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Help! M63- The Sunflower Galaxy and FOCUSING experiment!


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Afternoon everyone

Yesterday I did some experimenting with the FOCUS.

I use a Bhatinov mask, and in Live View in APT, I focus and fix the focus knob.

A member here on the forums advised me to use the FVMH option in APT, and I tried it yesterday. After intial manual focusing with the Bhatinov mask, I took it off, then tried the FVMH option.

I simply found it very fiddly, and did not fully understand it? On ARCTURUS, it kept jumping arounf 19.00 to 21.00, and when I tthough I got the smallest possible figure, when I applied the focus fix thumbscrew, it would start playing arounf again?

Even without touching the focuser, the number would not be steady?

SO I chose in Liveview a dimmer star, and still numbers would not be steadt, hovering around 2.50 to 3.00?

Live view was looping at 2 seconds at 1/4 exposure.

So, I chose Bhatinov Aid in APT, and that seemed easier, and I got the message IN FOCUS.

I then went on to image M63:

44L 90 seconds, 30D also at 90 seconds, 30F & 30DFs

I do not think the result is good? Looks like I was out of focus?

Or is it that I took 90 second exposures WITHOUT GUIDING?

 

 

 

M63 cropped.png

M63.png

Edited by oymd
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The focus seems alright. In the middle. But at the edges, the stars definitely start to suffer from an uneven flat field.

What is your gear, and are you using a field flattener?

The star shapes can definitely be affected by the 90 second exposure. It doesn't even have to be a steady drift, but small errors in the gear of your mount even. So best is to judge from shorter exposures with high gain/iso to see if focus is good.

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2 hours ago, The-MathMog said:

The focus seems alright. In the middle. But at the edges, the stars definitely start to suffer from an uneven flat field.

What is your gear, and are you using a field flattener?

The star shapes can definitely be affected by the 90 second exposure. It doesn't even have to be a steady drift, but small errors in the gear of your mount even. So best is to judge from shorter exposures with high gain/iso to see if focus is good.

My gear is AZEQ6 Pro, ED80 and ASI294MC Pro. 
I have the 0.85 SW reducer, but have never tried it yet, as I am just getting into imaging, and do not want to mess up my imaging train until I get some more experience. 
I posted over the past few days some good first results, but they were all 30 second subs. 
I wanted to push the sub duration a little to see if that allows more data collection. 
I really did struggle with the FOCUS AID in APT. 

Pretty sure it’s my lack of understanding. 
 

I ended up putting the bhatinov mask back in and manually adjusting focus. 
 

Could not get my head around FVMH and LWH, or whatever they are called!

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I

2 minutes ago, oymd said:

My gear is AZEQ6 Pro, ED80 and ASI294MC Pro. 
I have the 0.85 SW reducer, but have never tried it yet, as I am just getting into imaging, and do not want to mess up my imaging train until I get some more experience. 
I posted over the past few days some good first results, but they were all 30 second subs. 
I wanted to push the sub duration a little to see if that allows more data collection. 
I really did struggle with the FOCUS AID in APT. 

Pretty sure it’s my lack of understanding. 
 

I ended up putting the bhatinov mask back in and manually adjusting focus. 
 

Could not get my head around FVMH and LWH, or whatever they are called!

I'd say, just continue using the Bahtinov mask. If of good quality, it can produce near perfect focus. There is even tools (sharpcap has it), that analyses the Bahtinov spikes, and help you focus.

When working with FWHM (full width half maximum), just get the number as low as you can, that is the best focus.

Alright. The 0.85 SW reducer, will definitely help your image, in the edges. I'd personally go for it, as assembling and disassembling an imagetrain can be training in itself.

I read about someone, who when processing an image, would get to a point where he was happy with it, and then delete it. Just to do it over again. If he could do it once, then he should be able to do it again, and use that part as training (can be a bit extreme, but I hope the point comes across :D)

 You say that you take flats too? It seems that they aren't calibrating the image properly, as there is still quite some vignetting and dust visible :)

But again, focus in the center doesn't seem too shabby, might just need some fine tuning.

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19 minutes ago, The-MathMog said:

I

I'd say, just continue using the Bahtinov mask. If of good quality, it can produce near perfect focus. There is even tools (sharpcap has it), that analyses the Bahtinov spikes, and help you focus.

When working with FWHM (full width half maximum), just get the number as low as you can, that is the best focus.

Alright. The 0.85 SW reducer, will definitely help your image, in the edges. I'd personally go for it, as assembling and disassembling an imagetrain can be training in itself.

