Pentax 7x50 Marine Binocular (1 Viewer)

This week I found myself needing something with a larger exit pupil than I had on hand for some experiments with exit pupil size versus eye pupil size.

I was looking on the auction site for something very cheap because I thought it would just be used for a few tests and retired to the “reference bino” pile.

I found a Pentax 7x50 Marine for $135 shipped. The fact that it has a compass and reticule on it is a plus to me, being a surveyor. It probably does not appeal to many others.

I received the binos Thursday evening by way of the Fed Ex truck. It may have been the large objectives, but first impression was these were pretty good for $135 so I decided to kill a few hours today (Saturday) and do a few basic tests to see how they actually compared to my usual choices.

Long story short, these are approaching about the Monarch ATB level. I have attached some basic measurements in two PDF's because of pictures and file size. Those who are upset by numbers can quit reading here.

Best
Ron

Wow, great information. In the set 1 file, what do the two images in "basic view" represent? One definitely looks sharper than the other. Great illustration of edge sharpness; was that the point?

On set 2, do you have some really bad jpg or PDF conversion artifacts on the first two images or is that pretty true to actual?

Which Monarch ATB are they comparable to? I wasn't under the impression that the Monarch was a particularly noteworthy reference - not bad just not sure of meaning.

Any event, I've rarely met a 7x50 I didn't like. I love my Olympus EXPS.

Matt_RTH said:

Wow, great information. In the set 1 file, what do the two images in "basic view" represent? One definitely looks sharper than the other. Great illustration of edge sharpness; was that the point?

On set 2, do you have some really bad jpg or PDF conversion artifacts on the first two images or is that pretty true to actual?

Which Monarch ATB are they comparable to? I wasn't under the impression that the Monarch was a particularly noteworthy reference - not bad just not sure of meaning.

Any event, I've rarely met a 7x50 I didn't like. I love my Olympus EXPS.

Click to expand...

Matt the basic photos I keep setup most of the time so I can just point a bino at it and get some basic information. The grid lines are 1 degree increments with .1 and quarter degree tick marks, the circles are radially spaced 1 degree. This is the target I use for checking collimation also. The picture showing the 5 minute grid is of the center of the left target boosted to 42x. The USAF is just printer quality but element 2-1 represents 1 minute so it gives a fair idea of the defocus for various points in the FOV.

The crappy photos for the K values were done by importing the basic images into autocad so I could calculate and overlay the K grids. I just did a screen capture of the results, so you are looking at screen resolution.

The only reason I mentioned the ATB's is because it is one of the few budget binoculars I am familiar with and they are pretty much regarded as one of the top in their price range, $250-$300.

Have a good night
Ron

Nice work, Ron!

Thanks Henry.

Matt, et al,

A few more comments about my basic test that may not be obvious to most. This target has some of the following advantages:

The same view from different optics and tubes;

Consistent lighting;

Consistent focus, infinity;

View of full FOV (with eyes, depends on camera);

All points in the FOV are a consistent distance or focus distance;

In the USAF portion, group 2 element 1, a black line is about equivalent to a 1x5 inch object at 100 yds, quick resolution estimate;

Gives a quick estimate of focus and distance from center as a percentage of the FOV for any point in the FOV;

A quick way of estimating curvature or astigmatism with reference to the center;

You can zoom up any section and evaluate CA by width and position and width by reference to the tick marks;

Other curvilinear distortions by reference to the grid;

The consistent focus is useful for setting focus for other tests and for setting diopter, etc;


Visual check of horizontal versus vertical focuses any place in the FOV.

I am sure I am leaving out several and I tend to come up with other uses on the fly. The nice thing about this is it is very easy to set up and can be adapted to almost any lens. Very fast evaluations are possible between optics. Usually, a quick look will tell you what you want to know.

I have attached the target I use. It can be scaled to fit your needs but remember the USAF grid cannot be scaled since it is supposed to be a finite size so if you scale the PDF remember to allow for that.

Ron,
This kind of report is welcome for any binocular. I like 7x50s, but 7x50 roofs are rare, making it the more interesting to me at least. That MTF looks like a "double black diamond" ski slope! I suppose it would become less terrifying if you stopped the lenses down to something approximating the eye's pupil in bright daylight, say 20mm. Looking forward to the results of your intended tests.

It is just awesome that you can measure MTFs and transmission curves!
RonH