Imaging with an 8 inch SCT - some results

[Craney]

Evening everybody.

Spent a lot of internet time over Christmas looking and dreaming of scopes with which to image galaxies and the smaller DSO's.  It struck me that not many of the pictures associated with this niche are taken with SCT's.  Why not  I wondered ? .... the SCT design has lots of aperture and focal length in a very compact design. 

My SCT is a Meade LX-55, used primarily for planets, Lunar and double stars.  Thought I would give it a go on the clear night we have just had.

There was a Gibbous Moon and a cheeky Northerly wind to tickle the mount, so imaging conditions were not ideal.

I decided to go for the full native F10 ( 2000mm !!!!!....) and used an unguided NEQ6, modded 600D  with a Baader UHC filter to combat the Moonshine (!)...no I hadn't touched a drop.

Exposures were between 30 and 60 mins  with 1 or 2 min subs at ISO 1600.  DSS, then bit of cropping and tweeks in PS.  

 

 

 

( M81,M82, NGC891, Ring, Dumbell and Crab.)

I was pleasantly surprised at the outcome. so then.... let's start at NGC 001.....

Sean.

[michael8554]

Hi Sean

Well done with a challenging focal length.

Michael 

[Knighty2112]

Great images. Well done!  

[newbie alert]

Fantastic Sean...lots of new found friends at my astro club image with sct's..with images as good as I've ever seen...like you say the fl and image scale on galaxies is great..im going to get mine out again..

[Luna-tic]

Outstanding. Those are as good as I'd ever expect from my own efforts, and to see that they are unguided gives me hope I can do it, too, with some more practice with the Edge.  Going to try first light with my new 80APO tonight, see if I can catch the Moon between clouds.

[Craney]

Yeah!!  good to hear @newbie alert   I was very surprised that I had enough usable subs to construct an image at all, this was 4 times the FL of my usual set up.

  I think my memory of 'early attempts' with an SCT  (one 5 minute shot resulting in a blurred piece of abstract art ) sort of led me away from this avenue of investigation.

Getting the NEQ6, refining technique and becoming familiar with DSS have all put me in a much better position in terms of results.   Lets hope aperture fever does not kick in !!!!!!

Sean.

[Craney]

Hi @Luna-tic,

8 " SCT  and a quality 80mm refractor......with a good mount underpinning it all.....  that's a winning combination which covers a lot of options for imaging.

Good luck with the first light.

S.

[tooth_dr]

Excellent shots Sean, a great set of captures from an evening, I’d love to see what you could with M82 if you imaged over a whole night, because that one you posted above is a cracker. 

[Craney]

Indeed @tooth_dr,    it does open up possibilities. 

The SCT is such a multi-functional tool that I could let it loose on  ..... let's say,  a crescent Moon in the early evening.... maybe an odd planet thrown in ... and then bag some DSO's on long extended capture runs  ( F10 or F6.3)..... not missing out on any pre-dawn solar system objects as well to round off an object packed night.

All without changing the scope on the mount.   Amazing versatility.

The next couple of dark clear  nights I hope to lower the ISO and up the exposure time on the DSO's I have imaged above. Just to see the difference it makes.

Cheers,

SEan.

[Moonshed]

Those are great images, well done indeed. I also own an 8" SCT F10 and 2000mm FL, in my case a Celestron mounted on an EQ5. What I would like to ask is how on earth do you manage such long exposures unguided? The most I can get without star trails is around 150 - 180 seconds. When you say unguided do you literally mean you centre the image, after of course accurate PA and star alignment, and then just let it run for that length of time without any adjustments to re-centre the image? If that is indeed the case then it must be that the EQ6 mount is in a different league to my EQ5. I am clearly misunderstanding something, please enlighten me.

Cheers, Keith

[Craney]

6 hours ago, Moonshed said:

 What I would like to ask is how on earth do you manage such long exposures unguided? The most I can get without star trails is around 150 - 180 seconds.

Re: @Moonshed

Thanks Keith.    There is no magic spell I summon up on the mount.. although I do use a lot of Anglo-Saxon at times !!.... what I mean in the descriptions is that the total exposure is 30-60minutes, comprised of  1 to 2 minute subs.    eg.   60mins on M82 was from  30 x 2mins.   With the Moon so prominent I went for a lot of 'shorter' subs to improve the signal to noise.    

Yes, you are correct in that by 'unguided' I let good PA and good luck dictate the outcome.  I hope to deploy a finder/guider later when I get my head around it.

So your mount may be able to do the same.  I was only experimenting and testing the waters on what I could get away with.    I was very happy that the subs produce usable shots with non-trailing stars.   Because of the long FL and narrow field of view I always do a preliminary shot at 12800ISO to make sure all is well and to centre the object because due to nature of them they generally do not leap out of the frame.  

As a bit of advice always assess the exposure duration of the subs per object.  eg.  different altitudes may mean you can get away with longer.  A galaxy in Ursa Major near the Zenith has different tracking dynamics to M42 on the celestrial equator.   The different orientation of the scope can also introduce gremlins.... always spend time on the balancing when setting up.   Also when processing you may have to invoke 'narrow band' options in DSS as there wont be many stars  in the field of view and the program will not stack any of your hard earned subs..... grrrr!!!...     I use SharpCap for polar aligning.... marvellous tool.

Have a go Keith, all part of the fun. 

 

Sean.

