Louis D

2 minutes ago, vlaiv said:

I don't think that distance will be much of an issue. It can only contribute to bit of spherical aberration, but with most of these eyepieces and their focal lengths it is too low impact to show on images. Field stop will be in focus - close focusing just moves focal plane further out but does not change focal plane of the eyepiece (which is ideally at field stop to make it sharp).

On the other hand - use of field flattener that has exact operating distance could be an issue for edge performance of some of the eyepieces. You did get about good spacing for it - it should be located at about 128mm away from focal plane, and GSO diagonal adds 110mm of optical path + 15mm of optical path of SCT/M48 adapter that makes about 125mm total - let's call it close enough. This would be generally ok if all eyepieces had their focal point right at the shoulder - but eyepieces vary by quite a bit and some may need up to 10mm of adjustment either way - that would make field flattener introduce significant astigmatism - which would show as EP astigmatism.

However, focusing out distance issues with your eye can move the image plane away from the field stop as I stated above, thus I focused wearing distance corrected eyeglasses.

I know about the shoulder issue.  I face the same issue with my GSO CC.  Luckily most of my eyepieces focus within 5mm of the shoulder.  To test your theory, check my image below of my 12mm Nagler T4 which focuses 19mm from the shoulder in two inch mode.

Just now, vlaiv said:

I was under impression that you were using DSLR and a lens. In case you have one - we can easily calculate focal length of lens that you would need to capture all eyepieces up to field stop. Let's take 100 degrees to be maximum AFOV currently available. If you use APS-C sized chip (most likely in consumer type DSLR) - that is about 28mm across. You would need something like 12mm lens to get it covered.

Btw - what scope did you use it with?

And what was the distance to rullers?

It's not possible to use DSLR lenses for digiscoping with most eyepieces because you'll get severe vignetting due to the huge mismatch in diameters between the eyepiece eye lens and the camera lens's objective lens.  You have to use cameras with tiny lenses.  Today phone cameras are perfect for this task.  They are surprisingly well corrected and high in resolution compared to what was available in digital P&S cameras 15 to 20 years ago.

That other camera is 135 degrees on the diagonal (LG G5).  Unfortunately, it's only 5 megapixels.  It also has a weird white balance that is consistently yellowed.

You can't use eyepiece projection directly onto the sensor, either, because most eyepieces don't project a flat field.  You really need a lens on the camera to emulate the human eye's interaction with the eyepiece's exit pupil.  In my case, the depth of field of the camera lens actually makes eyepieces with field curvature look better than they do to my presbyopic eyes.

Your other two questions are answered in my earlier post I was composing when you responded.

12 minutes ago, John said:

The edge distortions will depend on the spec of the scope that the eyepiece is used in. In an F/10 or slower scope, most eyepieces are sharp to the edge of the field of view. At F/4 most will show some distortion.

Scopes also have some distortions of their own to add to the mix eg: coma with a newtonian and field curvature with refractors.

I don't know what spec of scope Louis D's field photos were emulating. It would be interesting to know

They were taken through my f/6 AstroTech 72mm ED with a TSFLAT2 field flattener ahead of the 2" GSO 99% dielectric diagonal spaced at 15mm with an SCT to M48 thread adapter (original diagonal nosepiece removed) with about 35 feet of separation indoors between the target and the scope's objective.  As I said above, it's clear that certain camera/eyepiece combinations will yield sharp images to the diagonal limits of the camera (a Galaxy S7 phone camera).  Check both edges for sharpness because I sometimes ended up with one or the other being slightly sharper due to camera tipping or centering issues.  There's very little residual field curvature or edge aberrations from the objective itself.  It's also unobstructed, so that's one less variable when it comes to evaluating eyepieces.  The images I captured pretty closely resemble what I saw through each eyepiece with my eyes while wearing eyeglasses to correct for my strong astigmatism.  Each eyepiece was focused for infinity corrected vision to hopefully show the field stop sharpness at its best since focusing for near or far sightedness can move the image plane ahead of or behind the field stop location causing it to look fuzzy.

4 minutes ago, Deisler said:

Hi Louis,

May I ask if the distortion at left-right boundaries of the visible part of the ruler was because of the image taken by a camera, or it will look like that visually?

The Aero one does seem to have very bad distortion at boundaries.

Cheers

 

Nope, not the camera, it's the eyepiece.  Notice how sharp the 40mm Meade SWA is right almost to the edge with nearly the same apparent field of view.  You can also see that the 30mm ES-82 is fairly sharp nearly to the edge.  I tilted the camera to get the edge in sharpest focus possible to show the field stop sharpness in that little extra bit of image to the right of the main image since my camera only goes to about 75 degrees on the diagonal.  I bought a second super wide field camera to capture the entire field in one go in the "full width" images.  However, it is a lower resolution camera and I had to up-sample the images to match the image scale of the 75 degree camera, so the utility of those images isn't all that great.