I read about someone, who when processing an image, would get to a point where he was happy with it, and then delete it. Just to do it over again. If he could do it once, then he should be able to do it again, and use that part as training (can be a bit extreme, but I hope the point comes across :D)

 You say that you take flats too? It seems that they aren't calibrating the image properly, as there is still quite some vignetting and dust visible :)

But again, focus in the center doesn't seem too shabby, might just need some fine tuning.

I will try and fit the SW 0.85reducer tomorrow night if clear. 
 

can I please check regarding cal ration frames?

if I fit the reducer tomorrow, and redo the targets I took over the past week, and I keep all my settings the same, temperature, exposure time etc, DO I NEED TO REPEAT THE DARKS, FLATS AND DARK FLATS with the reducer attached?

or I can use my existing MASTER calibration frames that were taken WITHOUT the reducer and stack them with the NEW Light subs taken with the reducer?

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1 minute ago, oymd said:

I will try and fit the SW 0.85reducer tomorrow night if clear. 
 

can I please check regarding cal ration frames?

if I fit the reducer tomorrow, and redo the targets I took over the past week, and I keep all my settings the same, temperature, exposure time etc, DO I NEED TO REPEAT THE DARKS, FLATS AND DARK FLATS with the reducer attached?

or I can use my existing MASTER calibration frames that were taken WITHOUT the reducer and stack them with the NEW Light subs taken with the reducer?

You'd need to redo the flats yes. Anytime you change your setup/remove camera/remove filter, you need to take flats again, as they only work when you keep the imaging train the same as the lights.
Darks you don't need to take again. Not sure with dark-flats as I've never used those.

Flats should be taken after each session, as dust can have changed positions. Darks you can reuse, if the settings are the exact same, hence why some people make "dark-libaries", where they have a collection of dark frames with different exposure/temperature/gain values.

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You should use FWHM/HFR on not so bright star - star that does not saturate in single exposure. You need nice star profile for software to be able to calculate these values properly. Saturated star will be clipped at the top and won't have nice shape.

Also - try to get at least a 1-2s exposures when looking at the value. When using less exposure, seeing can make star dance around and FWHM value will also change. This happens even with two second exposure - it is not unique value, it will change as seeing changes star profile. More it "dances" around - worse the seeing is (or at least tilt component of it).

Just mentally average FWHM value when you look for the smallest one (sometimes software has aid for that - like displaying "train" of values so you can know if you are getting lower or not).

If it was particularly windy night - it can impact results and image will look "smeared" a bit.

To me - image looks like it was stacked with some good subs and some smeared subs (stars have well defined core but also large wings - core comes for good frames, wings come from smeared subs). This means that it was either wind gusts or moments of rather poor seeing on some subs.

In poor seeing it is also hard to get perfect focus as it "moves" in and out because of the seeing.

What I'm more worried about is the fact that you took calibration frames but your image above looks like completely uncalibrated image. How so? Did you apply darks, flats and flat darks?

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9 hours ago, oymd said:

DO I NEED TO REPEAT THE DARKS, FLATS AND DARK FLATS with the reducer attached

Just to add the answer regarding darks for your flat frames. You will only need to redo these if you use a different exposure length for your new flats. If your new flats are the same exposure as the original flats then the existing darks should calibrate them. However, in practice, I find my flats always have different exposures. I do a test exposure to a fixed ADU value and use a light source that is variable - sunlight - so they vary quite a lot between sessions. However, because my light source is so bright my flats only take a second or two to expose so it's very quick to run off 30 new darks per filter (each filter also changes my exposure time).

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Big improvement, still showing faintly in a couple of places though.

Best thing would be a strip down and clean, I think I need to do that myself going by tonights subs.

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8 hours ago, oymd said:

I redid my flats yesterday....

I think its a better result now?

This shows what happens when you take flats after taking your rig apart - you can never get everything back together as it was before (in terms of exact positions / orientations).

Dust shadows make that emboss signature because flats are slightly offset to lights (center is properly calibrated, one side is over corrected and opposite side is under corrected).

It is all however good practice - just make sure you take proper flats with scope & camera at same position and focus.

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On 07/04/2020 at 08:28, vlaiv said:

It is all however good practice - just make sure you take proper flats with scope & camera at same position and focus.

Hi Vlad

Today I started my imaging session by setting up in the afternoon, and started by taking flats and dark flats.

I then went on to do the Lights when it got dark.

I have just realised that I took my flats and dark flats with the focuser all the way racked in, just as the scope was when I took it out of the case!!

I have a mark I did with a sharpie pen on the focuser tube to mark my focus, but I completely forgot to move the focuser out to that position!

Does that mean that the flats and dark flats I took today are rubbish and useless?

