Five galaxies

Dave,
darks for your flats, thats a good one, :lol: I hadn't thought of that, but there comes a point were it becomes abit of a pain.
You've just described the best and easiest method I've come across for flats, so I'll try that.

I'm over 2000 posts now

Woo hoo! And what a way to get there

Darks for flats - yes, used by the 'serious' imagers out there. Really. They use techniques that put us well towards the bottom of the learning curve... I'm not sure why they do it because these folks have kit running well into 6 figures - if I had that kind of gear and I saw a dust mote on the primary mirror of my 24" Richey-Chretian, , I'd throw a wobbler...

The t-shirt flat is well documented by Ron Wodaski. He came across it when he was imaging and fell asleep. When he woke, it was too late to shoot his flats using his previous method - dawn flats. Here, you shoot the dawn sky in a few different ares. You'll pick up some stars but if you then combine different areas of the sky, the stars are combined out. So, as I was saying, he just threw a t-shirt over the OTA and was surprised at the result. It turned out so well, that he recommends it in cases where you don't have a light-box ... to go along with your 6-figure observatory Light-boxes are another ball game altogether...

I tried the t-shirt flat method and got super results. Very easy to do, cheap and they can make a big difference if your optical path has motes, vignetting and other odd peculiarities. I never bothered with the flat-darks though

Cheers

Dave

Dave Mc,

I discovered that I would often try to take a flat when the sky was in twilight, but discovered that most times there was a lack of linearity in the sky due to cloud irregularities. I rather got frustrated with this methodology and decided that I needed something that would guarantee a flat every time I would use the telescope.

If you do plan next year to make a light box, I designed and built one during the summer for my own telescope. Here follows the detailed report on the making of the light box. I have pictures of the light box that I can send on to you, or any body else, that is planning to improve their imaging with there telescopes. However, the dimensions in this case are big, but in smaller instruments you will be able to obtain the same results using the same materials.


Light Box:

The light box needs to be light in weight and ease of use, uniformity of illumination and ultimately acceptable flat field correction.
The light box is constructed of 1/4" foam core. Each sidepiece is exactly 41.25” x 41.25" (4 pieces). The top is 40.75" x 40.75". The assembly is held together by a combination of glue and thin aluminium. The completed box is attached to the white plastic plate by glue. There are two diffusers each square is 40.00” x 40.00” positioned 2” apart within the square box. Each diffuser is bonded to a circular opening 38.5” each with the separation of 2”. The whole structure is tenaciously bonded with glue. All the edges are sealed with thin aluminium.

The whole structure is solid and incredibly light for man handling.
The illumination source and box proportions are key to a successful design with uniform illumination.

The ideal geometrical arrangement is when the most uniform illumination occurs when the distance from the inside top of the box to the LED's is equal to the separation of the LED's. The concept is that the top of the box acts as a first diffuser and by locating the illumination sources near the corners of the box, the resultant light combines to a uniform level at the plastic diffuser. The diffused light from the first diffuser projects to the next diffuser. The next diffuser smoothes out any remaining gradients. Flat field should be better than 0.5% with this design.

The design uses 8 LEDs. They are ultrabright white LED 5mm, 11000mcd. Nichia in Japan manufactures the bright white LEDs. They combine a high quality phosphor with their recently commercialized indium-gallium-nitride (InGaN) blue LED. They found that when blue light from the InGaN die passes through a thin phosphor coating, a portion of the blue light is down-converted to yellow light. This yellow light mixes with the remaining blue light to create a bright white light.

The emission spectrum of this bright white LED shows the blue emission from the InGaN die at ~460nm and the yellow (shifted light from the phosphor) peaking near 560nm. There is little blue intensity below 450nm, where as astronomical blue filters on CCD cameras extend down to about 370nm. The yellow shifted light extends to about 750nm, which covers most red astronomical filters.

Eight micro drives modules were built to power the Nichia LEDs. The driver was designed to provide maximum illumination to the LED while mimicking the light drop off of an incandescent bulb, which dims as the batteries are used up. Unlike an incandescent bulb, the driver’s current consumption drops at very low voltages, allowing usable light to be produced much longer. The optional universal power supply 3-12 Volt/800mA provides better sustainability.

A second key item were the LED holders. These holders support the LED and act as a baffle to prevent the light from directly illuminating the diffuser.

The LED's and holders are mounted near the centre of a 1" x 1" square of foam core, glued to the inside corners of the box with adhesive and located approximately above the plastic diffuser. They are located around 10.00” above the plastic. Spacing is not critical except to maintain the dimensional ratio mentioned above. Leads are through the side of the foam core and the wiring is outside of the box.

Eamonn A

I was out tonight all set to take a few images of these galaxies.
I got the canon setup and focused, the laptop was booted and all ready to go, I got the skylux guiding scope alligned to the 12", I focused with a 3x barlow and a toucam, I even setup the PEC. I just started focusing the Canon on Rigel through the 12", and then it dimmed :shock: , a massive blanket of cloud was crossing the sky, it had been clear all night and just as I was ready to start taking pics, it clouded over, just typical of our damn weather.

So this is my first attempt at SN hunting

Hard luck Dave! Its that Murphy guy screwing you around again!

Dave.
I tried getting those galaxies, but as my scope is a fork mount, I cannot image near the pole using the canon as there isnt enough clearance, I cant reach those galaxies!, I thought that this might be a problem as soon as I saw where in the sky those objects were.

If you like at my avatar, you'll see the issue, the GEG+uFocuser+300D, will hit the bottom of the mount, if I remove either the GEG or uFocuser it will clear but I loose that functionality and it screws up the scopes balance which is not as easy as you might think to setup, you'll also find that people with 8" SCT have even less clearance and will also have this problem.
The setup as is can definitely go up to 65 degrees north and up to 71 in certain areas.
While I was out I got this luminance tesat image of M51. can we mot use this object as its big and bright?

www.irishastronomy.org/user_resources/fi...-300s-1600-004_3.jpg

This is an un-guided image, its just to see if it was feasible to get a reasonable bright image using a 5 min exposure, this is a single frame whos levels were altered in photoshop, minimal processing. I didnt take DF/FF/BF.