APM 140mm doublet - focal reducer

[Kunwar]

Hi all

I recently bought an APM 140mm doublet and now looking to source a focal reducer for it for astrophotography. The recommended reducer by APM is the Riccardi Reducer but it's very dear, nearly €500.

I'm wondering if there is such a thing as a "universal" reducer which I can use, that would be more economical? 

I'm reading on this topic and it seems focal reducers are very specific to the brand and model of a scope. I don't fully follow the science of it all so this is a shot in the dark if anyone can provide advice.

 

 

[KP82]

Yes it's generally recommended to use dedicated reducer/flattener for imaging, but there are quite a few universal models (for refractors) under various different brands. For example:

TS Optics 3" 0.79x (there is also a cheaper 2" model available):
https://www.teleskop-express.de/shop/product_info.php/language/en/info/p6085_TS-Optics-REFRAKTOR-0-79x-3--ED-Reducer-Korrektor-bis-Vollformat.html

Stellamira 2" 0.8x:
https://www.firstlightoptics.com/reducersflatteners/stellamira-2-0-8x-reducer-field-flattener-with-m48-adapter.html

As long as the focal ratio of your scope falls within the supported range, they will work. However you will have to work out the precise optimal backspace yourself through trial/error as most of them only provide a rough guideline. I personally have the TS Optics 2" model for my Altair 80 f/6 triplet. It took me several nights (trial/error then buying combinations of extension tubes with different lengths) to find out the optimal backspace for my cameras (about 61.5mm). Once that was sorted out the results were quite pleasing.