First Light (at last) on DSO

[Maxrayne]

M45 @ 400mm

 

First light!! My first attempt at a DSO (deep sky object) using the ST80 mounted on the SW SA. Massively happy with this as a first attempt

Had to run it thru a couple of times as I'd inadvertently kicked the tripod on a couple of exposures, and I'm struggling with CA on this. 

 

EXIF:

 

Mount: Sky Watcher SA

Imaging Scope: Sky Watcher ST80

Focal Length: 400mm

Exposure Length: 30 seconds

Total Exposure Time: 3900 seconds

ISO 800

Capture Device: Nikon D5300 (non modded)

Software: Sequator & LightRoom

Bortle 5 skies

[tooth_dr]

Despite the obvious CA that’s a really striking image of the seven sisters. A nice combo of ST80 and SA ??

[Maxrayne]

Thank you

Any thoughts on that ca? I've tried the obvious defringing but that just leaves desaturated halos around the stars and actually looks worse

[Ags]

I think the hot blue stars of the Pleiades bring out the worst of the ST80's blue fringing. I don't think you can correct the fringes as anything you do to them will affect the nebulosity they are mingled with.

One option would be to stop down the ST80 to 60mm (F7), which should reduce the fringes somewhat, but you would need to double the number of subs you shoot.

[vlaiv]

7 minutes ago, Maxrayne said:

Thank you

Any thoughts on that ca? I've tried the obvious defringing but that just leaves desaturated halos around the stars and actually looks worse

Couple of suggestions on handling CA "in hardware".

Use simple wratten #8 filter (yellow) - it will cut off offending violet/blue frequencies that don't come into focus and cause star bloat. Your white balance will be slightly off, but star bloat will be much smaller.

Create aperture mask - this will have negative impact on SNR and you will need to increase total imaging time to match current quality but it will definitively produce better stars.

Try couple of masks - like 70mm and 60mm (if you have standard SW ST80 it should have two part lens cover so you should already have aperture mask in size 50mm) - and see which one creates acceptable stars while being largest (the least loss of light gathering).

For best results - combine above two techniques.

[Maxrayne]

Thanks guys. It does indeed have the two part lens cover, so that's going to be the simplest to try first I think without needing to spend anything. Have no issue staying out longer to grab more subs, although for the next week at least, conditions aren't looking favourable. If that doesn't work, I'll try the other suggestions. Thanks guys

[Ags]

I've used my ST80 for daytime photography, and stopping down with the lens cap really does improve the image quality, although you have to double exposure time.

[vlaiv]

Yes, it indeed works, I've done some tests with ST80 bigger brother - ST102, which should have even more CA because of additional aperture.

Here are some results that I've got:

Columns represent different level of stretch of data, so same image but more aggressively stretched in each column. Rows go like this: Full aperture, Full aperture + Wratten #8, then successive smaller apertures made with aperture masks (I believe I used 80mm, 75mm and 66mm or something like that, can't remember now), again alternating rows have filter applied to it.

In the end I think I opted for second smallest aperture + filter. This sort of image can be produced with such combination (it is 2x2 mosaic done with planetary type cam and then binned to recover some SNR):

If you want to avoid "spikey" stars make sure your aperture mask is smooth, I made mine by cutting hard plastic (PVC type) and apparently did not do enough of sanding to smooth out edges - hence those ray of light from bright star

 

 

[MarsG76]

Excellent, especially for a first light!!!. Thats way more nebulosity than what I ever picked up on the Plieades.

 

[Maxrayne]

8 hours ago, vlaiv said:

Yes, it indeed works, I've done some tests with ST80 bigger brother - ST102, which should have even more CA because of additional aperture.

Here are some results that I've got:

Columns represent different level of stretch of data, so same image but more aggressively stretched in each column. Rows go like this: Full aperture, Full aperture + Wratten #8, then successive smaller apertures made with aperture masks (I believe I used 80mm, 75mm and 66mm or something like that, can't remember now), again alternating rows have filter applied to it.

In the end I think I opted for second smallest aperture + filter. This sort of image can be produced with such combination (it is 2x2 mosaic done with planetary type cam and then binned to recover some SNR):

If you want to avoid "spikey" stars make sure your aperture mask is smooth, I made mine by cutting hard plastic (PVC type) and apparently did not do enough of sanding to smooth out edges - hence those ray of light from bright star

 

 

Oh wow, many many thanks for this. Going to be going back out for another crack using the stock aperture mask to start with and see what results I get with that. 

[Maxrayne]

7 hours ago, MarsG76 said:

Excellent, especially for a first light!!!. Thats way more nebulosity than what I ever picked up on the Plieades.

 

 

Thank you ? Think I got lucky. I've been struggling so much with focus and was literally just about to bin the evening. It's not perfect by a long shot, but it's remotivated me ?

[MarsG76]

19 minutes ago, Maxrayne said:

 

Thank you ? Think I got lucky. I've been struggling so much with focus and was literally just about to bin the evening. It's not perfect by a long shot, but it's remotivated me ?

Never get disheartened... astrophotography is a hit and miss... sometimes more misses than hits, that's what makes a success that much more rewarding.

[Maxrayne]

25 minutes ago, MarsG76 said:

Never get disheartened... astrophotography is a hit and miss... sometimes more misses than hits, that's what makes a success that much more rewarding.

Definitely more misses than hits but learning to turn it around and using that to motivate me. Need to take my own advice more lol

[happy-kat]

That's great and you used your ST80. Startools has some great CA minimising functions. 

[Maxrayne]

33 minutes ago, happy-kat said:

That's great and you used your ST80. Startools has some great CA minimising functions. 

Keep meaning to have a look at that! Thank you for the reminder ?