Using 500 rule with EFS lenses?

[kcvpr]

Hello everyone!
I have been really interested in astrophotography lately. I've been trying to figure out which of my lenses would work best with as little star trail as possible. I have found and used the 500 rule with some success. But all my shots so far using the 500 rule have been with EF lenses and not EFS lenses with a 1.6 crop sensor. I know that using a EF lens on a crop sensor changes the effective focal length.

All that being said, has me confused on using an EFS lens and the 500 rule with a crop sensor. Does using the EFS lens mean I could use a longer exposure than an EF lens of the "same" (EF 24mm F/2.8 VS EFS 24mm F/2.8 for example) focal length?

Lens list:

EFS 24mm F/2.8
EF 17-40mm F/4L
EF 24-70 F/4L IS

Thanks for the help!

 

[Braineack]

accordingly to this you want to use the 400 rule with a crop sensor

How to Avoid Star Trails by Following the '500 Rule'

 

[Didereaux]

EFS lens are built to fit the crop sensor cameras. You treat them exactly as EF lens as concerns focal lengths. Just NEVER try to mount one on a full frame camera!
a rather useful explanation Crop Sensor (APS-C) Cameras and Lens Confusion

 

[petrochemist]

The '500 rule' is a guideline based on the cameras FOV, so the 35mm equivalent focal length should be used to give the same results on crop sensors (or larger sensors for that matter).

 

[Ido]

The 500 Rule assumes a 35mm (Full Frame) camera, so to follow it you need to take the crop factor into account by multiplying the focal length. Better yet, divide 500 by 1.6 and you'll get 500 / 1.6 = 312.5. Round it down to 300, and you have your new 300 Rule. Now all you need to do is divide the number 300 by the focal length that's written on the lens, and you're good. No more messy calculations.

 

[TCampbell]

It's really the 600 rule, but some imagers prefer to be conservative so they use 500. But if you've got an APS-C crop-frame camera (or any crop camera) you have to divide the value by your camera's crop factor. E.g. a 1.5 crop-factor camera would take 600 down to 400. A 1.6 crop factor camera would take it down to 375. In reality there's not much difference between a 1.5 or 1.6x crop factor because even that value is rounded.

However... if you do the math you quickly realize that the shorter the focal length of the lens, the longer you can image. With my full-frame camera I use a 14mm f/2.8 lens. I have the Canon "L" series 14mm f/2.8L USM -- which is very expensive... a much more practical lens would be the Rokinon (or Samyang -- same lens just a different label) 14mm f/2.8 (which is COMPLETELY manual -- but that makes it affordable.)

If you have a crop-frame body you can even use a 10mm lens.

All of this assumes the camera is on a stationary tripod (that's the whole point of the rule.) If you've got a tracking head then you can image MUCH MUCH longer.

Since the head is 'tracking' so the stars don't move and smear, you can use longer focal length lenses and capture deep-space objects (DSOs).

This one is several minutes (using a 135mm f/2 lens), but I was taking test shots at 8 minutes and they were still tack sharp. BUT the camera was on a tracking head. In my case it's a Losmandy StarLapse mount (attached to a sturdy photographic tripod.)

Lower Region of Orion by Tim Campbell, on Flickr

But notice there is no foreground (that would have been blurred and I have examples of that as well if you're interested in seeing what happens even after just a couple of minutes.)

The tracking head has to be precisely "polar aligned" -- meaning it's axis of rotation is exactly parallel to Earth's axis of rotation. That way as the Earth spins from west to east, it tracks from east-to-west at exactly the same rate and this causes anything in the sky to be held in position without drifting.

The Losmandy StarLapse is one of the more expensive tracking heads... the more popular and economical heads are the iOptron SkyTracker or ... somewhat recently new offering ... the Sky-Watcher "Star Adventurer" head.

 

[beagle100]

It's really the 600 rule, but some imagers prefer to be conservative so they use 500. But if you've got an APS-C crop-frame camera (or any crop camera) you have to divide the value by your camera's crop factor. E.g. a 1.5 crop-factor camera would take 600 down to 400. A 1.6 crop factor camera would take it down to 375. In reality there's not much difference between a 1.5 or 1.6x crop factor because even that value is rounded.

However... if you do the math you quickly realize that the shorter the focal length of the lens, the longer you can image. With my full-frame camera I use a 14mm f/2.8 lens. I have the Canon "L" series 14mm f/2.8L USM -- which is very expensive... a much more practical lens would be the Rokinon (or Samyang -- same lens just a different label) 14mm f/2.8 (which is COMPLETELY manual -- but that makes it affordable.)

If you have a crop-frame body you can even use a 10mm lens.

All of this assumes the camera is on a stationary tripod (that's the whole point of the rule.) If you've got a tracking head then you can image MUCH MUCH longer.

Since the head is 'tracking' so the stars don't move and smear, you can use longer focal length lenses and capture deep-space objects (DSOs).

This one is several minutes (using a 135mm f/2 lens), but I was taking test shots at 8 minutes and they were still tack sharp. BUT the camera was on a tracking head. In my case it's a Losmandy StarLapse mount (attached to a sturdy photographic tripod.)

But notice there is no foreground (that would have been blurred and I have examples of that as well if you're interested in seeing what happens even after just a couple of minutes.)

The tracking head has to be precisely "polar aligned" -- meaning it's axis of rotation is exactly parallel to Earth's axis of rotation. That way as the Earth spins from west to east, it tracks from east-to-west at exactly the same rate and this causes anything in the sky to be held in position without drifting.

The Losmandy StarLapse is one of the more expensive tracking heads... the more popular and economical heads are the iOptron SkyTracker or ... somewhat recently new offering ... the Sky-Watcher "Star Adventurer" head.

right, if you had one of the star tracker mounts you wouldn't a 600 rule or 500 or whatever it is. But I live near a city so I can't see the night stars no matter what