1316 replies to this topic

[desertlens]

One trick pony. It looks a bit busy but is simple, intuitive and joyful in practice. The Takahashi turret is a remarkably effective tool in either of the FOA-60s.

 

Edited by desertlens, 19 March 2025 - 06:40 PM.

[VA3DSO]

Inspired by Jon, I have my 70mm f/7.1 on the AZ4 mount ready in the backyard waiting for darkness to set in.

 

It is "over-mount Wednesday", right???

 

For those curious, I have an Orion prism diagonal in it.

 

 

Clear skies!
 

Rick

Edited by Rick-T137, 19 March 2025 - 06:53 PM.

[Erik Bakker]

 

Last night's story....

 

Erik and others have been observing with their small refractors through double pane glass.  Due to the age of our home and the climate, we only have one window with double pane glass and it's access to the sky is blocked by shrubbery.  Because of this, I was forced to go outside to the backyard to do some observing..   

 

Venus is about to pass between the Earth and the Sun and I wanted to get one last glimpse.  Last night it was about 10 degrees from the sun and about 7.6 degrees elevation at sunset.  I chose to use my new to me AT-70 ED and used my normal technique to find Venus in the twilight, a digital level held to the tube by a rubber band.  I positioned the scope so the sun was behind a tall house and began searching when Venus was at about 14 degrees elevation.. The sky was bright..,. 

 

I was about ready to give up but with Venus at 8.4 degrees elevation, I finally spotted her,.  1.7% illuminated, pretty thin.  I cranked up the magnification to about 130x and watched her sink into the sunset.  At about 5 degrees, a neighbors roof put an end to the evening.

 

I messed around with my 10 inch Dob for a couple of hours and then decided it was time to pack up.  This is where things got interesting.  In another thread, someone had mentioned the view of Algieba in a 4 inch achromat..  It's a pretty wide double, 4.7" and unequal by about 1.3 magnitudes, that's a factor of over 3.

 

Tony Spina had given me an older made in Japan 60mm F/5 Meade achromat and I thought I would give it a try... I dug up a 1.25 inch diagonal, it happened to be a prism type star diagonal and with the 22 mm Panoptic, I easily found Albieba... Cranking up the magnification with the 3.5 mm Nagler (86x), things did not look good. There was a strong flare, something I had seen before with this scope. I could make the split but it was not pretty.

 

I only have one decent quality 1.25 inch diagonal, an older Vixen/TeleVue unit I have with the Ranger.. I went inside and dug it out...  I found Albieba again and cranked up the magnification to 86x.. 

 

WOW  The flare was gone leaving just a beautiful pair, clean and bright.  At 60x, it was a clean split, at 120x it was a clean split.. What I thought was a substandard scope turned out to be just a case of the wrong diagonal..

 

I have used prism star diagonals in ST-80s without too much difficulty in the past, maybe this is just a poor quality prism diagonal..  I am pretty excited.. That little Meade turned out to be quite good and I just need to get a decent mirror diagonal for it.

 

 

 

Jon

 

An image I took last night that illustrates thge scene you observed. I used an 8x42 EDG to view this beutiful scene with the big thin crescent of Venus easily visible in these binoculars.

 

The crescent of Venus can even be seen to the right of the centre a few degrees above the horizon at 100% on the original image taken with a Nikon Df and Nikkor AF-S 85mm @ f/5.6. The colors were this intense for 5 minutes or so.

 

[VA3DSO]

Inspired by Jon, I have my 70mm f/7.1 on the AZ4 mount ready in the backyard waiting for darkness to set in.

 

It is "over-mount Wednesday", right???

 

For those curious, I have an Orion prism diagonal in it.

 

Clear skies!
 

Rick

Well nuts!

 

That didn't go as expected.

 

Using my 70mm f/7.1 Sky-Watcher Mercury tonight. The seeing was pretty poor. Looking at Mars which is near Zenith at 100x, I could maybe make out the polar cap, but nothing else. More disturbing was that the body of Mars appeared to smear out about a full diameter to the "left" of the planet. I then booted over to Regulus and saw the same thing (the smear). Just outside of focus, the star image was triangular - can't recall if it did it on both sides of focus and changed 90 degrees (indicating astigmatism) but at the very least it was showing perhaps pinched optics. I tried different eyepieces and diagonals - all with the same result.

 

I brought out my Celestron Omni AZ 102 to compare with, and it showed an Airy disk when viewing Regulus, with the diffraction ring broken around it and dancing like crazy. In moments of steady seeing, it would firm up - but regardless, it was showing a MUCH better star image. Inside and outside of focus were round and identical. I double checked my eyepieces and diagonals with the Omni and they all worked fine.

