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Planetary Eyepiece - mobile phone photography?

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So I was thinking about carrying out some astrophotography of some of the more esthetically pleasing planets. Due to my budget constraints, I was planning on doing it with my mobile phone, with a suitable mount and eyepiece. 

As I only have the stock 10mm, and 25mm EPs (and an aftermarket barlow) I was thinking about getting a new eye piece for this. I have a Skywatcher, 130P (130mm diameter, 650mm focal length).

I was looking at something like the 6mm Vixen NPL, or the 6mm Baader Classic, BST StarGuider ED (5 or maybe 8mm), Celestron X-Cel LX eyepiece (5 or 7mm), or maybe Sky-Watcher UWA (5, 6 or 7mm). But I've got no idea which would lend itself best for what I am attempting to do.

Any advice from the community?

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14 hours ago, Don Pensack said:

Yes, look for a long eye relief eyepiece so your camera lens can pick up the field.

Thanks, that is one of the things I have tried to look for, but not all the EPs seem to give a number to eye relief. I'm guessing that's either because it's tricky to give an accurate number to, or because it shows the EP's weakness maybe.

It's a bit like the field of view number, not all EPs seems to advertise that. But at least, when doing planetary viewing, that's less important than it is for DSOs (though will keep the planet in view for longer without having to move the scope).

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The First Light Optics website gives the eye relief and apparent field of view of the eyepieces that you list in the specifications for each eyepiece or eyepiece range if the eye relief is consistent across the range. Eg:

"The new enhanced Celestron X-Cel LX eyepiece series are 6-element fully multicoated eyepieces designed for comfortable high magnification observing.

Wide 60-degree field of view.

Parfocal so require little or no focusing when changing from low to high power.

Generous 16mm eye-relief

Twist-up eyecups. 

1.25" barrel threaded to accept filters."




Edited by John
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56 minutes ago, RickEm said:

Does it matter if eyecups are up or down?

You may have to flip the eye cup down to be able to get the camera close enough to properly couple with the eyepiece's exit pupil.  The eye cup being up may help block stray light, though.  You'll just have to experiment and see what works best.

Having taken all of those afocal images of my eyepiece apparent fields of view in this thread, I've found it is possible to couple cell phone cameras into eyepieces with as little as 3mm usable eye relief.

Here's a new one I haven't previously released.  It's of a generic 6mm Huygens I got with a $25 70mm x 300mm refractor off of ebay with just 3mm of usable eye relief:


This was with the AT72ED and a Galaxy S7 rear facing camera.  It is actually not that bad of an eyepiece at f/6.  It shows that with skill, it is possible to use eyepieces with very little eye relief.  I was hand holding the camera using my finger edges to maintain alignment with the eyepiece.  It's an acquired skill.

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5 hours ago, Don Pensack said:

Yes, cell phone cameras don't require as much eye relief as DSLRs.

And DSLRs are extremely difficult to use for afocal projection.  Generally, the entrance pupil of most DSLR lenses lie deep within them, making it difficult to get it to coincide with the exit pupil of the eyepiece unless it has very long eye relief.  Zoom lenses just compound the problem by burying it even deeper than with prime lenses.

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In some ways longer eye relief can be more difficult with smartphone imaging as you need to hold the camera further away from the exit lens to get properly on the exit pupil and see the field stop. A mount which allows adjustment towards and away from the eyepiece helps here, like the Celestron NeXYZ.

Also eyepieces with straight sides of a reasonable length are easier to clamp on to than those with bevelled or very short edges. I’ve not tried the BST Starguiders but it looks like you could clamp onto the fattest part near the top quite easily despite them not being flat. Some of the very short ones (like 5 and 6mm orthos or plossls) can be so short it is trickier to find space to clamp onto them. A lot depends on the exact eyepiece design and the mount you are using.

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I use the Hyperflex clone 7.2mm - 21.5mm zoom when I image through the scope with a mobile phone. My cheap clamp seems to hold the top of this eyepiece well and having the zoom makes it a flexible tool.

With a 2.25x barlow lens the zoom becomes a 3.2mm - 9.55mm.



Edited by John
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