45 replies to this topic

[jmerran]

Cosmos: I still use my Ioptron Alt-Az Pro mount with the Celestron Edge 8". Will I get better results with this telescope using a focal reducer (from f/10 to f/7 ?

 

As far as processing I use the free DSS program to stack all my pictures and the bias , flats and black and let the DSS process the image. 

[jmerran]

Cosmos: I still use my Ioptron Alt-Az Pro mount with the Celestron Edge 8". Will I get better results with this telescope using a focal reducer (from f/10 to f/7 ?

 

As far as processing I use the free DSS program to stack all my pictures and the bias , flats and black and let the DSS process the image

[jmerran]

Forgot to say last night we had a near full moon in the sky white taking the pictures. Maybe not helping with my attempt to photograph the whirlpool galaxy ?

[bobzeq25]

Forgot to say last night we had a near full moon in the sky white taking the pictures. Maybe not helping with my attempt to photograph the whirlpool galaxy ?

"Not helping" is an understatement.  It will really mess things up.

 

I never try to image DSOs with dim detail on a moonlit night.  The results are not good enough for me.

 

I'll image star clusters, solar system targets, or gather some Ha data.

Edited by bobzeq25, 04 April 2023 - 11:47 PM.

[jmerran]

Thanks for the input.

[jmerran]

Need help ! I am using DSS to stack 430 pictures (M51) of 20s exposure, ISO 1250 with 25 each of Bias, flats and dark pictures. After registering I get a  message that only 1 picture will be stacked !  What am I doing wrong ?

[jmerran]

Could it be bad focus ?

[bobzeq25]

Need help ! I am using DSS to stack 430 pictures (M51) of 20s exposure, ISO 1250 with 25 each of Bias, flats and dark pictures. After registering I get a  message that only 1 picture will be stacked !  What am I doing wrong ?

Need a lot more information.  Mount, light pollution level, scope, camera...

 

You can upload a light (not the one DSS liked) to something like Dropbox, create a public link, and ask people to look at it.

 

I hate DSS (because people often have problems with it), recommend Astro Pixel Processor.

Edited by bobzeq25, 11 April 2023 - 06:24 PM.

[jmerran]

My gear setup:

 

Ioptron Alt-AZ mount

Explore scientific  telescope FCD 102, F/7

D7500 Nikon camera

pollution 5 on the Bortle scale

[bobzeq25]

My gear setup:

 

Ioptron Alt-AZ mount

Explore scientific  telescope FCD 102, F/7

D7500 Nikon camera

pollution 5 on the Bortle scale

This is REALLY simple.

 

The Alt-az mount absolutely dooms you.  20 seconds of star motion, and the motion magnified by the 714mm focal length, will turn stars onto long streaks.   You can't stack streaks.

 

There are three important things for DSO imaging.  Tracking, tracking, and tracking.  Analogy.  You're in a car trying to shoot a picture with a long telephoto lens.  At night in a rural setting.  The car is moving and the road is bumpy.  What kind of a picture do you think you'll get?

 

A proper mount for DSO imaging with that scope would be something like an iOptron CEM40.  A bit over $2000.  You'd still need an autoguiding system to correct errors due to the inexpensive (honest) mount.

 

https://www.ioptron....uct-p/c402a.htm

 

The inexpensive workaround is to shorten the focal length a lot, by using a camera lens.  That magnifies tracking error less, and you can use an inexpensive equatorial mount, a $300-500 camera tracker.  The setup looks like this.  Note that the lens is not a long telephoto, 200mm is about the limit, you're well advised to start with maybe 50mm. 

 

 

What you're trying can't possibly work.  The mount is the most important part of the setup.  NOT the scope or the camera.  Your target is moving and .005mm pixels need to follow it PRECISELY.  1/1000 of an inch error is way too much.

 

I recommend this book. 

 

https://www.astropix...bgda_index.html

 

Also, scroll down to the picture of the expert author on that webpage.  That's a $500 70mm refractor on a $1500 HEQ5 mount.  He did not choose those because he had them lying around.  If you want to image DSOs with a scope, on a $2000 budget, that's the best use of the budget.  That's what can work.  Again, your setup cannot _possibly_ work for DSO imaging.  At all.

 

Honest.  <smile>

Edited by bobzeq25, 12 April 2023 - 01:51 AM.

