Louis D

5 minutes ago, John said:

I was going to suggest just that eyepiece as well but I decided to stick with commenting on the two that @chrispancho had mentioned.

My personal choice would be the 20mm / 100 degree eyepiece because I love hyper-wide views. Not everybody does though.

 

I just threw that out there in case the OP hadn't considered non-TV options.  I'm pretty constrained in my choices due to my astigmatism, but perhaps the OP is not.

With the extremely long focal length of a C11 (2800mm), adding a tele-extender doesn't make much sense.  You'll already be working at powers that may be too high for typical UK seeing conditions with that 9mm.

You might also want to investigate the APM XWA HDC eyepieces.  Reports here and on CN generally regard them as slightly sharper, lighter, and less costly than their ES-100 counterparts.

At the other end of the power spectrum, you might want to consider a 56mm Meade 4000 Plossl or similar to get to a 5.6mm exit pupil for OIII filter usage at 50x.

3 hours ago, Don Pensack said:

THERE IS A SPEERS-WALER SERIES 4.  THESE NEED TO BE TESTED BY SOMEONE........

Only if they had at least 18mm of usable eye relief.

I am toying with the idea of getting a 40mm Pentax XW for Christmas at the current sale price.  I'd mostly be comparing it to my decloaked 40mm Meade 5000 SWA.  What do you think, @Don Pensack, should I do it?  Worst case, I figure I can resell it for $500 or more in 5 to 10 years once they're discontinued and become sought after on the secondary market again. 😁  After all, I only paid $125 for my 40mm Meade SWA in 2012 or thereabouts and could probably get around $150 for it today.  With inflation, I'd at least be close to breaking even.

3 hours ago, Don Pensack said:

Some of the eyepieces are so bad I wonder why they're being saved.

Because the return on trying to sell them is so much less than keeping them around for reference purposes.  The only exceptions I can think of right off hand are the 12mm/17mm Naglers and 27mm Panoptic.  Those are tying up over $700 of funds.  I'm thinking of donating them to my daughter someday if her interest in astronomy grows more.

4 hours ago, vlaiv said:

Not sure how you plan to cut such thin lines . At some point I wanted to make very narrow slit - like 10µm slit (which 100 per mm) and that was simply beyond my skill by far. In any case, I suspect that it will start behaving like solid and reflect light. In fact - most of the things that we perceive as solids are very empty and we could argue that they are extremely fine gratings (crystals for sure) - some transmit light and others reflect it, but that depends on internal structure.

Even if material was transparent and had very fine "molecular" level "grooves" in crystalline structure, I think there would no longer be diffraction effects. Diffraction happens because of different distance between light paths. Once slits are too narrow - difference in distance between adjacent paths vanishes and so does phase difference for interference. Wavefront will just pass undisturbed (transmission) or get reflected back (reflection), but there won't be diffraction.

More of a theoretical question.  Someone could probably use a scanning electron microscope to move atoms into the desired positions to empirically check this.

I figured that once the slits are too narrow, the waves wouldn't be able to pass through.  At that point, they're either going to be absorbed or reflected.

2 minutes ago, HollyHound said:

Thanks for the information. I shall look forward to seeing how it performs. I do also have a Panoptic 24mm as well, so have options 👍

It will definitely be much lighter and more compact than either a 35mm or 41mm Panoptic, so there is that.

17 minutes ago, vlaiv said:

You reach a point where mask starts working as diffraction grating. You can see that as one gets more line density - spectrum starts to form in different orders, like in this image:

With higher density you are both increasing length of diffraction edge and spacing of the grooves - second one just makes spectroscope of higher and higher resolution. Diffraction gratings have hundreds of grooves per mm and produce nice rainbow spectra - like StarAnalyzer.

This is 100 lines per mm - very stretched out central spike of bahtinov mask. B mask has 3 distinct angles of grooves and that creates three different spectra at an angle.

That's what I was thinking it reminded me of.

However, what happens when the line width is narrower than the wavelength of visible light?  For instance, say, greater than 10000 lines per mm?  Do you just get a really good spectral analyzer or does something else start to happen?

