Ruud

The knob is probably to prevent focus creep, but everyone else already said that. I have a question:

I've been looking at this telescope. I thought I'd buy it for birding and as a super portable visual scope, as well as a bit of photography. Do you think this telescope would be a good choice for that?

A decade or so back, we had a year with many more good nights than I was used to. It felt like I could take out the telescope every night. There was a great increase in my observing, but after a few weeks I began to get bored! Too blase to bother.

No chance of that happening these days in which sessions are so few and far between. I now feel I've invested in a hobby that can never wear out. Impossible at this rate!

Yes, a finder eyepiece with an incredibly small fov. I think Vixen's logic is in the calendar. It's the right day for a joke.

I like my SCT, I love my refractor. Tighter stars and less diffracted light just makes for a better visual experience.

I saw an 8" refractor the other day. A CFF impossiscope. Cost €25,000 for the OTA, weight 23 kg. I suppose refractors are nice up to 5 or six inch, but beyond they make no sense at all. This one was sold but still in the shop, waiting for the buyer to finish the observatory for it. He also still had to decide on a mount for it. 

http://cfftelescopes.eu/refractor-200mm-f8-2/

I don't use one but I would certainly like to. Mine is metal and plastic. Wooden eyepiece boxes are so much more  beautiful, especially handcrafted ones. Looking forward to the pictures.

The first Naglers (1980s) had spherical aberration of the exit pupil (SAEP). They were also the first commercially available UWAs that were sharp across the entire field.  I still have one: the 4.8 mm.

The smaller the exit pupil, the less problems you have with kidney beaning from SAEP. That's why I only got the 4.8 mm. That's a zero problem eyepiece even at f/5 when its exit pupil is 1.2 mm wide. I've never seen a kidney bean in it, even at daytime.

With larger exit pupils, say 3 mm and larger, kidney beaning did occur in the first Naglers, especially on sunny days when the observer's pupil got narrower.

In spite of their SAEP, the first Naglers were well received. Then already, they were the best around. NaglerT2 addressed the kidney beaning issue, T4 is a small series with long eye relief and very little AMD. A special series. Bulky though, and not everyone was prepared for a combination of ultra wide and long eye relief. The eye relief problem comes from having the eye hover over the eyepiece, missing the exit pupil from time to time. This you can see in the post above. The problem disappears with practice and if you have no control over it, a different eye guard will probably help.

The wide angle issue occurs when you want to scan the entire field of an UWA eyepiece. For that you eye has to move. This is needed because while turning your eye from 41° left via straight forward to 41° right, the pupil changes position, and you need to compensate for that. It must stay on top of the exit pupil.

You can see that here. The centre of the eyeball has to move from left to right as the eye scans from right to left.

That some people need an eye guard for long eye relief eyepieces is not a design fault of the eyepiece. It's a motor control issue of the observer  that can be remedied by an eye guard or practice. That the problem existed for some observers only became apparent after such eyepieces became widespread.

Try before they buy and be prepared that you may have to get used to a new eyepiece. Having to keep your eye still enough and having to move it as well can be a bit tricky, but it can be learned!

Here's the source file for the animation above: glasses and UWA.ggb
To open it and play with the sliders you need to download the free app Geogebra from https://www.geogebra.org

An ironing stool is fine! 

A bit of practice will have to do the trick then. I think that once you are used to it you will love the spacious eye relief. Happy observing!

Do you sit or stand while observing? If you sit it is easier to keep your head still. I have a hight adjustable stool. The seat screws up and down, like a drum stool. It cost only €20 and made a world of difference.

Kidney beaning or blackout? The first is rare in modern designs.

There's also vignetting.

When the eye relief is very big, eye placement becomes a problem. There's no feedback from your eye socket touching the eye cup. As a result your head will float about over the eyepiece. This causes vignetting and blackout.A higher eye cup will help you bring your brow or cheek  in contact with the eyepiece . Sometimes it is just a matter of getting used to an eyepiece.

Vignetting makes you lose the edge of the field. With blackout it is as if a curtain is drawn over the view and the whole view disapperas.

Kidney beaning is very specific. A bean-shaped part between the edge and the centre of the view disappears. See the bean on the Moon above. It is caused by spherical aberration of the exit pupil (which does not effect sharpness, btw).

4 minutes ago, Stub Mandrel said:

Six minutes of video? The live commentary said 'at X seconds the sparklers will ignite to clear away leaked hydrogen'.

Too long?

The purpose of the video is not to show the fireball, but to explain it. It tells you why and how this rocket is different than many others. That takes 6 minutes.

Here's a video by Scott Manley that explains the fireball right before takeoff. It's meant to be that way.

It just jumped off the launch pad!

This might give you some clues, but there will be differences between this telescope and yours.