 

Brought the 70mm inside the house and checked to see if a screw or bolt was getting into the light cone and causing the streak - but it all looked fine. I then took the lens cell off and took the doublet out of it - and I discovered the issue. At first I thought it was moisture between the crown and flint lens, but as I tried like Hercules to pry them apart it dawned on me - it's a cemented doublet and the cement is failing! There's a big spot off to one side about the size of a quarter that looks like a water spot or bubble between the lenses. I'm pretty sure it's causing the smear, and likely if the cement is failing, the lenses are no longer properly aligned with each other causing other visual aberrations.

 

I'm actually kind of happy in a way, as I'd be disappointed to take this little scope somewhere tropical only to get some bad views. The Omni was SOOOOOO much better even though the seeing was poor.

 

What this means is I get to go shopping for a new travel scope! YAY! I feel bad for the little 70mm Mercury, but I only paid $75 for it about 10 years ago, so it really owes me nothing. I can't complain.

 

The joy of small refractors with continue for me...

 

Clear skies!

 

Rick

Edited by Rick-T137, 19 March 2025 - 09:17 PM.

[John R.]

That is a sad story Rick. 
I’m a little bit surprised the SW 70mm was cemented and not air spaced. My understanding is having the pair spaced gives the optical designer another tool for color correction, besides alleviate any stress between the crown and flint elements due to different thermal responses. 
Not sure if the cement can be removed by some solvent and the elements separated. Then perhaps you could clean them up and use foil tabs to air space them. 
 

Might be worth a try. 

[VA3DSO]

That is a sad story Rick. 
I’m a little bit surprised the SW 70mm was cemented and not air spaced. My understanding is having the pair spaced gives the optical designer another tool for color correction, besides alleviate any stress between the crown and flint elements due to different thermal responses. 
Not sure if the cement can be removed by some solvent and the elements separated. Then perhaps you could clean them up and use foil tabs to air space them. 
 

Might be worth a try. 

Hi John,

 

I am very glad you encouraged me to investigate further!

 

I was wrong - the lenses aren't cemented... just stuck together really good. I used some plastic tools for disassembling laptops and managed to gently pry them apart. I will try to clean up what looks to be a water stain on the bigger lens.

 

I took the entire telescope apart and I found what might be another issue. In the focuser, there are two skid plates / shims that push the draw tube upwards against the adjustment screws. For whatever reason these plates are white. From the front of the scope, I can clearly see them. I wonder if when viewing a bright object (ie: Mars, Regulus) that these plates are reflecting light and causing some issues...? Otherwise there are no screws or other items getting into the light path. The tube even has a couple of nice baffles!

 

What does everyone think? Should I just paint these flat black? Or will that make the focuser harder to use?

 

 

I really appreciate any input on this. I'm hoping I can bring my little Sky-Watcher back into action!

 

Thanks!

Rick

[Polyphemos]

 

Hi John,

 

I am very glad you encouraged me to investigate further!

 

I was wrong - the lenses aren't cemented... just stuck together really good. I used some plastic tools for disassembling laptops and managed to gently pry them apart. I will try to clean up what looks to be a water stain on the bigger lens.

 

I took the entire telescope apart and I found what might be another issue. In the focuser, there are two skid plates / shims that push the draw tube upwards against the adjustment screws. For whatever reason these plates are white. From the front of the scope, I can clearly see them. I wonder if when viewing a bright object (ie: Mars, Regulus) that these plates are reflecting light and causing some issues...? Otherwise there are no screws or other items getting into the light path. The tube even has a couple of nice baffles!

 

What does everyone think? Should I just paint these flat black? Or will that make the focuser harder to use?

 

 

 

I really appreciate any input on this. I'm hoping I can bring my little Sky-Watcher back into action!

 

Thanks!

Rick

 

Do not paint the focuser sliders. You’ll likely ruin your focuser’s action and do nothing to improve light control. At normal focus those sliders are mostly if not entirely covered by the draw tube anyway.

[maniack]

I took the entire telescope apart and I found what might be another issue. In the focuser, there are two skid plates / shims that push the draw tube upwards against the adjustment screws. For whatever reason these plates are white. From the front of the scope, I can clearly see them. I wonder if when viewing a bright object (ie: Mars, Regulus) that these plates are reflecting light and causing some issues...? Otherwise there are no screws or other items getting into the light path. The tube even has a couple of nice baffles!

 

What does everyone think? Should I just paint these flat black? Or will that make the focuser harder to use?

