New to DSLR Imaging - Please Help

[MishMich]

Get a dog and let it out the back every ten minutes or so. After a week they'll get so sick of it they'll disconnect it - or the bulb will blow and they'll never be able to find a replacement.

You can stack them in something like Deep Sky Stacker (can be downloaded free - search on those words). You can do basic enhancements using Gimp (can be downloaded free - search on Gimp + graphic or software, otherwise you'll get all sorts of things you might not want), but that converts images to 8-bit colour from 16-bit. Paintshop Elements is relatively cheap, and basic stuff can be done in 16-bit, but anything more intricate (such as astronomy plugins) involves conversion to 8-bit. After those, the only thing I know is Painstshop Pro, which comes in at the hundreds. Pixinsight some people rave about - but that isn't cheap either.

Alternatively, something like AstroArt looks like it does a lot, and that's not much over £100. Maxim DL is supposed to be best, but costs a fortune. Iris can be downloaded free - but it is a bit incomprehensible to me (& I have a Masters in IT, used to develop software and administered UNIX systems).

M.

M.

[themos]

For processing of single Canon RAW files, the included Digital Photo Professional Canon Europe - Digital Photo Professional is pretty good.

[davidscanlan]

Thanks

I assume raw is best for all astro pics from constellations to telescope work?

[themos]

Yes, keeping your data in RAW files is best.

[davidscanlan]

Thanks for the advice

Shame there isn't a begineers chart kind of thing giving iso, exposure times, f stops etc etc as a basic starters guide

Dave

[MishMich]

There is something somewhere for the moon, but I forget where. If I remember, I'll let you know. It lists the phase of the moon, showing the ISO & exposure for that phase. It might be in the book in the Patrick Moore series on using a DSLR for astrophotography.

M.

[Cornelius Varley]

Here is a link to a useful exposure calculator Free Astrophotography Software

Peter

[narrowbandpaul]

good start.....with regards the ISO debate....ISO does not gather you more photons, so it does not give a better picture.....

i have written a document which explains this with measured data....

here it is...

http://stargazerslounge.com/imaging-discussion/87450-experiment-into-camera-isos-imaging-folows-what-iso-thread.html

[MishMich]

Thanks Cornelius, very useful.

When this lists exposure time, do you know if this applies to single frames, and how would that apply to stacking? For example, if I select faint nebula, at ISO 800, it suggests (for my setup) an exposure time of 20 minutes. So, does mean 10 x 2 minute images for stacking, or ten exposures of 20 minutes each? If I drop to ISO 200, it suggests nearly 1.4 hours. Would that mean 10 images of 8.4 minutes each, or 10 images of 1.4 hours each? Or does this only apply to single images, and is there some other method of calculating exposures for stacking?

M.

[MishMich]

Hi Paul,

nobody suggested that ISO 1600 gives you a better picture than ISO 100 - quite the reverse. The point is, it gives you a picture with shorter exposures (which means less photons than longer exposures), so is a good starting point - but there will be more noise, etc. Perhaps it would be helpful to non-physicists (like me - who's long forgotten all the maths I did at Uni many years ago) if you provided some simple evidnce. Something like an image taken in RAW at ISO 1600 - say ten minute's worth of subs - and an equivalent at ISO 100 of the same exposure. M42 should do it. Stacked and processed to illustrate the point that there is no benefit in using ISO 1600 over ISO 100. It would be the easiest way to test this, and the evidence would illustrate your point more clearly than theory. Then I can confidently approach a cold night of imaging the flame nebula at ISO 200, knowing I won't have stayed up all night for nothing.

M.

[Psychobilly]

Not exactly what you were after...

Composite of 2 subs on 900s(15mins) at ISO1600 and the other 1800s (30mins) at ISO800 during a tracking test over 2 nights...

I tend to do the majority of my exposures at ISO800 normally with subs between 5 and 10 mins and I occasionally mix in some subs at ISO1600 losing 1800s subs to cloud is really not nice at all (family friendly version)

M42 soemtimes gets a mix of ISO200,400 and 800...

Billy...

