[WITHDRAWN] Bahtinov masks for telephoto lenses

[Stefan Buda]

Originally Posted by elken2004

I got a test 67mm mask at .2mm to try out below is the link to ATM thread

http://www.iceinspace.com.au/forum/showthread.php?
p=1182574#post1182574

where are the clear skies?

Clive,

The experimental mask I sent you (the top one in your post) has 0.5mm slits, rather than 0.2mm.

[Jen]

thank you Stefan I received mine safe n sound it looks very sexy in the red hehe
My scope is all aligned tarped up waiting for the weekend so I will check out how snug it fits then

[elken2004 (Australia)]

A perfect fit on 80mm

Now for a star test tonight clouds permitting

[Phil Hart]

I can confirm that these little Bahtinov masks are damn handy.

I've tried them with 24mm and 80mm lenses and they do help get sharp focus quick. At 80mm I can focus in liveview on a good star but at 24mm it's better to take very short exposures and review - but the mask shows really quickly when you're at the sweet spot and if not which direction to go. With lens aberrations, when trying to focus very fast lenses seeing the correct focus point just with Live View without a mask is not as easy or as robust as you might think.

With longer lenses it's a snap to get sharp focus real quick. They also make life much easier if you're trying to use lenses on a camera system that doesn't have Live View.

Thanks Stefan

Phil

[elken2004 (Australia)]

Originally Posted by philiphart

I can confirm that these little Bahtinov masks are damn handy.

I've tried them with 24mm and 80mm lenses and they do help get sharp focus quick. At 80mm I can focus in liveview on a good star but at 24mm it's better to take very short exposures and review - but the mask shows really quickly when you're at the sweet spot and if not which direction to go. With lens aberrations, when trying to focus very fast lenses seeing the correct focus point just with Live View without a mask is not as easy or as robust as you might think.

With longer lenses it's a snap to get sharp focus real quick. They also make life much easier if you're trying to use lenses on a camera system that doesn't have Live View.

Thanks Stefan

Phil

I absolutely concur with that, after my tests last night with my canon 60d and 18 -135mm lens, even at 18mm little harder to see it, live view at 10x gives you a little show. but using the three part objects, once they line up, focus is achieved, and with a pic taken you can see the pattern.
and that was using the experimental .5mm mask.

[Stefan Buda]

Thanks Phil and Clive,

I think we broke some new ground with these tests, as I never heard of anyone using focusing masks for wide angle lenses. In fact when I set out to make these things, I only had telephoto lenses and small refractors in mind.

[Jen]

Mine fits beautifully woohooo

[DavidTrap (David)]

Collected mine today from my office - look fantastic. Will report back when I've had a chance to try them out.

Thanks,

DT

[Regulus (Trevor)]

Originally Posted by Stefan Buda

I think its time for a bit of theory now.

Thanks for that Stefan, it was useful info I have never had before.

Cheers - Trev

[Stefan Buda]

Thanks Jen, David and Trevor for the feedback!

I now have 3D models for the following filter size/slit size:

55/0.9 55/2 58/0.9 62/1 67/0.9 67.0.5 67/09 67/2 72/2 77/2 82/1.2

Also models for the following refractors:

FS60, Zenithstar 70 ED, Megrez II 80 and 5" refractor with 147.25 ID dew shield.

I would also like to develop models for 4" refractors, so please don't hold back if you require one.

[Stefan Buda]

Another size added to my list: 77mm filter size with 0.9mm slits.

Suitable for lenses down to 50mm focal length.

[gavcol (G)]

G'day Stefan

I am interested in getting a couple of masks.

Are you still making them?

Looking for one for an SW ed80 Pro, SW 150/6" Achro and a couple of camera lenses.

Can you give me an idea on cost and what further information you might need for lenses etc?

Thanks

Gavin

[Stefan Buda]

Hi Gavin,

Yes I still make them and I have most sizes for camera lenses in stock for $20 a piece or less for multiple orders.
If you tell me the focal lengths of your lenses and the filter thread sizes, then I can choose the right masks for you.

The 80mm refractor size is $25 and I need a good measurement of the inside diameter of the dew shield.

Sorry but I can't help with the 6" refractor size as the largest diameter I can print in one piece is 150mm.

Cheers,
Stefan

[gavcol (G)]

Hi Stefan

Thanks for the reply.

Will send you an email in the coming week, once I figure out exactly what I need.

Thanks

Gavin