92 replies to this topic

[jrazz]

I've been swayed by certain people on this forum () and off to buy a 100mm BT (OB 100XL-SD). Now that I'm fully bought in, I'm looking for recommendations for eyepiece focal lengths that would be useful with this BT (560mm, F5.6)

 

So, what are your recommendations and why? Should I go for wide field x25 (22mm) or focus on really deep 80x (7mm). Something in the middle? Anyone has experience with this BT and can tell me what are the most useful focal lengths/magnifications?

 

 

[Fiske]

I have no idea who you might mean by "certain people." I mean none whatsoever. 

 

The eyepieces used most frequently in my 100XL-SD are 20mm, 14mm, and 10mm. 20 for wide filed. 14 for more detail but still wide enough to be starhop friendly, 10s for higher magnification. 7s are also used fairly often, but typically after a DSO has been located with a longer FL eyepiece or for objects that are easy to point to. 5mms are used rarely, when extra ooph is needed for something like resolving the double double in Lyra. For me 5mms (112x) is the magnification limit for the 100XL. It just gets to be a lot of work. Better to switch over to a telescope after that, IMO.

[dave85374]

I had the Oberwerk BT-XL-ED with their 70 degree 14mm and then I purchased Explore Scientific eyepieces 82 degree 8.8mm & 6.7mm eyepieces for the wider views.  Oberwerk had their own 70 degree 7mm eyepiece but I couldn't get a good focus with it and returned it for the 6.7mm.  On my BT, the 6.7mm was just about too much power and was a little dark but I loved the other two.

 

I sold the BT and went to a Evolution 8 telescope and it showed much more than you can see in a binocular telescope.  Now I am into EAA and that beats anything out there.  Short 8 second shots stacked show things you could never see with a BT or telescope with an eyepiece.  I also went whole hog and got a HyperStar 8 to get down to f2 instead of the normal f10 or f6.4 with a reducer.

[Rich V.]

So, what are your recommendations and why? Should I go for wide field x25 (22mm) or focus on really deep 80x (7mm). Something in the middle? Anyone has experience with this BT and can tell me what are the most useful focal lengths/magnifications?

I'd always go for the widest field possible with the first pair of eyepieces.  Around 25x-30x gives a great view of the many larger summer Milky Way areas that can be so spectacular.  That would be about a 2.5° FOV or thereabouts.  I think around 80x on the top end for now.  I know I use 75x frequently in my 100mm BT as well as pairs in the 40x or 50x middle range.  Three pairs of eyepieces will get you a long way., though.  I don't like switching eps a lot anyhow, it can break the magic spell sometimes.

 

You already have a scope for best higher mag planetary details.      If you like what you see at 80x, and think you want to push it more, you can still expand your collection later.  I rarely use my 150x pair, frankly, but in a pinch, if I don't have a scope out, they'll show me Jupiter's GRS and lunar transits, Saturn and maybe five of its moons as well as some decent lunar views if it intrudes into the night.

 

Rich

[jrazz]

 I don't like switching eps a lot anyhow, it can break the magic spell sometimes.

 

That's how I feel!

OTOH, I like the "portability" of binoculars. I think this is something I can take to a dark site and have at least some of the flexibility.

 

I am really not sure about going above 80x. The exit pupil is already so small I'm thinking it would be abysmally dim and you're right, I have my telescope for higher mags.

[MT4]

For my APM 100mm SD APO BT, I have the following eyepieces:

 

     APM UFF 24mm:       23x, 65 degrees. <-- Came with the APM

     Nikon SW 17.5mm:    31x, 72 degrees

     APM 12.5mm:            44x, 84 degrees

     Morpheus 6.5mm:      85x, 76 degrees

 

These are all long eye-relief, wide-to-superwide eyepieces.   I think for use with my APM 100mm BT, I'll be happy with these eyepieces for a long time to come.   (For use with my Tak TSA-120, lower-FL eyepieces and Barlow lenses will be part of the attraction.)

[Fiske]

I am really not sure about going above 80x. The exit pupil is already so small I'm thinking it would be abysmally dim and you're right, I have my telescope for higher mags.

It's not that the views are dim above 80x, at least not at 112x with 5mm eyepieces. It's that eye position becomes more challenging, the FOV is small, and stability becomes a significant factor. On a p-gram 80x is going to be pushing it, frankly.

 

Rich nailed it, as usual. 

[jrazz]

For my APM 100mm SD APO BT, I have the following eyepieces:

 

     APM UFF 24mm:       23x, 65 degrees. <-- Came with the APM

     Nikon SW 17.5mm:    31x, 72 degrees

     APM 12.5mm:            44x, 84 degrees

     Morpheus 6.5mm:      85x, 76 degrees

 

These are all long eye-relief, wide-to-superwide eyepieces.   I think for use with my APM 100mm BT, I'll be happy with these eyepieces for a long time to come.   (For use with my Tak TSA-120, lower-FL eyepieces and Barlow lenses will be part of the attraction.)

