Flats (2);-)

[Steve Cuthbert]

Hi guys

Not having an Alpy calibration module I`m setting up a rig whereby after an evenings observing I can just park the scope up, slip this diy light diffuser over the end of the tube and I will have a Halogen light in place to then take all the flats.

Its supposed to be similar to the setup shown on Christians web site, but I`d be interested in how others take flats without the convenience of a calibration module please.

thanks

Steve

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[Robin Leadbeater]

Hi Steve,

At least the ALPY is stable enough not to have to go to the extreme of taking flats with the scope still aimed at the target  like you have to do with the LHIRES if you have a camera with small scale ripples.

http://www.astrosurf.com/buil/fringes/index.html

Before I had the calibration module, I injected the light from the RELCO calibration lamp via a reversed flip mirror. Perhaps a diffused incandescent light source could also be used this way to produce a flat.

Cheers

Robin

[Mr Allan Brittan]

Does it need to be a halogen light or is there other options?

kate

[Steve Cuthbert]

Hi Kate

I did try a ring of led`s thinking that would be ok but instead got some weird lines which seemed to make things worse??.

Steve

[Tony Rodda]

Steve, Kate,

I find that the diffuser (or simply a sheet of artists quality tracing paper taped to the end of the tube) works well for twilight flats.   A mate of mine uses a clean white thin t-shirt!

For more formal flats I constructed a lightbox out of white (artists) foam mounting board from Hobbycraft.  A couple of A2 boards was enough for me.

It’s very light (no pun) and can be cut with a craft knife or Stanley but is really rigid and can be glued with PVA.  I constructed mine in two halves.  The first contained a (tracing paper) screen which fits the end of the scope with an outer ring of LEDs powered by a common switchable 12v adapter supply.  The LEDs face outward and do not directly illuminate the screen..

The LEDs work down to 5V so by switching the adapter you can change the brightness.

Skyflats need just this unit.

If no ‘sky’ than I put another foam box over the end and turn the LEDs on.  The box internally reflects the light so as not to produce any direct light or shadows onto the paper.  Evenly illuminated without any interference patterns.

Works a treat.

Regards

T

[Robin Leadbeater]

Is this for spectroscopy?  If so you can’t use twilight or LEDs.  You need a light source with a smooth spectrum with no features. 

EDIT: you might be able to get away with LEDs in some parts of the wavelength range in higher resolution spectroscopy but I dont know of any LEDs which have a smooth enough spectrum or wide enough wavelength coverage for the ALPY for example

Cheers

Robin

[David Dunn]

Hi all,

If I remember correctly, one needs to use a tungsten based source. Attached are the spectrums of a “white” LED and a fluorescent.

David

[Mr Allan Brittan]

Thank you all.

I never realised taking flats could be so confusing, but I have a pillow case and will find a Halogen light to use.

Kate

[Mr Nicholas John Atkinson]

I installed halogen bulbs in my light box.and they were OK

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