Peter Drew

Search www.astronomycentre.org.uk and click on "instrument special feature" to see our 750mm F4.1 Dobsonian to give you some idea of overall sizes. 😀

Do you already have a suitable mirror blank. I really do advise that this is imperative before other considerations as it could significantly determine the mounting design. 😀

I have a Lunt 1.25" fit HW which I'm happy with. I tried later a Lacerta version and thought it comparable although cheaper. If I was starting again I would buy the Lacerta as it is a larger unit and would probably dissipate heat more easily. 😀

I have been through all the ramifications of such a project, believe me!. The Nasmyth configuration looks good on paper but the convex secondary imparts an amplification to the focal length as with traditional Cassegrains, increasing the already long focal length of a large primary mirror, not ideal for imaging. The extra weight (and expense) of the additional optics and their support requires an even more robust construction. I've been looking into the possibility of re-imaging via a Mersenne arrangement or a flat circular secondary and transfer system directing the focus through the primary as a relatively non amplified focal length, again expensive. 😀

I have a Lunt 1.25" fit HW which I'm happy with. I tried later a Lacerta version and thought it comparable although cheaper. If I was starting again I would buy the Lacerta as it is a larger unit and would probably dissipate heat more easily. 😀

We have a similar project, currently "on hold" due to problems caused by being ring fenced by wind turbines that create bad seeing turbulence. The scheme was initiated before the turbines were erected or we would not have started the project in the first place. A first priority, if you don't already have one is to source a mirror blank. An 800mm diameter thin blank and fast focal ratio would be a challenge for a top professional and would probably need to be a slumped meniscus configuration to provide adequate stiffness. Our mirror blank is 1070mm diameter and 76mm thick fused ceramic, pre-generated to curve and a 76mm bored core, weight is 160k. An alt-az mount would be relatively easier and cheaper to make than most other mounts and best made of metal for long term stability. I went ahead at the time and built the all aluminium tube assembly once the mirror blank was secured, as mentioned in an earlier post, a concrete dummy mirror was used for handling experimentation. Despite heavier weight, I think a traditional 8 component truss would be needed for stiffness if longish exposure imaging is planned. 😀

I'll see what room I have. 😀😀

It might result in considering solar observing and imaging a higher priority than at present. 😎

Thanks for the image Charl, confirms what I saw earlier today before it clouded over. 😎

Some clear gaps in the clouds at last!. Just in time to catch a globe of material, probably the size of the Moon, rising amongst the fainter image of the brighter of the two proms. Best proms for a while. 150mm PST mod x150. 😎

Looks perfect. 😀

Unfortunately there are more morons than thinking persons. As far as the Beeb is concerned, the important thing is "bums on seats" even if they are only in front of the telly. 😟

Sunspots can easily be seen naked eye if they are large enough. Although the Sun can be viewed apparently comfortably when low or shrouded in mist it is still dangerous if prolonged, some of the radiation doesn't hurt until too late, bit like sunburn. 😎

Top end'ish of" Yellow" field. Current plan, 6"F10 PST mod on HEQ6 for daytime and 6" F5 SW achro for night time. 😀

I don't think the glue will cause a problem, just avoid getting any on the area in use as you can't really clean the filter. The filter material is very light and tricky to handle during the construction process. I would recommend putting a thin bead of adhesive round the maximum diameter of the holder and then carefully drop it on to the filter material that has been laid on a flat surface. Remember that the filter material needs to be in a relaxed state, not tight like a drum skin, wrinkles have no affect on the performance. 😀

Not for me I'm afraid, can't stand any form of distraction whilst observing. 😀

If you are using a monochrome camera, a grey featureless disc is pretty much all that is visible at the moment!. Check out the daily GONG Solar images, you should be able to match them on a good day. 😀

Is anyone getting less than the 0.5 meg upload that we have to put up with whilst paying a business rate for it?

If anything reduces our broadband speed then we would have none! 🙄

Nice shot of a nacreous cloud. 😀

Hello Zaida, welcome to this forum. Zenith binoculars are mass produced entry level instruments. As such, they can be variable in quality but usually perfectly adequate. If you are not experienced it may not be helpful for us to be too technical. If, as Ben suggests, you can try them yourself you will be able to judge whether they suit you. The safest way forward is to have an understanding with the seller that you can return them for a refund if you are not satisfied. 12x50 is about the maximum size and magnification that can be hand held, some form of tripod arrangement would make a big improvement. 😀

I think it highly unlikely that a Jim Hysom mirror would have a rolled edge or native astigmatism. It is quite easy to introduce astigmatismt mechanically. Make sure that the three retaining clips are barely touching the mirror. The design of the secondary mirror adjustment looks as though it could stress the aluminium backplate which might print through to the mirror and introduce astigmatism. 😀

I am somewhat opposite. I don't "mollycoddle" my equipment as most of it is at the mercy of the general public. I don't abuse it though and try and make sure it's in good working order. Given the choice between a white finder or a black one for a white telescope I'd take the white but I'm not fussy. As far as cutting a couple of inches off the length of the telescope or drilling some extra holes, if it improves the use for me then I don't think twice about doing it, even on a Tak. I'm not interested in resale value as I always keep them. 😀😀😀

The perfect Tak finder: 10x50 RACI, decent adjustable alignment bracket like the SW types, visible crosshair, Tak quality optics, painted in appropriate Tak colour. Specs in order of importance. 😀

You might have needed those for a flood barrier at this rate. 😀