9 minutes ago, ursamajorro said:

My home made mask is a Bahtinov simplified at maximum. I used mosquito net. It practically costed me nothing.  How it looks intra and extrafocal see video:

Reminds me a bit of my home brew apodizing mask made from black window screen.  That mask causes some really wild spectral artifacts in the outer field.

3 hours ago, HollyHound said:

Oh damn, if I'd have spotted that one earlier, I wouldn't have bothered ordering the 10" Bresser dob and saved myself some money 🤣

See if they'll price match and refund the difference. 😉

Reposting detailed description from another thread of how I captured these images so I can find it more easily in the future:

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.

13 hours ago, orions_boot said:

17 hours ago, HollyHound said:

I’m hoping the Aero ED 35mm will make a good wide angle eyepiece and I have a good mix of others too 👍

This is what I ordered and will wait to see how it is.

The Aero ED 35mm will be pretty good at f/4.7, but not Panoptic sharp in the last 25% of the field, so temper your expectations, and you should be happy with it.  Here's how it looks at f/6 in a field flattened 72mm ED scope:

If you are trying to block sky glow, I'd probably recommend a UHC filter.  If you're already in dark skies but want to go after faint outer tendrils, I usually go with an OIII.  Both filters make the Trapezium look really odd, so remove them for enjoying views of it.

5 minutes ago, vlaiv said:

William optics seems to think so

However, their rationale that it will help with narrowband and make spikes stronger / more contrasty is wrong. Strength of spikes depends solely on length of diffraction edge - in this case, density of the grooves.

 

Do you mean that by having more closely spaced, finer grooves, you will have stronger spikes?  If so, that sort of makes sense.  However, don't you reach a point where they are so fine they just look gray to the incoming light?

If you don't need the eye relief, you might want to check out the 20mm APM XWA HDC.  It will show a larger patch of the sky and probably be as sharp as that portion which overlaps the 22mm Nagler.

1. Try loading Skeye on your phone and then strapping it to a non-ferrous part of it or put a large block of foam in between and use it in DSC, push-to mode.  You can align on Mars and go from there.
2. Buy long eye relief eyepieces and wear eyeglasses at the eyepiece.  I've been doing this for 20+ years and have never had an eyepiece fog up.  The eyeglasses act as a vapor barrier to prevent body moisture from fogging the eye lens.

What about being made from clear acrylic?  Would there still be enough diffraction at the edges to work?

1 hour ago, Karen Johnson said:

Thanks Louis, that’s very helpful, I did find some older threads eventually after much searching and these eyepieces were recommended by others so I shall take your advice.  Is there any benefit to me buying a Barlow 2x to go with these do you think?

I tend to avoid Barlows because they're a pain to keep putting in and pulling out of the focuser.  Once in, I tend to leave them in.  That said, if you can locate a quality Barlow, they're fine.  I tend to buy vintage, Japanese made Barlows myself.  Chinese made stuff tends to be all over the place quality-wise.

A Barlow would not be useful with the 5mm because 2.5mm would be much too high a power for that scope on most nights.  That, and a 0.5mm exit pupil is verging on being a pain to use due to eye floaters.

The Barlow would make the 12mm a 6mm effectively, which is quite close to the 5mm.  So, again, not a big gain.  I would probably spend the money on the 8mm BST SG to split the difference in power.

Thus, you'd have 28mm, 12mm, 8mm, and 5mm eyepieces for 23x, 54x, 81x, and 130x respectively.  That scope's short focal length doesn't lend itself well to high powers.  In my experience, 30x per inch is usually doable with fast reflectors which equates to ~150x for your scope.  This would equate to a 4mm to 4.5mm eyepiece, but it would not be that big of a jump over 130x visually.

You can see below in my comparison image of AT Paradigm (BST Starguider) and Meade HD-60 apparent fields of view how the image scale changes at different focal lengths:

Scammers are getting smarter because they actually send you something (not all what was advertised), which makes it harder to claim fraud than if they sent nothing at all.  They also steal in smaller amounts than in the past.  Governmental authorities tend not to investigate petty theft like this.

