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

General Astronomy >> Beginners Forum

Pages: 1 | 2 | 3 | 4 | (show all)
lamplight
Carpal Tunnel
*****

Reged: 09/18/12

Loc: western MA, U.S.
Hypothetical 4" budget APO choices.. WWJD?
      #5641698 - 01/24/13 10:59 PM

Vixen ED 100mm sf w portamount $1000
Meade 102mm ED APO $1000 used
Skywatcher pro SW ed 100mm about $750ish new

I like the 4" range for size and visual use, don't want to go bigger.. But I don't also want to go smaller... Might do a 90mm if there's some good value in a certain scope..

Pros and cons? Why are the skywatchers SO much cheaper than other APOs? (Other than looks ) Do they suck horribly? Are others in this price range less than great as well? I'm leaning towards the vixen, decent reviews, brand resell value.. I guess Meade would have that too. although I don't need the portamount it mount it might prove useful.

Find myself browsing refractors and while im happy with the xlt I would like an apo at some point so just .. You know.. Kicking the tires. Thanks!


Post Extras: Print Post   Remind Me!   Notify Moderator  
Jon Isaacs
Postmaster
*****

Reged: 06/16/04

Loc: San Diego and Boulevard, CA
Re: Hypothetical 4" budget APO choices.. WWJD? new [Re: lamplight]
      #5641986 - 01/25/13 06:35 AM

Quote:


Pros and cons? Why are the skywatchers SO much cheaper than other APOs?




Skywatchers are good, bascially the same scope as the Orion ED-100, sometimes one sees these on astromart for $400. It's your standard Synta FPL-53 F/9 Doublet.

Both the Meade and the ED-100 look over priced to me.

Jon


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

Reged: 09/18/12

Loc: western MA, U.S.
Re: Hypothetical 4" budget APO choices.. WWJD? new [Re: Jon Isaacs]
      #5642018 - 01/25/13 07:13 AM

Thanks Jon just looking but noted. Will keep eyes peeled and keep reading

Post Extras: Print Post   Remind Me!   Notify Moderator  
Jon Isaacs
Postmaster
*****

Reged: 06/16/04

Loc: San Diego and Boulevard, CA
Re: Hypothetical 4" budget APO choices.. WWJD? new [Re: lamplight]
      #5642069 - 01/25/13 08:10 AM

Quote:

Thanks Jon just looking but noted. Will keep eyes peeled and keep reading




There is a lot to know about refractors and apo's in particular. In my mind, the Synta 100EDs such as the Skywatcher represent an incredible value. Good optics, good color correction, reasonable mechanical components, nice scopes. At F/9 these scopes are 36 inches long, they are not so handy, definitely not a bird watching scope.

So then the search begins... maybe the ultimate in quality is the search. But often it's a shorter focal length, a sliding dewshield, these start bringing the 4 inch apo closer to being an overgrown 80mm... F/7 is pretty nice. The scopes are there, the 102EDs... like the Lunt and the StellarVue.

But the color correction suffers... so that means a triplet, eventually an FPL-53 triplet... So now were are at about $2000 and rising. Nice scopes, reasonably compact, excellent color correction, good quality mechanicals, a nice wide field of view, 3.5 degrees maybe.

A final step is dealing with the field curvature. Refractors have a curved field of view. The lowest magnifications, widest fields of view, the stars at the edge of the field are slightly out of focus when the stars in the center of the field are in focus. Photographically this is a problem, refractors require the use of a field flattener for this reason.

Visually, it's not a big problem but if one wants to spend even more money... There's the TeleVue NP-101 and Takahashi 106 FSQ. These are both 4 element apo-refractors with a two element rear section that acts as both a focal reducer, field flattener. The Takahashi is designed with astrophotography in mind and is capable of imaging a 10 degree field of view. The TeleVue is more aimed at the visual market place and with a 31mm Nagler provides an essentially perfect 4.5 degree field of view.

For most objects, the difference in the view between a TeleVue NP-101 and a SkyWatcher ED-100 is small. In some ways you don't get a lot for your extra $3000.

Jon


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

Reged: 05/10/10

Loc: Oklahoma City, OK
Re: Hypothetical 4" budget APO choices.. WWJD? new [Re: Jon Isaacs]
      #5642111 - 01/25/13 08:45 AM

Might also look at the TMB 92 series . . . very nice optics and solid build.

Post Extras: Print Post   Remind Me!   Notify Moderator  
howard929
Member
*****

Reged: 01/02/11

Loc: Low End of High Ground
Re: Hypothetical 4" budget APO choices.. WWJD? new [Re: Jon Isaacs]
      #5642116 - 01/25/13 08:47 AM

Quote:


For most objects, the difference in the view between a TeleVue NP-101 and a SkyWatcher ED-100 is small. In some ways you don't get a lot for your extra $3000.

Jon




Tsk. Tsk. True planetary observations are better left to those who are talented enough to buy the VERY best equipment. Any, even a slight deviation from the true path of excellence is left to those poor unwitting souls who are satisfied to (nose very high in the air here) settle for anything less.

I'm joking of course but I have read threads like that here on the forum. Crying out loud, they make it seem like Mount Rushmore would crumble into dust if they deviation from that path. And the dog would just explode.

Jon, good stuff there (as always). Really. Write a book.


Post Extras: Print Post   Remind Me!   Notify Moderator  
Fogboundturtle
professor emeritus


Reged: 05/20/09

Loc: Burnaby, BC
Re: Hypothetical 4" budget APO choices.. WWJD? new [Re: howard929]
      #5642377 - 01/25/13 11:26 AM

the Skywatcher is the best bang for the buck. I have the 80mm version and it been working great for me as visual and guiding scope.

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

Reged: 07/14/12

Loc: Banana Republic of California
Re: Hypothetical 4" budget APO choices.. WWJD? new [Re: lamplight]
      #5642496 - 01/25/13 12:34 PM

Quote:

...

Pros and cons? Why are the skywatchers SO much cheaper than other APOs?




The question about the Sky-Watcher might be, why are the others so expensive? Indeed, why? I've seen numerous posts here on CN, guys who've sold their TV 102s (or at least have both) and kept the Sky-Watcher ED100 because it's simply that good for the money! I'm impressed. Sky-Watcher would be my choice for sure for an ED of that f ratio.


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


Reged: 07/15/12

Loc: SE Ma.
Re: Hypothetical 4" budget APO choices.. WWJD? new [Re: Paco_Grande]
      #5642511 - 01/25/13 12:43 PM

lol Matt you gonna buy another scope..lol

Post Extras: Print Post   Remind Me!   Notify Moderator  
Fogboundturtle
professor emeritus


Reged: 05/20/09

Loc: Burnaby, BC
Re: Hypothetical 4" budget APO choices.. WWJD? new [Re: Paco_Grande]
      #5642528 - 01/25/13 12:54 PM

Quote:

Quote:

...