Yes, everything has to go back exactly the way it was. I saw a youtube video on servicing an SCT and there were thin cork shims, for instance, that had to go back in exactly the same spots.

I looked again at the pictures. I think that on the inside of the secondary there are still traces of the glue that came loose.

You'll need to find the right glue too. Look for an expert website. There's one for Celestron SE telescopes so I imagine there will be one or two for the ETX. Also check on Cloudy Nights.

Yes, the baffle of the secondary. The secondary itself is the silvered spot. There might be a base for the baffle still glued to the corrector plate, and the baffle might have unscrewed itself from that, or the baffle was glued directly to the corrector plate. 

This is a tricky problem! If you open the telescope you could in principle glue the baffle back in place, or screw it back on, but then you'd have to reassemble the telescope well enough so that it can still be collimated. That's the tricky bit. 

You need to find a dedicated Meade ETX website, maybe some youtube videos of people servicing their ETX.

Hi Mark, thank you for a most interesting post!

I downloaded the excellent .tif and tried the method you suggest in Photoshop. My result was pretty close to what you achieved - almost as good. It was quite a bit of work, though, so I thought I'd suggest a method for when you want a quick result: use Topaz Adjust.

Here you see a screenshot of the 'raw' tif opened in Adjust with some adaptive exposure and adaptive saturation applied. The small window is the original, the large one is the preview of the result. Just move the sliders around till you're happy. It takes a minute or two.

Topaz Adjust runs in any program that can handle photoshop filters, like the freeware IrfanView for instance.

Congratulations, a field of 200 m at 1 km is something like 11.4°. That is wonderfully wide!

Low power binoculars have interesting properties for  amateur astronomers. Their bright and wide fields make them excellent for rich field observing. And of course, low power means you won't need a tripod to get shake free views.

I have experience with 4x22, 17° field binoculars. Their exit pupil is 5.5 mm (22 divided by 4), which makes them bright enough to make targets like the Orion Nebula or the Andromeda galaxy stand out well. They offer impressive views of the constellations, and the the Milky Way is remarkable in them.

Low power ensures that individual eyepiece focussing is hardly an inconvenience. Lower magnification comes with a greater the depth of field, which actually is  a great benefits for nature observers. Unless your target is really nearby, it will look sharp, like everything else all the way to the horizon. Especially young children, whose eyes can accommodate over many diopters, will rarely need to adjust the focus of a low power pair of binoculars.

My 4x22 Kasai seem to have the same eyepieces as yours. Mine are from an inexpensive line made by Kunming United Optics. I guess your 6x30s come from the same factory.

Enjoy them!

What a handsome piece of gear!

27 minutes ago, happy-kat said:

The mirror coating a word of caution is extremely THIN just breathing on it marks it

This is an interesting phase. I wonder: before you reassemble everything you probably want to blow any dust out. Do you suppose using a bulb blower (like the Giotto Rocket Blower) would be safe for the mirror coatings?

Good luck with the rest of the project and thank you for documenting it so well.

Altogether it is an amazing idea and the concept is proven.

Congratulations!

6 minutes ago, happy-kat said:

That's it payment sent and now the waiting starts. It will be in ABS white translucent 200 microns. Quite excited to see the fruition of this project and how it might workout on this mini Mak. It's a hobbyiest printing it through the hub but with great feedback so I hope all wiill be well.

I do hope it works as planned!

Just now, michaelmorris said:

Where do these great graphics come from?

Hi, I made them in Geogebra. It's a freeware tool used in maths education.

32 mm Plössls have a long eye relief and may take some time to get used to, especially when the exit pupil is close in size to the user's pupil. 

Kidney beaning, however, should not happen with TeleVue or any other Plössls as they tend to have well behaved exit pupils. (Kidney beaning comes from spherical aberration of the exit pupil. Until the first generation Naglers this was a rare phenomenon.) Could it be blackouts that you're seeing?

I have a 32mm GSO Plössl. Had some blackouts at first, but got used to the eyepiece, and the blackouts disappeared. I think you too may get used to your 32mm Plössl.

Here is how blackouts occur.

With long eye relief, steady eye placement becomes difficult. The movements of the eye cause blackouts in which the image disappears from one side to the other. When the image is partially illuminated, it is as if a curtain is drawn over one side of the image

Here is how kidney beans occur

With kidney beaning a kidney shaped shadow forms between the centre and the edge of the field, while both centre and edge remain fully illuminated. Kidney beans arise from even subtle eye movements, especially with larger exit pupils. When the eye movements get larger, blackouts will also occur.

Below, a kidney bean occurs as one of the red rays can not enter the eye, yet the more extreme off-centre green ray still can. (The brain inverts what's on the retina, hence the shadow appears below the centre.)

Fortunately, spherical aberration of the exit pupil is, to a large extent, a thing of the past.

Wow, John, that is a beautiful telescope!