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About Tommohawk

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  1. ZWO Ha filter 31mm wanted

    Wanted - ZWO HA filter, 31mm unmounted. Must be in good order please. Would also be interested in OIII and SII filters (same size)
  2. BTW I do like the idea of having 2 lock screws, both top and bottom. This helps to prevent the lock screw pushing the opposing tensioner out of adjustment, and also helps ensure the focuser tube remains orthogonal. +1 for the design!
  3. Hi - sorry my fault for raising an old thread but the detail on the focuser strip down was so good and I was desperate to figure out the bearing size! Turns out the bearings are 2mm so I got some and replaced these and cleaned the focuser. There was no visible rust on the spindle or elsewhere but lots of bits of something. Despite a good wash in petrol and new grease it's still a bit crunchy, though by the time the top tensioner and the focuser tension are set, this seems indiscernible. I think the main problem may be an irregular bearing slide. Anyhow the main reason I stripped it is because initially it had quite a lot of play and this is now eliminated so I'm happy for now though I agree with otheres that the design/materials are a bit cheap. That said, for the price the Quattro is still really good value, so I'm not complaining! All I need is some clear sky to check it out and there's no sign of that! Re the SW autofocuser, for starters I don't know why this is called auto focuser - this implies it can find focus automatically - would be better referred to as a motor focuser. Pedantic? Maybe! Anyhow, by chance my Quattro, bought used, was fitted with the SW motor focuser. The way the previous owner did it was to only use two of the mounting screws, and also he spaced the motor away from the bracket. Fitting with 2 screws obviously not ideally but this doesn't seem to compromise things. Main issue for me is I prefer to use manual focus for general set up - finding focus with new optical train etc - and just use motor for fine focus esp on high mag planetary stuff.... but there's no way to disengage. Heres a pic of the motor only - he used the 2 holes which have been countersunk. BTW if doing this I advise loosening the top tensioner first, tightening the 4 focuser knob assy plate screws fully, and then retensioning the top plate. ON mine the top was over tensioned, so the focuser plate could not be fully tightened - hope that makes sense! Then tension the 2 screws on the underside so the focuser has the desired level of friction.
  4. Portable 250mm Newt

    Slight delay over the New Year etc - hope you all had a good time! OK thanks all for the input. I have been looking for a cheap 10" F4 for some time with a search running on ebay for a 10" Quattro for over 12 months. Bizarrely, given this current thread, a couple of days back one came up on ABS for a good price which was only 10 minutes away! I'm now in the process of sorting it out a bit - it had lost a couple of ball bearings from the focuser and the focuser alignment and secondary position look a bit off so I'll have a fiddle with that. Looking at the forecast I'll have plenty of time before first light! So now I'm on the lookout for a duplicate bare tube or some kind of Gladius or truss type thing to mail out to Spain for planetary use later in the year. I'll post back sometime when I've had a chance to check it out. Thanks to all!
  5. Hi! I know this is an old thread, but I have similar problems plus some of the ball bearings are missing. Don't suppose you know the diameter? I dont have a micrometer.
  6. Portable 250mm Newt

    Hi Peter - brilliant I get the idea now. When thinking of "Gladius" style, does this mean the method of constructing the scope on a single "back-bone" type strut, or does it refer specifically to the method of supporting the secondary. Or maybe just the whole thing? Certainly looks like it has possibilities for me. Obvious main issue is that with a newt rather than a Cassegrain the focuser/filter/camera mas may cause flexure in the main strut - but that should be fixable esp for a smaller camera. Need to do some drawings.... and some thinkings!
  7. Portable 250mm Newt

