From: "Milton Aupperle" <milton@outcastsoft.com>

Date: January 31, 2009 10:42:33 PM MST

To: Astro_IIDC@yahoogroups.com

Subject: Re: M37 Image

Hi Alberto;

--- In Astro_IIDC@yahoogroups.com, albe albo <richter1956@...> wrote:

Very nice,  patient and ICY work!

I noticed you used a OAG (i'd like to try it too) but i also figured

out that the OAG should work at its best into a star  cluster!

Actually a single star works fine and is preferred for doing the

calibration.

Normally I heard that the OAG is terrible in order to catch a star.

Example around M51 or M82 i guess that it should be very hard.

Is it? 

Actually it isn't that bad at all. M51 has a Mag 7.0 star on the inner

edge. M82 is a bit tougher, but a Mag 8.4 star is present placed

there. M101 wasn't bad at all this summer from a dark site with a Mag

8th star and I was shooting 20 minute exposures too.

As long as I have a Mag 6/7 (in Urban Calgary) star within 20 to 35

arc minutes of the center, it's pretty easy to find. For dark site

with mag 5+ skies, you can go deeper.

See the image

OAG_Visual_Representation.png

in the Other File folder for some idea what you can see.

In addition i would use the OAG on a f. 3.3 reducer but it is less

forgiving  than the 6.3reducer.

I don't really see why you would say a shorter focal length is less

for giving. Your imaging with the same scope.

I use a F 6.3 reducer and wind up with a real reduction of F 5.14 (C8

2000m delivers actual measured focal length of 1028 mm). I'm going to

shorten the distance between the CCD and Focal reducer with a shorter

T thread to SCT adapter next week.

Time ago i read that even Mark Gaffney would use the OAG on a f 3,3

reducer but i couldn't read if he or someone else succeeded in this task.

The only concern with a F3.3 reducer is that you likely don't have

enough inward movement to achieve focus.

Ii fully agree about decent RGB even if it seems impossible.

All my color images done with TIS DMK exploited very old color

imagery i did years ago (at my beginning) with my EOS300D.

They were absolutely filthy, noisy and blurry  but they worked fine

as RGB!

http://www.makina.it/SAA/DSO_%28DMK+EOS%29.html

For this reason now i'm experimenting the double TIS camera

grabbing: DMK =Luma  + DBK binned = one-shot-RGB (i did only M1

because since i own the DBK  the sky is permanently cloudy here).

The result was  encouraging in order to continue further experiments.

This is the link with the reprocessed M1:

http://www.makina.it/SAA/DSO_%28DMK+DBK%29.html

About M37: I guess that you correctly left the natural result  "as

is" so I did a little aesthetic experiment trying to reduce the

already small horizontal ovalization of the stars .

I tried with 0,67 px at center but it is different at the corners.

It's different throughout the image largely because of coma,

especially on the left side.  It could be because I have pushed the

Focal reducer too far back and you wind up with some distortion (which

I hope to test by shortening the distance with the new adapter). Or

the CCD it's slightly off axis with respect to the scopes optical

axis. Or that is that I have to adjust the collimation for shooting

with the focal reducer. The last time I did the collimation, I did it

at 4 meter focal lengths and I know it's off a bit with the Focal

Reducer in place.

Do you want to see it?

Sure.

TTYL..

Milton Aupperle