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Post by Rick in NWArk on Jul 10, 2014 3:32:31 GMT
Has anyone tried this with video? I have yet to see it mentioned (and maybe for good reason!)
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Post by Deleted on Jul 10, 2014 6:13:00 GMT
Has anyone tried this with video? I have yet to see it mentioned (and maybe for good reason!) Hi,
I have used EP projection as well as various mag factors of Tele-negative optics, Barlow's with & without field flattener's, for 20 odd years or more, with considerable success. In microscopy, it is standard practice to use various magnification projection eyepieces to achieve various fields of view, as well as changing objective mag. As such, good eyepieces work very well for both still and video imaging. One of my early Takahashi Apochromtic telescopes came with an 'optional' expensive unit which enable one to use eyepieces as magnification/projection optics. I think that over recent years, Barlow lenses have increased in quality, size options, and magnification factors, that the older techniques using eyepieces have been replaced. In the early days, getting an Apo Barlow with a field flattener component was near impossible until the Power-Mate range came along. I still have some really excellent war surplus Barlow optics that equal to-day's optics, but of course they are no longer available.
*** The downside with using Barlow lenses is that the imaging train starts to become longer & heavier in terms of leverage if using a heavy camera, especially on a Newtonian telescope. This is one of the reasons I build my Newtonian's with a combined sliding diagonal/focuser plate which moves away from(with Barlow) or closer to the mirror using (focal reducers) and the camera remains close to the telescope and final fine focus is with the electric focuser. The keeps the camera, say a pro DSLR (heavy) rigid and non flexing in the focuser unit.
*** Projection eyepieces are designed to form an image at a distance from the eye lens, several centimeters, as distinct from a normal EP optic which is designed to focus close to the eye lens -into ones eye several millimeters.
Clear skies... Shevill
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Post by Rick in NWArk on Jul 11, 2014 1:20:57 GMT
Thanks Shevill, I thought that if anyone had, you would have given this a go!
So far its just thought experiment and research, but for larger scale planetary video with limited focal length (< 2000mm), higher barlows than 2x are needed and with those, longer extensions to get the camera at prime focus. EP may be the solution to large image scales without a meter long image train, lol.
Even without a barlow, a 4mm ep that is 14mm away from the CCD will give my VRC8 an effective f/l of 4060mm (f/20) and a 5.2' x 3.35' field of view in the Jr Pro.
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Post by Deleted on Jul 11, 2014 2:31:18 GMT
Thanks Shevill, I thought that if anyone had, you would have given this a go! So far its just thought experiment and research, but for larger scale planetary video with limited focal length (< 2000mm), higher barlows than 2x are needed and with those, longer extensions to get the camera at prime focus. EP may be the solution to large image scales without a meter long image train, lol. Even without a barlow, a 4mm ep that is 14mm away from the CCD will give my VRC8 an effective f/l of 4060mm (f/20) and a 5.2' x 3.35' field of view in the Jr Pro. Hi,
For planetary work you need to be about f/30, there are some purpose made orthoscopic eyepieces made for EP projection. I have a 12 mm version, bought it from University optics USA.
Just a note, Barlow lenses are named after the English astronomer, mathematician etc. Peter Barlow who invented it, so a capital B.
en.wikipedia.org/wiki/Barlow_lens
Many folks do not know this and I like to pass on these little gems.
Eyepiece, eyepiece holder, adjustable min tube screws into focuser. Ready to assemble, two lock screws hold the assembly securely in place. Fully Extended. Fully closed-and variable between the two extremes. Clear skies... Shevill
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Post by Rick in NWArk on Jul 19, 2014 2:05:33 GMT
Thanks Shevill, I will definitely look into this. I'm very interested in seeing what can be done to get larger planetary views. But as last weekend showed, I need to focus more on getting regular viewing down, before I start thinking too far ahead and dreaming, haha.
Its funny that you mention Barlow... I didn't know that fact until I started researching this just before I posted this.
I appreciate you sharing your experience; thank you!
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