Jump to content


Photo

LX200R back focus


  • Please log in to reply
21 replies to this topic

#1 k8jb

k8jb

    Newbie

  • Members
  • Pip
  • 3 posts

Posted 17 August 2007 - 01:18 PM

Does anyone what the design back focus is for the 10" LX200R?

#2 Mark Sibole

Mark Sibole

    Advanced Member

  • Administrators
  • 2368 posts

Posted 17 August 2007 - 01:33 PM

What kind of info are you looking for??

Mark
Mark Sibole
MTSO Observatory
Fife Lake, Mi.

http://astronomy.qteaser.com

#3 k8jb

k8jb

    Newbie

  • Members
  • Pip
  • 3 posts

Posted 17 August 2007 - 02:37 PM

What I would like to find out is where the focal plane should be (i.e., where it was deigned to optimally be) relative to the rear cell of the telescope to achieve the advertised 2500mm FL and f/10 focal ratio since focusing by primary mirror movement has a dramatic effect on the focal length. 

I'm using an Astro-Physics CCDT67 focal reducer with my 10" LX200R, ST-8, CFW9 filterwheel and Feathertouch focuser and I measured an effective focal length of 1880mm which is about 0.75 reduction even though the CCDT67 when spaced properly yields closer to 0.67.  I modeled the telescope in OSLO and given my own measurements discovered that the actual focal length of the telescope was closer to 2690mm as a result of pushing the primary closer to the secondary to force the image plane fall on the CCD chip. 

Since a true RC should have the mirrors precisely at their design positions (even though I doubt this is really critical with the 200R's), I was just curious if anyone knew where the design position of the focal plane is. My guess is it's about 50mm or so inward from where I now have it - which doesn't allow much room for cameras, diagonals, etc.  It almost looks like a focal reducer must be mounted directly on the rear cell with the camera spaced as required from that point - then of course we'd have to use the coarse focuser, and we know how well that would work.

#4 Mark Sibole

Mark Sibole

    Advanced Member

  • Administrators
  • 2368 posts

Posted 17 August 2007 - 06:27 PM

all good questions.
Im by no means an expert of the design of the telescope but from past expierences id guess the calculated position is anout half way through the travel.
Or to make it closer it would be the position of the rear cell when you are at focus with the diagonal and 26 mm eye piece.
Now like I stated im no expert and im just going on a guess here.
Although the rear cell moves and the focal length does change im not sure if there is a very noticable difference visuallyt but you would more than likey see it on a ccd chip.
Sorry I couldnt be more help.
Maybe some 1 else will chi,me in with better answers.

Regards

Mark
Mark Sibole
MTSO Observatory
Fife Lake, Mi.

http://astronomy.qteaser.com

#5 k8jb

k8jb

    Newbie

  • Members
  • Pip
  • 3 posts

Posted 18 August 2007 - 10:26 AM

It's definitely noticeable on the CCD - I'll bet that's why Meade only has the rear cell focal reducers - now if someone would design one for the 200R...I was browsing the RCOS website (dreaming, of course) and they provide much more technical info for their products.  Of course, I'd expect that for an OTA starting at $15K! But so far, I'm pleased with the 10" LX200R, it's quite a step up optically from my old 8"LX200GPS which I thought was reasonably good.

#6 gardner4m

gardner4m

    Newbie

  • Members
  • Pip
  • 5 posts

Posted 20 August 2007 - 06:40 AM

Does anyone know if Meade or another mfr. is planning to offer a Focal Reducer designed exclusively for optics of the LX200R?.....thanks for info...

#7 Mark Sibole

Mark Sibole

    Advanced Member

  • Administrators
  • 2368 posts

Posted 20 August 2007 - 11:11 AM

This im not sure of but ill do my best to find out.

Regards

Mark
Mark Sibole
MTSO Observatory
Fife Lake, Mi.

http://astronomy.qteaser.com

#8 gardner4m

gardner4m

    Newbie

  • Members
  • Pip
  • 5 posts

Posted 21 August 2007 - 11:21 AM

Thank you Mark...I look forward to more information on this before I purchase the current Meade f6.3 FR.

#9 gardner4m

gardner4m

    Newbie

  • Members
  • Pip
  • 5 posts

Posted 06 September 2007 - 11:22 AM

Mark.....any info on this?.....will the current Meade f6.3 focal reducer work fine on the LX200R or will there be a version for the "R" series....Thanks in advance.

All the best,

Gardner

#10 Mark Sibole

Mark Sibole

    Advanced Member

  • Administrators
  • 2368 posts

Posted 07 September 2007 - 07:37 AM

Gardner,
I apologize as I forgot about this subject.
I just E mailed them to see if I can find anything out.
When i get an answer ill let you know.

Regards

Mark
Mark Sibole
MTSO Observatory
Fife Lake, Mi.

http://astronomy.qteaser.com

#11 akjudge

akjudge

    Advanced Member

  • Members
  • PipPipPip
  • 116 posts

Posted 07 September 2007 - 10:07 AM

If it helps...

I am using the Meade f/3.3 focal reducer on an 8" LX200r without any problems.

While the margin of error (train length) is not as forgiving as the f/6.3 focal reducer, it works fine for me.

Since the "advanced" RC design of the R series supposedly produces a flatter-field and is coma-free, the standard Meade focal reducers should work even better than on the classic RC, shouldn't they?

