[tuggie76]

I'm in the cold dark north and finally had a clear night that didn't freeze you in 5 seconds! I took this at 13mm, 64 secs for iso 100. The advice on getting astrotracker to work was great, but I think I have focus issues

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Last edited by tuggie76; 02-24-2020 at 07:14 PM.

[Aaron28]

focus seems ok but not convinced..alotta folks mark infinity on certain lenses to get it set in the dark....there appears to be a decent amount of haze though..…..there also appears to trailing along the edges which is not uncommon especially that wide but maybe over all.....I get it when using a bower 14/f2.8....the foreground doesn't seem blurry enough for 60+sec...were you in bulb mode? reckon that's silly because i'm pretty sure that must be set to do precise calibration...

[Imp]

Ooh, i'm glad astro-tracker worked. I'd be excited to try that, unfortunately not an option with my K-3 (and no, not planning to buy a separate gps )

I noticed you shot the picture at f/4.5 - It's clearly not a depth of field issue because of how wide your lens is (14mm), so that shouldn't matter. But maybe try taking the picture at f/8 or f/11 next time?

So you're probably right that it's a focus issue. Sometimes I take a test shot at iso1600 (so I don't have to wait to long for the exposure) to check my focus on the back screen.

[MossyRocks]

For that lens at 13mm and a 64 second shot the ground does seem blurred enough for astrotracer. It wouldn't have moved much since if one was using the rule of 200 you coudl have taken a 15 second shot without trailing so 64 seconds is only about 4x as long so untracked you would have had only very minor trails. The foreground is only slightly blurred so it seems your tracking was good.

If you are thinking you have some focusing issues and are basing this off of looking at the star cluster in the upper right that is the Pleiades (M45, the 7 sisters, in Japan Subaru) which is a reflection nebula with some very bright blue stars so at 13mm expect this to look blurry. Across orion you have some high level clouds so here again I wouldn't be looking for or judging focus in this area.

If I were to look at this image I would judge focus in the area of Taurus (Between Orion and the Pleiades). Here it looks like you are close but without looking at the full size image I can't tell if it is a focus issue or a purple fringing issue. I don't own this lens but it looks like you were shooting wide open or very close to it at f/4.5 so what you are seeing my just be from the lens being used wide open. Most lenses need to be stopped down by 1 to 2 stops for them to cleanup nicely for astrophotography. Even great lenses under normal shooting circumstances may have issues when doing astrophotography. One of my favorite examples is the D FA 100/2.8 WR Macro for astro, this lens purple fringes and haloes like mad to where it is basically unusable. Astrophotography will show every issue a lens has so you just have to accept some things and will likely have to stop down to get acceptable results.

With a wide to ultrawide lens you really can't use a focusing aid like a bahtinov mask (you won't be able to make fine enough slits) so you are stuck minimizing stars in magnified live view. To do this I turn focus peaking off as I don't want it to highlight the edge as that bloats the star. Instead I get a really bright star centered and manually adjust the focus until I get the star as small as I can. When done right you will be very close to a perfect infinity focus, and good enough for wide astro shots like this.

[Bob 256]

Quite true. If you use the Astrotracer for any significant time, anything not in the sky will blur though the stars should hold steady. The exception is for really wide lenses where Astrotracer is not able to correct for all the image and edge stars can blur. Only a tracking mount can fix that.

[tuggie76]

Thanks for all the advice, it looks like tonight is too cloudy, maybe I'll try again tomorrow.

[FozzFoster]

for atrso shots, don't think of ISO the same way as regular shooting. It's more about the 'signal to noise' ratio and using a higher ISO allows you to capture way more signal.
It can also allow you to close down just a bit and that might take care of some aberration.
Can always use a lil de-noise in post! Nice shot!

[DeadJohn]

...I think I have focus issues...

One way to assess focus is to take a test shot without astrotracer, boost ISO, and shorten exposure. You'll get extra noise but the shorter exposure will let you isolate focus issues. As you gain confidence in your focusing technique you can start using the tracker and longer exposures.

Other issues can be mistaken for poor focus. Vibration can be caused by a weak tripod, wind, dangling cables or camera strap, and walking near the camera. There's a thin cloud diagonally across the photo; haze creates bloated glowing around stars.

IMO the Pleiades (the star cluster near upper-right) and other bright stars look too purple. Haze can contribute, but I suspect the 10-17 design might not be ideal for astrophotography. I've encountered similar with other lenses. Use raw, and apply CA correction or just reduce the purple slider, might help.

[tuggie76]

Thanks for the help guys. The sky cleared so I took another shot, this one's 170 secs f5.0. I removed chromatic aberrations and straightened it. Using the back screen for focus is impossible as all I see is noise, so I set the lens to infinity.

[panonski]

I think for astro photography - such Long Exposures are not good.

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Turning ISo low - to the 100 - is not good, because you have to shoot with more exposure times.

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That leads to more noise, no matter - that ISO is just 100.

The sensor heat itself,
and heat is main enemy for noise free images.

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And Shadows are always so much - not recoverable.

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I'm not an expert in Astro,

but far as I see other photo techniques

( also here in this forum )

the ISO 800 could be great start.

( please do your search here )
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some articles on this

https://petapixel.com/2017/03/22/find-best-iso-astrophotography-dynamic-range-noise/

[DeadJohn]

...Using the back screen for focus is impossible as all I see is noise, so I set the lens to infinity...

I aim at a very bright star to get focus, then carefully recompose without bumping the focus ring. Your technique of going to the hard stop at infinity seems okay with your 10-17 but that definitely won't work with some lenses.

[tuggie76]

I aim at a very bright star to get focus, then carefully recompose without bumping the focus ring. Your technique of going to the hard stop at infinity seems okay with your 10-17 but that definitely won't work with some lenses.

That's why I use the 10 to 17, my other lenses don't have an infinity mark..

[tuggie76]

I think we're getting there, 55 secs at f5.0 iso800.

[DeKay]

I think we're getting there, 55 secs at f5.0 iso800.

Bump your iso up to 1600 and be amazed at the difference

[mkgd1]

I think we're getting there, 55 secs at f5.0 iso800.

Much better.
I tried my first astro shot myself a few days ago. Conditions were not perfect but I managed to get some of the milky way. I do not have a gps so I went with shorter exposure and more iso