28 replies to this topic

[Serack]

When it comes to focuser travel, my Pentax XWs need to be the furthest in, and my 30mm UFF has to travel the furthest out.

The JMI focuser on my PortaBall has only 1.7” of travel, and I’m going to have to shorten down the second hand truss poles I’ve got for it, as they put the focus point several inches inside the upper tube assembly, closer to the secondary mirror than the focuser.

I need a rough idea of how much further in or out the focuser travel may be on my future potential eye piece choices, with emphasis on in, as it’s easier to get extension adapters.

If it matters for responses, I love the Pentax XWs for their eye relief as I observe with glasses.

[SeattleScott]

The XWs focus at the shoulder. ES and TV focus further out, but I suspect you will be hard pressed to find things that focus further in. I think the 17.5 Morpheus focuses 2.5mm further in.

[CrazyPanda]

I agree with SeattleScott - Pentax XWs focus at lowest setting of the Paracorr for me, as do many other eyepieces. The only two eyepieces I have that seem to require more in-travel are the Docter in 1.25" mode and 17 Nikon NAV-HW.

 

There's also accessories to consider. If you plan on a Paracorr, that needs about 3/4" of in-travel vs using the eyepiece by itself. Some barlows require in-travel.

 

Also consider any myopia you have and whether you plan on wearing glasses. If you have myopia but don't wear glasses, that requires you to focus further inwards to reach focus, so set your focal plane accordingly.

[Ernest_SPB]

Most TV eyepieces have front focus out, see parameter F in the table https://www.televue....page.asp?id=214

[PJBilotta]

The 17.5 Morpheus and 17.3 and 14 Delos are the ones that come to mind for me.

[Far Star]

The 24 mm Baader Hyperion needs much "focuser-in-travel", because its field stop is in the upper barrel.

 

"Field Stop Displacement to reference plane -20 mm"

>>>  https://www.baader-p...n-variable.html

[Serack]

The XWs focus at the shoulder. ES and TV focus further out, but I suspect you will be hard pressed to find things that focus further in. I think the 17.5 Morpheus focuses 2.5mm further in.

 

 

The 17.5 Morpheus and 17.3 and 14 Delos are the ones that come to mind for me.

I’ve had the Pentax XWs (10mm and 5mm) and my Delos 14mm for about 2 months.  Although my memory may be flawed, I thought I had to adjust the focuser out when I switched from the Pentax to the Delos.  

[Serack]

Most TV eyepieces have front focus out, see parameter F in the table https://www.televue....page.asp?id=214

 

 

The 24 mm Baader Hyperion needs much "focuser-in-travel", because its field stop is in the upper barrel.

 

"Field Stop Displacement to reference plane -20 mm"

>>>  https://www.baader-p...n-variable.html

I'd understood "field stop" as a diameter, and hadn't gone on from that to think of it in terms of placement along the axis.  The televue diagrams and explaining text do a decent job of explaining that "F" is where the field stop is along the axis.  

 

It seems people bounce around between "focal plane" "field stop displacement" and maybe a few other terms like parfocal (which I understand to be more that the location is the same amongst a group of ep's but some commenters are sometimes more loose with this term).  

 

As for some comments about Paracorr... I've never used one and at f/5 and with some balancing limitations, I may be able to avoid using one with my current eyepieces...  I'm considering committing to a truss pole length that puts the Pentax XW at about 3/4" from all the way in.  

 

Thanks for the input everyone

[SeattleScott]

I’ve had the Pentax XWs (10mm and 5mm) and my Delos 14mm for about 2 months. Although my memory may be flawed, I thought I had to adjust the focuser out when I switched from the Pentax to the Delos.

Most Delos and other 1.25” TV eyepieces focus a quarter inch further out than XWs. But I believe the 14 and 17.3 Delos are different.

So you get the picture, you can find some oddballs here and there that focus further in. But not like a whole eyepiece series.

[ji4m]

I find the Tele Vue EP website info so very well done.  It generates belief in its accuracy.  They supply drawings I can understand.  There may be other companies of similar execution, but in my US-centric perspective, TV is exemplary. 

 

Not that the OP would seek one out, but wasn't the 35mm Ultrascopic (et al) know as a classic infocus gobbler?  Maybe I have it backwards, but I really liked that EP.

[Serack]

Most Delos and other 1.25” TV eyepieces focus a quarter inch further out than XWs. But I believe the 14 and 17.3 Delos are different.

So you get the picture, you can find some oddballs here and there that focus further in. But not like a whole eyepiece series.

Huh, I guess I remembered what my fingers did in the dark incorrectly.  And with the perspective I've gained here in this topic, I can interpret the info in Earnest_SPB's link to agree with just what you say.  

