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Bahtinov Mask – Does not work ?

johnb

By johnb
in Imaging - Discussion

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johnb

johnb

Posted
Posted

Hi

Well ok im sure it works and its me. I set the scope to Sirus and attached my DSLR a Sony A350 in live view and I could see the star, I put the mask on the scope and was really please that I could see 3 blobs of light (the instructions say that I will see that if its way out of focus) anyway I started to adjust the focus and the 3 blobs of light then came together in a single point I kept going but could see no diffraction pattern at all, in fact it went past as single point of light and back to a 3 blob pattern. So im not sure what’s wrong, pointers appreciated.

Regards

John B

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davew

davew

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Hi John,

I can't say for sure but I imagine that type of mask would require a 15 / 20 second exposure and zoom. I don't see how such a small amount of light would show up in live view [ Bahtinov spikes ] . Unless you have eyes like an errrr....brick out house rat.

Dave.

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johnb

johnb

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Hm

Well the instructions dont mention any limitations.I note a couple of you say mention longer exposures ?, err if im in lieve view im not sure how that is achieved. Would it just be simpler to get a "Proper Bahtinov Mask" (sorry dont want to make one), can someone point me to an appropriate one

Regards

John B

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johnb

johnb

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Ahh (im getting this slowly) so get a single point, leave the mask on, take a 20 sec exposure then zomm in and see if I see a diffraction pattern and then work from that with finer focusing - seems like a way forward but a bit of a nightmare to do each time ?

John B

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Psychobilly

Psychobilly

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If your not already doing it....

Wind the ISO right up whilst your taking the focusing images and then set it back to whatever setting your going to use for the imaging run... although I normally take the framing shots at Max ISO as well ..... then drop it down...

With a traditional Bahtinov I get a decent images with a 4s exposure at ISO1600 on the Megrez72 FF III combo (around f4.8)

Peter...

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davew

davew

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Hi John,

It just may be the nature of the beast. I don't have live view on my present camera and have to do this every time.

Unfortunately I can't comment about the Sony, I've never used one.

Dave.

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johnb

johnb

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Thanks to all, really helpful. I think the problem was my understanding in that I thought I would simply see the diffraction pattern directing in Live View with out having to actually take a shot.

Thanks again

Regards

John B

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Shibby

Shibby

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Even with full aperture mask on a bright star, I have to take at least 8s exposure to see the spikes, zoomed in on camera. Which is a bit annoying because it means one has to align the scope for tracking before focusing it...

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