Well of late i have been slowly transforming my 10" dobsonian tuned for the visual user into a tuned for the astro photographer.
Motives for doing this.
- 100% illumination of the imaging plane standard = 8mm... BAD
- Primary mirror cell = pitiful
- focuser while it'll do for now = sub standard
Things that I have done so far.
- Increased the 100% illumination of the imaging plane from 8 --> 24mm
- Pulled the primary mirror cell apart and made some adaptions so that the mirror is held in place around the bottom of the mirror. Ive had heart destroying problems for over 6 months trying to figure out what the hell was wrong! Problem here was the mirror cell for the actual mirror is flimsy when i locked the collimation off it would warp the cell, now i thought that using a tissue to make sure that the mirror clips where JUSToff the mirror surface was fine. but once the cell twisted it pushed the mirror into the mirror clips thus causing ASTIGMATISM....... The fix for this was to remove 2 of the felt pads and insert a thin piece of rubber just on the inside of the cell, under the mirrors own weight it should just fall in (maybe a bit of lubricant on the rubber so it doesn't stick), replace the shotty collimation springs and your done! reliable collimation, a mirror cell that doesn't pinch the optics.!
-focuser is still to come! i need some more time in the prototyping lab!
If anybody has done something like this then shout up
The next thing i would like to do is run some baffling down the inside of the OTA, has anybody got any good ideas?
I'm in the process of doing exactly the same thing with my 10". I have a focuser on the way - a Moonlite DC motorised one. Once that turns up, I'll test focus and believe I may need to cut the end down a little to achieve focus with the camera. Lining the tube to cut down reflections, increase contrast, I've been recommended to go to somewhere like Spotlight and get some A4 sheets of felt. I also need to put a fan and probably some sort of dew control.
Could you please explain what you mean by "100% illumination of the imaging plane standard = 8mm... BAD" and how you've increased it from 8 to 24mm? I haven't heard of this.
+1 what Troy said Brendan!?
Do you mean you moved the primary up to increase size of imaging plane, or fiddled with the secondary perhaps?
Great to see more Newts being pressed into imaging service. I think they've been un-necessarily in the minority for too long. I couldn't originally strectch funds to an EQ6 and 10", so will be very interested to hear how you both go.
I changed the secondary from 53 mm to a 70mm version, i would have gone 75mm but i couldn't get that size all in all for 49 +P&H it was the best investment for the 10" since the MPCC!
As for the baffling, i have done some research, finding that baffling is used to stop the reflections from light sources not inline with the mirror, or reflections that come from the front of the OTA onto the mirror which make it into the focal plane.
Using flocking does stop a lot of this because it captures the light before hand. Seeming though the flocking is a little bit exy for my budget, i am using cardboard painted in flat black paint (perfect) so ill let you know how that goes! though as for the felt squares in the focuser it would be perfect!
A good tool for you to have a look at troy is Newt 2.5. you can fiddle and play around with everything in there to let you see whats happening!
Well i was robbed! bloody skywatcher and their infernal shortcuts! the tube diameter is 291mm... basically killing all baffling ideas, onto flocking!
the next thing that is making this 10" more astrograph than visual is the addition of 2 things
Cats eye collimation kit -auto-collimator and cheshire kit.
Feather touch 3" focuser (thanks k rudd)
I believe before to long i will be upgrading the mirror cell to be far more structurally sound. everything should be here Friday week/ early the next so ill put a bit of a write up and photos.
that was the source of my problems that i had for close on 6 months. i thought it was the miss alignment of focuser/primary axis, a chat to a few members saw my problem as astigmatism. I found the problem last weekend...
I set the mirror clips just above the mirror.. all good.
installed the mirror to the OTA, went on my business to collimation.
collimation complete then I'd go for a star test/view... everything was dead. and i know how to collimate a newtonian, done it more times than i could poke a pointy stick at successfully....
what was happening as i would tighten the lock nuts to hold collimation the lock nuts would press onto the mirror cell, from that the mirror cell warped just enough to push the floating mirror into the mirror clips and causing the primary to pinch, of coarse when i pulled it apart to check! no problems as it returned to what it was previously.
hence ill get a decent mirror cell to hold the mirror better, and have increased accuracy in collimation after all with photography you need a whole new level of accuracy
Brendan why don't you just silastic the mirror in ?
I did that with my 10" dob and it held collimation very well.
The blobs of silastic only have to be 1mm thick and will keep the beast collimated very well without astigmatism.
On ya Brendan.
I have been tinkering with my old 10" f5 for a while now, and baffling I can do. Mirror cell I tried from C/F as well, as I had some scraps over from the tube. Really though, (and more especially given your ability with metal) why not build a cell. I have an idea or two for one.
Here is where I am at so far, but if I get the opportunity I will "re-cell" it.
Obviously a bit more flat black on the spider could be handy as well, LOL.
Gary
ide love to start doing some work with CF. might look into that one soon enough
My problem is just the skywatcher snot, its purely built for visual and all corners have been cut where they could be cut! no good for photography, but in saying that i have got some good photos out of it. but better to come!
I will be looking at starting a custom optics project in the near future with a full CF Truss and super fast optics in the F 3 - 3.5 and somewhere between 10-14" and running a keller corrector. If i can get it to be under 14kgs ill be ecstatic.
I have decided to become a aperture infected wide field whooze!
Well i have been stuck in Uni for the last few months with only a little bit of time to run the telescope outside while studying inside . Now i am on holiday I have been a busy munch kin.
1. Brocolli flats box total cost 34 dollars works extremely well.
2. Orion Primary mirror rebuilt all the mountings for it and made adjustments to the mounting positions of the mirror cell to OTA its a very positive fit now.
3. Still making the new secondary Spider vanes/secondary holder but should be finished by tomorrow. The SW spider vane is so substandard its not funny, when your trying to make adjustments for a autocollimator and the whole secondary twists about 10 mm each way... argh. so a 40mm secondary stem (lightened) and 1.7mm Stainless vanes for strength.
4. The new FT 3015B-A installed. oh that is a DREAM to use! the best investment untill i get a automatic focus system
Any questions/ comments/ ideas i would love to hear and discuss about!
Well i finished up in the prototyping lab, and got the secondary holder and vanes to a stage where i can test them out. If all is well then ill get them anodised and flat black for the vanes.
Oh and some explanation of the flats that i last posted. if you can see that in the first image there is only a small amount of fully illuminated area, where as the second one is a lot bigger. that is due to the increased secondary size! i was happy to have something to quantify it.
yep that little Wilbur worm is a pain in the aasss and it moves around so its actually in the sensor of the camera ill get it out one day.
The new spider vanes should work well i have given them a bit of a twist and they barely move which is what i was looking for, plus the 1.5mm vanes will throw nicer diffraction spikes
all in all for 49 +P&H it was the best investment for the 10" since the MPCC!
its all good now, but i would like a better solution than what it currently is. 