 

Thank you very much.  

[Starman1]

The XWs focus at the shoulder. ES and TV focus further out, but I suspect you will be hard pressed to find things that focus further in. I think the 17.5 Morpheus focuses 2.5mm further in.

Tele Vue 31mm Nagler, 21mm Ethos, 17mm Ethos focus about 10-10.2mm farther in than the focal plane of the scope.

If you use a 10mm tall 1.25" adapter, the 17.5mm Morpheus focuses 12.5mm farther in than the focal plane of the scope.

The Tele Vue Delos 14mm and 17.3mm focus 12.7mm farther in than the other focal lengths of Delos, so 5.8mm + the height of the adapter farther in than the focal plane of the telescope--potentially 15.8mm in.

Pentax XW 1.25" eyepieces focus in from the focal plane of the scope by the height of the adapter used.  2" XWs focus at the focal plane of the telescope.

 

3/4" out is an excellent recommendation.  It should allow the use of a Paracorr and/or many Barlows that focus inward.

 

So, it might be useful to have some figures at your fingertips for the height of various adapters.

You can tune the position of your eyepieces in the scope based on the height of the adapter.

A zero height adapter (rare) puts the eyepiee right at the focal plane of the scope if the eyepiece's focal plane is at the shoulder (most aren't).

 

(positive means above the telescope focal plane level, negative means below the level)

 

TeleVue Hi-Hat and brass adapters  +16.5mm

Tele Vue Paracorr 2 adapter  +10.5mm

Many twist-Lock types  +10mm-10.5mm

TeleVue flat top adapter +9.5mm 

Baader Click-Lock adapter  +9.5mm

Astrosystems flat top adapter  +6mm

Tele Vue In-Travel adapter if the eyepiece rests on the outside of the adapter  +4mm

Baader Push-Fix adapter  +1.0mm

Glatter Parallizer adapter +0.0mm if the eyepiece fits in exactly to that point.

Starlight Instruments flat adapter  +0.0mm

Tele Vue In-Travel adapter if the eyepiece rests inside the outer lip  -1.5mm

Astrosystems ultra-Low adapter  up to -12.7mm depending on how far down inside the adapter the eyepiece fits.

[Serack]

Tele Vue 31mm Nagler, 21mm Ethos, 17mm Ethos focus about 10-10.2mm farther in than the focal plane of the scope.

If you use a 10mm tall 1.25" adapter, the 17.5mm Morpheus focuses 12.5mm farther in than the focal plane of the scope.

The Tele Vue Delos 14mm and 17.3mm focus 12.7mm farther in than the other focal lengths of Delos, so 5.8mm + the height of the adapter farther in than the focal plane of the telescope--potentially 15.8mm in.

Pentax XW 1.25" eyepieces focus in from the focal plane of the scope by the height of the adapter used.  2" XWs focus at the focal plane of the telescope.

 

3/4" out is an excellent recommendation.  It should allow the use of a Paracorr and/or many Barlows that focus inward.

 

So, it might be useful to have some figures at your fingertips for the height of various adapters.

You can tune the position of your eyepieces in the scope based on the height of the adapter.

A zero height adapter (rare) puts the eyepiee right at the focal plane of the scope if the eyepiece's focal plane is at the shoulder (most aren't).

 

(positive means above the telescope focal plane level, negative means below the level)

 

TeleVue Hi-Hat and brass adapters  +16.5mm

Tele Vue Paracorr 2 adapter  +10.5mm

Many twist-Lock types  +10mm-10.5mm

TeleVue flat top adapter +9.5mm 

Baader Click-Lock adapter  +9.5mm

Astrosystems flat top adapter  +6mm

Tele Vue In-Travel adapter if the eyepiece rests on the outside of the adapter  +4mm

Baader Push-Fix adapter  +1.0mm

Glatter Parallizer adapter +0.0mm if the eyepiece fits in exactly to that point.

Starlight Instruments flat adapter  +0.0mm

Tele Vue In-Travel adapter if the eyepiece rests inside the outer lip  -1.5mm

Astrosystems ultra-Low adapter  up to -12.7mm depending on how far down inside the adapter the eyepiece fits.

My portaball has a JMI single speed focuser that seems to be specially designed to have the adapter shoulder sit flush with the 2" adapter by having notches for the adapter's set screw.   A feature of the design of the telescope is the low profile of the focuser allows the entire upper tube assembly to fit inside of the "ball" of the lower assembly.  

 

A month before I got the Portaball I was aspiring to get a 31mm nagler, but I'm glad that didn't pan out, as the portaball may have struggled with the weight. 

 

Thank you very much for all the reference values, I feel validated in what was basically a cut once and live with it choice.  

