Return to the Cloudy Nights Telescope Reviews home pageAstronomics discounts for Cloudy Nights members
· Get a Cloudy Nights T-Shirt · Submit a Review / Article

Click here if you are having trouble logging into the forums

Privacy Policy | Please read our Terms of Service | Signup and Troubleshooting FAQ | Problems? PM a Red or a Green Gu… uh, User

Observing >> Deep Sky Observing

Pages: 1 | 2 | 3 | (show all)
azure1961p
Postmaster
*****

Reged: 01/17/09

Loc: USA
12" versus 16" for galaxy structure
      #5664102 - 02/05/13 06:17 PM

I'm in the middle of choosing between a 12" or 16" reflector. I love dust lanes in galaxies and such but the 16" is twice the cost of the 12". I've looked through both but for galaxies would u guys strongly recommend the 16 or is it a shrug? 20" is huge but simply out of my budget.

Thanks in advance. My sky's are generally 6.2-6.5v where I'd use it.

Pete


Post Extras: Print Post   Remind Me!   Notify Moderator  
Achernar
Postmaster
*****

Reged: 02/25/06

Loc: Mobile, Alabama, USA
Re: 12" versus 16" for galaxy structure new [Re: azure1961p]
      #5664194 - 02/05/13 07:15 PM

A 16-inch will always show more than a 12-inch from the same site, but a 12-inch will also show a lot on galaxies from a good dark site. Are you looking for a mass-produced or a premium Dob? If you can afford a 16-inch without breaking the bank, I would take that route if you are looking for a telescope that will be more than enough aperture for observing galaxies. A 16-inch takes in about 80 percent more light than a 12-inch, a signifcant difference that will show through the eyepiece.

Taras


Post Extras: Print Post   Remind Me!   Notify Moderator  
Dave MitskyModerator
Postmaster
*****

Reged: 04/08/02

Loc: PA, USA, Planet Earth
Re: 12" versus 16" for galaxy structure new [Re: Achernar]
      #5664236 - 02/05/13 07:47 PM

I recommend getting the 16-inch for galaxy and other DSO observing.

Dave Mitsky


Post Extras: Print Post   Remind Me!   Notify Moderator  
IVM
scholastic sledgehammer


Reged: 01/07/08

Loc: Western New York
Re: 12" versus 16" for galaxy structure new [Re: azure1961p]
      #5664357 - 02/05/13 09:37 PM

Galaxy structure is probably my primary observing interest. Although I never did a side-by-side comparison, it seems that my 12" driven SCT is roughly equal to my undriven 16" "Dob" in how much they reveal in practice, and my undriven 12" "Dob" is not very far behind. When the magnification used with a 12" is 3/4 of the magnification used with a 16", the surface brightness in the two scopes is the same. This theoretical relationship fits with my impressions. I use the 16" most of the time only partly because of its aperture (due to its design it happens to be the most portable of my 3 large scopes).

Post Extras: Print Post   Remind Me!   Notify Moderator  
JayinUT
I'm not Sleepy
*****

Reged: 09/19/08

Loc: Utah
Re: 12" versus 16" for galaxy structure new [Re: IVM]
      #5664493 - 02/05/13 11:32 PM

Aperture wins, always. Having said that I have a 14 inch I use and am content on that. The 16 will show you more. Weight is a concern.

Post Extras: Print Post   Remind Me!   Notify Moderator  
HellsKitchen
Pooh-Bah


Reged: 09/05/08

Loc: Melbourne Australia
Re: 12" versus 16" for galaxy structure new [Re: JayinUT]
      #5664669 - 02/06/13 05:49 AM

My 12" can show galaxies as faint as visual magnitude 14 from my outer suburban location. A good 12" is a very nice thing to have, but for faint fuzzies, aperture is king.

If weight, size, portability and transport are not an issue, get a 16". The mass produced asian ones (e.g GSO, Lightbridge) have large and heavy bases which may be an problem for handling it, but are quite affordable and you really do get a lot for your money (especially compared to even a decade ago). Alternatively there are several flavours of premium models that may be lighter and incorporate a variety of features that facilitate portability and are often customizable to your needs. But you'll be paying at least triple the price of a mass produced model.

Edited by HellsKitchen (02/06/13 05:50 AM)


Post Extras: Print Post   Remind Me!   Notify Moderator  
Feidb
Pooh-Bah


Reged: 10/09/09

Loc: Nevada
Re: 12" versus 16" for galaxy structure new [Re: HellsKitchen]
      #5664904 - 02/06/13 10:04 AM

I'd recommend the 16-inch also. I've been using one exclusively for 25+ years. First one I made, a 16-inch f/6.4 but it just got too cumbersome to lug around. I now use a 16-inch f/4.5 commercially made and you just can't beat the aperture for not only catching the faint fuzzies, but for structure. I've compared my commerical one side by side with 12 inchers from standard to premium optics and there is still a noticeable difference.

