Rosliston Astronomy Group


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PD camera, lenses, filters & the Holy Grail

Orion Nebula, Flame Nebula, Horsehead Nebula

Roger Samworth



One of the problems with the PD is that its sensor is small. This gives quite a narrow view with telescopes of "normal" focal lengths, given that many deep sky objects are, in fact quite large. It was for this reason that I invested all of 25(!) on a 50mm f/1.4 lens. This gives a field of view of 7 degrees. With the 80mm f/5 window-sill refractor (FL= 400mm) plus a focal reducer I can get down to 200mm, but it would be nice to have a lens at 100mm too. There didn't seem to be much available (cheaply!) with a c-mount, however. I then remembered that I had got an old pair of (very cheap!) binoculars that I dismantled for one of the objectives some time ago. I still had the other objective and this turned out to have an aperture of 70mm with an FL of 200mm (=f/2.8). With a focal reducer this would come down to 100mm at f/1.4.

In the best Blue Peter traditions involving bits of plastic plumbing pipe and sticky-backed plastic, I fabricated a lens that fitted on the 1 1/4 adaptor on the PD. (See photo).

I also decided to invest in a UHC filter, and made an adaptor (more Blue Peter stuff) so I could use it with the 50mm lens (see photo).

It then remained to try both of these things, but as we have all noticed, the weather has been somewhat un-co-operative of late. 

Returning home late on Friday night, (unfortunately not from the quiz), I could see stars! (although it was not exceptionally clear). The forecast threatened clouds within the hour- not enough time to get the kit out and set up, so I resorted to the indoors window-sill. I had manufactured a simple bracket to mount the PD on the window-sill equatorial drive that normally accomodates the 80mm f/5, so that is what I did.

First stop was the Rosette nebula with both lenses (and the UHC), and I could now get the whole nebula in frame. As I said, it was not brilliantly clear, and there is a fair bit of work with GIMP (and the GMIC plug in) to get the attached images.

I then turned my attention to the area around Alnitak (the LH end of Orion's belt). Even though it was not that clear, I could make out the Flame nebula, so I recorded images there also.

Later, as I was stretching the contrast in GIMP, look what started to.appear! - the Holy Grail! - the Horsehead nebula! Admittedly It is not that clear, but it was very gratifying it was there at all - especially since it was through the glazing! and with a lens costing 0.00! They aren't a patch on Geoff's recent images, of course, but hey, what the heck!

Clearly from the images, the 200mm binocular lens does not really like the focal reducer so if we ever get another clear night, I will try stopping it down a bit. I might try from outside too!



Monoceros Rosette (a)_Samworth_111215
Monoceros Rosette (b)_Samworth_121215
Orion_flame_Samworth (a)_111215
Orion_flame_Samworth (b)_111215
Orion_flame_Samworth (c)_121215
PD plus 50mm lens with UHC filter_111215
PD with 200mm binocular lens_111215
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