Pros and cons? Why are the skywatchers SO much cheaper than other APOs?




The question about the Sky-Watcher might be, why are the others so expensive? Indeed, why? I've seen numerous posts here on CN, guys who've sold their TV 102s (or at least have both) and kept the Sky-Watcher ED100 because it's simply that good for the money! I'm impressed. Sky-Watcher would be my choice for sure for an ED of that f ratio.




my only pet peeve and its really a minor thing, I found the 2 speed focuser to be not to my standard. That's because I have an very good focuser on my Meade Triplet. That's my only minor complaint about the Sky-Watcher. Its an easy fix too.


Post Extras: Print Post   Remind Me!   Notify Moderator  
JoLo
sage


Reged: 02/09/10

Loc: Highland, IL
Re: Hypothetical 4" budget APO choices.. WWJD? new [Re: Fogboundturtle]
      #5642595 - 01/25/13 01:28 PM

I luv my AT106 triplet but have a gripe similar to Mr. Turtle's above....the two speed focuser is good, but not great. When using barlows and an extension with my Imaging Source camera, I run into some slippage...with just my DSLR, no problems. I am going to replace the focuser and be a happy boy.

For less than 2K, I got the 106, the ATQ65, and a flattener for the 106. Both are excellent scopes, the 65 does triple duty as a guide scope, my primary birding scope, and a mighty fine wide field imager in its own right.

Joe


Post Extras: Print Post   Remind Me!   Notify Moderator  
csrlice12
Postmaster
*****

Reged: 05/22/12

Loc: Denver, CO
Re: Hypothetical 4" budget APO choices.. WWJD? new [Re: JoLo]
      #5642611 - 01/25/13 01:35 PM

J would take that 4" and reshape it into a large mirror............

Post Extras: Print Post   Remind Me!   Notify Moderator  
Jon Isaacs
Postmaster
*****

Reged: 06/16/04

Loc: San Diego and Boulevard, CA
Re: Hypothetical 4" budget APO choices.. WWJD? new [Re: Paco_Grande]
      #5642646 - 01/25/13 01:54 PM

Quote:

Quote:

...

Pros and cons? Why are the skywatchers SO much cheaper than other APOs?




The question about the Sky-Watcher might be, why are the others so expensive? Indeed, why? I've seen numerous posts here on CN, guys who've sold their TV 102s (or at least have both) and kept the Sky-Watcher ED100 because it's simply that good for the money! I'm impressed. Sky-Watcher would be my choice for sure for an ED of that f ratio.




If "that good for the money" is the deciding factor, then a good quality, less pricy scope will nearly always win. One can make the same argument for the 102mm F/10 achromat versus the Synta ED-100's. As one moves up the ladder the differences are smaller and smaller.

No doubt about it, the Synta ED-100s are an amazing value. When they hit the market 7 or 8 years ago, they were about $1000 and that was a bargain. Now, they have come down in price, it's a lot of scope for the money. Mechanically, they are sufficient, very similar to the Synta Achromts, nothing fancy. If a three foot long, 100mm F/9 refractor will serve you needs, then it's certainly a good place to start.

Myself, I am generally on the budget side of things not in this case. I worked my way up to a 4 inch as a step up from an 80mm. Short focal length, short scope, well suited for an alt-az mount... an 100mm apo with body of an ED-80.

The classic is the Astro-Physics Traveler. These are the original 4 inch F/6 triplet... They haven't been made for about 10 years, used ones go for around $5000. Sue French uses an Traveler for her column.

Jon


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

Reged: 05/18/06

Loc: Cambridge, MA, USA
Re: Hypothetical 4" budget APO choices.. WWJD? new [Re: Jon Isaacs]
      #5642659 - 01/25/13 02:02 PM

Quote:

I am generally on the budget side of things not in this case.




There's something to be said for that. One might argue that if you want a budget-priced refractor, why not buy a reflector? A 150-mm f/6 reflector would be roughly the same size and weight as a 100-mm f/9 refractor, considerably easier to mount, even more free from false color, and have much greater resolution and light-gathering.

At some level, perfection is the whole draw of refractors -- at least in the larger sizes.


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

Reged: 07/14/12

Loc: Banana Republic of California
Re: Hypothetical 4" budget APO choices.. WWJD? new [Re: Fogboundturtle]
      #5642702 - 01/25/13 02:25 PM

Quote:


my only pet peeve and its really a minor thing, I found the 2 speed focuser to be not to my standard.




I was going to mention that, but who knows? Each of us makes various trade-offs with our toys. I mean, the scope costs $750 and a Feathertouch costs half of that. But for a couple hundred a nice GSO might make sense.


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

Reged: 07/14/12

Loc: Banana Republic of California
Re: Hypothetical 4" budget APO choices.. WWJD? new [Re: Paco_Grande]
      #5642710 - 01/25/13 02:29 PM

BTW, I understand it's just not really fair to compare the SW and the TV, it's like comparing a Mini Cooper to a Porsche. It's simply the value quotient, and that usually changes for each of us over time. What was important becomes less important, or vice versa, etc..

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

Reged: 01/23/04

Loc: Sterling, VA
Re: Hypothetical 4" budget APO choices.. WWJD? new [Re: lamplight]
      #5642801 - 01/25/13 03:27 PM

I wasn't aware that Jerry was interested in astronomy.

Edited by panhard (01/26/13 09:02 PM)


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

Reged: 09/18/12

Loc: western MA, U.S.
Re: Hypothetical 4" budget APO choices.. WWJD? new [Re: bierbelly]
      #5642834 - 01/25/13 03:41 PM

I ask him all the deep questions (I am a fan)

Post Extras: Print Post   Remind Me!   Notify Moderator  
Jon Isaacs
Postmaster
*****

Reged: 06/16/04

Loc: San Diego and Boulevard, CA
Re: Hypothetical 4" budget APO choices.. WWJD? new [Re: Paco_Grande]
      #5642839 - 01/25/13 03:43 PM

Quote:

BTW, I understand it's just not really fair to compare the SW and the TV, it's like comparing a Mini Cooper to a Porsche. It's simply the value quotient, and that usually changes for each of us over time. What was important becomes less important, or vice versa, etc..