[Cornelius Varley]

Thanks Cornelius, very useful.

When this lists exposure time, do you know if this applies to single frames, and how would that apply to stacking? For example, if I select faint nebula, at ISO 800, it suggests (for my setup) an exposure time of 20 minutes. So, does mean 10 x 2 minute images for stacking, or ten exposures of 20 minutes each? If I drop to ISO 200, it suggests nearly 1.4 hours. Would that mean 10 images of 8.4 minutes each, or 10 images of 1.4 hours each? Or does this only apply to single images, and is there some other method of calculating exposures for stacking?

M.

The program is a few years old -before DSLRs became popular and accessible, so the exposure times are based on single frames. The program is still useful for DSLR lunar and planetary photography but probably less so now for DSO photography with a DSLR which uses a different technique (multiple stacked images rather than single shot).

Peter

[Psychobilly]

There are several big advantages with Digital...

The immedeacy - you can normally see straight away if your headign in th eright direction

The Cost per shot... just keep re-using those memory cards that hold thousands of shots ...

And the ability to tweak away till your hearts content without all those nasty chemicals in a dark room - still miss it though

Dont be frightened to experiment....

Get to know your way round the camera in daylight its buttons etc what they do it easier than fumbling around inthe dark withthe manual and the camera

Billy...

[cloudbuster]

Hi David

Like you, Im new to astrophotography. \i hope you dont mind me posting this, my first ever deep sky image, of the orion nebula. its not brill - poor alignment, composition, light pollution etc - but i am only a beginner!. It is a sandwhich of more than 30 images, ranging from 10sec to 120sec exposures, taken with my canon 300d DSLR, mounted on my Orion Europa 150 telescope,and processed on my pc using GIMP.

cheers

Bob

[narrowbandpaul]

if you read the document, you will see falling read noise with higher iso...this is due to the capacitance changing on the sense node...so a higher ISO may give better results...if you are read noise limited, then changing ISO is good, but for shot noise limited performance, it wont matter a jot....there may be other effects that occur at high ISO that i didnt allow for....

but a high DR certainly occurs at a low ISO

[MishMich]

Thanks Billy, that is an interesting comparison, nevertheless. The object appears as bright in both - yet the Light Pollution appears greater in the ISO 800 at double the exposure time. Was that cloud, or were the two under similar conditions?

I think I've seen about three nights where there has been no cloud in the past three months. My subs all came out that lilac colour the other night. Don't recall it being so bright before (& usually more amber).

M.

[Sparrow]

Hope you don't mind but I thought I'd add my ten penneth to this thread.

Dave - I've got the EOS1000D - the smaller cousin of your 450D. Thanks to lousy weather I've not had as much chance to use it as I would like but early results have been very pleasing - to me anyway. (I've attached my image of M42).

First of all - I decided on the DSLR route because it was far more affordable than a dedicated Astro CCD cam and I could justify the cost to my wife because it could be used for ordinary photography as well. With the bundled software, the 45oD is a useful camera for astro work - the live preview makes focusing alot easier, and all the dat and shutter control is done through one USB cable from the laptop.

I've read alot of opinions about the ISO and this is an important issue with the DSLR work. ISO stands for International Organisation for Standardisation and originally was the scale for the sensitivity of conventional camera film. Different ISO films were actually more or less sensitive to light due to their chemical make up. The term has been "poached" for DSLR cameras to imply a variation in sensitivty - as has previously been said in this thread, the sensitivity of the chip is fixed and does not vary. On the DSLR, changing the ISO setting is actually applying more or less electronic amplification to the signal. Although this is useful, it does of course introduce more noise into the image so there is an element of compromise. ISO 1600 will certainly give an exposure quicker but will also introduce more noise. I do most of my imaging now at ISO 800. This keeps exposure times to a reasonable level without introducing excessive noise. (BTW - the new Canon 500D has a much improved signal to noise ratio at the higher ISO settings - things are improving all the time).

There's no doubt that you should be able to get some good results with the EOS450D. In my case, the biggest step forward was getting in to guided photography which has opened up a whole new world of much longer exposures - not as expensive as you might think.

