Hey robin,peter,
No it doesn't reduce the Vingetting introduced by the MPCC. but the difference is that the calculations i got when analysing my 10" Dobsonian from Skywatcher showed that on the 40d imaging sensor i only had a 8mm diameter spot that took full advantage of the 10" mirror. the edge had reduced to a mear 78% of the mirror's capacity.
With the upgrade i have gone from 8mm 100% illumination to 24mm diameter 100% illumination. so what i hear most people say?... it means that my image is copping 100% of the mirrors power right upto the MPCC to which mapping the vingetting with flats kills the rest of it. This allows fainter things to show up. not just in the middle of the image! but virtually right to the edge. The mpcc has a 22mm 100% though put corrected circle just for info.
look at this image and youll see what i mean, be sure to notice the faint blue nebulosity's extension to the right hand side, and the Ha loops in the bottom left, you don't tend to see those in M20 images at this kinda image scale and remember im only using a DSLR not a dedicated cooled Astro CCD...
http://s700.photobucket.com/albums/w...m20-worked.png
Taken in the back yard of my mates house in Secret harbor WA 40km from Perth CBD
8 x 10min iso 800 10" guided with finder EQ6pro and modded 40d
No flats, darks or bias taken so it shows the extent to which the 100% illumination is illuminating. Do note that the center 100% illumination isn't 100% in the center hence the vingetting is slightly offset. but now with the cats eye collimation gear + the 3" focuser thats on the way ill sort that when i install the new focuser!
http://s700.photobucket.com/albums/w...d.jpg&newest=1
This is the best photo that i can find that shows vingetting. with the same setup youll notice that the noticable darkness happens alot earler and that is without the MPCC... so thats just open with no vingetting due to focuser nor adaptors. Ill do a test this week with the flats box to make a definate comparison in relation to the increase in secondary size to vingetting spot size.
Rob,
everything i do has a alteria motive! i don't upgrade these parts for the mear fact of trying to get more juice out of a already squeezed lemon (figure of speach). Im working towards a premium ultra fast newtonian... or as some would call it UWFW... (ultra wide field whooze). As i cannot see myself getting a dome for at least 4 years maybe more making high res long focal length very hard. So having premium bits will allow me to get the best i can from this 10" sw dob before i custom make a CF tube and drop a fast F3 - 3.5 10-14" mirror, then ill swap everything straight over. Almost like layby... plus im a OCD tinkerer