M33/ modifed webcam, M33 Atik 314L

[Rocket Pooch]

I love this, all I did is went away for one day come back and look what happened.

So I assume we are all in agreement about the F no and S/N.

Shall we start on the pixel size and sensitivity well depth and also the ADU count?

John and I had a good chat about the following, this is a pop quiz.

If John and I take two images of a star using two different CCD's

John's has an ATIK ic16 QE68%
Mine a ATIK314L QE65%

Same scopes, same conditions, same night, same star & same duration of exposure, everything the same.

Why is my bright star at 64k ADU's and John's at 38ADU?

And how does this affect the price of fish?

[MarkS]

Daniel,

I'm really looking forward to seeing your results with the hyperstar -it sounds like a brilliant setup.  The learning curve may be steep and there are a few obstacles you may need to overcome:

1) At F2 focusing will be extremely critical as will alignment and collimation.
2) Light pollution might still be the main limiting factor because it will saturate the CCD very quickly forcing you to keep exposures short.  But then again short exposures is its main purpose!
3) Related to the above, some filters will not work very well at F2 - the steep angle of the light cone can cause loss of transmission and colour displacements (I also noticed this when putting my CLS filter on the front of a F1.8 camera lens).  Check out the manufacturer info for each filter you intend to try.
4) Will Hyperstar give pin sharp stars across the whole DSLR CCD (which is big) or just a central portion?

Good luck!

Mark

[MarkS]

If John and I take two images of a star using two different CCD's

John's has an ATIK ic16 QE68%
Mine a ATIK314L QE65%

Same scopes, same conditions, same night, same star & same duration of exposure, everything the same.

Why is my bright star at 64k ADU's and John's at 38ADU?

I guess you mean John's was 38k ADU?

You pose an interesting question.  The similar quantum efficiencies (QE) should mean they both capture the same proportion of photons. I'm not familiar with the ATIKs but here are some possibilities for the difference:
1) The pixels may be bigger on yours so each pixel collects more photons
2) The amplifier gain may be different i.e. electrons/ADU may be not be the same on each camera
3) At 64k ADU it also sounds like your pixels were saturated i.e. the light reached the full well depth.  Maybe both cameras had saturated and John's well depth is only 38k?

Not sure how the price of fish is affected - maybe it's the Observer Effect:  the very act of observing the Universe changes its state ...

Mark

[Mike]

Surely light pollution/sky conditions in the differ enet locations would have a huge effect on ADU.

[Rocket Pooch]

Same place, same time, same image, same type of scope same filters.  Same star being images for the same duration of time by both cameras.

The observer was a small mirror carp.

[Mike]

In that case one of you had the ability to deflect or attract photons and therefore making less of them go down one tube compared to the other.

[RobertM]

Same place, same time, same image, same type of scope same filters.  Same star being images for the same duration of time by both cameras.

So if everything was the same including the price of fish and the mirror carp wasn't under the influence of some exotic fish bait, no focal reducer used and the star was in the center of the FOV.  Is it possible that the fish had a dodgy eye and used that for focusing john's image.

[Mike]

In all seriousness, that might be why. If the focus was just a tiny bit different on each set-up (which it would have been) then the ADU would be slightly different.

Did you use the same carp for focussing both scopes?

[Rocket Pooch]

Ah ha everything is not the same, the cameras are different, the carp is exactly in the middle of the two scopes and is in a cardboard box.

So there is a difference, what's the answer?

[Mike]

If the carp is in the cardboard box, with a vial of arsenic, with the lid closed, and a tree fell in a forest with no-body around, would you see a rainbow?

[Rocket Pooch]

Ok, the Carp is in fact a Red Herring and has nothing to do with the images, but..

The cameras has similar QE give or take 5%, but they have different full well capacity, I think I got them backwards by the way.

So with the 314L to conversation between the photons collected in the CCD is of a greater scale than on the 16IC

Roughly the 314L has a 27k full well capacity, thats 27k photon to get to 64k ADU

The 16IC has a 30k+ (and its apparently more like 60k) therefore 27k photon get you approx 32k ADU

That's it.

[RobertM]

So how about doing a talk on that and image processing ? 

[Rocket Pooch]

Because I fear most of the people in the room will fall asleep.....

[RobertM]

I'm counting on that

[MarkS]

So both the well capacity and the gain are different for the two cameras ...