I think it is fair to compare a TeleVue 102 to the Skywatcher ED-100 They are both very similar scopes, the Televue has a focal length of 880mm, the Skywatcher 900mm. It is even fair to compare the Skywatcher ED-100 to the TeleVue NP-101 even though the NP-101 has a 540mm focal length with it's legendary flat field and total lack of chromatic aberration. I have made that comparison myself.

Comparisons are valuable because they provide information and understanding, awareness. There is a choice to made between a Skywatcher 100 and a TV NP 101... However, comparisons should be made without expectations...

Tony's point is an important one. Apo refractors are a pursuit of perfection. Without looking through a variety of scopes, looking at a variety of scopes, it's hard to understand what the differences are, what is the difference at the eyepiece between a $750 Skywatcher and a $4000 TeleVue?

The Skywatcher ED-100 is quite perfect. The TeleVue NP-101 is just about as perfect as we mortals will ever experience.

Jon

Edited by Jon Isaacs (01/25/13 03:58 PM)


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

Reged: 01/23/04

Loc: Sterling, VA
Re: Hypothetical 4" budget APO choices.. WWJD? new [Re: lamplight]
      #5642897 - 01/25/13 04:11 PM

Quote:

I ask him all the deep questions (I am a fan)




So do/am I...and I'm pretty sure I know what his answer would be...


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

Reged: 09/18/12

Loc: western MA, U.S.
Re: Hypothetical 4" budget APO choices.. WWJD? new [Re: lamplight]
      #5642921 - 01/25/13 04:26 PM

Well I bought a nice JMI focuser ona whim and then started thinking I should put this ona better scope.. So the comments on focuser upgrades are good news. I didn't realize there were such big differences even in APOs so ill get reading. I am just now understanding that the color correction needed varies from design to focal length and I d just assumed that all APOs had corrected color. Jerry would go for the purest view for sure. I'm wondering if its even worth it where I live as I've been using my achro a lot with the cold (easy to bring out) and I can't find a lot of the objects I have found with my SCT, so I just don't know. Now I see an sv102 for 700, and a vixen ed103s for 1500. See these used ones are going for about 75% of new, so while not a steal they're not breaking the bank. I did not intend this to be a teach me everything about APOs , this must get so boring for you guys.. Ill do my own research, but I do thank you for making me aware of some of the differences so I can go from there. I'm thinking at a used price it might be nice to just see side by side how one of these doublets compares to my achro.


So can I ask: in a more affordable doublet design, what kind of focal ratio should I be looking at in a 100mm 4" scope with the -least- chromatic aberration ? Nothing faster than say F/7 or is that pushing it? Is the question too oversimplified?

All the years combine.. They melt into a dream... - stellarvue, I mean Stella blue.


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

Reged: 09/18/12

Loc: western MA, U.S.
Re: Hypothetical 4" budget APO choices.. WWJD? new [Re: newtoskies]
      #5642928 - 01/25/13 04:29 PM

Quote:

lol Matt you gonna buy another scope..lol




Still have to pay the balance on my DOB when it is ready to ship so I have to, gasp, take it slow on this..


Post Extras: Print Post   Remind Me!   Notify Moderator  
Jon Isaacs
Postmaster
*****

Reged: 06/16/04

Loc: San Diego and Boulevard, CA
Re: Hypothetical 4" budget APO choices.. WWJD? new [Re: lamplight]
      #5642941 - 01/25/13 04:36 PM

Matt:

I suggest reading this review of the Astro-Tech 102ED, it's essentially the same scope as the StellarVue 102ED, the Orion 102ED Premium and the Lunt 102ED.

Astro-Tech 102ED

You might notice my able assistant, Monkulus who was pictured earlier this week viewing through a 125mm Cometron Jr.

Jon


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

Reged: 09/18/12

Loc: western MA, U.S.
Re: Hypothetical 4" budget APO choices.. WWJD? new [Re: lamplight]
      #5642942 - 01/25/13 04:36 PM

Maybe I need to rethink this . I have reflector and SCT for added light grasp. Only reasoni wanted to stay at 4" as that seemed the largest size that I wanted to deal with to get the most aperture. I just got a new book in to , the Messier objects, and was reading about M79 which I've been unable to detect other than as a faint star in the reflector. I'm sure part of that is the seeing as I haven't had anything good since the fall even on "clear " nights, but even so I'm sure I didn't have perfect conditions then and did not have trouble finding and viewing M79 with the SCT .

Maybe just an 80mm triplet for grab n go and occasional AP (NOT first priority!). But then extra aperture is always good right? Argh.


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

Reged: 07/14/12

Loc: Banana Republic of California
Re: Hypothetical 4" budget APO choices.. WWJD? new [Re: Jon Isaacs]
      #5643342 - 01/25/13 08:53 PM

Quote:



I think it is fair to compare a TeleVue 102 to the Skywatcher ED-100 They are both very similar scopes,




Well, yeah. Compare up to a point. I've owned both Mini Coopers and Porsches and can safely say the Mini is just as fun to drive, plus you don't have the worry of parking dings, nor the cost of repairs. That said, when it comes down to it, the lap times between a Mini and a Porsche don't provide any useful information to a prospective buyer. You also need to drive both to understand.

Edited by Paco_Grande (01/26/13 12:02 PM)


Post Extras: Print Post   Remind Me!   Notify Moderator  
Fogboundturtle
professor emeritus


Reged: 05/20/09

Loc: Burnaby, BC
Re: Hypothetical 4" budget APO choices.. WWJD? new [Re: bierbelly]
      #5643413 - 01/25/13 09:35 PM

Note to self : don't read the Beginner CN forum. Now I feel like I have to replace the focuser on my SW 80ED...grrrrr

Post Extras: Print Post   Remind Me!   Notify Moderator  
CJK
professor emeritus


Reged: 12/05/12

Loc: Northeast TN
Re: Hypothetical 4" budget APO choices.. WWJD? new [Re: Fogboundturtle]
      #5643800 - 01/26/13 04:51 AM Attachment (15 downloads)

Quote:

Note to self : don't read the Beginner CN forum. Now I feel like I have to replace the focuser on my SW 80ED...grrrrr






-- Chris


Post Extras: Print Post   Remind Me!   Notify Moderator  
0luke1
newbie


Reged: 12/15/12

Re: Hypothetical 4" budget APO choices.. WWJD? new [Re: CJK]
      #5643980 - 01/26/13 08:54 AM

I like to buy used gear and let someone else take the depreciation. I've never seen a hotter marketplace than this one. Good gear sells in hours. You may want to track the scopes you're interested in and see what sells the most quickly. May not mean it's the best equipment, but it will mean that, when you want to trade up, you can.

Btw, this is my first post after lurking for some time. This is a great forum and I've learned a great deal. Thank you.