Edited by Serack, 17 November 2024 - 08:53 PM.

[astrophile]

Is there a chance you’ll ever want to use a Leica 25-50 ASPH zoom? In a Starlight Instruments adapter, it requires much more in-travel than any other eyepiece including Nag 31–I haven’t measured how much, sorry. It does just barely come to focus before bottoming-out on all the dobs I’ve used it in.

Edited by astrophile, 17 November 2024 - 09:04 PM.

[areyoukiddingme]

For the Leica, the APM adapter allows for the most in-focus possible--bottoming out at the eyepiece barrel. The Starlight leaves about 8-10 mm on the shoulder of the adapter.

[Starman1]

Is there a chance you’ll ever want to use a Leica 25-50 ASPH zoom? In a Starlight Instruments adapter, it requires much more in-travel than any other eyepiece including Nag 31–I haven’t measured how much, sorry. It does just barely come to focus before bottoming-out on all the dobs I’ve used it in.

The 17mm Nikon NAV-HW focuses 0.6" below the focal plane of the scope.

I recall that was farther in than even the Leica.

[Serack]

Is there a chance you’ll ever want to use a Leica 25-50 ASPH zoom? In a Starlight Instruments adapter, it requires much more in-travel than any other eyepiece including Nag 31–I haven’t measured how much, sorry. It does just barely come to focus before bottoming-out on all the dobs I’ve used it in.

I haven't really considered any zoom eyepieces.  I always assumed the convenience had trade offs I didn't want to pay for.  

[Starman1]

I haven't really considered any zoom eyepieces.  I always assumed the convenience had trade offs I didn't want to pay for.  

I'd be tempted if there was a constant 80° and the range was 5-15mm and it had glasses-friendly eye relief and was astigmatism free at f/4.

It could replace 8 eyepieces for me.

That is never going to happen, though.  And even if it did, I'd bet it would be incompatible with a Paracorr or require 2" of focuser in-travel.

 

Zooms, though, never cover the entire range needed.  My eyepieces go from 3.7mm to 30mm, and that range isn't going to be covered by a zoom, even if the zoom is Barlowed.

[Serack]

I'd be tempted if there was a constant 80° and the range was 5-15mm and it had glasses-friendly eye relief and was astigmatism free at f/4.

It could replace 8 eyepieces for me.

That is never going to happen, though.  And even if it did, I'd bet it would be incompatible with a Paracorr or require 2" of focuser in-travel.

 

Zooms, though, never cover the entire range needed.  My eyepieces go from 3.7mm to 30mm, and that range isn't going to be covered by a zoom, even if the zoom is Barlowed.

Yah that.  Although I’m happy with 70° in exchange for the eye relief on my EP kit.  
 

It’s always a set of tradeoffs, and I’m only now moderately literate on what they are for standard EP’s.  I took it for granted that the added complexity of a zoom makes for even steeper trade offs.

 

My next big EP purchase will probably be a set of glasses dedicated to astronomy (I’ve got astigmatism), as the bifocals on my day to day glasses I started wearing right before I got my first scope 2 years ago became more of an issue once I upgraded from the redlines.  

[Starman1]

Yah that.  Although I’m happy with 70° in exchange for the eye relief on my EP kit.  
 

It’s always a set of tradeoffs, and I’m only now moderately literate on what they are for standard EP’s.  I took it for granted that the added complexity of a zoom makes for even steeper trade offs.

 

My next big EP purchase will probably be a set of glasses dedicated to astronomy (I’ve got astigmatism), as the bifocals on my day to day glasses I started wearing right before I got my first scope 2 years ago became more of an issue once I upgraded from the redlines.  

Having gone through many many glasses looking for ideal astronomy glasses, I'll give you my findings:

A) Progressives.  Nice for daily use, but a disaster at the scope.  The field is only in focus for a narrow vertical and horizontal range, and if you move your gaze, the image is out of focus.

B) Rimless glasses.  Another disaster for widefield eyepieces.  The attachment points for the bridge and side pieces in the glasses are always visible in your field of vision.  And, they can contact the lens of the eyepiece.

C) Classic bifocals.  Didn't work.  Every time I looked down, the field was out of focus because the tall bifocal section was in the field of view.

D) Everyday glasses with typical lenses.  Don't work.  Either the lens is too small vertically, or the frame is in your field of vision, or they are rimless (see above) or are progressive or bifocal.

 

A few things that did work:

1) Large, round, wire rim glasses with 50mm or larger lenses.  That put the frame outside the field of view and meant that pushing against the eyepiece contacted rubber all the way around.  Prescription for infinity only.

2) (from Costco--don't know if other labs will do it) Bifocals where the reader section is reduced to an 8mm tall streak across the bottom of the lens.  The reader section wasn't seen when looking through the eyepieces.

