Field flattener

[Robindonne]

hello and thx for helping in advance. Last week i asked about a problem with not getting in focus with a small zenithstar.   The solutions mentioned were, or an 2” extension-tube or a ff/fr.  Yesterday on our dutch marketplace website, an es mpcc came for sale.   It was so cheap i had to buy it.   On my way home I realized it is only a flattener and no reducer.  So my needed extra focus length was probably still not solved, except for the small amount of mm’s this flattener will extend my focus length.  I tried it at home and it indeed not solved my focusing problem i quess. i did managed to get in focus on some 100 meter away trees but i dont know if i will get in focus on the 100 ly away trees.  The flattener has about 35 mm tube that might be pulled out a bit but i dont think it will do the thighting any good.  
What would be a good option for me now?  Buy an m48/2” extension tube, an 2” extension, a seperate reducer that might fitt in the m48 thread or just forget about all this and look for an combined ff/fr?   In case of a seperate reducer, the distance between a reducer and the flattener is all abacadabra for me so maybe not the best option. Thx.  

Edited May 25, 2020 by Robindonne

[david_taurus83]

What is the focal length of your scope? You could measure from where the objective is down the scope to where your camera sensor needs to be. Should give you an idea of spacers if needed. I have done this with my 102EDR. With both 1.0 flat and 0.8 reducer, the length is still approximately 710mm.

[Robindonne]

The fl is 418 mm.  Do uou mean i just take a rule and measure the distance from the lens to the camera?    I think im in short of length to have some margin but how do i get these extra mm’s the best?

[david_taurus83]

21 minutes ago, Robindonne said:

The fl is 418 mm.  Do uou mean i just take a rule and measure the distance from the lens to the camera?    I think im in short of length to have some margin but how do i get these extra mm’s the best?

Yes it should give you an idea of where you need to be.

[Robindonne]

1 hour ago, david_taurus83 said:

Yes it should give you an idea of where you need to be.

Oke done.  Its definitely on the edge.  At least when i start from glas and end approx. Where the sensor sits inside the camera.   
if i have to extend, lets say 20 mm, to still keep some margin in the focuser, do i go for a small extension tube with filter-thread to connect it to the flattener, or a 2” extension with the tightning screws, or should i better search for a focal reducer? I want to add more length anyway.  Or better just go for an combined ff/fr?

[alacant]

3 hours ago, Robindonne said:

have to extend, lets say 20 mm,

Hi. Best to get a set to cover all eventualities. Far cheaper than buying new glass.

HTH.