    Bartel refers to Vladimir Sacek's site "telescope-optics": << Bartel says: Diagonals act to degrade optical performance, the larger the diagonal, the worse the degradation. A one-third obstruction, a much larger ratio than the customary visual Newtonian uses, degrades the optical quality by one-sixth wave (less than what is commonly quoted - see http://www.telescope-optics.net/obstruction.htm >> He also refers to his experiment which seems to show that a larger secondary may give improved views compared to a smaller one - not what one would expect - and gives some thoughts on why this might be. Interestingly, Legault's work also implies that at high spatial frequencies larger CO's may indeed give improved contrast. But at medium and low spatial frequencies contrast will reduce with a larger CO. He says: << The MTF curve below (see What is a MTF curve ?) shows that the contrast is modified in a complex manner. Indeed it decreases in comparison with the unobstructed instrument, but only in low and medium frequencies (left part of the curve). On the other hand, in the high frequencies, the contrast is not decreased, it is even slightly increased..... ... In conclusion: The effects of obstruction are: 1) the general contrast of the images is lowered, the instrument (diameter D, obstruction d) has approximately the same efficiency as an unobstructed instrument of diameter Deff = D - d 2) the resolution power is not modified on high contrast structures: Moon, double stars, Cassini division, shadow of a ring or a satellite, edge of a planet,... 3) the resolution power may be lowered on low contrast objects: surfaces of Mars, Jupiter and Saturn. The effective resolution depends on the contrast of the object and the technique used, it is at least the resolution of an unobstructed telescope of diameter Deff >> It seems to me that the key thing is that a scope with too small a secondary will not fully illuminate the sensor (or eyepiece field). So when doing wider field work a larger secondary is necessary, as demonstrated/calculated by Newt-for-the-Web. However, when considering planetary work, even at high magnifications the object may be only a matter of a couple of millimeters across and a larger secondary is unnecessary and will degrade the image. Leaving all that aside (!) I'm very grateful for your link to FPI-protostar - some great stuff there and its given me a lot to think about. Finally thanks especially for the link to your bino-viewer build. What an amazing project, especially for a first build!! Your research was obviously meticulous, the execution precise, and the re-purposing of household and general items for such a demanding instrument is really amazing - I love it!
  8. Portable 250mm Newt

    Hey thanks again for all that!. Stellafane's Newt-on-the-web I'm very familiar with and have found it invaluable in the design and limitation of newts generally - all theoretical as yet! Mel Bartels pages are very handy esp. for basic stuff like C of G calculations for balance points. - I wasn't familiar with them. Sacek's telescope-optics, which Bartel refers to, is phenomenal! As it happens I have already read this pretty much from start to finish getting the drift of some of it and following the maths in almost none of it! (I was looking to convert a damaged SCT (Schmidt plate broken) to a Klevtzov type corrector) Bartels comments about central obstruction are interesting but he's comparing a 20% obstruction (linear) with a 12.5% obstruction. Its quite likely that there is minimal difference at these smaller CO's but of course most newts and SCT have CO's much larger than this. The general consensus seems to be that at low spatial frequencies CO does have a significant effect and this is nicely summarized here. And from a subjective perspective my 8" Newt with a 26% CO consistently matches my C9.25 with a 35% CO. But... that's for another thread maybe!
  9. Portable 250mm Newt

    Thanks for that! So it seems my idea of cutting the tube in half isnt original - I searched on this but didnt think to use the term "split tube". I think the way forward for me is going to be: 1. acquire conventional F4 250mm OTA. 2. for now ship the tube only witohut mirrors to my destination in Spain. 3. travel out with the mirrors out and assemble there 4. figure out a way to make a featherweight portable tube (either truss or split tube) using these mirrors for a longer term solution. Thanks again for your input. PS would still be interested to see your DIY scope pics if they are around!
  10. Portable 250mm Newt

    OK I get what you mean - truss type thing. I did consider this but the commercial ones seems so heavy I figured I wouldn't be able to replicate this any lighter. The Altair F4 250 would be good, but is 16kg. I guess they're uber solid design and maybe I could get away with some weight saving. I don't need cooling fans really I suppose for a start. Also if I'm going to fabricate the frame myself it would be easy to mail one frame to my preferred foreign destination, and keep a similar one at home, and then just travel with the mirrors. Worth some thought for sure. Would be interested to see your pics if you can dig them out
  11. Portable 250mm Newt

    ok Peter thanks. Can't quite visualise that though. Don't suppose u have a pic?
  12. Portable 250mm Newt

    That sounds amazing! I need to review Bartels thoughts on that. Haven't done any welding for about 40 years and never touched ally, so not sure how I'd cope with that. Do u happen to have a pic of the finished scope?
  13. Portable 250mm Newt

    Wow! So do you mind me asking how you attached the focsuer?
  14. Portable 250mm Newt

    Hi Peter - thats an interesting design. Not sure how I could make this as a newt though? Focuser would need some kind of sideways strut and would be prone to flex dont you think?
  15. Portable 250mm Newt

    That's a remarkable result with a 150 aperture - nice job! Makes me wonder if I should forget the aperture fever and think more about my setup location. I could get to Sierra Nevada mountains fairly easily, so perhaps the 3000m would get me something extra. Thats really all I'm after I guess - a better result than I've had before. But..... a 250mm at 3000m would be even better!