chrispj

I looked again, and again, then tried the focal extender, then drew a line on the barrel with a Sharpie, took another look and then checked again... It is so slight I'd discounted it but yes the shoulder is there, as it should be. It did amaze me to think that a company with Takahashi's reputation might have missed such a feature!

Following up on Ags' test, on the last clear night here in Devon I did a similar completely subjective test, though given the results you might also call it an exercise in confirmation bias. Again looking at Epsilon Lyra. In this case the three diagonals are the StellaMira 1.25" 90° di-electric, the StellaMira 2" erecting prism and the Takahashi 1.25" prism. In all cases looking through the StellaMira 80mm f10 refractor. This was the first time out for the Takahashi prism so no idea what to expect here. First up, I worked my way down through the focal lengths and all 3 diagonals split both pairs with a 7mm Pentax XW. In the case of the di-electric, both components would merge into lozenges intermittently with the seeing, but not an unpleasing result. The 2" erecting prism normally lives in the ST102 (along with a 35mm Panoptic) as the second scope on my SkyTee as a super-sized RACI finder so hasn't been used at other than low powers before (looking at the likes of the moon and Pleiades through this have always been crystal clear and just beautiful). Through the erecting prism, both pairs were cleanly split, colours were more blue than the warmer colour of the di-electric, a definite discernable difference between the mirror and the prism. Now for the Takahashi, and this may be where the confirmation bias steps in. Not a distinct step up over the StellaMira erecting prism, but back to back for my eyes the stars seemed slightly tighter in focus, the split was cleaner. No great difference in colour. If I didn't try them back to back then I would be very happy with either image and struggle to say there was any difference between them. I stepped up to a 5mm StellaLyra LER and compared the two 1.25" diagonals. A clean split for both diagonals, but again a more pleasing image through the prism. Finally I swapped to the OVL binoviewer. I haven't used this on anything except the moon before and only for quite low power viewing. With a pair of Astro Essentials 20mm plossls, I swapped through first a 2x then 3x ES focal extender, splitting both pairs with the 3x extender (so ~6 2/3mm equivalent focal length). Merging the 2 views did become a challenge with the stars much off centre, which doesn't seem to be an issue looking at the moon. To finish I stepped up again to an ancient TeleVue 2.5x barlow, which seems to magnify slightly greater than 4x with the binoviewer so with the 20mm plossls would give <5mm equivalent or slightly higher than 160x magnification. Again, through the prism no problems to bring the stars to focus (I didn't try the mirror for this). Edit - I was wrong with this next paragraph - there is a safety stop, it's so slight that I'd discounted it but it is there. One thing to note with the Takahashi prism - unlike the StellaMira 1.25" mirror diagonal, there is no stop at the end of the eyepiece holder to stop an over-long barrel going in too far and impacting the prism. The ES 2x focal extender does have an exceptionally long barrel so I will need to fit a par-focal ring otherwise there's potential that I'll mark the prism over time. So to conclude, all 3 diagonals give a perfectly serviceable image, with the two prism diagonals for me giving a discernibly sharper and subjectively more pleasing image, the Takahashi prism being a marginal step up again on the SM prism.

Inspired by @Ags diagonal comparison (& my 1st piece of Takahashi kit!), a new prism diagonal....

Not any more, GM sold them to Peugeot a couple of years ago...

The postman delivered this just now: which (alongside the 2x FE and a 2.5x Barlow) gives me 2x, 3x and ~4x magnification for the 18.2mm Delites in the binoviewer, for an equivalent 9mm, 6mm and 4.5mm or 89x, 133x and 177x in the 80mmm f10 StellaMira. I can't remember last time we had a clear night with a moon to look at but given the forecast I'm hopeful for tonight....

Inspired by this thread I just picked up a slightly smaller case to hold my binoviewers with eyepiece pair, 1.25 diagonal, Barlows etc. There's room left at the moment to add a 3x focal extender if I can ever find one or possibly a pair of ~12mm eyepieces otherwise...

Thanks very to much to @Alan White for replying to my wanted ad that was posted in hope more than expectation and for very quick delivery: an 18.2mm Delite giving a matched pair for binoviewing. Now will the clear skies over Exmouth just now hold out until this evening...?

Ah, didn't realise the ES focal extenders worked similarly to the Powermates, that's good to know!

I did wonder about trying this, but there is a thread mismatch between the Televue Barlow lens cell and the BV nosepiece. Interesting to try different things and see how they work anyway...

Adding to this, this morning I tried an old TeleVue 2.5x Barlow I just picked up, without the 2x Barlow that came with the binoviewer. This freed up around 2cm of in focus, but appears to magnify to perhaps 4x given approx only half the FOV I could see with the 2x Barlow was visible. Intriguing, I might try a similar long 2x Barlow and see what result that gives (I presume somewhere between the 2) since its easier to swap out the Barlow than 2 eyepieces...

Out peering at the moon tonight with my new binoviewer. Lovely and clear until the cloud started drifting over around 21:00. Viewing with two eyes seems so comfortable and more immersive. The ST102 is set up as a supersized RACI finder with a 2" erecting prism diagonal, works very well with usually a 35mm Panoptic giving a good field of view!

The 2 new ones have been returned, the 2 second hand have passed on to a new owner so the short-lived BST chapter is over for me. But thanks for the suggestion!

It's probably wrong to say the Plossls aren't sharp, I'm stuffed with cold and not good with finding the right words today. More that being £25 Plossls the assumption would be the view can be improved (isn't that why we buy £200+ eyepieces!). I also have no idea on the width TBH - the Delite looks and feels like there should be no problem to use as a pair and from what I remember of the SLV (I had a 9mm before) that should be ok, OTOH my XW would almost certainly not work from the look of it! I haven't seen a Hyperion IRL, only photos. What would a Barlow be likely to do to the focus, I don't have much in-focus left to adjust so if it will be par focal or need out focus that would work. interesting ideas anyway, more to think about... Thanks!

After successful first use of my new binoviewer last night in the F10 refractor I'm weighing up options for additional eyepieces. I used a pair of Astro Essential 20mm plossl last night (essentially bought as a proof of concept), which worked well but obviously aren't the sharpest. I had the sad disappointment that the Starguiders don't work for my deep set eyes/long nose and I need to stick with types offering the full 20mm eye relief. I expect when they are back in stock I'll double up with a match for my existing single 18.2mm Delite. However I then have a big gap down to my next 10mm eyepiece. So I'm pondering either the 12 or 15mm Vixen SLV or the 13mm Hyperion. Concerns being the 15mm might not be a big enough jump in magnification from the Delite to notice a meaningful change, the exit pupil on the 12mm might be small for comfort (given the 2x Barlow in the binoviewer reduces it to a 6mm equivalent or 0.6mm EP - I struggle with my existing 6mm eyepiece sometimes), and there seems to be very few enthusiastic user reviews out there for the Hyperion. Any thoughts or other suggestions gratefully received. I can only really justify buying one additional pair unless the right SLVs start popping up secondhand...

Snap! The high cloud cleared after 9pm for me and I had my first look through the new binoviewer at the moon, using a pair of Astro Essential 20mm plossls. Lovely viewing, much more comfortable for me than using single eye. Will look forward very much to using them on the planets later in the year, though I'll need to add to my eye piece collection first...