There just is no free lunch when it comes to wide field and good image correction across that field.  If you want both at the same time, it means getting a big, heavy eyepiece.  Notice how nicely corrected the Baader Scopos Extreme is.  However, it's weight slots it between my 12mm and 17mm ES-92 eyepieces, which is to say very heavy.  Your best bet for well corrected and lighter weight is the 30mm APM UFF.  However, it is fairly expensive, though still cheaper than TV Panoptics.

2 hours ago, Deisler said:

Hi guys,

Just to summarise what I have learnt so far from great advice you guys have given me and what I decide to do for my EP upgrade -

1) will get BST StarGuider 60º 5mm/15mm ED EPs - ~£45 each

2) will get a wide field low-power EP, currently leaning towards Aero 2'' 30mm (£100), but 32mm GSO Plossl (£33) is much cheaper but with some negative comments (like distorted view). 

3) will get a filter - still need to research this topic, i.e. UHC v.s OIII;

4) Next, probably in a six months time, I will buy a TV barlow or a TV PM, depending on if I need greater eye relief on my BST EPs.

 

Re. the wide field low-power EP, can you guys comment on 'Aero 2'' 30mm vs 32mm GSO 1.25'' vs other options' for my 200P Dob? 

I quite enjoy low-power view (through my stock 25mm) and found it very relaxing - so I want to buy a good one that will always be in my EP case. Any advice?

Cheers

Deisler

Remember, FLO offers increasing discounts on BST Starguiders as you buy more of them.

I compared them to their Meade HD-60 equivalents in this thread and found them quite comparable despite their lower price.

In my previous post, you can compare the 32mm GSO Plossl to the 35mm Aero ED.  Even the 30mm 80 degree eyepiece (Agena UWA above) (generically available for low cost on ebay) shows at least as much well corrected field in the center as the 32mm GSO Plossl while providing a poorly corrected outer field for context.

If you live under heavily light polluted skies, I'd get a quality OIII filter because it really blocks light pollution quite well.  You give up the Hydrogen Beta line as seen below, but I've never missed it:

I rarely use Barlows any more despite owning 7 of them in 1.25" and 2" sizes as well as a TV PBI.  Individual eyepieces are just easier to deal with unless you leave the Barlow in the focuser all night to operate continuously at higher magnifications.

Now that we're talking about low power 2" eyepieces, I'll add that found the 35mm Aero ED to be quite usable, but definitely not perfect.  It has nearly the maximum true field of view available in a 2" eyepiece.  I haven't tried the 30mm Aero ED because I've got the 30mm APM UFF which would be hard to improve upon.  Below are some comparison photos I took of and through my wider eyepieces to give you some idea of what to expect.

First, I'd double check my collimation as @vlaiv suggests above just to be sure it's my eyepiece.  He's also got a point about seeing conditions.  If stars are twinkling due to atmospheric turbulence, anything above about 80x to 100x is going to be mush.  Usually, I wait a day after a strong front passes through for the best seeing conditions.

I've got some really cheap 9mm eyepieces (a Kellner and a Meade Plossl) as seen below in some images I took of and through them, and they produce remarkably good images on axis in my f/6 AT72ED refractor.  Even off axis, they're pretty good.  You can judge for yourself how much of an improvement you get by moving up to Vixen LV (SLV nowadays), Meade HD-60 (BST Starguider equivalent), Morpheus, or even Delos eyepieces.

If you go to this thread I started, you can check out a bunch of other eyepieces from my collection including the BST Starguiders and several zooms.

More expensive eyepieces buy you wider fields of view, better corrected imagery across those fields of view, and longer eye relief.  They also tend to have sharper and contrastier images due to better polish, coatings, and stray light control.

I'm guessing the 130pds has a metal tube.  One of my dobs has a sonotube tube and has never had dewing issues on either mirror.  Perhaps you could try wrapping the entire tube with closed cell foam to insulate it to see if that prevents dewing any better.  Seems like a low cost experiment to try.

Has anyone tried this new collapsible MiniMax stool for astro observing?  I saw it in a B&H Photo email.  It might be useful for soggy lawns and refractors.  The price isn't too bad, either.  Add to that how compactly it folds away, and it might be really handy for camping trips.

Sure would be nice if field flatteners came with a helical focuser to fine tune the separation.  Something like the old Tamron 2x Macro teleconverter would be nice:

5 hours ago, pregulla said:

On the other hand I found that wide filed eyepieces (ES82 11mm, ES68 16mm) show lateral color in the outer field so the useful field is pretty close to that of a zoom eyepiece.

