Louis D

Check out this CN'ers solution.  You'll want 1/4" or 6mm wide pinstripe tape.

2 hours ago, NGC 1502 said:

 

Indeed, the Radian colour cast issue is something I could never detect myself.  The other issue often raised with Radians was blackouts.  But all the long eye relief eyepieces I’ve ever tried could be made to blackout if my eye was too close to the eyelens.  If the Radian eyeguard is correctly deployed, zero problem, just a sharp comfortable view......

Ed.

It was daytime blackouts due to massive SAEP.  I compared them side-by-side with Pentax XLs in an astro shop when they first came out in 1998.  I could not find any position to avoid kidney-beaning with the Radians, but no issues at all for the XLs.  I bought the 14mm and 5.2mm XLs and have never regretted that decision.  I gave Al another chance with the Delos line 13 years later, and with Paul D.'s help, he got long eye relief right that time, so I own a 10mm version now.

1 hour ago, Sini said:

I have got a lot of useful info from here, so thanks from that! Of course, you cannot get everything to be perfect right at the start, and I am also keen on practicing and learning. I know there are also a lot of personal preferences depending on what is important and prioritized (the debate between 8'' SCT or Dob seems to be around 50-50). I measured our car trunk, and it is around 110cm wide. In principle, the 8'' dob could fit there if I place it somehow diagonally with other end of the OTA higher than the other. So needs proper support if it is safe to transport OTA that way anyway. However, it is not a problem to put it to the backseat, if necessary. 

I decided to go to the 8'' dobson. It seems to be much cheaper to the 8'' SCT + eq mount, considering I also need to by eyepieces etc. at some point. And what I have understood, it should be relatively easy to use "general" telescope. During assembly, it is not a problem here to leave stuff alone, so that won't be a problem. Wet grass etc. wont be a problem yet, as I planned to bring the telescope to my parents' home, where they have huge terrace and also a big dock by the lake (not floating one, but like, solid?) which I think are super practical places to start observing. Sure, it is probably not the best grab-and-go telescope due to its size, but at the current state of my life that is not something I can do (unfortunately) anyway (having kids and all). 

Dobs are great with kids because they are practically impervious to damage in use or transport.  You may need a step stool for shorter kids to get them up to the level of the eyepiece for viewing objects near zenith.  Pick up a collimation cap at the very least to check primary mirror alignment each time it is setup.  It also makes a nice dust plug during storage while allowing for a tiny amount of fresh air to reach the inside of the tube (assuming the main tube's ends are capped).

No, stacking narrowband filter won't work as others above have pointed out.  However, OPT is selling Radian Triad tri and quad band filters that simultaneously transmit H-alpha, H-Beta, and Oxygen III or H-alpha, H-beta, OIII, and SII respectively.  They would achieve what you want to do.  Keep in mind that you would need to use a color camera to retain color data.  A monochrome camera would show all bands as various shades of gray in a single image that would be immune to post processing into a color image.

While using my TSFLAT2 field flattener visually in my AT72ED, I do not see any evidence of coma in the refractor's image at the edge.  However, with it removed, the defocused stars at the edge due to the severe field curvature of such a short focal length refractor masquerade as coma-aberrated.  Stars at the edge need to be refocused to see if they come to a better focus before declaring coma in a refractor.  With true coma, refocusing does not improve the tightness of the image.

As for high quality eyepieces, I would tend toward anything made by Televue, Pentax, Nikon, Zeiss, Takahashi, and Vixen.

For plain barlow lenses, the Televue 2x is hard to beat for the money.  If you want to splash out more money for a telecentric model, get a Televue Powermate.  Some rather high end barlows include the Carl Zeiss 2x Abbe Barlow and the Astro-Physics 2" Advanced Convertible Barlow (BARADV).

35 minutes ago, ollypenrice said:

Shown on screen at full size (one camera pixel equals one screen pixel) the smaller and larger chip of the same pixel size will give an identical object size.

Yes, but the term 'crop factor' originated for terrestrial cameras where it's the entire frame that is of concern, not just the object being imaged.  The larger chip will show more of the image circle while the smaller chip will show less of it.  Crop factor has been a useful term for nearly 20 years for consumers (especially older ones raised on 35mm photography) to understand what is going on with smaller than 'full size/35mm' sensors.  Truly, the image circle is being 'cropped' relative to a 'full size/35mm' sensor.  Once photographers got used to that, jumping to image scale was more intuitive as they started working with images on their computers.

