Mounting A Dot Sight on The Olympus 300mm f4

Carbonman

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I finally made time to finish the dot sight mounting project. The picatinny rail is mounted where it is at about 90° from the tripod mount because of the way I use a sling to support both the camera body and 300mm and minimize the stress on the lens mount. The permanent mounting should almost eliminate the need to realign the sight each time I go shooting. The sight comes off easily by loosening the pair of clamping bolts slightly.
Lexan Filler Plate.jpg
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300mm Tripod Collar Profile Scribed Out.jpg
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Bottom Lexan Filler Plate.jpg
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I would simplify my workflow and minimize the number of steps in the process were I to do it again. I would file out the scribed profile and not worry about making room for the slight curve of the tripod collar. This added a step of filling under the rail with epoxy to mimic the curves of the collar.
The only power tool I used was a Dremel drill. Other tools included vise grips, a good Starrett tap and tap handle, a sharp scribe, utility knife and a couple of sharp files. The other useful clamp was a pair of Peak Design messenger bag tripod fastening straps.
A quick thanks to Harvey Melvin Richards for his technical advice.

Drilled & Tapped Mounting Hole.jpg
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Masking Tape Alignment Guide.jpg
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There are 2 Lexan filler plates simply because I had a strip laying around and it was somewhat less than ½ the thickness I required. Contrary to the photo I removed almost all the paint under the main part of the rail mount with 99% iso alcohol (who knew it would help remove the paint!) and then some emery cloth.

I drilled and tapped the collar and discovered the metal part was a little thinner than expected. It did serve as a useful alignment/anchor point in the epoxying process. Epoxy tape or paste is highly recommended for this type of work.
Second Epoxy Fastening.jpg
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Sling Carry Configuration.jpg
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Lifting to Shooting Position.jpg
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Aiming With Dot Sight.jpg
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The first time I epoxied it in place, I tried to keep it all under the rail. After it set solidly, I was concerned that sideways pressure might break the bond and damage the collar or cause the dot sight to fall off. I then took the leap, cleaned and roughed a variety of points along the rail and collar to provide really solid surfaces to take the epoxy. A thin roll of epoxy was applied on each side, then on the rear as a tidying afterthought. The epoxy was smoothed with a moistened fingertip and allowed to set for several hours. There were a couple of places where a utility blade was used to remove obvious disruptions to the smooth lines, the black satin model paint was used to make it all look nice.
Dot Sight On Rail 2.jpg
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Dot Sight On Lens.jpg
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I hope to get out shooting in the next week or so and will report back on my results.
 

11GTCS

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I’m currious what the zeroing will be like. On the one hand, a photo is a much larger total area than a bullet, but, on the other hand, the distance above the “bore” is fairly high compared to most flattop rifles
 

Carbonman

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  • #5
I’m currious what the zeroing will be like. On the one hand, a photo is a much larger total area than a bullet, but, on the other hand, the distance above the “bore” is fairly high compared to most flattop rifles
I think it will be fine. Horizontal alignment will stay true while the vertical parallax error should be very small. The camera can be set to 2 sizes of center spot focusing points or any of the other focus sensor patterns or field sizes. A handful of seconds of arc vertically shouldn't be a problem when the vertical angle of view of the 300mm + MC-20 is about 1.2 degrees (4,200 seconds). In comparison, the Olympus EE-1 dot sight sits at about the same vertical displacement in the hot shoe.
 

JanW

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Very nice setup Graham! The painted epoxy finish looks really nice!
The vertical parallax error is something to think about when adjusting the dot sight. If the target you use to adjust the dot sight is too close you will have a very noticeable error on longer distances.
When adjusting at a distant subject the error at close range is a bit too much.
In the end I settled at a distance of approx. 10m which comes close to the real world use. The error at longer distances is hardly noticeable but there is still a bit of error on MFD (1.5m on my Panasonic 100-300mm).
 

Carbonman

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What improvement do you expect to see over an EE-1?
There are 3 main improvements I wanted/expect:
  1. Repeatable sight alignment without re-zeroing each time it's put on the camera
  2. Choice of dot pattern
  3. Choice of dot color
  4. All metal construction with no moving/expanding construction
Now all I have to do is get out using it!
 

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