moon with a dslr and 8" dob

[rmuhlack (Richard)]

Decided it was time to mod the 8" f6 dob so that I could achieve prime focus with the DSLR. So, removed the mirror cell from the tube, checked the thread size of the adjustment bolts (6mm for a GSO/Bintel dob), and after a quick trip to bunnings I had some new 50mm long screws and new compression springs. 10 minutes or so to fit, 5-10 minutes to do a quick recollimate using the laser collimator thingy, and i'm in business!

Confirmed this evening that i still have (when using a 35mm extension tube) a workable scope for visual use. And the clincher - yes i have the correct Bahtinov diffraction pattern with the DSLR at prime focus (this time without the extension tube). So thought I'd bust out a couple of prime focus shots of the moon.

This is a 1/4000s single uncalibrated exposure at ISO400 with the modded 400D and MPCC, on the dob mount. No tracking - just a fixed shot, together with a crop of the same shot to illustrate the detail a bit better.

The OWL Diagonal Calculator indicates an illumination of ~93% at the edge of the DSLR sensor, with 100% illumination out to about 0.4" field radius - so will be some minor vignetting, but that's what flats are for right!. Anyway - can't wait to set up with the NEQ6 and try this baby out on a couple of my previous targets - M83, NGC6744 and M20.

[jjjnettie (Jeanette)]

Sweet as.

[Forgey (Paula)]

very nice

[2stroke (Jay)]

Thats mint lol wish i did that with the old 6" F8 before taking a angle grinder to the tube haha

[stephenb (Stephen)]

Very nice work, Richard! Wait for a first or last quarter Moon and watch those craters jump out at you!

[stephenb (Stephen)]

Very nice work, Richard! Wait for a first or last quarter Moon and watch those craters jump out at you!

[Colin_Fraser]

Great job Richard. Really like the full moon

[Rex]

Beautiful Richard. Very sharp.

[cpoc]

I know this is an old post but I only recently got my dobsonian (used to have one but had to sell it... so back in the game now).
In terms of swapping out the screws... do you remove the entire primary mirror portion (ie unscrew the screws on the side of the telescope)... then remove all (I think it's 6 on mine) screws at the bottom and replace. Three have springs three don't, my understanding is three are for colimating and three are for locking in place, do they all get replaced with the same length screws but only three have springs? Thanks for any help... otherwise I might give it a try later anyway (and possibly take video if I can, to help anyone else who wants to try it.)

[raymo]

Good job. You wouldn't have had to bother with longer screws etc if you'd
bought a Skywatcher.
raymo

[Allan_L (Allan)]

Originally Posted by cpoc

I know this is an old post but I only recently got my dobsonian (used to have one but had to sell it... so back in the game now).
In terms of swapping out the screws... do you remove the entire primary mirror portion (ie unscrew the screws on the side of the telescope)... then remove all (I think it's 6 on mine) screws at the bottom and replace. Three have springs three don't, my understanding is three are for colimating and three are for locking in place, do they all get replaced with the same length screws but only three have springs? Thanks for any help... otherwise I might give it a try later anyway (and possibly take video if I can, to help anyone else who wants to try it.)

What sort of scope is it that you have?
As Raymo said, if its a Skywatcher you don't need to adjust it at all.

[cpoc]

Originally Posted by Allan_L

What sort of scope is it that you have?
As Raymo said, if its a Skywatcher you don't need to adjust it at all.

It's a 10" Bintel. I've already tried the barlow lens and taking the adapter out to have it sitting as low as possible in the focuser but it's just a smidge out of range of focus.

I managed to get some bolts today (including the rare m7 bolts as my mirror is fastened with both m6 and m7 bolts).


So am I correct in that I need to take the whole primary mirror portion off (by unscrewing the screws around the side of the base of the OTA)... then carefully unscrew the bolts that are currently in place and replace each one (as I go, ie take one out, put replacement in.... move on to the next, take it out put replacement in etc)?


I haven't found any extensive video yet for how to do it (my preferred learning aid)... but I think I have an idea of how to do it.
Just nervy doing anything to/near the mirror.