#1  
Old 24-09-2007, 10:29 AM
Aprid
Registered User

Aprid is offline
 
Join Date: May 2006
Location: Ferntree Gully
Posts: 24
Advice on imaging

Hi,
I'm trying my hand at Autoguided astro photography for the first time whilst the Autoguiding seems to work ok I'm a bit miffed as to whether it is best to shoot shorter exposures with high ISO or longer exposures with lower ISO
settings also is it better to use the incamera noise reduction or dark frames ?
The camera in question is a K100d Super ( I know, it's not a canon)the attached image is a single frame shot at ISO 1600 60 sec exposure with incamera noise reduction, image has been resized and black level adjusted in photoshop It was only taken to test the Autoguiding and is rather grainy so the next step would be to take multiple and stack.

Thanks
Aprid
Attached Thumbnails
Click for full-size image (IMGP1.jpg)
181.8 KB75 views
Reply With Quote
  #2  
Old 24-09-2007, 11:26 AM
citivolus's Avatar
citivolus (Ric)
Refracted

citivolus is offline
 
Join Date: Sep 2007
Location: Carindale
Posts: 1,178
In camera noise reduction typically uses a half length dark, doubled and then subtracted. As such, a series of full length darks, median combined, will give you better results, but obviously take more work to do.

The advantage of using in camera noise reduction is that the dark will be taken at very close to the same temperature as the light frame, so if the temperature is changing rapidly it may possibly give better results.

I'm not familiar with your camera's sensor, so I can't comment much on ISO other than to say an intermediate ISO setting can be better than a low setting, depending on amp design, as long as you are stacking or stretching your images. The reason is that the amp basically stretches the image as it reads it, rather than afterwards via software which loses precision. If you stretch a low ISO shot, you will end up with as much noise as the higher ISO shot, but there will be quantization effects that actually degrade the image quality.
Reply With Quote
  #3  
Old 24-09-2007, 11:33 AM
[1ponders]'s Avatar
[1ponders] (Paul)
Retired, damn no pension

[1ponders] is offline
 
Join Date: Nov 2004
Location: Obi Obi, Qld
Posts: 18,778
The general rule is the longer the better and more of them for improved signal to noise ratio. However if your tracking doesn't allow for that then you can stack lots of shorter exposures, but you won't get as deep.

The internal noise reduction is ok to use but there are disadvantages. One is that they take up valuable time that could be used for imaging. As long as you don't get variations in ambient temperature you can always take darks in 'blocks" during the night or even at the end when you are packing up. A good routine would be take 10 lights and then 5 darks, 10 lights 5 darks, for shorter exposures. For longer exposures you could try 5 and 2, 5 and 3. That way no matter what happens you will have lights and darks to work with.

As for ISO 400 to 800 seems to be fairly standard.
Reply With Quote
  #4  
Old 24-09-2007, 01:33 PM
ving's Avatar
ving (David)
~Dust bunny breeder~

ving is offline
 
Join Date: Nov 2004
Location: The town of campbells
Posts: 12,359
looks nice to me. the pentax seems to do a good job
Reply With Quote
  #5  
Old 25-09-2007, 12:29 AM
Aprid
Registered User

Aprid is offline
 
Join Date: May 2006
Location: Ferntree Gully
Posts: 24
Well thanks for the advice and I'll try with the dark frames and lower the ISO and see what comes out.

Yes Ving I was pretty happy to get some sort of result considering its just an entry level DSLR and I'm only accustomed to point and shoot cameras.

Thanks Guys
Reply With Quote
  #6  
Old 26-09-2007, 06:28 AM
Roof
Registered User

Roof is offline
 
Join Date: Jun 2007
Location: Brisbane
Posts: 15
Quote:
Originally Posted by Aprid View Post
Hi,
I'm trying my hand at Autoguided astro photography for the first time
Can i ask a quick question , Did you do this piggybacked or through the scope ?

Cheers

Roof
Reply With Quote
  #7  
Old 26-09-2007, 10:09 AM
Aprid
Registered User

Aprid is offline
 
Join Date: May 2006
Location: Ferntree Gully
Posts: 24
It was shot through a 200mm f6 Newtonian prime focus with a Pentax K100D Super autoguided through a 80mm Gerry built 80mm refractor with a modified long exposure Toucam all sitting on a poor little Eq5.
Thank for your interest
Aprid
Reply With Quote
  #8  
Old 26-09-2007, 11:59 AM
Roof
Registered User

Roof is offline
 
Join Date: Jun 2007
Location: Brisbane
Posts: 15
I have a Skywatcher 130mm Reflector and a K100D and i have been trying to do some astro photography, But can't reach focus. I only tried the moon as i think it is the easiest to begin with.

