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

Announcements and News >> Discussion of CN Articles, Reviews, and Reports

Pages: 1 | 2 | 3 | 4 | 5 | 6 | 7 | (show all)
starpal
professor emeritus
*****

Reged: 08/06/04

Loc: Mid-USA
Re: CN Report: The Tele Vue NP101 new [Re: Tom T]
      #2172744 - 02/06/08 04:50 PM

[snip, spaceydee]

Lastly, please see my reply to sixela about Crayfords vs. R&Ps. In high end they are more complex and more costly to manufacture. They have greater performance parameters for all scopes and applications. Just because TeleVue or Astro-Physics simply don't use them doesn't really justify their approaches. That's why I mentioned factor of cost just as you have at the beginning of your article. yes R&Ps can be excellent but equasl quality Crayfords are better especially with faster scopes. They provide a more precise focus for critical applications.

Edited by spaceydee (02/10/08 01:35 PM)


Post Extras: Print Post   Remind Me!   Notify Moderator  
starpal
professor emeritus
*****

Reged: 08/06/04

Loc: Mid-USA
Re: CN Report: The Tele Vue NP101 new [Re: blandp11]
      #2172763 - 02/06/08 04:59 PM

And what you are saying is that the dew issue is one that cannot be rectified?

Like I said, just because others use rack and pinion instead of Crayford design really tells us nothing definite about advantages. The points made regarding the Crayford are valid more diversified pointing toward a better product.


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

Reged: 04/16/04

Loc: Where the Kittens Are
Re: CN Report: The Tele Vue NP101 new [Re: starpal]
      #2172767 - 02/06/08 05:02 PM



Folks lets keep all "personal remarks" to ourselves from this point forward.

Thanks

your moderator


Post Extras: Print Post   Remind Me!   Notify Moderator  
starpal
professor emeritus
*****

Reged: 08/06/04

Loc: Mid-USA
Re: CN Report: The Tele Vue NP101 new [Re: Jeff Morgan]
      #2172795 - 02/06/08 05:17 PM

Jeff,
I stand corrected. Very interesting since my life long experiece with long f/ratio to short seemed to indicate otherwise viewing the planets. I've learned something new and exiting today.
Thank you.


Post Extras: Print Post   Remind Me!   Notify Moderator  
starpal
professor emeritus
*****

Reged: 08/06/04

Loc: Mid-USA
Re: CN Report: The Tele Vue NP101 new [Re: starpal]
      #2172803 - 02/06/08 05:21 PM

Quote:

Include to this the absolutely desireable depth of focus from them that more accurately compensates for atmospheric changes to focus at high powers. An f/5.4 quickly falls flat on it's face in this regard.




This that I stated above is incorrect. Jeff Morgan points to a helpful article done by our friend Bryan Greer that shows this long held understanding to be invalid.


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

Reged: 06/16/04

Loc: San Diego and Boulevard, CA
Re: CN Report: The Tele Vue NP101 new [Re: starpal]
      #2172854 - 02/06/08 05:45 PM

Quote:

Let's not forget that fact about a company keeping a product as cost effective as possible. A question might be why for example would a rack and pinion focuser be used when a Crayford is better and now the industry standard?




Actually I believe it's the mid range scopes that use Crayfords, the high end use premium rack and pinions like theR&P Feathertouch, I believe that's what A-P uses among others. I think the reason to use a Rack and Pinion is that R&P focusers are better at handling heavy loads. They are however more expensive to manufacture.

Dollar for Dollar you get more with a Crayford but friction has it's limits as a drive mechanism and so at the point where a designer quits playing the best value game and goes for the best design regardless of cost, a rack and pinion again becomes the design choice.

Jon

Edited by Jon Isaacs (02/06/08 05:54 PM)


Post Extras: Print Post   Remind Me!   Notify Moderator  
starpal
professor emeritus
*****

Reged: 08/06/04

Loc: Mid-USA
Re: CN Report: The Tele Vue NP101 new [Re: Jon Isaacs]
      #2172878 - 02/06/08 06:03 PM

Hi Jon,
As someone in the engineering field I believe you to know quite a bit. How confident are you of the R&P costing more to produce? And especially when are weight loads so high the Crayford of excellent quality insufficient? It is my understanding from specifications and use that they handle up to 8-10 pounds. A TeleVue having to hold that much would impress me.
Thanks.


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

Reged: 08/23/05

Loc: Virginia
Re: CN Report: The Tele Vue NP101 new [Re: starpal]
      #2172887 - 02/06/08 06:07 PM

An AP 2.7 or 4" focuser R&P is designed to be subjected to flattener, TC and a big honking SBIG that could easily exceed the 8-10 lbs you refer to. Some of these CCD cameras and filter wheels add a lot of weight (let alone additional optics in train), so even a TV could be subjected to loads in excess of 10 lbs by high-end imagers. My understanding is that the IS version focusers were designed with that in mind as well.

