Cheaper astro imaging techniques / software.

[tooth_dr]

I'm doing a bit of public outreach and I'm feeling a bit unprepared!

What are the current options out there that would allow the average punter to go out and start imaging with little cost / using own equipment? What apps are people using on their phones?  What is the limiting exposure time for lenses on static tripods - is there a formula?  What events or objects lend themselve better to imaging on a budget?  What is particular good objects this time of year?

 

Thanks in advance

 

 

[jjosefsen]

Hi,

Cool that you are doing an outreach event!

For calculating the maximum exposure time on a non tracking tripod, one can use the "500 rule":

500 / (focal length*crop factor) = exposure time

Remember to factor in the crop factor if not a fullframe dslr.

Example for a canon 600D with 50mm lens

500 / (50*1,6) = 6,25 ~6 seconds.

I believe the standard crop factors for Nikon and Canon are 1,5 and 1,6 respectively, but I honestly don't use lenses much.

 

As for gear I like this writeup from a pretty good astrophotographer I follow ("DarkArchon" is his internet moniker).

https://darkskies.space/starting-with-astrophotography-part-1/

https://darkskies.space/starting-with-astrophotography-part-2/

 

I really like the stellaris app on my phone, and would recommend it to anyone.

 

As for software you know as well as I about DSS, APP, PI and PS/GIMP.

As for capture software, I feel like the BackYard Nikon/BackYardEOS software is pretty straight forward and easy to use.

Personally I recommend new people who wan't to shoot tethered, to go for APT if they are not using a GOTO mount, like a Star Adventurer or such.

If they are jumping right into goto mounts and ASCOM, then I recommend N.I.N.A. - but it is more of a free alternative to SGP. I will be doing a post on this forum about it one of these days..

[daz]

For imaging with lenses, it's the 500 rule. 500 divided by the focal length (taking into account crop factor) gives the approx number of seconds before trailing becomes an issue.. So, my Canon 600D has a crop factor of 1.6x (I think!!) so if I use a 20mm lens, I multiply by 1.6 to give 44, and divide this into 500 = 11 seconds

Phones are great for widefield of course!

 

Ha! Type faster Daz!!

And yes, the crop factor is 1.6 - not 1.4!!

[Pompey Monkey]

Crop factor does not factor!

The criterion for round vs streaky stars is all about pixel scale. 

The "500" rule works well, but I can assure everyone that none of the pixels knows if the sensor is cropped or not.

<rant over>

[vlaiv]

What's wrong with sidereal rate and arc second / pixel calculation?

 

[Star Struck]

I suggest you take a read of this:  https://petapixel.com/2017/04/07/npf-rule-formula-sharp-star-photos-every-time/

 

I tried using the 600 rule and then the 500 rule, but they never really worked to my satisfaction.

The above link is far more accurate and is based on sensor size/pixel pitch.

 

[tooth_dr]

Thanks everyone, really useful info. 

@jjosefsen thanks especially for the links. Exactly what I was after - structured groups of kit level that I can easily remember. 

[rickwayne]

Crop factor by itself is, as previous commenters have noted, not the issue. But it does imply that, for a given image circle, images from a smaller portion of it will be enlarged to the viewing size (print, monitor, portion of a webpage, whatever). So the viewer ends up essentially looking more closely at the same angular-size star trails. If you blow up an APS-C image to the same viewing size as a full-frame one for the same optical train (e.g. the Horsehead is 2cm high on each image) the star trails will look exactly the same. This is true regardless of the size of the pixels on the sensor. To exaggerate, a trail might cross 10 px on a fine-grained sensor's image and only 3 on a coarse-grained one. But if the final results are portrayed so the objects are the same size, the star trails will be too.

[Rick Spencer]

I tried N.I.N.A, and while it looks good and has decent functionality, it would not recognise my cheap plug n play camera that uses windows internal driver "USB2.0 5M UVC Camera". This camera works perfectly in other software such as SharpCap.

[Knight of Clear Skies]

Hi, I put together a bit of a guide for getting started with a DSLR and kit lens that you might find helpful. Other real budget equipment includes basic mounts with RA motors such as the EQ3 and old M42 thread prime lenses. With careful purchases of second hand equipment it is possible to d a great deal of imaging on a sub-£400 budget.

Good luck with the outreach event.

[happy-kat]

Not forgetting can build a barn door mount either manual or motorised.

I built my manual barn door mount for around £25 (already had a camera ball head) and with DSLR and 40mm lens get reliable 3 minute (180 seconds) exposures. Link in my signature.

[tooth_dr]

Thanks for the input on the thread. The event was successful and it was even partly clear so there was some live observing done.

My presentation looked ok on the huge tv too ?