That's not a lens...
For a very long time, I’ve been pondering the idea of getting a longer focal length telescope for my astro imaging. The SW72ED is a great scope for the imaging I do and my current skill levels. There have been times when it’s 420mm focal length was too short for the target I wanted to capture.
I’ve seen some 500mm ‘mirror’ lenses on eBay selling for a couple of hundred dollars. I’ve always been put off by the fact that they don’t have a standard Nikon mount, and seemed too cheap to give good results. I was also put off by the (relatively slow) F-ratios of F8 or F11.
I was randomly browsing through Gumtree one evening when I stumbled across something really cool and didn’t know even existed. A 1000mm focal-length, mirror (technically a catadioptric) lens. The price was reasonable (certainly a lot less than a 1000mm telescope!) and the seller stated that it had a T2/M42 thread on the back.
T2 or M42*0.75 is the standard thread for astro cameras. I have an astro camera, as well as a T2 to Nikon adaptor.
You can see where this is going, can’t you?
Yes, I bought the monster of a lens.
Now, I was sensible - I tested that my standard astro fittings did, in fact, fit perfectly. With my DSLR attached, it’s a handful to hold and focus. The field of view is tiny - any wobble or movement takes you away from your target almost immediately.
It was only when I got home with it that I realised I had no way to easily mount it to my HEQ5-Pro and use it for astro work. However, that’s in the process of being resolved and I should have a working solution fairly soon.
Useful information:
- Maker: Unknown. Lens collar stamped with “Reflex Birdscope 1000”
- Year of manufacture: Unknown
- Country of manufacture: Japan
- Focal length: 1000mm
- Aperture diameter: 104mm
- Aperture: F11 (fixed)
- Focus: Manual
- Weight: 1516g
- Length: 195mm (dew shield retracted), 245mm (dew shield extended)
Surprisingly, quite a few companies manufacture these style of lenses. Big names such as Nikon, Canon and Sony have offered (or still offer) these lenses, along with smaller companies such as Tamron, Samyang, Vivitar and Opteka. There have also been Russian (Soviet-era) companies that offered catadioptric lenses. I imagine the Russian ones would be pressed into service as a blunt weapon without damaging their optics…
When I was searching for information about this lens, I found a UK-based website (https://mirrorlenses.co.uk/) that has information and photos about a large number of these lenses. I have contacted them with information about mine, but have not heard back yet.
What’s a catadioptric lens?
In a nutshell, these lenses contain both refractive components (like your usual camera lens) and a set of mirrors (reflective components) that “fold” the light path within the lens. Thus providing a longer focal length in a lens of reasonable physical size.
Wikipedia has a good explanation of catadioptric lenses and telescopes here: https://en.wikipedia.org/wiki/Catadioptric
OK, Viking, you’ve bored us all with the wall of text. What does the thing look like?
Ready to capture some photons
It's rather large, eh?
