you can see it next to the truss on their in-store web cam. tell them you want that one!! and you can't wait! (I don't know if they would do it LOL, don't get me in trouble!) All kidding aside, whatever you get, make sure it fits in your car, and if you can get the PDHQ, it's nice enough that you should, and worth the difference in price IMO. (now comparing the GS to the regular DHQ I don't think it's worth the difference ~$150 for a 10")

As for eyepeices, I'm on a budget, and so far I've bought 2 ep's, 1 barlow, and a filter set. I bought a $40 celestron filter set at fry's, includes one moon filter, and 3 color filters. For the barlow, I got the meade 3x barlow for $40 so I would not repeate the powers on the ep's I had at the time, I might get the 2x that orion has on sale. The ep's I ended up getting were a 32mm Celestron plossel ($40) and the 10mm Celestron X-Cel ($65 - although I saw it in S&T for $55!). The loaner ep's I had were a 40mm a 20mm and a 12.5mm, that is why I got the 3x, but as you can see the ep's I got are better suited to a 2x, I will probably keep both though. In the future I plan on getting some of the Antares W70 series ep's for the larger FOV.

..........Curtis

#12 mikes1212

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Posted 01 February 2004 - 08:17 PM

Curtis,

My fault. I understand that the Tele Vue Power Mate, is a Barlow type EP accessory. I wrote that reply early this morning and I did not explain very well at all that I would want the Power Mate in addition to a couple of quality EPs for additional magnification.

I'm a rookie and I have a lot to learn! :tonofbricks:

#13 Relativist

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Posted 01 February 2004 - 09:20 PM

So which scope are you going to get, did you decide? Don't get paralysis by analysis! There is also always the 12.5" meade, but, IMO it's probably better to get the GS 12".


..........Curtis


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