Mythbusters - matched pairs for binoviewers?

[Moonshane]

During a recent discussion with DRT Derek, he asked about whether closely matched pairs are required for binoviewing as there seems to be a commonly held view that it's essential or at least 'best'. I shared this view and in my quest for a set of paired Televue plossls from 32mm-8mm I have always insisted upon similar models e.g. if the one I had already had the chamfered inset on the nose I definitely would only buy one with the same as its twin. However, I recently bought a pair of 32mm and one has the chamfered inset and the other the 90 degree inset. I did not check that they were matched and the seller has not had any issues with them being slightly different. The length of the nose is the same too so I am not that bothered if they work. Worst case is if my 'OCD' (occular comparison disorder) kicks in I could always buy another in due course and sell the odd one out. 

Looking online there are lots of threads suggesting that this idea of needing matched pairs is purely an urban myth / sales strategy for buying new. e.g. 

https://www.cloudynights.com/topic/258992-matched-ep-pairs-for-optimal-image-merge/

https://www.cloudynights.com/topic/569966-matched-eyepiece-pairreally/

I'll be able to tell hopefully later today if my 32mm are fine despite being from very different runs but would be interested to hear your own experiences?

Personally I am convinced there's not a problem as long as you use the same brand and basic design (and focal length naturally!) but it would be good to hear from others. I think that even if there were differences, either the diopter adjustments or your own eye/brain combo would be able to accommodate them.

 

[Racey]

Shane

I concur. Sussie and I have only one matched pair, the WO 20mm Plossls that came with the Binoviewers I bought from another member from this parish.

Since then, we've bought further previously owned plossls from the classifieds. We now have "pairs" of 32mm plossls and 12mm plossls. And don't see any adverse effects using the 32s and 12s when we swap them for the 20s.

It could be our untrained eyes, or the fact we're focusing on enjoying the targets rather than critiquing the eyepieces  An eyepiece reviewer might spot things we haven't. But we've not had any grumbles to date.

Simon

 

[Peter Drew]

I've found that mechanical differences have a more noticeable effect than any optical difference between eyepieces of the same stated focal length. I like my eyepiece tops to be level when focused. Small differences in stated focal lengths seem to have little effect in most cases but if you are using in excess of 4000mm native telescope focal length (16" SCT) then this soon adds up. 

[alanjgreen]

I also agree that "matched pairs" is nonsense (at least with Televue EPs). I have usually added a 2nd EP of one I already own to make a "pair" and have had no issues (with one exception that I will come onto)

I did purchase "2 of" on some occasions but these will likely be EPs "from the same batch" but suppliers just "pick 2 of the shelf" so they would not be "matched pairs" either.

I have had pairs of Panoptics, Delos & Delite and they have all been excellent

My only failure was a pair of 12mm Delos (which I bought as a "pair"), these would just not focus "at the same time" in my MarkV binoviewer. They worked great either individually or when inserted separately to both left & right sockets. But when used together they just reached focus at a very slightly different point. This would have been an internal eyepiece focal length or lens placement difference I think. The focus point difference was miniscule but it was enough I just moved on to something else and forget about it! Also note that I could still merge the image with no issue, just the image was always slightly out of focus!

The keys concepts to worry about when buying EP for binoviewing are eye relief (more is better) and FOV (huge widefields are not needed), so Delos/Delite are perfect with good eye relief and reasonable FOV.

Weight of binoviewer & EPs also needs to be considered, such that your focuser is not overloaded. I had to upgrade the basic chinese focuser on my LUNT to a Baader for example - as everything needs to be nice & solid.

 

Alan

[GavStar]

Alan raises an excellent point about mechanical aspects of binoviewing. I've found the systems can easily get too large and heavy if I'm not careful and create issues even for best feathertouch focusers. I have very different criteria for my eyepiece choices for mono and bino. Im like Alan - for bino I aim for small eyepieces that have good eye relief and medium fov (65 degrees or so) and decent but not necessarily top end optical quality.

On the original topic of matched pairs, I've not had any issues in this respect!

[Moonshane]

Cheers all

- looking good so far 

I agree on the weight front. This is one of many reasons I prefer plossls for BVs. I do though find it easy to merge even when using 11mm TVP (it's easier actually with these than my 15mm TVPs) and 10mm BCO. I am considering a pair of 8mm TVPs too and suspect I'll be fine with those.

[Stu]

Agreed about mechanical issues being more important. You may remember a little while back I bought a second 18mm a BGO (I think!) and it was different from my other one; the top of the eyepieces we at different heights and that was definitely something my OCD could not deal with. Sold!

[Moonshane]

I agree totally Stu and if the 32mm plossls would have had differing nose lengths it would have bugged me. in about 45 minutes I should be able to tell what the score is 

[Moonshane]

I am delighted to confirm that (at least in Ha) despite the 32mm plossls being obviously from different eras, they both performed excellently with literally no difference in the view and no merging issues. The only issue which was known was the ludicrous eye relief which I will eventually cure with the eyeguard extenders. Even if the extenders are bought new I am still more or less buy one get one free against overall new costs for a pair. I may still decide to make up a 'proper' pair in due course as the net cost will be negligible. I'm happy. There was a little vignetting but I am sure I'll still get full lunar disk in white light with the 120Ed and 2.6x gpc that's required for focus with the Baader wedge.

[Peter Drew]

As well as a full solar disc.  

[Moonshane]

LOL - I thought the lunar disk was a bit dim 

[Louis D]

Agreed about mechanical differences being far more important than exact focal length matching.  I have two 19mm Konigs that have their field stops at slightly different positions relative to their shoulders which makes using them a pain because first I have to get each focused individually and then I have to deal with one being a few millimeters higher at the eyecup than the other, which makes using them with eyeglasses a pain.  They are identical optically, though.  Coatings changed, but not the lens formula between the first and second one.  I can't detect any difference due to the coatings.

I have no problem matching focal lengths with my two Celestron Regal zooms that don't have click stops.  I just spin them both about the same amount, and then fine tune one to match the other once I'm at a magnification I like.

[DRT]

12 hours ago, Moonshane said:

The only issue which was known was the ludicrous eye relief which I will eventually cure with the eyeguard extenders. 

I might have a spare one in the case that I can sell you at the usual mate's rates

Let me check when I get home and I'll get back to you.

[Louis D]

On 5/18/2017 at 07:03, Moonshane said:

The only issue which was known was the ludicrous eye relief which I will eventually cure with the eyeguard extenders.

And yet I'm annoyed by their deeply recessed eye lens that makes using them with eyeglasses less comfortable.  I can't even make a 25mm/26mm plossl work very well with eyeglasses despite their generous eye relief because of this same issue.

[Moonshane]

Vive la difference!

[marcus_z]

Yesterday night I had a Takahashi Abbe 32 and a LE 30 together in my binoviewer - they match! You can do even nastier stuff with your brain, with focal length differences of 25%.