BTX collimation issue (3 Viewers)

[Birdister]

Perhaps those who are experienced in the technical aspects of optics can answer this question.

I have a BTX unit which has developed what appears to be an issue with collimation. If I look at the top of the image, there is an overlap between what can be seen in the left image and when can be seen in the right image. I have posted two cropped images below to show this. You can see that the leaves in the left eyepiece are cut off compared to the right. The overlap is quite noticeable and if I look at it I start to get a bit of eye strain.

The unit has been back to Swarovski twice (!) and I have been told that there is nothing wrong with it. But there is, isn't there?

 

[Binastro]

The actual collimation procedure can cause overlap.

Probably other BTX units have less overlap or even no apparent overlap.

Once you notice this, it may be difficult to ignore.

Show Swarovski your photos, preferably several at different distances.

I don't know what they will do.

Regards,
B.

 

[jring]

Hi,

from what I know about bonoculars (and the two times I had the privilege to a try a fellow birder's very good example of BTX95), I would expect to have the images of two barrels of a well collimated pair to have very much to complete overlap...

But the image of from the view through the left EP looks quite wrong to me - like serverly truncated exit pupil - that is if the dark triangular area is really the edge of the exit pupil...

Can you take images of the whole exit pupil?

Joachim

 

[Birdister]

The dark area in the view through the left eyepiece is an artefact - I was hovering over the eyepiece with my phone to take the photograph.

It would be helpful to know if other BTX users have an overlap.

The response from Swarovski has been to say that there are certain 'tolerances' involved with optical equipment, and that the BTX unit is within those tolerances. But their latest suggestion has been to 'go below the tolerances', whatever that means (which would naturally involve a third trip to Austria and a total of six months without the use of the telescope).

I just find it hard to accept that having a significant and noticeable overlap between the two images is normal and to be expected. We are not talking here about a cheap telescope. This is meant to be a precision instrument.

 

[Birdister]

Swarovski have now confirmed that they are not willing to provide me with a loaner, and so the only option is to send it in for a third time, lose the use of the telescope for another two months, and pray that they actually bother to fix it. Atrocious customer service.

 

[Ignatius]

Maybe you could offer them to buy this POS back at a reasonable price. Say 3% under list price, it being gently used and all, well, almost never.
Luckily my BTX 85 seems to be a thoroughly good one, unless this starts developing at later stages too. But on the whole I appear to be reading quite a lot recently about quality issues with Swarovski products. Maybe just as well, that my equipment list is currently shifting towards the big Zed with my Swaro gear being sold off piecemeal.

I wish you luck, even though at these prices, luck should have absolutely nothing to do with it.

 

[DRodrigues]

...

It would be helpful to know if other BTX users have an overlap.

The response from Swarovski has been to say that there are certain 'tolerances' involved with optical equipment, and that the BTX unit is within those tolerances. But their latest suggestion has been to 'go below the tolerances', whatever that means (which would naturally involve a third trip to Austria and a total of six months without the use of the telescope).

I just find it hard to accept that having a significant and noticeable overlap between the two images is normal and to be expected. We are not talking here about a cheap telescope. This is meant to be a precision instrument.

I don't understand what you are complaining about...
Do you have regular binoculars? Even on binoculars there are an huge amount of overlap, that try to replicate what your eyes see normally - without binoculars, there is an huge overlap on what each of your eyes see...
I'm not a BTX user but an binoviewer user - see CR-binoviewing - the BTX module has a binoviewer - by the way, the best I've seen, without visible artefacts, common on other binoviewers...
Unlike using binoculars, using binoviewers you get a "pseudo binocular" view with a "false sense of field-dept" since the overlap on both eye images is complete or almost complete - on binoculars the overlap isn't so complete. So a binoviewer is collimated when vertically you see both images at the same level and horizontally there is also a complete overlap or the left image shows a bit more field to the left than the right image, and vice-versa.
If you don't use binoculars, that probably explains your problems with the BTX - my wife isn't able to use binoculars comfortably...
When you are having problems of merging both eyes images, assuming you have adjusted correctly distance within your BTX eyepieces, it helps if you close one eye and focus the other, do the opposite (and confirm the focus position is the same - other wise adjust it on the eyepiece - don't remember what eyepiece have focus adjusting...), and then use both eyes again.

 

[grackle314]

Thanks for your post details and question. Here are some observation results with your post in mind. For these observations, a BTX115 with no extender was used, i.e. 30x setup. Observing focussed on the region at the top of the view, from about 11:00 - 13:00 on object around 50 m away, bright daylight.

First, focussed with left eyepiece and having set interpupillary distance for my normal viewing. Focus set up on left eyepiece with left eye without wearing glasses. Observe image along the exit pupil edge.

Second, move left eye over to right eyepiece and focus using diopter adjustment. Compare image seen on both eyepieces with same eye. There is some top edge difference between the two.

Third, return to left eye on left eyepiece. Move eye around and in/out some, no change in image edge along top of exit pupil observed while moving eye.

Fourth, return to left eye on right eyepiece. Move eye around and in/out some, change of image edge along top of exit pupil observed dependent on eye position. Broaden the observation to note that eye position around and in/out and diopter adjustment on right eyepiece caused varying level of image edge difference compared to left eyepiece. There was a diopter and eye position setting for me where there was zero observed difference between right and left eyepieces using my left eye. Same result for my right eye, there was a combination of diopter and eye position where there was zero observed difference between right and left eyepieces.

To be roughly quantitative, at 50 m there was a maximum total range of image non-overlap of about 5 mm (+/-2.5 mm from overlap) by moving diopter setting and eye position. I note camera placement on BTX can be similar to the eye position variation discussed here. A total non-overlap range of 5 mm at 50 m is an angular difference of 0.0001 radians or 0.0057 degrees at the test distance, seeming well under 1 degree apparent.

While your question is addressed directly in my observations above, I also note that I never see such non-overlap of images anywhere in my normal imaging using the BTX, regardless of whether I am using glasses or not and have different eye location and diopter setting in those different circumstances. I always strive to put objects of interest more to the center than the outer 1 degree of apparent observation. My observations above apply only to the top outer edge as described. It appears the diopter setting and eye/camera placement of the right eyepiece give the variation you describe. It also appears there is a setting where such non-overlap is not observed. This might warrant a change in glasses prescription for a person unable to achieve satisfactory non-overlap at that very top edge.

I use the Swarovski phone adapter on the BTX for use with my mobile, this uses only one of the eyepieces so the overlap issue does not register in the individual images.

 

[rollingthunder]

I have recently purchased the BTX module, to go with both the 65mm and the 95mm. I haven't had any of these issues and as it is under warranty it would go straight back to the dealer. I also have the excellent 12x42 NL Pure binoculars. The new VPA2 phone adapter and the 2 rings needed both work well and are quickly attachable.

The BTX module is very comfortable to use. I am happy to use it for hours if required. I have the angled module so a choice of viewing and zoom options are available but the BTX is a game changer and sits on the 65mm for general birding as it is a lighter weight combo to cycle and travel abroad as hand luggage.

Swarovski is not cheap and has to be right - just saying that I have had no problems and no regrets with the equipment purchased.

Good birding -

Laurie -