Curiously - Roland recently posted something germane here


Post Extras: Print Post   Remind Me!   Notify Moderator  
Tom TAdministrator

*****

Reged: 02/26/02

Re: CN Report: The Tele Vue NP101 new [Re: Jon Isaacs]
      #2172892 - 02/06/08 06:10 PM

[post deleted by spaceydee]

Edited by spaceydee (02/10/08 01:40 PM)


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

Reged: 06/16/04

Loc: San Diego and Boulevard, CA
Re: CN Report: The Tele Vue NP101 new [Re: starpal]
      #2172945 - 02/06/08 06:39 PM

Quote:

Hi Jon,
As someone in the engineering field I believe you to know quite a bit. How confident are you of the R&P costing more to produce? And especially when are weight loads so high the Crayford of excellent quality insufficient? It is my understanding from specifications and use that they handle up to 8-10 pounds. A TeleVue having to hold that much would impress me.
Thanks.




My thinking goes like this: Precision gearing is expensive to manufacture because of the difficulty in accurately machining a complex tooth profile. We all know what a good RA drive costs. Crayfords eliminate the problem of quality gearing by using a friction drive. It's a compromise because you are now putting side loadings on the shaft unless you use a backing bearing (ED-80)in order to provide the traction. With a light load this can make for a nice smooth, easy focuser but as the loads on the focuser increase, the side loadings which provide that traction must increase, not so good. I like Crayfords on a dollar for dollar basis but they are more finicky than a good rack and pinion.

So at some point, a designer probably says, enough is enough, lets quit trying to force the issue and just provide a positive gear drive. In the case of the gear drive, side loading on the draw tube may be what keeps it in place once it is focused but it is not required for focusing.

Jon


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

Reged: 01/10/07

Loc: Jacksonville Florida
Re: CN Report: The Tele Vue NP101 new [Re: Jon Isaacs]
      #2173379 - 02/06/08 09:44 PM

Ford ( GT ) and Ferrari ( Enzo ) use R&P steering on their 200MPH+ cars, must do pretty well under pressure.

All I have to say is I may go the route of an NP127 instead of waiting for my name to be called on the AP wait list. I'm 8 months in on the 160 list. Speaking strictly visual only one can't go any better that the NP series, the obligatory IMHO.

Again, thanks for a great telescope article Tom.


Post Extras: Print Post   Remind Me!   Notify Moderator  
starpal
professor emeritus
*****

Reged: 08/06/04

Loc: Mid-USA
Re: CN Report: The Tele Vue NP101 new [Re: Tom T]
      #2173544 - 02/06/08 11:00 PM

[post deleted by spaceydee]

Edited by spaceydee (02/11/08 12:46 AM)


Post Extras: Print Post   Remind Me!   Notify Moderator  
starpal
professor emeritus
*****

Reged: 08/06/04

Loc: Mid-USA
Re: CN Report: The Tele Vue NP101 new [Re: Jon Isaacs]
      #2173613 - 02/06/08 11:44 PM

Hi Jon,
Thanks for elaborating so fluidly on this from an engineering standpoint, is most appreciated.

Let me, if I may, add some more thoughts to this. One is that all focuser designs have inherent compromises built into them. Even a precision rack and pinion assembly has its weaknesses. Both the types under discussion of course also have their strengths and there is new work being done regularly to improve both.

Another aspect to ponder is that the R&P has only two moving parts, the rack and the pinion gear. With that are the outer housing with machined clearance channel and drawtube (often with a shallow machined trough).

The, Crayford, OTOH, has more and complex parts to offset the high pressures involved from the roller against the land placed on the drawtube. To do this well, small roller bearings are set at the opposite side to the force placed on the drawtube. The outer casting now becomes more elaborate with needed stations for the small roller bearings. The land itself, where the focuser roller shaft comes in contact, is best made wear resistant as bearing surface itself (hence the more advanced Feathertouch model with hardened steel plate). These things require quite a bit of machining/processing to be done right, and there is significantly more again needed when one considers a 2-speed model with a planetary gear assembly.

I'm not sure that a R&P with a high precision gearing assembly is all that costly against an equivalent (or approximately) heavy duty Crayford. Not talking the 4" model type, here. The actual R&P gears in this size for any of them are not really that expensive to obtain. Probably well under $100 in many cases, AFAIK.

The first highly successful JMI Crayford was quite expensive to produce due to the design time, set up to manufacture, and other related expenses. Do you suppose there is a real difference here today in cost comparisons and overall performance when talking about the best of both types of these focuser mechanisms? Is probably too hard to quantify but the above should give something of a general feel.