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

Reged: 09/18/12

Loc: western MA, U.S.
Re: Hypothetical 4" budget APO choices.. WWJD? new [Re: Jon Isaacs]
      #5644044 - 01/26/13 09:46 AM

Good review monkey, thanks.. More is revealed. I was afraid i was seeing some CA on some stars.. Chris you meanie. Lol
Welcome lurker. Tonight should be clear so there will be more doubles to be split. I signed up on astromart so, yea.. Keeping eyes peeled . That review was perfect Jon


Post Extras: Print Post   Remind Me!   Notify Moderator  
dr.who
scholastic sledgehammer
*****

Reged: 01/05/12

Re: Hypothetical 4" budget APO choices.. WWJD? new [Re: lamplight]
      #5644866 - 01/26/13 06:29 PM

Afraid I have to beat my favorite drum here. While just shy of half again the price at $1,400 the new carbon fiber explore scientific is worth a look for what it comes with.

Post Extras: Print Post   Remind Me!   Notify Moderator  
Jon Isaacs
Postmaster
*****

Reged: 06/16/04

Loc: San Diego and Boulevard, CA
Re: Hypothetical 4" budget APO choices.. WWJD? new [Re: Paco_Grande]
      #5644963 - 01/26/13 07:26 PM

Quote:

Quote:



I think it is fair to compare a TeleVue 102 to the Skywatcher ED-100 They are both very similar scopes,




Well, yeah. Compare up to a point. I've owned both Mini Coopers and Porsches and can safely say the Mini is just as fun to drive, plus you don't have the worry of parking dings, nor the cost of repairs. That said, when it comes down to it, the lap times between a Mini and a Porsche don't provide any useful information to a prospective buyer. You also need to drive both to understand.




The mini-Cooper and the Porsche are not all a like, different displacement engines, different engine designs, different tires, different wheel bases, different weight distributions, different suspension systems.

By comparison, the Synta ED-100 and the TeleVue 102 are basically twins, they have the same aperture, the same focal length, both are doublets and both use the best quality ED glass available.

There is not going to be much difference at the eyepiece...

Jon


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

Reged: 09/18/12

Loc: western MA, U.S.
Re: Hypothetical 4" budget APO choices.. WWJD? new [Re: Jon Isaacs]
      #5645660 - 01/27/13 09:22 AM

At106LE ooh.

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

Reged: 07/14/12

Loc: Banana Republic of California
Re: Hypothetical 4" budget APO choices.. WWJD? new [Re: Jon Isaacs]
      #5646006 - 01/27/13 12:50 PM

Quote:


The mini-Cooper and the Porsche are not all a like, different displacement engines, different engine designs, different tires, different wheel bases, different weight distributions, different suspension systems.





Sure. But they both have 2 doors, a windshield, an engine, 4 wheels and disc brakes. They both have glove boxes, and steering wheels. They're both meant to be driven. And they both have [ad nauseam...]

We could go on forever debating this point.


Post Extras: Print Post   Remind Me!   Notify Moderator  
Jon Isaacs
Postmaster
*****

Reged: 06/16/04

Loc: San Diego and Boulevard, CA
Re: Hypothetical 4" budget APO choices.. WWJD? new [Re: Paco_Grande]
      #5646237 - 01/27/13 03:11 PM

Quote:

Quote:


The mini-Cooper and the Porsche are not all a like, different displacement engines, different engine designs, different tires, different wheel bases, different weight distributions, different suspension systems.





Sure. But they both have 2 doors, a windshield, an engine, 4 wheels and disc brakes. They both have glove boxes, and steering wheels. They're both meant to be driven. And they both have [ad nauseam...]

We could go on forever debating this point.




There is something worth understanding here. Comparing the Mini Cooper to the Porsche is like comparing a 3 inch apo to an 8 inch apo, they are just very different animals and there is no reason to expect that they would perform at all alike.

The Skywatcher 100ED and the TeleVue 102 are in all optical aspects essentially identical, the same aperture, the same focal length, the same materials. One would expect them to be very similar in performance and in fact, they are very similar in performance, whether it's splitting double stars or hunting down faint deep space objects, both perform as one might expect a very good 4 inch telescope to perform.

One difference between cars and telescopes: There are theoretical limits the govern the resolution and contrast of a telescope of a given aperture. High quality telescopes perform very close to those levels, within a few percent of less and even moderate quality telescopes perform at similar levels. These limits are determine by the very nature of light passing through an aperture.

Jon Isaacs


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

Reged: 03/07/10

Loc: Columbus, OH
Re: Hypothetical 4" budget APO choices.. WWJD? new [Re: Jon Isaacs]
      #5646721 - 01/27/13 07:06 PM

My Sky-Watcher 120ED consistently gives fantastic views. Very impressed at how deep it can go at dark sites with only 120mm aperture. Not a light bucket by any means but the views are still pleasing.

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

Reged: 05/18/06

Loc: Cambridge, MA, USA
Re: Hypothetical 4" budget APO choices.. WWJD? new [Re: lamplight]
      #5646949 - 01/27/13 09:08 PM

Quote:

I was reading about M79 which I've been unable to detect other than as a faint star in the reflector.




That doesn't sound right at all! Are you sure you're looking in the right place? M79 is not a particularly difficult object, even in light-polluted skies.


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

Reged: 07/14/12

Loc: Banana Republic of California
Re: Hypothetical 4" budget APO choices.. WWJD? new [Re: Jon Isaacs]
      #5647006 - 01/27/13 09:45 PM

Quote:



There is something worth understanding here. Comparing the Mini Cooper to the Porsche is like comparing a 3 inch apo to an 8 inch apo, they are just very different animals and there is no reason to expect that they would perform at all alike.






I have to disagree. The two cars (Mini Cooper S and any 2 door Porsche) are surprisingly similar. The average person will decide which one feels best and that's that, with no idea how each will behave when you push them closer to the limit. For most, they don't care.

But, performance-wise, they're very close except for the horsepower. Where the difference is how the car behaves near and at the limit, and where that limit is. Horsepower is an advantage on certain tracks, on some tracks it's a hindrance. Even at the limit they're not much different.

I guess my main point is, mechanically, the TV would be expected to be superior else it's not meeting up to its brand image - it had better be! Would you expect a Chinese focuser on a TV? I didn't think so. The SW ED's simply offer a lot of value for the money. Televue? Well, who sells the most telescopes?

Bottom line is, quality is in the eye of the beholder. Each person weighs what's important, considers the cost, and then makes a value judgment. We all do it, every single time we spend our money. And ultimately, contrary to what people typically think, every single buying decision is emotion, not rational.