The ES-92, Pentax XL, and some Pentax XWs and Morpheus don't show lateral color near the edge.  The 30mm ES-82 is horrible with lateral color at the edge.  So much so that earlier this year, Mars was showing as a widely separated red disk and blue disk at best focus near the edge.  I was trying to figure out why there wasn't a green or yellow disk in the middle.  You really do need to keep planets on axis for best results in just about all eyepieces regardless of correction level.

5 hours ago, Jiggy 67 said:

They are only for the winter, I’m hoping the grass will recover in the summer and I intend to lay them down again next winter.....but you’re right, I’ll keep an eye on it

That's too bad about your soggy winters.  Our winters in Texas tend to be fairly mild and dry.  Spring and fall tend to be our wet seasons, and everyone knows it is hot and dry in Texas during the summer.

Keep us updated with spring pics to see how your lawn did over the winter with those mats.

I can't compare the GSO/Revelation to the competition because it's the only one I've used in my scopes.  At f/6, it nicely cleans up and flattens the field for eyepieces focusing within 5mm of their shoulder with the 25mm extension I use.  Only the 12mm NT4 shows any appreciable coma because it focuses about 19mm from the shoulder.  Even then, it's a major improvement over no CC.  In my two ES-92 eyepieces, I can't see any star bloating at the edge not attributable to minor astigmatism, so it should do well even with 100 degree eyepieces.

The one shortcoming I've noticed is at high power.  It contributes a bit of spherical aberration on axis, so planetary images are sharper without it at small exit pupils.  It's my understanding that the 5 element Paracorr II does not exhibit this behavior, so it can stay in the focuser permanently.

The GSO/Revelation magnifies 1.1x vs. 1.15x for the Paracorr and 1.06x for the ES.  I know nothing of the SW and Baader CCs.  The GSO/Revelation requires about 10mm to 15mm of in-focus (I'll have to measure it exactly sometime).  The Paracorr is around 19mm and the ES is about 38mm.  Since I have so little in-focus available, the ES is a non-starter for me.

The GSO/Revelation does so well, I have never felt  a need to upgrade it.  At f/4.7, the Paracorr II might show a noticeable improvement, but at what cost?

I went CC-less for over a decade of observing and then saw a used GSO CC for sale and thought I'd give it a try.  After getting it setup and using it for a few night, I couldn't believe I had been living with so much outer field degradation due to coma and field curvature and never noticed it.  Once you see it, you can't unsee it.

We need to know your budget if we're going to spend your money for you. 😉

For most DSOs, something between 12mm and 17mm  will work well in your scope.  The 12mm and 15mm BST Starguiders (AT Paradigm) would work well, though only 60 degrees AFOV.  If you've got deep pockets and can balance heavy eyepieces, it's hard to beat the 12mm and 17mm Explore Scientific 92 degree eyepieces.

Below are some images taken of and through eyepieces in this range in an f/6 AT72ED fractor.

14 hours ago, johninderby said:

Wonder how it compares to a Siebert 4.3” observatory eyepiece?

 Well, the 30mm ES-100 only has a 52.2mm field stop, so not that much bigger than a 41mm Panoptic's 46mm field stop, and far less than the 3" format maximum of about 74mm.  I think the Sieberts have much wider true fields of view, though narrower apparent fields of view.  I have no idea how well corrected they are center to edge.

By the way, there's a refurbished 30mm ES-100 on ebay for $399.  However, there have been reports that these refurbs have been a total crapshoot as far as quality goes.

6 hours ago, Kronos831 said:

Thanks for the information guys,but I read somewhere that

binoviewers have clear apertures at 20mm eyepieces and that higher focla lengths eyepices , will suffer from vintaging. Is that true? What is vintaging and how can it affect my views?

Yes, there will be some vignetting in the 32mm Plossls.  I've seen it in my Arcturus binoviewers.  25mm or 26mm Plossls also work well and avoid the vignetting issue.  Since I use a 2x Barlow nosepiece operating at 3x to reach focus in my f/6 Dob with the binoviewers, I actually prefer the cheap Svbony/Vite/noname 23mm 62 degree aspheric eyepieces available on ebay and elsewhere.  They provide pretty close to a max, unvignetted field in my binoviewers and have sufficient eye relief to use comfortably with eyeglasses once the rubber eyeguard is removed.  At f/18, they are fairly well corrected across most of the field.  They are also super light and tiny, making them easy to balance and to get a large nose between them.

Below, you can see them at f/6 in my AT72ED refractor.  There are a few other binoviewer max field options shown in the same image.

If the ES 40mm 62 is basically a rebadged 40mm Meade 5000 Plossl (as has been suggested elsewhere), it's very sharp in the central 50% falling off in the outer 50%, especially the outer 25%.  It has very low distortion and is very easy to hold the exceptionally long eye relief.  Below is an image of and through the (decloaked) 40mm Meade 5000 Plossl.  I have no experience with any of the Panaview eyepieces, though I would recommend the 35mm OVL Aero ED in that range for about the same money if the tighter eye relief is not an issue.  Again, images below taken through an f/6 AT72ED refractor.  YMMV if you have a faster scope.