Post Extras: Print Post   Remind Me!   Notify Moderator  
coutleef
Post Laureate
*****

Reged: 02/21/08

Loc: Saint-Donat, Québec, Canada
Re: 12" versus 16" for galaxy structure new [Re: HellsKitchen]
      #5664910 - 02/06/13 10:11 AM

i would say get the biggest aperture you can transport to a dark site. looking through briefly a 16 inch i had the impression that the jump from 12 to 16 was similar to the jump from 8 to 12. so quite worthwhile. galaxies or details you could see with averted vision on the 12 were seen with direct vision on the 16.

it will be significant especially on galaxies. but the 16 was just too big a scope for me to handle.

Edited by coutleef (02/06/13 10:11 AM)


Post Extras: Print Post   Remind Me!   Notify Moderator  
Madratter
Post Laureate


Reged: 01/14/13

Re: 12" versus 16" for galaxy structure new [Re: Feidb]
      #5664917 - 02/06/13 10:12 AM

As others have said, bigger is better. But even with a 20" f/5 (my scope) you can only see so much in terms of structure.

The bigger reason I like the larger scope is I really enjoy groups of galaxies. And the more light you can pull in, the better.

If you are interested in galaxies, get the biggest scope you will use on a regular basis. Big scopes are MUCH heavier.


Post Extras: Print Post   Remind Me!   Notify Moderator  
GlennLeDrew
Postmaster
*****

Reged: 06/18/08

Loc: Ottawa, Ontario, Canada
Re: 12" versus 16" for galaxy structure new [Re: Madratter]
      #5665057 - 02/06/13 11:43 AM

It's not so much that the bigger aperture collects more light, but that extra light collected supports the 33% larger image scale at given exit pupil. For the observation of object structure, image scale is the primary consideration, and the larger aperture provides higher surface brightness at any particular magnification.

Unlike bright object observation, the dim fuzzies have your eye working at rather low resolving power. You need the extra light to afford every advantage in eaking out those subtle details you strive to see.


Post Extras: Print Post   Remind Me!   Notify Moderator  
killdabuddha
Pooh-Bah
*****

Reged: 08/26/11

Re: 12" versus 16" for galaxy structure new [Re: GlennLeDrew]
      #5665070 - 02/06/13 11:49 AM


Wow Glenn, you do have a way. Thanks for stating it so succinctly.


Post Extras: Print Post   Remind Me!   Notify Moderator  
Tony Flanders
Postmaster
*****

Reged: 05/18/06

Loc: Cambridge, MA, USA
Re: 12" versus 16" for galaxy structure new [Re: azure1961p]
      #5665119 - 02/06/13 12:17 PM

Quote:

I'm in the middle of choosing between a 12" or 16" reflector. I love dust lanes in galaxies and such but the 16" is twice the cost of the 12".




I must admit that I've never compared a 12-inch and a 16-inch side by side. But it seems to me that galaxies really start to open up in the 16- to 18-inch aperture class.

There are certainly plenty of galaxies that show a great deal of structure through a 12-inch scope. But the number of such galaxies really blossoms when you hit the next aperture bracket up.

It's sort of like globular clusters. An 8-inch resolves many of them, but also fails to resolve many. With a 12-inch, it's always a bit of a surprise when you find a globular cluster that doesn't show some degree of resolution.


Post Extras: Print Post   Remind Me!   Notify Moderator  
Ed D
Carpal Tunnel
*****

Reged: 04/30/10

Loc: Sunny South Florida
Re: 12" versus 16" for galaxy structure new [Re: Tony Flanders]
      #5666059 - 02/06/13 09:32 PM

Pete, for what you want to do the more aperture the better. So, it boils down to getting what you can afford, what you can lift and handle, and what fits in your vehicle. Also, keep in mind that you will probably want a good quality laser collimator, adding to the expenses if you don't already have one.

Also, Glenn hit the nail on the head about thinking in terms of exit pupil and image scale. An observing friend and I both find a 3mm exit pupil to hit the sweet spot for observing galaxies, if that helps.

Ed D


Post Extras: Print Post   Remind Me!   Notify Moderator  
azure1961p
Postmaster
*****

Reged: 01/17/09

Loc: USA
Re: 12" versus 16" for galaxy structure new [Re: Ed D]
      #5666151 - 02/06/13 10:21 PM

Thanks guys - a lot of wisdom there and its appreciated. I love long focus but I can't entertain even medium f/6 in 16" . I'm going to build the thing out of carbon fiber cloth and epoxy with some wood laminate.

Ill go with Agenas 16" .

Again, gratis.

Pete
Ps: short term goal is having spectrum put 98% reflectivity on my 8" for spring galaxies and such.


Post Extras: Print Post   Remind Me!   Notify Moderator  
jgraham
Postmaster
*****

Reged: 12/02/04

Loc: Miami Valley Astronomical Soci...
Re: 12" versus 16" for galaxy structure new [Re: azure1961p]
      #5667065 - 02/07/13 01:11 PM

I have two biggo scopes; a homebuilt 16.5" f/6.5 and a Lightbridge 16 which is f/4.5. While I dearly love my homebuilt monster, the shorter, lighter Lightbridge is a joy to use. I made the jump from a homebuilt 10" f/6.7 to my homebuilt 16.5" and when you get up into the 16" range the sky just starts to open up. Having said that, there's no substitute for dark, transparent skies. To this day the best galaxy observing that I've ever done was with a homebuilt 6" f/4.5 from a very, very dark site (35 years ago from Cades Cove in the Great Smoky Mountains National Park). Alas, these days I do all of my observing from my red zone back yard. A bonus for me with the larger scopes is that they give you enough light that filters start to become effective.