Post Extras: Print Post   Remind Me!   Notify Moderator  
Jon Isaacs
Postmaster
*****

Reged: 06/16/04

Loc: San Diego and Boulevard, CA
Re: Hypothetical 4" budget APO choices.. WWJD? new [Re: Paco_Grande]
      #5647145 - 01/27/13 11:02 PM

Quote:


I have to disagree. The two cars (Mini Cooper S and any 2 door Porsche) are surprisingly similar.




Let's get back to the comparison between the TeleVue 102 and the Skywatcher 100. The Porsche is a rear engine, rear wheel drive car, the Mini C is a front engine, front wheel drive car. Major differences...

The goal here is to provide some understanding of the differences between various 4 inch apochromatic refractors. It is worth noting that the TeleVue 102 has been discontinued and certainly one of the reasons was that the arrival of the affordable ED-100s that were very similar in capability.

These are the specifications for the Synta ED-100:

Aperture: 100mm
Focal length: 900mm
Optical design: FPL-53 doublet
Dawes limit: 1.16 arc-seconds

These are the specifications for the TeleVue 102:

Aperture; 102mm
Focal length: 880mm
Optical design: Doublet Unspecified glass, most likely: FPL-53.
Dawes Limit: 1.14 arc-seconds.

Mechanically, the Televue is superior with it's rack and pinion focuser and overall robustness but the Synta mechanicals are sufficient that they are not a hindrance in getting the best quality views. In a comparison, the views will be very similar, probably depending on the optics in the particular scope.

The TeleVue NP-101 is a very different scope than either of these, a more sophisticated design with a 540mm focal length, perfect color correction and a flat field of view.

Jon Isaacs


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

Reged: 07/14/12

Loc: Banana Republic of California
Re: Hypothetical 4" budget APO choices.. WWJD? new [Re: Jon Isaacs]
      #5648026 - 01/28/13 12:29 PM

So Jon, based on your comments, there is no reason to purchase (even if you could) a new TV102 at four times the cost of the Sky-Watcher.

Post Extras: Print Post   Remind Me!   Notify Moderator  
Fogboundturtle
professor emeritus


Reged: 05/20/09

Loc: Burnaby, BC
Re: Hypothetical 4" budget APO choices.. WWJD? new [Re: Paco_Grande]
      #5648111 - 01/28/13 01:00 PM

Quote:

So Jon, based on your comments, there is no reason to purchase (even if you could) a new TV102 at four times the cost of the Sky-Watcher.




That's not what he was saying. He was saying. You will be a lot more money for that 1-2%. Sky-watcher series is 98% there.


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

Reged: 07/14/12

Loc: Banana Republic of California
Re: Hypothetical 4" budget APO choices.. WWJD? new [Re: Fogboundturtle]
      #5648191 - 01/28/13 01:33 PM

So, what do you get for the additional $2,500 cost of the TV?

Post Extras: Print Post   Remind Me!   Notify Moderator  
Fogboundturtle
professor emeritus


Reged: 05/20/09

Loc: Burnaby, BC
Re: Hypothetical 4" budget APO choices.. WWJD? new [Re: Paco_Grande]
      #5648228 - 01/28/13 01:45 PM

Quote:

So, what do you get for the additional $2,500 cost of the TV?




My guess ? Probably a flatter field of view, a better focuser and probably an minimal better color correction. Is it worth 2500 more ? some perfectionist will tell you that 1-2% difference is worth it. Others will never notice.


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

Reged: 09/29/10

Loc: SE Indiana
Re: Hypothetical 4" budget APO choices.. WWJD? new [Re: Fogboundturtle]
      #5648316 - 01/28/13 02:19 PM

There was a book who's author's premise was the 80/20 rule;that is the first 80% of whatever is derived with 20% of the effort(cost) and every increase in performance costs more on an escalating curve.It actually does seem that way in real life.

So it comes down to is that last incremental improvement needed and can you pay for it ?

Barring winning a major lottery prize(and I hear you must buy tickets to have a chance of winning),I will likely never have a $5000 scopes but will be awed by the not-quite-perfect views of the $1000 (or less) scopes.

I'd love to have an ED version of my Celestron 150mm f8 refractor.


The $7000 current price of the Skywatcher 150 ed f7 is not quite what I had in mind.Interesting,well,terrifying, that there is such a huge jump in cost for 50% increase in aperture The doubling of cost for a more modest 20% aperture increase from 100 to 120 is enough of a shock.


Post Extras: Print Post   Remind Me!   Notify Moderator  
Jon Isaacs
Postmaster
*****

Reged: 06/16/04

Loc: San Diego and Boulevard, CA
Re: Hypothetical 4" budget APO choices.. WWJD? new [Re: Paco_Grande]
      #5648653 - 01/28/13 04:36 PM

Quote:

So Jon, based on your comments, there is no reason to purchase (even if you could) a new TV102 at four times the cost of the Sky-Watcher.




I am not sure what the TV-102 cost new, I think it was about $2500 and that included a case, a clamshell and a 2 inch Everbright diagonal. There are good reasons to purchase a TV-102, the quality of the construction, the fact that TV services it... A nice scope. But side by side, at the eyepiece, these scopes are very similar.

The ED-80 and the ED-100 represented a revolution in terms of ED/apo telescopes. When the ED-80 arrived on the scene for $500, it was controversial as to whether it was an real ED/apo or just another scope with "fake ED glass" that was essentially an achromat. The Synta ED-100s pretty much eliminated the competition in the longer focal length 4 inch doublet market...

The remaining TeleVue 4 inch is the NP-101 which is very different scope than the TV-102 or the Synta ED-100s. It's a 4 element scope with two ED doublets, one is the objective, one is the dedicated field flattener/focal reducer. These are about $3000 more than the Synta/Skywatcher and for that money, you get a 540mm focal length with perfect color correction and 5 degree field of view that is free from field curvature and other aberrations.

Jon


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

Reged: 07/14/12

Loc: Banana Republic of California
Re: Hypothetical 4" budget APO choices.. WWJD? new [Re: Jon Isaacs]
      #5649123 - 01/28/13 08:04 PM

I'm just being the contrarian on this, or maybe just stirring the pot a little. The TV102, as best as I could tell from a Google search, sold for around $3,200. MSRP was $4,600.

Status is an important ownership value when you enter the high end market in any field. This field is no different. It's like spending $3,000 for two 3ft custom audio speaker cables. Some claim they can tell the difference. A tiny few probably can, the rest are blowing smoke.


