Jump to content

  •  

CNers have asked about a donation box for Cloudy Nights over the years, so here you go. Donation is not required by any means, so please enjoy your stay.

Photo

So many variables so few clear nights, beginner's imaging

  • Please log in to reply
13 replies to this topic

#1 Jabonet

Jabonet

    Sputnik

  • -----
  • topic starter
  • Posts: 29
  • Joined: 31 May 2020

Posted 04 July 2020 - 11:22 AM

Hello all.
I have been involved is astronomy for over 30 years but recently got myself into astrophotography again(last time was with a film camera, what a change!) My philosophy is to use what I have the best possible way ànd only if I know I have reached my limit consider to buy something to pass that limit. No sense buying a new camera until you have master alignment, collimation, focus and a long etc.
That being said. I have a celestron C8. CG5 mount, usually installed on a fixed pier, nikon D40 dslr,the light pollution is not the worst, no street lights, but some towns towards the east. Atmospheric conditions are bad, plenty of thermal turbulence almost all night. And dew that attacks in a matter of minutes.

Alignment is around 10minutes checked and double checked. I plan to improve it by drift alignment, but I believe this is not the limiting factor.
My main issue now at the moment is collimation and focus, I 3d printed a Duncan mask and have a bahtinov mask for focusing, but I can't focus thru the camera eyepiece with any filter install. I focus without the filter and once focused I take the camera out screw the filter and reinstall. I believe this small difference is messing up my focus. When I focus without NB filter the bahtinov mask works as a charm.
So if you already had your growing pains in all this and would like to tutor a newbie go thru his, drop me a private message or a reply in this thread.
Thanks

#2 kathyastro

kathyastro

    Surveyor 1

  • *****
  • Posts: 1,955
  • Joined: 23 Dec 2016
  • Loc: Nova Scotia

Posted 04 July 2020 - 11:44 AM

You do need to focus through the filter.  A typical filter is 3mm thick, which makes a 1mm difference to the focus position.  A 1mm shift in focus is a lot, so you will not be able to focus unless you do it through the filter.  If you can't see well enough to focus with the filter in place, you will need a clear glass "filter" that matches the filters you use.  It will be sold as a "luminance" filter.

 

You would focus using the Bahtinov mask and the Luminance filter, then switch to the NB filter, being careful not to mess with the focus as you do so.  You will need a filter wheel or filter drawer to do so.

 

If changing filters is not possible, then you will need to find a way to focus through the NB.  Try cranking up the ISO to maximum.  If that doesn't work with live view, try taking test exposures of several seconds at high ISO to focus.


  • drd715, SonnyE and Jabonet like this

#3 Gipht

Gipht

    Vanguard

  • *****
  • Posts: 2,414
  • Joined: 12 Nov 2016
  • Loc: Prescott Valley, AZ.

Posted 04 July 2020 - 11:57 AM

Have you tried a 10  sec exposure through the NB filter with the Bahtinov mask on?  This can be time consuming but still is better then poor focus.



#4 SonnyE

SonnyE

    Surveyor 1

  • -----
  • Posts: 1,989
  • Joined: 01 Nov 2015
  • Loc: Cali for ni a

Posted 04 July 2020 - 12:27 PM

If you are determined, I think you will love imaging, especially digital.

I love digital imaging! Gone is the cutting room floor.

Now you just tap a delete key, and it goes out the fan of your computer in a green cloud. (Figuratively speaking, like a fart)

And nobody is any the wiser. Let's you hide the evidence of big screw-ups. wink.gif

 

And Post Processing opens a whole new realm of tearing your hair out.

 

I presume your D-40 is unmodified, so you will be getting color images.

I prefer shooting with a color camera myself. But early on, I realized I would literally beat my Nikon D3300 to death taking my Picturds.

So I got a dedicated Astro camera. But it was a poor choice, a horrible bad choice. A couple of years later a friend offered to loan me his Atik Infinity OSC (One Shot Color) camera.

I resisted. He persisted. I asked, "What if I like it, and want to keep it?" He said, "Then we can work something out."

He sent it, and the very first night, the very first picture, everything changed!

It shown my tracking and guiding were good, I just needed a decent camera.

 

But by all means, do start out (again) with your D-40.

