swag72 Posted February 6, 2012 Share Posted February 6, 2012 I am looking at a new scope and so need to think about spacing etc. I have looked at the Atik 314L specs here and it says that the focus distance to the T2 thread is 10.1mm to the back end. If I'm not using a T2 thread, then how do I know what the distance is? I have seen many people post their imaging train, but I just don't get where the measurements go to and from. Obviously from the sensor - But then to where? The focus tube, an adaptor / flattener? I really don't know. So if buying a new scope via the internet, how can I ensure that I have the spacing distance right? Does it matter whether I use a flattener or not? Does that have any impact on spacing?If someone can explain this in one syllable words that I can understand, that would be nice!!Thanks guys. Link to comment Share on other sites More sharing options...
Merlin66 Posted February 6, 2012 Share Posted February 6, 2012 I could help Sara, but I'm not sure about the "one syllable" words restriction ;-)Most camera have the "backfocus" ie the 10.1mm distance from the face of the front adaptor (usually T thread) to the surface of the CCD inside.Each flattener/ correcting lens is designed for a specific distance between the lens and the CCD chip ie 65mm. If this were the case you'd need a "spacer" (65-10.1 = 54.9mm) long between the camera body and the lens.Hope this helps. Link to comment Share on other sites More sharing options...
swag72 Posted February 6, 2012 Author Share Posted February 6, 2012 Cheers Ken!So, my spacing from the sensor to the front adaptor is sorted I think as it works fine with the current setup I am using.If I put it onto another scope, with a different reducer / flattener - How do I know what distance I have to work with? For example at the minute I have the following.Atik 314L ----- Trutek filter wheel ----- SW x0.85 reducerIf I change the reducer as I'm using a differnt scope, how do Iknow how much distance I need? Is that the right way to ask the question? Link to comment Share on other sites More sharing options...
Merlin66 Posted February 6, 2012 Share Posted February 6, 2012 Sara,Whichever new reducer etc you use should come with the necessary data - i.e. the design distance to the CCD. For instance, on my SCT the Meade x0.63 reducer is "designed" for a distance of 110mm. Many reducers are different! Link to comment Share on other sites More sharing options...
swag72 Posted February 6, 2012 Author Share Posted February 6, 2012 So, if I get a reducer that states it needs a distance of 100mm and I have an camera and filter wheel in the mix. I measure the distance from the sensor to the end of the filter wheel (The end which will connect to the redcer) and that will tell me how much spacing I will need? Link to comment Share on other sites More sharing options...
ollypenrice Posted February 6, 2012 Share Posted February 6, 2012 Yes, just add up everything between the back of the flattener and the surface of the chip. Add 1/3rd of the filter thickness (usually 3mm thick so add a mm.)Since I can no longer read the markings on traditional Verniers I like to use these things which are now very cheap, insignificantly different from the old ones.The Digital Vernier CaliperTolerance is usually +/- about 1 mm on very fast systems but double that on slower ones and from here to Timbuktoo on SCTs.Olly Link to comment Share on other sites More sharing options...
themos Posted February 6, 2012 Share Posted February 6, 2012 Ok, where is the "back of the flattener"? Some specs say it's one of the glass surfaces (the scope facing one) and some assume you measure from the end of the mating surface. There is clearly no standard as far as I can see. Link to comment Share on other sites More sharing options...
themos Posted February 6, 2012 Share Posted February 6, 2012 What I've learned is that focal reducers will produce a different reduction ratio as you vary their distance from the imaging sensor. Only near their design point will they produce a pretty flat field though. Oh, and 6.3 reducers vary a lot in their focal length and consequently on the required spacing.Useful Formulae Link to comment Share on other sites More sharing options...
Merlin66 Posted February 6, 2012 Share Posted February 6, 2012 The "wilmslow" link is out of date.I've tried to get him to update based on the good work done by Lord etc, but nothing's changed.There was ONE bad batch of x0.63 reducers MANY YEARS AGO....since then all the commercial reducers are the same.... Link to comment Share on other sites More sharing options...
swag72 Posted February 6, 2012 Author Share Posted February 6, 2012 Yes, where is the back of the focuser? That gadget looks interesting Olly. Link to comment Share on other sites More sharing options...
MikeWilson Posted February 21, 2012 Share Posted February 21, 2012 Hi Sara,When spacing my QHY8L, via SX USB filter wheel and TRF-2008 I spaced using the mating T-threads as well as the back of the glass element of the TRF-2008.The correct answer for the correct spacing was to use the back of the glass of the TRF-2008. But a bit of trial and error was needed to get accurate spacing.I hope this helps!All the best,Mike Link to comment Share on other sites More sharing options...
swag72 Posted February 21, 2012 Author Share Posted February 21, 2012 I won't need all this with my Pentax 75 I think as it has a built in flattener!!!All makes sense and will hopefully help others! Link to comment Share on other sites More sharing options...
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