Post Extras: Print Post   Remind Me!   Notify Moderator  
Jon Isaacs
Postmaster
*****

Reged: 06/16/04

Loc: San Diego and Boulevard, CA
Re: Hypothetical 4" budget APO choices.. WWJD? new [Re: Paco_Grande]
      #5649829 - 01/29/13 08:15 AM

Quote:

I'm just being the contrarian on this, or maybe just stirring the pot a little. The TV102, as best as I could tell from a Google search, sold for around $3,200. MSRP was $4,600.

Status is an important ownership value when you enter the high end market in any field. This field is no different. It's like spending $3,000 for two 3ft custom audio speaker cables. Some claim they can tell the difference. A tiny few probably can, the rest are blowing smoke.




I looked it up...

TV-102

Orion ED-100

The TV-102 OTA with a very solid, fiberglass case sold for about $2200 in 2006. At that time, the bare Orion ED-100 sold for $1000.

Status may be a reason for some to purchase a telescope but that is not of interest to me nor does it enter into my comments concerning these telescopes. I buy telescopes to look through and I spend a lot of time looking through telescopes of all qualities. The difference between an NP-101 and a ED-100 is easy to quantify analytically, easy to see at the eyepiece. It doesn't doesn't take any special skill to see the different both at the eyepiece or just looking at the quality of the construction. At the eyepiece, seeing the difference between an TV-102 and a ED-100 is difficult but just looking at them, the difference in the mechanical quality is quite apparent.

Jon


Post Extras: Print Post   Remind Me!   Notify Moderator  
Kon Dealer
professor emeritus


Reged: 01/05/11

Loc: Cambridge UK
Re: Hypothetical 4" budget APO choices.. WWJD? new [Re: Jon Isaacs]
      #5649959 - 01/29/13 10:03 AM

Kson 1026 ED (f/6) in carbon fibre.
Short, unbelieveably light and cheap.
Small amount of CA on the very brightest objects, but
a great G&G.
I think it is a real bargain
http://store.smartastronomy.com/ksopmiedapor.html
(no affiliation and didn't buy here)


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

Reged: 09/18/12

Loc: western MA, U.S.
Re: Hypothetical 4" budget APO choices.. WWJD? new [Re: Jon Isaacs]
      #5649968 - 01/29/13 10:12 AM

ive upgraded. in my mind, to the 120mm size. it seems manageable enough still and is somewhat still grab n go for me. in my LP i feel its worth the extra bit of aperture. ive gotten lost in the minutia and arguments over the different FPL glasses..over the last few days.. i can see its a hot topic..i am not inclined to learn the meaty details so im relying on the general opinion of those more experienced.. looks like im down to one of the following which i believe use all the same or similar lens elements that get good feedback and offer value for this aperture, price and f/ratio (120mm aperture at F/7.5):

EON 120 : not liking the finish. one on astromart for 1600.. too much.

WO Megrets 120ED : very nice. dont see any for sale.

Sky-Watcher "equinox" 120ED (like the design/mechanicals better than american version), but will probably have to order from canada. is there a big tax increase? VAT or something or is that only EU?. my current "top pic". i just dont know yet what it would cost me. would love to find one used!

Sky-Watcher Pro ED 120. nice all around for this range, $1600 new. a couple going slightly less used here and there..

TS 120 which looks incredible, but i dont think i can get in U.S. either.. looks to be about 2400+shipping. yikes.. id lean more towards the "equinox"

then theres the black diamond version of the sky-watcher which i havent compared yet.... still reading and looking and comparing.. these ones seem to have pretty good reviews regarding CA. im not really looking at or reading about spherical aberration as for visual i dont see it as an issue too much. it helps me get to sleep at night ironically.


Post Extras: Print Post   Remind Me!   Notify Moderator  
Fogboundturtle
professor emeritus


Reged: 05/20/09

Loc: Burnaby, BC
Re: Hypothetical 4" budget APO choices.. WWJD? new [Re: lamplight]
      #5650070 - 01/29/13 11:11 AM

Might as well go for a triplet if your budget allows it. I have an Meade 127mm APO Triplet F7.5. I love this scope. First of all, the focuser is awesome. You got an ridiculous amount of tube. There is not one camera that I was not able to obtain focus. The color is very well corrected. It comes with an flight case and a very good diagonal.

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

Reged: 09/27/06

Loc: Seattle, WA
Re: Hypothetical 4" budget APO choices.. WWJD? new [Re: Fogboundturtle]
      #5650475 - 01/29/13 02:46 PM

Is the OP now looking for a budget 4.7" APO?

I agree that the 102 is matched optically by the 100 ED, which can be had for $400 used (tube only). They are fantastic refractors at a bargain price. I'm also on board with the low-cost 4.7" ED doublets. Still a bargain if you can find one, but quite a bit more cost than the 4" models.


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

Reged: 09/18/12

Loc: western MA, U.S.
Re: Hypothetical 4" budget APO choices.. WWJD? new [Re: SteveG]
      #5652561 - 01/30/13 03:35 PM

Quote:

Is the OP now looking for a budget 4.7" APO?





yes i think so. ive learned budget is not the right word. thanks for all the help everyone, im on the right track (to bankruptcy!)


Post Extras: Print Post   Remind Me!   Notify Moderator  
Jon Isaacs
Postmaster
*****

Reged: 06/16/04

Loc: San Diego and Boulevard, CA
Re: Hypothetical 4" budget APO choices.. WWJD? new [Re: lamplight]
      #5652594 - 01/30/13 03:47 PM

Quote:


ive upgraded. in my mind, to the 120mm size. it seems manageable enough still and is somewhat still grab n go for me.




I have owned a couple of 120mm refractors. I prefer a 4 inch, preferably faster, shorter. A 120mm F/8 refractor is about as much effort to deal with as a 8 or 10 inch Dob. A 4 inch F/6-f/7 more like dealing with an 80mm on steroids.

Jon


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

Reged: 05/18/06

Loc: Cambridge, MA, USA
Re: Hypothetical 4" budget APO choices.. WWJD? new [Re: Jon Isaacs]
      #5652747 - 01/30/13 04:49 PM

Quote:

I have owned a couple of 120mm refractors. I prefer a 4 inch, preferably faster, shorter.




And I will repeat my previous question. As you move up in the aperture leagues, what's wrong with a 6-inch reflector? More portable than a 120-mm refractor, much cheaper, and closely comparable light gathering and image quality.


Post Extras: Print Post   Remind Me!   Notify Moderator  
Jon Isaacs
Postmaster
*****

Reged: 06/16/04

Loc: San Diego and Boulevard, CA
Re: Hypothetical 4" budget APO choices.. WWJD? new [Re: Tony Flanders]
      #5653197 - 01/30/13 08:55 PM

Quote:

Quote:

I have owned a couple of 120mm refractors. I prefer a 4 inch, preferably faster, shorter.




