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Found 7 results

  1. I hope this is not a stupid question (guess I will find out shortly...). Can you use a Bahtinov mask on a normal wide angle camera lens? I have tried taking a few star trail photos using a DSLR and a normal wide angle camera lens but have had an awful job in getting the focus right. Infinity seems to move and is not actually on the infinity marker on the focus scale. It has been a real pain so I am looking for some help here. Tony
  2. I came across a video on youtube of a flymesh bahtinov , not focal length dependant has anyone ever tried this method before ? mesh he used is approx 1.5 mm sq and one half of the mesh is at 45deg to the other half ,found after i purchased a mask for my mak but still need one for my 130pds . https://youtu.be/IeUs7pFwMJw
  3. Hi, Decided to have a go at a Bahtinov Mask today. I used the generator at http://astrojargon.net/maskgenerator.aspx to create an image which I printed on a laser printer. This was then taped to a piece of thick black card and the slots carefully cut out using a scalpel. I left some tabs of card around the edge. I then took a strip of black card and joined the ends so it fitted around the end of the scope. The front was then attached via the tabs and it was all taped up with black insulation tape. No stars out tonight to test it on so had to make do with a distant street light. Not ideal but it shows the principal. Very happy with this simple tool and can't wait to try it out for real. The mask front cut-out with tabs around the edge Assembled In focus Out of focus
  4. Hello all. I have a quick question regarding Bahtinov masks, Im considering buying one for my Newtonian which im finding great difficulty nailing the focus. My question is regarding the design, how closely matched does the design have to be to the instrument focal length, i.e I operate my Newtonian at F5.6, would a mask designed for F5 be sufficient and accurate? Thanks
  5. Hi, Slightly embarrassing question I should probably know better..... My collimation is spot on with my F4.7 Dob (use a combination of cheshire and laser to get everything spot on) and I wondering if i'm missing something: For bright stars such as Vega, Altair etc: Despite achieving perfect focus (visually or in conjunction with a Bahtinov mask), bright stars always look slightly squiffy and I'm wondering if the stars magnitude is the critical factor in all this. Fainter stars (Mag 3+) appear as perfect points of light. Whereas brighter stars I can focus them down to almost a perfect point but when approaching 'perfect' focus the star always develops a very small arc (think of the Wembley Stadium Arch...random I know) along one axis, which too me looks off. It only happens on really bright stars. I'm about to delve into AP soon and know a coma corrector is a must with my scope, but even when centred in the eyepiece I'd expect the bright stars to look like bright symmetrical points as per the fainter ones. Any ideas where I'm going wrong here? Is this the limitation of a reflector telescope? Is it simple physics at play? (ie a facet of wave-particle duality?) For background info I've rechecked collimation and focusing when observing, I've carried out numerous defocused star tests and my defocused star 'light rings' are perfectly uniform. Thanks
  6. I am starting to get to grips with some of the features on Sharpcap and last time out I tried to use the focussing assistant using a bahtinov mask. The first thing I noticed is how sensitive it is. The attached screenprint involved the tiniest movements of the fine focusser knob on my Star71, which caused it to sweep from +1 to -1 without stopping in the middle. I decided I wasn't going to do any better than that (but could probably waste an awful lot of clear-sky-time trying!), so decided to accept that. After all, from what I have read, an FWHM of about 1 is reasonable. But now comes my confusion. I was assuming that the scale was FWHM units. But, as can be seen from the screenprint of the log, the FWHM of each individual sub was just under 4. I realise it would not necessarily be the exact same figure as when I was focussing, but 4x that figure? This would seem to suggest that either the scale on the focussing assistant is not FWHM units (so what is it?), or my focussing went way out during my imaging session. The resultant image can be seen here. So, are these the sort of results I should be expecting? Or where am I going wrong? Thanks.
  7. I'm want to get into AP iamging DSOs but have focusing issues - nothing new there I guess. My basic question is this: Is it possible to use a DSLR and USB link to display live images on a Windows PC (or Android Tablet) with sufficient resolution to use a Bahtinov grating for focusing? If so, which DSLR have people used in this way? And which software? I have been trying without success to use my Sony A300 DSLR but the built-in LCD display is far too low resolution to see the fringes from a Bahtinov grating. The grating works great with an eyepiece so nothing wrong with the grating. And the Sony video out is of similar low resolution to the LCD display. And unless I'm missing a trick (please tell me if I am!) there is no way to get live images over the USB link. As a very poor second best, is there any single software (for Cannon, Sony, whatever) that will allow triggering of images (Bulb mode) and upload the image almost immediately. I guess I could live with that just so long as I end up with a properly focused system. My scope is a 6" f10 CS. And yes, I know f10 is too slow and I need a field expander but it's where I'm at at the moment. And unless I can crack the focusing all other issues are secondary. Many Thanks for reading this far! Geo
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