I bought sets of the HD-60 and Paradigms (BST Starguiders) and compared them for field of view, edge correction, and eye relief and compiled my results in this thread.  Under the stars, they're pretty equivalent as far as contrast and stray light control.  At the shorter focal lengths, there isn't much to distinguish between them and the more premium eyepiece lines other than field of view and eye relief.  It's in the longer focal lengths (12mm and up) where the edge of field really starts to fall apart compared to premium lines.  In the center 50%, they're pretty equivalent to the premium offerings even in the longer focal lengths.

Just now, Cornelius Varley said:

Both terms are inaccurate. Nothing is "cropped" or "magnified". The correct term in astrophotography is image scale. 

But the term originated in terrestrial camera photography and may have been inappropriately applied to astrophotography.  Do you have a problem with the term when used for consumer DSLRs?  Would the term 'image scale' cause less confusion among the unwashed masses when shopping for camera bodies and lenses?  Is it more intuitive?

7 minutes ago, ollypenrice said:

The term 'crop factor' is an irritating one since it leads precisely to the confusion under discussion! In implying a relationship between the size of the sensor and the focal length it leads people astray.

Would you prefer the earlier term 'magnificaton factor'?  That was the going term about 20 years ago when less than 'full size/35mm film' digital sensors started showing up in camera bodies to help people understand why their traditional lens focal lengths weren't providing the image scales they were accustomed to with the new camera bodies.  Enough readers of camera magazines and nascent camera websites argued for the more accurate term 'crop factor' since the image circle was being cropped relative to a traditional 'full size' sensor and there was no optical magnification going on at all.  Depth of field and perspective remained exactly the same as before, just 'cropped' in camera.  Amazingly, there was a wholesale shift away from 'magnification factor' to 'crop factor' within a year or two across the industry.  If you're good with 'magnification factor', feel free to return to it.  As for me, I'll stick with crop factor as being more accurate.

On 22/09/2019 at 03:56, garryblueboy said:

A move around in the cases since last time I posted on this thread feel like I have a nice balance of eyepieces now we’ll maybe a couple more wouldn’t hurt 😂🤣 

 

 

How do your Televue eyepieces feel about the two Myriad eyepieces?  Do they play nice with them, or do they gang up together to bully them for not having green lettering? 😉

7 hours ago, wesdon1 said:

I ended up buying second hand and saved some cash in the process!. I bought a Televue 2X barlow, which the quality of which is simply astounding!??

I have the 1.25" TV 2x, and it is quite good as you say.  Another oldie but goody is the Meade 140 2x barlow.  It's a three element Japanese made design from the late 90s that yields about 2.4x compared to the TV's 2.1x (for shoulder focusing eyepieces).  Back-to-back comparisons on the Trapezium last winter showed it to be just about identical in performance to my TV barlow.

They usually go for $40 to $45 used here in the US.  A big plus to them is that the optical nosepiece is 1.25" filter threaded, so it can be threaded onto the front of eyepieces for about 1.6x or as a binoviewer OCS/GPC at about 3.0x.  The TV barlow nosepiece uses a nonstandard 1.25" thread, so it can't be used for these purposes.

The only older barlow I own that outperforms the TV is the Japanese made 1.25" Orion Deluxe Fully Baffled 2x barlow.  However, it's about 6 inches long, so it's uses are limited by that.  The difference is subtle on scatter, but it is there.  All else is about the same including the 2.1x magnification.  The unit is a single piece, so the nosepiece cannot be removed.  These come up very rarely second hand, but they're usually also about $35 to $45 here in the US because few people know much about them.

12 hours ago, Rob Sellent said:

It'll be interesting to hear about your own experience with exit pupil and how it compares with the little table above

I usually struggle monoviewing with exit pupils below 0.7mm due to floaters in my observing eye.  Binoviewers can help get me down to 0.5mm, but beyond that, it's pretty annoying trying to look through the myriad floaters.

Yes, that's the secondary mirror's shadow.  You might try other slightly shorter focal length eyepieces as well to see if they react better to the moon/telescope/eyepiece/camera combination.

As far as technique goes for afocal photography, first, focus with your glasses you use for distance vision.  That way, the image is focused for infinity focus which makes life easier for the phone's camera.  Second, work the camera in toward the virtual image until you just see the field stop pop into view.  Make sure your camera is centered and level relative to the eyepiece and focused on the image (you may need to tap on the edge of the moon on the phone's screen where contrast is greatest to get best focus), and then snap a series of photos as you think you've achieved best alignment and focus.  Putting your thumb and forefinger between the eyepiece and phone can help steady and level the interface.  Try this all in the daytime focused on a distant object to get the hang of it first.

3 hours ago, bingevader said:

I thought this was going to be about Jaffa cakes, or at least looking at them through an expensive EP.

