Bahtinov mask question?

[rcheshire]

Hi fellow astrophotographers. I have a question about using a Bahtinov mask with an 80mm refractor and DSLR?

I notice that the mask works fine on bright objects such as Venus, the spikes are clearly visible in the view finder. Antares is a different matter, it's not as bright and the diffraction spikes are impossible to see. So focus is a matter of the sharpest blur if that makes sense.

Would it be better to have a mask with finer, that is narrower elements - currently about 6mm - would that improve definition of the spikes?

[asimov]

I've made one for my ED80 & DSLR 400D but haven't had the right weather to test it. To me, it'd make more sense taking a (correct) exposure of the star & making focus adjustments that way than using the view finder.

[Omaroo]

Rowland - Bahtinov masks aren't really used that way.

Firstly, don't use a planet as it's a disk. Use a point-source of light such as a medium-bright star only. The planet will not work - at all.

Secondly, don't view it through the viewfinder - you won't be able to see the diffraction pattern on a star anyway. Center the star in your viewfinder and then take a 5-10 second exposure at ISO800 or so. Zoom in to 10x and see the pattern on your rear screen. Keep adjusting focus in the same direction and taking shots until you see the central bar in position. If you go too far, come back.

Here's a page out of a manual I wrote a while back where you can see the progression to focus and then beyond it.

Once you've reached it - don't forget to take the mask off. I do this ALL the time. LOL!

[rcheshire]

Thanks guys. That makes much more sense, and is fairly obvious when you think of it.

[bartman]

Where can I get a mask for my DSLR Chris?
Cheers
Bartman

[Omaroo]

PM'd Bart.

[Octane]

Chris,

How can I get hold of one of those for my 200mm f/2.8L II USM? It's a 72mm filter mount.

Cheers, buddy.

H

[Omaroo]

PM'd Humayun

[Omaroo]

Humayun - I use my 52mm filter and connect it to a 72mm adapter I made up for my larger lenses. Works great - one mask does the lot.

Sorry about the pic quality...

[leon]

By the way H you wont need a B/Mask on the Tak, ;) it just snaps into focus.

I am 60 and I have never used any computer, and/or any focusing device to get focus, and I am half blind, LOL, and some of my pics are pretty reasonable :shrug:

Just move it into and past focus, you will see the B/Mask effect instantly, in the scope. :thumbsup: :thumbsup:

I bought one once and sold it the next day totally useless on a Tak mate.

But that is only MHO :shrug:

Leon :thumbsup:

[Octane]

Leon,

Yep, I'm expecting the FSQ to be far easier to focus than any other scope I've had in the past. Was just wondering about it for the 200mm lens. :)

Hopefully first light this weekend!

Will get in touch with you regarding a couple of adapters -- I have no idea what to use a couple of them for. :D

H

[Octane]

Thanks, Chris!

H

[leon]

Don't ya, well we surly can fix that. ;)

Leon :thumbsup: