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Are there any generic field flatteners, e.g. for a 178ED?

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#1 deanbrown3d

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Posted 17 February 2019 - 12:54 AM

Hello all,

 

I've been experimenting with astrophotography using a Meade 178ED refractor, and I wanted to ask about a field flattener (I can't find anything specific for this scope). Can you tell me - are field flatteners usually made for specific OTAs or are there some that are generic for different telescopes?

 

As far as I know there is no filter thread on the scope that could be used for this. It would have to be mounted on a 2" tube or something like that.

 

Any advice appreciated!

 

-Dean


Edited by deanbrown3d, 17 February 2019 - 12:54 AM.


#2 Ian Robinson

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Posted 17 February 2019 - 01:15 AM

I would expect any FF designed for a f9 APO will work.

https://www.365astro...refractors.html

Edited by Ian Robinson, 17 February 2019 - 01:18 AM.


#3 sg6

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Posted 17 February 2019 - 03:10 AM

Usually a manuacturer will say it is for a specific scopeof theirs, however years back they were described as more generic, actually not scope specific then.

 

They were and in many cases are focal ratio specified, not so much focal length which would seem to be the factor as focal length appears more related to curvature. But that is not what they refer to.

 

Not really seen one for f/9 - assuming that is what yours is from one reply.

 

WO have a fair selection of flatteners but you likely have ES, Skywatcher and on the TS site there will be a few with their name on them. TS may be a fair option as TS items are/were often GSO sourced and Meade used GSO equipment.


Edited by sg6, 17 February 2019 - 03:11 AM.


#4 Ian Robinson

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Posted 17 February 2019 - 05:28 AM

Easy to find the specs for this online
meade-ed-refractors-old.png

#5 junomike

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Posted 17 February 2019 - 08:27 AM

Ian's link in post #2 will be your best bet.  How are the pics sans a flattener?



#6 carolinaskies

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Posted 17 February 2019 - 09:20 AM

Flattners are made in both generic and specific designs. 

Specific flattner designs are carefully matched to the Petzval field curvature of a specific lens set. However that doesn't mean they won't work on a similar focal ratio telescope.  The reason is that the focal ratio of aperture to focal length creates a similar curvature so the 'correction' to flatten the curvature even of dissimilar elements will have some similarity in Petzval curvature.   

This is the general principle behind the generic flattners.  It's also why they tend to be much cheaper because less 'fine tuning' is done but rather a generic correction.  As with all things the effective result is going to depend on how well the specific flattner corrects a specific telescope lens set.   

Serious imagers spend the big bucks for matched flattners to get the best possible results, often the flattner can cost 30% or more of what the telescope itself sold for. 

The need for a flattner increases with the curvature therefore the shorter focal ratios (F/7 and faster) have more flattners made for them. 
 


Edited by carolinaskies, 17 February 2019 - 09:22 AM.



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