Stargazing Level of details in prime focus vs eyepiece images

[PhysicoRaj]

View attachment 289606When I’m shooting invisible things in the night sky, since I don’t use an equatorial mount that automatically slews to the target, I have a cord that transfers the pictures to my phone and I upload a test shot to http://nova.astrometry.net/upload to see where I’m pointing and then adjust… I was able to capture supernova remnant Simeis 147 a few months ago on my dslr with a composite RGB image and a Ha narrowband image through a clip-in 6nm Ha filter…

Yup I stumbled upon astrometry a few days back and that's amazing to know. Seems like doing AP stuff manually and with less expensive gear is not really too much of a headache nowadays.

There is still one member at my Astro Club who does it all manually. Results pretty fair too. Reminds me of the joke with the punch line "And before you ask, standing up in a hammock"

I don't want to get sucked into the spending hole, so this is an inspiration :)

 

[sophiecentaur]

with less expensive gear is not really too much of a headache nowadays.

No problem any more with registering multiple images; software will do that for you (even when the mount is not equatorial). The can still be a problem with star trails from long exposures and long exposures beat multiple exposures for really faint objects.

But hell, there is so much photogenic stuff up there that the main limitations are cloud and your dedication.

 

[Devin-M]

My next upgrade will be because I want to image in the narrowband Hubble palette, but I don’t want it to take multiple evenings of imaging… It’s hard enough to find a clear night with no moon, and takes enough time to get to my bortle 2 location, the thought of having to do that 3 or more times for 1 image is disheartening… and I already have the Hydrogen, Oxygen and Sulphur clip in filters for my DSLR, so what I plan to do is buy 2 more DSLR bodies, 2 more 300mm lenses and 2 more 2x teleconverters and 2 more trackers and then I’ll be able to image through all 3 narrowband filters simultaneously… Each exposure through these filters is often 5 minutes long even with very high ISO sensitivity settings, and I’m expected to take 20-40 or more of these through each filter and manually re-acquire the target each time… no thank you, I’d rather have 3 cameras. Switching between filters would be such a hassle as it often takes me 30-45 minutes just to focus the camera and then get it pointed in the right direction.

 

[PhysicoRaj]

long exposures beat multiple exposures for really faint objects.

Heard that long exposures have less bias / read-out noise compared to sub-exposures. And, for the reason Devin-M mentioned, making full use of one perfect night / travel means I should be taking in as much signal and less noise as possible, which is possible with tracking (at least manual, nightmare in an alt-az mount).

@Devin-M, does the use of NB filters increase the exposure time needed since you will be receiving less photons per second than ideal?

I'm also thinking if it makes more sense to shoot planets on my scope using EP projection? The prime focus image as I see on Stellarium (and some 'cloudy' tests outdoors), is very small, but with the barlow and eyepiece in, I could record a video on my phone instead of the DSLR [I have a way to stick my phone into the EP, but not the half-kilogram DSLR] and ask software to help with the rest. I don't see a reason why I would need a DSLR for EP projection of planets when all I need is to just grab a few hundred FHD frames at 60 fps and stack them - might turn out better than a prime focus image?

 

[sophiecentaur]

2 more 300mm lenses and 2 more 2x teleconverters

What would that be in f number, altogether? I think your solution would be 'unusual' so it could be worth submitting the idea to a couple of dedicated astro forums (like stargazers' lounge). Making almost simultaneous exposures would probably be best on a common, heavy duty mount.
It's catch 22 really. A single big lens will give you worth while data in a fairly short time but, and this annoys you, needs multiple exposures (extras for H alpha etc.. But the results can be stunning.

Pretty much every combination of kit will have ben tried, at least by someone and their opinion could be worth going for. From what I hear from fellow club members (I am such a casual hands on that my experience is not worth listening to) they are very opportunist about gathering data- spreading their exposures over several suitable nights.

PS did you consider a Newtonian? Long focal length and massive light gathering power. Very popular with people with a chunky mount.

