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Old 05-11-2019, 10:07 PM
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A Tale of TWO Arrays

A Tale of two arrays: yes, but a very unfinished one. What follows is a peg in the ground of what I'm sure will be a very long journey. It's all about the journey anyway, right?

Hello folks,

I have recently acquired enough of the bits to almost make a telescope/lens array (or two) possible, using ~6 inch aperture very fast lenses:
Three Nikkor 400mm f/2.8 lenses which if combined on the same patch of sky could yield a 400mm f/1.6 lens (in light gathering terms) and on a full-frame sensor a 5.2º x 3.4º field of view. Image Scale 3.1 to 2.5 arcseconds/pixel depending on whether using Nikon D600 or D800 camera.
Three Nikkor 600mm f/4 lenses which if combined on the same patch of sky could yield a 600mm f/2.3 lens (in light gathering terms) and on a full-frame sensor a 3.4º x 2.3º field of view. Image Scale 1.6 to 2 arcseconds/pixel depending on whether using Nikon D600 or D800.
I'm motivated by trying to maximise imaging time given our not always beautiful weather and I'd use the system initally with fullframe DSLR and potentially use the system for simultaneous RGB mono or narrowband imaging later. The lenses all have filter holders that can be used for such purposes, but some modification and trial will be required to try to suit typical astro filters.

In addition to the lenses I have three Nikon D800 cameras as well as 2 D600 cameras and various Nikon 2x and 1.4 teleconverters to try. Initially the lenses would all point to the same patch of sky, but later could be splayed out or turned 90º(Landscape to Portrait) for various size 3x1 really wide mosaics.

The remaining issue is a sufficiently robust mount to run the show. That I don't really have but I will either load an NEQ6 to the max of around 20kg or initially try things with two lenses.

I will post an image of the 3 in a row side by side by side I'm considering as a trial, also using tube rings on the rear of the lenses for extra support in addition to the normal tripod foot mount. The lenses are quite heavy at 5.2kg each for the 400mm f/2.8 Nikkor and 6.3kg each for the 600mm f/4.

The real problem I have with continuing the evolution of either of these systems is the lack of a permanent observatory, although crazily enough I've tried to make my mounting setup as modular as possible for "ease" of transport to somewhere dark.

Anyway that's all I have for now. I will post some proper pics of the stuff, but here is a mockup image in which I've added a 3rd lens to a picture I already had of two of the 400mm Nikkors.

Best
JA
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Last edited by JA; 05-11-2019 at 11:33 PM.
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  #2  
Old 05-11-2019, 10:34 PM
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Atmos (Colin)
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If you can find a way of rigidly attaching them to, let’s say a 14” Losmandy D Bar horizontally and then attach another D bar underneath vertically to put onto your EQ6 it could work well. I mean, you’re imaging with short exposures and a larger image scale so you can probably deal with the weight okay.

Ambitious project but one I’ll certainly be watching
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Old 05-11-2019, 10:46 PM
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Originally Posted by Atmos View Post
If you can find a way of rigidly attaching them to, let’s say a 14” Losmandy D Bar horizontally and then attach another D bar underneath vertically to put onto your EQ6 it could work well. I mean, you’re imaging with short exposures and a larger image scale so you can probably deal with the weight okay.

Ambitious project but one I’ll certainly be watching
Hi Colin,

That's almost what I'd intended. I can use (and have) a 14inch Losmandy D, but that's only enough room for 2 lenses. I really need a 17, 19 or 21, but I'd like to keep it as laterally compact as possible. It probably means some custom work.

I will post a pic later, that shows how I intend to try and stiffen the mounting: Each lens is mounted to an 11inch Losmandy D bar in 2 places (one at the lens tripod foot and at another point towards the back of the lens via at an added Parallax style mounting ring), Each of the lenses are then slid on to a typical Losmandy side by side mounting with 2 saddles. I just need to extend/mod the 14 inch bar dual saddle to make it longer and make it a triple saddle AND THEN...... join each of the mounting rings with a bar across their top. It's much easier to see in an image, which I will take and load tomorrow. I could make a lighter and even more rigid arrangement from scratch, but I prefer, for now, to try this sort of very modular approach for development.

Best
JA

Last edited by JA; 05-11-2019 at 11:04 PM.
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Old 06-11-2019, 02:53 PM
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I think there are some systems already available. I'd have a look at Losmandy's website.

I think you would need to be able to tweak each lens so they look at the same patch of sky. Some sort of tilt/tip adjustment on the mount for the small corrections needed to line them up.

It could be a very cool project.

What about looking at that setup someone had with several FLI Microline cameras all mounted on one setup. It should be at the FLI site.

Greg.
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Old 06-11-2019, 03:18 PM
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Originally Posted by gregbradley View Post
I think there are some systems already available. I'd have a look at Losmandy's website.

