What will a reducer do for me?

[SmokeyJoe]

  Money is tight and I've been down many a wrong road persuing this wonderful frustrating hobby so I want to make sure I'm getting bang for my buck so to speak.   I've got a couple of hundred quid to spend on astronomy and one of the items on my 'to buy' list is a reducer for my SW ed80.  Currently using an EQ5, Canon 450D, ZWO 120mm through supplied SW finder scope for a guidescope all run from an Asiair Pro. 

  Not too bothered about FOV at the moment (well not bothered enough to spend 200quid).

  Not too bothered about edge distortion (photshop crop). 

  So given my current setup what practical difference can I expect between  f7. 5 and f6. 37? 

[vlaiv]

You named the main two - and you are not too bothered by either

Focal reducers do just that - reduce focal length. Sometimes field flatteners also act as focal reducers. These flatten the field and remove aberrations further from optical axis.

FF/FR for ED80 does both - it reduces focal length and hence increases FOV and also fixes optical issues that you would otherwise crop away.

There is one more thing that is important if you are only introducing FF/FR into optical train and keeping both scope and camera as they are at the moment. Resolution reduces and "speed" - or Signal To Noise ratio achieved in given time - increases. Different way of thinking about it - you can get as good image in less time but at lower sampling rate.

[SmokeyJoe]

 

6 minutes ago, vlaiv said:

There is one more thing that is important if you are only introducing FF/FR into optical train and keeping both scope and camera as they are at the moment. Resolution reduces and "speed" - or Signal To Noise ratio achieved in given time - increases. Different way of thinking about it - you can get as good image in less time but at lower sampling rate.

Thanks for your prompt reply. I was aware of this, just wondered by how much, i.e. will there be a noticeable effect and given my setup whether it was worth spending £200, or do I put the money in the piggy bank towards a better mount or a dedicated astro cam.