Wednesday, June 22, 2011

Field of View templates

I have known about Ponoko for a while, but never had a burning (haha) desire or project that I felt was appropriate.

As an exercise I calculated the field of view for my 4 most used eyepieces for my three scopes (10.1" f4.5/C8/C5).  Unfortunately degrees doesn't really translate into "what can I see in this eyepiece" in my head very well.  A little googling got me a page which converted degrees to cm for the Pocket Sky Atlas (my main goto chart).  It happens to be .4991 cm per degree.

Armed with this information, I used Adobe Illustrator to design 3 small guides --->

In addition to the eyepiece FOV circles I included a set of Telrad and Rigel QuickFinder rings as well.  Before I sent them off for laser cutting I printed them out on paper and did a quick check to make sure my measurements were correct.

It took some fiddling about before Ponoko would accept my design for cutting but once I figured out the idiosyncrasies and decoded the somewhat cryptic error I was getting from Ponoko I was able to select my material, in this case 1mm PETG plastic, and submit my designs for lasercutting.

I was pretty excited when they showed up.
The shipping was quite fast
Once I submitted my design and had it approved, it was a short 12 day wait.  On a side note, because I don't subscribe to the prime service, I was a week between when the materials were ready, and the job was actually run.  I don't know if this was legitimate due to the queue of jobs in front of mine or because I don't have the Ponoko prime service (which is 40 bucks a month).

I received the results today in the mail.

What was in the box.
All the materials are standard sizes, and you get a full sheet regardless of how much of it you use.  Since I used the smaller size (181mmx181mm) I got the whole sheet with my three observing aids on it.

 I quickly removed my pieces from the attached paper which is attached to the sheet in order to keep the parts from falling out and getting loose in the box.

Here are two of them with the film removed for contrast
The plastic comes with a protective film on one side
Hence the "frosted" appearance

 A quick check of my guide against my Pocket Sky Atlas using the Telrad scale shows that my measurements were good and the final result matches well.

Another check using the FOV for
my 24mm panoptic matches
what I have seen in the scope
using M81 and M82

Overall I am very pleased with the results however the engraving was difficult to read.  As and experiment I have used an oil pastel to fill in the engraved lines.  I think the results speak for themselves.  Before I do it to the others I plan on seeing how well the coloring holds up under normal use.  I think paint might ultimately be the final permanent solution.  It took me about an hour or two to design the guides and get it to be accepted.
Costs :  $19.36 for making costs (time on the laser)
$1.86 Materials Costs
$9.75 for shipping
$30.98 total plus $1.98 international transaction fee from my bank since Ponoko is based out of NZ, something to be aware of should anyone else use their service.


  1. As you make changes, you might want to keep a backup copy of your last working template so you don't have to go back to work from the original template file if you mess something up.