Binoviewer

[constantino]

I'd like to get a binoviewer to use with my 8se and I have a choice between Celestron (£200 bare unit) or William Optics (£280 including barlow and pair of 20mm EPs)

How likely am I to need the WO barlow and EPs? I was thinking of investing the £80 difference towards another 7mm X-CEL LX eyepiece (I already have one and very pleased) or 7mm Celestron Luminos (for 82* FOV)

Should these work ok with the Celestron bv and 8se without barlow?

Am I missing anything?

Thank you

[Stu]

You should not need the Barlow in order to reach focus with the 8SE as you have enough focus range. You can of course still Barlow to reach different mags, or you can obviously use different f/l eyepieces as you suggest.

Not sure which Celestrons you are referring to but there are other cheaper but just as good bare bones options out there. I have used TS and Antares variants which are great as they have self centring eyepiece holders and individual dioptre adjustment to help balance focus between channels which is important. 

http://www.teleskop-express.de/shop/product_info.php/info/p1855_TS-Optics-Astro-Binoviewer-for-telescopes--with-compression-ring.html

[alanjgreen]

As the 8SE is an SCT type scope, the barlow is not needed to reach focus - you have a huge focus range available with the SCT.

I used a bino on my C11 without a barlow. But I needed a barlow to get focus with my Lunt refractor.

You will be fine without the barlow.

A further point about the 82 degree eyepieces that you mention - they will be overkill in a bino as you are unlikely to get your eyes close enough to the binos to make use of the full FOV - your nose will likely prevent this. 70 degree eyepieces are perfect in binos so save some money here.

 

[constantino]

Many thanks both.

I understand binoviewers may increase magnification, even without a barlow.

At the moment I can use my X-CEL LX 7mm for planets/moon but I'm wondering if it could work well with a bv or the total magnification will be too high?

If too high then maybe I need to get a separate pair of slightly less magnification (8-10mm?)

[Louis D]

2 hours ago, constantino said:

I understand binoviewers may increase magnification, even without a barlow.

Yes, you'll either need to add a barlow nosepiece to reach focus (I use the front of a Meade 140 APO 2x on mine) or move your mirror forward to throw the focus point further back.  Doing either increases the magnification, though very little with the latter in comparison to the former.  Moving your mirror forward also increases spherical aberration in the image because you're moving away from the optimal mirror separation of the design.  Many folks won't notice the added image aberrations, though.

I highly recommed the self centering eyepiece holders.  Without them, it can be difficult to merge the images.  I also recommend eyepieces without safety undercuts when using said holders because they tend to pop eyepieces upward at cockeyed angles during tightening.  I find I have to mash them down into the holders while tightening to avoid this popup effect.  You can fill in the undercut with automotive pinstriping tape to good effect.

The only downside to holders with diopter adjustments is that they will preferentially spin when changing focal lengths with zoom eyepieces.  I find I have to crank down the diopter adjusters as tightly as possible to avoid this.

I find 60 to 65 degree eyepieces to be about right when using binoviewers because you can't swivel your eye around to take in the whole view without lose one or both exit pupils.  They seem much wider in bino mode than in mono mode.  Good eye relief is also important so you can get the bridge of your nose between the eyepieces.  Too little, and you'll need quite narrow eye guards.

The usual challenge is trying to get to lower powers with binoviewers.  Many folks use 24mm Panoptics, but these will vignette with 22mm to 23mm clear aperture, entry level binoviewers.  I've found the 23mm 62 degree aspheric eyepieces on ebay work well for this function for not a lot of cash outlay.

[alanjgreen]

You are correct. As you move the primary mirror in to reach focus in the SCT, an increased magnification is the result.

It used to turn my 24mm into 21mm (ish) in the C11 (2800mm focal length)

The C8 is 2050mm focal length so your 7mm is giving almost x300. If the primary moves increases this further then at >300x you are limited on the useful targets!

