Creative Solutions to the Problem of LARGE (8"+) ERF Cells

Frankenscope? Let's see it!***be advised that NOTHING in this forum has been safety tested and you are reading and using these posts at your own peril. blah, blah, blah... dont mess around with your eyesight when it comes to solar astronomy. Use appropriate filtration at all times...
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marktownley
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Creative Solutions to the Problem of LARGE (8"+) ERF Cells

Post by marktownley » Wed May 15, 2019 7:20 pm

Looking at this problem from the perspective of 'what would I do in this situation' here is my take:

I would get a rigid dew shield for my C11 https://www.teleskop-express.de/shop/pr ... scope.html I would take the ERF and would carefully wrap the perimeter in electrical tape until it made a tight interference fit with the inner of the dew shield. The ERF should then fit in tightly like the stopper in a biscuit tin / coffee jar. I use this method with a few of my ERFs.
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Re: Creative Solutions to the Problem of LARGE (8"+) ERF Cells

Post by MalVeauX » Wed May 15, 2019 8:40 pm

Hrm,

I wonder if it would truly hold a 2.5kb or heavier piece of large glass, safely though?

I defnitely wracked my mind around the idea of just mounting my D-ERF in a premade filter holder, or sandwitching it between cardboard and sealing that, or making it from plywood blocks and cork board.

I think wood (ply) & cork would hold nicely, simple cuts, wood glue, could even make it "open" and it would allow for easy posts to secure to the front of virtually any size scope.

I previously had my 6" ERF mounted in a 3D printed cell. I really do think a thick enough polymer 3D printed material like PVC would be fine. It's just a matter of getting a 3D printer big enough to do larger models like this. My previous 6" ERF in its 3D printed cell was secure and used a threaded retaining ring, all 3D printed, it was plastic/vinyl.

Very best,

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Re: Creative Solutions to the Problem of LARGE (8"+) ERF Cells

Post by marktownley » Wed May 15, 2019 8:59 pm

I think if the ERF was mounted immediately infront of the objective, not at the 'far end' of the dew shield and would be ok. Some velcro pads on the OTA and outside edge of the dew shield with a velcro strap securing the dew shield / holder to the OTA would work as a 'belt and braces' addition.

3D printing would be an option. Just need a CAD file for it. Bed size on the printer is the limit here, mine at work is 8" max. These guys seem to be able to work upto 305mm so I think with the right CAD file you could print a cell for an 11" scope. No idea how much the print costs are though.

https://3dprintcompany.co.uk/?gclid=Cjw ... jMQAvD_BwE

Another option would be if the OTA had radius blocks fitted diametrically opposite on the corrector plate end of the OTA would create a pair of fixing points that a cell could be bolted to.
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Re: Creative Solutions to the Problem of LARGE (8"+) ERF Cells

Post by marktownley » Mon May 20, 2019 9:31 pm

These guys have the tooling, and they're astronomy based so there may be a chance? https://www.jtwastronomy.com/services
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Re: Creative Solutions to the Problem of LARGE (8"+) ERF Cells

Post by george9 » Thu May 30, 2019 2:59 pm

Is anyone actually interested in purchasing a cell for a 295mm filter today? It would lower the costs to have more than one person. JTW is potentially interested in producing large ones. Thanks for the link, Mark.

George

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Re: Creative Solutions to the Problem of LARGE (8"+) ERF Cells

Post by LTHB » Thu May 30, 2019 7:15 pm

It would certainly be great to have a supplier for large filter cells, but my experience with JTW Astronomy (trying to purchase a spectroscope from them) makes me sceptical that they will be a reliable producer. In any case I would never again make any down payment when ordering from them.

Regards,

Frank

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Re: Creative Solutions to the Problem of LARGE (8"+) ERF Cells

Post by marktownley » Sat Jun 08, 2019 8:57 am

marktownley wrote:
Wed May 15, 2019 8:59 pm
Another option would be if the OTA had radius blocks fitted diametrically opposite on the corrector plate end of the OTA would create a pair of fixing points that a cell could be bolted to.
My HaT has rails top and bottom of the OTA, I think if I was looking to mount a ERF on a large aperture SCT etc I would start off getting one of these nifty adaptors from ADM https://www.firstlightoptics.com/adm-mi ... nting.html

This gives a mounting face parallel with the ERF. I would then make a sandwich cell construction for the ERF which could be plasma cut metal, laser cut plastic or even jigsaw cut ply. An 'ear' coming off would allow it to be mounted to the ADM using the 3 mounting points. For a belt and braces approach you could have mounting points on top and bottom on the OTA and 2 ears on the cell.
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