I think you would need to be able to tweak each lens so they look at the same patch of sky. Some sort of tilt/tip adjustment on the mount for the small corrections needed to line them up.
I agree - Originally I had planned to build a cradle to hold all 3 lenses with individual horizontal angular adjustment via precision screw thread and possibly handle vertical adjustments with shims. What I have planned now is far simpler, but can morph to more complicated, as I already have some precision stages that I could use as part of the horizontal adjustment mechanisms. As simple as it might sound I will try a custom made 3-way side by side by side arrangement without adjustement (except for play in screw holes) also with parallax mounting rings to help further rigidly support the lenses. Given the field of view is anywhere between 5.2 and 3.4 degrees wide (400mm & 600mm focal lengths respectively) I may be able to tolerate a small alignment error. Small enough that it might wash out in later image stacking and tiny cropping. Of course precision H & V adjustment would be best, but I'd like to try it simpler at first. I will show a pic of the intended arrangement soon.

Quote:
Originally Posted by gregbradley View Post
It could be a very cool project.

What about looking at that setup someone had with several FLI Microline cameras all mounted on one setup. It should be at the FLI site.

Greg.
I'll check that reference. Thanks Greg

Best
JA
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Old 06-11-2019, 04:01 PM
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I believe the setup that Greg is referring to is the Dragonfly Array.

https://www.dragonflytelescope.org/
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Old 06-11-2019, 04:09 PM
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Thanks Colin. I know of the Dragonfly setup (it piqued my interest in the first place a couple of years ago), but I did find a FLI 16801 array, that may have been what Greg was referring to, but it uses a splayed array of four 400mm f/2.8 lenses to cover an 11 x 11 degree field. They use a very rudimentary, what appears to be one bolt mounting of the lens via only the the tripod foot. It would also allow them basic lateral adjustment. If it works, it's good.

It's seen here - The Alsubai Project ....
https://www.flicamera.com/alsubai/alsubai.html

Best
JA
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Old 06-11-2019, 04:30 PM
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Originally Posted by JA View Post
Thanks Colin. I know of the Dragonfly setup (it piqued my interest in the first place a couple of years ago), but I did find a FLI 16801 array, that may have been what Greg was referring to, but it uses a splayed array of four 400mm f/2.8 lenses to cover an 11 x 11 degree field. They use a very rudimentary, what appears to be one bolt mounting of the lens via only the the tripod foot. It would also allow them basic lateral adjustment. If it works, it's good.

It's seen here - The Alsubai Project ....
https://www.flicamera.com/alsubai/alsubai.html

Best
JA
I had not heard of that one, an interesting and quite simple setup.
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Old 06-11-2019, 09:50 PM
Sunfish (Ray)
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I have two 800mm side by side attachments to a vixen dovetail, a 3.5 kg refractor with lrgb astro camera and guider and a 3.5kg Nikon Ed 800 lense with dslr. Seems to work , surprisingly , guided to 4min on the HeQ5 and I have combined the images just for interest. I think I need to add an aluminium plate 6-8 mm to stiffen the top of the vixen bar but if it is not pushed it seems fine. The torsion vibration on the bar could be an issue with three of those. I can post an image if you are interested once the painters have left my house. I would be interested to hear how you would combine images.
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Old 07-11-2019, 09:37 AM
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I have two 800mm side by side attachments to a vixen dovetail, a 3.5 kg refractor with lrgb astro camera and guider and a 3.5kg Nikon Ed 800 lense with dslr. Seems to work , surprisingly , guided to 4min on the HeQ5 and I have combined the images just for interest. I think I need to add an aluminium plate 6-8 mm to stiffen the top of the vixen bar but if it is not pushed it seems fine.
Hi Ray,

That's definetly worth doing, or you could go for a more seamless solution: a wide-top vixen bar. I've seen a few so it's made by various manufacturers, there is an example (90mm wide and 290mm long- too short perhaps??) in the image below, from ...
https://www.firstlightoptics.com/dov...ail-plate.html

Quote:
Originally Posted by Sunfish View Post
The torsion vibration on the bar could be an issue with three of those. I can post an image if you are interested once the painters have left my house. I would be interested to hear how you would combine images.
If doing OSC from three DSLRs then I would probably somehow route the images to separate folders, perhaps with multiple instances of control software running or use multiple camera mode in Digicamcontrol, (albeit with a more limited control set, that I've yet to delve in to in detail). Since they are "identical" lenses, imaging the same piece of sky, in the first instance I would simply try to stack them in a photo-stacking app and take it from there. That may be oversimplifying things as there may be some differences in lens vignetting or dust spots etc, that one might want to control with flats, etc... some testing would be required.

If doing Narrowband, control as above and stack images from each camera's folder to create Ha, OIII, SII masters and then combine by normal techniques and to taste in photosoftware. Of course the narrowband from DSLRs could be somewhat compromised, compared with mono, but hopefully a large sensor can ameliorate that somewhat). One of my Nikon D800 cameras is modified so that could be used for the Ha image or use a multi-narrowband type clip in filter (STC or similar).

