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bryand

Little and large

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bryand

I’ve just acquired a rinky-dink little 800 mm mirror lens.  80 mm aperture and a T2 connection for my bits.  I bought it without knowing a lot about it (neither did the vendor, which is why it was cheap!).  But the more I dug up about it, the more interesting - and the better - it got…

It seems it was made by Towa in Japan some  time in the late ‘80s, and sold in a number of guises:

·         Bausch & Lomb 8080 spotting scope

·         Bresser Pulsar 48-6000

·         Paralux MMC 80

·         Tasco MMC-80SS

·         and others

There has been quite a bit of online debate as to what design it is.  Some distributors call it a ‘modified Schmidt-Cassegrain’ but that doesn’t hold water.  Others call it a Mangin-Cassegrain (Wikipedia to the rescue here) but the secondary mirror is front-silvered and flat, rather than a back-silvered meniscus which would be a Mangin configuration. 

Turns out it is a Dilworth Relay Cassegrain. 

 

No, nor had I.

 

 I have summarised some of their characteristics in the chart below:

large.1375271695_smokemirrors.JPG.eea14c690493556b5056558017c183c0.JPG

 

In operation it is small and light with a long  focus travel.  At F:10 it isn’t the brightest of lenses, but it delivers crisp views and is fun to use in a grab-and-go sort of way.  It mounts easily on a camera tripod, though the Field of View is so narrow that locking it accurately in position can be a game.

 

large.camera_setup.jpg.aef8e25f60ac8ac2049a45dd30b46121.jpg

 

It is supplied with a 1¼” diagonal which yields a right-way-up, right-way-round image  for terrestrial viewing and a T2 extension tube to which you can add your favourite camera adapter (EOS-M in my case).  Either layout comes to focus easily, though they are not parfocal.  Also supplied were 13mm and 30 mm Plössls, but I preferred to use a 10mm Baader Hyperion, giving  80X magnification.  I also tried it with the 40mm Plössl  that came with my C9.25 (first time it had ever been used) and it gave a sensible 20X view.

The camera rig uses the T2 adaptor directly screwed into the back of the lens, so there isn’t anywhere to put a filter.  That meant that my stripped-out Canon M10 wouldn’t be useful, so I put the M6 on the back of the lens instead.  They were parfocal (why wouldn’t they be?)  and  I got reasonable pictures of the Moon given the ‘average’ seeing conditions.

 

large.moonpic.jpg.094adb7eb288cce422bff113cb3d880b.jpg

Canon EOS M6, 1/80th sec @ ISO 640

 

 

For comparison, here’s the little 8080 and my large C9.25:

large.littleandlarge.jpg.ac62577d5154840cd8f65a013a9de966.jpg

 

The verdict: well, early days but the lens definitely has uses for planetary/lunar work, and will be mounted  in parallel with my main scopes for documenting  astro sessions (something I am not good at, at the moment).

And when the Ospreys return to Rutland Water, I’ll be getting a lot closer than last year.

 

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Bino-viewer

Interesting and enjoyable read Bryan.

 

I have a particular interest in the different designs of Catadioptric telescopes, especially those with a Russian heritage.

I'd not even heard of the Dilworth Relay Cassegrain design before.

 

Your Bausch and Lomb 8080 in a nice find and an interesting design : i have seen something fairly similar

made by Russian company Ylena, but that is a Maksutov design. Its still available from Widescreen (see link)

 

https://www.widescreen-centre.co.uk/ylena-e70-mm-f71-wide-field-photomak-telescope.html

 

It looks nice on your iOptron AZ Pro mount : i like the way you can add a counterweight to one side to balance it.

Really nice set up you have there : The C9.25 looks great on the AZ Pro as well, though i suspect finding a good balance is tricky ?

Is it a simple matter of having 10kg on one side and about 10 on the other adding counterweights and /or moving the counterweight shaft out as required ?

 

 

Edited by Bino-viewer

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bryand
4 hours ago, Bino-viewer said:

Really nice set up you have there : The C9.25 looks great on the AZ Pro as well, though i suspect finding a good balance is tricky ?

Is it a simple matter of having 10kg on one side and about 10 on the other adding counterweights and /or moving the counterweight shaft out as required ?

 

 The 4 Kg counterweight is on there for the sake of the photo.  In use, I would probably add another 2 Kg weight, or juggle my 3.7 Kg battery pack and assorted weights. 

The camera and lens are probably only another 1 Kg.

iOptron aren't really dogmatic about Azimuth balance, so you can get away without being very precise, provided the mount is levelled.   Elevation balance is quite sensitive - adding my ES 2" 2X Barlow can be enough to upset the balance. 

The mount complains loudly if you take liberties!

Edited by bryand

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