 

[sophiecentaur]

Heard that long exposures have less bias / read-out noise compared to sub-exposures.

Slippery slope here. That's why people buy dedicated astro cameras with Peltier cooling. There's really no substitute for that when you start to get really fussy.

 

[PhysicoRaj]

That's why people buy dedicated astro cameras with Peltier cooling. There's really no substitute for that when you start to get really fussy.

Oops. I have started a project on peltier cooling my DSLR because I already have a couple modules and heat sinks lying around. But I am trying to avoid 'breaking-in' to my camera (warranty) and finding a way to cool it non-invasive, like at the backside where the flip-screen fits, or in case the mounting hole at the bottom connects to the sensor shield somehow, forms a thermally more conductive path.

 

[sophiecentaur]

finding a way to cool it non-invasive,

There's a possible way in, via the optical tube. A waft of cold air passing over the sensor would cool it. But you'd need a glass window (coated etc) to stop the objective getting dew on it if the cold air got up that end.
But you may just need to bite the bullet and get a cold camera.

 

[PhysicoRaj]

But you may just need to bite the bullet and get a cold camera.

They're very expensive here. I already carry my DSLR around for hikes and I can easily set it up for an astroshot, without a laptop.

I also learned today about how pixel size on the sensor affects my image. It turns out that I need bigger pixels to collect more light from faint objects (DSO) and smaller pixels if I need more detail out of small but bright objects (SSO). This makes me think, a DSLR with moderate pixel size at prime focus is really not very good for planetary, better stick to DSO's and build my gear around it. Those dedicated planetary cams seem to have tiny pixels that can pickup details with small area since the photons are abundant from an SSO.

 

[Devin-M]

What would that be in f number, altogether? I think your solution would be 'unusual' so it could be worth submitting the idea to a couple of dedicated astro forums (like stargazers' lounge). Making almost simultaneous exposures would probably be best on a common, heavy duty mount.
It's catch 22 really. A single big lens will give you worth while data in a fairly short time but, and this annoys you, needs multiple exposures (extras for H alpha etc.. But the results can be stunning.

Pretty much every combination of kit will have ben tried, at least by someone and their opinion could be worth going for. From what I hear from fellow club members (I am such a casual hands on that my experience is not worth listening to) they are very opportunist about gathering data- spreading their exposures over several suitable nights.

PS did you consider a Newtonian? Long focal length and massive light gathering power. Very popular with people with a chunky mount.

The 300mm lens is f/4.5 & adding a 2x teleconverter makes it 600mm f/9.

My goal is to get full Hubble palette data on a target in a single night.

With 1 camera we’re talking 30-45 minutes setup. Each exposure is in the neighborhood of 5 minutes so if I want 60 images to stack from 1 narrowband filter we’re talking 5 hours or 6 hours including camera setup. Multiply 6 hours times 3 filters and we’re talking 18 hours which is obviously too long for 1 night of imaging… & honestly I start getting pretty bored and tired after only around 3 hours.

But if I have 3 cameras going simultaneously, I could get 15 hours of data in only 5 hours, for example, which is doable in a single evening.

If I were to have to find 3 separate nights with appropriate moon/weather that also fit my will/determination and schedule it could take weeks or months.

So I’d basically be spending around $500x2 for the dslr bodies, $500x2 for the trackers, maybe $500x2 for the lenses + teleconverters, so I’m basically looking at spending around $3k in order speed up the process of acquiring a single Hubble palette image from weeks or months to a single eve.

Alternatively I could capture 3 targets in the time it currently takes to capture 1 target.

Three cameras on a single mount would require an expensive mount. I could get 2 more trackers for about $1k ($500 each) but I am already basically pushing the weight limit for a single tracker.

 

[Devin-M]

@Devin-M, does the use of NB filters increase the exposure time needed since you will be receiving less photons per second than ideal?

