UPDATED: Uh oh! Interesting, but ????

11.15.06 - From discussions generated by the MallinCam Yahoo Group I'm pretty sure that the problem lies in the refractor. Either it's hopeless in terms of getting true color, or I have to make serious changes to the camera settings - particularly white balance. I'm looking forward to experimenting along these lines as I would like the one-degree fov that the ShortTube 80 can deliver - but it doesn't interest me if its going to bloat red stars and generally distort reality. For more images and to see comments from others thatled me in this direction, you can simply scroll down or jump directly to the update.

I've been experimenting with using the Color Hyper MallinCam on the Orion ShortTube 80. With FR and 10mm extension it gives me roughly a one degree field. Last night I took the above image of the Double Cluster, which on first glance pleased me - but as I later examined it, I was confused. I thought I knew which cluster was which, but when comparing it with star charts and other images, I couldn't make sense of things. Finally, I found another color image here - and suddenly i understood. My image had greatly inflated the brightness of every red star!

So what went wrong? A white balance setting? What should have I done - or should I do - to get images that are at least close to the visual experience?

Update 11.15.06

After reviewing the comments below from various folks with much more experience and knowledge than I have, I think the problem lies with the refractor - but the solution also rests with fine tuning the settings of the camera no matter what scope or lens its on and for this, the suggestions from the camera developer, Rock Mallin, certainly are the best place to start. But for those interested in video astronomy, thee's other info here that's helpful as well.

Here's the discussion in the order I received it.

Greg,

I,too, have noted bloated stars on a few occassions. If you look at my
album on Color HYPER images using my 6" refractor at f/5, many of the
brighter stares are bloated.

http://tech.ph.groups.yahoo.com/group/mallincam/photos/browse/c63e

I thought that this was due to possible condenstion on the objective, as
some of the large stars are blue - not red like in your image. Perhaps
Rock has an explanation.

Jack

Greg, Jack

To my opinon there are at least two reasons for the bloating:

1. The FWHM (Full Width Half Maximum) of the Airy disk for red stars (700-800
nm) is about twice as large as for blue stars (~400 nm) so by optical theory red
stars will cover more CCD area. But this depends on focal ratio's how much
pixels will be covered (the higher the FR the more pixels will be covered). At
F/5 a star should cover only 2,0 um (at 400 nm) and 3,6 um (at 700 nm). The
Mallincam CCD is ~8 - 9 um. So even the red stars should cover only one pixel.

2. The focussing plane for the blue and red wavelength aren't necessarily at
exactly the same plane. So you either focus on the blue stars and have out of
focus red stars or visa versa.

I personally experienced that using an UV-IR cut-off filter give sharper views
(with CCD) on planets as well as star fields. Of course you will loose then some
sensitivity of the CCD for the very very deep red/IR (>700 nm). But it's what
you prefer: Sharper views with (some) reduced sensitivity or unsharp views a
(some) higher sensitivity. If imaging is your goal you could get around this by
taking images with UV-IR cut-off filter (window between 400-700 nm) and
combining these with images using a IR pass filter (window > 700nm).

Nevertheless camera and CCD specific issues could play a role as well. Rock
might be able to resolve those aspects.

Regards,
Henk

Greg, Jack, Henk,

Henk is right all the way. Try this setting: Go in the W/B and
set it to ATW Auto White Control. Also reduce the sensitivity Red will
appear bigger with many refractors dependent of their quality glass.
Camera picks up what you feed it. Id say to reduce sensitivity and try
the setting mentioned above. Make sure the AGC is set to MAN for MANual
and select the red, blue settings by reducing the RED. You can also
experiment with setting the MAN in 5600K. I have not fully finish
experiment with refractors yet.

Rock M.

At this point Dave Buhrman, who is using video as an observing instruction tool much as I am trying to do, sent me this B&W image taken through the same type of scope and showing the same problem. Dave wrote:

Greg,
You're no doubt getting good responses to your query on the MallinCAM group, but since I also have a captured raw frame with a MallinCAM B/W Pro with 0.6 focal reducer (128x two second integration) taken thru a short tube 80 that (to some extent) also shows the same engorged stars, I thought I'd share it with you.

dave

Re: oops - need color help???

Rock, I have a William Optics FLT-110 triplet APO that I have just
recently tried with the MallinCam Color Hyper. I was unable to
achieve enough in-focus to use the focal reducer until Jack Heurkamp
recommended that I try a 1.25" diagonal to shorten the light path.
Well, I got the 1.25" TeleVue Everbright in the mail yesterday and
put the camera in last night with the focal reducer and it worked
beautifully. The 1.25" diagonal created about a 1/2" shorter light
path which gave me about 1/3" of freeplay with the focal reducer in
place. I was noticing in my brief time (clouds were coming in) that
my highly color corrected APO refractor was showing more blue than
red in the images. I got a chance to lower the blue on the ATW
settings. It appears that the camera is behaving differently when
the image comes through a set of lenses. I will report back more
info when I get a chance to do more experiments. It won't be this
week because I am taking the MallinCam down to Chiefland Astronomy
Village to their big starparty where we are going to experiment with
it in two 28" f/3.66 Kennedy-mirrored telescopes (a Starmaster and a
Starstructure). We plan to remote the image to my friends Toy Hauler
so that we can have all of the screens shrouded (I will have my DVD
player, 13" Sharp Aquos LCD TV, 14" Dell Laptop and a 10" Sanyo 800
line B&W monitor to experiment with. Should be a lot of fun!

Bob Schilling

Hi Bob,

Thank you for sharing the report about the refractor behavior
with the color video camera. It is known that refractors do not focus
red, blue colors at the focal point. Even with the most excellent optics
such as APO's, a lens is a lens to the ccd sensor which picks up a lot
wider range than the human eye. The clear solution is a reflector. Also
we have to consider the lens in the focal reducers. Using the same focal
reducer on a newtonian, result vary immensely compared to a refractor
with some of the test I've done. Other focal reducers such as Meade etc,
have the same results. When going through too many lenses, red will
focus at a different point compared to blue for instance. The beauty of
the Hyper Color is in the W/B using the MANual menu, the red and blue
can be adjusted to some ones specific telescope.
To get a good color balance, the key is to get a sky background close
to dark brown / black in color. By achieving this, the result will be
getting the best color balance to true life. Often I use the sky
background to get the right color balance with various telescope
including refractors. Once I have a dark brown / black sky background, I
know I'm very close to the best color balance allowing me to focus on
all stars including red, and blue.

Rock