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10" F4 Schmidt Newt - first light


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Just had first light with the 10" F4 Schmidt Newtonian last night. I'm well impressed.

I mainly wanted to find exactly where prime focus is. Took a while, 'cos I couldn't get focus at all initially. Eventually I pulled the ep right out of the focusser (which is a low profile dual speed JMI, but was fully extended) and found focus hand held in mid air. I then used my extension tube (barlow minus lens). I still wasn't out far enough until I clamped the tube further out and clamped the ep further out on the tube. Measured prime focus (ie: shoulder of ep where the 2" shiny barrel meets the black body of the ep). All eps focussed between 160mm and 165mm from the outside of the tube. Plenty of back focus so I can now have Graham make me a 2" filter slider for between the tube and the focuser. I will check prime focus more exactly, probably by using a small off axis mask and projecting the sun onto card, and then do some accurate drawings of the optical path and see how vignetting occurs. This will help me design other possible mods, including the filter slider and extension tube. I have already been in touch with Graham about a filter slider mainly to hold up to four 2" visual filters including UHC, OIII and Hb.


I was amazed at just how many stars were in each field of view with my big ep. (It has been a while since I last looked through such a scope this size). The Explore Scientific 14mm 100 degree gives 73x and a 1.38 degree real field. Everywhere I looked, it was like I'd found a star cluster. Stars were crystal clear and the scope looked well aligned after its long van ride from up north, testament to Perkil8r Mikes good driving in his scope transporter van. This was a pleasant surprise as the optics are definitely in need of a good clean. The Ring Nebula just jumped out big and bright with more detail than I had seen for a while. Split some doubles and saw some good colours in certain stars. By the time I'd set up, managed to find focus and aligned the finder, I didn't really have time to see that much as I had to get to bed for an early start.

The Skytee is a nice simple, robust mount, but is certainly not designed to have a 10" SNT swinging off the side. It wobbled and strained under this massive load and would benefit from a 350mm pier extension atop the tripod to stop the SNT hitting the tripod legs and also put the ep at eye height when pointing at the zenith. The Skytee is ideal for visual observation with smaller scopes and I am pleased that it allowed me to try out the 10". I have my name on a Meade LX80 altaz/eq goto mount from Telescope House, but they are not yet available in the UK for a while.

Anyway, first light was a success and the light grasp and bright clear images left me well pleased. I know now that this scope will deliver the rich field views I had hoped for, and I've managed to suss out a few things about the scope despite the overburdoned mount. I even managed to "walk" the whole contraption including the counterbalance (Damians ST120) across the lawn to see around some trees, but that really is a fine balancing act in the dark and one false move could have had the whole lot crashing down, so not recommended :o .

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Guest Tweedledum

Hi Pete,

Very nice report, I'll have a 10lb weight welded onto the 120 to help balance your scope out :) ... It would also help if you left that handgrenade in the 120mm


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Make that a 10 KILO weight, especially if the hand grenade is also on the SNT side :)

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Be careful mounting the scope. I had one drop to the floor once with very unhappy ending.

It was my fault as i was rushing at the time.

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Nice to see you've finally got to use it Pete. Nice write up too, I look forward to getting a butchers through it one night ;) and even more so to you capturing your first images through it :D you know you want to ;)

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nice one pete, ive long been interested in those scopes, at f4 it sounds like a fast scope indeed, hopeyou get to use it a bit more soon and dont forget to bring it to a meet :)

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