And I will repeat my previous question. As you move up in the aperture leagues, what's wrong with a 6-inch reflector? More portable than a 120-mm refractor, much cheaper, and closely comparable light gathering and image quality.




Tony:

Indeed... over the years, the traditional 6 inch F/8 Newtonian gained the reputation as an "apo-killer." The classic Criterion RV-6 (last built about 1978) has a light weight phenolic tube, a small secondary and a simple clean aluminum mirror cell. The optical tube assembly weighs 8 lbs and these are very capable performers as planetary and double star telescopes.

Jon



Edited by Jon Isaacs (01/30/13 08:56 PM)


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

Reged: 07/14/12

Loc: Banana Republic of California
Re: Hypothetical 4" budget APO choices.. WWJD? new [Re: Jon Isaacs]
      #5653268 - 01/30/13 09:47 PM Attachment (15 downloads)

My apo-killer I'm still a refractor fan.

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

Reged: 07/14/12

Loc: Banana Republic of California
Re: Hypothetical 4" budget APO choices.. WWJD? new [Re: lamplight]
      #5653291 - 01/30/13 09:57 PM

Quote:



Sky-Watcher "equinox" 120ED (like the design/mechanicals better than american version), but will probably have to order from canada. is there a big tax increase? VAT or something or is that only EU?. my current "top pic". i just dont know yet what it would cost me.




Matt, I ordered my Sky-Watcher newt from Brandon Optics in BC, Canada. No special taxes. But shipping is more expensive and you'll have to pay someone to handle the customs process. If it's UPS, they'll give you a bill and won't deliver until you pay. $

40 for shipping to Northern Calif and $60 for custom's fees.

Bottom line, it cost me about $100 for shipping and customs fees to get that SW newt here. I have no regrets. It's one of those scopes you can't imaging selling, like a laid back Chihuahua.


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

Reged: 09/18/12

Loc: western MA, U.S.
Re: Hypothetical 4" budget APO choices.. WWJD? new [Re: Paco_Grande]
      #5653760 - 01/31/13 07:52 AM

I responded yest but I guess I never pushed send.

Re: why refractor: I like the ease of setup, lack of maintenance (generally), fast cool down, sharp images and good contrast, the usual..my Achro has been my winter scope, But since I'm in LP I want more aperture..as much a s s reasonable to handle between this and a DOB I have coming.. Another ing pushing me to explore an APO is that I see the CA more lately... (Maybe just because I've been using this scope all winter every chance I can)

Jon the 4.7" range doesn't seem all that much bigger (??). The ones I'm looking at look really well built and everywhere I see good reviews of very low to no visible CA. I worry that if I went a triplet and stayed in the 100mm range (about same cost as these exceptionally good doublets) I would not get a noticeable upgrade in light gathering.

Edited by lamplight (01/31/13 08:46 AM)


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

Reged: 09/18/12

Loc: western MA, U.S.
Re: Hypothetical 4" budget APO choices.. WWJD? new [Re: lamplight]
      #5653810 - 01/31/13 08:39 AM

The skywatcher 120ed is 11.3 lbs, my xlt 100 is 9lbs
The 120 ed (f/7.5) is 38", the 100 xlt is 39.5"

So in this comparison is really negligible increase in terms of what I and the mounts ill use can and would handle.

However, I'm looking at the beefier equinox and TS tubes which weigh in slightly under 16lbs with rings. Still very doable to me, and I don't see tube length info on these websites.. But it has to be similar to the skywatcher 120.

I THINK this would be the upper limit of practicality in size and weight for me (for a portable refractor).

Edited by lamplight (01/31/13 08:43 AM)


Post Extras: Print Post   Remind Me!   Notify Moderator  
Gert K A
sage


Reged: 07/16/12

Loc: Copenhagen, Denmark
Re: Hypothetical 4" budget APO choices.. WWJD? new [Re: lamplight]
      #5653854 - 01/31/13 09:00 AM

Quote:

-- Matt:
I don't see tube length info on these websites..




Your link from APM say "The TS 120/900mm ED APO" so 900mm or 34½" betting on the dewshield is retractable


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

Reged: 10/20/10

Loc: NC
Re: Hypothetical 4" budget APO choices.. WWJD? new [Re: Jon Isaacs]
      #5653882 - 01/31/13 09:19 AM

Ah pretty:) It was my first real scope in 1964!
Bob


Post Extras: Print Post   Remind Me!   Notify Moderator  
Jon Isaacs
Postmaster
*****

Reged: 06/16/04

Loc: San Diego and Boulevard, CA
Re: Hypothetical 4" budget APO choices.. WWJD? new [Re: lamplight]
      #5653888 - 01/31/13 09:23 AM Attachment (14 downloads)

Quote:

Jon the 4.7" range doesn't seem all that much bigger (??). The ones I'm looking at look really well built and everywhere I see good reviews of very low to no visible CA. I worry that if I went a triplet and stayed in the 100mm range (about same cost as these exceptionally good doublets) I would not get a noticeable upgrade in light gathering.




It all depends on what you are looking for in a telescope. In terms of light gathering, the difference between a 4 inch and a 120mm is not much if there is a 10 inch Newtonian sitting nearby.

The fact that it takes as much effort to setup the 120mm refractor as it does the 10 inch Newtonian is clue that maybe the 120mm is on the big side of easy to use and portable. Myself, I look to refractors to do the things smaller scopes do best, easily portable, compact, wide fields of view, with the ability to go to higher magnifications, remembering that there is a limit to what scopes this size can do.

When small is good, bigger is not necessarily better.

For the things I use a refractor for, an 80mm is a better choice than a 120mm and a fast 4 inch is about ideal. In terms of fast 4 inch refractors for visual use, the NP-101 is about as good as it gets.

Jon


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

Reged: 09/18/12

Loc: western MA, U.S.
Re: Hypothetical 4" budget APO choices.. WWJD? new [Re: Jon Isaacs]
      #5654074 - 01/31/13 10:53 AM

( is that a vixen head on your TV? nice !)

thanks.. well if it will be smaller than what i have but only a bit heavier with bit more light and less CA it seems a no brainer for my needs. except cost which is contrary to practical. "but..."

this has been SO educational thanks! this hobby is a continuation of not knowing what i didnt know.. how many times is this going to keep happening? sheesh.