That's the thinking so far, but the proof is in the application. I'm sure there will be many things to work around as far image capture is concerned, including multicamera control and dithering. Anyway it's something to keep interested with.

Best
JA
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Old 07-11-2019, 10:23 AM
Sunfish (Ray)
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Interesting thanks. I have two DSLR with slightly different sensor size. Would be an experiment to see if they combine from the two 800 at f8 or the C8 and 800 at f6.
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Old 08-11-2019, 07:07 AM
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Just a suggestion. Would it perhaps be better to use shorter bars and arrange the array with 2 lenses mounted on a single rail down the bottom and another bar over the top with the 3rd lens mounted centrally ? My thought is that the entire array is then closer to the mounting dovetail and as such has better weight distribution and less chance of flexure between the outer 2 lenses.

Ryan
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Old 08-11-2019, 07:16 AM
Sunfish (Ray)
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I tried mounting the camera lense under the front of the dovetail on the refractor but it was very hard to balance and point. But my 800 lense weighs 3.5 kg and the whole assembly is quite long. . Side by side worked and point aligned first time and guided fine so I can see why this is widely used. Might depend on the weight and length of the lense assembly.

Quote:
Originally Posted by RyanJones View Post
Just a suggestion. Would it perhaps be better to use shorter bars and arrange the array with 2 lenses mounted on a single rail down the bottom and another bar over the top with the 3rd lens mounted centrally ? My thought is that the entire array is then closer to the mounting dovetail and as such has better weight distribution and less chance of flexure between the outer 2 lenses.

Ryan
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Old 09-11-2019, 11:31 AM
JA
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Originally Posted by RyanJones View Post
Just a suggestion. Would it perhaps be better to use shorter bars and arrange the array with 2 lenses mounted on a single rail down the bottom and another bar over the top with the 3rd lens mounted centrally ? My thought is that the entire array is then closer to the mounting dovetail and as such has better weight distribution and less chance of flexure between the outer 2 lenses.

Ryan
Hi Ryan,

That's a noble idea (lazy text diagram follows)...
__O__
O....O

and certainly would be good at reducing the moment transferred to the mount saddle, but unfortunately would only work with smaller diameter lenses as the distance between the bottom of the dovetail slide in the NEQ6 saddle and the NEQ6 RA axis housing is approximately 160mm. Even if I discarded the mounting plates and saddles that I intend to use on the 3-way side by side losmandy type bar, I would still need approximately 230mm not including lens hood to suit the diameter/lens foot mount of the Nikkor 400mm f/2.8 lenses let alone the slightly larger 600mm f/4 lenses.

Along the same lines of minimising the transferred moment, that your idea suggests, if there were 4 lenses, one could build a zig zag type of mounting bar for the 4 lenses: 2 on either side for balance, either right side up or inverted, sort of ...

_O_O_---- _O_O_

Or downsize to 2 lenses. It would all be a good challenge to perfect, especially with adjustement, but for the moment I will try it as simple as possible to put a peg in the ground.

Best
JA

Last edited by JA; 09-11-2019 at 12:07 PM.
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Old 09-11-2019, 01:59 PM
RyanJones
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Originally Posted by JA View Post
Hi Ryan,

That's a noble idea (lazy text diagram follows)...
__O__
O....O

and certainly would be good at reducing the moment transferred to the mount saddle, but unfortunately would only work with smaller diameter lenses as the distance between the bottom of the dovetail slide in the NEQ6 saddle and the NEQ6 RA axis housing is approximately 160mm. Even if I discarded the mounting plates and saddles that I intend to use on the 3-way side by side losmandy type bar, I would still need approximately 230mm not including lens hood to suit the diameter/lens foot mount of the Nikkor 400mm f/2.8 lenses let alone the slightly larger 600mm f/4 lenses.

Along the same lines of minimising the transferred moment, that your idea suggests, if there were 4 lenses, one could build a zig zag type of mounting bar for the 4 lenses: 2 on either side for balance, either right side up or inverted, sort of ...

_O_O_---- _O_O_

Or downsize to 2 lenses. It would all be a good challenge to perfect, especially with adjustement, but for the moment I will try it as simple as possible to put a peg in the ground.

Best
JA
JA,

My idea was along those lines but not with lenses below the mounting bar. Instead using 2 dovetails. One lower as the main bar and the upper supported by pillars to mount the third lens.
( my crude design follows )

___O__
|_O__O_| <———— Pillars
.....^
mounting bar

A bit of artistic license required but essentially with the two lower lenses as close together as practical and the upper lens forming a triangle ?

Thoughts ?

Ryan
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Old 09-11-2019, 06:47 PM
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Oh Ok thanks Ryan, I misunderstood. I think in that case I'd probably try the simpler approach rather than the 2 tier as i sort of have most of the bits, except for some custom work or a longer dovetail bar (maybe 17-19inch).

Best
JA

Last edited by JA; 09-11-2019 at 07:33 PM.
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