Had to look up Jaffa cakes.  A bit disappointed because I thought they sounded vaguely Stargate-esque:

These guys are known as the Jaffa (pronounced jah'FAH).  I was thinking, "Cool, Stargate inspired food!".  But no, not even close.

1 hour ago, johninderby said:

They aren’t actually Tak eyepieces but are bought in from an outside supplier  Daiichi Optics in Japan. Apparently quite sharp on axis but not so good off axis. Think they are really intended to go with the Starbase achro which again is made for Tak as a “beginners” scope but the Tak name isn’t used on the scope.

The same eyepices are made for other brands by Daiichi. 

Kind of defeats the purpose of an ortho if it isn't well corrected across its narrow field.  Might as well package Kellners or RKEs.  Seems like a decent Chinese made Plossl might be a better option unless those orthos have exceptional polish and stray light control.

Alt-Az tends to be more stable on consumer grade mounts.  Many wedges are not sturdy enough and tend to add another place for vibration to emanate from during visual observations leading to longer settling times after focusing or someone bumping the eyepiece.

From what I understand, these Chinese eyepiece factories will crank up production on whatever you want and label it however your want so long as you meet their prepaid minimum order standard which seems to be somewhere between 100 and 300 units.  So, until some vendor like FLO, TS, or Astronomics decides to place an order, there won't be any more produced.

It boggles the mind that the 40mm Aero ED/Sky Rover is sold out everywhere and the Chinese factory isn't churning out any new ones.  Clearly there's a demand for it worldwide.

On 18/09/2019 at 10:54, heliumstar said:

This one is going to be hard.

Maybe something like this : http://www.desertskyastro.com/DSV-2.html

It's 4kg with balancing system but much less without it. It has slow-mo controls. Now the issue becomes the tripod. It gets expensive with Gitzo. I guess SS 1.75" could potentially handle it but not sure about the weight. Might be slightly above than what you are looking for all together. 

I use a DSV-2B mount for my grab-and-go mount.  However, Raul is very difficult to contact and has a very long back order list.  I ended up locating a used mount.  It's a nice mount and easily handles my AT72ED and 127mm Mak side-by-side with heavy two inch eyepieces as seen below.  However, on a sturdy tripod, it's still a heavy rig.  A carbon-fiber mount might be an option if money is no object.

I tend to prefer my Meade 5000 SWA 40mm (same as the Maxvision) to my 35mm OVL Aero ED and 30mm ES-82 for scanning wide swaths of the sky.  I also really like my Baader Scopos Extreme 35mm due to it being super sharp in the center 60% of the field (better than any of my other wide fields).  The downside is it only has a 39mm field stop compared to the 46mm Meade, 44mm Aero, and 42mm ES.  The 30mm Wide Scan clones (Agena UWA 80 below) are great in the center 50% and then have severe field curvature out to their 44mm field stop.  If your eye has loads of focus accommodation like a camera lens, it might be a cheap option bought used.

Here's my composite of wide field eyepieces I posted elsewhere:

On 12/09/2019 at 21:05, cletrac1922 said:

Not sure what the advantage is using 2" eyepieces, as opposed to 1.25"

As @bingevader says, much wider true field of view (TFOV).  You can only take in a 27mm diameter view of the image plane with a 1.25" eyepiece, but a 46mm diameter view with a 2" eyepiece.  That's a 46*46/27*27=2.9x more viewable area.  For instance, it makes viewing large objects like the Pleiades and Collinder 70 much easier in moderate focal length telescopes.

With each doubling in power, surface brightness is quartered (squared rule).  This isn't such a big deal for stars because they are not extended objects, so star clusters end up taking power quite well.  This is why you can really crank up the power to split tight doubles.

Since you went up roughly 4x in power going from 26mm to 6.1mm, surface brightness went down by 16x, which is quite noticeable as you discovered.  To avoid this darkening, just increase your aperture by 4x in diameter to 300mm (12 inches or 1 foot) by buying a larger telescope. 😉

You could try adjusting the spacing between the flattener and sensor if it doesn't look good at the edges.  As long as it requires more distance you're okay.  If it requires less distance, you're probably out of luck.  Unfortunately for you, field curvature increases with decreasing focal length in refractors regardless of focal ratio (roughly 1/3 of focal length).  Thus, your 100ED will have more field curvature than your 120ED, so a 120ED flattener will be less aggressive with the same back focus, so it would require greater separation to work in the 100ED.  I'm pretty sure your 100ED flattener is more aggressive than a 120ED flattener would be and would require less separation to work in the 120ED.