Post Extras: Print Post   Remind Me!   Notify Moderator  
k9yr
super member
*****

Reged: 05/21/08

Loc: Far North suburbs of Chicago
Re: 12" versus 16" for galaxy structure new [Re: jgraham]
      #5668059 - 02/07/13 11:03 PM

I have a 13" and built a 16" 2 years ago. The best thing I can say is the 16" has wow factor on basically everything. I took the 16" to dark skies in MN last year and M51 spooked me out. Go with a 16" and a gym membership

Post Extras: Print Post   Remind Me!   Notify Moderator  
Jeff Morgan
Postmaster
*****

Reged: 09/28/03

Loc: Prescott, AZ
Re: 12" versus 16" for galaxy structure new [Re: GlennLeDrew]
      #5668137 - 02/07/13 11:49 PM

Quote:

It's not so much that the bigger aperture collects more light, but that extra light collected supports the 33% larger image scale at given exit pupil. For the observation of object structure, image scale is the primary consideration, and the larger aperture provides higher surface brightness at any particular magnification.

Unlike bright object observation, the dim fuzzies have your eye working at rather low resolving power. You need the extra light to afford every advantage in eaking out those subtle details you strive to see.




Yep, my reasoning in moving from a 12.5" to a 16".

With the 12.5 I felt that most galaxies didn't have much to offer, I was just checking off items from a list. Of course given the vast number of faint galaxies, that might be nearly as true with the 16!

Another big improvement for me in moving up in aperture is the addition of tracking. Based on past experience I suspect this will be as big a jump in performance as the added aperture.


Post Extras: Print Post   Remind Me!   Notify Moderator  
azure1961p
Postmaster
*****

Reged: 01/17/09

Loc: USA
Re: 12" versus 16" for galaxy structure new [Re: Jeff Morgan]
      #5668608 - 02/08/13 09:44 AM

Thanks for the input.

I'm going with the 16. I've got a lot of fiberglass/composite experience so Ill make the whole thing out of carbon fiber with aluminum or steel where needed. I m looking at Kriegs ultralight dobs as the way to go. I want the lines as clean and low profile as possible for ease of transport and storage. It's going to have a minimilast thing about it. I was going to buy the optics first THEN build it but ill probably do it the other way around

Has anyone got dob parts suppliers for truss tubes, mirror cell, etc. I'm going with Novak for the diagonal.

Jgraham, ill bet that longer focus 16 is a beaut but alas the size of it all. I'm 51 and back in the day when I was 30 or younger I had distant dreams of a 16" reflector at f/7 and the glorious climb up the ladder to contrasts views bare none. That was then lol. Now even the short step ladder for my 8" f/9 is about all I want to bother with. I've gotta believe though the big 16 turns out some spectacular sights given great seeing.

Normally I'm skittish about an f/4 or f/5 system as I never liked my ten, but here's no other way for me to comfortably use 16" in anything longer and it'd be a custom pricey order so the overwhelming light gathering advantage is swamping my resistance on several points.

It'd be great to see eyes in the owl, dust lane on 891, even some obscure galaxies coughing up do e goodies now and again.


I question how good a figure Agena can turn out on a 16" glass. That's a chin rubbing factor I'm not settled on.

Probably start building at the end of feb.

Pete

Edited by azure1961p (02/08/13 09:45 AM)


Post Extras: Print Post   Remind Me!   Notify Moderator  
Doug Culbertson
Post Laureate
*****

Reged: 01/06/05

Re: 12" versus 16" for galaxy structure new [Re: GlennLeDrew]
      #5668835 - 02/08/13 11:54 AM

Quote:

It's not so much that the bigger aperture collects more light, but that extra light collected supports the 33% larger image scale at given exit pupil. For the observation of object structure, image scale is the primary consideration, and the larger aperture provides higher surface brightness at any particular magnification.

Unlike bright object observation, the dim fuzzies have your eye working at rather low resolving power. You need the extra light to afford every advantage in eaking out those subtle details you strive to see.




I just thought that this needed saying again. Thanks for putting it in such a succinct manner.


Post Extras: Print Post   Remind Me!   Notify Moderator  
deepskydarrell
member


Reged: 03/09/08

Loc: Abbotsford, BC Canada
Re: 12" versus 16" for galaxy structure new [Re: azure1961p]
      #5668901 - 02/08/13 12:23 PM

Quote:



Jgraham, ill bet that longer focus 16 is a beaut but alas the size of it all. I'm 51 and back in the day when I was 30 or younger I had distant dreams of a 16" reflector at f/7 and the glorious climb up the ladder to contrasts views bare none. That was then lol. Now even the short step ladder for my 8" f/9 is about all I want to bother with. I've gotta believe though the big 16 turns out some spectacular sights given great seeing.

