Bahtinov Mask: I was wondering if anyone knows of a good solution for a Bahtinov mask that would fit the front of a Rokinon 14mm lens?

Basil Loc: New Mexico

I was wondering if anyone knows of a good solution for a Bahtinov mask that would fit the front of a Rokinon 14mm lens?

SHWeiss

The problem is the spokes of the mask are too far apart for that short of a focal length. A bahtinov mask isn't really useful at less than 100mm focal length. In order to get the difraction pattern at 14mm focal length the distance needed between the spikes is measured in microns.
Focus to infinity during the day and mark focus ring with a silver sharpie or tape the focus ring with gaffer tape

Basil Loc: New Mexico

SHWeiss wrote:

The problem is the spokes of the mask are too far apart for that short of a focal length. A bahtinov mask isn't really useful at less than 100mm focal length. In order to get the difraction pattern at 14mm focal length the distance needed between the spikes is measured in microns.
Focus to infinity during the day and mark focus ring with a silver sharpie or tape the focus ring with gaffer tape

That makes sense. Thanks.

bwana Loc: Bergen, Alberta, Canada

Basil wrote:

I was wondering if anyone knows of a good solution for a Bahtinov mask that would fit the front of a Rokinon 14mm lens?

I use and like the SharpStar2 focusing mask (https://www.lonelyspeck.com/sharpstar/). Works very well.

bwa

Basil Loc: New Mexico

bwana wrote:

I use and like the SharpStar2 focusing mask (https://www.lonelyspeck.com/sharpstar/). Works very well.

bwa

Can I ask if you use it with wide angle (14mm)? (See SHWeiss comment above)

I see that blog has a chart that suggests it would work with a 14mm down to f2.8 aperture

bwana Loc: Bergen, Alberta, Canada

Basil wrote:

Can I ask if you use it with wide angle (14mm)? (See SHWeiss comment above)

I see that blog has a chart that suggests it would work with a 14mm down to f2.8 aperture

I've never used it with a 14mm lens. Not really needed since the focus range at 14mm is huge, i.e.: very easy to get a good focus simply by watching the stars on the liveview screen.

bwa

Basil Loc: New Mexico

bwana wrote:

I've never used it with a 14mm lens. Not really needed since the focus range at 14mm is huge, i.e.: very easy to get a good focus simply by watching the stars on the liveview screen.

bwa

That's how I do it now but never feel sure how good I have the focus.

Desert Gecko Loc: desert southwest, USA

Basil wrote:

That's how I do it now but never feel sure how good I have the focus.

I too thought of the SharpStar2 when I read your initial post. But I must confess to never having used it despite reading very good things about it not just on Lonely Speck, but elsewhere. I should add that there are alternatives, as well. I've seen them on Amazon, if memory serves.

I see you have a Canon R5. Is that what you use for astro? I shoot with Sony, and I take advantage of mirrorless capabilities. "Live view" is inherent, so there's that. I use focus magnification and pick a bright star (or better, a planet) to focus on -- even if it won't be in my composition. And I use focus peaking. Finally, I rock focus back and forth, narrowing until it's spot-on. A star not in focus will be larger and softer, while in focus it'll be smaller and more of a pinpoint. Faint stars can disappear completely when not in focus.

I know, I could avoid all this with a mask. Maybe I'll finally get one.

Basil Loc: New Mexico

Desert Gecko wrote:

I too thought of the SharpStar2 when I read your i... (show quote)

Yep, R5 is what I use. It's not my only camera but it's my only Interchangeable lens camera (not counting my old T-70 film camera). I used to use my old Canon R6 for Astro and it was very good for that. I went and bought a rear screen magnification loop to assist with focus, which does help some. I rock back and forth too when trying to nail focus, but it seemed that the mask might make it easier. Never tried focus peaking - I'll have to try that next time.

Desert Gecko Loc: desert southwest, USA

Basil wrote:

Yep, R5 is what I use. It's not my only camera but it's my only Interchangeable lens camera (not counting my old T-70 film camera). I used to use my old Canon R6 for Astro and it was very good for that. I went and bought a rear screen magnification loop to assist with focus, which does help some. I rock back and forth too when trying to nail focus, but it seemed that the mask might make it easier. Never tried focus peaking - I'll have to try that next time.

Doesn't the R5 have built-in focus magnification? It's quite strong on Sonys. As an alternative, you can focus, take a shot, and then review it with magnification. I'm not against using a loupe; I have one, too. But I thought I'd use it more than I do. For me, built-in magnification is easier and usually good enough.

bwana Loc: Bergen, Alberta, Canada

Desert Gecko wrote:

I too thought of the SharpStar2 when I read your i... (show quote)

I also shoot with Sony and use the same technique.

bwa

Basil Loc: New Mexico

Desert Gecko wrote:

Doesn't the R5 have built-in focus magnification? It's quite strong on Sonys. As an alternative, you can focus, take a shot, and then review it with magnification. I'm not against using a loupe; I have one, too. But I thought I'd use it more than I do. For me, built-in magnification is easier and usually good enough.

Yes, and that's what I do now. I just thought using a mask "might" make the process easier and more precise.

Desert Gecko Loc: desert southwest, USA

Basil wrote:

Yes, and that's what I do now. I just thought using a mask "might" make the process easier and more precise.

Ballard Loc: Grass Valley, California

Basil wrote:

I was wondering if anyone knows of a good solution for a Bahtinov mask that would fit the front of a Rokinon 14mm lens?

When using a DSLR for astrophotography with a camera lens I always connect a laptop to the camera in live mode and use 10x magnification to get the focus correct.