3) Single vision glasses with large lenses, with a pair of readers hanging around the neck on a lanyard.  Switch glasses when reading notes, reading a chart, or looking at the screen of a DSC or hand controller.

4) Single vision glasses with large lenses and a 4" diameter magnifying glass stuck in the pocket for reading.  Pull it out to red notes, charts, etc. and never need to change glasses.

#1 works well.

#2 above is best, but may not be available. 

#3 only works in warm weather.  In cold weather, the glasses hanging around your neck get very cold and fog up instantly when you put them on.  I suppose you could use an anti-fog coating on the glasses, 

but I never tried that (though I use that on my outside mirrors on my car)

#4 What works well for me in the cold.  You have to keep the magnifying glass in your pocket or it ices up.  I never need both hands free when reading or writing.  My magnifying glass has a dark red LED light in it, which was too bright initially

until I covered the LED with dark red fingernail polish.  If you do that, a white LED would work, and there is a lot more choice in magnifiers with white LEDs.

 

No ideal solution.  You find what works for you and stick with it until it becomes second nature.

[SeattleScott]

I haven't really considered any zoom eyepieces. I always assumed the convenience had trade offs I didn't want to pay for.

Generally yes, trade offs, although the Leica zoom is high enough quality that there likely aren’t significant trade offs. Of course it’s expensive.

[Serack]

Having gone through many many glasses looking for ideal astronomy glasses, I'll give you my findings:

A) Progressives.  Nice for daily use, but a disaster at the scope.  The field is only in focus for a narrow vertical and horizontal range, and if you move your gaze, the image is out of focus.

B) Rimless glasses.  Another disaster for widefield eyepieces.  The attachment points for the bridge and side pieces in the glasses are always visible in your field of vision.  And, they can contact the lens of the eyepiece.

C) Classic bifocals.  Didn't work.  Every time I looked down, the field was out of focus because the tall bifocal section was in the field of view.

D) Everyday glasses with typical lenses.  Don't work.  Either the lens is too small vertically, or the frame is in your field of vision, or they are rimless (see above) or are progressive or bifocal.

 

A few things that did work:

1) Large, round, wire rim glasses with 50mm or larger lenses.  That put the frame outside the field of view and meant that pushing against the eyepiece contacted rubber all the way around.  Prescription for infinity only.

2) (from Costco--don't know if other labs will do it) Bifocals where the reader section is reduced to an 8mm tall streak across the bottom of the lens.  The reader section wasn't seen when looking through the eyepieces.

3) Single vision glasses with large lenses, with a pair of readers hanging around the neck on a lanyard.  Switch glasses when reading notes, reading a chart, or looking at the screen of a DSC or hand controller.

4) Single vision glasses with large lenses and a 4" diameter magnifying glass stuck in the pocket for reading.  Pull it out to red notes, charts, etc. and never need to change glasses.

#1 works well.

#2 above is best, but may not be available. 

#3 only works in warm weather.  In cold weather, the glasses hanging around your neck get very cold and fog up instantly when you put them on.  I suppose you could use an anti-fog coating on the glasses, 

but I never tried that (though I use that on my outside mirrors on my car)

#4 What works well for me in the cold.  You have to keep the magnifying glass in your pocket or it ices up.  I never need both hands free when reading or writing.  My magnifying glass has a dark red LED light in it, which was too bright initially

until I covered the LED with dark red fingernail polish.  If you do that, a white LED would work, and there is a lot more choice in magnifiers with white LEDs.

 

No ideal solution.  You find what works for you and stick with it until it becomes second nature.

I haven't done a lot of question posting, mostly just reading posts supplied by google searches, and I've seen your helpful comments come up a lot in those queries.  I must say that the level of helpful information in your responses lives up to what I'd already seen when I was just lurking.  Rockstar level.

 

Thanks.  

 

Generally yes, trade offs, although the Leica zoom is high enough quality that there likely aren’t significant trade offs. Of course it’s expensive.

Which is another trade off.  In fact, it was part of why I chose those specific words

 

Edit:  Huh, this topic compares it really favorably to my stock of Pentax XWs and Delos 14mm.  Of course, used it also costs about what I could get for the 3 of them on the classifieds.  

Edited by Serack, 18 November 2024 - 01:36 PM.

[K-night]

For the same target object, will an Ethos 6mm reach focus at the same depth as an Ethos 8mm?

[Serack]

For the same target object, will an Ethos 6mm reach focus at the same depth as an Ethos 8mm?

Judging by the table Ernest_SPB linked, yes.

[K-night]

Judging by the table Ernest_SPB linked, yes.

The difference between each parameter B gave me cause for concern.