Eyepieces for binoviewers.

[Franklin]

I've doubled up my SLV 25mm and SLV 12mm for use in a binoviewer. Does it make any sense to go shorter than 12mm, like a pair of SLV 6mm or is it better just to barlow the 12mm's for higher power?

 

[Ricochet]

If you can achieve focus with a more powerful barlow then that would usually be the better way to go as it will narrow the light cone entering the binoviewer and reduce prismatic effects. However, with my binoviewer I see some additional reflections with the more powerful barlow so you may find that smaller eyepieces are preferable in that instance. 

[Stu]

The commonly held view on this is that it is better to Barlow than use short focal length eyepieces. That’s certainly the route I follow; I only have 25mm orthos for solar white light, and Barlow them like crazy to get powers up to x200 in my Tak. I like the large exit lenses and comfortable eye relief. There is sometimes concern that merging images is harder in short focal length eyepieces.

However…. there are no hard and fast rules in this game. @Highburymark has just purchased a second 4mm TOE (off me!) and has had some good early success with them with images merging easily.

So, it seems likely that either route can work well. If going shorter then I would choose eyepieces with good relief. The SLVs have this, plus a good reputation for sharpness so could well be worth a try.

 

[Paz]

I stick with longer wavelength eyepieces for binoviewing and Barlow them. I have the following pairs for binoviewing...

40mm and 30mm Vixen NPLs - used mostly for solar to bring down the magnification.

20mm SLVs sometimes for solar mostly for lunar.

17.3 Delos - used for all sorts of targets but in particular dso binoviewing.

15mm and 12.5mm plossls - I got these just to try shorter focal lengths. They do their thing ok but I don't really use them due to short eye relief.

If I can find a second 12mm Delos I'll add a pair of those to my binoviewing lineup and maybe a pair of SLVs at 15mm or 12mm would also be used  but 12mm would be the shortest I would probably go with binoviewers. 

[Louis D]

I like to use cheaper 60 degree wide fields that perform perfectly at f/18 with a Barlow element operating at 3x to keep down weight and bulk.  I can't get my nose between pairs of Delos or Morpheus.  That, and the combined weight of two Delos and binoviewer is just too much for most of my scopes.

[Highburymark]

14 hours ago, Stu said:

The commonly held view on this is that it is better to Barlow than use short focal length eyepieces. That’s certainly the route I follow; I only have 25mm orthos for solar white light, and Barlow them like crazy to get powers up to x200 in my Tak. I like the large exit lenses and comfortable eye relief. There is sometimes concern that merging images is harder in short focal length eyepieces.

However…. there are no hard and fast rules in this game. @Highburymark has just purchased a second 4mm TOE (off me!) and has had some good early success with them with images merging easily.

 

It’s an experiment really, knowing I could easily sell on the extra eyepiece if things didn’t work out. So far have just tested the TOE 4mm pair during the day with 60mm and 120mm refractors in two binoviewers - Zeiss and Maxbright II - and all combinations merged very nicely. I was slightly conscious of a little eye strain at first, but that feeling disappeared after a few seconds. If binoviewer isn’t perfectly collimated though, I can imagine that using 4mm EPs or similar would be an unpleasant experience. Floaters seemed to be well controlled. The major issue will be dimness - hence will only be usable on the Moon, and I hope, bright planets. I’ll try them with a Herschel wedge but think I’ll be happier with longer eyepieces for solar.