Bahtinov focus mask with an SLR lens?

[Dangerous-Dave]

Has anyone tried this before? Are the principles much the same as using the mask with a telescope, or does the greater number of elements affect the physics of the pattern?

I'm sure light grab will not be a problem for me as I will be using Pentax medium format lenses (200mm/f4 and 300mm/f4) which have a decent aperture on them.

Many thanks

[steppenwolf]

I have tried this with a DSLR lens - I have made masks for both my Canon 200mm Focal Length L series lens and my Olympus 135mm lens. It works very well on the 200 but not as well on the 135. The reason for this is the star size image which I find is too small to get a good enough diffraction pattern to ascertain when focus is achieved when you get too short a focal length.

[Dangerous-Dave]

Cheers Steve. I take it the principle for making it is the same as for telescopes?

[angusb1]

i'm planning to use this to generate one.

[steppenwolf]

I take it the principle for making it is the same as for telescopes?

Yes it is, Dave

[Dangerous-Dave]

Many thanks all.

[davew]

Hi Dave,

I've had good results with an easier solution. The " Y " mask. The one shown here fits a small scope and large lens. I have another for small lenses. Also shown is a result of using the mask.

It's very easy to make !

The size I've used should say 3 to 4 mm by the way, not 3/4.

Dave.

[kirkster501]

This is an old thread to reboot but saves starting a new one. Why do you need a Bahtinov to focus with a DSLR and a lens? Why can't you leave the focus hard over at infinity shown on the lens job done?

Steve

[Psychobilly]

While the infinity mark is perfectly acceptable for terrestrial targets it's often not accurate enough for astro... Also a lot of modern camera lenses have travel beyond "infinty" ...

Peter...

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[kirkster501]

Thanks Peter that explains it.

Steve

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