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What flattener (not reducer) for an 140mm F/6.5?

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#1 Der_Pit

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Posted 08 March 2020 - 04:50 PM

Hi Refractor-lovers!

 

I'm seriously considering to buy the new Sharpstar AL-140PH (as TSAPO140), but am unsure about what flattener to get.  Sharpstar themselves do have a 3" reducer, but no dedicated 1× flattener (and seem to recommend their 2.5" one).

I was looking at the APM Riccardi v1.  Would you consider that one reasonable, or are there (now) probably better ones for a 910mm F/6.5 APO?


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#2 MirkoV69

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Posted 09 March 2020 - 08:15 AM

Hello there.

 

I am looking into the same OTA ( smile.gif )  , from my research I found TS has a 1x Flattener 3" , see here:

 

https://www.teleskop...-Anschluss.html

 

 

 

Mirko



#3 drd715

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Posted 09 March 2020 - 10:52 PM

Interesting new scope. Probably perfect for astrophotography. The focuser seems similar to my APM152ED with the 3.7inch focuser. I am using the Ricardi 1X flattener. It connects with an 82mm threading and APM made the spacing extension to the zwo camera face.

Check with TS to confirm the 4 inch focuser has an 82mm threaded connection for a Ricardi flattener.

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#4 Der_Pit

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Posted 10 March 2020 - 03:06 AM

Interesting new scope. Probably perfect for astrophotography. The focuser seems similar to my APM152ED with the 3.7inch focuser. I am using the Ricardi 1X flattener. It connects with an 82mm threading and APM made the spacing extension to the zwo camera face.

Check with TS to confirm the 4 inch focuser has an 82mm threaded connection for a Ricardi flattener.

Thanks!  So are you satisfied with it?

The scope side thread might be an issue, there is only M102, M88 and M68 available (see here), so I'd need a special adapter.  The exit side of the Riccardi seems to be M68x1 female, so I should be able to use the original adapters of the telescope from there on (i.e., 'replacing' the M88→M68 step with the flattener).



#5 drd715

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Posted 10 March 2020 - 12:10 PM

Thanks! So are you satisfied with it?
The scope side thread might be an issue, there is only M102, M88 and M68 available (see here), so I'd need a special adapter. The exit side of the Riccardi seems to be M68x1 female, so I should be able to use the original adapters of the telescope from there on (i.e., 'replacing' the M88→M68 step with the flattener).

I'm using the larger Ricardi diameter. I think they make a slightly smaller diameter also. The larger one comes in two versions (in 1X), basically the same but designed for longer fl and shorter fl with an overlapping range at about F-7 plus or minus. Inquire about the thread size on the 4 inch focuser directly to TS for exact details on the focuser threads for best information, specifically ask about the fitment of the Ricardi flattener. Also Markus ludes at APM has some back focus charts with spacing for the Ricardi flatteners (to a large variety of different telescopes) . The Ricardi 's are first class quality. The larger diameter version will provide a flat field to cover all of a full frame sensor. APM will make special back focus spacers that thread onto the Ricardi - you may have to specify the optical train as having a specific camera imager setback sensor and if using any devices are in between such as filter slider or wheel and OAG device.

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#6 Der_Pit

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Posted 24 March 2020 - 02:43 PM

So I finally decided for the version 1 Riccardi flattener (for FL up to 1m).  There is no dedicated M82-to-M88 or M82-to-M102 adapter, but an M82-to-M68 one.  For now, I use that one.  It's still more than enough for my ASI1600.  Supposed BF is 90.7mm.  I also ordered a M68 Baader VariLock, to have some room for adjustment.




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