My 2" Crayford arrived from Aust on Monday ( Thanks Stacey ) and last night I got enthusiastic and decided to swap the old 1.25" out. A few extra holes and it was on. Dragged the scope outside the garage door and bingo, a perfect fit. All EP's working and mid ranged on the travel and the barlow still works.
So, feeling very enthusiastic I built a T connector for my DSLR from a spare body plug and 2" diameter alum tubing epoxied together. I think I will have enough intravel for this to work but if not I have another plan. My strut tubes just slide down behind the corner clamps and seat on the cell mount blocks. I can slide the struts up, place some 20-30 mm spacer blocks beneath, then reseat the tubes and I'll gain an extra 20-30 mm intravel. Yes, it was in the original planned functionality in case I got my calcs wrong.
Then feeling even more ambitious I attacked my 114mm f5 Newt, the instigator of my aperture fever. After viewing through the 10", the little 4.5" was showing it's faults. One of it's major faults was diffraction and poor acuity. The prime suspect looks to be the cheap cast aluminium front cap/spider/hub assembly. Although the diag mirrors minor axis is only 23 mm the hub is 40 mm and the 'vanes' are 5 mm wide !
Newt reveals it is failing on all vignetting points and obscuring 12% of the available photons + probably another 3% or so for the vanes, maybe more.
I have/had an old 4" newt I was given which has the same size tube as the 4.5". The spider and hub is a tiny little thing on three screw in rods of about 2.5mm diameter. The hub is about 18 mm across. I can attach the bigger mirror for the 4.5" to the hub with Silastic and replace the heap of scrap currently there I can fix all three vignetting factors and only obscure 3% of the available photons plus maybe 1-2% for the vanes. The vanes are currently chromed !! ...Flat black spray paint will fix that and I'll modify the outer ring of Alum so it stabilizes the OTA tube. I just gained about 10% more photons for free ! I may replace the vanes with 1mm alum like the 10" one day but for now I'm happy. Mirror still needs to be attached and aligned but I'll post the results when thats done.
I'll poke up a few pics of the Crayford install and if anyone is interested the mods to the little 4.5". I want to take this away as a grab and go for a 2 week travel trip next year so if I can improve it's performance, especially for nothing then it will have been well worth while. And if friends come round then I have another scope to share.