And Please share your results. grin.gif



#5 Stelios

Stelios

    Cosmos

  • *****
  • Moderators
  • Posts: 9,473
  • Joined: 04 Oct 2003
  • Loc: West Hills, CA

Posted 04 July 2020 - 02:16 PM

Do you have a laptop? Very likely Backyard Nikon supports your camera (possibly so do NINA (free) and SGP). 

 

A laptop makes it trivial to focus using its screen. Astrophotography just using the camera and intervalometer is simply too hard for a sustained hobby. 



#6 Szumi

Szumi

    Viking 1

  • -----
  • Posts: 531
  • Joined: 01 Oct 2016
  • Loc: NLP, Michigan

Posted 04 July 2020 - 02:28 PM

I'm assuming you have a narrow band filter?

 

Can you focus on the moon to get close?  I have no experience with NB filters but that has to be bright enough to see something.

 

I've shot just a few pictures with my T5i / C8 Edge just to see if I could do it.  I'm awaiting a 8.5mm adapter for my OAG and then I'm going to play for real.  I had to take a series of pictures at high iso/long exposure moving focus until I saw the stars in the captured image and I worked from there.

 

I noticed that with my Canon, live view gets brighter if I crank up the ISO, no experience with Nikon. 

 

It would seem that once you get close, you can use that Bahtinov to nail your focus.



#7 Jabonet

Jabonet

    Sputnik

  • -----
  • topic starter
  • Posts: 29
  • Joined: 31 May 2020

Posted 04 July 2020 - 03:17 PM

You do need to focus through the filter. A typical filter is 3mm thick, which makes a 1mm difference to the focus position. A 1mm shift in focus is a lot, so you will not be able to focus unless you do it through the filter. If you can't see well enough to focus with the filter in place, you will need a clear glass "filter" that matches the filters you use. It will be sold as a "luminance" filter.

You would focus using the Bahtinov mask and the Luminance filter, then switch to the NB filter, being careful not to mess with the focus as you do so. You will need a filter wheel or filter drawer to do so.

If changing filters is not possible, then you will need to find a way to focus through the NB. Try cranking up the ISO to maximum. If that doesn't work with live view, try taking test exposures of several seconds at high ISO to focus.


Thank you all for the support. It's wonderful to have such an active forum.
Kathyastro. Excellent idea. The nikon d40 has a maximum exposure of 30 seconds and a maximum iso of 1600. It has a 3200iso but with noise cancelling, which eliminates a lot of the stars. My vision is quite poor so I can't trust my eyes for focusing.
I don't think that focusing on the moon with the bahtinov will work as the difraction pattern must come from a point source. But it's worth a try. But Jupiter for example is not bright enough for the bahtinov plus the narrow band filter.
On top of that the d40 doesn't have live view. So focusing will be a slow process of shooting and zooming in. I will try it tonight.
I do plan to have a laptop for controlling all this from inside the house/car. But for now the weather is nice.

#8 Jabonet

Jabonet

    Sputnik

  • -----
  • topic starter
  • Posts: 29
  • Joined: 31 May 2020

Posted 04 July 2020 - 03:25 PM

If you are determined, I think you will love imaging, especially digital.
I love digital imaging! Gone is the cutting room floor.
Now you just tap a delete key, and it goes out the fan of your computer in a green cloud. (Figuratively speaking, like a fart)
And nobody is any the wiser. Let's you hide the evidence of big screw-ups. wink.gif

And Post Processing opens a whole new realm of tearing your hair out.

I presume your D-40 is unmodified, so you will be getting color images.
I prefer shooting with a color camera myself. But early on, I realized I would literally beat my Nikon D3300 to death taking my Picturds.
So I got a dedicated Astro camera. But it was a poor choice, a horrible bad choice. A couple of years later a friend offered to loan me his Atik Infinity OSC (One Shot Color) camera.
I resisted. He persisted. I asked, "What if I like it, and want to keep it?" He said, "Then we can work something out."
He sent it, and the very first night, the very first picture, everything changed!
It shown my tracking and guiding were good, I just needed a decent camera.

But by all means, do start out (again) with your D-40.
And Please share your results. grin.gif

Buying fresh film, together with other people, hypersensitizing the film in those little cans. Praying that the weather is nice the mount aligned etc, and right after running to the lab to develop the film before it looses the signal. It was hell.
Now click, I like it take another 300 of them. Even a bad one today is better than that.

