Distance objects and smart phone

[Andy350]

Hi all, I was hoping that I would have been a lot more active by now, but life gets in the way.

I was bought the Celestron nexyz phone adapter and would like to start using it, I have a few recommended settings got the phone that I can try for some long exposure.

My question is really, what setup would be best for taking some shots of possible galaxies.  I only have a Super 10, and super 25 eye pieces.  I also have a 2X Barlow.

Andy

[Dave scutt]

Hi Andy 350.

There's a section in imaging where there using smart phones and getting some great results. 

I brought this from amazon because every time I touched the phone to take pictures it would shake. 

[Andy350]

Ok thanks for your help.  Yes, I've seen one of these, If I can get something to work I will get one of these.

[powerlord]

deepskycamera is good for stacking etc.

However, I think other than M31 you'll stuggle to get any galaxies tbh, even if OTA is long enough. moon should be fine though, and M42 is pretty easy to get a 'decent' pic on a phone.

here's one I took last year when I started and before I went down the imaging rabbit hole.

[Andy350]

15 hours ago, powerlord said:

deepskycamera is good for stacking etc.

However, I think other than M31 you'll stuggle to get any galaxies tbh, even if OTA is long enough. moon should be fine though, and M42 is pretty easy to get a 'decent' pic on a phone.

here's one I took last year when I started and before I went down the imaging rabbit hole.

Thanks for the image.  Looks great.  I had a play last night, couldn't see anything via the phone, like others have said I need to line up to something first.  But without phone I did see Jupiter and Saturn for the first time which was good.

[ollypenrice]

Galaxies are normally imaged at prime focus, so without an eyepiece. With an eyepiece the galaxy's projected image will be too large to fit on you chip.

Olly

[Andy350]

37 minutes ago, ollypenrice said:

Galaxies are normally imaged at prime focus, so without an eyepiece. With an eyepiece the galaxy's projected image will be too large to fit on you chip.

Olly

Hi Olly, I do have an older digital SLR camera with an adapter, so could use that for prime.  forgot to mention that!!

[ollypenrice]

1 hour ago, Andy350 said:

Hi Olly, I do have an older digital SLR camera with an adapter, so could use that for prime.  forgot to mention that!!

That would be the best way but it involves taking multiple images and stacking them. Exposures need to be long so you need to track accurately. It's a business...

😁lly

[vlaiv]

2 hours ago, ollypenrice said:

Galaxies are normally imaged at prime focus, so without an eyepiece. With an eyepiece the galaxy's projected image will be too large to fit on you chip.

Olly

Not necessarily.

Ratio of image scale in prime focus vs afocal method - depends on ratio of focal lengths of eyepiece and camera lens

In this case we have smart phone camera and lens. We need model to determine parameters of eyepiece as there are couple of things we need to adjust properly.

I'll randomly select phone model to give example of how calculations work.

Say we go for Galaxy S8 (random pick)

Here we have pixel size, sensor size, F/ratio of the lens and its equivalent focal length for 35mm film.

1/2.55" sensor has crop factor (here term is actually useful) of ~6.1 - which means that actual focal length of phone camera lens is 26mm / 6.1 = ~4.25mm

That is first parameter that we need - FL of camera lens

Next is entrance pupil (which we must match with exit pupil of scope + eyepiece combination) - we have F/1.4 lens and it has 4.25mm of FL - so our entrance pupil is 3mm - we must not have larger exit pupil than 3mm

It will therefore depend on scope what is the best eyepiece.

Say it is 6" SCT telescope in question. It is F/10 scope so highest focal length that can be used will be ~30mm (anything above will create too large exit pupil and waste light).

Using this calculator:

https://www.pointsinfocus.com/tools/depth-of-field-and-equivalent-lens-calculator/#{"c":[{"f":13,"av":"8","fl":50,"d":3048,"cm":"0"}],"m":0}

we can see how big FOV sensor captures in terms of degrees:

So it is about 80°

We need 30mm 80° AFOV eyepiece and phone for optimum performance (so we cover whole sensor and don't waste light with exit pupil).

From above parameters, we can calculate pixel scale and any needed binning since pixels are rather small.

 

 

[JuliusKlugi]

It depends on what your aim is. What I take from your post is that you’re not really wanting to do/expecting proper astrophotography - you just want to know if it’s possible to get something with your phone. Well you’re not going to get much detail with a smart phone but if you just want to just take no frills photos to convey as close as you can what you see through the eyepiece then snapping galaxies is entirely possible. A good app to use is Nightcap as it allows you to adjust exposure time and ISO. For galaxies these will need to be close to maximum. You can also set up a timer and turn on light boost. You’ll have to set up the internal programmer to around 10 seconds which will allow the camera to take 10x1 second shots, so the ability to track will be a requirement. Here’s some to the results you can expect in a bortle 6 junk sky area with no fancy processing. Again, they won’t win prizes but will convey to others what you are seeing - sort of. I see the purpose as more akin to sketching without the ability to actually draw anything. 