 

[Moonshed]

Hi Sean, thanks for the clarification, thought I must have misunderstood something. I have had my Celestron for 25 years and originally took images using film, quite a challenge. I started digital astrophotography last winter and found that it was a steep learning curve! Here are some that I took. I hope to get better this winter.

 

[Craney]

Nicely done.   M33 has a very low surface brightness and I'm sure does not like being photographed. You have got it looking like a galaxy.

AP using film...... blimey!!     I remember waitng for 2 weeks to get my first Orion constellations shots (with a Zenit-E with 50mm lens)  back  from the mail order processing.

All of them had Quality Control stickers on them.  Did better with KodaChrome, but it was about £5 for 24 shots.  The other night I took 600 shots on digital.

[Moonshed]

Yes, using steam powered film for AP is very demanding. It was impossible to tell if the focus was correct, or the exposure time correct until you had the film back two weeks later as you say. To get my first image of M42 that was halfway decent took around 3 rolls of film with 24 exposures. I lived in a light polluted area and would have to drive out to a forest and setup under my car headlights. Getting a decent PA squinting through the mount was a nightmare and a bit hit and miss. I had to learn how to find my way around the night sky and to identify the main stars, no GOTO mounts back then! This is my first M42 image taken with film, after getting through three rolls of film in trial and error, it was a 13 minute exposure if I remember correctly. It looks awful now but at the time, back n 1993, I was so proud of it.

[ollypenrice]

19 hours ago, Craney said:

Indeed @tooth_dr,    it does open up possibilities. 

The SCT is such a multi-functional tool that I could let it loose on  ..... let's say,  a crescent Moon in the early evening.... maybe an odd planet thrown in ... and then bag some DSO's on long extended capture runs  ( F10 or F6.3)..... not missing out on any pre-dawn solar system objects as well to round off an object packed night.

All without changing the scope on the mount.   Amazing versatility.

The next couple of dark clear  nights I hope to lower the ISO and up the exposure time on the DSO's I have imaged above. Just to see the difference it makes.

Cheers,

SEan.

I take your point but the DS images which may have launched your interest in this subject will not have been taken in an hour or two (or three) between early evening and dawn. You can't bag DS images in just a few hours, other than exceptionally. It simply does take time.

1 hour ago, Moonshed said:

Hi Sean, thanks for the clarification, thought I must have misunderstood something. I have had my Celestron for 25 years and originally took images using film, quite a challenge. I started digital astrophotography last winter and found that it was a steep learning curve! Here are some that I took. I hope to get better this winter.

 

One snippet of advice: when you bring in the black point, do so far more gently. These images are 'black clipped,' meaning that much of the precious faint data you have captured has been thrown away. Your data, most certainly, has more to give.

Healthy:

Clipped:

Olly

[Craney]

Yes, very true @ollypenrice,  I have learnt one thing so far, that small imaging victories are hard earned. ..... over long time periods.

At this stage in my experience I am trying to image as many DSO's as I can. ... hey !!.. what the hell..... I like doing it.

Maybe after a full year or two of 'collecting'  I will focus on particular objects and get that 'calendar shot'.

Well done with that film image... I think that would have exhausted my patience after roll one.....

 

Sean.

[Moonshed]

Olly, thanks for the advice on the black point, I will be more careful next time. It does seem to me that it takes about an hour to get the image and a several hours to bring out the detail correctly. Practice, practice, practice, and hopefully I will improve.

[ollypenrice]

7 minutes ago, Craney said:

Yes, very true @ollypenrice,  I have learnt one thing so far, that small imaging victories are hard earned. ..... over long time periods.

At this stage in my experience I am trying to image as many DSO's as I can. ... hey !!.. what the hell..... I like doing it.

Maybe after a full year or two of 'collecting'  I will focus on particular objects and get that 'calendar shot'.

Well done with that film image... I think that would have exhausted my patience after roll one.....

 

Sean.

What I continue to learn after 10 years as an 'imaging provider' is that nobody ever had too much data. I honestly think that, if you really want to learn, you should not take ten images but just one. Then you'll have a data set which will allow you to learn what can be achieved in processing. I used to think that 3 hours made a good image. Then I thought it was 6 hours. Then 12. Well, 12 is OK but 20 is better. The name of our game is 'Signal to noise.'

Olly

[Jbro1985]

I love my 8"SCT.  Observing, planetary and DSO.  Although it's a bit tricky with the DSOs.  I am fairly new to SGL so not many images uploaded so far - here's one from November on the 8" SCT.  I have to say, imaging with the narrow field of view and long focal length (even with reducer) is somewhat tricky and I'm looking to get a 80mm refractor to help with widefield imaging, but there's no way this guy is going in the cupboard.  Imaging on the frac ticking along through SGP whilst observing on the c8 is my idea of a great night!

 

[Craney]

Absolutely agree.... I usually have two mounts going simultaneously.    Narrow and wide field...... narrow and wide band !!!

Hell of a job to get them covered if a shower comes in, like a Keystone Cops movie.     With the UK climate it is always good to maximise opportunity and to get the data in whilst you can.  There are plenty of windy, wet nights with which to process it.... and then reprocess it....

I tried to get M33 the other night with the SCT, failed to lift anything out of the noise.   Nice shot btw.

 

Sean.

[lune lupine]

this was orion the other night in between clouds. 8" Evo SCT. 20x10s exposures on canon 550d. no darks,flats etc; wanted to see what stacking simple subs can do and quite pleased with it for fist go