Pete




Consider one thing before you write off a longer 16" -- An orchard ladder. I use a six foot, three legged, aluminum with a flared base. It grabs onto any uneven terrain and is the most solid, stable thing I've ever climbed. It cost under $100, is excedingly light but very solid and if it didn't fit in my vehicle it rode the bike rack on the back.

I'm 58 and can understand the age concern, but I hope I'm climbing those two or three wide steps for many years to come.

And the 2.6 inch secondary gives excellent contrast.

All the best on your building endeavour.

DSD.


Post Extras: Print Post   Remind Me!   Notify Moderator  
GlennLeDrew
Postmaster
*****

Reged: 06/18/08

Loc: Ottawa, Ontario, Canada
Re: 12" versus 16" for galaxy structure new [Re: deepskydarrell]
      #5669112 - 02/08/13 01:52 PM

If the emphasis is on the observation of dimmer, low contrast, extended objects, a short f/ratio system is no impediment. The larger secondary will impart absolutely no detectable reduction in image contrast on galaxies and nebulae. Sure, the planets and crowded globular cluster cores will suffer some degradation, but in the regime of the faint, our eyes' resolving power is *very* much the weak link.

With this knowledge in mind, a squat system which keeps one's feet always on the ground is entirely justified. That's what I'd do. Indeed, an f/3 system is not at all off-putting, if it keeps me Earthbound.


Post Extras: Print Post   Remind Me!   Notify Moderator  
Dave MitskyModerator
Postmaster
*****

Reged: 04/08/02

Loc: PA, USA, Planet Earth
Re: 12" versus 16" for galaxy structure new [Re: GlennLeDrew]
      #5669149 - 02/08/13 02:09 PM

I've used a couple of the new f/3.3 and f/3.6 Dobs and the views were excellent. That includes the planetary views. Being able to stand with two feet on the ground while looking through a 22" Newtonian is wonderful.

Dave Mitsky


Post Extras: Print Post   Remind Me!   Notify Moderator  
Jeff Morgan
Postmaster
*****

Reged: 09/28/03

Loc: Prescott, AZ
Re: 12" versus 16" for galaxy structure new [Re: azure1961p]
      #5669788 - 02/08/13 09:16 PM Attachment (23 downloads)

Quote:

Has anyone got dob parts suppliers for truss tubes, mirror cell, etc. I'm going with Novak for the diagonal.

Jgraham, ill bet that longer focus 16 is a beaut but alas the size of it all. I'm 51 and back in the day when I was 30 or younger I had distant dreams of a 16" reflector at f/7 and the glorious climb up the ladder to contrasts views bare none. That was then lol. Now even the short step ladder for my 8" f/9 is about all I want to bother with. I've gotta believe though the big 16 turns out some spectacular sights given great seeing.




Look at Aurora Precision for a mirror cell. I really like the design and construction on mine. Which BTW is a 16" f/7, Zambuto mirror. Here is a photo after daylight testing of the ServoCAT. Looking forward to First Light, weather is conspiring against me currently.


Post Extras: Print Post   Remind Me!   Notify Moderator  
Jeff Morgan
Postmaster
*****

Reged: 09/28/03

Loc: Prescott, AZ
Re: 12" versus 16" for galaxy structure new [Re: deepskydarrell]
      #5669793 - 02/08/13 09:21 PM Attachment (16 downloads)

Quote:

Consider one thing before you write off a longer 16" -- An orchard ladder. I use a six foot, three legged, aluminum with a flared base. It grabs onto any uneven terrain and is the most solid, stable thing I've ever climbed. It cost under $100, is excedingly light but very solid and if it didn't fit in my vehicle it rode the bike rack on the back.




For mine I'm going to use a rolling platform ladder. It has siderails, a large top platform, and it folds. It is surprisingly easy to handle, balances very nicely on the large wheels. Even on a reasonably uneven surface (that being, one level enough to set up a scope) there is zero - zero chance of a topple.


Post Extras: Print Post   Remind Me!   Notify Moderator  
Jeff Morgan
Postmaster
*****

Reged: 09/28/03

Loc: Prescott, AZ
Re: 12" versus 16" for galaxy structure new [Re: Jeff Morgan]
      #5669795 - 02/08/13 09:23 PM Attachment (37 downloads)

This is what it looks like next to the scope. Suitable for scopes up to about 120" of focal length. And they make bigger - much bigger - models.

Post Extras: Print Post   Remind Me!   Notify Moderator  
azure1961p
Postmaster
*****

Reged: 01/17/09

Loc: USA
Re: 12" versus 16" for galaxy structure new [Re: Jeff Morgan]
      #5669812 - 02/08/13 09:37 PM

Wow you fellas have some phenomenal sixteens - and a Zambuto!!! Yeah your going to have heavy cloud cover for six weeks.

It's interesting how there's both extremes here - the testimonials of fine f/3 and the proponents of the long focus designs. It is amazing too that with super huge aperture that despite the fast focal ratio the secondary can remain startelingly small .

I appreciate the points made in that with the eyes resolution of dim images the contrast boost of a small secondary is not realized . I think in stars it would be but not on objects like the Veil.

