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Widefield Eyepiece Help


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Hi All,

Looking for some much needed help and advice before I dive in and buy a new eyepiece. I currently have 2 scopes (Altair Astro 80ed and a Skymax 150 and I currently have the following eyepieces : Baader Zoom and Barlow, Altair Astro LER 6mm 55 degree and a BST 15mm and I feel its time to start to look for a few new eyepieces . With the 150 I'm more than happy with the Baader zoom and although I use it in the 80ed I'm looking at something for more wide views. What is everyones thoughts on a Baader Hyperion Aspheric ? Any thoughts on any problems that might occur with the 80ed which is f/7? Any other suggestions for a 30mm ish eyepiece that I could use in both scopes? I have about £200 to spend and I live in a Bortle 6 area. Any help or suggestions would be greatly appreciated.

 

Clear Skies Tim.

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2 hours ago, John said:

Are you able / prepared to use 2 inch eyepieces in both scopes ?

 

...or are you able / prepared to go and venture down the 'Green & Black' rabbit hole ?

 

Edited by Philip R
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I would go with the 30mm APM UFF.  It has replaced my 27mm Panoptic in that range.  Better flatness of field, better edge correction of lateral color, much wider true field of view, and much better eye relief.  It might be a tiny bit less sharp in the center, but the 10% difference in magnification makes it a difficult comparison.

See below for some comparison photos of eyepieces around 30mm.

1503910180_29mm-30mm.thumb.JPG.beb0e0b0d494a0fb027e38e2a180acef.JPG1270098715_29mm-30mmAFOV.thumb.jpg.b72cf50a97eb28a4217fd5188677c85a.jpg

Edited by Louis D
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10 hours ago, Philip R said:

...or are you able / prepared to go and venture down the 'Green & Black' rabbit hole ?

 

Ha ha I'd love to venture down the rabbit hole but second hand would have be the option. No problem with that at all. Tim

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6 hours ago, Louis D said:

I would go with the 30mm APM UFF.  It has replaced my 27mm Panoptic in that range.  Better flatness of field, better edge correction of lateral color, much wider true field of view, and much better eye relief.  It might be a tiny bit less sharp in the center, but the 10% difference in magnification makes it a difficult comparison.

See below for some comparison photos of eyepieces around 30mm.

1503910180_29mm-30mm.thumb.JPG.beb0e0b0d494a0fb027e38e2a180acef.JPG1270098715_29mm-30mmAFOV.thumb.jpg.b72cf50a97eb28a4217fd5188677c85a.jpg

Thank you, I'll have a look at that eyepiece, not come across it before. And thanks for the above info, something for me to think about. Cheers

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5 hours ago, Louis D said:

Since you originally mentioned the Baader Hyperion-Aspheric eyepieces, and because I just remembered there being a decent comparison article, I'll add the following translation link for you to read up on them and their Aero ED SWA counterparts.

That's my reading sorted for today, I appreciate your help. Tim

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With your scopes the Skywatcher Aero ED 30mm would work pretty well. I have the 30mm and 40mm in that range which I find very good with my refractors of F/6.5 and slower. I do use Tele Vue's with my 12 inch F/5.3 dobsonian though.

It's well worth watching the used market though - the Aero ED's can be had for around 50% of the new price in nice condition. Tele Vue's tend to commant somehwat more.

There are also good wide angle eyepiece ranges from Explore Scientific and some other brands which can be had for substantially less than Tele Vue prices.

I was a bit disappointed with the Baader Hyperion Aspheric though, for it's price. Too much outer field astigmatism even at F/8 for my tastes.

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4 hours ago, bluenotetim said:

Ha ha I'd love to venture down the rabbit hole but second hand would have be the option. No problem with that at all. Tim

Nothing wrong with second hand if you buy from SGL or UKAB&S. Most of my kit is from both sites, so you know what you are expecting. Two of my TeleVue 13mm’s are from SGL members

There are a few Astro-dealers on that well known auction site that I would recommend too; (not sure if this is the place to advertise them). If you would like the details, then please do not hesitate to send me a PM.

