Jump to content


Photo

focus shift in LX850

  • Please log in to reply
27 replies to this topic

#1 cherokeeridge1

cherokeeridge1

    Lift Off

  • -----
  • Posts: 10
  • Joined: 29 Mar 2011

Posted 18 October 2013 - 10:48 AM

I have a new LX850 with an Optec TCF focuser attached. I use Focusmax to focus and have noticed a huge difference in the focus position, depending on where I aim the scope. For example if I focus at 40 degrees zero hour angle and then slew to -5 degrees +4 hour angle the focuser has to move out about 650 steps to reach focus. When I move back to 40 degrees 0 HA it has to go back in 650 steps. The focus at other sky angles is somewhat proportional to this. I suspect the mirror is moving in the scope because nothing external is moving but Meade claims there is no mirror shift in these new scopes. Does anyone have any knowledge about this?

Attached Files



#2 Spacetravelerx

Spacetravelerx

    Surveyor 1

  • -----
  • Posts: 1772
  • Joined: 23 Dec 2012
  • Loc: New Mexico

Posted 18 October 2013 - 11:05 AM

Is your mirror locked?

What size mirror do you have?

I have noticed some subtle focus shift over time (2-3 hours), but I have attributed it to either temperature changes and/or the electric/motor focuser that comes with the LX850.

#3 cherokeeridge1

cherokeeridge1

    Lift Off

  • -----
  • Posts: 10
  • Joined: 29 Mar 2011

Posted 18 October 2013 - 02:08 PM

My LX850 does not have a lock. It is a 12". Yes, I would expect some change as a result of temp change and hopefully my TCF focuser will take care of that. This new crayford type focuser was advertised as not needing a lock but it looks like it does. I know that the crayford that I have on a refractor does need to be locked.

#4 Spacetravelerx

Spacetravelerx

    Surveyor 1

  • -----
  • Posts: 1772
  • Joined: 23 Dec 2012
  • Loc: New Mexico

Posted 18 October 2013 - 02:19 PM

My LX850 does not have a lock. It is a 12". Yes, I would expect some change as a result of temp change and hopefully my TCF focuser will take care of that. This new crayford type focuser was advertised as not needing a lock but it looks like it does. I know that the crayford that I have on a refractor does need to be locked.



Ahhh, I am not an expert, but the Crayford focuser only helps really with image shift while focusing. That works fine and works as advertised by Meade (see also page 21 of the user manual). It does not help with mirror flop which is what you are experiencing it sounds like.

My 14" has a mirror lock. I thought all the LX850s had mirror lock. Is yours new or part of the recalled LX800 batch?

#5 cherokeeridge1

cherokeeridge1

    Lift Off

  • -----
  • Posts: 10
  • Joined: 29 Mar 2011

Posted 18 October 2013 - 02:29 PM

I just got mine new about 6 weeks ago.

#6 maugi88

maugi88

    Postasaurusrex

  • -----
  • Posts: 3394
  • Joined: 25 Aug 2013
  • Loc: SE MN

Posted 18 October 2013 - 02:32 PM

Mine has no lock

#7 cherokeeridge1

cherokeeridge1

    Lift Off

  • -----
  • Posts: 10
  • Joined: 29 Mar 2011

Posted 18 October 2013 - 02:56 PM

Apparently there has been a change in the design and depending on when the scope was made, you might get a lock and you might not! It is needed for imaging.

#8 Alph

Alph

    Surveyor 1

  • -----
  • Posts: 1759
  • Joined: 23 Nov 2006
  • Loc: Melmac

Posted 18 October 2013 - 03:15 PM

It does not help with mirror flop which is what you are experiencing it sounds like.


It appears so. I have noticed a similar behavior with my 12 incher. While I was testing a focal reducer, I have noticed that stars on one end of the CCD changed shape from round to elongated when I slewed to a different location in the sky. On the other hand a 60 point TPoint model usually gives me pointing error under 10 arc-second which seems to indicate that the mirror flop is not that bad.

#9 Alph

Alph

    Surveyor 1

  • -----
  • Posts: 1759
  • Joined: 23 Nov 2006
  • Loc: Melmac

Posted 18 October 2013 - 03:16 PM

Apparently there has been a change in the design and depending on when the scope was made, you might get a lock and you might not! It is needed for imaging.

