Well I've been meaning to do this for a long time so last night I fixed up my camera piggy backed on my Meade LX100. Camera is Pentax istDL, lens cheapo Tamron zoom set at about 90mm . B setting 277 sec at f8 with ASA set to 1600.
The only processing I have done is with Windows photo editor - I tweaked about with the brightness, contrast andv hue. Oroginal size is 1.8 meg JPEG.
forgot to add that it is Eta Carina of course
Jimmy, Not too bad at all really. In addition to Monte's comment re flat fields, your image would benifit from the application of Dark frame subtraction. Both these things require specialised S/W which you might not have at present. On the otherhand. the guidiing is good and the focus seems good. You would see an immediate improvement if you were to reduce the ISO setting to 800.That will reduce the amount of noise. I hope you don't mind, I have applied a few processes to try to reveal some of the detail that has been masked by the absence of flate frame division and dark frame subtraction (Calibration).
Thanks guys - Monte and Doug - for that More questions... How do I subtract a flat field? And what exactly is a flat field? Something to do with the camera lens?
Same with dark frames. How do
I do that? I only have the Meade Autostar suite software and I think I downloaded a copy of Iris. Not too familiar with the processing side. So you think ASA800 would be better?? I will try next time. I attach a corner, Monte - well I think it is 100% - I just opened the 1.77Meg file with.. and cropped it till it was 149K
Thats a nice pic, Doug. Was all that sparkly stuff noise, when I thought it was stars
Last edited by JimmyH155; 13-06-2007 at 09:25 AM.
Reason: wrong name
You'll find loads of free info on the net for all those questions.
A Dark is a shot with the same camera for the same time at preferably the same temperature (of the camera) but with the lens cap on. When you do it you will see lots of little "stars" This is just noise in the camera and when it is is combined with the real image and then subtracted these "stars" will dissapear. Have a look at the good pictures posted by some of the members and you will see they are not there.
A flat field is a shot of an evenly illuminated area (white wall e.g.) with the exact lens and camera combo as in the photo.
You should have a greyish image with the centre more illuminated than the outsides. If you apply this with the appropriate software you will see the sides of your shot brighten and the centre fade (as in the example in the reply) and it will be a more pleasing image.
Also go to 800 and try going down a stop to 5.6. If you don't get coma (little comets in the corner of the frame that point towards the centre) or it is minimal try one more stop. I am guessing for a cheap lens 5.6 would be the limit. If you are not sure of what I am talking about take a shot at f1.4 or the most open you have and you will see!
I can't recommend any free/basic software but someone else surely can. Go the software forum in IIS and ask there. They will certainly know.
When you have more confidence with some software you can stack multiple exposures and create some really great shots. Your equipment is capable of some good work, you just need to be patient and read up as much as you can here and in the wider web.
Last edited by montewilson; 13-06-2007 at 10:04 AM.
G'day Jimmy, Flat field frames are images of the flatness or lack thereof of the light coming thru the optical system to the camera sensor. It provides information about the brightness levels (Vignetting) across the field of view, including any shadows caused by dust particles and such. The flat field is not subtracted from the light frame it is divided into it. It is a special form of 'Pixel Math'. Iris can be used to take Calibration frames (Dark, Flat) and apply them to the light frame. The light frame is the actual image such as the one you posted.
Dark Frames are sort of exposures taken with the lens cap in place. In general, though not exclusively, Dark Frames are of the same exposure diration and ISO speed as the Light frame. A more advanced system using Bias frames allows dark frame scaling, but don't worry about that yet.
I see Monte has just replied and replied well, so I see no need to duplicate his efforts, but will just add that IRIS will do all that you want with the possible exception that it might not be able to controll your particular Canera. I don't use Iris myself, but I see under the processing dropdown there are menu items for using dark frames and flat field images.