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The great news is, you already have a nice Baader zoom. You could put it through its paces and see what low power/sky background contrast/sharpness etc you are comfortable with. From there you'd be able to make a more informed decision. I think the Baader zoom at 24mm only has 48º field of view, at 20mm 53º fov, at 16mm 58º, at 12mm 63º and at 8mm 68º fov. Certainly looking at these figures, your f7 deserves a nice widefield which after all, is its forte.

Your own millage may differ but in terms of exit pupil, I've found:

  • 6mm - 4mm - if skies are sufficiently dark this range is nice for star fields, milky way and large open clusters.
  • 4mm to 3mm - nice contrast, good on star-fields.
  • 2.5mm to 1.5mm - nice contast and a good workhorse for most DSOs and casual lunar/planetary viewing.
  • 1.6mm to 1mm - nice contrast and resolution on planets, Moon and globs.
  • 1mm to 0.5mm – finer detail on planets, lunar, tight doubles - dependent on seeing conditions.
  • 0.5mm to 0 – super tight doubles but really not much call for use.

For a general foundation from which to build an eyepiece collection around, 2mm exit pupil is a good, solid baseline. Accordingly, in the f7 something around 13mm to 14mm, giving about 40x is going to be a useful eyepiece. In a widefield of about 70º, you'd be able to get just under 2º of night sky. In the f12, you'd be looking at around 24mm, giving about 75x and with a 70º eyepiece around 1º of night sky.

From here, you could drop down to about a 3mm exit pupil eyepiece, for lower magnification and hopefully a wider field of view. I don't know your night sky conditions, but maybe in an urban setting this would be edging towards the maximum you'd want to push before the sky background washes out too much. In this case, for the f7 something around 19mm to 24mm would be useful and in the f12, something around 36mm. 

Just looking at the numbers, then, for the f7, for general viewing you're looking for something around 20mm, 14mm, and 7mm and for the f12 something like a 36mm, 24mm, and 12mm. If you took a happy medium, an eyepiece between 20mm to 24mm would double up as decent low power in the f7 and a solid workhorse in the f12. If that were the case, I'd be scanning the secondhand market for something like a Panoptic or Nagler, or although I have no experience with them, those already mentioned by @Johnor @Louis D .

Sorry for the ramble but I hope that has helped a little :thumbright:

 

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Hi Rob, many thanks for this great reply, really good info. Plenty for me to think about after all of the above replies to my question. Great to see people taking the time to share their knowledge. Its all really appreciated. Tim. 

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  • 1 year later...
On 24/10/2019 at 14:50, Louis D said:

I would go with the 30mm APM UFF.  It has replaced my 27mm Panoptic in that range.  Better flatness of field, better edge correction of lateral color, much wider true field of view, and much better eye relief.  It might be a tiny bit less sharp in the center, but the 10% difference in magnification makes it a difficult comparison.

See below for some comparison photos of eyepieces around 30mm.

 

Cool comparison photos - how did you do that focus-on-ruler test, if I may ask?

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7 hours ago, Tasman Skies said:

Cool comparison photos - how did you do that focus-on-ruler test, if I may ask?

