The Skywatcher 130p is a perfectly respectable 130mm Newtonian on an equatorial mount that's fine for simple visual observations. With a 2x Barlow adapter you can see planets reasonably well (quite amazing seeing Saturn's rings!), and with an adapter I could attach my camera (Canon EOS 60d), but only via the Barlow adaptor. It's not possible to focus a camera without the Barlow adapter (at least, with a dSLR), because you run out of room on the focuser - it would need to push too far "into" the telescope tube.
After a while that became a little limiting: The Barlow degrades the image quality too much for satisfying photography, and you end up with a focal length which isn't great for deep sky objects on a telescope this size.
So, rather than giving up on this telescope, which after all is just a metal tube with a couple of mirrors and pretty much the same technology that Newton himself had, I started a "journey" to try to turn it into something that worked better for astrophotography! Here are the things I wanted to do:
The following sections document how I modified the telescope, as outlined above. Hopefully they'll give you confidence to make (careful!) modifications to your own Newtonian telescope, if they would improve its usefulness to you. I was quite nervous at first, but when I thought of it as simply a metal tube then it became easier!
Disassembling the end of the telescope. Note that I used pieces of tape to make sure I didn't have problems aligning things when rea-ssembling - it turns out that they're not necessary because there's a notch anyway!
Unfortunately I didn't take photos of the steps here. However, after taking the end off, the mirror is mounted so that it "floats" above the metal cap underneath it. It is held in place by three bolts which pull it down, and three grub screws which push it up. When assembled, these are adjusted to carefully align this primary mirror so it points exactly towards the centre of the secondary mirror/eyepiece further up the tube, and to hold it firmly in place. As supplied, the original six bolts/screws are very short - I replaced them with much longer ones to hold the mirror further away from the end:
Here you can see more clearly that I used:
This shows the bolts and grub screws and the springs. Ignore the rubber washers - not sure why I left them there! This is looking from the "back" of the telescope - normally there's a metal disk which covers this hole.
After modifying this primary mirror, I could attach my camera, but the distortion of the stars away from the centre of the field was quite unsatisfactory:
After looking at the price of a new focuser and noting that it would have been as cost effective to simply buy the 130p-ds version of the 130p (which is already set up for astrophotography), I decided to press ahead in spite of common sense!
I purchased the Dual-speed 1.25/2" Crayford focuser from FLO, along with a coma corrector, light pollution filter, and t-adapter ring.
This is the original focuser. It is 1.25" diameter, very imprecise, and quite wobbly, so I wasn't sorry to see it go! The tape on the cap covers a tiny hole I drilled (perfectly centred) for collimating.
After removing the original focuser(with its three bolts), here's the new one. I'm sure it's MUCH bigger in real life than on the FLO web page! It obviously isn't going to fit in that little hole...
Here I'm measuring up the hole that needs to be made in the main telescope to fit this tube, which has a diameter of 93mm. Note that the circle will be distorted as it projects onto the cylinder...
Writing F = the radius of the focuser tube (46.5mm) and T the radius of the telescope tube (79.5), we can calculate and plot the projection of the focuser circle onto the telescope cylinder, resulting in the purple shape here:
I printed that (via the share button, out of sight to the right), making sure to use the "zoom square" option in the graph settings. It (obviously) came out the wrong size, so I measured it, scaled the graph, and then printed again. Note it's actually the outer part that I wanted to keep for my cutting guide.
After removing the red dot finder mount, I started covering things up to stop the secondary mirror getting damaged when cutting the metal.
Taping the cutting guide to the tube, aligning it carefully.
Time to start cutting! I used a dremel with cutting blades, taking it slowly.
Done!
After a little bit of filing, the focuser fitted snugly, though note that it's really designed for a larger diameter tube, so the edges aren't quite flush with the main telescope.
I marked the mounting holes and drilled. Actually I used a fine drill bit first to get the placement accurate. I found that placing the drill bit against the metal before starting it helped prevent squirreling.
I worried that if I ignored that gap around the edge of the focuser mounting plate, then it might distort the telescope tube when I tightened the bolts, so I used two washers as spacers. It was quite fiddly getting everything to stay in place, so I tacked the washers in place with a glue stick.
Looking good...
After giving it all a really good vacuum/clean, I re-fittted the primary mirror
The red-dot finder wouldn't quite fit, so I shunted it over and just used one bolt to keep it in place. It actually feels very secure. I have subsequently covered the hole (visible here) with tape to avoid stray light etc. Other than collimation, it's all ready to go!
It works pretty well - here's the Rosette Nebula and M33 galaxy, each with about 150 x 60s exposures and a Canon EOS 60D (unmodified), as first test images:
The one remaining problem is that at focus (approximately here), the focuser tube is quite a long way inside the telescope body:
Long distance view showing the degree of obstruction.
This will:
I am already pushing against the noise levels with the 60d, so wanted to fix this. However, I was reluctant to make the bolts supporting the primary mirror even longer (the tiniest wobble there will adversely impact the image), so decided to shorten the tube by 1.5cm, whilst retaining my existing bolts. I didn't want to take any more off the tube than necessary, since in the future I might need to move the focus plane back into the telescope if, for example, I replace the camera with a non-dSLR type.
Time to remove the primary mirror again, and I made a 1.5cm strip of tape to mark what I wanted to remove:
Stuff the tube with paper/towels to stop the metal dust going everywhere
The Dremel and the cutting disks again. Make sure you have enough - they wear down fast. I used about seven (getting better at using as much of them as possible each time!).
After smoothing off the edge, I used masking tape to mark the position of the mounting holes. When drilling the holes, make a small pilot hole first. I found it reduced squirreling if I only started the drill after placing the bit in the correct position.
The only two things remaining are collimation, and waiting for the clouds to clear!
Here's the Iris Nebula 100x30s (total 50 minutes) with that setup plus a Canon EOS R5 (no guiding):
