Recommend me a lens for astrophotography

[andy435]

I want to try astrophotography. I've got a APS-C Canon DSLR a have just bought a Star Adventurer. I'm in the market for a lens and I have narrowed it down to two choices:

Canon 200mm f2.8L II

Samyang 135mm f2

I believe both are regarded lenses for astrophotography. I buy second hand to avoid big investments in the beginning.

What would you recommend and why?

[Alien 13]

I think the Samyang has the edge for AP and can reportedly be used wide open, the Canon is probably better as an all round lens for AP and normal photography.

Alan 

[lune lupine]

I've just picked up a second hand samyang f2 16mm. Not tried it yet (only got it yesterday) but reviews very good on this site and online. Came across this site Lonelyspeck which is very useful.

 

I also have aps-c camera; canon 760d. Got the above lens for milkyway and star field shots ideally

[andy435]

17 minutes ago, Alien 13 said:

I think the Samyang has the edge for AP and can reportedly be used wide open

I've read that too. But the 200mm f2.8 cant be that bad wide open either? It's a good lens according to this test: http://www.photozone.de/canon-eos/582-canon_200_28_apsc

[Alien 13]

I dont know why but f/4 seems to be the magic number for Canon lenses the f/2.8 is from what I have read a bit iffy if you dont have a perfect example.

Alan

[andy435]

Ok, but with f/4 it means less light and longer exposures. With no guiding how is that with the Star Adventurer?

 

[MARS1960]

If you are choosing a lens specifically for AP then I would consider forgetting the expensive L glass and high end samyangs

I've had many Different L lenses and plenty of samyangs, you can get fantastic images with much cheaper glass, I now have only the two lenses in my sig, they are tak sharp and both together cost me less than £150.

[andy435]

7 hours ago, MARS1960 said:

If you are choosing a lens specifically for AP then I would consider forgetting the expensive L glass and high end samyangs

I've had many Different L lenses and plenty of samyangs, you can get fantastic images with much cheaper glass, I now have only the two lenses in my sig, they are tak sharp and both together cost me less than £150.

Please elaborate, I'm open for suggestions. Thank you.

Canon lenses are easy to source second hand. Currently the 200mm f2.8L lens is withon my budget.

[andy435]

What I haven't thought about is the 1.6 crop factor of the aps-c sensor which makes 135 = 216 and 200 = 320...

320 is pretty long focal length and maybe difficult to start with?

[Knight of Clear Skies]

I have the 200mm f2.8 L II and am a bit disappointed with it really, it's great for DSOs but very difficult to get a good starfield. It is useable wide open but while the stars are better at about f3.5 (using a front aperture mask) they are still a bit messy.

I've heard good things about the Samyang 135mm f2, forum member @Uranium235 has one so it might be worth taking a look at some of his recent images. (I don't know if he has any RGB examples taken with just the lens though.)

2 hours ago, andy435 said:

What I haven't thought about is the 1.6 crop factor of the aps-c sensor which makes 135 = 216 and 200 = 320...

320 is pretty long focal length and maybe difficult to start with?

It's not particularly difficult to image unguided at 200mm focal length, you'll probably be taking 1-2 minute subs with a decent polar alignment.

[Alien 13]

Another lens worth a look is the Canon f/4L 70-200 mm zoom its cheap (relatively 2nd hand) and versatile.

Alan

[andy435]

6 hours ago, Alien 13 said:

Another lens worth a look is the Canon f/4L 70-200 mm zoom its cheap (relatively 2nd hand) and versatile.

Alan

I can get the 200mm much cheaper than the 70-200mm f/4L

I tend to avoid zoom lenses as I like prime lenses better.

[alexbb]

13 hours ago, andy435 said:

What I haven't thought about is the 1.6 crop factor of the aps-c sensor which makes 135 = 216 and 200 = 320...

320 is pretty long focal length and maybe difficult to start with?

Focal length remains the same regardless of the sensor size.

What it's different, it's the image area covered by the sensor so the apparent recorded image appears larger or smaller.

Check out here how DSOs look with different focal lengths and sensor sizes and the resolution in arcseconds per pixel.

http://astronomy.tools/calculators/field_of_view/

[dannybgoode]

13 hours ago, andy435 said:

What I haven't thought about is the 1.6 crop factor of the aps-c sensor which makes 135 = 216 and 200 = 320...

320 is pretty long focal length and maybe difficult to start with?

Actually this is not strictly true. The crop factor does not magnify the image at all, it is merely the equivalent fov. 

If you crop an FF image to the same size as an aps-c sensor the images will be near identical hence 'crop factor' not 'zoom factor'.

The advantage with an aps c sensor is that you do not have to crop to achieve this. 

[almcl]

13 hours ago, andy435 said:

What I haven't thought about is the 1.6 crop factor of the aps-c sensor which makes 135 = 216 and 200 = 320...

320 is pretty long focal length and maybe difficult to start with?

I have the Canon  EF 200 2.8 lens and three of the images in my album were taken with it (Orion widefield, Witches head & Sadir region).  

I have really been quite pleased with it but have nothing much else to compare it with.

Since going to an Alt Az EQ6, I find it doesn't need guiding and 4 minute unguided subs are no problem, given a decent polar alignment.  Using a front mask helps to reduce diffraction spikes and doesn't impact light gathering too badly.

[andy435]

1 hour ago, moise212 said:

Focal length remains the same regardless of the sensor size.

What it's different, it's the image area covered by the sensor so the apparent recorded image appears larger or smaller.

Check out here how DSOs look with different focal lengths and sensor sizes and the resolution in arcseconds per pixel.

http://astronomy.tools/calculators/field_of_view/

I know, my point was that it's more difficult with narrower FOV

[MARS1960]

17 hours ago, andy435 said:

Please elaborate, I'm open for suggestions. Thank you.

Canon lenses are easy to source second hand. Currently the 200mm f2.8L lens is withon my budget.

Lenses like Carl Zeiss,  Rokinon, Takumar and super Takumar, these are all great prime lenses for AP and give stunning images for a fraction of the cost of L glass.

[alexbb]

1 hour ago, andy435 said:

I know, my point was that it's more difficult with narrower FOV

Given you have 2 sensors with the same pixel size, the sensor size doesn't matter for the final result when you zoom in to 100%. If you downscale the final results to fit the same area (ie. 800x600), then that's another story.

That's why I also mentioned earlier the resolution in arcseconds per pixel.

With a Canon 6D and 200mm, you'll get 6.74 and with a Canon 760D and 135mm, you'll get 5.65. Therefore, with the 760 and 135mm you'll aim for a more detailed image than with the 6D and 200mm even though the FOV is about the same.

I hope I was more clear this time.

Alex

[andy435]

13 hours ago, moise212 said:

Given you have 2 sensors with the same pixel size, the sensor size doesn't matter for the final result when you zoom in to 100%. If you downscale the final results to fit the same area (ie. 800x600), then that's another story.

That's why I also mentioned earlier the resolution in arcseconds per pixel.

With a Canon 6D and 200mm, you'll get 6.74 and with a Canon 760D and 135mm, you'll get 5.65. Therefore, with the 760 and 135mm you'll aim for a more detailed image than with the 6D and 200mm even though the FOV is about the same.

I hope I was more clear this time.

Alex

Thank you for detailed explanation.