Paul R (1ponders) has written a fantastic article about the hartmann mask for the IceInSpace How-To's page.
He goes into great depth covering topics such as how the holes in the mask affect the diffraction spike patterns, the best configuration of holes to get the sharpest spikes and therefore sharpest focus, how to actually use a hartmann mask to get crisp focus, and of course how to construct one.
It's a really nicely written article, thanks heaps for taking the time to do it Paul. Read the article here:
I just ordered a T Ring and Adapter for my 10" Hardin last night, for doing some prime work with my digital Rebel, so the article was very timely for me
A quick question...
I see that the mask and different patterns were tested on a SCT and that the 3 triangles appeared to give the best/cleanest/easiest pattern to work with. If I was going to try and do the same thing with a 4 vane spider, would the 3 triangle pattern work?
Depending on the size, at least one of the triangles will be disected by a spider and more than likely, the other two will have some portion of a spider crossing them.
Using two triangles opposite each other would be fine. Or you could use four triangles. I just found that three made it easier for me to view the "coming together" of the multiple images. As an experiment you might want to try with just circles and use the mask with each circle placed over a vane (either two or four holes). This might be enough to create diffraction spikes anyway. As you mentioned I experimented with different designs on and SCT, but also a 4" refractor. I didn't have access to a Newt at the time. I would be interested in any results you come up with. If there is anything different the original article could be updated with the new info relating to newts.
just when you thought it was safe, Paul now makes us play with scissors? I thought the electrodes were enough!! or is this the result of the electrodes Paul.. Were you always seeing things in double or triple! Great article!!
thank you very much. My two and five year olds have helped make me a hartmann mask for my 10" dob. Instructions were very easy to follow. The template has been coloured in with pink, blue and green textas and there is a picture of barbie and a dog, but apart from that, it is a very manly project!!!
I made a 2 hole version for my 10" Dob years ago. Originally cut 1 x 90 mm hole but found it fouled the spider/2ndary. I then added the 80 mm in the correct position clear of the tube sides & spider etc. This is the one I use as the aperture stop. Works extremely well with focusing, even being slightly diff. sizes. Just used 200 gsm card stock from the newsagents. Sprayed it with clear lacquer to waterproof.
HTH. L.
I found out something last night about aperture masks: I setup with the 12.5 reflector, just waiting for mars, but the wind come up cancelling out the nights viewing. But anyhow, while I was out there stuffing about, I decided to muck around with my 3 round holed aperture mask, by blocking up 2 of the 3 holes, knocking back the aperture from 12.5" to 5" I hopped straight to a medium bright star, & had a bit of a gander. I decided to de-focus for some reason, & low & behold the diffraction rings & airy disc were SOOO much easier to see than usual.
I'll be collimating the scope this way from now on I think?
Yeah. It usually takes time to collimate a primary by using a star, & half of this trouble is from poor seeing & not being able to see the diffraction rings clearly enough. Last night was exceptional seeing though (while I was setup I mean)
Can't wait for crappy seeing now (go figure!? ) to see if the mask works as I think it may!
Actually I've tried collimating with a contrast booster on, it works to an extent as well. I've often tried with the 3 holed mask but this is the first time I've reduced the aperture so far...no assistant, but I'm pretty quick at getting to the primary screws L.
The only thing that's Ps me off is having to re-align the finder if one has to move the primary a fair ways. This is the 1st time I've seen a airy disc so clear before....Just the ticket for splitting Sirius too I reckon!
Actually I've tried collimating with a contrast booster on, it works to an extent as well. I've often tried with the 3 holed mask but this is the first time I've reduced the aperture so far...no assistant, but I'm pretty quick at getting to the primary screws L.
The only thing that's Ps me off is having to re-align the finder if one has to move the primary a fair ways. This is the 1st time I've seen a airy disc so clear before....Just the ticket for splitting Sirius too I reckon!
I used a Hartmann mask in Feb 2005 to try and split Sirius, I found what appeared to be a blob (the pup maybe?) sitting just out on the start of one of the diffraction spikes. I showed Astro_south+ this observation when we met up out at Leyburn. I think a hartmann mask is good for this type of use as it seems to tone down the glaring primary. Still I'm not sure or can remember if he was convinced.
Rob, Why not try the diff shaped masks, as per my pic? You slowly rotate them over the hole, to get rid of/move the spikes. Might pick it up a little easier. Damn hard object tho! L.
The styrofoam is a great idea--strong and easy to work. Saves a lot of time stuffing around trying to cut plywood circles or sticking cardboard cutouts to the scope with masking tape. I now have a decent mask with less than 30 min work.
Thanks
Geoff
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excellent read Paul great work , got some work to do for the WE 
Great Article - Quick Question
I then added the 80 mm in the correct position clear of the tube sides & spider etc. This is the one I use as the aperture stop. Works extremely well with focusing, even being slightly diff. sizes. Just used 200 gsm card stock from the newsagents. Sprayed it with clear lacquer to waterproof.
I hopped straight to a medium bright star, & had a bit of a gander. I decided to de-focus for some reason, & low & behold the diffraction rings & airy disc were SOOO much easier to see than usual.
