Narrow band flats

[Davey-T]

Just been doing some narrow band flats, never bothered before just used light flat or just dark frames.

Looking at them the HA and S11 look normal but the O111 looks strange is this normal or will it do more harm than good if I use it ?

Dave

[ollypenrice]

I wonder if the filter was in the right place? Also, did you expose he O111 for long enough to get a third of the way up to saturation? It does look a bit suspicious, that one.

Olly

[Davey-T]

I get a value of 27000 ish saturation on the flats

Also these flats are the first ones I've done with Maxim, Ive just updated to Maxim 5.22 and thought it's about time I got to grips with it as I've had it for years but only used it for calibrating and stacking.

Always found it really annoying that you can't just autosave subs without filling in the auotsave boxes.

I end up using the Artemis Capture that came with the Atik camera as it's much easier and quicker to set up, just pick a folder and check autosave and off you go.

Also when I take a flat using Artemis using home made light box if I increase the light I eventually get a white sub, but if I do the same in Maxim the more I increase the light the darker the sub gets untill it

goes black.

Heres a comparison between an Artemis O111 flat and the same thing in Maxim they look like positive and negative of the same image ?

Dave

[ollypenrice]

No, they are both positives. The dust bunny circles are darker than the background in both. Clearly the Artemis version looks more likely but to what extent are you just looking at the screen stretch here? The incoming images will be linear in reality and you have to compare them with the same screen stretch applied.

The Artemis image seems to have a more central bright region which adds to my suspicion that the filter might not have been centralized in the wheel in the first one. Also the dust bunnies are not in the same place so something is not right here. More evidence of a misplaced filter in one image? (I can't quite decide if one image might be the same as the other but flipped 180 degrees, which can happen. I don't think this is so but what do you think?)

I love Artemis Capture and use it all the time. It has only two 'traps' - failing to cancel the sub frame window and failing to click Autosave. They could have a warning flash up if you have Autosave checked while the sub frame is active. That would remove one of the traps!

Olly

[Davey-T]

Thanks for the input Olly

I think that Maxim flips the image probably some box I haven't ticked.

Can you explain why the Artemis image gets lighter with more light and the Maxim one gets darker ?

Dave

[ollypenrice]

Thanks for the input Olly

I think that Maxim flips the image probably some box I haven't ticked.

Can you explain why the Artemis image gets lighter with more light and the Maxim one gets darker ?

Dave

Nope!

Are you sure it really does, or is it an effect of some kind of auto screen stretch?

Olly

[Davey-T]

Now I remember why I gave up with Maxim and stuck with Artemis capture and PHD

Heres a O111 sub taken without the filter being altered between taking the flat

Dave

[SteveA]

Hi Dave...

I think Oly has identified the crux of the problem here...its the screen stetch that's the problem.

In Maxim...launch the histogram and give the image a stretch....by default I suspect iMaxim is only applying a very low stretch...

[SteveA]

Screen Stretch Window

The Screen Stretch window controls the brightness and contrast of the displayed image without affecting the contents of the stored image. There are several automatic stretch settings. There are two graphical methods to manually control screen stretch: Quick Stretch and Histogram. You can also set the stretch settings using the keyboard. With a few exceptions, the Screen Stretch window is available even while a processing dialog box is active.

Display of the Screen Stretch window is controlled by the button on the toolbar, or by the Screen Stretch Window command in the View menu. The window can remain open as a floating toolbox without interfering with other commands.

You can stretch image buffers, or the Preview Image that appears in most processing dialog boxes. Click anywhere on an image to select it, or click anywhere on the dialog box to select the Preview Image. (Note: when the Preview button is down, the preview image has a separate stretch setting; when it is up, the preview image and main image buffer share the same settings). A Full Screen Preview is stretched exactly the same way as the original image in whose window it appears. Full Screen Preview stretch settings are lost as soon as the preview is dismissed or regenerated, typically when you change a control in the processing dialog.

Although the image data pixel values are unaffected by changes to Screen Stretch settings, you should be aware that the stretch mode and limits are saved to FITS files as part of the header, in the keys CSTRETCH, CBLACK, and CWHITE. When the file is loaded into MaxIm DL later, the Screen Stretch window will be reset to the state which was in effect when the file was saved, giving the same display appearance.

Once you have selected an image, you can use one of the following methods to stretch it.

Manual Stretch

The Minimum field sets the brightness level in the image that corresponds to black on the display. The Maximum field sets the brightness level in the image that corresponds to white (full brightness) on the screen.

Modifying the values in the Minimum and Maximum fields directly will only change the stretch when you press the Enter key or click the Update button. It will force the stretch mode combo box to "Manual".