I personally would not start with a pair of 7mm, you will not get much use out of them. I would be looking for something around x150 for good everyday use, so a pair of 14mm would be a good start. You can't go wrong with a pair around 20mm either. (x100 is a really useful magnification). My most used pair is a pair of 24mm which gave me around x120 on the C11 and gives me x125 on the big dob (where I use a x1.7 glass path compensator [barlow]).

Alan

[constantino]

11 minutes ago, Louis D said:

Yes, you'll either need to add a barlow nosepiece to reach focus (I use the front of a Meade 140 APO 2x on mine) or move your mirror forward to throw the focus point further back

Are you sure I need this on Celestron 8SE with a Celestron binoviewer? Other people seem to think barlow is not necessary with 8SE

This is the EP I use most at the moment (7mm) and  I was planning to get another one:

https://www.firstlightoptics.com/celestron-eyepieces/xcel-lx-7.html

or 13mm: https://www.lcegroup.co.uk/New/celestron-ultima-lx-13-mm-eyepiece-_3790.html

 

[Stu]

20 minutes ago, constantino said:

Are you sure I need this on Celestron 8SE with a Celestron binoviewer? Other people seem to think barlow is not necessary with 8SE

Louis is saying that you need the Barlow on a refractor, but the focus range on an SCT is enough to accommodate a Binoviewer without a Barlow. The point is, I think, that by increasing the distance to the eyepiece when using binoviewers, i.e. having a longer light path, you increase the focal length so increase the magnification a little.

This is an interesting thread from Yong on the subject.

 

[constantino]

Many thanks all. I got the Celestron BV in the end (about £175 delivered from US, https://www.celestron.com/products/stereo-binocular-viewer ) and an additonal 7mm EP (https://www.tringastro.co.uk/celestron-x-cel-lx-7mm-eyepiece-594-p.asp)

I also ordered a pair of 13mm Celestron Ultima LX (http://www.opticstar.com/Run/Astronomy/Astro-Accessories-Telescopes-Celestron.asp?p=0_10_5_1_4_15) but a bit concerned about the size...not sure if they will fit.

Haven't had the chance to test them yet due to the weather but will let you know how it goes, as soon as we get some clear sky.

[Louis D]

1 hour ago, constantino said:

I also ordered a pair of 13mm Celestron Ultima LX (http://www.opticstar.com/Run/Astronomy/Astro-Accessories-Telescopes-Celestron.asp?p=0_10_5_1_4_15) but a bit concerned about the size...not sure if they will fit.

I tried the 17mm Astro Tech AF70 version of these, but my nose was being jabbed by the upper housing edge.  The Celestron version is shaped differently, but might still have similar issues.  You will have the issue of trying to tighten the locking screw through the little notch in the 2" barrel since the Celestron version's 2" barrel is nonremovable, unlike the Astro Tech version.  You might need to go to the hardware store to find longer replacement screws.  I found it best to stick with smaller form factor eyepieces in binoviewers.

[YKSE]

Congratulations for entering the binoviewer world.

Merging the image is the first big obstable (to me at least), so try to siege the oppotunity for testing it on the Moon.

My guess is that your choice of EP pairs is a bit on the high-mag side, shorter focal length EPs are more difficult to merge than longer ones, using barlow or OCS with longer fl EPs is a way mitigate the merging difficulty too. The Ultima LX are monsters, For not using a barlow or OCS, I'd have chosen 9mm(or 11mm) X-cel LX and 18mm ) X-cel LX, if I were you.

[constantino]

I already had a 7mm X-CEL LX which I worked well for me...so I thought I'd try a pair. I will probably go through a few different sizes/pairs until I figure out what works for my eyes/setup

 

[constantino]

On 8/3/2017 at 15:24, YKSE said:

Congratulations for entering the binoviewer world.

Thank you - to say "Impressive" is a massive understatement. I only managed to peek at the moon (between passing cloud patches) but I found the experience mind-blowing, compared with standard one-eyed viewing.