[vidrazor]

Need help ! I am using DSS to stack 430 pictures (M51) of 20s exposure, ISO 1250 with 25 each of Bias, flats and dark pictures. After registering I get a  message that only 1 picture will be stacked !  What am I doing wrong ?

Could it be bad focus ?

Are your images out of focus? If so, whay are you even bothering? If not, what exposure? If your exposure is too low there won't be enough stars to find to align.

 

Also, did you compute the number of detected stars in DSS? Click on Register Checked Images and in the Advanced tab, click on Compute the number of detected stars. You don't want a high number, around 150-175 will suffice. Counterintuitively, moving the slider to the left increases the sensitivity to detect stars. If you haven't done this, do this first.

 

As others have mentioned, using an Alt-Az mount is futile for DSO imaging, however there are apparently some hacks around it, to a degree I imagine. I don't know how well the iOptron mount you have takes to a wedge, but if so you can build a wedge and turn the mount into a proper equatorial mount if your funds for an equatorial mount are nonexistent at the moment.
 

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[jmerran]

ISS, Soyus, thanks for the explanations.

 

The maximum number of detected stars was 14 at the 2% threshold ! Does this indicate the problem ?

 

My goal is to practice with the equipement I have before investing in an additional EQ gear. I will try again with 500 pictures at 15s and be carefull with focusing.

[Dpasqa]

This is REALLY simple.

 

The Alt-az mount absolutely dooms you.  20 seconds of star motion, and the motion magnified by the 714mm focal length, will turn stars onto long streaks.   You can't stack streaks.

 

There are three important things for DSO imaging.  Tracking, tracking, and tracking.  Analogy.  You're in a car trying to shoot a picture with a long telephoto lens.  At night in a rural setting.  The car is moving and the road is bumpy.  What kind of a picture do you think you'll get?

 

A proper mount for DSO imaging with that scope would be something like an iOptron CEM40.  A bit over $2000.  You'd still need an autoguiding system to correct errors due to the inexpensive (honest) mount.

 

https://www.ioptron....uct-p/c402a.htm

 

The inexpensive workaround is to shorten the focal length a lot, by using a camera lens.  That magnifies tracking error less, and you can use an inexpensive equatorial mount, a $300-500 camera tracker.  The setup looks like this.  Note that the lens is not a long telephoto, 200mm is about the limit, you're well advised to start with maybe 50mm. 

 

skytracker-with-camera-and-lens-444x545.jpg

 

What you're trying can't possibly work.  The mount is the most important part of the setup.  NOT the scope or the camera.  Your target is moving and .005mm pixels need to follow it PRECISELY.  1/1000 of an inch error is way too much.

 

I recommend this book. 

 

https://www.astropix...bgda_index.html

 

Also, scroll down to the picture of the expert author on that webpage.  That's a $500 70mm refractor on a $1500 HEQ5 mount.  He did not choose those because he had them lying around.  If you want to image DSOs with a scope, on a $2000 budget, that's the best use of the budget.  That's what can work.  Again, your setup cannot _possibly_ work for DSO imaging.  At all.

 

Honest.  <smile>

Why does an eq mount track better? With my az mount for visual the target seems to keep an object centered for ever?

[kgb]

Why does an eq mount track better? With my az mount for visual the target seems to keep an object centered for ever?

You won't get discernible field rotation in an EQ mount. Whereas in an Alt/Az the field will show rotation. The closer you get to the poles the more obvious the rotation. Here is a good reference for that concept.

https://kelly.flanag...ted-telescopes/

[vidrazor]

ISS, Soyus, thanks for the explanations.

The maximum number of detected stars was 14 at the 2% threshold ! Does this indicate the problem ?

My goal is to practice with the equipement I have before investing in an additional EQ gear. I will try again with 500 pictures at 15s and be carefull with focusing.

Well first, our call names are on the darker colored bar above where you see ISS, Soyuz, Sputnik, etc.

 

And yes, you just don't have enough stars. Either your images are too out of focus (which should be obvious to you), or your exposure time is too low, which is probably the case (or possibly both).

 

The field of view of your 102, combined with field rotation, is restricting your longest possible exposure time. You could try going up a stop in ISO if you're not high already. I wouldn't go above 1600. That along with a short enough exposure time may help, but you're simply shoveling crap against the tide.

