Angle from scope to lightbox?

[ollypenrice]

What do you think? I have modified my lightbox to get a better spectrum and it now stands on the floor with the light panel facing up and horzontal. Do you think the scope needs to be perpendicular to the illuminated surface? I'm thinking about the inverse square law. Squaring the difference in distance between the near and far side of the lens will make it significant. On the other hand all parts of the lens contribute to all parts of the image so it shouldn't matter. I'm not good at this kind of stuff... Erm...?

Olly

[Shibby]

I often wonder this too... I point my scope at the TV, but the OTA isn't at the same height as the TV, so I wonder if this is a problem?

[Psychobilly]

My light box hangs from the obs roof and I just roughly square the scopes to it...

Billy...

[roundycat]

square is best. In theory the front node of the lens is a point and it is that which would be used to calculate any squares.

Dennis

[old_eyes]

Olly,

I think it matters in principle, but may not in practise. After all the whole point of the optical train is to create an image of what is in front of the objective at the focal plane/sensor. So although all parts of the lens contribute to the final image, the optical transform takes all those paths and recreates an image on the sensor.

But experiment should rule. If there is no gradient that is invariant as you rotate the camera, I guess it doesn't matter.

old_eyes

[ollypenrice]

Hi,

Yes, in practice I will indeed experiment but for tonight I just want some flats for what's in the can!! I can't rotate the camera because then the flats would, of course, be invalid. I set up the box about perpendicular and did shift it around a bit to see what difference that made. It looked like none but... dither dither...

It does seem to be giving a nice spectrum but closer analysis will confirm or refute that.

To be continued.

Olly

[martin_h]

I use an EL panel between 2 sheets of opal perspex and just point the scope straight up and lay the panel over the dew shield. I dont know if that negates any focuser droop that I may have tho?

[ollypenrice]

If you have focuser droop (at your age!!!) the effect on the flats will be the least of your worries. You will have dodgy stars which will be more significant.

I know EL panels are easy and much to be preferred but mine, which was quite expensive, pegged out at an early age and in a fit of righeous indignation I decided to go back to light boxes. My new one, somewhat over engineered, is a less than light light box but I put up with it because it was cheap and so I gave myself permission to buy a new 26mm Nagler as a reward...

Olly

[martin_h]