These strips allow the focuser tube to move more smoothly. They are not in the light path so the color doesn't make a difference. Painting them will ruin their functionality though.

 

If you do want smoother focuser movement you can replace them with teflon strips.

[VA3DSO]

Thanks for the advice guys! I am leaving those strips alone.

 

I cleaned up the lenses and reassembled the scope. Unfortunately, the triangle shaped out of focus image remains - along with the smear line. I can only conclude this is coming from the objective lens itself. I don't recall seeing it before, but may I wasn't paying close enough attention until I got my Omni AZ 102 which has beautiful Airy disks?

 

The last thing I'm thinking about is the little black spacers between the lens elements. Could they be causing issues?

 

[John R.]

I forgot to add an important bit of information Rick. 
On many achromat pairs the rotation orientation of the elements, relative to each other, is marked in some way on the edge of each element. It can be important to retain this orientation when reassembling the elements. 
If you don’t see any marks on the edge of the elements, it is useful to put a mark across the edges to show how they go back together, I use a permanent marker to do that. 
 

Hope I’m not too late with this advice. 

[John R.]

We posted together. The next thing to try, to see if it is the objective, is to remove the lens group, and rotate them 180 degrees (mark the edges with a marker to make sure) and reinstall them. If the smear is still on the same side, and did not rotate, then it is unlikely the objective is the problem.

If however the smear rotates also, then yes, most likely the objective is the source of the aberrations. 
 

Edit; Another thing to check. With the lenses removed carefully check the edges for any orientation marks. It may only be a faint scratch in the element edge, or a ‘>’ shape across both elements that lines up only in one position. If you do find a mark then that is the orientation the elements must be reassembled with. 

Edited by John R., 20 March 2025 - 12:20 PM.

[Polyphemos]

Thanks for the advice guys! I am leaving those strips alone.

 

I cleaned up the lenses and reassembled the scope. Unfortunately, the triangle shaped out of focus image remains - along with the smear line. I can only conclude this is coming from the objective lens itself. I don't recall seeing it before, but may I wasn't paying close enough attention until I got my Omni AZ 102 which has beautiful Airy disks?

 

The last thing I'm thinking about is the little black spacers between the lens elements. Could they be causing issues?

 

Are you perhaps over tightening the lens cell?

 

Those black spacers provide the separation between the elements required for proper correction and unless damaged should be left alone. If you over tighten the lens cell retaining ring the elements will be slightly distorted by those spacers and may cause a triangular shaped image. Correct tightening of the Synta type achromatic doublet lens cell retaining ring is when the elements “rattle” just a tiny bit when the assemble lens cell is shaken. You want to barely hear a rattle when you hold the cell up to your ear, but no rattle probably means you’ve over tightened the retaining ring.

[Oldfracguy]

Thanks for the advice guys! I am leaving those strips alone.

 

I cleaned up the lenses and reassembled the scope. Unfortunately, the triangle shaped out of focus image remains - along with the smear line. I can only conclude this is coming from the objective lens itself. I don't recall seeing it before, but may I wasn't paying close enough attention until I got my Omni AZ 102 which has beautiful Airy disks?

 

The last thing I'm thinking about is the little black spacers between the lens elements. Could they be causing issues?

 

Yes, especially if they are not all exactly the same thickness.  Having spacer rings of uneven thinkness will cause your star test pattern to be distorted.  However, from the severity of that smear you are seeing, the spacer rings might not be the source of the problem.

[VA3DSO]

Okay, this will likely be my last post on this - as I am totally hijacking this thread and that's not my intention!

 

The lens cell was too tight - I loosened it off, and the triangle visibly was less pronounced - but still there. I backed the screws and the retaining ring such that things would rattle - but the view didn't improve any further.

 

The spacers are visible in the out of focus star image, and just before focus, the triangle sides are exactly where the spacers appear! I've inspected the objective closer and front facing element has a lot of little scratches on it. I wonder if I forgot to put the end cap on it one time and it was rattling around banging into things?

 

Anyway, what I decided to do was order another lens - same specs (70mm effective, 72mm actual, 500mm focal length) from China and we'll give it a shot. It was only $20 with free shipping, so I really have nothing to lose at this point.

 

Meanwhile, I've started saving up for a nice AT70ED to replace this with. I really appreciate all the advice!

 

Thank you!

 

Rick

[Polyphemos]

It can be a lot of fun playing with, trouble shooting, and improving inexpensive achro scopes. Kudos for diving in there.

[John R.]

Okay, this will likely be my last post on this - as I am totally hijacking this thread and that's not my intention!

…..big break……

 

Meanwhile, I've started saving up for a nice AT70ED to replace this with. I really appreciate all the advice!

