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A couple questions about digi-binning (1 Viewer)

pbjosh

missing the neotropics
Switzerland
Hello folks,

I'm not particularly versed in digiscoping / digibinning but have done a bit here and there.

In any case, lately I've been trying to understand optical distortion in binoculars more and I've been wanting to take photos of the FOV of some of my bins in order to see a fixed image without my accommodation.

For reference, at the moment I'm playing with two bins with relatively large AFOV (Kowa BDII 6,5x32 and Nikon MHG 8x30), and using an iPhone 8 Plus that has two rear cameras - 28mm equivalent and 56mm equivalent. With the 56mm I cannot even begin to capture the entire FOV. With the 28mm I can get close but I can't seem to get it all. I assume this is just an artifact of the AFOV of the binoculars, and thus the angle of the cone of light coming out of the objective lens, being greater than the FOV of a 28mm lens? Or is there something that can be done to capture the entire FOV?

A second question - does anyone have recommendations for more successfully handholding a cel phone to bin? Perhaps a good home-brew adaptor? I find it very difficult to align the phone and the exit-pupil of the bin reliably and completely avoid vignetting or blackouts.
 

Hauksen

Forum member
Hi,

A second question - does anyone have recommendations for more successfully handholding a cel phone to bin? Perhaps a good home-brew adaptor? I find it very difficult to align the phone and the exit-pupil of the bin reliably and completely avoid vignetting or blackouts.

3D printing might be one way to arrive at a solution.

Here's one adapter that's quite popular:

https://www.thingiverse.com/thing:3384088

Here's one I designed for myself:

https://www.thingiverse.com/thing:2836677

Mine is for digiscoping and only partially adjustable, but it's configurable before printing.

Regards,

Henning
 

pbjosh

missing the neotropics
Switzerland
Hi Hauksen,

I was thinking about milling something similar at some point in the future, then I thought about 3-D printing, but now I'm thinking I might just used a second tripod and build some sort of simple aluminum arm to hold the cel phone out about in the right location, and use a remote release of some sort.

I have had a couple phoneskope / phone cases that mate to scope eyepieces in the past and thought they were pretty much a waste of money. Too finicky, not-reproducible results, and too much work to change your phone's case every time you wanted to take a picture. So I didn't consider this kind of adaptor like you linked for this use. Do you have good results as far as ease / speed / repeatability of use?

Since I don't want to use this in the field, and want the best quality photo of the entire FOV with absolutely not vignetting / blackouts, the extremely finicky matching of the exit pupil to the cel phone lens seems more a problem of alignment than of mounting. Perhaps a second tripod with a micro-adjustable arm/mount for a phone, then use a remote release, might be easier. I'm imagining some milling/machining arm mounted on a tripod and then something as easy as an automobile cel phone holder or the like. It's the micro-control over the arm / mount positioning that is what seems difficult.

Further thoughts welcome :)
 

pbjosh

missing the neotropics
Switzerland
Also - regarding camera lenses and binocular exit pupils and FOV's:

A 28mm equivalent lens theoretically has about a 74-75 degree FOV, but you're only capturing onto a rectangular sensor, so there is a square crop of a circular FOV. So yeah, I can fit a binocular's whole AFOV (about 65 degrees) into the lens, but the phone's sensor will crop it. I will be able to see the field stop in the corners of the resulting rectangular image but it will almost certainly be cropped out at the top and bottom and perhaps also at the sides...

I guess you'd need a quite wide lens to capture the entire FOV as it would have to fit within the vertical crop of the sensor. With such a wide camera lens you are then introducing a lot of lens distortion in the resulting image, so I'll make do with the 28mm iPhone lens and rotate it around to capture the top and bottom of the FOV if I feel like it's necessary.
 

Hauksen

Forum member
Hi,

I have had a couple phoneskope / phone cases that mate to scope eyepieces in the past and thought they were pretty much a waste of money. Too finicky, not-reproducible results, and too much work to change your phone's case every time you wanted to take a picture. So I didn't consider this kind of adaptor like you linked for this use. Do you have good results as far as ease / speed / repeatability of use?

I would say that this was the most successful one I designed, measured by the criteria you mentioned:

https://www.thingiverse.com/thing:2800241

It's small enough you can leave your phone in and use it normally without the combo becoming too unwieldly, and it's quite quick to install and remove with repeatable alignment. As it's printed from nylon, inserting and removing the phone is quite quick too.

The downside is, it's totally non-adjustable either for different phones or different scopes.

Regards,

Henning
 

Chosun Juan

Given to Fly
Australia - Aboriginal
Also - regarding camera lenses and binocular exit pupils and FOV's:

A 28mm equivalent lens theoretically has about a 74-75 degree FOV, but you're only capturing onto a rectangular sensor, so there is a square crop of a circular FOV. So yeah, I can fit a binocular's whole AFOV (about 65 degrees) into the lens, but the phone's sensor will crop it. I will be able to see the field stop in the corners of the resulting rectangular image but it will almost certainly be cropped out at the top and bottom and perhaps also at the sides...

I guess you'd need a quite wide lens to capture the entire FOV as it would have to fit within the vertical crop of the sensor. With such a wide camera lens you are then introducing a lot of lens distortion in the resulting image, so I'll make do with the 28mm iPhone lens and rotate it around to capture the top and bottom of the FOV if I feel like it's necessary.

If you want to somehow map or determine a binocular's distortion profiles, then the best way to do that without introducing a whole host of other compounding distortions (either camera/phone lens, or indeed your own eyes) is - to turn it around.

ie. Photograph/ view through the objective end. This way you are using the central portion of the lens /eye which should be practically distortion free. The binocular's distortion profile will be in exactly the same positions and magnitudes, but reversed - pincushion appears as barrel distortion etc.

You can use either grid paper and/or a circular object to view which you then move the fixed lens+binocular rig over (most accurately on a perpendicular fixed distance jig). ie. if you move over a circular object (such as a screw head) along the horizontal axis, the changing shape of the circle as you move from the centre of the field to the edge will 'map' the distortions /AMD effects.

Just remember everything appears reversed !!







Chosun :gh:
 

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