According to one of the OP's links, they'll actually send you a 25mm monocular instead of a 12" Dob, for which $20 isn't such a bad price (should be about $10).  Thus, it's not even petty theft.

3 hours ago, jock1958 said:

although rather soft compared to my sharp cyclops images.

Try swapping out the WO OCS/GPC with a high quality Barlow nose piece.  The two OCSs/GPCs that came with my Arcturus BV were both garbage.  They added a weird coma effect to all stars across the entire field, as if there was a tilted element in there somewhere.  I generally use the nose piece from a vintage Meade 140 2x Barlow.  The views are super sharp.  I also recently tried a Parks Gold Series 2x (same as Celestron Ultima and Orion Shorty Plus) Barlow, and it was equally sharp.

To nicely frame the moon, you'll want somewhere around a 1 degree true field of view eyepiece since the moon is 1/2 degree across.  I would probably recommend a BST Starguider for your rather demanding on eyepieces f/5 reflector.  Since these eyepieces are 60 degrees apparent field of view, this equates to needing 60x in power (60degrees/60x=1 degree).  Given your scope's 650mm focal length, this would equate to 650mm/60x=10.8mm.  The closest available focal length would be 12mm for 650mm/12mm=54x.  This would also be a useful power for looking at many open clusters and larger nebula as well as for solar viewing with a full aperture solar filter.

Now, to get better, close-up views, I would recommend jumping up to the 5mm Starguider for 650mm/5mm=130x.  You would still have a very reasonable 1mm exit pupil (eyepiece focal length/scope focal ratio=exit pupil).  Exit pupil is how big a circle of light is coming out of the eyepiece and into your eye.  Below about 0.7mm and floaters can start to be an issue.  This power would also be useful for looking at brighter nebula, planetary nebula, and planets themselves.

From Agena Astro's Sky-Watcher 6" Dob webpage:

• OTA length: 44.5"
• OTA width: 7.125"
• OTA weight (with accessories): 15 lbs
• Base weight: 25 lbs
• Base dimensions: 29 x 20.5"
• Zenith eyepiece height: 44.5"

Since the focuser is at least 6" from the end of the tube, figure it sits about 50 inches tall or slightly more.  Remember, though, it could be stored in two parts to save a bit of height or with the tube at an angle to save some height.  You could also store it to the side toward the front of the closet but just back a bit with the coats up against it since it's less than 8 inches wide.  That's how I store my 8" Dob in our other downstairs closet.  Literally no one ever notices it in there.

I also store a bunch of astro gear in our under-stairs closet at the back where it's too low for hanging coats.  It's really surprising how much space there is back there.

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.

12 minutes ago, johninderby said:

Better yet solar powered with no battery. 😁

Notice I said solar charged and not solar powered.  I had originally typed powered and realized how stupid that sounds.

1 hour ago, johnturley said:

Actually they can, my Skywatcher Esprit 150 is superior to a early (pre Starfire) 6in f8 Astro Physics Refractor that I used to own in terms of sharpness of the image, and vastly superior to it regarding colour correction.

John 

I wouldn't doubt it with the advances in low dispersion glass and improved Chinese lens polishing.

The question then arises, are their lens cells as well designed to hold collimation as temperatures drop for astrophotography?

1 hour ago, gorann said:

How does this one compare to US prices?

https://www.astrobuysell.com/uk/propview.php?view=167429

I found this AP 130 EDF scope resold twice in the last two years on CN classifieds:

https://www.cloudynights.com/classifieds/item/146793-astro-physics-130-edf/

https://www.cloudynights.com/classifieds/item/165492-astro-physics-130-edf/

First, for $5000 in 2018 and then $5150 in 2019.  In 2020, I would guess it would fetch $5300 or more.  There's a wanted ad for one, so there's still demand for them.

The ad you linked to has it listed for £4195 which would be about $5400 at today's exchange rates.  As such, there really isn't much of a price difference between the UK and the US vis-à-vis A-P scopes based on this one data point.