Yes the narrowband filters let almost no light through so each exposure is around 5 minutes even if you set the ISO sensitivity very high. Also, they make it impossible to use the viewfinder or live view so the only way to frame the shot that I’ve found is by taking test shots and then uploading them to http://nova.astrometry.net/upload for plate solving.

& unfortunately if your town has switched to LED street lighting as mine has, the narrowband filters won’t block out the sky glow so you would definitely need to go to a dark sky area in that case.

 

[Devin-M]

Here’s what you could expect from a clip-in narrowband Ha filter:

Heart Nebula - IC 1805 - Sharpless 2-190 - 7500 light years
45 minute exposure - 9 x 5min - 6400iso - 600mm f/9 - Moonless Bortle 2 (3/3/21)
Nikon focal 300mm f/4.5 + Nikon TC-301 2x teleconverter
Nikon D800 w/ Star Adventurer 2i Equatorial Mount
Astronomik Narrow Band (6nm) Hydrogen Alpha Filter For Nikon Full Frame DSLR

 

[PhysicoRaj]

& unfortunately if your town has switched to LED street lighting as mine has, the narrowband filters won’t block out the sky glow so you would definitely need to go to a dark sky area in that case.

Its LED here, does that mean even standard light pollution filters would not work? My camera is unmodded, so I wouldn't be able to use the NB filters but I was thinking of an LP filter.

 

[Devin-M]

Its LED here, does that mean even standard light pollution filters would not work? My camera is unmodded, so I wouldn't be able to use the NB filters but I was thinking of an LP filter.

LED spectrum is broadband so the sky will be glowing in whatever wavelengths your light pollution filter let's through.

 

[PhysicoRaj]

LED spectrum is broadband so the sky will be glowing in whatever wavelengths your light pollution filter let's through.

Bittersweet, that prevents me from spending on another accessory but its hard to find a darker area. My area now is a Bortle 5 - 6 according to clearoutside.com but there is some localized LED pollution.

 

[Devin-M]

My camera is unmodded, so I wouldn't be able to use the NB filters but I was thinking of an LP filter.

My camera is unmodded but I still use the narrowband filters… as far as I understand it the wavelengths the narrowband filters allow to pass through are in the visible spectrum.

 

[Devin-M]

The EP view is 35x magnification and my 'brain' does see more details, but I feel stacking and sharpening is giving me satisfactory details for the optics I have. I particularly think the 60mm aperture is limiting a bit (?)

What happens if you add something like this into the mix… that should in theory get you up to 2100mm f/36…

http://oldshutterhand.com/equipment-reviews/kenko-3x-teleconverter-review/

 

[PhysicoRaj]

My camera is unmodded but I still use the narrowband filters… as far as I understand it the wavelengths the narrowband filters allow to pass through are in the visible spectrum.

Even the H-alpha? I have seen some people do a full spectrum mod and even use UV narrowband on some targets. But I did not know that narrowband imaging in Visible wavelengths is going to add something extra. Have to read up on that.

What happens if you add something like this into the mix… that should in theory get you up to 2100mm f/36…

http://oldshutterhand.com/equipment-reviews/kenko-3x-teleconverter-review/View attachment 289691

I cannot use a teleconverter as I am sticking my DSLR into my scope focus tube for planetary. Or so I think. But, I do have a 3x barlow that will give me 700x3=2100mm focal length, but that is too much for the moon. Also I am finding that much magnification a little lossy, not sure if I am over-magnifying or its just the low quality of the barlow.

I am eager to try Saturn and see what I can get out of 2 meters of focal length (the best thing about Saturn is I don't have to worry about surface details, just resolving the rings is an achievement.. which is as large as Jupiter in ang. dia.) but the clouds wouldn't let me

 

[Devin-M]

Even the H-alpha? I have seen some people do a full spectrum mod and even use UV narrowband on some targets. But I did not know that narrowband imaging in Visible wavelengths is going to add something extra. Have to read up on that.

Yes H-alpha is visible light.

