Bahtinov Mask

[centroid]

In true Blue Peter style 'here's one I made earlier'

While still hoping that 'Billy' will get his Bahtinov Mask project 'off the ground', and inpired by the 'Blue Peter' style mask that I made for the 80mm APO, I thought I'd have a go at making one for the 12" LX.

Like the 80mm version, this one is also based on an idea 'posted' by Phil (phil6194), using a printed paper mask, enclosed in a heat sealed laminating pouch.

However, whereas the 80mm mask, could be used 'as is', one the 12" scope would be far to floppy, and in need of some sort of support framework.

So, having some black Foam Board to hand (I bought this to make my Hartmann Masks from), I decided to see if I could use this for Bahtinov mask. I suppose I could have stuck a paper template to the Foam Board, cut the mask out directly from the board, but decided to try as describe below.

Firstly, I downloaded a mask template, set for the 12" LX200R at f/6.3. Not having an A3 printer, which would have made the task much easier, I had to print the mask out onto two sheets of A4. Even then some of the outer perimeter of the mask couldn't be printed onto A4, but this didn't matter, as it did not impact of the slotted area of the mask.

After careful trimming and aligning of the two halves, they were sealed inside an A3 laminating pouch (fortunately I have a A3 laminator).

The slots in the now laminated mask, were then cut out using a scalpel.

I then drew a 345mm dia circle (the OD of 12" LX's corrector plate cell) on the foam board, and cut out the disk with the scalpel.

I then drew an inner circle, at just over the full width of the mask slotted area. The mask was than laid in postion of the foam board, the and the shaped outer edge of the angled slot areas, marked on the board. I could have ingnored these two odd shapes, and just cut out a ring, but thought that they would provide a bit more support to the very 'floppy' mask.

Next I cut out the inner circle, and these two side shapes from the foam board disk, again using the scalpel.

This now left me with foam board ring, with the two shaped areas at each side.

Using Bostik, the laminated mask, was glued in postion on the foam board ring.

In the photo below, you can see what is effectively the back of the mask, showing the non printed side of the laminated paper mask, and the foam board frame to which it is glued.

I will most likley cut a duplicate of the foam board frame, and stick that to the other side, effectively sandwhiching the laminated mask.

Both sides of the laminated mask, will be painted with blackboard paint, to make it more opaque, and give it some extra protection.

The laminated mask is rigid enough to use, as its glued to the foam board ring, but never the less will require careful handling if its not to be damaged.

I see the 'Blue Peter' mask, being very much an interim measure, in the hope the Peter (psychobilly) wil eventually get his laser cut steel version 'off the ground'

Dave

Dave

[centroid]

Tried it on the 12" LX tonight, just as you see it (unfinished), and it works a treat

Dave

[centroid]

Here's the finished 'Blue Peter' style Bahtinov Masks.

One for the 80mm APO, and the other for the 12" LX200R

I would point out, that the 12" version was much easier to cut out, whereas with the 80mm version, the slots are very thin, as is the remaining material in the bars.

Each mask, was given two coats of blackboard paint, giving a matt black finish.

Dave

[Doc]

Look very professional Dave.

Good job you have made.

[centroid]

Look very professional Dave.

Good job you have made.

Only if you don't look too close at my scalpel on foam board cutting skills.

Dave

[Wobbly Bob]

They look pretty dam good Dave, have you tried them yet ?

[centroid]

Yep, I sure have Bob.

I tried them both before bothering to make them a bit more durable, and easier to handle.

Once I knew they worked, and worked very well too, I then finished the job.

Dave

[RobH]

Interesting Dave.

I have made a couple of 'Blue Peter's' for the TMB as an interim measure, and also have an A3 laminator.

I'd considered laminating them but didn't think it would work well in the slots.

Obviously, it does!

I shall laminate mine too....thanks.

Rob

[centroid]

It ceratainly does Rob, but note that I laminated first, and then cut out the slots.

The 80mm version was quite fiddly, as the slots are very narrow. I really don't think I'll attempt one for the ZS66.

I followed Phil's logic, and put it through the laminator again, once the slots were cut, to hopefully seal the edges.

Dave

[fil6914]

glad you got it sorted Dave, there looking really good. i use my 80mm for the WO all the time its a god send

Phil

[Jarndyce]

Very impressed with your mask, Dave.

I've had a go at making one too, in 3mm acrylic.

Though not in Billy's league, I do have access to a 50W laser cutter. Drawing it in CAD is straight forward. Only thing is that I had to cut the slots in two sets - if I cut it in one go, the heat distorts the slots.

And it works!

Tried it for the first time tonight. My camera doesn't have liveview, which is a pain, but generally very pleased. Thanks to Billy for his help and advice.

[centroid]

That looks just the job, and will withstand handling better than mine will.

The resulting focused image looks 'spot on'.

Dave

[johninderby]

Kendrick is about to release Bahtinov Masks made from thin plastic and they should be about £8.00 to £30.00 or so depending on size. They already do the aluminium ones but they're more expensive of course.

John

[Psychobilly]

Very nice John, the Metal cutting one is only 3000W...and cuts up to 12mm mild steel...

It will be interesting to see the full retail price of the Kendrick Flexi ones as I have already found somone who can do them just got to see if its going to be economic....

Billy...

[Jarndyce]

Thanks for your comments, Dave.

Acrylic can be brittle, but it does tend to hold its shape. However, if dropped on hard ground, it would probably crack.

Mine pushed onto the dewshield with 4 small legs, but I may borrow your idea and add a concentric step, so it fits like a bung.

I'm having a go at creating one with thicker - 6mm - slots, rather than 2mm on the existing one.

Also creating one for the C6-S with small and large slots.

I wondered if the thickness of the panel - 3mm - would interfere with the effect. I'd read somewhere that the masks have to be less than 1mm thick.

This isn't the case.

Now all I have to do is learn more about astrophotography.

Hoping to pick a lot of brains at SGL4 in April...