I notice that the LX200R/RCX400 Astrophotographer's Kit on page 137 of the catalog lists the standard Meade f/6.3 reducer.

Meade also says that it's f/3.3 focal reducer can be used on any RCX series (which also has the same "advanced" RC design as the LX200R.

Jim

#12 gardner4m

gardner4m

    Newbie

  • Members
  • Pip
  • 5 posts

Posted 07 September 2007 - 11:10 AM

Jim...thank you...that's the answer I was hoping for. I'll go ahead and get the f6.3 now.

I'll take a look at the AP kit on page 137 of the catalog too...I missed that info somehow....

Mark....thank you for checking into this...I look forward to hearing the results of your email inquiry.

All the best,

Gardner

#13 Mark Sibole

Mark Sibole

    Advanced Member

  • Administrators
  • 2368 posts

Posted 07 September 2007 - 06:59 PM

Gardner
I heard back from my contact today and explained things to them.
They are going to look into this and when I hear more ill get back with you.
Im not sure how long this process will take but at least they are willing to look into this for us.

Regards

Mark
Mark Sibole
MTSO Observatory
Fife Lake, Mi.

http://astronomy.qteaser.com

#14 gardner4m

gardner4m

    Newbie

  • Members
  • Pip
  • 5 posts

Posted 08 October 2007 - 01:23 PM

Hi Mark,

Any responses from your contact regarding the f6.3 reducer?.....thanks for looking into this.

Gardner

#15 Pete_Albrecht

Pete_Albrecht

    Newbie

  • Members
  • Pip
  • 2 posts

Posted 17 October 2007 - 10:30 AM

Hi, Mark.

I just stumbled on this thread.

Yes, I too would really truly like to know the location of the "design" focal plane for the LX200GPS.

I know Meade has some specific distance; after all, in the shop, their mirror test rigs, for use while the primary and secondary are being figured are set up with specific distances.

It would be good to know where this is _intended_ to be (regardless of whatever range may be provided by the coarse focus knob, regardless of whether a microfocuser is in the path or not, etc).

Reason for my interest: not so much to get exactly f/10.0000 (highly unlikely anyway) but to know where the inherent aberrations of the design are (allegedly) at their minimum, and to go from there in placing focal reducers or native-focus cameras.

What we would need is not the distance behind the primary mirror surface, because we can't reach that for measurements; we would need distance behind the backplate, or behind the SCT threads.

Thanks in advance,

Pete

#16 lcoffey

lcoffey

    Newbie

  • Members
  • Pip
  • 3 posts

Posted 03 December 2007 - 05:14 PM

I too would also like to know this.
I am doing a month long mosaic at the moment so I am not so bothered but I refuse to use the focal reducers now.
I have come across some serious problems with using meade focal reducers with the Meade "Ritchey-Chrétien" scopes.

I always thought Ritchey-Chrétien scopes were meant to have a secondary mirror focus to allow the mirrors to stay true to each other, else doesn't that fail one criteria of a Ritchey-Chrétien if a mirror shift is used for focus?

#17 Mark Sibole

Mark Sibole

    Advanced Member

  • Administrators
  • 2368 posts

Posted 30 August 2015 - 05:36 AM

I think someone at Meade forgot about us and my questions.Ill have to resend e mails to them to see if we can get an answer.I know in the past the .3. focal reducer was designed for the small ccd chips of the time.Ive tried the 3.3 on my lx200R with no success.Way to much coma on the edges.I do infact use the .63 focal reducer with no problems.You can play with the spaceing to vary the reduction and see what yeilds the best results.I found for me anywars a reduction in spacing yelided the best results giving me roughly a .7ish reduction.

 

Mark


Mark Sibole
MTSO Observatory
Fife Lake, Mi.

http://astronomy.qteaser.com

#18 Mark Sibole

Mark Sibole

    Advanced Member

  • Administrators
  • 2368 posts

Posted 30 August 2015 - 05:44 AM

I sent out an e mail today to see if anything has been done about this and also even though its sunday ill make a phone call later in the day to an old friend who may be able to shed some light on this if Meade has made no progress on their focal reducers.

 

Mark


Mark Sibole
MTSO Observatory
Fife Lake, Mi.

http://astronomy.qteaser.com

#19 Stratocaster

Stratocaster

    Member

  • Members
  • PipPip
  • 10 posts

Posted 07 September 2015 - 11:32 AM

Does anyone know if Meade or another mfr. is planning to offer a Focal Reducer designed exclusively for optics of the LX200R?.....thanks for info...

 

I have an LX200 ACF (which is supposed to have the same optics as the R).  I use an Optec Lepus reducer, which is made for ACF optics.  Changes the F/10 to F/6/3.  It works great!

 

-stan in Brooklyn



#20 meademods

meademods

    Member

  • Members
  • PipPip
  • 24 posts

Posted 23 September 2015 - 11:25 AM

I can help fix your scope.

I know how to remove 95% of mirror slop in the Meade LX200 GPS/R/AFC telescopes.

I have performed this work On many club members scopes. I also have upgrades as well on cloudy nights.


Howard County Astronomical League  

Telescope repairs and Upgrades

Meade LX200 GPS 10" F10

Meade Series 5000 80MM APO triplet F6

Meade Model 320 80MM F11

Cloudy Nights

 

 

Meademods





0 user(s) are reading this topic

0 members, 0 guests, 0 anonymous users