Only the 14 incher was upgraded with a mirror lock.

#10 Spacetravelerx

Spacetravelerx

    Surveyor 1

  • -----
  • Posts: 1772
  • Joined: 23 Dec 2012
  • Loc: New Mexico

Posted 18 October 2013 - 03:30 PM

That is the problem then...no mirror lock for the 10" and 12" models.

So if I understand correctly you will need to refocus whenever you move to a different part of the sky.

#11 cherokeeridge1

cherokeeridge1

    Lift Off

  • -----
  • Posts: 10
  • Joined: 29 Mar 2011

Posted 18 October 2013 - 03:35 PM

So does your 12" have the lock or not? Yes I also achieved under 10" pointing accuracy with TPoint on my MX mount and that's why I had ruled out mirror flop but then I noticed a huge difference in focus at different locations in the sky so I wondered what's going on. Don't know whether or not the mirror lock would help this problem.

#12 Alph

Alph

    Surveyor 1

  • -----
  • Posts: 1759
  • Joined: 23 Nov 2006
  • Loc: Melmac

Posted 18 October 2013 - 03:43 PM

no mirror lock for the 10" and 12" models.


That's correct. During tests, the 14" model exhibited image shift when guided with the starlock. They did not notice a similar image shift with smaller models.

#13 maugi88

maugi88

    Postasaurusrex

  • -----
  • Posts: 3394
  • Joined: 25 Aug 2013
  • Loc: SE MN

Posted 18 October 2013 - 04:47 PM

I bought my 12" to use it for photography. I planned on getting the camera next year. I am going to be really *BLEEP* if I cant us it for rock steady imaging as meade has claimed. I paid for a professional class instrument. It better work great.

#14 Spacetravelerx

Spacetravelerx

    Surveyor 1

  • -----
  • Posts: 1772
  • Joined: 23 Dec 2012
  • Loc: New Mexico

Posted 18 October 2013 - 04:53 PM

I bought my 12" to use it for photography. I planned on getting the camera next year. I am going to be really *BLEEP* if I cant us it for rock steady imaging as meade has claimed. I paid for a professional class instrument. It better work great.


Well, it may all depend.

I am not familiar with the specs of the smaller mirror systems, but if you are looking at doing guided images longer than a couple of hours you might have some small mirror flop issues.

My guess is you will be ok though.

#15 maugi88

maugi88

    Postasaurusrex

  • -----
  • Posts: 3394
  • Joined: 25 Aug 2013
  • Loc: SE MN

Posted 18 October 2013 - 05:10 PM

I bought my 12" to use it for photography. I planned on getting the camera next year. I am going to be really *BLEEP* if I cant us it for rock steady imaging as meade has claimed. I paid for a professional class instrument. It better work great.


Well, it may all depend.

I am not familiar with the specs of the smaller mirror systems, but if you are looking at doing guided images longer than a couple of hours you might have some small mirror flop issues.

My guess is you will be ok though.


I live in red suburban skies. I will be doing several hour exposures. This is NOT OK. I spent thousands on this thing as everybody knows, anything less than exceptional crisp images are not acceptable. Any mirror movement at all is a deal breaker.

I am expecting a fix for this MEADE you listening?

#16 cherokeeridge1

cherokeeridge1

    Lift Off

  • -----
  • Posts: 10
  • Joined: 29 Mar 2011

Posted 18 October 2013 - 05:24 PM

Maugi88
I would suggest you take this up with Meade while it is still under warranty because it does cause a problem maintaining focus while imaging. If you will refer to my original post I attached some graphs of the effect I was seeing in changing focus positions at different points in the sky. When you get started imaging you will face enough other problems that if you can prevent this one by sending it back to Meade now I think you will be glad you did. Meade may or may not be willing to upgrade your scope but it's worth a try. I noticed your location is just "up river" from mine so good luck from a fellow mid westerner.

