Photometry first steps with IRIS = Nemesis.
I am attempting to do DSLR photometry at prime focus on my 12" SCT.
To avoid questions later I'll try and describe the full set up and procedure.
- 12" SCT on a eq wedge.
- Drift aligned such that a star stays centred in excess of 15 minutes with 9mm illuminated reticle.
- Pentax K10D DSLR, PEF RAW format images. 1600 ISO.
- Camera is on an off axis guider at prime focus on the scope.
- I use a mirror diagonal and eyepiece with similar FOV to the camera to frame the field then the camera on an off axis guider to do the imaging.
- I have made the 9mm illuminated reticle and camera parfocal on the off axis guider so I can just focus to the reticle and know the camera is in focus (or not).
- 30s exposures and then varies because I don't have the pentax disk with the SW on any more to set exposure times beyond what is on the camera. i.e. Manual >30 second exposures otherwise.
- I have taken bias, dark and flat images. I understand I need to take these each evening I'm imaging.
- The reason I'm using IRIS is that it handles the PEF RAW format and it's free.
The reason I'm using the scope and not the DSLR on a tripod is:
- Dimmer targets such as CVs, RCbs and BL Lacs interest me most.
- No spare money for new toys or SW means I have to use what I have to hand. I.e. Telescope and off axis guider.
The issue I have with IRIS depends upon what I attempt. I am using the guidelines at http://www.citizensky.org/content/iris-beginner
I have some images I've put up on boxnet along with the bias, dark and flats I've been playing with here: https://www.dropbox.com/sh/1sncy54f4vwz7eb/aMx5LNBMuN
Hopefully people can get to that.
Processing the master-offset, master-bias, master-dark and master-flat causes no issues.
If I process the 7 30 second images (see boxnet) I've taken, this is the result:
At step 4.1 in iris-beginner I set the output files type to Color. Thus later on when Iris complains about having incompatible colour and B&W images it's a total mystery as to how.
At step 4.2 stellar registration fails, less than two stars in common between the images apparently.
It seems reasonable then that step 4.3 would fail for some reason, but it complains about incompatibility between color and B&W images. Very confusing. So that's my give up point for processing multiple 30 second exposures.
If I process a single 300 second image (see boxnet), this is the result:
I get to step 5 in iris-beginner and then find that I can separate the channels but cannot adjust thresholds. The button on the Iris toolbar to do so is simply unavailable.
I've played around with just jumping to doing the photometry, but without the preparation working beforehand I don't have anything that I'd want to ever submit - which kind of defeats the object of the exercise.
If someone who knows Iris well could take a look at the images I've provided (hopefully - let me know if you can't download the images and I'll share them explicitly) and tell me what is wrong with the images or what I am doing wrong in Iris would be awesome.
- Carl Knight (KCD)