H-Alpha + RGB composite:

No filter RGB:

H-alpha filter only:

The RGB with no filter is a lot noisier because I had to histogram stretch the image a lot more to show the nebula, the stars are over-exposed and it suffers a lot more from the effects of light pollution.

 

[Devin-M]

What I intend to do going forward is capture an RGB image for the stars that isn’t over exposed so it still shows their natural color (yellow or blue) and then I will blend in each of the 3 narrowband images, one into each color channel to show the nebula in Hubble palette, after removing all the stars from the narrowband images with the dust and scratches tool in Adobe Photoshop.

 

[PhysicoRaj]

What I intend to do going forward is capture an RGB image for the stars that isn’t over exposed so it still shows their natural color (yellow or blue) and then I will blend in each of the 3 narrowband images, one into each color channel to show the nebula in Hubble palette, after removing all the stars from the narrowband images with the dust and scratches tool in Adobe Photoshop.

Wow. Never thought a stock DSLR would be so capable. I thought the H-alpha is 100% blocked out by the stock IR-cut filter in front of the sensor.

 

[Devin-M]

https://www.astronomik.com/en/photographic-filters/h-alpha-6nm-ccd-filter.html

 

[PhysicoRaj]

From your link:

This is probably my next purchase when I re-open my wallet!

 

[Devin-M]

Needs a tracker since you’ll be doing 5 minute exposures…

 

[sophiecentaur]

From your link
This is probably my next purchase when I re-open my wallet!

From what you say, your wallet has limited capacity (join the club!). That means you need to profit from the mistakes of others. Just follow some of the 'beginner' threads in astro forums. There are very experienced AP'ers who have been through it all before and their recommendations are really worth taking seriously. Time spent doing this will probably be worth at least 'the minimum wage' for you (and with no income tax involved).

Needs a tracker since you’ll be doing 5 minute exposures…

OP needs to read all the reviews on trackers. There are good ones and not so good ones. People often use a tracker to start with and move on up. So you can expect to find perfectly good s/h ones at good prices.

 

[PhysicoRaj]

Yes Thanks. I started reading some of those stargazing and AP forums. There's a ton of info there

 

[Devin-M]

I saw from your website you live in Mysuru, India. Here’s where I’d personally go to get away from the light pollution. It’s a flat area in a clearing so not many trees in a Bortle 2 zone, but it’s around a 2 hour drive…

11.8720050, 76.1713820

https://goo.gl/maps/8MVWhZWGJdKMrikd6

https://www.lightpollutionmap.info/

 

[PhysicoRaj]

I saw from your website you live in Mysuru, India. Here’s where I’d personally go to get away from the light pollution. It’s a flat area in a clearing so not many trees in a Bortle 2 zone, but it’s around a 2 hour drive…

11.8720050, 76.1713820

I have traveled along that riverbank a couple of times during the day, and that place is sandwiched between two reserved forests and it might get scary at night (I could hear a faint tiger roar occasionally at dusk when we stopped for water ).

So I was planning to have this Bortle 4 place which is under an hour drive for casual AP (bright and easy targets) and this Bortle 2 for serious stuff. The Bortle 2 is a 3 hour drive, but its a mountainous area with lots of camping sites available, which means I can plan for the entire night.

 

[Devin-M]

I just ordered 2 more d800 dslr bodies, 2 more 300mm lenses, 2 more 2x teleconverters, and 2 more star trackers to use with my 3 narrowband filters so hopefully next time I venture out I’ll be getting full Hubble palette data in a single night… I do wonder if I have 3 cameras with 600mm f/9 going simultaneously, what is the effective f ratio?

 

[sophiecentaur]

what is the effective f ratio?

Because you have thrown away, effectively, about two thirds of the light entering each camera because of the filters, you are back where you started. With narrower band filters, you are losing even more light; people need long exposures to reveal the low levels of Hydrogen lines in some DSOs. The pictures are pretty and impressive but not 'reality'.
I look forward to hearing the results of your unusual approach.