That looks pretty much like what I have in mind: Wide, medium power, high power.

What do you use most of the time?

 

 

 

It's not that the views are dim above 80x, at least not at 112x with 5mm eyepieces. It's that eye position becomes more challenging, the FOV is small, and stability becomes a significant factor. On a p-gram 80x is going to be pushing it, frankly.

 

Rich nailed it, as usual. 

The p-gram is a stop-gap. It's what I have right now. Probably will change in the future.

Same question for you though, what do you use most of the time?

 

 

And yes, Rich nailed it.  

[Fiske]

The p-gram is a stop-gap. It's what I have right now. Probably will change in the future.

Same question for you though, what do you use most of the time?

20mm -- 40%

14mm -- 30%

10mm -- 20%

07mm -- 8%

05mm -- 2%

 

If the base of the eyepiece is wider than the lock ring diameter on the BT, swapping eyepieces becomes a major pain. It is much(!) easier to swap eyepieces if the base is the same diameter or smaller because the lock can be easily tightened and loosened.

[MT4]

That looks pretty much like what I have in mind: Wide, medium power, high power.

What do you use most of the time?

 

 

 

I've only had 4 or 5 viewing sessions with my APM 100mm SD BT since I got it in mid March.  The weather has been really dismal since early April and is probably going to be equally bad for another couple of months before it gets any better.

 

I've tested all those eyepieces to make sure that I could merge the images with them.   The ones that I've used the most so far are the APM 12.5mm 84-deg eyepieces, but that's only because I wanted to see how a super-wide AFOV would feel in binocular vision.  There's definitely a place for the Nikon SW 17.5mm and the Morpheus 6.5mm in my team.   

 

The only eyepieces I am not quite sure about are the APM UFF 24mm.   Nothing really wrong with them per se but after experiencing the 84-deg AFOV it can be tricky to switch to 65-deg AFOV when I have better options to choose from.  Besides, my local skies are so light polluted that I prefer smaller exit pupils to get darker background sky.

 

When the sky clears up later in the summer and I get to use my APM BT more I'll know better which eyepieces I prefer and for what occasions.

[garret]

For my APM 100ED/ APO I have/ use

 

22mm Vixen LVW 20% 

17.5mm Morpheus 2%

12mm Delos 50%

9mm Delite 20% (galaxies, small objects)

5mm Delite 8% (moon, planets, and doubles)

 

A 6.5mm is on my wish-list...

[jrazz]

That 12mm Delos is right at the 2mm sweet spot. Seems like an awesome EP set. Would they work with a narrower IPD? 

[garret]

. Would they work with a narrower IPD? 

I have 64mm IPD, 61mm IPD should be OK ...if  facial physique cooperate...

[jrazz]

Mine is 61-62... So probably marginal 

 

 

 

Anyone have experience with Oberwerk's offering? (22mm, 14mm, 7mm) 

[dustyc]

I have the 22, 14 and 7mm sets from Obie. 

22 are a good alternative to the Pans. Only thing I noticed was the soft field stop. Just barely enough eye relief.

14 are better in both areas mentioned above. 

7 are a little "eh" for me. Eye relief is tight so glasses get tossed (the Dioptrix don't fit ). Hold your head steady or it's blackout time. EOFB is evident in this one but not really bad compared to some others I've had. 

Given their prices, a great value. Plus they color match the trim rings on mine (ED version) and the red dot sight.

Also have a set of Morpheus (9mm). Truly a treat. Feels like you really are looking out a porthole! But for the price and a few bucks more you can get 2 pairs of the Obies!

[jimhoward999]

Here is one more person's $0.02.

 

I very much like 9mm TV Delites in the 100XL-SD.  The image quality is noticeably better than the Oberwerk eyepieces.  I am sure the Pentax XWs would be equally good or maybe better, I just happen to have the TV.    I find 9mm (62x) is the highest mag that I can comfortably merge.   Very nice.

 

I find long ER 5mm eyepieces to be useful for high mag.  The magnification is not empty, but personally I can't readily merge such images, so it becomes a one eyed view; and not quite as good as a 4" refractor.  But if you are already observing with the BT100, are you going to drag out a telescope just to make your 110X view a little better?  For me no.  So the 5mm is useful.

 

The 14mm eyepieces that come with the telescope produce a comfortable view.    I still use those eyepieces, but I wonder if Teleview  or Pentax eyepieces of the same focal length would produce noticeably better views at 40X.  I bet they would.