#17 maugi88

maugi88

    Postasaurusrex

  • -----
  • Posts: 3394
  • Joined: 25 Aug 2013
  • Loc: SE MN

Posted 18 October 2013 - 05:27 PM

Maugi88
I would suggest you take this up with Meade while it is still under warranty because it does cause a problem maintaining focus while imaging. If you will refer to my original post I attached some graphs of the effect I was seeing in changing focus positions at different points in the sky. When you get started imaging you will face enough other problems that if you can prevent this one by sending it back to Meade now I think you will be glad you did. Meade may or may not be willing to upgrade your scope but it's worth a try. I noticed your location is just "up river" from mine so good luck from a fellow mid westerner.


Seriously thinking about it. I am going to talk to them about it for sure.

Really like the scope and already bought and foams out a pelican case for OTA.

Not happy :mad:

#18 maugi88

maugi88

    Postasaurusrex

  • -----
  • Posts: 3394
  • Joined: 25 Aug 2013
  • Loc: SE MN

Posted 18 October 2013 - 07:08 PM

To be fair to MEADE I feel like I should post what just happened pertaining to this issue.

I emailed Meade about my concern about the mirror flop possibility and immediately received a call by the head of the customer service department.

Of course he assured me that there are not mirror flop issues with the 12" lx850 as a whole and unfortunately some scopes make it out of manufacturing with regrettable flaws.

I then told him that my concern was that I won't be able to afford a camera for well after my warranty is expired to test my scope. He assured me that Meade will absolutely stand behind their products and make it right if I have a problem.

It did make me feel better that they responded so quickly. Thinking about the extended warranty and really want to get my hands on a camera to test it.

#19 maugi88

maugi88

    Postasaurusrex

  • -----
  • Posts: 3394
  • Joined: 25 Aug 2013
  • Loc: SE MN

Posted 18 October 2013 - 07:31 PM

I noticed your location is just "up river" from mine so good luck from a fellow mid westerner.


How far "up river" am I from you. You have no location on your profile.

#20 cherokeeridge1

cherokeeridge1

    Lift Off

  • -----
  • Posts: 10
  • Joined: 29 Mar 2011

Posted 18 October 2013 - 09:47 PM

Southeast Iowa

#21 maugi88

maugi88

    Postasaurusrex

  • -----
  • Posts: 3394
  • Joined: 25 Aug 2013
  • Loc: SE MN

Posted 18 October 2013 - 10:02 PM

I have been down in the
Dewitt area but not as far as Davenport

Beautiful country.

#22 Alph

Alph

    Surveyor 1

  • -----
  • Posts: 1759
  • Joined: 23 Nov 2006
  • Loc: Melmac

Posted 19 October 2013 - 01:12 PM

I use Focusmax to focus and have noticed a huge difference in the focus position, depending on where I aim the scope.


Just looked at your spreadsheet. If you had temperature compensation enabled then you should turn it off and repeat your tests

#23 niteman1946

niteman1946

    Ranger 4

  • -----
  • Posts: 314
  • Joined: 16 Feb 2008
  • Loc: Fort Worth, TX

Posted 19 October 2013 - 04:28 PM

Sorry guys, can't help myself. I have a 12" Classic and thought it was the last generation without mirror lock. The GPS model does have the lock feature, and I thought all subsequent SCTs had it. I remember Jason Ware's posts including mention of his LX850 having the mirror lock.

Why would Meade abandon this? Or am I missing something fundamental, and a version of this feature is still there?

#24 cherokeeridge1

cherokeeridge1

    Lift Off

  • -----
  • Posts: 10
  • Joined: 29 Mar 2011

Posted 19 October 2013 - 04:42 PM

I had the temp compensation disabled while doing the focus runs and you can see those focus points in the data but then I factored in temp comp to do the graph. In the data you will see one column for actual focus reading and another for compensated readings. I am now convinced that my primary mirror is moving and that's why I see the large spread as I move the telescope around the sky.

#25 cherokeeridge1

cherokeeridge1

    Lift Off

  • -----
  • Posts: 10
  • Joined: 29 Mar 2011

Posted 19 October 2013 - 04:46 PM

I believe that Meade thought the newly designed focus mechanism (dubbed as Crayford like) would not need a lock but they are finding out now that it does. Seems like something that should have been tested before marketing.






Cloudy Nights LLC
Cloudy Nights Sponsor: Astronomics