#9 kathyastro

kathyastro

    Surveyor 1

  • *****
  • Posts: 1,955
  • Joined: 23 Dec 2016
  • Loc: Nova Scotia

Posted 04 July 2020 - 05:40 PM

I don't think that focusing on the moon with the bahtinov will work as the difraction pattern must come from a point source. But it's worth a try. But Jupiter for example is not bright enough for the bahtinov plus the narrow band filter.

No, you won't be able to use the Moon through a Bahtinov mask.  Even Jupiter is too big to use it with any accuracy, and there isn't going to be much, if any, light in the NB wavelengths.  You need a first magnitude star.
 


  • dghent likes this

#10 17.5Dob

17.5Dob

    Fly Me to the Moon

  • ****-
  • Posts: 6,325
  • Joined: 21 Mar 2013
  • Loc: Colorado,USA

Posted 04 July 2020 - 09:22 PM

Trying to shoot Narrow Band through a C-8, using an un -modded D40 , mounted on a CG5, is about as close to "impossible" as you can get....

Get rid of the filter, get a focal reducer...and you'll improve your odds to at least a snowball in Hades



#11 Jabonet

Jabonet

    Sputnik

  • -----
  • topic starter
  • Posts: 29
  • Joined: 31 May 2020

Posted 05 July 2020 - 03:44 AM

Trying to shoot Narrow Band through a C-8, using an un -modded D40 , mounted on a CG5, is about as close to "impossible" as you can get....

Get rid of the filter, get a focal reducer...and you'll improve your odds to at least a snowball in Hades


I am getting to the same conclusion. Last night results:
Taking a 10s exposure with the filter and bahtinov mask is the way to go for fine focusing. I first focus without the filter which puts me in the ballpark and then put the NB and check with 10s exposures while tuning the focus. I will 3d print a big knob for the focuser to help me with the resolution.
Nevertheless the filter may help in light pollution but seems like it's not the best for skyglow.
Another thing I found is that even if you hibernate the mount when you start it up again a one star alignment is way worse. The declination info seems to be lost and centering stuff on the frame gets much harder.

Also I found a very small Freeplay between the t ring and the camera body. The camera lenses don't have this play at all. But the ring has. That is probably messing with the focus also.
But in general focus got better.

#12 Jabonet

Jabonet

    Sputnik

  • -----
  • topic starter
  • Posts: 29
  • Joined: 31 May 2020

Posted 05 July 2020 - 04:33 AM

I got much better results with 20s exposures without filter than with 120s with filter. As 17.5Dob says I think that the NB is not really helpful on these conditions.
Stacking 3 pictures 60s total I managed magnitude 12 on beta lyra. And this was with a big moon and clouds very very close. Actually I didn't take more pictures because it got covered. Probably I can achieve at least one more magnitude in a couple of weeks.

#13 Jabonet

Jabonet

    Sputnik

  • -----
  • topic starter
  • Posts: 29
  • Joined: 31 May 2020

Posted 05 July 2020 - 11:35 AM

I am getting to the conclusion that the narrow band filter is taking so much light out that is maximizing other problems for a very marginal benefit.

I wonder which are the ideal conditions where a narrow band filter makes a big improvement.

Attached Thumbnails

  • IMG-20200705-WA0000.jpg
  • IMG-20200705-WA0001.jpg


#14 Jabonet

Jabonet

    Sputnik

  • -----
  • topic starter
  • Posts: 29
  • Joined: 31 May 2020

Posted 07 July 2020 - 05:29 AM

<p>Picture last night, just before the moon. No narrow band filter, just 30x55second exposures and then pick the best 50%. Substacted the noise and the bias in DSS</p>
<p>I can see clearly magnitude 15.3 and the limit I saw was 16.5.</p>
<p>Focusing with bahtinov on a bright star and then fine tuning the foto with 10s exposures (no live view on my camera).</p>
<p>Total exposure around 15 minutes.</p>
<p>Question: does more exposure time mean more magnitude? If I stack 3 hours total time will I get some more?</p>
<p>Anyway to see pluto there is a limit of a few minutes before the planet moves, but for star fields should be interesting.</p>

Attached Thumbnails

  • rps20200707_121956.jpg



CNers have asked about a donation box for Cloudy Nights over the years, so here you go. Donation is not required by any means, so please enjoy your stay.


Recent Topics






Cloudy Nights LLC
Cloudy Nights Sponsor: Astronomics