 

Thank you!

 

Rick

Didn’t think you were hijacking the thread, just an aspect of living with a small refractor, 

sometimes things don’t go to plan. 
 

Good call on the AT70ED, it’s becoming one of my favorite small refractors, and even the regular price is a bargain. 
It also looks like you already have a mount it will be happy on. 

[Jon Isaacs]

Thanks for sharing Jon. Always love hearing how experienced observers use inexpensive equipment to still get good results. 
I was curious about the diagonal story however. In one photo of your equipment I saw a Svbony sv188p dielectric 1.25 diagonal. I would not think it would come up to TeleVue standard, but I have two and they seem to be ok, although truth is I have no ‘gold standard’ diagonals to compare them with. 
The first 188P I bought did have a problem, the interior was not dead black and was unusable until I fixed it. The second came properly blacked out inside. 
Just wondering what your thoughts are regarding sub $100 diagonals. 

 

John:

 

The Svbony 188P dielectric diagonal arrived yesterday and I had a chance to try it out.  I checked the collimation with my Howie Glatter 1.25 inch collimator in the AT-70ED and it seemed spot on.  The seeing wasn't the greatest but I compared it to the 2 inch TV Everbrite splitting Zeta Orionis, 2.4", mags 1.9-3.7.  Both provided very similar, clean splits at 131x and 168x.   

 

I think I got a good one.

 

Jon

[maniack]

John:

 

The Svbony 188P dielectric diagonal arrived yesterday and I had a chance to try it out.  I checked the collimation with my Howie Glatter 1.25 inch collimator in the AT-70ED and it seemed spot on.  The seeing wasn't the greatest but I compared it to the 2 inch TV Everbrite splitting Zeta Orionis, 2.4", mags 1.9-3.7.  Both provided very similar, clean splits at 131x and 168x.   

 

I think I got a good one.

 

Jon

Maybe there was a bad batch at one point in time. I double checked my 2" unit as well as one of my 1.25" units and the mirrors look great. The views are also great in them, with no difference detected between the Svbony 2" and a WO dielectric 2".

[JimP]

You guys are a great help! I appreciate your thoughts very much. When I started observing way back in the 1960s aperture was what it was all about. The need to see more detail on the moon and planets required more and more aperture as did deep sky observations . Over the next 50–60 years, I moved up in aperture.

Then, I was diagnosed with cancer of the throat and underwent radiation and chemotherapy. When I completed that I had lost from about 150 pounds to 130 pounds and was very weak. The only thing I could do to continue observing was to move down to smaller aperture scopes. At the time, I could barely handle my 6 inch AP scope so I moved down to a 5 inch which was OK, but still seemed a little heavy. I finally moved down to a variety of 4 inch scopes, which I like very much. My latest, an NP 101 is a wonderful scope! I love it!
So there I am, minding my own business, and just looking at what's out there for sale and much to my amazement. I came across an 80 mm aperture refractor just like one I owned decades ago. I fought the urge to get it because I kept telling myself 80 mm aperture was just too small. But now, after reading your thoughts regarding small apertures, even smaller than 80 mm, maybe I am wrong. Maybe I should reconsider that 80 mm scope.

Thanks for your thoughts and comments

Jim Phillips.

[Jon Isaacs]

 

 

But now, after reading your thoughts regarding small apertures, even smaller than 80 mm, maybe I am wrong. Maybe I should reconsider that 80 mm scope.

Thanks for your thoughts and comments

Jim Phillips.

 

Jim:

 

I try to observe as often as possible for as long as possible. My observing in 2024 was limited by caregiving for both sister and my wife. I still managed 99 nights, down from my typical 170-180 nights. And they were shorter sessions.

 

One key to a observing as much as possible is having a variety of scopes of a large range of apertures. It's not every clear night that I have the energy or the opportunity to use a big dob.

 

There are nights when a 70 mm or 80mm are the best match for the moment, the best match for my energy level. 

 

There's always something to see, it doesn't have to be something new, something beautiful is more than enough.

 

If any of this rings true, I say get that 80 mm. You'll enjoy it.

 

Jon

[revans]

You guys are a great help! I appreciate your thoughts very much. When I started observing way back in the 1960s aperture was what it was all about. The need to see more detail on the moon and planets required more and more aperture as did deep sky observations . Over the next 50–60 years, I moved up in aperture.