 

The nature of your Alt-Az mount restricts you from shooting long exposures and from having effective subs due to field rotation. As I mentioned earlier, there apparently are some techniques for shooting DSOs with your mount, but I don't know if the habits developed are helpful in the long term.

 

If an EQ mount is out of the question for you at this time, I suggest building your own wedge for your Alt-Az mount so it becomes an EQ mount from one of the tutorials out there that may best fit your situation, if you can work with some basic woodworking tools (or know someone who does). I don't know how well this would work with your particular mount, but it may be worth a try.
 

Edited by vidrazor, 12 April 2023 - 01:34 PM.

[vidrazor]

Why does an eq mount track better? With my az mount for visual the target seems to keep an object centered for ever?

Because of field rotation. It winds up turning you images into looking down the top of an Osterizer Blender.

 

If you can't afford an EQ mount at the moment, you may be able to convert your Alt-Az mount into an EQ mount by building your own wedge for it if you can work with some woodworking tools. This will eliminate field rotation and allow you to have longer exposure times.
 

Edited by vidrazor, 12 April 2023 - 01:32 PM.

[17.5Dob]

Why does an eq mount track better? With my az mount for visual the target seems to keep an object centered for ever?

Yes, it's staying centered, but it's continuously rotating. If you tried imaging a circumpolar target like M81, it would do a full 360° circle over 24 hours. Magnify that constant rotation by using a telescope, and you end up with photos that look like you shot a star trail photo of the pole with everything spinning around the center. An EQ mount matches the rotation, so you can shoot an exposure as long as your local light pollution allows with no field rotation. Your mount is only intended for visual use, iOptron doesn't even have an EQ conversion option available for it's software to use it on a wedge so you are limited to a short enough enough exposure, that field rotation doesn't trail your stars so badly that stacking software doesn't recognize them as stars.

Edited by 17.5Dob, 12 April 2023 - 01:25 PM.

[Dpasqa]

Yes, it's staying centered, but it's continuously rotating. If you tried imaging a circumpolar target like M81, it would do a full 360° circle over 24 hours. Magnify that constant rotation by using a telescope, and you end up with photos that look like you shot a star trail photo of the pole with everything spinning around the center. An EQ mount matches the rotation, so you can shoot an exposure as long as your local light pollution allows with no field rotation. Your mount is only intended for visual use, iOptron doesn't even have an EQ conversion option available for it's software to use it on a wedge so you are limited to a short enough enough exposure, that field rotation doesn't trail your stars so badly that stacking software doesn't recognize them as stars.

I get it, I didn’t know this, thanks. 

[jmerran]

I have attempted another session to photograph the Whirlpool galaxy.  I used the following configuration:

 

Ioptron Alt-Az Pro mount

ES 102mm f/7 telescope with 0.7 reducer (f/4.9)

DLSR Nikon D7500 camera

742 exposures of 8s

ISO 1600

32 Bias frames, 32 dark frames, 32 flat frames

Stacking with Deepskystacker

Some basic rocessing with Photos (windows) 

 

Here is the the original picture (taken 742 times) https://www.dropbox.... 1600).nef?dl=0

 

Here is the staked picture with some basic photo processing - https://www.dropbox...., 2023.TIF?dl=0

 

I am happy with some good progress. What do I need to do differently with my setup to improve image quality and color.  Any ideas ? Thanks

Edited by jmerran, 25 April 2023 - 12:44 PM.

[BPoletti]

I've had better luck with Sequator for stacking.  

[jmerran]

I have attempted another session to photograph the Whirlpool galaxy.  I used the following configuration:

 

Ioptron Alt-Az Pro mount

ES 102mm f/7 telescope with 0.7 reducer (f/4.9)

DLSR Nikon D7500 camera

742 exposures of 8s

ISO 1600

32 Bias frames, 32 dark frames, 32 flat frames

Stacking with Deepskystacker

Some basic rocessing with Photos (windows)

 

Here is the the original picture (taken 742 times) https://www.dropbox.... 1600).nef?dl=0

 

Here is the staked picture with some basic photo processing - https://www.dropbox...., 2023.TIF?dl=0

 

I am happy with some good progress. What do I need to do differently with my setup to improve image quality and color.  Any ideas ? Thanks