Post Extras: Print Post   Remind Me!   Notify Moderator  
CJK
professor emeritus


Reged: 12/05/12

Loc: Northeast TN
Re: Hypothetical 4" budget APO choices.. WWJD? new [Re: Jon Isaacs]
      #5654148 - 01/31/13 11:29 AM

Re: your photo -- Who knew Home Depot sold telescope mounts?

-- Chris


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


Reged: 12/13/12

Loc: Dunmore, PA
Re: Hypothetical 4" budget APO choices.. WWJD? new [Re: Jon Isaacs]
      #5654260 - 01/31/13 12:43 PM

Quote:

Quote:

Quote:

I have owned a couple of 120mm refractors. I prefer a 4 inch, preferably faster, shorter.




And I will repeat my previous question. As you move up in the aperture leagues, what's wrong with a 6-inch reflector? More portable than a 120-mm refractor, much cheaper, and closely comparable light gathering and image quality.




Tony:

Indeed... over the years, the traditional 6 inch F/8 Newtonian gained the reputation as an "apo-killer." The classic Criterion RV-6 (last built about 1978) has a light weight phenolic tube, a small secondary and a simple clean aluminum mirror cell. The optical tube assembly weighs 8 lbs and these are very capable performers as planetary and double star telescopes.

Jon





Tony or Jon,
I have a question. Would a 6 inch reflector f/8 be better for planets than say a 8 inch f/6 or does the aperture cancel the longer focal length out? I have see quite a few ads for planet killer refractors f/11 or more. I have read how some people love these but the FOV is very limited. So would the a longer focal length help with planets or double stars on reflectors as well? I understand this would make them less portable. I am trying to understand the trade offs over wide field or better planet viewing. From what I am understanding it sound like only a select few refractors like the NP-101 does both things well.

Ken


Post Extras: Print Post   Remind Me!   Notify Moderator  
Mike4242
Pooh-Bah


Reged: 11/02/11

Loc: Memphis, TN
Re: Hypothetical 4" budget APO choices.. WWJD? new [Re: kenrenard]
      #5654405 - 01/31/13 02:12 PM

The main benefit of a longer focal length is that you get a higher magnification with a given eyepiece; however, this also restricts your maximum field of view.

Focal length also comes into play with achromatic refractors because longer focal lengths reduce the amount of chromatic aberration.

In the case of reflectors collimation is more forgiving with a longer focal length.

An 8" f/6 should give better planetary views than a 6" f/8 if both scopes are cooled, properly collimated, and the seeing conditions permit. The 8" will be more affected by atmospheric seeing than the 6".

I'm probably missing some points here, but I'm sure Jon and/or Tony will chime in.


Post Extras: Print Post   Remind Me!   Notify Moderator  
Mike4242
Pooh-Bah


Reged: 11/02/11

Loc: Memphis, TN
Re: Hypothetical 4" budget APO choices.. WWJD? new [Re: Mike4242]
      #5654409 - 01/31/13 02:14 PM

Here's a good article I just remembered about the pros and cons of short and long focal lengths:

http://www.chuckhawks.com/telescope_focal_length.htm


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


Reged: 12/13/12

Loc: Dunmore, PA
Re: Hypothetical 4" budget APO choices.. WWJD? new [Re: Mike4242]
      #5654420 - 01/31/13 02:26 PM

Thanks Mike,
Good article. When I put the different focal lengths comparing say a XT8 f/5.9 and XT6 f/8 in an eyepiece calculator they have the same magnification. So in essence looks like a wash? At least thats the way I'm understanding things.

Ken


Post Extras: Print Post   Remind Me!   Notify Moderator  
Mike4242
Pooh-Bah


Reged: 11/02/11

Loc: Memphis, TN
Re: Hypothetical 4" budget APO choices.. WWJD? new [Re: kenrenard]
      #5654426 - 01/31/13 02:29 PM

You have to look at the actual focal length value instead of the ratio for magnification. Since the F ratio is the focal length divided by the aperture, a larger aperture will have a lower/faster F ratio with the same focal length.

But, yes, it is essentially a wash. The collimation tolerance of the 8" will be tighter, but the 8" should give better views if atmospheric seeing permits.


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


Reged: 12/13/12

Loc: Dunmore, PA
Re: Hypothetical 4" budget APO choices.. WWJD? new [Re: Mike4242]
      #5654444 - 01/31/13 02:37 PM

OK I understand. Thanks for clearing it up. I found a few other old post explaining why we don't have long focal length reflectors. Size and weight seem to be the biggest answer. As well as better mirrors today.

Ken


Post Extras: Print Post   Remind Me!   Notify Moderator  
Jon Isaacs
Postmaster
*****

Reged: 06/16/04

Loc: San Diego and Boulevard, CA
Re: Hypothetical 4" budget APO choices.. WWJD? new [Re: kenrenard]
      #5654468 - 01/31/13 02:51 PM

Quote:

Thanks Mike,
Good article. When I put the different focal lengths comparing say a XT8 f/5.9 and XT6 f/8 in an eyepiece calculator they have the same magnification. So in essence looks like a wash? At least thats the way I'm understanding things.

Ken




Ken:

The article was comparing telescopes of the same aperture and is not really applicable in this situation because the question here is involves two scopes of the same focal length but different apertures. It is also rather dated so many of the comments about eye relief and eyepieces are no longer valid.

This is a favorite saying:

"The best 6 inch F/8 is an 8 inch F/6."

In terms of viewing the planets, the benefit of the larger aperture is greater resolution, increased planetary contrast and a brighter, potentially more colorful view. The resolution and contrast are proportional to the aperture, so assumming the seeing (atmospheric stability) is not the limiting factor, the expectation is that an 8 inch F/6 Newtonian will provide noticeably better planetary views than a 6 inch F/8 Newtonian.

This is very consistent with my experience. I do have the classic 6 inch F/8 but if want the good planetary views, it's not the 4 inch apo nor the 6 inch F/8 Newtonian but rather the 10 inch F/5 or something even larger.

Jon


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


Reged: 12/13/12

Loc: Dunmore, PA
Re: Hypothetical 4" budget APO choices.. WWJD? new [Re: Jon Isaacs]
      #5654557 - 01/31/13 03:36 PM

Thanks Jon,
As always you are a wealth of information.


Ken


Post Extras: Print Post   Remind Me!   Notify Moderator  
Pages: 1 | 2 | 3 | 4 | (show all)


Extra information
15 registered and 26 anonymous users are browsing this forum.

Moderator:  WOBentley, kkokkolis 

Print Thread

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


Thread views: 3011

Jump to

CN Forums Home


Cloudy Nights LLC
Cloudy Nights Sponsor: Astronomics