I used the 7mm X-CEL LX I already had (and bought an extra one on ebay). I found merging the images was surprisingly easy...not sure if it was just my luck or credit to the BV/EPs. Achieving a crisp image on 7mm took some fiddling with the focuser, but worth the effort. Now I'm wondering if am 8-9mm would be easier to focus while keeping the impressive high magnification.

I also tried a Luminos 7mm (mono viewing) but despite the advertised 82º , the FOV seemed narrower than my 7mm X-CEL LX I already had (60º) - not sure if that's "normal" or because of my setup

I didn't have the energy to keep going to test the 13mm Ultima LX (already long past midnight when the sky became clear enough) but hoping summer isn't over yet, so looking forward to the next session.

[Stu]

Great news! Hope you continue to enjoy them. I mainly use mine for high power solar observing but the moon is very good too.

[YKSE]

Glad that you had easy time for merging.

IME, 7mm might be too high for binoviewing with f10 SCT, with binoviewer without GPC, C8 is operating around f12 (110mm binoviewer length increases scope's focal length with about 340mm), you were practical using 340x on the Moon, the focusing difficulty you had were likely the atmospheric disturbance. Also, without GPC or barlow, the increased focal length of SCT resulted in too much inward focus travel, i.e. much more forward moved primary mirror, therefore increased spherical aberration, which contributes to less sharp image too.

That 7mm Luminos has narrower AFOV than X-cel LX seems odd, are you sure you saw the field stop in Luminos? it has shorter ER and wider AFOV, you need to place your eye noticeable closer to see the field stop.

 

[Louis D]

On 8/10/2017 at 02:02, constantino said:

I also tried a Luminos 7mm (mono viewing) but despite the advertised 82º , the FOV seemed narrower than my 7mm X-CEL LX I already had (60º) - not sure if that's "normal" or because of my setup

That's probably because of the reduced eye relief of the Luminos relative to the X-Cel LX.  It's more difficult to cram two eyes in close enough, and then hold still enough, to take in an 82 degree view than it is with one eye.  The IPD has to be set perfectly or you'll lose one or the other.  You also have to hold perfectly still which gets tiring.  I've found that 60 degrees is about perfect because you can't swivel your eye around to take in more anyway without lose either or both views.  I've found that 60 degrees looks way wider in bino mode than in mono mode, so I don't miss my 72+ degree eyepieces at all in bino mode.  Stick with 60 to 65 degree, longer eye relief, narrow eyepieces with binoviewers and you'll be happier for it.

On 8/10/2017 at 02:02, constantino said:

I didn't have the energy to keep going to test the 13mm Ultima LX (already long past midnight when the sky became clear enough) but hoping summer isn't over yet, so looking forward to the next session.

You may find that the Ultima LX is too wide to use comfortably in binos.  I couldn't use their bretheren, the Astro Tech AF70s, in binoviewers for this reason.  The top edge cut into the bridge of my nose.

[Louis D]

On 7/17/2017 at 08:27, constantino said:

Are you sure I need this on Celestron 8SE with a Celestron binoviewer? Other people seem to think barlow is not necessary with 8SE

Let me clarify.  It's not necessary to use an extra optical element to bring binoviewers to focus in SCTs and Maks because they have such large amounts of available back focus.  This is achieved by moving the primary mirror forward during focusing.  This motion is magnified by the secondary, moving the focus point backward immensely based on small movements in the primary.  However, moving the primary so far from its optimal design point introduces additional spherical aberration into the image which degrades the sharpness and contrast of the image.  Many observers never notice this, other more experienced observers may become annoyed by it.  It also increases the focal length of the scope, decreasing true field of view.  If you're going for magnification, this is actually a benefit.

To start with, just bring the binoviewer to focus using the SCTs focus knob.  If you find the image pleasing, then there is no need to invest in any optics to extend focus through the binoviewers as would be required for a Newtonian scope.