To keep costs down Im not going with a custom focal ratio but I understand the points made - and the agricultural ladder was well taken.

Thanks guys.

Pete


Post Extras: Print Post   Remind Me!   Notify Moderator  
azure1961p
Postmaster
*****

Reged: 01/17/09

Loc: USA
Re: 12" versus 16" for galaxy structure new [Re: azure1961p]
      #5669815 - 02/08/13 09:39 PM

Jeff,

That's amazing. You've got the whole thing worked out and in style. That is going to be a phenomenal performer. Please post your experiences. Even 5" planetaries are going to show well in that.

Pete


Post Extras: Print Post   Remind Me!   Notify Moderator  
IVM
scholastic sledgehammer


Reged: 01/07/08

Loc: Western New York
Re: 12" versus 16" for galaxy structure new [Re: Jeff Morgan]
      #5670952 - 02/09/13 03:57 PM

A real Serrurier, wow.

Post Extras: Print Post   Remind Me!   Notify Moderator  
Jeff Morgan
Postmaster
*****

Reged: 09/28/03

Loc: Prescott, AZ
Re: 12" versus 16" for galaxy structure new [Re: GlennLeDrew]
      #5672091 - 02/10/13 10:19 AM

So a question to current 16 owners from a new 16 owner:

When hunting down "the faint ones" how close do you go to the theoretical limit for the aperture?

I realize this will be dependent on weather, dark site quality, and a few other things, but on a "typical" night from your best site was what I was thinking.

The reason for the question is that I am using Astroplanner to generate observing plans (by constellation) for SkySafari and there are a couple of issues here:

1) Sheer mass. Going from magnitude 14 to 15 (the limit of SkySafari Plus) about doubles the number of galaxies. Should I upgrade to Pro and go down an extra 0.7 magnitudes I would expect a similar increase, and;

2) Catalog issues. I was seeing some "drop out" of list targets when going from Astroplanner to SkySafari. Bill at Southern Stars was right on top of it, and said the source data can have some conflicts depending upon the measurements were done in. The difference could be a couple of full magnitudes in cases.

So my concern was that pressing to the theoretical limit could end up in a lot of time wasted chasing ghosts, and I'm curious what the experienced Galaxy Hounds do about it.

Or perhaps I should set the limit at 14.0 and marvel at how bright they all look and how many show detail?


Post Extras: Print Post   Remind Me!   Notify Moderator  
azure1961p
Postmaster
*****

Reged: 01/17/09

Loc: USA
Re: 12" versus 16" for galaxy structure new [Re: Jeff Morgan]
      #5672117 - 02/10/13 10:44 AM

In my 8" the faintest galaxies I could see with standard coatings was 13.5 under 6.2v sky's and stellar limit of 15. Moving to 16 I would think should add at least a full magnitude onto that and maybe 1.5v extra? I would also think the galaxies extended surface brightness would have a bigger improvement than the stellar. Seeing where I am is lousy often and the 8" with small CO produces some fine tight stars that larger apertures and COs tend to bloat and soften. Great seeing is another matter.

Ok that's my view from 8" anyway.

Pete


Post Extras: Print Post   Remind Me!   Notify Moderator  
Madratter
Post Laureate


Reged: 01/14/13

Re: 12" versus 16" for galaxy structure new [Re: Jeff Morgan]
      #5672601 - 02/10/13 04:03 PM

Quote:


Or perhaps I should set the limit at 14.0 and marvel at how bright they all look and how many show detail?




I have a 20". The dimmest galaxy I have bothered to hunt down was listed at 16.0 (NGC 913). That was under good but not great skies (a little better than 6.0). I have bagged four others listed between 15-16. That said, a) I don't think the catalog values are all that accurate for visual work and b) personally, I don't go hunting for the really faint ones unless they are part of a group. They just aren't that interesting and there are plenty of brighter, more interesting ones that I still haven't seen.


Post Extras: Print Post   Remind Me!   Notify Moderator  
faackanders2
Carpal Tunnel


Reged: 03/28/11

Re: 12" versus 16" for galaxy structure new [Re: Madratter]
      #5672774 - 02/10/13 05:57 PM

Quote:

Quote:


Or perhaps I should set the limit at 14.0 and marvel at how bright they all look and how many show detail?




I have a 20". The dimmest galaxy I have bothered to hunt down was listed at 16.0 (NGC 913). That was under good but not great skies (a little better than 6.0). I have bagged four others listed between 15-16. That said, a) I don't think the catalog values are all that accurate for visual work and b) personally, I don't go hunting for the really faint ones unless they are part of a group. They just aren't that interesting and there are plenty of brighter, more interesting ones that I still haven't seen.




