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Pentax 7x50 PCF viewing issue

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#1 aa5te

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Posted 27 January 2013 - 04:07 PM

I purchased a Pentax 7x50 PCF (made in Japan) some time ago that required complete disassembly to clean (it had been submerged for some time in my estimation). The views are crystal clear, vivid, sharp, and very contrasty. But, I notice that, no matter how well I've conditionally aligned it (I've checked, rechecked and re-aligned it with objects a mile away; it's better aligned than some of my other binos), it always seems to make my eyes feel funny, a bit crossed inwards after viewing for a few minutes, and it seems to have the worst "rolling ball/fisheye" effect when panning of any bino I've used. When I pull it away from my eyes and immediately naked-eye refocus on the object I've been viewing, my eyes undergo a slower and more laborious job of having to refocus than with any other pair of binos I have (I've tested this with other 7x35s, 7x50s, and 8x40s). Any ideas here? Or are these notorious for that rolling ball effect?

Also of note is that the field stops of both barrels overlap but don't merge; as far as I can tell, this seems to be somewhat common with this bino and the 16x60. Disassembly/cleaning

#2 Mark9473

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Posted 27 January 2013 - 04:18 PM

Check the collimation on a bright star with one side in focus and the other side completely out of focus. If the dot and the blob don't overlap, collimation is off.

#3 KennyJ

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Posted 27 January 2013 - 04:20 PM

You appear to have ignored the comment made in the linked thread about this bino still being out of alignment.

In my experience,"eyeball adjustments" in daylight using objects a mile distant are not guaranteed to produce collimation within the tolerances required for astro use.

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#4 aa5te

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Posted 27 January 2013 - 04:39 PM

You mean the one by RichD w/regard to EdZ? Nah, I didn't ignore it at all. I was just wondering if there was something I was overlooking or if this was common problem with this bino.

#5 aa5te

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Posted 27 January 2013 - 04:41 PM

Check the collimation on a bright star with one side in focus and the other side completely out of focus. If the dot and the blob don't overlap, collimation is off.

Thanks, Mark. I'll give that a try ASAP. It's supposed to be cloudy here tonight, though.

#6 KennyJ

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Posted 27 January 2013 - 04:49 PM

Yes, what you appear to be overlooking is that the bino is NOT likely to be collimated, which is why you are seeing the overlap and why looking through them is temporarily damaging your eyesight.

It probably ISN'T/ wasn't a COMMON problem with that model, but whether it was or not seems almost irrelevant as far as the existing problem goes.

Kenny

#7 EdZ

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Posted 27 January 2013 - 04:51 PM

You mean the one by RichD w/regard to EdZ? Nah, I didn't ignore it at all. I was just wondering if there was something I was overlooking or if this was common problem with this bino.


it's certainly not a common problem.

I do agree that I would put a lot more emphasis on merging of stars tthan I would put on any terrestrial "alignment".

#8 GlennLeDrew

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Posted 27 January 2013 - 06:06 PM

Another possibility is that the images are differentially rotated with respect to one another. This would be caused by a prism slightly rotated out of square.

#9 BillC

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Posted 27 January 2013 - 10:56 PM

i.e. lean.

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#10 Gordon Rayner

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Posted 28 January 2013 - 02:15 AM

You list an Orion binoviewer in your collection of instruments:

Remove the eyepieces, and look backward through the binoviewer at a star. The images should be superimposed. If not, then adjust the BV ( if it is adjustable) until the two images are superimposed.

Use the BV backward, without eyepieces, as a comparator to check for superposition of the two images of a star seen through the binocular telescope and the BV.

Similarly, use the backward, eyepiecesless BV to compare the images ,through the binocular telescope, of a flagpole, building edge, etc. for superposition and absence of any relative rotation, "lean".

#11 GlennLeDrew

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Posted 28 January 2013 - 09:31 AM

To augment Gordon's useful comments...

If the binocular has been conditionally aligned for your IPD, the binoviewer must be set so that it can test at that IPD. Due to the BV's rear prism apertures being larger than the bino's exit pupils, there is some room for over- and under-adjustment on the BV's IPD, but perhaps not enough to find a setting where the BV's own internal mis-collimation is minimal and at the same time allow both images from the binocular to be seen simultaneously. If so, don't worry about it; use what you've got. If the BV does noticeably displace its two images, you could note the offset and see if that same offset is seen through the binocular; this will indicate good collimation.

The checking for image lean will be tricky, if not impossible. Your eye us forced so far back from the bino's exit pupils that only a very tiny fraction of the field can be seen. I suppose you could examine a vertically oriented object and tilt the BV in the up/down plane to sweep along its length, looking for a variation in horizontal displacement.

#12 Gordon Rayner

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Posted 28 January 2013 - 01:38 PM

One might add a low power , inverting or non-inverting, telescope to the reversed binoviewer, to magnify any errors. 2x or 3x would be useful. Those are not easy to find. I have used 5x20 golf scopes experimentally, instead of my 1920's antique Navy inverting auxiliary scope at 2.5 or 3X (?), but 5x is very sensitive and difficult to use freehand. Perhaps a 2.5X air rifle or a pistol sight ( which have very long eyerelief), or other weapon sight?

Mounting this magnified test equipment, perhaps with an angular motion available to sweep up and down, or side to side, as suggested by Glenn above, could be helpful.

#13 aa5te

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Posted 28 January 2013 - 07:49 PM

Thanks for the advice, Glenn and Gordon! I'll give those a try as soon as possible.

#14 Gordon Rayner

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Posted 29 January 2013 - 12:46 PM

The crosshair in a low power weapon sight can be useful to check for lean, alone, without attachment of the sight to a reversed binoviewer or to the JTII "hand collimator" or equivalent:

As described in US Army repair manuals,and repeated in 1953 book by Truman Henson (published by Greenberg, New York, long out of print, but in some libraries) such a scope is mounted on a surface gage, which is then slid on a straightedge or other support with two flat surfaces, between the eyepieces of the binocular.

That arrangement also shows the parallelism, or lack of it, of the two optical axes , at one interpupillary distance. If the setup is rigidified, such that the weapon sight, a line from the target center, and the hinge, are parallel, 3- axis parallelism of the binocular can be checked to within tolerances which have been satisfactory for some collectors/hoarders who had high quality binoculars without the mechanical shortcomings of many modern low price imports .

Surface gages are used on flat surface plates, for pre-machining layout of metal parts. Blue dye-paint is used to show the lines made by the sharp scriber tip mounted on the surface gage. Adjustments provide angular motion around the axis of a tiltable arm.
For the use described above, the two cylindrical pins should be in their down position , to slide against the vertical flat edge of the straightedge. The body of the surface gage is held by gravity against the horizontal flat surface during the slide. Enco, Manhattan supply, Starrett, Lufkin(?), Brown & Sharpe, and the other usual suspects.

Deja vu. (Please add the right sloping and left sloping accent marks, if desired.)

#15 BillC

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Posted 29 January 2013 - 09:07 PM

Dear Genial Procrastinator:

I thought about doing a series or articles on the problems caused by that. But, I've just never gotten around to it! :shocked:

BillC

#16 Gordon Rayner

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Posted 31 January 2013 - 07:28 PM

A series of articles about procrastination? Or, if you mean information about Army-Henson sliding surface gage technique shortcomings, just one submission, to this forum, should suffice.

Whatever its limits, Army-Henson provides an easy check for lean.

#17 BillC

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Posted 31 January 2013 - 08:46 PM

In the immortal words of Mr. F. H. Leghorn:

"I keep throwin'em and you keep missin'em."

It was a joke.

BillC






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