Good quality 3D printed Bahtinov masks for telephoto lens. Slits are 2mm wide, so they are suitable for focal lengths of over 200mm. The smaller one fits 67mm thread size and the larger one is for 72mm thread. They are slight push fit, no need to mess with screwing them in.
The red rim is for red torch visibility.
If there is demand I can make these for all sizes up to about 140mm clear aperture.
You can have these for $30 or I can separate them for $20 each. If you are not from Melbourne and can't pick up then a $5 postage charge aplies too.
Update: The size 72 is sold, the 67 is available for $20.
Last edited by Stefan Buda; 20-07-2015 at 10:04 AM.
Reason: update
Stefan, if I send you my mask diagram as an .svg (I generated it using the Baht generator online), can you custom make one? It is for a 78mm f/6.4 scope.
Stefan, if I send you my mask diagram as an .svg (I generated it using the Baht generator online), can you custom make one? It is for a 78mm f/6.4 scope.
DXF file would be better but I should be able to convert the svg to a format that my CAD understands.
Whichever the format, I still have to produce a 3D model for printing.
At the moment I'm working on a model to fit 77mm diameter filter threads and on the weekend I'll be working on one to fit an 80mm refractor.
Is it not possible to make them with narrower slits for the myriad of smaller lenses out there like my 18-200mm which would need one of 62mm diam? I'd buy one immediately.
raymo
Maybe I am missing something, however when I used to use my Canon 500mm lens for any astro work, I would auto focus with the center focusing point only on the camera, then turn the lens to manual and image away.
During the night if the temp fell dramatically I would do an other auto focus and go again,
So why the need for a Bahtinov Mask on long lenses.
For top results people attach DSLR lenses to CCD cameras and in that case, at least with the current generation of CCD cameras, the auto focus feature is lost. Also there are old telephoto lenses that don't have auto focus.
I can now answer raymo's question about finer slits: Yesterday I made a 55mm one with 0.9mm slits for my 135, f/2.8 lens and a 58mm one requested by a well known Victorian astro imager, also with 0.9 slits. Tomorrow night I hope to test mine on the sky.
cheers,
Stefan
Last edited by Stefan Buda; 17-05-2015 at 10:48 AM.
Looks promising Stefan. Having not looked into the technicalities of
Bahtinov masks, I don't know if one would work with a zoom lens, or
if they are limited to prime lenses.
raymo
This post should really be in the ATM section but the thread I started there, to share my experiments, got promptly locked - probably because I mentioned potential commercial activity.
Anyway, last night I did some testing using various combinations of lenses and masks, with interesting and somewhat surprising results.
Lenses used were my trusty old Pentax 50 f/1.7 and a Mamiya 135 f2.8 attached to a QHY8 camera.
Bahtinov masks with 0.9mm and 2mm slits were tested with both lenses.
Main things learned:
2mm slits work well for 135mm focal length which came as a bit of a surprise.
0.9mm slits produce too much diffraction with the 135mm lens and the patterns are hard to interpret, also a surprize.
2mm slits are not quite good enough down at 50mm, as expected.
0.9mm slits work very well with the 50mm lens.
One needs to choose bright stars for the diffraction pattern to overcome light polluted sky background.
It will take me a while but eventually when I've done all the cutting, pasting and labeling required, I will post the images from last night.
Cheers,
Stefan
Last edited by Stefan Buda; 18-05-2015 at 01:42 PM.
It will certainly work for the 100 to 300 range but having not tried it down as far as 70, I cannot be sure.
Most likely that if you have a bright enough star in the field and the sky is not too bright you should be able to see a good diffraction pattern.
I will soon follow up with the test pictures I promised a few days ago.
Finally I have processed some of the test images. What a pain! I had to debayer them one at a time in DSS then develop and crop them in Star Tools, and then assemble them in Paint.
The fourth panel is with the mask removed after focusing was achieved.
That panel shows quite well that the lens was designed for film, as it produces red rings around reddish stars.
Tomorrow I'll try and present the images captured with the 50mm lens through a mask with 0.9mm slits.
Here are the test images with the 50mm lens and a mask with 0.9mm slits. It is obvious from both sets of images that my sky is very bright and these masks should work even better under a dark sky.
I did only used Canon 5D.
