Hartmann Mask - Made a prototype, now a few questions!

[CKemu]

Just made a very rough prototype Hartmann mask, no compass, and limited tools.

Will probably give it a "proper" go tomorrow, however I do have a few questions.

I'm doing a three holes mask, all circular, and roughly placed them at every 120deg around the front correcting mirror. Is that correct, or is there a more optimal position?

Does the accuracy of my circles make any significant difference? Eg; does the odd wonkey edge degrade focusing performance?

My scope is a Meade LX90 8" ACF, which is an f10 scope, each circle is roughly 300mm across, it's a cloudly night, so focused in on a bright reflection on a car down my street, and the image was bright, will those holes me to small, or to big?

Thankyou for any help!

[astrovirus]

Nor really an answer but more a remark. Why not make a Bahtinov mask instead, I believe most prefer Bahtinov over Hartmann nowadays for improved accuracy. OK, it's a bit harder to cut out all these slots bt it's do-able.

Good luck with your mask choise.

[Demonperformer]

You could also try a simple 'Y-mask'. This gives a brighter image, as most of the front lens remains uncovered (the 'Y' is the bit that is covered, not the bit that is cut out - not intended to be patronizing, just i got it wrong:iamwithstupid: first time out)

[Merlin66]

For an 8" the 30mm holes should be OK.

The hartmann masks work pretty well.

[Hoshikomi]

Before I went down the Bahtinov route, I used a 2-hole mask but used triangles rather than circles - one point up, one point down. The triangles create 3-pointed diffraction spikes on your star so when you have focus, your star has 6 spikes radiating from the centre.

[steppenwolf]

You have described a classic Hartmann Mask and the dimensions that you have will be fine BUT a Bahtinov Mask would knock the spots of it (pardon the pun) and would also require the minimum of tools/materials to make - cardboard and a sharp scalpel type blade.

[CKemu]

Thankyou for the replies folks.

I have considered a Bahtinov mask, however I want to give an adaptation of the Hartmann mask a go, that and I'm really not accurate yet with a scalpel!

I haven't finished the template yet, though photos will follow in due course, basically three holes, but each hole has a line/strip going through it, radiating from the centre of the mask, this should give me defraction spikes, I'm also going to try the triangle based version to see if that is similiar to this idea (and see which one works the best).

Today has been a good day, think I may have found an Eq wedge for my scope to!

[astrovirus]

Thankyou for the replies folks.

I have considered a Bahtinov mask, however I want to give an adaptation of the Hartmann mask a go, that and I'm really not accurate yet with a scalpel!

No need to be that accurate on the cutting. My first one was a very rough cut out one and functioned like a beauty. My new one is laser cut:D

[CKemu]

Laser cut! Now thats just fancy!

Just completed my first mask, needs a little tweaking to make it fit a bit more snug, but voila!

Sorry about image quality, took these shots on my phone!

[CKemu]

Well she works, and despite the fact the glue didn't hold up massively well on one of the "grip", I think the defraction pattern is rather handy for such a simple mask.

Betelgeuse

Sirus

[mark7331]

Very nice result. Looks exactly like mine which works a treat too.

Mark