I'm looking for some help with a lightbox design. Since getting the paracorr I've been able to use my 400D with the 10" newt however vignetting is now an issue. I'm looking for some ideas for building a lightbox suitable for the 10" newt. I'm thinking foam-core construction. It looks like I'm also going to need some perspex for the diffuser.
Thanks Allan. I did take a look at this website (thanks Baz). I've got the foamcore board sorted and need to find some opaque perspex. I reckon you need a lightbox too - are you tempted to come shopping tomorrow?
What I use is a computer screen. Tape a diffuse plastic screen over a computer screen after opening notepad for example, so the screen is nearly all white. Move the monitor/scope combination towards each other and line them up. Start taking your exposures to work out how long they need to be, then its happy flat frames time! You can do this next day if you want to. Don't always expect your flats to be white in colour. If you're using a Canon and DSS, it will treat them like a grey frame and subtract it properly anyway. Mine are traditionally bluish in colour. Give it a try!
I've got the foamcore board sorted and need to find some opaque perspex.
Peter, I got mine from a glassier in moss street. He's about 1/2 way between the springwood end of moss street and the first bend at the top of the hill, on the left. They cut it to size for me and it was only $10 for a 10 inch square.
Thanks Dennis - I've seen your bucket and would have done a similar thing only I couldn't find a big enough bucket for the Newt at the ota is 12" diameter. I'm planning to follow Baz's design and have now found some perspex - at Reverse Garbage. How do you power the LEDS?
The LEDS I bought where stock number Z3980 5mm White Lite LED 2000mcd.
$7.80 for 4 plus 35c for a 5watt 120 ohm limiting resistor.
I run them off 12 volts and they are in parallel.
I hot glued them in and pointed them up to the back of the box.
Thanks Dennis - I've seen your bucket and would have done a similar thing only I couldn't find a big enough bucket for the Newt at the ota is 12" diameter. I'm planning to follow Baz's design and have now found some perspex - at Reverse Garbage. How do you power the LEDS?
Hi Peter
I ended up wiring the 6 LEDs in Series with a 120 Ohm Resistor. I use a 24V 1A regulated mains adapter, left over from my Tak mount which operates on either 24 or 12V.
I cut a circular disc from thin aluminium sheet and placed this at the bottom of the bucket after I had abraded the surface with an orbital sander. This acts as a diffuser and scatters the incident light à la Lambertian Scattering (see link below).
Wow - you are hitting them with a fair current at 12V with a 120 ohm resistor - I calculate you needed 270 ohm. Are they lasting ok?
Yes they are fine. You'd need the data sheet that comes with the LEDs to get the current needed for optimal performance. Once you have the current you can calculate the resistor. 2000cmd is bretty bright for an LED, I only used 4 of them. The data sheet also gave me the FOV of the LEDs, which was very narrow, so I didn't use internal baffles etc, I just pointed them to the back of the box. I adjust exposure time to get the recommended 30% well depth for a flat.
Dennis - did you change the LED's to Series? I though your wiring diagram in the other post looked like they were in parallel?
Hi Peter
Yes – the project started out with the circuit diagram showing LED’s in parallel, but as I had a spare 24V 1A mains adapter and with the simpler wiring/soldering of in series LEDs, I settled on wiring them in series with a single 120 Ohm resistor.
You can do this next day if you want to. Don't always expect your flats to be white in colour. If you're using a Canon and DSS, it will treat them like a grey frame and subtract it properly anyway. Mine are traditionally bluish in colour. Give it a try!
