A question for Bjørn...

[Akira]

Maybe the rest of the front part of the plate work as counter weight to cancel the weight of the camera?  But isn't there any possible flare caused by the reflection of the sunlight from the plate?  I wonder if the reflection is ignorable enough because of the extremely dense ND filter to shoot the sun?

So long as there is no mechanical stress between the inner barrel and the outer barrel of the zoom, the fixture looks fine.

[CS]

Sorry for that, Carl, holiday time and smartphone reading/writing .... Thanks for the info, the software link and the pictures. It is very interesting to see the final set up, I did not expect it to be like that. I did not realise the camera would be that far back relative to the head. Any reason for that?

 Your friend's set up is impressive. I'm eagerly waiting to see the pictures.

I don't know the exact reasoning behind the camera position, Bruno, but I will ask.

[Bjørn Rørslett]

Interesting solution. I agree about the potential for creating glare into the front element, but a long sun shade on the lens and/or felt flocking of the outer metal part should alleviate such issues.

[CS]

Maybe the rest of the front part of the plate work as counter weight to cancel the weight of the camera?  But isn't there any possible flare caused by the reflection of the sunlight from the plate?  I wonder if the reflection is ignorable enough because of the extremely dense ND filter to shoot the sun?

So long as there is no mechanical stress between the inner barrel and the outer barrel of the zoom, the fixture looks fine.

There is a steel bar for counter weight on the front of the mounting plate.

I will ask, Akira. I do know that in the moon shot that I posted yesterday, the moon was so bright that it necessitated a 6 stop ND filter on the lens.

He used shims to set the alignment. If he loosens the screws that clamp front collar together, then he can set the focus. Once locked down no telescoping is allowed between the inner and outer barrels, even pointed at 90˚.

[CS]

Maybe the rest of the front part of the plate work as counter weight to cancel the weight of the camera?  But isn't there any possible flare caused by the reflection of the sunlight from the plate?  I wonder if the reflection is ignorable enough because of the extremely dense ND filter to shoot the sun?

Here's his response your questions, Bruno and Akira:

"This is correct - I left the extra length at the front for 2 reasons -
1) With no extra length, the  C.O.G. is pretty much right under the existing tripod mount on the 80-400mm lens. I need to move the C.O.G. forward to have a place to drill the holes for the tracker mount.

2) I wanted the entire assembly to be as massive as practical, to give the whole system extra damping.

In practice, I will be using the lens hood on the 80-400mm lens, and the front of the mount is out of it’s field of view, so I’m not too worried about reflections (I did move the chunk of iron counterweight to the back, in an over-abundance of caution). But, one can’t be too careful, so I’ll hit it with some matte black spray paint later today…"

[Akira]

I will ask, Akira. I do know that in the moon shot that I posted yesterday, the moon was so bright that it necessitated a 6 stop ND filter on the lens.

He used shims to set the alignment. If he loosens the screws that clamp front collar together, then he can set the focus. Once locked down no telescoping is allowed between the inner and outer barrels, even pointed at 90˚.

Thanks, Carl, for forwarding my questions to the owner.

I think the brightness of the moon and the sun is totally incomparable.  A 6-stop ND filter reduces the light to 1/64 whereas the ND filter for shooting the "normal" sun does that to 1/100000 (which was what I used to Transit of Venus a few years ago).  To shoot the moment of the total eclipse wouldn't need a 1/100000 ND,

To eliminate the reflection from the plate, putting a rippled plate like a wash-tab might work better than the black paint or a sheet of felt.

As for the clamp, I was concerned about the bending force between the inner barrel and outer barrel when the inner barrel zoomed out is locked.  In order to minimize this bending power, the center of the outer barrel and that of the inner barrel should be perfectly aligned when the clamp is tightened.  Otherwise, the lens can be damaged, or at least the image quality would suffer.  That said, the owner should already know about these potential problems of the rig.

[David H. Hartman]

I don't like the look of all that aluminum sticking out in front. It can do any good  for flare. An ND filter makes no difference. The ND will reduce both image forming light and non- image forming light. The ratio will be constant. The mass surely is enough to make a difference. If more mass is needed it can be add easily another way.

To black the bracket VHT Case Paint adheres well to clean aluminum. I've used it on negative carriers and it stands up well to heavy use over many years. A groved surface would be better than a flat one. Cutting it off would be better unless so use other than mass is for seen.

Dave

[CS]

Thanks, Carl, for forwarding my questions to the owner.

I think the brightness of the moon and the sun is totally incomparable.  A 6-stop ND filter reduces the light to 1/64 whereas the ND filter for shooting the "normal" sun does that to 1/100000 (which was what I used to Transit of Venus a few years ago).  To shoot the moment of the total eclipse wouldn't need a 1/100000 ND,

To eliminate the reflection from the plate, putting a rippled plate like a wash-tab might work better than the black paint or a sheet of felt.

As for the clamp, I was concerned about the bending force between the inner barrel and outer barrel when the inner barrel zoomed out is locked.  In order to minimize this bending power, the center of the outer barrel and that of the inner barrel should be perfectly aligned when the clamp is tightened.  Otherwise, the lens can be damaged, or at least the image quality would suffer.  That said, the owner should already know about these potential problems of the rig.

I wasn't comparing shooting the moon with shooting the sun. I mentioned the 6 stop ND filter as an aside to the main topic, the eclipse, because it isn't obvious when viewing the moon images.

[CS]

The angle to the sun will all but eliminate flare from the top face of the plate because the sun will not be looking at the top surface of the plate, but the front edge instead. But, he has added the felt to the face anyway.