  1. I taped some rulers and yardsticks together on their back sides with packing tape and then wedged them under the edge of one of my kitchen cabinets, but hanging off to the side.  I always align the 17 inch yardstick mark with the edge of the door for consistency.  I turn on every light in the kitchen/dinette area and open all the blinds to maximize the available light.
  2. I put my AstroTech 72ED telescope on its leveled alt-az mount at the other end of our rather open plan house, about 35 feet away and close to level with the yardstick and close to perpendicular with it.
  3. I put a 2" GSO dielectric diagonal in the focuser with a TSFLAT2 field flattener spaced 15mm in front of the diagonal body on the scope side.  This pretty effectively flattens the otherwise severely curved focal plane of the scope.  Luckily, I don't need to add any extension tubes to reach focus, unlike when I try this with a 127mm Synta Mak.
  4. I put each eyepiece in the diagonal and focus the image with my eyeglasses on so the afocal image is focused close to infinity for the camera.  This allows the field stop to be at its sharpest if it was correctly positioned during assembly and allows the camera to focus at infinity.
  5. I then center the yardstick in the field of view and lock the altitude clutch.  Next, I nudge the mount left/right to put the edge of the ruler at the edge of the visible field stop, or at least the edge of the field for those without field stops.  This can be a judgement call for eyepieces that use the barrel for the field edge as the edge will fuzz out.  Also, you can move your eye off center and see more of the field with them by peeking "around the corner" of them, so to speak.  That's why some don't show the edge when the camera is centered.  I'll sometimes take an image with the camera way off to the edge looking at the other edge at an angle to get a clearer image of this effect, just like your eye would be doing in this situation.
  6. I use the high resolution, normal wide angle rear facing cell phone camera for most of my images.  In my case, a Galaxy S7.  I cup my thumb and forefinger around the top of the eyepiece to make a landing pad for the phone.  I start well away from the eyepiece and move the camera in toward the afocal image using the screen to guide my movements.  It's important to keep the camera level and centered.  That's where your thumb and forefinger come into play.  With practice, you can get it down to a fraction of a millimeter.  You can roll your fingers get fine height adjustment.  I've tried using adjustable height eye cups on eyepieces that have them to do this, but I couldn't get them to work very well.
  7. Now, you have to move the camera phone in and out until the edge of field or field stop just pops into view.  You're at the correct exit pupil distance for that camera at that point.  Any further out, and you miss some of the field.  Any closer, and you start to get blackouts.  If there is spherical aberration of the exit pupil (SAEP or kidney-beaning), you're going to be fighting a dark shadow all around the field.  If you are perfectly centered, you will get a dark circle with a bright center and a bright edge ring.  This cannot be helped as it a defect of the eyepiece and not the camera or scope.  In this situation, you may need to turn down exposure to -1.5 to -2 to avoid the autoexposure circuit trying to make the shadow 18% gray while blowing out the bright areas.
  8. Make sure to use the camera's diagonal to get the widest image possible for super wide angle and wider eyepieces.  You'll have to rotate the image in image processing software later.
  9. I then proceed to take a series of 3 to 5 images to later pick out the best of the bunch on a large computer screen.  I've found that it's impossible to critically judge these images on the phone's screen.
  10. I then take an angled image of the edge for super wide angle or wider eyepieces since the edge of field of even the best camera lenses is not as well corrected as the center.  It may also be cropped off for ultra wide field and wider eyepieces, so this is a necessity for them.
  11. If your phone has an ultra wide angle camera, use it to take all-at-once images of ultra wide field and wider eyepieces.  I bought a second hand LG G5 phone for $25 off ebay just for its ultra wide angle camera since my S7 doesn't have one.  That's what I use to take my "full view" images.  I scale them up to match the scale in the center 20% of the S7 images.  Differences in angular magnification across each camera's field of view accounts for the slight width difference in the final images when using the same eyepiece.  Unfortunately, the G5's a 5 megapixel camera compared to the 12 megapixel S7 camera.  When combined with the smaller image scale, these "full view" images are pretty low resolution by comparison.  I'd love to acquire a 24 megapixel or higher ultra wide camera for this purpose.  Anyone know of used ones that sell for cheap on ebay?
  12. In post-processing, I do not do any exposure adjustments or sharpening.  I just rotate and flip them to be more readable.  I also crop and composite them for comparison images.

Hopefully, that answers your question.  If I missed something, let me know.

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  • 2 weeks later...
On 03/11/2020 at 06:47, Louis D said:

Hopefully, that answers your question.  If I missed something, let me know.

Super detailed and helpful. I was thinking you would just tell me that it was with a telescope and not the eyepiece on it's own, but you have given me the information to do something similar with my own gear, and for that I thank you most sincerely 💯

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7 minutes ago, Tasman Skies said:

Super detailed and helpful. I was thinking you would just tell me that it was with a telescope and not the eyepiece on it's own, but you have given me the information to do something similar with my own gear, and for that I thank you most sincerely 💯

I'm an engineer who has to regularly write up detailed processes on how to perform complex tasks, so I can't help it.

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