517 replies to this topic

[cnstarz]

Dennis,
I like this focusing mask thanks for the links and info. I'll try to make one like you've pictured, but first I may use the diffraction angles you've given on a mask like this...LINK
I've been experimenting with the three holed Hartman mask and I think breaking up the symmetry with diffraction spikes like you've described will make it more useful.
Regards,

[Dennis Sakva]

Hi Matt,
The main advantage of the mask proposed by Pavel is that you see very clearly where are you right now (before focal point, after it) and there two diffraction spikes give nice and easy reference to compare to. The mask at your link provides no such "reference" lines. The picture just gets messy when not in focus. But one thing for sure it's much easier to make and to try.

[Dennis Sakva]

The are a few free vector based graphic software.
http://www.inkscape....wnload/?lang=en

[cnstarz]

Dennis,
I understand your point, I'll give it a try. I see the key to this is to have two elements that are complementary and a third that contrasts Like here ... MASK
And as your pictures show, the ability to gauge in and out focus is enhanced by the diffraction spikes. I've experienced some frustration using just the three circle mask so I'm eager to try this novel design.
Thanks

[Jerry3672]

Dennis, I followed your link to Pavels design. I drew up a DXF file in Pro-E and cut this out on a water jet. I made the mask out of Aluminum and just painted it black. I will test this as soon as the clouds break.

Thanks for passing on the design.

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[John Wunderlin]

Can't wait to hear your results. This looks like a potential holy grail of focusing. And a business opportunity for someone with machining tools...

[Dennis Sakva]

Wow... Nice! Looks professional Please let me know how it works for you.

[Jerry3672]

Thanks, I was going for a professional part.

John- I do have some nice machine tools and engineering software. I'll have to cut Dennis and Pavel in on the action. Couldn't you just see the look on Pavels face when big royalty checks start rolling in?

I do think I have an understanding of how the design works, and why you can't just scale it for other size scopes.

The axis is centered for the "left" side and has a precise light block of 50%. The "right" side has a 20 degree angle that is centered to blocked area of the left. The right side has a light block of 40%. The axis of the right open area must align to the center of the left blocked area. If it centered, then the spikes you see when in focus will align correctly.

I don't read Russian, so I had to look a photos and calculations that Pavel posted.

If this works like I think, then it will be simple for me to draw this design for any size scope.


darn clouds

[Joe Bruessow]

This looks really cool... but I have not been ambitious enough to download the translating software... I'll wait until one of you geniuses posts this all in English

Thanks...

[MtnGoat]

not sure how much they'll be, but I'll volunteer for a couple. I tried doing one with card board and X acto knife last night...horrible. way too many long fine cuts, then when removing material one cut doesn't go all the way through and tears the solid piece next to it. After fixing four breaks at less than 25% done, I said &&&$*$## it.

[Dennis Sakva]

Actually it's important to keep lines straight and free of burrs as those will interfere with diffraction pattern making it blurred. If you don't like cutting you may try gluing strips of something opaque on mask template.

[Jerry3672]

Not reading Russian made it hard to understand what the sketch was trying to say.

i see now.

My lines are very straight.

[Dennis Sakva]

Yeah, cutting with laser or water-jet gives very nice cuts, working with X-Acto knifes (MtnGoat) is hard

[blueman]

It is too bad that no one is making these for sale!
Blueman

[Jerry3672]

someone will soon

[Jerry3672]

One test complete.

This blows my hartman mask away.

Here is my test image going from in focus to out of focus in both directions.

This was only a very small movement with the focus knob

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[John Wunderlin]

Beautiful! Did you have a chance to image using the resulting focus point?

[Jerry3672]

I did image 5 of Jupiter's moons. I need to do some work in Photoshop for the final image. Himalia is a mag 15 and Jupiter is -2.5, so I have subs from .001 to 60 seconds.

I plan on using them in the August Challenge in the beginner imaging thread.

[Nocturnal]

This is the best image I've seen yet to demonstrate a focusing technique. Thanks for posting! I use Nebulosity 2's HFR technique which works very well too. One of the nice things of quantified focusing is that you can chart it to see trends.

How does this mask deal with seeing? Does the central line shift as seeing changes? That would be a terrific benefit of this mask if it's seeing independent.

[John Wunderlin]

That's what I currently use as well, but I have to go back and forth many times before I'm comfortable that I've gotten it even close. I usually spend 10-20 minutes messing with focus and by the time I actually image, the focus may have changed! This looks to be a few seconds to lock it exactly. What a time saver! You'd be able to quickly and easily recheck focus between images and scope movement.

[Jerry3672]

Not sure if seeing changes the image. I just used it for the first time last night. I have lots of testing to do.


here is a 60 second exposure of Jupiter. I was attempting to bring in the mag 15 moon Himalia. This was with a Meade DSI Pro. You can see the spikes off of the other moons are equal in all directions. i think the focus was dead on.

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[Dennis Sakva]

It works when the seeing is bad too. Seeing will blur the pattern a bit, but you still see where the true focus is. Yesterday it was very windy and the seeing was terrible. Without the mask I wouldn't be able to focus at all. As FHWM was jumping like crazy.

[FoxK]

I may try to make one..since we got lots of clouds rolling in lol...

I drink ALOT of coffee....seems the plastic covers on the cans can be exacto'd easier than cardboard. Will give it a go

[Nocturnal]

Ok so that's very interesting indeed to be able to focus through seeing. Thanks!

[MtnGoat]

gee, thanks for showing us how good it works. now wanting one is even worse!