+1


Post Extras: Print Post   Remind Me!   Notify Moderator  
IVM
scholastic sledgehammer


Reged: 01/07/08

Loc: Western New York
Re: 12" versus 16" for galaxy structure new [Re: Jeff Morgan]
      #5672984 - 02/10/13 08:17 PM

This is not exactly galaxy structure anymore but it seems that the original poster does not object, so... As far as deliberately going after faint galaxies, I usually stick to those plotted in Uranometria. This means to visual mag. 15.0 (that's what Uranometria says) and photographic just under 16 (my guess/generalization). The real limit (hitting the 0 probability of detection) for me with the 16" seems to be another half-magnitude fainter at around 16.5, although freaky exceptions even with normal morphology may go beyond 17.0 and still be visible. I don't mind wasting time

EDIT: I meant to say that my probability of detection at photographic mag. 16.0 is 50/50, and it is better than 50/50 for these faint, non-NGC galaxies in Uranometria that seem to concentrate in the photographic 15.5-16.0 range. Around photographic 15.5 the probability tends to 100% with my 16".

Edited by IVM (02/10/13 09:15 PM)


Post Extras: Print Post   Remind Me!   Notify Moderator  
george golitzin
Carpal Tunnel
*****

Reged: 02/24/06

Re: 12" versus 16" for galaxy structure new [Re: Jeff Morgan]
      #5673172 - 02/10/13 10:09 PM

The dimmest galaxies I found in a 16-inch were between mag 15.5 and 16, in the Corona Cluster--that was definitely pushing the envelope for that aperture. Like Madratter, I don't hunt these down unless part of a galaxy cluster: it's a particular sort of game.

You bring up a topic of interest with regards to charting. Once you step up to 16 or 18 inches, ordinary charts cannot really go deep enough for certain situations--Uranometria only goes so far (although it does contain deeper maps of specific regions), and so one must pick and choose magnitude limits for specific targets: one size no longer fits all. Last night I had several different charts with very different parameters--the deepest was the Perseus cluster, where I was able to identify 36 galaxies within a 1-degree field. For that chart I put no effective mag limit. For wider maps, that's usually not possible.

-geo


Post Extras: Print Post   Remind Me!   Notify Moderator  
HellsKitchen
Pooh-Bah


Reged: 09/05/08

Loc: Melbourne Australia
Re: 12" versus 16" for galaxy structure new [Re: george golitzin]
      #5673209 - 02/10/13 10:32 PM

I have a 12" Zambuto and where I live in the outer suburbs of a large metro area, the faintest galaxies I can detect are about V mag 14. The faintest stellar object I've seen is the Quasar HE 1015-1618 in Hydra which NED lists as V mag 15.7. My NELM is approx 5.5, I would say that at mag 13.5 for galaxies and mag 15 for stellar is where things start to get challenging.

Post Extras: Print Post   Remind Me!   Notify Moderator  
Jeff Morgan
Postmaster
*****

Reged: 09/28/03

Loc: Prescott, AZ
Re: 12" versus 16" for galaxy structure new [Re: azure1961p]
      #5673341 - 02/11/13 12:07 AM

Quote:

In my 8" the faintest galaxies I could see with standard coatings was 13.5 under 6.2v sky's and stellar limit of 15. Moving to 16 I would think should add at least a full magnitude onto that and maybe 1.5v extra? I would also think the galaxies extended surface brightness would have a bigger improvement than the stellar. Seeing where I am is lousy often and the 8" with small CO produces some fine tight stars that larger apertures and COs tend to bloat and soften. Great seeing is another matter.

Ok that's my view from 8" anyway.

Pete




The 15.7 magnitude value is what Astroplanner thinks the limit is on a 16" when you define your scope.

SkySafari Plus goes down to 15.0 so drops list components fainter. I'll probably be upgrading to Pro (which goes much fainter) when observing season gets rolling.

And it doesn't always seem to work "by the numbers". I've caught IC4617 near M13 with my 12.5" Royce - from the backyard no less! SkySafari lists it at magnitude 15.17, where Astroplanner doesn't provide a magnitude at all. I have yet to repeat that observation.

It should be interesting to track success rate vs. magnitude, but after awhile I could see myself putting a brighter limit on searches.


Post Extras: Print Post   Remind Me!   Notify Moderator  
Ed D
Carpal Tunnel
*****

Reged: 04/30/10

Loc: Sunny South Florida
Re: 12" versus 16" for galaxy structure new [Re: azure1961p]
      #5673728 - 02/11/13 10:02 AM Attachment (22 downloads)

Quote:

Jgraham, ill bet that longer focus 16 is a beaut but alas the size of it all. I'm 51 and back in the day when I was 30 or younger I had distant dreams of a 16" reflector at f/7 and the glorious climb up the ladder to contrasts views bare none. That was then lol. Now even the short step ladder for my 8" f/9 is about all I want to bother with. I've gotta believe though the big 16 turns out some spectacular sights given great seeing.

Normally I'm skittish about an f/4 or f/5 system as I never liked my ten, but here's no other way for me to comfortably use 16" in anything longer and it'd be a custom pricey order so the overwhelming light gathering advantage is swamping my resistance on several points.

Pete




Pete, I attached a picture of my friend's truss Dob he made using a 16" f/4.5 LightBridge mirror he picked up used for $150, not pristine or like new, but it does give great views. As you can see it's not all that tall, requiring using the first step of a folding step ladder only around zenith. He made it using the Kriege and Berry design. BTW, the mirror box weighs 50#.

Ed D


Post Extras: Print Post   Remind Me!   Notify Moderator  
IVM
scholastic sledgehammer


Reged: 01/07/08

Loc: Western New York
Re: 12" versus 16" for galaxy structure new [Re: Ed D]
      #5674153 - 02/11/13 02:25 PM

I like how this 16" was apparently delivered to the site in the two-door car...

Post Extras: Print Post   Remind Me!   Notify Moderator  
Ed D
Carpal Tunnel
*****

Reged: 04/30/10

Loc: Sunny South Florida
Re: 12" versus 16" for galaxy structure new [Re: IVM]
      #5674931 - 02/11/13 10:37 PM

Didn't even occur to me to point it out, but that is the car it rode in. It breaks down very compactly and leaves enough room for all the other stuff. We each bring our own cars loaded with our scopes and other gear. The big Dob is actually easier to transport than my other friend's 8" GEM mounted Newt seen in the pic.

Ed D

Edited by Ed D (02/11/13 10:43 PM)


Post Extras: Print Post   Remind Me!   Notify Moderator  
ThreeD
Pooh-Bah


Reged: 12/23/08

Loc: Sacramento suburbs
Re: 12" versus 16" for galaxy structure new [Re: IVM]
      #5675016 - 02/11/13 11:55 PM

Quote:

I like how this 16" was apparently delivered to the site in the two-door car...


Since I built a new base for my LB16 easily fits in my Prius. I'm still using the original OTA too and that bottom tube is tall. Lots of room left in the car too...

Post Extras: Print Post   Remind Me!   Notify Moderator  
Mta472
super member


Reged: 02/28/06

Loc: CT
Re: 12" versus 16" for galaxy structure new [Re: azure1961p]
      #5677133 - 02/13/13 07:35 AM

If you do not live in a dark zone, IMHO you would be throwing money away on a 16 inch vs a 12 inch because of light pollution. I live in CT and went from an 8 to 12 inch and it did NOT make much difference.

Post Extras: Print Post   Remind Me!   Notify Moderator  
Starman81
Carpal Tunnel
*****

Reged: 03/06/08

Loc: Metro Detroit, MI, USA
Re: 12" versus 16" for galaxy structure new [Re: Mta472]
      #5678078 - 02/13/13 05:49 PM

Quote:

If you do not live in a dark zone, IMHO you would be throwing money away on a 16 inch vs a 12 inch because of light pollution. I live in CT and went from an 8 to 12 inch and it did NOT make much difference.




Really? I would like to hear more about that since I do plan on going to 12" of aperture at some point...

Also, what's with people with big dobs always having smaller cars? It is a trend that I've noticed. It's like the challenge of hauling around a big dob wasn't enough so you want to try to do it with smaller and smaller cars to add to the accomplishment.


Post Extras: Print Post   Remind Me!   Notify Moderator  
GlennLeDrew
Postmaster
*****

Reged: 06/18/08

Loc: Ottawa, Ontario, Canada
Re: 12" versus 16" for galaxy structure new [Re: Mta472]
      #5678080 - 02/13/13 05:50 PM

It doesn't matter the degree of light pollution, the same benefits from an aperture increase accrue as they do under dark skies. If an object is seen in a smaller scope, more detail will be seen with a bigger scope. The brighter sky merely restricts to objects having higher surface brightness. Of course, beyond some amount of sky glow, practically nothing but the brightest central cores of galaxies is to be seen, with a concomitant dearth of interesting structure to be observed anywhere.

Post Extras: Print Post   Remind Me!   Notify Moderator  
azure1961p
Postmaster
*****

Reged: 01/17/09

Loc: USA
Re: 12" versus 16" for galaxy structure new [Re: GlennLeDrew]
      #5678491 - 02/13/13 10:27 PM

+100 on what Glenn just said. Contrast thresholds don't take a holiday with poor sky's. a poor sky will never look pretty but everything else is the same in terms of resolving power which works on a number of levels. The laws of light are the same - city or country.

Pete


Post Extras: Print Post   Remind Me!   Notify Moderator  
deepskydarrell
member


Reged: 03/09/08

Loc: Abbotsford, BC Canada
Re: 12" versus 16" for galaxy structure new [Re: azure1961p]
      #5678757 - 02/14/13 04:07 AM

Am I wrong, I've always equated a city view thru my 16.5 as about the same as a 4 inch in the dark? Perhaps that's too simplistic.

As for the larger the aperture the smaller the vehicle, the tendency may be the larger the aperture the farther one drives to the dark therefore the better fuel economy needed?

DSD.


Post Extras: Print Post   Remind Me!   Notify Moderator  
deepskydarrell
member


Reged: 03/09/08

Loc: Abbotsford, BC Canada
Re: 12" versus 16" for galaxy structure *DELETED* new [Re: azure1961p]
      #5678758 - 02/14/13 04:07 AM

Post deleted by deepskydarrell

Post Extras: Print Post   Remind Me!   Notify Moderator  
drbyyz
sage
**

Reged: 11/04/12

Re: 12" versus 16" for galaxy structure new [Re: deepskydarrell]
      #5679089 - 02/14/13 10:14 AM

Quote:

Am I wrong, I've always equated a city view thru my 16.5 as about the same as a 4 inch in the dark? Perhaps that's too simplistic.




