M13 LRGB 28th June

[MartinB]

This was taken whilst I was waiting for M16 to cross the meridian. It was taken with my ED120 and the WO 0.8 field flattener and QSI 532 camera

LRGB all unbinned 120:140:140:180 secs 7 of each channel. Was tempted to get a load more but I wanted to have a look at M16.

Captured and combined in Maxim and processed in PS. Collected a flat yesterday evening but can't get it to work.

(click to enlarge)

[LostNSpace]

That is a nice M13 Martin, some lovely colours in there.....

Mark

[MartinB]

Thanks Mark

[anthony]

Very Nice Martin. Well processed and nice even background from where I am looling

Anthony

[MikeD]

Very nice result Martin.

Shame about the flat, with a flat I think you could push it a bit harder.

Mike.

[steppenwolf]

Another cracker of an image with well formed stars

[CELESCOPE]

Very nice indeed Martin , some beautiful colour in there .

Rog

[Beyond_Vision]

I love the blue and gold colours in your M13, very nice.

Regards

Kevin

[MartinB]

Thanks guys. You're right about the flat Mike, the background was definitely a limiting factor along with the short overall exposure time. I'm not sure what's doing it. I think it's because the FITS header for the flat is 0.07 secs and for the dark is 0.06secs. Maxim might be recognising the mismatch and refusing to cooperate. I will try later with some 0.07sec darks or change the fits heeder

[steppenwolf]

Martin, the exposure time of the FLAT recorded in the FITS header is not read by Maxim when it does it's calibration as it is highly unlikely that your flat will match the 'light' frame anyway so I don't think this will be your problem. All that has to match are the X and Y pixel counts which must match the light frame.

What error message are you getting?

[MartinB]

I was trying to do a dark subtraction from the flat. However I have had another look and I can't get maxim to use the flats full stop. Maxim does use the FITS header as part of it's automated operation to select the most appropriate set of darks to use and I think it is supposed to match up the flat to the appropriate dark frame. It should automatically do a dark subtraction of the light frame, then do a dark subtraction from the flat using a dark frame which matches the flat exposure, then it should apply the flat to the dark subtracted light frame. From what I understand it does this all automatically once you have generated your calibration frames and groups.

The error message I'm getting if I try to subtract the flat from the light frame is "No applicable groups were found for this image. Please run Set Calibrate" Well I've done that and have my master flat ready to go but no joy. Neither the flat nor the light frame are binned, the pixel counts are the same. I've boobed with the flats and they are too bright, I wonder if this could be picked up by maxim, I would have thought it would give a different error message if that were the case.

The darks are being subtracted without a problem.

A bit stumped at the mo. Any advice would be much appreciated Steve

[FLO]

That's beautiful Martin, the propeller is nice and clear too

[steppenwolf]

Aha, that makes perfect sense! I don't dark frame subtract my flats as I don't see any point in doing so as they are such short exposures so noise isn't an issue here (although BIAS still is, of course!) and you are quite right about the mismatch here because Maxim is treating the FLAT as a LIGHT for the purposes of this particular subtraction!

This is the procedure that I use:-

1. I take BIAS frames (16 or more)

2. I take DARK frames of known exposure time (again 16 or more)

3. I take LIGHTS of the same exposure time as the DARKS

4. If I need FLATS, I take these ensuring 30% saturation irrespective of the exposure time.

I then MANUALLY delete all my existing groups from my chosen calibration directory - this is important as Maxim does not let you run the 'Replace w/Masters' routine if any masters already exist. I then let Maxim Auto generate my Groups and when it has done that, I run the 'Replace w/Masters' routine with the following flags set:-

Calibrate Bias Calibrate Dark Calibrate Flats Bias Subtract Flats

This gives me MASTERS for BIAS, DARKS and FLATS. My DARKS are BIAS subtracted as are my FLATS. Once the masters are produced, I select the FLATS master and tick 'Apply Boxcar Filter' but you won't have to do that as you don't have a Bayer Matrix to worry about!

When I then calibrate my LIGHTS, they are automatically BIAS, DARK and FLAT processed with properly calibrated calibration masters using the same flags set as above! Note that the 'Dark Subtract Flats' is left unticked for the reason mentioned above.

[MikeD]

I do the same apart from I don't do replace with masters is that step necessary?

mike.

[MartinB]

Thanks Steve for taking the time to run through that process. I sounds pretty similar to what I did but it may be that I didn't set the flags properly at first so I will start again from scratch.

One thing you mention which I don't think is necessary is to bias subtract the darks since the bias is contained within the dark, so a bias subtraction is automatically done when dark subtracting. My understanding is that the only time you need to bias subtract the darks is when you need to scale them because they are shorter exposure than the light frames. That's why you might as well dark subtract the flats although a 0.07 dark is effectively a bias frame!

Right, I shall start again from scratch setting all the necessary flags and see how it goes. Thanks for the help Steve, I'll get back.

Mike, replacing with masters isn't necessary but speeds things up the next time you want to calibrate an image since Maxim doesn't need to do another combine.

[steppenwolf]

I do the same apart from I don't do replace with masters is that step necessary?

mike.

No, it is not necessary for the calibration to work but the advantage is that the 'groups' that are now 'mastered' have already be stacked and BIAS subtracted and their FITS headers annotated to this effect so they are 'instantly' available for use to calibrate your LIGHTS whereas 'Groups' that have not been 'mastered' still have to be stacked and BIAS calibrated each time they are invoked to get to work on the LIGHTS.

[MikeD]

Thanks, you had me worried for a mo then.

Mike.

[centroid]

A very nice result Martin!!

Glad to see that some of you 'stalwarts' are still out there imaging, while I'm hard at work on an obsy ugrade.

Dave

[Martin 2]

Thats a lovely image Martin, I'm getting really confused with bias frames and dark frames, must do some more reading.

Martin

[markcol]

Very nice M13, Martin.

Mark

[Sam]

Stunning image Martin! and the processing discussion I have found very informative.

[Keagle]

Nice and neat - good job Martin!

[RobH]

Nice job Martin

I still do my dark, flat and bias the slow way and manually set the calibration. I bias subtract the flats but don't dark subtract them. I found that if I tried to do both, my flat would be under or over applied.

Cheers

Rob

[MartinB]

Thanks everyone. I've sorted the problem. I did a t-shirt flat during the early evening and needed to use an Ha filter to avoid over exposing. I put in an Ha suffix and it was this that Maxim was objecting to using on a luminence frame. You just have to politely ask it to remove the filter and it's sorted. I now have a lovely flat background. My new computer won't work properly with my monitor so they have both had to be sent to PCspecialist so I can't reprocess until I get it back.