Orthoscopic vs BST EP's for Planetary Observing?

[Ian McCallum]

I've became a bit of a fan of planetary observing recently and I'm wondering what advantage over the full range of BST eyepieces I have at the moment, would orthoscopic eyepieces give me?

[scotty38]

You'll get the answers it all depends on conditions etc and I've been tempted down this rabbit hole but I'm going to stick my neck out and say that unless you're after the last few % then probably not a lot at all.

Take that with my inexperienced pinch of salt though 🙂

[Zermelo]

I'm also thinking about this, so I'll follow this thread.

My thoughts so far:

Tracking - your picture shows a (manual?) dob, so the BSTs' 60 degree AFOV compared with 40-50ish for an ortho will mean fewer nudges. I have a motorized mount so not an issue for me.

Sharpness - I would guess that you would see a difference comparing a BST with a very fine ortho. But the BSTs are good, so they may not be an obvious second best compared with a more average ortho. Towards the edge of the field some of the BSTs can be a bit softer (again, not an issue for planetary targets with a motorized mount).

Brightness - the simpler ortho design ought to transmit more light than a more exotic EP, other things (coatings) being equal. But on the (major) planets that probably won't be so much of an issue.

Contrast - again, you would expect a bit more from a decent ortho? Contrast is important to bring out the more subtle details on planets, but then contrast is also affected by the scope. Anything with an obstruction like the dob is going to take a contrast hit in any case. I imagine if you were using a decent APO then you might be more inclined to preserve the contrast that it's delivering.

Im my own case, I've identified a magnification 'gap' in my line-up at 10mm, which sits in the middle of two Starguiders. So I was considering the Baader Classic Ortho 10mm, and wondering whether it would be a better bet for solar system objects.

Edited August 25, 2021 by Zermelo

[wookie1965]

Here is what S@N said.

[John]

The comfort of the BST Starguiders compared to using shorter focal length orthoscopics should not be overlooked in my opinion.

I tend to opt for observing comfort over small differences in ultimate optical performance these days - I'm getting old !

Manually tracking with a 40 degree AFoV, small eye lens and tight eye relief, at high power is somewhat harder work than with a nice big eye lens, 60 degree AFoV and reasonably generous eye relief.

[Zermelo]

55 minutes ago, John said:

The comfort of the BST Starguiders compared to using shorter focal length orthoscopics should not be overlooked in my opinion.

Good point John. The Starguiders, and their ilk, can factor in eye relief within their more complex design, but in orthos (and plossls) it tends to be a function of the focal length (though orthos are a little better than plossls in that respect).
In the 10mm F/L I'm looking for it shouldn't be a problem, but it might be if I wore glasses to observe. Something more like a 5mm F/L would be a pain for me in an ortho or plossl (c.f. the 5mm Starguider, offering 16mm relief), but as I'll be doing planetary with my Skymax I won't need to go that low.

I see Astro-Baby has an interesting page on orthos.

[Mr Spock]

If you have tracking, don't mind the small eye relief, then orthos are unbeatable for planetary.

If anyone wants to dip their toes, ENS has a 9mm Circle-T for £55. A bit on the expensive side but from the performance of my 9mm I'd say it's worth it. Build quality is superb on these and with an all to rare separate, adjustable field stop.

[Franklin]

3 hours ago, Zermelo said:

Im my own case, I've identified a magnification 'gap' in my line-up at 10mm, which sits in the middle of two Starguiders. So I was considering the Baader Classic Ortho 10mm, and wondering whether it would be a better bet for solar system objects.

I had the same dilemma. 12mm & 8mm BST's, both great eyepieces. I got the 10mm BCO to fill the gap and it's now one of my mostly used eyepieces giving x112 in my scope. Don't find the smaller AFOV and tighter eye-relief a problem with the 10mm BCO but the 6mm BCO can scratch your eye if your not careful. 

[Louis D]

It also depends on how fast your scope is.  Orthos tend to have poor edge correction below about f/8.  If you have an f/5 or faster Dob, you'd really notice how poor the edge correction is.  You'd have to be constantly trying to keep the object centered, and by the time the scope settled, you'd have to do it all over again!  Of course, if your scope/mount tracks, this isn't an issue.

Also, if you have really strong astigmatism in your observing eye, you can see it in views at 1mm and below sometimes, necessitating wearing eyeglasses to get the sharpest image possible.  This isn't going to happen with an ortho below 25mm.

[Ian McCallum]

Given the fact that I'm using a SW 200P, I don't think I'll be buying an Ortho any time soon.

Edited August 26, 2021 by Ian McCallum

[IB20]

The 10mm Baader Classic Ortho is my most used planetary EP. I find it gives better views in terms of sharpness and contrast than both the 12mm & 8mm BST for planetary use. I use the 200P Skywatcher dob and an 80mm Scopetech refractor. When Mars was at its recent opposition the 10mm BCO with 2x Barlow gave better views than the 5mm BST (it was close however). 

I’m fairly certain that for the cost, there isn’t a better EP currently than the 10mm BCO. I use it for lunar, double stars and white light solar (with appropriate solar films/wedges) observing too. For an ortho it is very comfortable to look through where my 6mm ortho can be quite difficult for eye placement.

Edited August 26, 2021 by IB20

[John]

When I used to do eyepiece reviews for the forum, much of my testing was done with my F/5.3 12 inch dobsonian. I didn't notice too many field edge issues with the various orthoscopics that I used to be honest

The Baader Classic Ortho's do loose sharpness over the final few % of their AFoV in all scopes I used them in but that was, I believe, accepted by Baader when they stretched the field stop to deliver 52 degrees rather than the traditional ~40 degree ortho field.