Good luck with the camera and hope you have some enjoyable imaging sessions

Regards

John

[Psychobilly]

M,

My LP varies dramatically as track objects across the sky and with 30 min subs theres a fair distance (7.5 degrees) travelled...

If I ever get a chance I'll do you the exposures your after on M42...

Will keep the same EV from ISO 100 through to ISO1600 sp a couple of runs

120s ISO1000 -> 7.5s ISO1600 for the shorter exposures

460s ISO100 -> 30s ISO1600 for the longer ones...

I'm pretty sure I did soemthing lkike this before and prodcued a "sheet" showing the results "developed" to a similar level...

Havent got a clue where the iamge is likely to be though... will set a search going...

B...

[Mark at Beaufort]

I have been taking general photos through a SLR for 25 years so fully understand ISOs etc. However, I want to start taking astro photos and I am still trying to understand the exposure times/iso settings discussed above and why using higher settings won't necessarily provide me with more detail.

I have a Celestron CG5 mount with motors to both axis I don't have an extra scope with a guide camera so I just let the camera run. The maximum exposure that I can get before I start getting star drifting is 120secs. I therefore assumed to get any decent photo it would be best to set the camera for 120 secs at 1600 iso rather than 100 iso?

I also went to a Canon lecture last year when they stated that their new models 5D mk2 and 7D could take photos at 6400 iso with very little noise.

Therefore would it not be best to take 20 stacked frames at 120secs at 6400 iso because I assume I might get a better photo or I am being naive!!

Mark

[room16]

I have a Celestron CG5 mount with motors to both axis I don't have an extra scope with a guide camera so I just let the camera run. The maximum exposure that I can get before I start getting star drifting is 120secs. I therefore assumed to get any decent photo it would be best to set the camera for 120 secs at 1600 iso rather than 100 iso?

Mark

Is this basically just prime focus point and shoot? or are you adjusting manually via the motors? Sorry, just trying to get some clarification as some have said on here that taking exposures that long is a no-go due to rotation?

I'd be happy if i could get 1min exposures without trailing lol.

Couple o hundred of those should get a half decent image i should imagine?

[Psychobilly]

Noise reduction...

Now theres another interesting one...

Where's the best place to do it ....?

Do you let the Camera do it ... or sort it out later....

Possibly the noise reduction in the camera is optimsed for terestrial use and will develop an appettite for the stars in the image...

Billy...

[MishMich]

Hi Billy,

To verify/falsify the theory, the exposures would need to be of the same length - to ensure that (as near as possible) the same number of photons hit the sensor. If you double the exposure length, then you double the number of photons collected. The argument was that as the same number of photons are collected regardless of ISO, the RAW file contains all the necessary information to produce a processed image regardless of ISO.

M.

[Psychobilly]

Indeed it is 'M' they would but If i am going to waste a few hours precious imaging time i might as well make sure I have data to show something else as well

Chances are I will never bother doing it anyway... as It's probably much better if people "discover" things for themselves...

'B'

[MishMich]

Hi Mark,

I have an HEQ5, but have not had an opportunity to image since I upgraded it to Synscan last week. I found that when I got a good polar alignment I could push exposures up to 120 secs, and then error in the mount became more significant (i.e., for those frames that did show trailing, they were not in the one direction. Hopefully the syntrak will improve this. The next step for me is to get set up for guiding. What I noticed when I dropped from ISO1600 to ISO800 was that while the image appeared 'fainter', some detail appeared 'finer' - specifically the trapezium appeared less blown out, and whisps of nebulosity appeared to have more definition. The trapezium looked better to me at ISO 800 than for an equivalent length of exposure at ISO 1600.

I'd like to follow this up further, and see how low it is possible to set the ISO - but had assumed that running at ISO 800 meant doubling the exposure time. Like you, it has not been possible for me to do that for exposures longer than 3 minutes or lower than ISO 800. However, if the ISO level is not that significant, that is quite important - and it needs to be verified/falsified, because it has substantial implications.

M.

[MishMich]

Point taken, Billy.

M.