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AlentejoSkies

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Posts posted by AlentejoSkies


  1. Great thread. Thanks.

    As I will soon have a nice 8" f/6 mirror set in the post thanks to @Stu, I've been giving a bit of thought to putting together a dob optimised for binoviewing, and was out again last night trying a few eyepiece combinations with the kit I have to see if this is the way to go. Here's a few rambling notes from last night's testing...

    Targets: Jupiter and Saturn. Site: Alentejo, Southern Portugal.

    Scope 6" f/8 homebuilt dob, WO binoviwers, a couple of glass path correctors (GPCs)

    In the last four years I've put some effort into learning about and using astronomical optics - and I already had a good professional background in optics. I've learned a lot, but what most amazes me is what I see through the eyepiece now using actually the first equipment I bought and made. When I first built this scope I was impressed to see faint lines on Jupiter. Now I see swirls and patterns, a wealth of colour. The question is not whether I can detect the GRS, but how does it look tonight. The globe is full of features. What once looked like an aspirin now looks like a photo with character and characteristic. I have acquired quite some equipment since those first days, but I'm talking about using exactly the same setup as I started with. The only thing that changed there was me. And a lot of that had to do with getting comfortable and using binviewers.

    Anyway, I was actually checking  a few eyepiece combinations, bino versus single.

    First test: Televue 15mm Plössl on one eye, Vixen 15mm NPL on the other. 2 X GPC correctors for a total magnification of about 220. I can only reach focus with stacked GPCs at the moment. Next scope should be different. Hence the experiments.

    These two 15mm Plössls are not parfocal, but with a bit of fiddling around, I was surprised to find it works. The difference between the two eyepieces was minimal center and edge. I could convince myself either way which was better, and will keep that question open for now. What was obvious is that the Plössls were way better off-axis than the WO 20mm pair that came with the BVs, that I usually love.

    On these planets, I just love the immersive view of two eyes. I can watch the planet move across the field of view again and again. One-eyed viewing for me seems technical in comparison.

    But then just as I was convinced again that nothing beats binoviewing, I did try a nice little 9mm volcano top ortho with one GPC srewed directly into the bottom to more or less match magnification to the above pairs. And then I had to admit that there was clarity and detail there that was not with the combinations I have available for binoviewing. Tried to see if that still held true if I just used half the binoviewer and my one ortho, but the need to stack GPCs gave too high magnification - horrible.

    Not a super-fair test as the unmatched magnifications makes a big difference in itself. But this morning I couldn't resist buying that second 9mm Ortho that's been on ABS for a while! Let's see what happens with two! And the next scope will definitely be built with some way of setting up for binoviewing with and without GPCs.

    Will try tonight with the ETX-105. Totally different beast, but it has a much larger range of focus and can handle binoviewing without GPC.

    • Like 1

  2. Thanks for the link. I may very well do that at some point. But somehow the psychological price border for something I don't really need (had never considered it before yesterday) seems to lie around the 20 pounds mark today!


  3. So, to follow up:

    This thread can be closed.

    I did the job - dead-easy, thanks John - but immediately realised that the focus rod is stiff. I'd never noticed before, but now it was obvious. Torsion would build up in the cable until it was enough to overcome stiction and then suddenly it would make a half-rotation in one jump. Gear cable wasn't even strong enough not to uncoil in the one direction. The brake cable fared better, but I think flexifocusing is out of the question until the focus itself is smoother.

    I'll see about stripping down and regreasing sometime soon. Looks like the back of the OTA will unscrew once it's deforked. But that's getting a bit off-topic for the classifieds.

    • Like 1

  4. Hi,

    Does anyone know where I can find a suitable potentiometer to replace the brightness control on a GP-DX polar axis illuminator? It's an 850k ohm pot according to the text printed on it - I guess logarithmic - but it needs to be the same size as the original to fit on the PCB and I just can't find one...

    If someone can tell me what this style is called it should be easy, but they come in a bewildering range of sizes and forms!

    It needs replacing as a previous owner of the mount left a leaky set of batteries in it for too long.

    Thanks in advance

     

    side view.JPG

    back side.JPG

    front side.JPG


  5. Hey welcome Eduardo!

    I'm also in Portugal - near Odemira, Alentejo. Not into astrophotography though, purely visual.

    So far I didn't find many amateur astronomers around here. Might help if I spoke a bit better Portuguese!

    Anyway, welcome to the forum.

    • Like 1

  6. Looking for Bob's Knobs for a C8 (standard 6/32 for Fastar compatible C8 with silver phillips factory screws)

    29 dollars seems a bit much for 3 screws, and so does 23 pounds. On the other hands, they would make life so much easier...

    Anyone have an spare set hanging around, before I checkout?

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