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What would be the results is a FR is installed backwards.

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8 replies to this topic

#1 BobW55

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Posted 11 September 2019 - 09:39 PM

I have a Stellarvue 0.8X focal reducer installed on my ES ED 102mm FDC100. Scope

I have been comparing some before and after images of the same target, and It appears as though the ones shot without the FR look better??

When the focal reducer arrived, there were no instructions or and indications as to which end went towards the objective lens.

What would be the results if a FR is installed backwards?


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#2 Jon Rista

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Posted 11 September 2019 - 10:23 PM

Is it even possible to install it backwards? Threads are male and female...so, they generally only go one way. To install the adapter backwards I suspect you would need a custom adapter that would allow you to join the same gender threads together...


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#3 sg6

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Posted 12 September 2019 - 01:49 AM

Without looking the unit up you say "focal reducer", not "flattener reducer".

The wording therefore reads that all you have done is reduce the image size and it is not necessarily flattened. So if the edge stars (the usual culprits) are not flattened and the flat central section is now smaller (everything being smaller) so a small flat part and the rest still curved. It could appear worse.

 

There is also the option that is just reducing additional curvature is added so making a greater % of the image curved.

 

Basically what did you purchase?


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#4 BobW55

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Posted 12 September 2019 - 06:15 PM

A stellarvue 0.8x Focal Reducer



#5 richorn

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Posted 12 September 2019 - 06:21 PM

My Skywatcher .8x was specifically called a “flattener/reducer. Is it possible that unit is just a focal length reducer, and you need a flattener?

#6 Chuckwagon

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Posted 13 September 2019 - 12:35 AM

Do you know which model of reducer it is?  I assume since you are using an ES ED102 that it's the SFFR102.  If so, then it's both a reducer and flattener, and it should say it right on the barrel.  It's designed for the f/7 Stellarvue SV102T to make them f/5.6, but also works with the 102 Access refractor too.  I'd suspect it should work with the ES ED102 as well.

 

I don't see any Stellarvue reducers listed on their site that are not also flatteners.  (Though there are flatteners that are not reducers.)  So it should not be a field curvature issue.

 

As noted, I don't think you can install it backwards.  But just to be sure, the side with the female threads is toward the scope, the male threads are toward the imager. 

 

If you are getting odd shaped stars, it may be tilt, or sag from the added length and weight of the reducer.  Also, did you verify your spacing from the reducer to your imaging sensor is 55mm?  If that spacing isn't correct, performance will not be optimal.


Edited by Chuckwagon, 13 September 2019 - 12:37 AM.


#7 BobW55

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Posted 13 September 2019 - 07:46 AM

 

As noted, I don't think you can install it backwards.  But just to be sure, the side with the female threads is toward the scope, the male threads are toward the imager.

Chuck THANK YOU,

 

This is the information I needed and "IS" the way I have it installed.

I do have the correct 55mm back focus to my imager ( ASI294 MC Pro).

Now that I have eliminated that possibility need to look at my capture settings. 

 

Thanks



#8 terry59

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Posted 13 September 2019 - 07:49 AM

Chuck THANK YOU,

 

This is the information I needed and "IS" the way I have it installed.

I do have the correct 55mm back focus to my imager ( ASI294 MC Pro).

Now that I have eliminated that possibility need to look at my capture settings. 

 

Thanks

I'm going to guess the issue is spacing or a poor optical match between scope and fr



#9 Chuckwagon

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Posted 13 September 2019 - 10:45 AM

Chuck THANK YOU,

 

This is the information I needed and "IS" the way I have it installed.

I do have the correct 55mm back focus to my imager ( ASI294 MC Pro).

Now that I have eliminated that possibility need to look at my capture settings. 

 

Thanks

If it's correctly spaced, and not backward, then maybe post a sample of how the images differ.  Seeing what changes in the image between the two setups would help diagnose the type of issue.




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