Then, I was diagnosed with cancer of the throat and underwent radiation and chemotherapy. When I completed that I had lost from about 150 pounds to 130 pounds and was very weak. The only thing I could do to continue observing was to move down to smaller aperture scopes. At the time, I could barely handle my 6 inch AP scope so I moved down to a 5 inch which was OK, but still seemed a little heavy. I finally moved down to a variety of 4 inch scopes, which I like very much. My latest, an NP 101 is a wonderful scope! I love it!
So there I am, minding my own business, and just looking at what's out there for sale and much to my amazement. I came across an 80 mm aperture refractor just like one I owned decades ago. I fought the urge to get it because I kept telling myself 80 mm aperture was just too small. But now, after reading your thoughts regarding small apertures, even smaller than 80 mm, maybe I am wrong. Maybe I should reconsider that 80 mm scope.

Thanks for your thoughts and comments

Jim Phillips.

There is always the Questar 3.5" to consider as well.  The optics are beyond belief.  I could see M1 (from a bright suburban sky with a high bright moon as well) in my Q3.5 when it was invisible in my 127mm binocular telescope.  It just has razor sharp optics and tremendous contrast against the sky background.

 

Rick

[Dave Skywatcher]

You guys are a great help! I appreciate your thoughts very much. When I started observing way back in the 1960s aperture was what it was all about. The need to see more detail on the moon and planets required more and more aperture as did deep sky observations . Over the next 50–60 years, I moved up in aperture.

Then, I was diagnosed with cancer of the throat and underwent radiation and chemotherapy. When I completed that I had lost from about 150 pounds to 130 pounds and was very weak. The only thing I could do to continue observing was to move down to smaller aperture scopes. At the time, I could barely handle my 6 inch AP scope so I moved down to a 5 inch which was OK, but still seemed a little heavy. I finally moved down to a variety of 4 inch scopes, which I like very much. My latest, an NP 101 is a wonderful scope! I love it!
So there I am, minding my own business, and just looking at what's out there for sale and much to my amazement. I came across an 80 mm aperture refractor just like one I owned decades ago. I fought the urge to get it because I kept telling myself 80 mm aperture was just too small. But now, after reading your thoughts regarding small apertures, even smaller than 80 mm, maybe I am wrong. Maybe I should reconsider that 80 mm scope.

Thanks for your thoughts and comments

Jim Phillips.

Jim, I'm with you here. I've got an 8" SCT which I love, but it's a hassle sometimes to set it up on the GoTo mount; I have it on a heavy-duty AltAz mount and use that most of the time. But because of light pollution around my house, I sometimes take one of my smaller scopes and move it around my house, or take it to a local park after sunset. I'm enjoying the 90mm refractor when I want to see a wide view, and a 127mm SCT for planetary/lunar. I'm debating whether I should get a 102mm ED refractor to be able to see better views of galaxies or nebula, or maybe go smaller with a 72mm or 80mm ED telescope. Do I really "NEED" another telescope?? Not exactly, but I'd like to eventually get into astrophotography and I know I'll want an ED doublet or triplet (if I can ever afford one) to get the best images.  Clear Skies!

[kmparsons]

Taking advantage of a cool front (probably one of our last of the season in SE Texas) I took out my little AT60ED last night to see what I could see. It is remarkable what you can see with a really small but quality refractor. Jupiter has been high overhead and not really in a position to view comfortably, but I did get a good look. The TV 3-6mm zoom compensates for the very short focal length and provided a razor-sharp view of the planet and three moons. With the 15mm Delite looking at Orion's sword, the entire asterism was perfectly framed. M41, the "Little Beehive Cluster" just below Sirius was visible but small in the Delite but filled the frame at 6mm with the zoom. The AT60ED is a mighty mite and a terrific travel scope. 

[Polyphemos]

….

Anyway, what I decided to do was order another lens - same specs (70mm effective, 72mm actual, 500mm focal length) from China and we'll give it a shot. It was only $20 with free shipping, so I really have nothing to lose at this point.

….

 

Rick

I’ve often wondered about refractor objectives offered for sale on AliExpress, and whether they were usable or just a curiosity. It would be great if you could post the results of your objective swap.

[VA3DSO]

I’ve often wondered about refractor objectives offered for sale on AliExpress, and whether they were usable or just a curiosity. It would be great if you could post the results of your objective swap.

Indeed! I am curious as well.

 

I am going to try to do a comparison with an artificial star with the original objective vs the new one. I have a cell phone eyepiece adapter, so maybe I can even gather some actual photographic evidence.

 

Even if the new lens isn't that great, it's worth the money just to try it.

 

In the meantime, I have a trip coming up next week to the mountains in Alberta and the lens won't be here in time. So I dusted off my modified Meade 50mm finder and I'll take that with me instead. It's like 1/2 of a binocular but I can swap out the eyepieces!