Useful Trick for creating flats with an iPad

[graemlourens]

Hi everybody.

I do my flats (every year once) for my observatory setup with an ipad. I set the scope so its pointing perfectly up and have an 'torch' application on the ipad, that creates a white screen with nothing else on it. The surface is just enough for covering my ED80.

My problem until now was, that in certain cases the metal of the scope is sending crazy commands to the ipad (as it is recognizing touch commands) and some times swipes left, up down taps, and i never found a good way to prevent this, as it destroys your flats immediately as your brightness changes. (a thin t-shirt doesn't always help, and a thick one will make my integration time for narrowband flats skyrocket).

Today i figured out how to solve that problem. iOS has an 'accessibility' feature called 'Guided access' where you can 'lock' an open application so no touch commands are executed and you can only get out of the app by triple-pushing the home button. I found it on a rather old blog entry here (it works for recent iOS-Versions): https://igamemom.com/how-to-lock-ipad-iphone-screen-so-kids-stay-within-the-app/

I am not sure if there are downfalls to using iPads as Flat light generators, but i have been doing this for years, and i have never had any issues with gradients or wrong flats at all (i'm using a mono-setup, maybe its different for OSC setups)

Just wanted to share!

Kind regards

[happy-kat]

I use my android 7 inch tablet to create flats and I also point the lens straight up and sit my tablet on top. There is a good application called Lightbox. In the app brightness is controlled by a slider so no changes occur on touching the screen I think app may also be in Apple store.

[iapa]

I remember reading an article/post about using an iPad and the author was taking about the technology used to create the image and that it may cause a pattern - will see if I can find it.

i used iPad from my 80mm refractor and reflectors <8” 

[Scooot]

I use my ipad. Took a photo of a white sheet of paper and use that with a white cotton cloth over the screen. I just hold it over the end of the scope with the grip that's on the reverse of my iPad case, (made by armourdog). Ive never had a problem with the screen shutting itself off.

[Xiga]

On ‎22‎/‎09‎/‎2017 at 09:15, graemlourens said:

Hi everybody.

I do my flats (every year once) for my observatory setup with an ipad. I set the scope so its pointing perfectly up and have an 'torch' application on the ipad, that creates a white screen with nothing else on it. The surface is just enough for covering my ED80.

My problem until now was, that in certain cases the metal of the scope is sending crazy commands to the ipad (as it is recognizing touch commands) and some times swipes left, up down taps, and i never found a good way to prevent this, as it destroys your flats immediately as your brightness changes. (a thin t-shirt doesn't always help, and a thick one will make my integration time for narrowband flats skyrocket).

Today i figured out how to solve that problem. iOS has an 'accessibility' feature called 'Guided access' where you can 'lock' an open application so no touch commands are executed and you can only get out of the app by triple-pushing the home button. I found it on a rather old blog entry here (it works for recent iOS-Versions): https://igamemom.com/how-to-lock-ipad-iphone-screen-so-kids-stay-within-the-app/

I am not sure if there are downfalls to using iPads as Flat light generators, but i have been doing this for years, and i have never had any issues with gradients or wrong flats at all (i'm using a mono-setup, maybe its different for OSC setups)

Just wanted to share!

Kind regards

I also use an Ipad for taking flats on my 80ED. I too had the same issue as you, with the screen having a fit with the metal dew shield, and my solution was also to use the Guided Access feature. But I then found a better way, which saves having to faff about with turning the Guided Access on and off (and also no longer having to remember to set the Ipad to not go to sleep, that one gets real annoying when you're mid capture!)

I found a great wee app called (I think) RGB Light. It costs $1 iirc, but it's $1 well spent. It not only gives you a lit clear full screen, but once it's active it over-rides the screen timeout setting, so you know it's not going to turn off on you at the most inopportune time. But even better, if you double-tap the screen, you get 3 sliders for R G and B, so you can set any tone you want. For me, using my DSLR and IDAS-D1 filter, this is invaluable. Before, when I used a white (actually, gray) screen, whenever the Green and Blue channels were properly exposed, the Red channel was always massively under-exposed (to be expected, obviously). So there was no way to get all 3 channels properly exposed. But now I just reduce the G and B sliders (the app even remembers the last ones you used) and using the (now pinkish) screen I can get all 3 channels to overlap perfectly right in the middle of the histogram.

I also now use a piece of opal plastic as a diffuser between the dew shield and the Ipad. It does a great job, and saves me having to stretch an old t-shirt over the end with an elasticated band, and hope there aren't any creases. Saves another few precious seconds, lol. I can't remember which one it was, but it something like this:

https://www.amazon.co.uk/Perspex-Light-Gloss-Acrylic-CHOOSE/dp/B073S51MY3/ref=sr_1_3?ie=UTF8&qid=1506343196&sr=8-3&keywords=opal%2Bsheet&th=1

Also, you don't want super fast flats (e.g 0.01s or suchlike), in case the screen refresh rate interferes with your exposures, I like to keep mine around 1s or so. And using the diffuser along with a low brightness setting makes this easy.

