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Whistlebare

What reducer do I need to view the moon in full with my ST80?

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Could some explain to me how to work out what I need to view the moon in full with my ST80. I know you can use a webcam or dslr to take lots of images and do a mosaic (one for the future)...my kids would like to see the whole moon rather than a section of it and the ST80 is just a wee bit powerful...

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What eyepiece are you using? A longer focal length eyepiece will give a larger fov.

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The moon is about half a degree, if you use a plossl giving about 50 degree that means a magnification of ~100x or less should show all the moon in one go. 100x would be the moon edge to edge and it drifts as does everything.

Go for 50x which would mean an 8mm eyepiece or longer should display all the moon and have a bit around it to act as a frame. A 10mm or 15mm may be better and easier.

It is bright and in an ST80 expect some CA to be apparent.

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What eyepiece are you using? A longer focal length eyepiece will give a larger fov.

I have the standard 10mm & 25mm which came with my 200p but I also have a 5mm, 9mm, 18mm and a 25mm x-cell lx...as well as my 1100d dslr and spc900 webcam.

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The moon is about half a degree, if you use a plossl giving about 50 degree that means a magnification of ~100x or less should show all the moon in one go. 100x would be the moon edge to edge and it drifts as does everything.

Go for 50x which would mean an 8mm eyepiece or longer should display all the moon and have a bit around it to act as a frame. A 10mm or 15mm may be better and easier.

It is bright and in an ST80 expect some CA to be apparent.

Thanks...I have the standard 10mm & 25mm which came with my 200p but I also have a 5mm, 9mm, 18mm and a 25mm x-cell lx...as well as my 1100d dslr and spc900 webcam. When I got the ST80 I had to adapt a cheap 2x barlow (removed the lenses) before I could focus on anything.

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Thanks...I have the standard 10mm & 25mm which came with my 200p but I also have a 5mm, 9mm, 18mm and a 25mm x-cell lx...as well as my 1100d dslr and spc900 webcam. When I got the ST80 I had to adapt a cheap 2x barlow (removed the lenses) before I could focus on anything.

That doesn't sound right, perhaps there was a part missing from your light path?

You should use a moon filter otherwise you'll get purple fringing from your retinas burning out.

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Are you using a diagonal with the ST80? I can't imagine why it wouldn't reach focus with one, but it might struggle without.

James

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Are you using a diagonal with the ST80? I can't imagine why it wouldn't reach focus with one, but it might struggle without.

James

No just the modded barlow and the lens / webcam...I'll post a pics of the st80 maybe you'll be able to identify what's missing.

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If you're not using a diagonal that may well be why you can't get focus. It probably adds about 60mm to the optical path, meaning the focuser can be 60mm further in when at focus than it would be without one. If you don't use one then it's not at all uncommon to have to add an extension to achieve focus.

James

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I found that I couldn't focus once when I tried using a certain eyepiece on my 150P, think it was the 38mm SWA. I had probably removed the 1.25" eyepiece holder and forgotten to replace it with a 2" holder as the eyepiece fitted in the focus tube.

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I cant get a full moon image comfortably in my 16" dob and this has a focal length of 1840mm so I'd think it would be very straight forward to see the full moon in your scope. I'd agree that 50-70x would give a nice scale in a plossl. I generally use a 32mm plossl giving 57x or a 25mm plossl giving 73x.

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I forgot to put my diagonal on when I first got my ST80 and had the same problem. Once it is on you should be able to get the moon in using either of the supplied eyepieces. It also makes viewing much more comfortable. If you bought the ST80 new there should be a diagonal somewhere in the box.

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I forgot to put my diagonal on when I first got my ST80 and had the same problem. Once it is on you should be able to get the moon in using either of the supplied eyepieces. It also makes viewing much more comfortable. If you bought the ST80 new there should be a diagonal somewhere in the box.

I purchased the ST80 2nd hand off ebay (i think) and i did not get a diagonal. I take it I'll need a standard 1.25 diagonal?....Time to go shopping!

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I purchased the ST80 2nd hand off ebay (i think) and i did not get a diagonal. I take it I'll need a standard 1.25 diagonal?....Time to go shopping!

Mine looks pretty standard! It's one of those items I look at and wonder why it costs as much as it does...

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ST80s are often used as guide scopes without a diagonal. It could be that it was originally sold without one, or that the diagonal was sold separately at some point in the past because it wasn't needed for guiding.

James

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ST80s are often used as guide scopes without a diagonal. It could be that it was originally sold without one, or that the diagonal was sold separately at some point in the past because it wasn't needed for guiding.

James

I've just purchased one from ebay for £20 - Skywatcher branded.

Even as a guide scope would it not to have something in place to achieve focus? Because without anything in mine (modded barlow) I can not get it to focus without that extra length.

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Even as a guide scope would it not to have something in place to achieve focus?

Probably depends on the camera that it was being used with. Some may have the sensor far enough back to find focus. Otherwise it would probably just be used with a separate extension as you have done.

James

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Probably depends on the camera that it was being used with. Some may have the sensor far enough back to find focus. Otherwise it would probably just be used with a separate extension as you have done.

James

Makes sense...Thanks for your help James.

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