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

Reged: 04/20/05

Loc: Cloudy HKG
Re: CN Report: The Tele Vue NP101 new [Re: starpal]
      #2173686 - 02/07/08 12:30 AM

Tom,

Thank you for the great and honest report. All of us appreciate your reviews, even if we don't all agree with you.

I'm a visual observer looking for a hassle free easy to use telescope, and so found myself looking at 4-5" APOs. I was looking at the TV101 for portability, but the new TV102 binoview package caught my eye - apparently it is the same size as a 101. Any thoughts?

Thanks again!


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

Reged: 06/16/04

Loc: San Diego and Boulevard, CA
Re: CN Report: The Tele Vue NP101 new [Re: starpal]
      #2173764 - 02/07/08 01:54 AM

Quote:

Do you suppose there is a real difference here today in cost comparisons and overall performance when talking about the best of both types of these focuser mechanisms? Is probably too hard to quantify but the above should give something of a general feel.




I do believe that a quality rack and pinion is more expensive to manufacture but really that is not the point here, that is really off topic.

The point here is that the 101NP uses a Rack and Pinion and you commented that Crayfords were better and this was in indication of TeleVues lack of commitment to quality.

Quote:

Let's not forget that fact about a company keeping a product as cost effective as possible. A question might be why for example would a rack and pinion focuser be used when a Crayford is better and now the industry standard?




In the context of the current conversation, that statement clearly does not stand up, at the high end, Crayfords are not the industry Standard nor are they clearly better.

So, I think it is time to get back on topic and discuss the NP-101 and not the difficulty of producing a high quality rack and pinion focuser. It is clear people are doing that and it clear that TeleVue is doing it.

Jon


Post Extras: Print Post   Remind Me!   Notify Moderator  
AL A.
super member


Reged: 12/11/05

Re: CN Report: The Tele Vue NP101 new [Re: Jon Isaacs]
      #2173927 - 02/07/08 05:58 AM

Tom, thank you for the excellent review. I have the NP101's big brother, the NP127, and I am extremely happy with it. Considering its optical performance, excellent build quality, and relatively light weight, I wouldn't trade it for any other 5-inch refractor.

Al


Post Extras: Print Post   Remind Me!   Notify Moderator  
Tom TAdministrator

*****

Reged: 02/26/02

Re: CN Report: The Tele Vue NP101 new [Re: Hermie]
      #2174080 - 02/07/08 08:38 AM

Quote:

Tom,

Thank you for the great and honest report. All of us appreciate your reviews, even if we don't all agree with you.

I'm a visual observer looking for a hassle free easy to use telescope, and so found myself looking at 4-5" APOs. I was looking at the TV101 for portability, but the new TV102 binoview package caught my eye - apparently it is the same size as a 101. Any thoughts?

Thanks again!




Hi Hermie,

Thank you.

The TV102 is a wonderful telescope, and the new package makes it even better. If you want to binoview, it's a superb choice. Off the top of my head, the only things you'll be "giving up" over the NP101 are the extreme wide and flat field, and you'll sacrifice a bit of performance due to the residual CA.

The 102 will be probably a bit lighter (although having to carry an extension tube probably makes up for not having the rear lens elements).

If I can make a suggestion - you might give TV a call, ask for Al and see what he recommends.

T


Post Extras: Print Post   Remind Me!   Notify Moderator  
Tom TAdministrator

*****

Reged: 02/26/02

Re: CN Report: The Tele Vue NP101 new [Re: starpal]
      #2174105 - 02/07/08 08:57 AM

[post deleted by spacyedee]

Edited by spaceydee (02/10/08 01:45 PM)


Post Extras: Print Post   Remind Me!   Notify Moderator  
Tom TAdministrator

*****

Reged: 02/26/02

Re: CN Report: The Tele Vue NP101 new [Re: Tom T]
      #2174111 - 02/07/08 08:59 AM

Thanks for your comments guys.

Post Extras: Print Post   Remind Me!   Notify Moderator  
RogerRZ
Whatta you lookin' at?
*****

Reged: 01/09/06

Loc: West Collette, NB, Canada
Re: CN Report: The Tele Vue NP101 new [Re: Tom T]
      #2174170 - 02/07/08 09:34 AM

No matter what anyone says, I still really enjoyed the use of my TV102 and TV76, and would like to someday, get my hands on a NP101...

Post Extras: Print Post   Remind Me!   Notify Moderator  
Pages: 1 | 2 | 3 | 4 | 5 | 6 | 7 | (show all)


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

Moderator:  droid 

Print Thread

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


Thread views: 16417

Jump to

CN Forums Home


Cloudy Nights LLC
Cloudy Nights Sponsor: Astronomics