These were new flats with the reducer in place!

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5 hours ago, oymd said:

Does that mean that the flats and dark flats I took today are rubbish and useless?

You should definitely have a read and try to understand what your calibration frames are doing.  This will help you when it comes to taking them!

The flats won’t be any use but the dark flats (taken with cap on) won’t be affected by focus position. However the exposure time may be wrong when you retake your flats.  But unless your flats are long then you might not even need them?  Some of my flats at 15s long so I use dark flats.

But you definitely on the right track here. This kit is what I had until recently and it’s very capable kit. Here is my M63 with a DSLR, ED80, reducer and EQ6. You have a cooled camera so lots of potential 👍🏼

St-avg-33600.0s-LNSC_1_3.0_none-x_1.0_LZ3-NS-full-qua-add-sc_BWMV_nor-AAD-RL-noMBB-session_1_session_2-mod--90degCW-1.0x-LZ3-NS-lpc-cbg-St.jpg

Edited by tooth_dr
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6 hours ago, oymd said:

Hi Vlad

Today I started my imaging session by setting up in the afternoon, and started by taking flats and dark flats.

I then went on to do the Lights when it got dark.

I have just realised that I took my flats and dark flats with the focuser all the way racked in, just as the scope was when I took it out of the case!!

I have a mark I did with a sharpie pen on the focuser tube to mark my focus, but I completely forgot to move the focuser out to that position!

Does that mean that the flats and dark flats I took today are rubbish and useless?

These were new flats with the reducer in place!

Like tooth_dr mentioned, flat darks don't care much about focus (but do take them regardless of the fact that they are short). I'm afraid that flats are probably going to be useless.

You know when you focus - star first is a circle then collapses into a single dot? Dust particles cast shadow that looks like this defocused star - this is because dust particles are some distance in front of the focus plane - they are "defocused" so they cast defocused shadow. Problem is of course that they are on optical element, like flattener or filter or whatever in optical train at a fixed distance to camera. When you bring sensor to focal plane - dust particles are at some exact distance from focal plane and cast shadows of certain diameters. If you change dust particle defocus - you make these shadows larger or smaller.  This makes an issue - larger shadows in flats (if flats were taken with focuser all the way in - dust the furthest from focal plane) can't properly calibrate out smaller shadows in lights.

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1 hour ago, tooth_dr said:

You should definitely have a read and try to understand what your calibration frames are doing.  This will help you when it comes to taking them!

The flats won’t be any use but the dark flats (taken with cap on) won’t be affected by focus position. However the exposure time may be wrong when you retake your flats.  But unless your flats are long then you might not even need them?  Some of my flats at 15s long so I use dark flats.

But you definitely on the right track here. This kit is what I had until recently and it’s very capable kit. Here is my M63 with a DSLR, ED80, reducer and EQ6. You have a cooled camera so lots of potential 👍🏼

St-avg-33600.0s-LNSC_1_3.0_none-x_1.0_LZ3-NS-full-qua-add-sc_BWMV_nor-AAD-RL-noMBB-session_1_session_2-mod--90degCW-1.0x-LZ3-NS-lpc-cbg-St.jpg

 

56 minutes ago, vlaiv said:

Like tooth_dr mentioned, flat darks don't care much about focus (but do take them regardless of the fact that they are short). I'm afraid that flats are probably going to be useless.

You know when you focus - star first is a circle then collapses into a single dot? Dust particles cast shadow that looks like this defocused star - this is because dust particles are some distance in front of the focus plane - they are "defocused" so they cast defocused shadow. Problem is of course that they are on optical element, like flattener or filter or whatever in optical train at a fixed distance to camera. When you bring sensor to focal plane - dust particles are at some exact distance from focal plane and cast shadows of certain diameters. If you change dust particle defocus - you make these shadows larger or smaller.  This makes an issue - larger shadows in flats (if flats were taken with focuser all the way in - dust the furthest from focal plane) can't properly calibrate out smaller shadows in lights.

Yes, it seems I’ve messed that up. I totally forgot to focus to the mark on the focuser when I took my flats. I’ll have to redo them. 
 

I suppose it’s time to invest in an ELP to save me the hassle, and get my flats done at the end of the session!

I’m buying something new almost every day in this new Hobby!

:)

 

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On 06/04/2020 at 01:23, oymd said:

I have the 0.85 SW reducer

Hi.

You won't be imaging without it, so maybe best to include it during your trial period too. Remove one of the (many!) variables at least;)

The focus looks OK to my untrained eye but maybe better to simply use 10x live view on 30s loop directly using the mask. View the spikes directly rather than the APT aid?

HTH

 

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