While I preferred the ergonomics of the classic "Circle-T" ortho design, the HD "flat topped" designs such as the Baader Genuine Ortho, the University Optics HD orthos, the Fujiyama HD orthos and the Astro Hutech HD orthos did seem to me to offer slightly better light scatter control and light throughput over the older, "classic" design, when I was comparing them "back to back". Probably due to more effective coatings:

https://stargazerslounge.com/topic/175014-baader-classics-the-story-so-far/

https://stargazerslounge.com/topic/184935-astro-hutech-orthoscopics-compared-with-baaders-orthoscopics/

The classic "Circle-T" orthos do perform very well though which is presumably why there is still a demand for them at £50 plus on the used market. A few years back you would have struggled to get £25 for one so they are better appreciated today

I rather liked this "short set" that I had a few years back:

 

 

[Mr Spock]

I'm using my orthos in a 250mm f4.8 newt and I can't see any edge issues.

I like the volcano top design of the Circle-Ts. I have an old 0.965" 4mm ortho which is difficult to use, yet the 4mm Circle-T ortho is relatively comfortable.

[chiltonstar]

In my 180 Mak, my 10mm Baader Ortho and a 9mm Circle T both perform very well indeed (to my non-expert eyes). While I like the FoV of the BSTs, (I have 8, 12 and 18mm) I do find the reflections I see of bright targets like Jupiter a bit distracting as they move across the field when you move your eye slightly. 

Chris

[Pixies]

I use a few short Orthos in my F6 200mm dob. At high power it can be a little hard work trying to keep up wirth the target. However, there have been quite a few cases when trying to split tight double-stars that I've found them more successful than some modern eyepieces.

[Louis D]

On a whim, I picked up a 25mm Edscorp Ortho which looks to be the same as other Tani made volcano tops.  While sharp in the center at f/6 and flat of field with very little distortion, it is blurry at the edge at f/6 in my field flattened AT72ED.  I went so far as to disassemble it and try all 4 orientations of the two groups (singlet and triplet groups) with respect to being possibly flipped by a previous owner, and the original orientation was still best, so it's a design issue with this ortho at f/6.

However, at f/12 in my 127mm Mak, all is well for the ortho as well as for the rest of my 25mm 3 or 4 element eyepieces.  A similar improvement can be had using a 2x Barlow with an f/6 scope, though I didn't take any photos of that combo yet.

[Mr Spock]

All I can say is that ortho must be an inferior type. Mine are all razor sharp in a 250mm f4.8 Newt which has no field flattening or other assistance.

Here's a few images I've just taken with that scope and the 25mm, 18mm and 12.5 mm Circle-T orthos.
This test was difficult: I had to put my chart at the top of the garden and my scope in the house. The plane wasn't centred or flat and I couldn't hold my phone in the right place, or hold it steady enough. Even so, I'm sure you can see the results.

The scope is in perfect collimation, which helps a great deal with sharpness. I just wish I could capture accurately what I'm seeing through the eyepiece. I think as a demo this is good enough though.

 

[markse68]

aren’t orthos by definition meant to keep straight lines straight though? Fair amount of pincushion distortion there 🤔 I love my orthos btw

PS Johninderby recently posted a link to the Zeiss brochure for the original ZAO eps (which Company7 refuse to unless you have crossed their palms with silver)(thanks again John!) where they say the original Zeiss Jena old school orthos were optimised for f10, but the new ZAOs catered for the modern trend for faster scopes -f8 (🤔😅) (they are talking refractors though) Would be interesting to know what the BGO and BCOs etc were optimised for. (ps i use the og Zeiss Jenas in my modern fast f8 scope and they are tack sharp to edge of field stop 👍)

Mark

Edited August 28, 2021 by markse68

[Louis D]

1 hour ago, Mr Spock said:

All I can say is that ortho must be an inferior type. Mine are all razor sharp in a 250mm f4.8 Newt which has no field flattening or other assistance.

Here's a few images I've just taken with that scope and the 25mm, 18mm and 12.5 mm Circle-T orthos.
This test was difficult: I had to put my chart at the top of the garden and my scope in the house. The plane wasn't centred or flat and I couldn't hold my phone in the right place, or hold it steady enough. Even so, I'm sure you can see the results.

The scope is in perfect collimation, which helps a great deal with sharpness. I just wish I could capture accurately what I'm seeing through the eyepiece. I think as a demo this is good enough though.

 

I'll agree, that's more what I was expecting.  It's the first time I've gotten such a disappointing used eyepiece.

[lunator]

I have a range of volcano top orthos.

I picked them up as a lot when Telescope House were selling them off.

For double star and planetary they are excellent. I have even been using them in my ST80 whilst watching RS Oph.

They way I look at it is, the lens layout is pretty much the same as an Apo refractor so by wouldn't the views be excellent 

Cheers

Ian

[Alan64]

I only go up to 12.5mm in focal-length with orthoscopics...

I've chosen the 12.5mm orthoscopics in the past only because they're so close to the 9mm.

But for the lower powers, I use Konigs at 12mm and 16mm, an Erfle at 20mm, and others.  In that I use those simply to find things for the orthoscopics to ogle, they serve their purpose...

I'm the type who would rather observe through a 0.5mm, if such existed, than a 25mm.

[Alan64]

I have these diminutive darlings as well...

[Ian McCallum]

Revisiting an old thread...

Now I've got a SW Evostar 120 refractor and decent mount (EQ5 Deluxe), would Orthos be any good for me? I'm contemplating motorising this mount.

[Ricochet]

3 hours ago, Ian McCallum said:

Revisiting an old thread...

Now I've got a SW Evostar 120 refractor and decent mount (EQ5 Deluxe), would Orthos be any good for me? I'm contemplating motorising this mount.

Yes, orthos would work well, but personally I prefer the extra comfort given by Vixen SLVs at that field size.