G'day Jimmy, Flat field frames are images of the flatness or lack thereof of the light coming thru the optical system to the camera sensor. It provides information about the brightness levels (Vignetting) across the field of view, including any shadows caused by dust particles and such. The flat field is not subtracted from the light frame it is divided into it. It is a special form of 'Pixel Math'. Iris can be used to take Calibration frames (Dark, Flat) and apply them to the light frame. The light frame is the actual image such as the one you posted.
Dark Frames are sort of exposures taken with the lens cap in place. In general, though not exclusively, Dark Frames are of the same exposure diration and ISO speed as the Light frame. A more advanced system using Bias frames allows dark frame scaling, but don't worry about that yet.
I see Monte has just replied and replied well, so I see no need to duplicate his efforts, but will just add that IRIS will do all that you want with the possible exception that it might not be able to controll your particular Canera. I don't use Iris myself, but I see under the processing dropdown there are menu items for using dark frames and flat field images.
cheers,
Doug
I agree.
I use Iris (although I don't use a colour camera) and it is a very powerful programme. It certainly has all the pre and post processing algorithms.
Go backto the Iris site and take a look at the tutorials on processing.
Jimmy, when looking at the corner crop you have provided, it looks like you've got a ghosting issue. The same star is present two or three times but in slightly different places. Don't mistake this for noise or coma. This could be caused by tracking or vibration the shutter - make sure you're tiggering this remotely, not touching the camera.
If this is a two or more frame composition, then they simply aren't aligned (registered) correctly. But if its a single frame (one exposure), then I'd look into the mount tracking, vibration, guide errors, etc.
HEY Guys, thats great advice and thanks for all that Regarding the ghosting, I do have a remote shutter release, but during the exposure, I was contorting myself underneath the scope trying to check that the Telrad was pointing in the right direction, and I goes and bangs me head on the finderscope, so maybe that set up some vibrations??
Yes the image is only one shot 277 sec. I will definately try at the weekend for 800ASA and will take a dark and try and process it in Iris BOY OH BOY, I've been playing with Iris at work all morning and I reckon you need a PHd and bar to work it. I only tried the saturation, brightness, then gamma, turned my 1.77 meg JPG image into a 4 meg BMP image, and the image went bright red, blue green, black, grey and negative. Great fun and I have lots to learn, but perserverence as they say. Thanks
Yep, wack'n your noggin on the scope will not help tracking. Look on the bright side - at least you know what caused it. Seriously, troubleshooting tracking issues and the like can take a lot of time and effort. Something you don't need to worry about yet, so you can concentrate on the feedback the others have provided.
thanks for that, Jase. Actually I have just realised that when I took that photo, I had forgotten to take off the skylight filter from the lens
Would this make a difference??? I guess it would - or maybe it would act like a pollution filter perhaps??
G'day Jimmy, there has been a lot of stuff thrown around here with little graphic explanation. So in the general belief that one picture is worth a thousand words I am posting a series of images.
The first image is a flat frame taken using the mid afternoon blue sky. (it very much affects colour balance with a one shot colour camera).
This flat would be applied before colour conversion, however it is clear that there is a lot more blue data, hence the problem of getting white balance.
Second image is a gray scaled flat. This is more or less what a good flat would look like.
Third image is a 900 second dark frame.
Forth Image is a 900 Second light frame of Antares and surrounds. This image is uncalibrated; ie. no dark frame subtraction and no flat field reduction.
The fifth image is the same light frame after calibration. You can see the effect of applying the flat field.
Next post will contain the sixth image I wanted to share.
THe sixth image I wanted to share is a combine (stack) of 12x 900 calibrated exposures.
The data is messed up by excessive light polution, however some of the nebulosity can be brought out. Feel free to down load and play around with it.
I forgot to mention that Light frames were taken at ISO=400, and the calibrated frames are G2V colour balanced.
Hope these images help clarify things previosly mentiond.
cheers,
Doug
More questions... How do I subtract a flat field? And what exactly is a flat field? Something to do with the camera lens?
