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Camera focus behavior, astro NV pics with cellphones

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#1 DMala

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Posted 06 December 2018 - 12:02 PM

In my quest for learning to take pics from my PVS-7 in prime focus mode and using a cell phone holder, I am now running into a stumbling block with the ability to properly focus. In summary:

 

- I am using a PVS-7 on a cell phone holder that clamps quite securely to the PVS-7 eyepiece. The phone is my old Galaxy S5 that has a very good camera and an operating system that allegedly supports extra photo parameter features . I found a nice camera app called Snap Camera HDR (the free trial version for now) that can stack/integrate 7-pic series to optimize low-light pictures. Normal (= pics of my living room holding the phone) low-light tests showed very good results.

- The app provides the following focus mode settings: auto, infinity, macro, fixed, continuous, continuous video.

- I presume that the focus mode of interest to me would be either infinity or fixed, but in all focus modes:

++ when there is no large target with some texture (eg planet or large nebula), but only small pinpoint stars, the camera does not focus properly, even when the focus command is pressed

++ the camera attempts to re-focus for each of the shots of the 7-shot HDR series, and because of the above-issue, blurred pics are generated.

 

Yesterday I took tens of pics of a plain starry field and only a couple pics came out OK in terms of focus. See one example below (ISO 800, recorded at 1/15 sec after a 7-shot series), which in my mind shows a lot of detail considering that it was shot indoors with just a 70mm refractor through a double-glassed insulated window! This shows me the good potential of the camera but I can not just keep shooting pics until randomly one is in focus. I am now contacting the app creator for clarifications, and I will report back if I hear an answer.

 

So, to keep looking at solutions, I would like to know:

 

- if you use your cell phone on a holder on your NV device, how do you adjust the camera focus? Pls specify phone, app, focus mode on the app and means to adjust it to proper focus.

- after your phone reaches focus, if you shoot a series of pics to be stacked/averaged, does the camera re-adjusts the focus for each shot or does it stay at the original setting?

 

With this info I hope to better understand what I have to look for to solve my problem. Thanks

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  • IMG_20181205_223951a.jpg

Edited by DMala, 06 December 2018 - 01:06 PM.


#2 Jeff Morgan

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Posted 06 December 2018 - 02:52 PM

So, to keep looking at solutions, I would like to know:

 

- if you use your cell phone on a holder on your NV device, how do you adjust the camera focus? Pls specify phone, app, focus mode on the app and means to adjust it to proper focus.

- after your phone reaches focus, if you shoot a series of pics to be stacked/averaged, does the camera re-adjusts the focus for each shot or does it stay at the original setting?

 

With this info I hope to better understand what I have to look for to solve my problem. Thanks

 

Focus is the big challenge! Here is my procedure:

 

1) Using the eye, turn the focuser knob for best image.

 

2) Check diopter adjustment for improvement (usually, there is none as I have been using the unit and it is already set).

 

3) Attach the phone. I'm using an iPhone X, Orion Steady Pix adapter.

 

4) Open the camera app (I use NightCap).

 

5) At this point I stop using my eye to try to focus. I either:

 

a) tap a brighter star (but not brightest as Halo may be an issue) on the screen triggering an auto-focus; or

b) Manual set the FOC slider to 1.0 (infinity).

 

Sometimes the camera autofocus dorks it up, my best results are using the FOC slider to infinity.

 

From there it is all a matter of choosing filter, ISO, and exposure times. Lots of bracketing is the key.


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#3 DMala

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Posted 06 December 2018 - 09:48 PM

Thanks, that's also what I basically do but after I press the shutter the autofocus kicks in and mostly misses it.

#4 DMala

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Posted 09 December 2018 - 11:13 AM

I may have found the source of the problem: it's a bit embarrassing to admit it but probably it was due to the fact that I was shooting indoors, through a double-glass window. I had one session outdoors and the focus problems became only occasional, and most pics were acceptable or good in terms of focus. See pic below. I guess that the diffraction of the image caused by the window glass threw off the autofocus mechanism. 

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  • IMG_20181207_224900a.jpg

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