I think a touch simplistic. Plus it really depends on what you mean by "city." My city sky is a Bortle 4/5, while someone else's may be a 9. Same with "dark" sky, mine is a 3, but others may have a 1.


Post Extras: Print Post   Remind Me!   Notify Moderator  
Tony Flanders
Postmaster
*****

Reged: 05/18/06

Loc: Cambridge, MA, USA
Re: 12" versus 16" for galaxy structure new [Re: deepskydarrell]
      #5679109 - 02/14/13 10:24 AM

Quote:

Am I wrong, I've always equated a city view thru my 16.5 as about the same as a 4 inch in the dark?




That doesn't make sense to me. It seems to me that there are many things that will show far better through your 16.5-inch scope in the city than through a 4-inch scope in pristine skies. These are objects that are small but bright -- most obviously planets, but also many planetary nebulae and tight double stars.

Conversely, there are many things that will show far better in the 4-inch scope under dark skies than in any scope, no matter how big, in city skies. These include essentially all galaxies and diffuse nebulae.

The only place where aperture and sky brightness are even close to interchangeable is in the ability to see faint stars. But here, it seems to me that the 16.5-inch should show considerably fainter stars in the city than the 4-inch does under dark skies.


Post Extras: Print Post   Remind Me!   Notify Moderator  
Achernar
Postmaster
*****

Reged: 02/25/06

Loc: Mobile, Alabama, USA
Re: 12" versus 16" for galaxy structure new [Re: Starman81]
      #5679166 - 02/14/13 10:55 AM

Might be due to the cost of gasoline, and the fact bigger vehicles cost more to own in general. Still, it's really cool to be able to build a large Dob that will fit in many cars. I can get my 15-inch into my car, and still take along a passenger.

For every time I do take the 15-inch to a darker site, I use it at least several times at home despite the heavy light pollution. With digital setting circles and nebula filters, a lot of enjoyable observing can be done from a city at home. I have observed quite a good many galaxies from my driveway, even quite dim galaxies. Whether or not one is in a city or a dark site, a larger telescope always shows more than a smaller one at the same site.

Taras


Post Extras: Print Post   Remind Me!   Notify Moderator  
JohnH
Carpal Tunnel
****

Reged: 10/04/05

Loc: Squamish BC Moved!!!!!
Re: 12" versus 16" for galaxy structure new [Re: deepskydarrell]
      #5679382 - 02/14/13 12:42 PM

The arguments for the step from a 12" to a 16" class follows good principles.

My current project is a 12 1/2" Dobsonian, which is a fair step up from my former go to scope, an 8" Maksutov. I want get some practice at a build while keeping weight under 60 lbs.

I chose this size as it meant about doubling the effective light gathered, which is roughly how much improvement is easily visible.

I was thinking that was where I would end telescope making,if it werent for a run in with a number of shorter, well corrected bunch of scope in the 16 to 22 inch sizes at some star parties.

So now I added 5 12 inch, 4 16 inch and one 18.625 blanks as fodder for larger, faster scopes in the future

Two of the 16s are full thickness, and I plan to send them to Glassfab to turn them into four 1.6 inch blanks more suited to portable instruments.

Edited by JohnH (02/14/13 12:59 PM)


Post Extras: Print Post   Remind Me!   Notify Moderator  
Ed D
Carpal Tunnel
*****

Reged: 04/30/10

Loc: Sunny South Florida
Re: 12" versus 16" for galaxy structure new [Re: Starman81]
      #5680163 - 02/14/13 08:25 PM

Quote:

Also, what's with people with big dobs always having smaller cars? It is a trend that I've noticed. It's like the challenge of hauling around a big dob wasn't enough so you want to try to do it with smaller and smaller cars to add to the accomplishment.




I don't think it's an astronomy trend or challenge as much as it is an overall social trend having to do with constantly fluctuating and elevating gas prices. While I miss my pickup truck I sure don't miss the all too frequent and expensive stops at the gas pumps.

Ed D


Post Extras: Print Post   Remind Me!   Notify Moderator  
azure1961p
Postmaster
*****

Reged: 01/17/09

Loc: USA
Re: 12" versus 16" for galaxy structure new [Re: Tony Flanders]
      #5680453 - 02/14/13 11:56 PM

Tony you mean the 16.5" on virtually all galaxies and nebula? If not Id be interested in your take.

Thanks,

Pete


Post Extras: Print Post   Remind Me!   Notify Moderator  
Pages: 1 | 2 | 3 | (show all)


Extra information
3 registered and 7 anonymous users are browsing this forum.

Moderator:  Dave Mitsky, Phillip Creed, okieav8r 

Print Thread

Forum Permissions
      You cannot start new topics
      You cannot reply to topics
      HTML is disabled
      UBBCode is enabled


Thread views: 2674

Jump to

CN Forums Home


Cloudy Nights LLC
Cloudy Nights Sponsor: Astronomics