Level of details in prime focus vs eyepiece images

[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.

 

[Devin-M]

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.

It’s most convenient if you know of a flat area with few trees.

 

[Devin-M]

By the way, when it comes time to balance your lens/camera on your star tracker, these come in very handy… They’re actually intended for focusing cameras with macro lenses but also work wonders for balancing a camera/lens combo on an equatorial mount.

https://www.bhphotovideo.com/c/prod...Adjustable_Camera_Platforms_6.html?ap=y&smp=y

 

[sophiecentaur]

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

Bortle 4 is fine for practicing the procedures and finding out precisely what you need for a session. It's only when doing this stuff 'for real' that you find out what you are doing wrong. A possible six hours of travel can be frustrating if you have to abort for some trivial reason. So wait until you can arrive, unload, put the kit together reliably (and the reverse) and get useful data at the slightly less-perfect site.
Until you can get all available data on the nearer site, you may not get any visible benefit from the better site. Astrophotography is a long-haul business and many urban astronomers manage to get pretty stunning results.

 

[Devin-M]

I look forward to hearing the results of your unusual approach.

I justified the cost in my mind of tripling my camera rig to capture through all 3 of the narrowband filters simultaneously by saying “well I could buy a brand new Sony A9 II mirrorless camera body alone with no lens for $4.5k, or I could buy 2 used nikon d800 bodies that each have 12 more megapixels than the sony, and 2 used 300mm lenses, and 2 used 2x teleconverters, and 2 new star adventurer star trackers, and 2 new intervalometers and 2 new tripods and 2 new macro rails for slightly less money than the sony body alone, and that will cut any given observation time by 2/3rds, but the sony alone would give no benefit to observation time without vast further financial outlays…”

 

[sophiecentaur]

I justified the cost in my mind of tripling my camera rig

I could see where you were going with it. However, cheaper still would be to do what 'everyone else' does and use just one camera. I think you'd need to consider the different exposure times that are necessary when using narrow band filters and that would probably mean that two of the three cameras may not actually be doing anything useful at times.
You will need to use your arrangement for some while before you can assess just how good your choice was in terms of Bang for Buck. I suspect you may end up using two or three mounts and imaging more than one object. That could be a real plus. I have a chum who does astrophotography and passes the time with his enormous Dobsonian doing visual stuff whilst the other kit is gathering data.

 

[Devin-M]

OTA’s received. They’re in better condition than my original rig…

 

[Devin-M]

 

[Devin-M]

quick test shot with the new optics while I'm waiting for the new equatorial mounts...

"anna's hummingbird" - 1/2500th sec, 6400iso, 600mm, f/9, 100% crop

https://www.speakev.com/attachments/img-4433-gif.150742/

https://www.speakev.com/attachments/img-4434-gif.150739/

 

[Devin-M]

the “goldman narrowband array” is nearly complete… astronomik narrowband hydrogen, sulphur & oxygen 6nm clip-in filters, 300mm lenses, 2x teleconverters, d800 dslrs, star adventurer 2i equatorial mounts, still just waiting on a couple tripods and intervalometers…

 

[PhysicoRaj]

Yikes. Is there an adapter that can fit a monochrome atsronomy camera to DSLR lenses directly? Three of them with your filters in them can probably do this job cheaper?

Edit:
Looks like it exists: (you still need 3 trackers, that's next one to address )

 

[sophiecentaur]

Is there an adapter that can fit a monochrome atsronomy camera to DSLR lenses directly?

A camera lens can obviously be adapted for any image sensor but going too far down that road is of questionable worth. Look around the suppliers; if there's a need for it then there must be something on the market.

A telescope OTA, is little more than a lens, a tube and a focus arrangement. The optical requirements are based on Astrophotography and not on general photography. A camera lens has an (auto) iris and a focussing arrangement (an internal motor perhaps) that is not intended for five minute exposures. Long lenses use telephoto optics which keep them short but involve several more elements. You are paying for stuff you don't need and you are not getting some of the things a regular scope can give you.

However, the quality of many good camera lenses (cheap and on the second hand market) will be a lot better than many entry level scopes.

One needs to ask oneself why nearly all the best astro images tend to be taken with scopes with large apertures and very simple lenses.

 

[PhysicoRaj]

A camera lens can obviously be adapted for any image sensor but going too far down that road is of questionable worth. Look around the suppliers; if there's a need for it then there must be something on the market.

A telescope OTA, is little more than a lens, a tube and a focus arrangement. The optical requirements are based on Astrophotography and not on general photography. A camera lens has an (auto) iris and a focussing arrangement (an internal motor perhaps) that is not intended for five minute exposures. Long lenses use telephoto optics which keep them short but involve several more elements. You are paying for stuff you don't need and you are not getting some of the things a regular scope can give you.

However, the quality of many good camera lenses (cheap and on the second hand market) will be a lot better than many entry level scopes.

One needs to ask oneself why nearly all the best astro images tend to be taken with scopes with large apertures and very simple lenses.

I agree. Was simply trying to think through avoiding having multiple DSLR 'bodies' for simultaneous narrowband exposures.

 

[sophiecentaur]

I agree. Was simply trying to think through avoiding having multiple DSLR 'bodies' for simultaneous narrowband exposures.

Horses for courses again. A DSLR will do loads of things that are not needed of Astro work and the sensor has the colour filters built in. Spending sever hundred quid will get you a very good sensor which you can buy to suit your planned subject and you can COOL it too. All the brains have to be supplied by your computer control but you can expect to be using a laptop out there in any case.

I can see that you are fully committed to a multiple camera solution. That is something you will have to learn about. Three DSLR systems, sharing a mount would need to be driven carefully- they can only be operated in sync because you can't poke around on one camera when another is making its exposure. That builds in a fair amount of necessary down-time; you won't get three times the exposure time.

BTW, have you read anywhere of anyone else who has operated a three camera system successfully? Do you have any links to other similar work or opinions about your system?

 

[Devin-M]

I doubt you can get 3 full-frame 36 megapixel astro-cameras for less than 3 second-hand dslr bodies. The D800’s were $3000 USD brand new but I picked up 2 averaging about $700 each…

“At the time of its release, the Nikon D800 became the Dxomark image sensor leader, replacing the Nikon D4 in the top position.[7]”

https://en.m.wikipedia.org/wiki/Nikon_D800

 

[sophiecentaur]

I doubt you can get 3 full-frame 36 megapixel astro-cameras for less than 3 second-hand dslr bodies. The D800’s were $3000 USD brand new but I picked up 2 averaging about $700 each…

“At the time of its release, the Nikon D800 became the Dxomark image sensor leader, replacing the Nikon D4 in the top position.[7]”

https://en.m.wikipedia.org/wiki/Nikon_D800

Are you comparing like with like here? I have to agree that there will be a premium on top end astro cameras but there will be a huge difference in the specs of the two different types of sensor involved. A high res monochrome astro camera does what it says on the tin whereas a colour DSLR camera is designed with different targets in mind.

People are free to make whatever choices they want, of course but unlike with HiFi equipment, there are many astro experts who can produce reliable numerical data to back up their choices of approach. I'd be inclined to read around a lot before committing to spending a lot on any astrophotography system.

Nevertheless, a standard colour camera can produce some really stunning images. It's all in the post processing.