Saturday, 16 February 2013

SkyWatcher Explorer 130M with Canon EOS DSLR

This weekend I borrowed a Canon EOS 1000D to try out for prime-focus astrophotography when connected directly to my SkyWatcher Explorer 130M (SK1309EQ2) telescope using a T-ring adapter.

Moon using Canon EOS 1000D, held at prime-focus with
SkyWatcher Explorer 130M telescope (SK1309EQ2).
Single exposure, no cropping, no editing.

As well as doing a lot of reading on assorted astronomy forums, I found this excellent blog post about using a (digital) SLR with the SkyWatcher Explorer 130M telescope very helpful, and this page on taking the SkyWatcher focuser apart was informative: The challenge is getting enough inwards focus travel.

T-Ring adapter

From online reading I knew getting the camera as close to the mirror as possible in order to focus on solar targets would be a problem. With a standard fat T-ring adapter an extra 10mm or so is added to the light path, which makes this worse. I therefore invested in a slim line "Low Profile Canon EOS T Ring" which only adds about 1mm to the camera body. This was £20 from Modern Astronomy, although I later noticed some very similar looking adapters on eBay using the term M42 (which actually appears on the face of my adapter). Apparently the T-thread and M42 are both 42mm, but with different pitches, so this is a bit confusing - the good news is mine fits on my telescope!

Canon EOS T ring adapter, says "KIPON M42/s-EOS"Back of T ring, showing Canon EOS fitting
Low Profile Canon EOS T Ring, with tool for unscrewing (note the two little holes on the face where the tool's teeth fit).

SkyWatcher focuser's T thread

The black metal 1.25" eye-piece holder on the SkyWatcher Explorer 130M also provides a 42mm T-thread for direct connection to a (digital) SLR camera. The physical connection of a camera is therefore quite simple - the problem is getting the heavens in focus. While I could get this to focus on some terrestrial targets (e.g. distant trees), I was not able to get the camera close enough to the mirror to get the moon in focus this way.

Canon EOS 1000D with slim line T Ring adapter fittedCanon EOS 1000D camera attached via T Ring to
SkyWatcher Explorer 130M telescope (SK1309EQ2)

SkyWatcher's Mystery 40mm thread

Unscrewing the black eyepiece holder (which is about 22mm long) exposes a 40mm screw thread on the silver metal cylinder of the focuser, and holding the camera with T ring against this by hand, I found get the moon in focus - with about 5mm of spare travel on the focus rack.

Eye-piece holder removed exposing 40mm threadT Ring resting on 40mm thread, in focus for moon

The "tasco" box attached to the focuser in the above photographs is my Tasco 1603EF motorised focuser - which did make fine focusing easier. The example moon image was taken holding the camera resting the 42mm T-ring adapter on the 40mm thread like this. Keeping it steady enough for a clear picture via the live-view on the LCD was fine, the problem I had was minimising the wobble while pressing the shutter button - not so easy without a shutter cable!

Moon using Canon EOS 1000D, held at prime-focus with
SkyWatcher Explorer 130M telescope (SK1309EQ2).
Single exposure, no cropping, no editing.

With access to metal working tools, perhaps the standard SkyWatcher Explorer 130 eyepiece holder could be replaced or reduced from 22mm to more like 5 to 10mm, but even so the focal travel would be quite tight for lunar/astrophotography.

Other documented alternatives for prime-focus astrophotography with this telescope involve modifying the telescope - either by raising the primary mirror springs, raising the primary mirror by shortening the entire tube (like the SkyWatcher Explorer 130PDS), or cutting back the plastic sleeve of the focuser to allow it to retract another centimetre or so (which in my case may be hampered by the focuser motor).

Alternatives include using a barlow lens (ideally one with an integrated T thread) and/or eyepiece projection - which should solve the focal distance problem (but has downsides like reducing the amount of light captured).

Something to ponder... maybe I should stick with the webcam for now?

Update: More photos two days later using the same approach.

Update: I moved the mirror on the SkyWatcher 130M telescope in order to reach focus with a DSLR camera.


  1. I'm guessing you didn't take the camera-to-40mm focuser tube thread any further since you moved your primary? If someone marketed that it seems it would be an excellent seller since it would be the least invasive method of achieving focus with a Newtonian/DSLR combo.

  2. Yes. There is a small business opportunity here, but also SkyWatcher sell a similar telescope which is already shorter suitable for immediate use with a DSLR camera.

  3. I've read your blog with great interest and noticed you've gone extensively to modify your telescope. Did you manage to take reasonable photos after all?
    I'm asking, because I have a similar rig (130p/650mm on EQ2), and facing the same problems as you described.

    1. Sadly life has not been conducive to my astrophotography, so other than some pleasing lunar photos and some experiments with Orion and planets, I didn't get to take this much further. Fingers crossed for 2017? However, the modification to the telescope I made to move the mirror (see later blog post) is in principle reversible, should you want to try it.