Aiming alternative: Open red dot sight mounted on the 300mm PF

[Øivind Tøien]

Due to a discussion in this thread, http://nikongear.net/revival/index.php/topic,7484.msg121515.html#msg121515, an idea surfaced to use a clamp to mount my red dot to the usually unused lens plate on the collar of my 300mm PF.  The 50mm clamp and a 2" long rail off ebay for a total of $12.40 shipped arrived the other day and had to be tried out. The clamp screw has a nice dampened feeling, but as many of the Amazon reviews suggested, I would have replaced the mounting screw with a better hex screw if I were to put more weight on the clamp. A hole was drilled in the rail for the mounting screw, and I expanded one of the keys of the clamp to fit with a key on the rail. As the keying did not get as precise as I had hoped, I simply applied a couple of drops of epoxy before permanently screwing it together, and immediately went outside to fine adjust the horizontal angle before the epoxy could set. Here is the resulting rig; during astrophotography I usually mount the camera to the tracker via the camera plate anyway due to the light weight of the 300mm PF as it gives better balance when aiming high so I do not need the lens collar for that purpose:










After the epoxy set a final adjustment was made with the horizontal/vertical correction screws on the sight, and I used reindeer at the Large Animal Research Station for handheld target practice, here aiming near the neck. This is a crop of slightly more than 1/3 of the center of the frame. It is lucky for the eartagged reindeer that I had a camera and not a firearm so it did not end up as reindeer steak:




The uncertainty of handholding, and a little variation in the how the lens collar mounts from time to time would have saved the reindeer below though. Is possible that the VR in sports mode also contributed to slight off center framing. Another crop of slightly more than 1/3 of the center of the frame:




Overall I would say it is a success. While there would be parallax deviations with close subjects, this is of course not a problem with night sky targets. It will be a few months before I can test it on a dark sky though, but this should eliminate the need to calibrate the open sight each time. The position of the sight forward on the lens is also more comfortable to use.

[Seapy]

Thanks Øivind for opening this discussion separately from the other discussion.

I am seeing this as a possible aiming aid for Polaris for my star trails photo's, not sure how it would mount with the 16mm Fisheye! Maybe a side pod bracket a bit like a Metz CT45 flash?

More thought needed...  I don't want Polaris, bulls eye, but a Northerly alignment at whatever inclination I need, to deal with the foreground.

[Øivind Tøien]

Thanks Robert for your comment. A possibility without a lens collar is the one Akira initially suggested back in the Night Sky thread, to mount the sight to the camera's the L-bracket (assuming one is used) with a clamp. So my construction above would in that case turn the clamp 90°. Perhaps a separate small L bracket could be added on the clamp to mount the sight in a more comfortable position. While this might not be as accurate as that of a lens foot mount, it would be good enough for fisheye use.

When I align my tracker in daylight/dusk for sun-imaging, moon eclipses etc., I simply use a level for initial tripod positioning, a compass (with applied correction for magnetic north deviation) to find polar north, and then the altitude scale on my tracker set to known latitude (the same steps as initially used during night time alignment, but then with the additional steps of using the polar scope).

[Seapy]

If I go much further down this astro photography path I think I will need a tracker, from what I have seen a 300mm lens, while obviously a bit short seems capable of some nice images.

Perhaps a path to a proper telescope...

[armando_m]

If I go much further down this astro photography path I think I will need a tracker, from what I have seen a 300mm lens, while obviously a bit short seems capable of some nice images.

Perhaps a path to a proper telescope...

of course ... if more quality is desired there is much better equipment available in the market, equipment gets bigger , heavier, and pricier

the beauty of the tracker shown in the night sky shots thread is that it is small, and the photos are done with regular lenses

[Øivind Tøien]

 
+1, and add more complicated to use to that list. One very quickly will need to bring a laptop computer and other accessory equipment. It is a slippery slope with respect to cost, once one go beyond the simple camera trackers, things get way more expensive. And one always has to compete with the quality from the Hubble telescope...

When I got into this, my attitude was that I needed something simple to be enjoyable to use out in the cold, and that some of the attraction was the challenge to see how far it is possible to take this simple equipment (for instance  one will see a lot of comments that say that these trackers are no good at 300mm, which many of us have disproved). If you go much beyond 300mm acuity is going to start being limited by seeing (stillness of air) anyway. Personally I think I have a long way to go before I have used my equipment to the limit, as proven by some results I have seen in various fora. A lot of that has to do with processing, but also I would need to get to darker sites.

One middle route, is to go for one of the more advanced camera trackers, like the Fornax LighTrack II, but quite expensive once one have put all the needed bits and pieces together.

With respect to the star trails, it seems that your custom panohead could be used to align towards the Polar star if the range is big enough?

[Seapy]

My aim would be to dabble, rather than make a serious challenge to Hubble, just for fun!  My ability to get truly dark skies is limited, probably North West Scotland would be my best hope but finding a weather window there would be a challenge indeed.

It's not something immediate, maybe next year?  I  intend to get a D810 when funds allow, that should open up many possibilities in this field.  I was intending a D3S but my D3 is fine (except for the dust bunnies!  ).

The suggestion to use the pano head for star trails is interesting... It should have the range, only snags I can see is the click stop rotation would need some method of locking and the ark of the curved rail might intrude, but there are easy ways of fixing that.

I have looked up the Fornax LighTrack II, seems to be liked on the forums with some reservations, I will of course look closer at this over time if I do go down this route.  I was interested to note the use of counterweights on the Fornax LighTrack, it seems Fornax themselves provide a kit for counterweights.  I am curious about the mount wedge, perhaps I could make something for that myself, I am already considering making a curved rail mount for elevation, ah-la my pano head but horizontal.

I have also been investigating stepper motors, they come in many forms, some with built in gearboxes, quite powerful and apparently accurate.

[Øivind Tøien]

There are the homemade barndoor trackers that can be put together quite cheaply. Most reports I have seen indicate that they do not exceed the performance of a good copy of the cheaper trackers though. And then in addition the problem of polar alignment has to be solved. One would anyway need to purchase a polar scope and find some way to mount and align it along the hinge.