The TPU Darkroom - Digital SLR and Photography Club

[de.das.dude]

I've found with my RF glass that focusing out of infinity is actually not the best for things like stars. In fact, it's almost like focusing all the way to infinity is like overshooting the right amount of focus. I usually set my camera up for manual focus when doing stars and I'll use the LCD to zoom in to one particularly pronounced star to focus off of and more often than not, focus is close to infinity, but not quite there.

This is an example from last winter, but this is shooting straight up on a clear night at 8s, ƒ4, ISO 1600 scaled down from the max width of 6240 to 5000px. This was with my 24-105mm ƒ4 L series len.
View attachment 363975
That's unprocessed. Now here is where it gets interesting. Using my (arguably,) inferior nifty 50 (50mm ƒ1.8,) I can get something like this at 4s, ƒ2, ISO 800:
View attachment 363976
...and with a little bit of post processing of that same image above, you get something like this:
View attachment 363977
However, if you look at the edges of the frame with the 50mm ƒ1.8, you can clearly see comatic distortion. It looks like this (from the top left corner):
View attachment 363978
Lower quality lenses have this kind of distortion around the edges wide open, but should be pretty sharp near the center of the frame. If you look at the image using the 24-105 ƒ4, you don't have nearly the same level of comatic distortion around the edges. If the center of the frame is blurry, then it's more likely that the subject is out of focus and since stars are so small, even a slight misfocus will make them look blurry. So it's worth taking the time to digitally zoom into a reference star and very slowly adjust focus until it's perfect on the LCD.

If you zoom in and you see something like this, it means your shutter speed is too slow and the stars are moving in the night sky during the shot. (This was at 105mm @ 10s)
View attachment 363980
I don't have an example of misfocus handy, but if they don't look elongated near the center, then it's probably misfocus.

this is a kind of problem on many lenses.

what i figured out is to get masking tape, and focus on infinity at the moon when its bright, and mark it on the focus ring works 100% of the time ninety percent of the time!

and the lens distortion can be fixed with the correct profile



this is with a cheap nikor 50mm 1.8g at full "infinity"

 

[Nuckles56]

this is a kind of problem on many lenses.

what i figured out is to get masking tape, and focus on infinity at the moon when its bright, and mark it on the focus ring works 100% of the time ninety percent of the time!

and the lens distortion can be fixed with the correct profile

View attachment 364001

this is with a cheap nikor 50mm 1.8g at full "infinity"

That's a much smarter way to do it than what I've been doing, which is to focus on a distant object and flick it over to manual focus and hopefully not bump the focus ring prior to taking the night shots.

 

[de.das.dude]

That's a much smarter way to do it than what I've been doing, which is to focus on a distant object and flick it over to manual focus and hopefully not bump the focus ring prior to taking the night shots.

you can lock the focus ring as well, if you dont mind. Persoinally those lenses i use for astro, are for astro only, so....

 

[Nuckles56]

you can lock the focus ring as well, if you dont mind. Persoinally those lenses i use for astro, are for astro only, so....

The glass I have doesn't have a lock for the focus ring, so I'd have to tape it.

 

[Hyderz]

Some of you might know or already know but your Nikon, canon or sony can now be remotely used from Apple Watch, which i think is pretty cool

 

[de.das.dude]

Some of you might know or already know but your Nikon, canon or sony can now be remotely used from Apple Watch, which i think is pretty cool

but mine is a D3300 it aint got the smarts for it haha.

 

[mouks]

I've found with my RF glass that focusing out of infinity is actually not the best for things like stars. In fact, it's almost like focusing all the way to infinity is like overshooting the right amount of focus. I usually set my camera up for manual focus when doing stars and I'll use the LCD to zoom in to one particularly pronounced star to focus off of and more often than not, focus is close to infinity, but not quite there.

Sorry for the late reply. I agree, I always shoot with manual focus lenses and I use magnification when I have the time like in this case (and peaking for moving subjects), that's how I noticed that the lens wasn't reaching infinity. As you said, the focus plane should be able to be set slightly beyond infinity and become blurry again past the sharpest point but this old 20mm/2.8 doesn't reach that stage, so it needs to be opened and calibrated.

Here is a shot from 2 weeks ago under the harvest moonlight with my MD Rokkor 24mm/2.8 around f/4, 10s, ISO 1600, JPEG with slight brightness and contrast boost in Windows photo editor (I did shoot RAW+JPEG but I don't have anything to do proper PP right now, I installed Rawtherapee but it keeps crashing everytime I try to use it)

 

[Nuckles56]

Got quite lucky to be out and about in an area with really dark skies with the camera, so got to see lots of meteors, they put on quite the show even if they were brief. I count 7 in the one 1.6 second shot, 50mm f1.8. I need to do a bit of post processing on it, but haven't had time for that in a while.

 

[de.das.dude]

View attachment 366322View attachment 366323

View attachment 366326
Got quite lucky to be out and about in an area with really dark skies with the camera, so got to see lots of meteors, they put on quite the show even if they were brief. I count 7 in the one 1.6 second shot, 50mm f1.8. I need to do a bit of post processing on it, but haven't had time for that in a while.

how do you differentiate between meteors and satellites?

 

[Nuckles56]

how do you differentiate between meteors and satellites?

I took multiple shots in a row, pointing in the same direction, if you couldn't see it again in the next frame, then it was 100% a meteor. Also, the length and colour of the trail is a dead giveaway, as a satellite doesn't move anywhere near as fast as a meteor does and a satellite will typically have a white trail whilst a meteor tends to be a broader range of colours (blue-white to yellow).