If it wasn't disclosed that it has clouding issues, I'd ask for a return and refund.  Something that obvious should have been disclosed up front.  You could always try it out anyway under the stars to see if it affects performance.

1 hour ago, davhei said:

Thanks Louis, much appreciated!

Problem with the 31 mm NT5 and I guess Ethos 21 as well is the weight. Just unbalances my scope too much att certain angles. I would trade some tfov for a lighter EP. With Ethos there’s the question of eye relief as well.

Realise I may have to compromise with a few things, no such thing as a perfect ep I guess.

The 20mm APM HDC XWA is only 24 ounces, 12 ounces lighter than the 21mm Ethos and the same as the 22mm NT4.  According to what I've read, it's better corrected than the 20mm ES-100 and not that far off the 21mm Ethos.  Eye relief is 15mm designed and 12mm-13mm usable.  How much eye relief do you prefer when using eyepieces?

First, I highly recommend getting a GSO/Revelation coma corrector and adding a 25mm extension to it or put the optics section on a Baader 2" ClickLock with 2" CL Extension 47mm.  It will massively improve edge performance on wide field eyepieces on your f/4.7 scope without breaking the bank like a Paracorr II would.

As far as wide fields at f/4.7, you'll want to stay below 33mm to keep your exit pupil at 7mm or less to avoid cutting off some of the light coming from your 10" mirror as it enters your eye and to keep the sky a little darker.  That leaves you with the 31mm NT5 and 30mm ES82 for widest field.  If you're willing to give up a bit of TFOV, there's the 30mm APM UFF.  You could jump up to a 21mm Ethos or 20mm APM XWA HDC Hyperwide to maintain a TFOV similar to the 30mm APM UFF but have a much darker sky background.  The 22mm Nagler has a TFOV more like a 27mm Panoptic or 28mm ES68, so not even close to widest TFOV.

Below are some photos I took through my f/6 AT72ED refractor of some of my wider and widest field eyepieces using a yardstick as a target and keeping the scope/target distance constant.  Your f/4.7 primary would be much more demanding on the eyepieces, so expect poorer edge correction on your scope.  They'll give you some idea of the differences you can expect (except that I don't have any 100° AFOV eyepieces).  The "full view" images were taken with an ultrawide, lower resolution camera and rescaled to match the on-axis image scale of the other camera's images.

5 hours ago, dan_adi said:

I must respect the flattener optimal distance to camera sensor.

That is all that matters.  Any extra in-focus added by a low profile focuser isn't going to change that.  As @vlaiv says above, if you can reach focus with the current focuser and flattener, then there's nothing to be gained in swapping focusers.

On 06/11/2019 at 08:34, dan_adi said:

I get stars with coma at the edge of the field.

Technically, that's not coma.  It's just defocused stars.  Verify this for yourself by defocusing a star on axis.  It's nice and circular.  Now move that defocused star to the edge, it becomes oblate/elongated.  That's why you should always star test exactly on axis.

57 minutes ago, FLO said:

Some photos from Tele Vue 🙂 

Beautiful packaging.  I'd be terrified to actually use the eyepiece for fear of ruining its collectible value.  That would be a shame to have it just sitting in a display cabinet unused.  Perhaps they could later issue an ugly, non-collectible version for the plebeian masses to actually use and enjoy.

I've read that the Dioptrx will grip outer diameters from 41mm to 44mm.  If so, the AT AF70 has a 43mm thread once the eyecup is threaded off, so it should work.  It has more than enough eye relief for comfortable use with eyeglasses, so that shouldn't be an issue.  The AT AF70 is discontinued, but the 22mm Omegon Redline SW is still available new and is identical in all respects but name.

I've read that the top of the Pentax XWs can be screwed off and the Dioptrx placed inside and the top threaded back on.  Since the revealed thread is also 43mm on the Pentax XWs, you could experiment to see if the Dioptrx will fit on it prior to getting the Omegon Redline.

Instead of using Dioptrx, I bought a pair of dedicated distance eyeglasses with my cylinder (astigmatism) correction that I only wear for stargazing.  I got them made with low index plastic lenses to reduce chromatic aberrations introduced by high index lenses.  Having dedicated, single vision glasses reduces the cost of replacement if I scratch them on an eyepiece and reduces the accumulation of microscratches that degrade the viewing experience.

48 minutes ago, Mick H said:

Should I buy the Televue Apollo 11 mm eyepiece or a Celestron Omni Plossl Eyepiece 12mm?

I cannot decide.😉

The choice is obvious. 😙