You may have encountered the terms "background" and "range". Background is equivalent to Minimum, and range is equal to Maximum minus Minimum

[Davey-T]

Still can't see why increasing the light on Maxim flats makes them go black and increasing the light on Artemis flats makes them go white ?

If I take a black Maxim flat no amount of stretching reveals any detail it just stays black.

Dave

[Davey-T]

Just done some more flats experimenting and can now stretch the Maxim one to white so thats something.

What needs adjusting in Maxim to get the flats to download looking "normal"

Attached images

Dave

[SteveA]

Hi Dave...you don't really need to do anything. The screen stretch you are applying in Maxim is only temporary anyway, its just a way of inspecting the image. When you come to calibrate your images you will be using the linear images which have not been stretched.

[Davey-T]

But if I take a 4sec flat with Artemis it looks "normal" If I take a 4sec flat with Maxim it is black . Do I use a black flat to calibrate the images ? or try to get one that looks "normal".

Why are they not identical ?

The black Maxim flat has saturation reading 65000 all over so can't see that it's any use even if I can stretch it on screen to look at it.

Dave

[SteveA]

Hi Dave,

When you are saving these flats what format are they in?

Clearly the images you are posting here are jpegs....but what do the original fits images out of Maxim look like..are they the same?

Just as an experiment I saved one of my own flats as a jpeg without using the Maxim option to autostretch the image....and I ended up with similar profile to your all white Artemis image.

To be honest though I'm really rather stumped here, the Maxim 4 sec flat lit image above doesn't have any data in it all ?.....very strange..

[carastro]

I find Maxim just as confusing with these different screen stretches and use Artemis for capture, but Maxim for examining the subs as they capture. I also have found completely black or completely white flats in Maxim, it's not very easy for beginners to use and understand.

Olly, was interested in a comment you made above. What is the sub frame window, I don't recall having to cancel such a thing? As you say a warning about cancelling the autosave would be helpful, often having to delete loads of looping frames I don't need. Maybe something we could post up on the Atik forum.

Carole

[Davey-T]

The original flats were FITS I saved as jpeg to post but they look the same as the originals.

As I said on the first post I thought I should try and get to grips with Maxim as I just paid to upgrade to 5.22 ,I only used to calibrate and stack subs before as it was so much hassle guiding and imaging

with it.

Using Artemi and PHD I can be up and running in minutes, I found I was wasting valuable imaging time faffing about with Maxim.

I know it has a simulator mode but only uses their supplied images. And , unlike Aretmis, you can't fill out the autosave sequence without the camera connected.

I did pay extra for the boxed version with printed manual so I'll have a browse through it to see if I'm missing something, failing that I'll put a post on Maxim forum.

Dave

[davew]

I'm a user of Maxim and due to the fact I'm slightly confused with some of the preceding posts I'll not try to answer the questions directly.

What I use in MaximDL to take flats is a little plugin that can be found here - http://winfij.homeip...l/skyflats.html

It's real intended use is for sky flats at dawn or dusk. I use it by telling the plugin what ADUs I require and how many. The process is automated and shouldn't go wrong ( Famous last words ).

I would pretty much ignore what you see on the screen. Some control for lights is easy with the screen stretch function but there's no advantage to be gained by looking at flats, darks or bias this way.

Dave.

Another thought here. I would use one program to do all my data collection. As you said earlier, one set of data may be reversed due to a tick box.

[Davey-T]

Another thought here. I would use one program to do all my data collection. As you said earlier, one set of data may be reversed due to a tick box.

Thats why i originally purchased Maxim, to do everything in one program .Before this I was using Artemis,PHD and DSS.

However as I said earlier this plan came to nowt as I didn't have the time, patience ? to get Maxim to do it all.

Dave

Just had a look at the plug , looks interesting, will give it a go.

Learnt something already, didn't realise Maxim filters started numbering from 0, I've always started with 1.

[davew]

I do understand the frustration. One aspect of Maxim is there's so much there that it's a bit over facing.

Now that you've spent the dosh it could be an idea to get to grips with it. It's an awful great chunk of money to write off !

I don't know what degree of success you've had so far but I suggest ( I should have started this way ) is to use Maxim to gather lights and use PHD to guide, if it's running ok. Use that plugin to gather flats ( So easy it's not true ) then use DSS to process with bias added for the flats.

Once that's all running cut DSS and learn the stacking routine. Then move to guiding. Knock them off one by one. Don't admire your handy work with the screen stretch.

Try the help files from time to time but if you're like me you'll find them over complicated at times. They should have used a dumb chump like me to proof read.

You should have tried the old Starlight software !

Any help ?

Dave.

Now why does someone living within the M25 use the word nowt ?

[Davey-T]

Now why does someone living within the M25 use the word nowt ?

Watching all those reruns of "Open all Hours" I expect

Dave