So that's why i'm a bit surprised that other can do with similar equipment.

I've asked here on the forum about how and what and they all say bring the mirror forward which i don't want to do.

Anyway i keep looking and trying till i find a way.....

Thanks

Roof
Reply With Quote
  #9  
Old 26-09-2007, 12:38 PM
Aprid
Registered User

Aprid is offline
 
Join Date: May 2006
Location: Ferntree Gully
Posts: 24
I wasn't able to achieve focus with the scope as it was, the way I remedied the problem by removing 50mm from the end of the tube with an angle grinder to move the primary up, it seems drastic but it's quite painless as long as you have the collimation skills to re align the primary. I doubt if a lower profile focuser would help you but there's no harm in asking.

Good luck
Reply With Quote
  #10  
Old 26-09-2007, 01:08 PM
Roof
Registered User

Roof is offline
 
Join Date: Jun 2007
Location: Brisbane
Posts: 15
Thanks for that.

I'm not really sure if i want to attack the scope with a angle grinder just in case i bugger it up. Anyway thanks again..

Roof
Reply With Quote
  #11  
Old 26-09-2007, 10:49 PM
little col
gosh i love imaging

little col is offline
 
Join Date: Jun 2007
Location: manchester uk
Posts: 286
same problem here but i found a solution , use a barlow lense with a screw thread attach it to your t- mount on the camera and you can achieve focus
Reply With Quote
  #12  
Old 27-09-2007, 06:09 AM
Roof
Registered User

Roof is offline
 
Join Date: Jun 2007
Location: Brisbane
Posts: 15
Cheers little col, Someone mentioned today to buy a new focusser and put that in it, So i might ring the shop today and see what that's gonna cost me.


Cheers

Roof
Reply With Quote
  #13  
Old 27-09-2007, 11:12 AM
Roof
Registered User

Roof is offline
 
Join Date: Jun 2007
Location: Brisbane
Posts: 15
Quote:
Originally Posted by little col View Post
same problem here but i found a solution , use a barlow lense with a screw thread attach it to your t- mount on the camera and you can achieve focus

Hey Colin, I had a bit of a look to see what kinda equipment you've got and it's about the same as me isn't it ? I looked at your shot they are quite spectacular.....
You were saying a screw head attached to it, I'm really new to all of this can you buy these screw heads or is it a complete barlow thing.

Cheers mate..

Roof
Reply With Quote
  #14  
Old 27-09-2007, 12:02 PM
[1ponders]'s Avatar
[1ponders] (Paul)
Retired, damn no pension

[1ponders] is offline
 
Join Date: Nov 2004
Location: Obi Obi, Qld
Posts: 18,778
JFYI, be aware that if you use a barlow, yes you will achieve focus, but....

1. you will double your f ratio which will mean 4 times the exposure length to achieve a similar image signal level (this is a big issue, ie a normal 5 min exposure will take 20 min to achieve the same result).

Taking shots of bright globs and open clusters might be ok but you will find that galaxies and nebula will be a challenge. For extended objects (planets, moon, sun etc) long focal length is important (using a barlow, ie; slow f ratio), for faint fuzzies with stars, aperture is more important (fast f ratio ie short focal length given the same aperture as above).

2. you will reduce your field of view

3. if you use a 1.25" barlow you will get strong vignetting around the edges and corners of your image, it may not be enought to encroach on the moon but any widefield images will be affected (assuming you are successful with them, see point 1). If you are going to use a barlow consider a 2" one. If you consider a 2" one try screwing off the lens cell of the barlow and screwing it to a Prime Focus Adapter. You may get enough focus movement without incuring the wrath of 1 and 2 too much.
Reply With Quote
  #15  
Old 27-09-2007, 12:13 PM
Roof
Registered User

Roof is offline
 
Join Date: Jun 2007
Location: Brisbane
Posts: 15
Thanks for that answer Paul, I think that i'm not asking to much as i only want to put my camera onto my scope and take some photo's of the moon to start with. But it seems to be something complicated (In my eyes) to realize all of this.

Maybe i should just get an angle grinder and cut a bit of the tube.

I'm not sure anymore, It's frustrating.