 

For wide FOV I use 25mm eyepieces. In theory, 20 or 22mm is as wide as you can go and focal lengths longer than that lowers the magnification without increasing the FOV.  But I like that little bit lower magnification.  It projects the TFOV into a slightly smaller AFOV and also assures that you can see all of the maximum FOV that your BT can transmit.

[jrazz]

I would love for the Pentax XWs to work for me. They are awesome in my telescope but they are too wide physically for my IPD though. 

I have also thought to get another 25mm Plössl since I already have one and they are cheap and since I think I'll use them more as a "finder" EP. OTOH I have an aversion to buying "cheap" optics. Sooner or later I'll buy a nicer set and then these will be relegated to the box never to come out and I'll feel guilty 

 

 

Anyone have experience with the Nikon SW's? They look very comparable to the Pentax and the Delos range. 

[oldmanrick]

If you like Pentax eyepieces, you might look for a pair of the XL's, as they are smaller in diameter than XW's.  I have pairs of XL14's and XW7's that I like in my APM and Lunt BT's.  I can barely use the XW's due to my IPD, but the XL's are easy.

 

The XL's have slightly narrower FOV's, but still nice for bino use.  The 10.5mm XL's are said to be very good, although I've never tried them.

 

Sorry, no experience with the Nikon SW's.

 

Rick

Edited by oldmanrick, 05 June 2022 - 10:35 AM.

[Dpasqa]

I have a Oberwerk BT-100 and love it. Here is my eyepiece selection. 
 

Oberwerk 7mm (70° AFOV) 80x, it works great for lunar closeups and viewing the planets.

 

10mm - Orion Ultra Flat Field  (65 AFOV°)  56x, it is also good for lunar and planets, it’s easier to focus than the 7mm

14mm - Oberwerk (70° AFOV) 40x, great for observing just about everything with its wide FOV

18mm - Orion Ultra Flat Field  (65° AFOV) 31x, I don’t use this often

 

25mm - Celestron X-Cel LX (60° AFOV) 22x, great for wide FOV 

 

When I first got into this I thought magnification, magnification, magnification. But when it comes down to it, these binoculars are really great for DSO‘s, and magnification doesn’t help. For planets, the 7 mm is going to be about as good as it gets, you could probably bump it to 5 mm and get a little larger view but the planets are not gonna be that big. My observing has shifted since I bought mine and I find myself more content searching out open clusters and globular clusters. I have found so many of these with my BT. I purchased the red dot finder scope that Oberwerk sells. With that I can find anything I see in the sky in a matter of seconds. A friend of mine has the Orion BT-72, my red dot finder does not fit on his, but Orion has two threaded holes on the top of the handle, he bought a regular red dot that that line up with the holes on top of the handle. Before I had the red dot finder I was always over shooting either too high or too low.

 

Back to eyepieces. These days I use my 14 mm for most observing. I switch over to the 25 mm when I want to do some general sky surfing because of the wider field of view. And once in a while I pull out the 7 mm to look at the moon. I will do the same when the planets come out. So if you’re on a tight budget, I think a 7 mm, 14 mm and a 25 mm would be fine. They don’t have to be those exact sizes but something close. Anyway just my two cents being a happy owner have a great astronomy tool. I also bought a Celestron Evolution eight Telescope. And I really like it because of the larger views you get, But it will never replace my BT’s. I think with the two instruments I can find everything reasonably available in my not so good skies.

 

I hope this helps you not waste money on needless expensive eyepieces. 

Edited by Dpasqa, 05 June 2022 - 11:06 AM.

[jrazz]

Thank you for that!

 

I'm trying to figure out what makes sense. Honestly, right now I'm really eyeing the APM/Orion/Celestron 24mm UFF EPs as the wide field. I think these are very much my jam but honestly I am the kind to think "magnification magnification" 

 

All this means is that I shouldn't buy anything until I get a chance to see what I actually use the darn thing though 

 

[Dpasqa]

Thank you for that!

 

I'm trying to figure out what makes sense. Honestly, right now I'm really eyeing the APM/Orion/Celestron 24mm UFF EPs as the wide field. I think these are very much my jam but honestly I am the kind to think "magnification magnification" 

 

All this means is that I shouldn't buy anything until I get a chance to see what I actually use the darn thing though 

 

astronomy_tools_fov (1).png

My guess is like me, your viewing concept will change the longer you own the BT. Like I said when I first got mine I thought highest magnification possible. But the BT is more like a short tube telescope with a 500+mm focal length. You can only push magnification so far with it. Those telescopes are best used for open clusters and other DSO’s. You’re smart using the Astronomy Tools site. That’s a good way to figure what you will see. It’s pretty accurate, I’ve tested all my eyepieces with that site and they’re pretty darn close. Anyway, you have to explore and try different things til you find what you actually use. Try to buy Eyepieces used, you can always get out of them without losing too much that way.