 

 

Edited November 18, 2021 by JuliusKlugi

[powerlord]

I'd suggest that that's all a bit of a waste of time for taking pics with a mobile. stick it up to the eyepeice, take a picture. Want to get fancy, I made a 3d printed mount that allowed me to fit phone in, and use it with any of my eyepieces, covering the whole eyepiece fov with each one - so you could go that route.

that way you can stack with deepskycamera.

But frankly, it will lead you to the conclusion that other than making a very effective cheap electronic eyepeice, it's pretty rubbish for any real pictures. You'd be far better using your DSLR that you have imho.

stu

[Andy350]

24 minutes ago, JuliusKlugi said:

It depends on what your aim is. What I take from your post is that you’re not really wanting to do/expecting proper astrophotography - you just want to know if it’s possible to get something with your phone. Well you’re not going to get much detail with a smart phone but if you just want to just take no frills photos to convey as close as you can what you see through the eyepiece then snapping galaxies is entirely possible. A good app to use is Nightcap as it allows you to adjust exposure time and ISO. For galaxies these will need to be close to maximum. You can also set up a timer and turn on light boost. You’ll have to set up the internal programmer to around 10 seconds which will allow the camera to take 10x1 second shots, so the ability to track will be a requirement. Here’s some to the results you can achieve in a bortle 6 area with no fancy processing. Again, they won’t win prizes but will convey to others what you are seeing - sort of. 

 

 

I suppose I'm not too sure, my scope was a present last Xmas.  Initially I was happy looking for planets.  It was only when I spoke to my brother in law that he mentioned that he had the Phone adapter, and it went from there.

I would like to be able to take some pics that I can keep, I really like some of the images that you've captured.  Not sure what you mean by proper astrophotography as I'm still new.  I'd like to take it as far as I can with what I have got.  Maybe at some point pick up a mount that can track.

I've just received a book called "Turn Left at Orion", so that might help.  I still need to make sense of what lens length means against what scope I have.

[Andy350]

5 hours ago, vlaiv said:

Not necessarily.

Ratio of image scale in prime focus vs afocal method - depends on ratio of focal lengths of eyepiece and camera lens

In this case we have smart phone camera and lens. We need model to determine parameters of eyepiece as there are couple of things we need to adjust properly.

I'll randomly select phone model to give example of how calculations work.

Say we go for Galaxy S8 (random pick)

Here we have pixel size, sensor size, F/ratio of the lens and its equivalent focal length for 35mm film.

1/2.55" sensor has crop factor (here term is actually useful) of ~6.1 - which means that actual focal length of phone camera lens is 26mm / 6.1 = ~4.25mm

That is first parameter that we need - FL of camera lens

Next is entrance pupil (which we must match with exit pupil of scope + eyepiece combination) - we have F/1.4 lens and it has 4.25mm of FL - so our entrance pupil is 3mm - we must not have larger exit pupil than 3mm

It will therefore depend on scope what is the best eyepiece.

Say it is 6" SCT telescope in question. It is F/10 scope so highest focal length that can be used will be ~30mm (anything above will create too large exit pupil and waste light).

Using this calculator:

https://www.pointsinfocus.com/tools/depth-of-field-and-equivalent-lens-calculator/#{"c":[{"f":13,"av":"8","fl":50,"d":3048,"cm":"0"}],"m":0}

we can see how big FOV sensor captures in terms of degrees:

So it is about 80°

We need 30mm 80° AFOV eyepiece and phone for optimum performance (so we cover whole sensor and don't waste light with exit pupil).

From above parameters, we can calculate pixel scale and any needed binning since pixels are rather small.

 

 

Ok, that was all very technical.  Thanks for the detailed response though.

My phone has the following specs for camera.

40 MP (Wide Angle Lens, f/1.6 aperture,OIS) + 20 MP (Ultra Wide Angle Lens, f/2.2 aperture) + 8 MP (Telephoto, f/3.4 aperture,OIS)

I have a dobsonian 150 6".  My eyepieces are a 25mm and 10mm.  If I can I will run in some calculations.

 

[vlaiv]

7 minutes ago, Andy350 said:

Ok, that was all very technical.  Thanks for the detailed response though.

My phone has the following specs for camera.

40 MP (Wide Angle Lens, f/1.6 aperture,OIS) + 20 MP (Ultra Wide Angle Lens, f/2.2 aperture) + 8 MP (Telephoto, f/3.4 aperture,OIS)

I have a dobsonian 150 6".  My eyepieces are a 25mm and 10mm.  If I can I will run in some calculations.

 

Another thing that you'll need is for your phone (if android) to support so called Camera2 API.

That allows for RAW files to be shot instead of using lossy compression like Jpeg (compression looses detail and prevents you from being able to stack your images effectively).

[Andy350]

5 minutes ago, vlaiv said:

Another thing that you'll need is for your phone (if android) to support so called Camera2 API.

That allows for RAW files to be shot instead of using lossy compression like Jpeg (compression looses detail and prevents you from being able to stack your images effectively).

Thanks forgot to say, I have a Huawei P30 Pro, and it does support RAW pics.