Thanks again for that explanation

Roof
Reply With Quote
  #16  
Old 27-09-2007, 12:43 PM
[1ponders]'s Avatar
[1ponders] (Paul)
Retired, damn no pension

[1ponders] is offline
 
Join Date: Nov 2004
Location: Obi Obi, Qld
Posts: 18,778
If all you want atm is to image the moon then Colin's method will work really well. If you want to image the planets later on with a webcam then that will also work well, infact it is the most common way. However when you eventually want to image deep space stuff you will need to look at other alternatives.
Reply With Quote
  #17  
Old 27-09-2007, 01:29 PM
Roof
Registered User

Roof is offline
 
Join Date: Jun 2007
Location: Brisbane
Posts: 15
Quote:
Originally Posted by [1ponders] View Post
If all you want atm is to image the moon then Colin's method will work really well. If you want to image the planets later on with a webcam then that will also work well, infact it is the most common way. However when you eventually want to image deep space stuff you will need to look at other alternatives.
Would you be able to advise in that matter.


Cheers

Roof
Reply With Quote
  #18  
Old 27-09-2007, 01:35 PM
[1ponders]'s Avatar
[1ponders] (Paul)
Retired, damn no pension

[1ponders] is offline
 
Join Date: Nov 2004
Location: Obi Obi, Qld
Posts: 18,778
Equipment wise (mounts, camera accessories), yes, what to do with your newtonian, well yes and no. I don't have a newt so I can't speak from experience, but if you can't reach focus (usually not enough infocus distance) then yes the mirror will most likely need to be moved up the tube. You don't have to cut the tube end off, but it does make it more difficult to reach the collimation screws.

Another option is a low profile focuser, but there is no guarantee that you will be able to reach focus with that either.

I've just gone back and read what scope you have, what do you have it mounted on?

If you meant can I advise you on planetary, luna and solar stuff, then yep np
Reply With Quote
  #19  
Old 27-09-2007, 02:25 PM
Roof
Registered User

Roof is offline
 
Join Date: Jun 2007
Location: Brisbane
Posts: 15
When i wrote photo's of the moon, That is to start with eventually i'll have a go at planets and move further from there on, It doesn't have to happen overnight but sometime in the future. I think if sombody else can do this why can't i....

My Scope

I would like to get some straight answers from someone, If somebody says to me if you go and do this or buy that and it all works i'm happy to look into that, Cutting a piece of the tube is not really an option at this point in time. Allthough i do understand what you meant by saying reaching collimation screws is going to be difficult with not cutting the tube. But say if i have the gutz to cut the tube is that going to change anything else, I assume little bit less focal lenght, But that should be it shouldn't ??

Thanks again for at least trying to help me, I think it's a complicated hobby.


Cheers

Roof
Reply With Quote
  #20  
Old 27-09-2007, 04:20 PM
[1ponders]'s Avatar
[1ponders] (Paul)
Retired, damn no pension

[1ponders] is offline
 
Join Date: Nov 2004
Location: Obi Obi, Qld
Posts: 18,778
Ok, totally different kettle of fish now. I don't think you will be able to cut anything off the length. You have what is commonly called a Mak Newt with a corrector plate at one end. A standard newt has the top end open. My belief is that if you shorten your tube the corrector plate will no longer be able to function as it should and you will degrade your view.

You mount will not be smooth or stable enough to do photography through your telescope anyway. You may be able to do piggyback with a camera and camera lens using a smaller scope as a guide scope, but that mount was never intended to to anything else except visual work.

Might I suggest you pay a visit to the Sunshine Coast on a new moon weekend. We have an IIS get together at a members place (Astroron) every new moon. There is plenty of room to pitch a tent and there can be anywhere up to 10-15 people there with all manner of scopes and equipment. It would be much easier to show you what is needed and how you could use your scope and mount to it's best.

If you keep an eye on the Observation Sessions and Star Parties Forum the next get together should be announced in the next day or so. It will be either Saturday week or Saturday Fortnight (or both if we are keen) as the New Moon falls near midweek ( Oct 11 - Thursday).

pm me if you would like more details.
Reply With Quote
Reply

Bookmarks

Thread Tools
Rate This Thread
Rate This Thread:

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off

Forum Jump


All times are GMT +10. The time is now 07:53 PM.

Powered by vBulletin Version 3.8.7 | Copyright ©2000 - 2019, Jelsoft Enterprises Ltd.
Advertisement
Lunatico Astronomical
Advertisement
NexDome Observatories
Advertisement
SkyWatcher Australia
Advertisement
Meade Australia
Advertisement
Bintel
Advertisement
Celestron Australia
Advertisement
OzScopes Authorised Dealer
Advertisement
Astronomy and Electronics Centre
Advertisement