 

Like I said, I observe mostly with my 14mm & 28mm eyepieces, they are good eyepieces this time of year when there is less to see out there. Magnification doesn’t do much for stars and often hinders seeing large open clusters. The Beehive cluster is a perfect example of what looks best through a BT, high magnification has too narrow a FOV, you can’t see all the stars. Your BT will shine when Cassiopia and Orion come in to view. Cassiopia is full of beautiful clusters that are best viewed through the BT as well as Orion nebula. They are perfect targets what’s the BT is capable of. Also pleiades is an incredible BT object to observe. I use SkySafari to find open Clusters to search for with my BT. Once I find a target I’m able to narrow down close to where it is by getting into that constellation. There are so many targets out there but unfortunately this time of year not as many. Anyway just my two cents

Edited by Dpasqa, 05 June 2022 - 04:57 PM.

[jrazz]

Made a super happy discovery today!

 

The Pentax SMC-XW rubber "jacket" can be removed easily which reduces the OD considerably. I tried this and was able to remove the outer jacket and replace it without any arm to the EP. It does lose some of it's charm and maybe I can 3D print a jacket just so it doesn't look so naked but it works and it reduces the OD to 56.8mm which is definitely doable for me!

 

So happy! I love my Pentax XW EPs. By far the best and most comfortable EPs I've tried. 

Along with the APF/Orion/Celestron 24mm UFFs I have a great range. 

 

 

 

Edited by jrazz, 06 June 2022 - 05:42 PM.

[jrazz]

I'd always go for the widest field possible with the first pair of eyepieces.  Around 25x-30x gives a great view of the many larger summer Milky Way areas that can be so spectacular.  That would be about a 2.5° FOV or thereabouts.  I think around 80x on the top end for now.  I know I use 75x frequently in my 100mm BT as well as pairs in the 40x or 50x middle range.  Three pairs of eyepieces will get you a long way., though.  I don't like switching eps a lot anyhow, it can break the magic spell sometimes.

 

You already have a scope for best higher mag planetary details.      If you like what you see at 80x, and think you want to push it more, you can still expand your collection later.  I rarely use my 150x pair, frankly, but in a pinch, if I don't have a scope out, they'll show me Jupiter's GRS and lunar transits, Saturn and maybe five of its moons as well as some decent lunar views if it intrudes into the night.

 

Rich

Now that I've had some time I think you absolutely nailed it!

 

My favorite EPs to use are the Pentax 10mm (56x) and the UFFs (23x). I've found that despite what I thought at first I am actually using the 23x far more and just like you I detest switching EPs.

 

I do have a question though. Looking at Saturn yesterday I think I might want a pair of high power (150x) eyepieces but I'm not sure I want or need super high end EPs. I don't think I need the FOV nor the sharpness across the field but having a nice, sharp center sounds really good for planetary viewing. 

 

So what would be a good set of EPs for planetary viewing? Something around the 4.5-3.5mm FL...

[Rich V.]

For me, around 120-150x is where planetary views start to be worthwhile in any instrument.  That's in the range of 4.5-3.5mms for you.  In a BT, I can see some finer planetary and lunar details but just not as clearly as in a telescope. Like is said in another post, BTs are a little muddled as would be in poorer seeing.  More than 150x in my 100mm BT would clearly be "empty magnificaton" with no further detail to be seen.  

 

In my typical seeing here next to mountains, my 130mm refractor shows me much more detail and I can push the mag much higher.  No scope I've ever looked through here along the Sierras has shown more detail than my c9.25 has under rare exceptional seeing.  That includes large dobs, sadly.  

 

Rich

[jrazz]

I completely agree. The BT is not the right instrument. I think I'm in the same boat as the "one eyed viewing" thread. If I only take the BT out, and I want to view planets, what would be a serviceable eyepiece set? Good enough to see details, cheap enough not to care if I only use them 5% of the time. I am not in the one-eyed viewing club. I really like using both barrels.  

 

I have a 5mm Pentax SMC-XW that I use on my Dob but I am eyeing (pun?) a set of BST 4mm eyepieces. They're $116 for the set and I won't feel bad about throwing them in the case and using them from time to time. Are they going to be as nice as a pair of Pentax EPs? Don't think so. Would they be serviceable? I guess that's the question

 

 

BTW, I tried my Dob at 240x (5mm) yesterday on Saturn and was really disappointed. It just didn't have the detail the BT-100 had at 80x. I know that's weird but it seems in line with what you said above. I was seeing Saturn in a really good site with fairly calm air while the dob was at home with less than ideal conditions.