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LX850 imaging train with Powermate

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#1 Oberon510

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Posted 12 April 2021 - 02:49 PM

Hi All,

 

I have a new 10" LX850 which I am using for AP work. It is configured for two setups - Solar System and DSO (where I use a Lepus reducer). I am hoping there are some owners out there that have gone down this path and can advise me on my setup. Unfortunately Meade would not provide a reference implementation for any setup apart from the back focus number below.

 

Meade advised that the back focus for the LX850 is 4.57".

 

My question is with Solar System imaging setup (1) below and whether I should be putting in extensions into the imaging train and where? Do I need to pad out 4.57" to the Powermate first lens or something else?

 

Setup 1 - 2" rear cell SCT adapter -> M48 T-adapter -> 48mm Extensions (???) -> TV Powermate w M42 T-adapter -> 42mm extensions(???) -> CCD

 

I expect this setup below is straight forward:-

 

Setup 2 - 2" rear cell SCT adapter -> M48 T-adapter -> 48mm Extensions -> M48-M42 (F/M) -> CCD  (length to CCD sensor from Meade rear cell flange is 4.57")

 

Any advise appreciated.

 

Ken



#2 carolinaskies

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Posted 12 April 2021 - 03:30 PM

Hi All,

 

I have a new 10" LX850 which I am using for AP work. It is configured for two setups - Solar System and DSO (where I use a Lepus reducer). I am hoping there are some owners out there that have gone down this path and can advise me on my setup. Unfortunately Meade would not provide a reference implementation for any setup apart from the back focus number below.

 

Meade advised that the back focus for the LX850 is 4.57".

 

My question is with Solar System imaging setup (1) below and whether I should be putting in extensions into the imaging train and where? Do I need to pad out 4.57" to the Powermate first lens or something else?

 

Setup 1 - 2" rear cell SCT adapter -> M48 T-adapter -> 48mm Extensions (???) -> TV Powermate w M42 T-adapter -> 42mm extensions(???) -> CCD

 

I expect this setup below is straight forward:-

 

Setup 2 - 2" rear cell SCT adapter -> M48 T-adapter -> 48mm Extensions -> M48-M42 (F/M) -> CCD  (length to CCD sensor from Meade rear cell flange is 4.57")

 

Any advise appreciated.

 

Ken

Remember that the powermate is changing the focal length by use of a lens to a specific spacing between that lens and your CCD. If you are shooting for a specific F/ratio for the Powermate to effect then you need to check this with platesolving to get the desired focal length.  116mm (4.57") is a figure where the 10" is expected to produce the 2032FL but by platesolving you can establish whether that is correct or not.  Once you establish the proper spacing (if that is what you are shooting to achieve) then you need to place the Powermate front lens at this point to achieve the multiplying factor. Typically you'll use the apropriate adapter to place the camera into the powermate so the sensor is at the position typical for the focal plane to be in focus once modified by the powermate's optics.  

An example of the math you need to figure for specific focal ratio shooting. If you are using the 2x Powermate with the F/8 10" then the focal length should be measured for 2032 * 2 or 4064mm.  Depending on the specific Powermate multiply the 2032 by that factor to see what your result should be.  

With an SCT since the placement of the primary does effect the focal ratio you will have to set and leave the focus knob alone once you have established the 2032(F/8) position and adjust for focus through extensions. This is one reason to consider using a helical focus tube in the system to finetune and get a final measurement.  

For me personally with my F/10 SCTs I don't care about a 'magical' focal ratio especially for planetary.  I simply would have the 2" adapter on the visual back, lock in the Powermate and slip on the camera and focus.  

 



#3 Oberon510

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Posted 13 April 2021 - 08:50 AM

Thanks Paul - It looks like I have some work to do and I appreciate some of the tips in your response also (ala helical focus tube).


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