Anyways, just thought I would share my workflow too in case it's of any help. Good luck! :-)

[graemlourens]

On 9/25/2017 at 14:57, Xiga said:

I also use an Ipad for taking flats on my 80ED. I too had the same issue as you, with the screen having a fit with the metal dew shield, and my solution was also to use the Guided Access feature. But I then found a better way, which saves having to faff about with turning the Guided Access on and off (and also no longer having to remember to set the Ipad to not go to sleep, that one gets real annoying when you're mid capture!)

I found a great wee app called (I think) RGB Light. It costs $1 iirc, but it's $1 well spent. It not only gives you a lit clear full screen, but once it's active it over-rides the screen timeout setting, so you know it's not going to turn off on you at the most inopportune time. But even better, if you double-tap the screen, you get 3 sliders for R G and B, so you can set any tone you want. For me, using my DSLR and IDAS-D1 filter, this is invaluable. Before, when I used a white (actually, gray) screen, whenever the Green and Blue channels were properly exposed, the Red channel was always massively under-exposed (to be expected, obviously). So there was no way to get all 3 channels properly exposed. But now I just reduce the G and B sliders (the app even remembers the last ones you used) and using the (now pinkish) screen I can get all 3 channels to overlap perfectly right in the middle of the histogram.

I also now use a piece of opal plastic as a diffuser between the dew shield and the Ipad. It does a great job, and saves me having to stretch an old t-shirt over the end with an elasticated band, and hope there aren't any creases. Saves another few precious seconds, lol. I can't remember which one it was, but it something like this:

https://www.amazon.co.uk/Perspex-Light-Gloss-Acrylic-CHOOSE/dp/B073S51MY3/ref=sr_1_3?ie=UTF8&qid=1506343196&sr=8-3&keywords=opal%2Bsheet&th=1

Also, you don't want super fast flats (e.g 0.01s or suchlike), in case the screen refresh rate interferes with your exposures, I like to keep mine around 1s or so. And using the diffuser along with a low brightness setting makes this easy.

Anyways, just thought I would share my workflow too in case it's of any help. Good luck! :-)

Hi Ciaran.

Thank you for your feedback.

Yes indeed, the app that i am using blocks the timeout of the Screen automatically (https://itunes.apple.com/us/app/torch-bright/id448315686?mt=8)

I tried at least 8 different apps, because most of them have advertising that randomly pops up, and destroys your sub (happened to me too many times :/ ). I'm very happy with this free App called 'Torch Bright' (link above).

Concerning the screen brightness, i reduce the screen brightness on the ipad to the minimum. In this case and in my setup The shortest flat is still in an acceptable level (about a third of a sec if i remember correctly)

Kind regards, Graem

[Xiga]

5 minutes ago, graemlourens said:

Hi Ciaran.

Thank you for your feedback.

Yes indeed, the app that i am using blocks the timeout of the Screen automatically (https://itunes.apple.com/us/app/torch-bright/id448315686?mt=8)

I tried at least 8 different apps, because most of them have advertising that randomly pops up, and destroys your sub (happened to me too many times :/ ). I'm very happy with this free App called 'Torch Bright' (link above).

Concerning the screen brightness, i reduce the screen brightness on the ipad to the minimum. In this case and in my setup The shortest flat is still in an acceptable level (about a third of a sec if i remember correctly)

Kind regards, Graem

Hi Graem 

I too have used that exact same app. It worked well for me too I have to say.  I also used another one called Digital Grey Card which was grand also. But I don't see myself ever changing from RGB Light now tbh. Being able to set the exact colour means that whether I'm using my Idas-D1 filter or not, I know I'll always be able to get perfectly exposed flats. Of course, this is not an issue for owners of mono cameras.

[Ouroboros]

My solution is to hold the iPad  steady above the scope for the duration of the 50 or so exposures I've programmed backyard eos to take. 

[graemlourens]

2 hours ago, Ouroboros said:

My solution is to hold the iPad  steady above the scope for the duration of the 50 or so exposures I've programmed backyard eos to take. 

Hi Ouroboros.

Thats also a solution, but doing 25 flats for 8 filters, 3 of them narrowband each narrowband sub having approx 1 minute exposure time, it would tire my arm a little too much . Gravity is really a great friend in this case!

Kind regards, Graem

[Ouroboros]

1 hour ago, graemlourens said:

Hi Ouroboros.

Thats also a solution, but doing 25 flats for 8 filters, 3 of them narrowband each narrowband sub having approx 1 minute exposure time, it would tire my arm a little too much . Gravity is really a great friend in this case!

Kind regards, Graem

Yep. . I suppose there have to be some advantages of using an SLR. 

[David Crane]

Does anyone know of an android app that does the same?

[happy-kat]

yes Lightbox is excellent for taking flats.

[David Crane]

Thanks for that. I have just downloaded it and it looks perfect.

David