Objective lenses

[jnp]

I already own a slowish f5 5 inch newt and like the idea of building a 'fast' refractor for planets. I would therefore be very interested to know if anyone has built their own refractor using achromats from Surplus Shed Surplus Shed (or better still a UK supplier if one exists).

Pity there aren't any reviews of the lenses (which range up to a 127mm diameter 1200 focal length). Its intersting to see the prices go up exponentially with diameter , but the 70/80/90mm seem good value. I guess it all depends on how good they really are compared to a cheap scope?

[Macavity]

No, but I used to look at a catalogue by a certain "H.W.English" back in the early 70s. They supplied UK Ex-government optical equipment "made regardless of cost". Things like 9" f4 lenses etc. Unfortunately my £12 in a post office book wouldn't stretch and nor would mother's flexibility re. having such things around the house?

More seriously, I sense a lot of the lenses were from (aircraft) camera equipment. I'm not sure whether such things (lens multiplets) are eminently suitable for telescope use. But they were something for a young lad to DREAM of...

[omneferuss]

Hi jnp, I'm not very experienced (1 yr in the hobby) but I made a 80/900 with S'Shed objective, and found it of equal quality to my SkyWatcher 70mm refractors.

At the moment I'm nearing completion of a 127/1200 but have not had 'firstlight' with it except to do the 'scope on a stick' test to determine tube length... focussed to a pinpoint star ..but that's all I managed hand-held

It will be a while yet, but I'll post in DIY-section when it's completed.

The objectives are worth it, in my opinion.. not 'huge' savings over retail scopes, about 30% off the price of equivalent SkyWatcher in my case.. but will vary very much depending on individual choices and circumstances I expect.

It was mainly the fun and challenge of it that drew me in

Russ

[John]

...I already own a slowish f5 5 inch newt and like the idea of building a 'fast' refractor for planets....

Maybe I'm getting confused but I thought F/5 was "fast" and longer focal ratios were "slower" ?.

John

[omneferuss]

I'm with you there John.. and achro's suffer CA more at 'faster' ratios too, I believe... That part of the post slipped by me I'm afraid.. my interest in the 127 objective was precisely because it's a longer Fl, ie 'slower' ratio..

...and I'd suggest that high f-ratios are what's generally needed for planets.. ie high magnification.. as they are bright but small targets.

mmmmmm.... jnp might like to respond to these questions ?

Maybe I'm getting confused but I thought F/5 was "fast" and longer focal ratios were "slower" ?.

John

[jnp]

Yes I agree! I do actually understand fast/slow concepts, my brain just had a 'slow' moment when I typed them the wrong way around .

Best of luck omneferuss with the 127mm, looking forward to find out how you get along. I would imagine the tube to accomodate 127mm 1200FL would be quite a beast to mount and swing about!

The 127mm and 102mm are out of stock so I will probably go for the 90mm 900FL first. I am thinking of using drainpipe and making a dovetail to fix to my existing EQ mount.

[omneferuss]

Goodo jnp ! thanks for the wishes, and I'm sure you'll enjoy your 90 too!

I expect you'll find pvc pipe/fittings to suit quite easily.. the 127 was a lil trickier than the 80 was.. but I'm getting there slowly.

The odd size of pipe I went with, 6", there's no rings to fit from astro wares, so I'm ad libbing with what I could find in the plumbing supplies. A photo of Mk1.. too wobbly.. (Mk2 in progress)

Russ

[jnp]

That looks good to me and I expect Mk2 will be even better. I am assuming this Mk1 of the 127 (not the 80?). I think improvising using odd bits is half the fun!

Out of interest, where did you get the focuser and 45 degree mirror from?

[omneferuss]

The focuser is a GSO brand 2" 86mm ext diameter.. (I'm in Australia, so I'm guessing you'll need to look around where's handy for you) The diag was gifted by a good friend Hi Km ..so I have no idea re brand or anything.

Yep.. the 80 is a bit smaller than this

[Merlin66]

I have a SShed 90mm f10 objective. It was temporarily mounted in a wooden square tube to use as a modded PST arrangement.

Work well, but an "opportunity" of a Vixen A80Mf replaced it.

Still available at reasonable cost, drop me a PM.

SShed have supplied beamsplitters, lenses and mirrors for my spectroscopes over the years... great value and responce.