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Old 15-11-2015, 09:36 AM
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lazjen (Chris)
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Canon Lens - 40 or 50mm?

I'm looking at getting a new lens for my Canon 6D (full frame) around the 40 to 50mm mark. Obviously the core purpose of the lens will be for astro images, especially for when I use the Polarie. I'm also getting it for travelling as well to have a smaller, lighter kit to use.

There's a few options around, with the Canon EF 40mm f/2.8 STM looking quite appealing. Has anyone got this and used it for astro? Should I look for faster lenses instead and go to 50mm for f/1.8 or f/1.4? Btw, I have no problems buying other brands, e.g. Sigma, etc if they're suitable.

Any thoughts or suggestions appreciated, especially any gotchas I need to keep in mind.

Btw, I didn't win lotto, so I think the "L" series lenses are out of budget at this time. *sigh*
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Old 15-11-2015, 12:22 PM
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I think the 50mm lens is such a gold standard of optical design that it would be the obvious choice for distortion and field flatness, which would always be better than the equivalent 40mm.
As for f ratio, I assumed that the Nikon f1.4 would be better than the f1.8, but you have to stop both of them down to get sharp stars to the edge, so I'm not sure if the faster lens will be necessarily better for astrophotography. There are a few sites that publish performance figures for different lenses, so it might be worth looking at chromatic aberration and edge sharpness measurements if you can find it. For example - I have an older Nikon 180mm and was a little surprised how much ca it had at f5, then discovered it worked much better at f2.8. Each lens design is subtly different! Normally a lens works best around f7-f11.
Cheers, and hope it's food for thought.
Andrew.
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Old 15-11-2015, 03:52 PM
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Chris, If you have the funds nothing will compete with The Canon 50mm F1.2 L Lens, a simply beautiful lens for what you are planing to use it for, my 2 cents worth.

Leon
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Old 15-11-2015, 03:58 PM
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At 4 to 10 times the cost of a non "L" series lens, it's just too far out my budget at this time - unfortunately.

As for the chromatic aberration and edge sharpness measurements, I'll start looking into that in more detail.
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Old 15-11-2015, 05:53 PM
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Quote:
Originally Posted by lazjen View Post
At 4 to 10 times the cost of a non "L" series lens, it's just too far out my budget at this time - unfortunately.

As for the chromatic aberration and edge sharpness measurements, I'll start looking into that in more detail.
Here you go - and sometimes the best performance isn't necessarily in the mid apertures either, and it looks like the Canon f1.8 doesn't do too bad for $100, and there's another for $125 that looks like a great performer.

http://www.dxomark.com/lenses/mount_...ataType=global
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Old 15-11-2015, 06:01 PM
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Chris, checkout reviews such as that at Photozone or Lenstip... http://www.photozone.de/canon_eos_ff/752-canon_40_28_ff

IMO the 40mm better of the two. I have the 50 II and it was a bargain but always wish I'd got the 40. I have to stop down the 50 to f/4 before it starts cleaning up, coma is a problem before that - and I'm using a crop chip!

The 40mm as tested above seems to put a good foot forward on a full frame chip even at f/2.8.

There are others in that focal range, but many are significantly more expensive, and even then some still need to be stopped down to behave themselves.
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Old 15-11-2015, 06:05 PM
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Hi Chris, I have the old Sigma 50mm f1.4 lens. However I have been thinking of upgrading it to the Sigma 50mm Art f1.4 Series. The new Art series lens is superb. You should be able to pick one up for under a grand if you shop around.
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Old 15-11-2015, 06:41 PM
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Thanks for the replies everyone.

Andrew: If I'm reading the info on your link right, the Canon EF 50mm f/1.8 STM is a good option, given the $125 price listed there.

Dunk: Interesting review - it's unfortunately a bit old and therefore compares against the older f/1.8 lens, not the newer one.

Jason: An advantage the Canon 40 and 50 mm lens have is the weight is much less. Although the didn't specify it explicitly in my original post, it's something I'm keeping in mind. The 6D is heavy enough and I notice that I have to be cautious with my current lens on the Polarie (they're really not that suitable).
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Old 15-11-2015, 07:11 PM
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Dunk: Interesting review - it's unfortunately a bit old and therefore compares against the older f/1.8 lens, not the newer one


The 40mm review is a couple of years, but since they haven't changed the lens since then, the measurements are still valid.

The 50mm STM review is from May 2015... http://www.photozone.de/canon_eos_ff/905-canon_50_18stm
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Old 15-11-2015, 07:52 PM
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Originally Posted by lazjen View Post
Thanks for the replies everyone.

Andrew: If I'm reading the info on your link right, the Canon EF 50mm f/1.8 STM is a good option, given the $125 price listed there.

Dunk: Interesting review - it's unfortunately a bit old and therefore compares against the older f/1.8 lens, not the newer one.

Jason: An advantage the Canon 40 and 50 mm lens have is the weight is much less. Although the didn't specify it explicitly in my original post, it's something I'm keeping in mind. The 6D is heavy enough and I notice that I have to be cautious with my current lens on the Polarie (they're really not that suitable).
That's how I read it too. Also I've been surprised how willing good camera stores are to let you try some of these things out before you buy them, particularly if you're doing astrophotography.

Regards the polarie - I found if you are extremely careful and use the polar scope you can get exposure out to two minutes with a 200mm lens on a full frame dslr. I've also built an adapter to hang off the front with a counterweight and shaft that has made the thing 100 times better for long exposure. But without the polar scope I wouldn't want to be using anything longer than 80mm or so.
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Old 15-11-2015, 08:00 PM
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Dunk, it's just a bit of wording confusion on my part, probably. I realise the 40mm hasn't changed and was trying to state that the 50mm had changed since that review. The review was making comparisons to the now older version of the 50mm lens.

If I'm reading the reviews you linked right, both seem to need to go to F/4 to become decent re: vignetting. The CA graph is interesting too.

I wonder if I really would be able to tell the difference between the 2, quality wise for similar conditions?
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Old 15-11-2015, 08:59 PM
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That's how I read it too. Also I've been surprised how willing good camera stores are to let you try some of these things out before you buy them, particularly if you're doing astrophotography.
Never thought of doing that. I'll may have to see what the local shop can do there.

Quote:
Originally Posted by alocky View Post
Regards the polarie - I found if you are extremely careful and use the polar scope you can get exposure out to two minutes with a 200mm lens on a full frame dslr. I've also built an adapter to hang off the front with a counterweight and shaft that has made the thing 100 times better for long exposure. But without the polar scope I wouldn't want to be using anything longer than 80mm or so.
I think I managed 135mm, but it was more the lens weight that caused me grief (balance - centre of gravity). I'll have to try the polar scope - I just drift aligned to get it close as I had the camera hooked up to the laptop.

Do you have a picture of your counterweight setup?
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Old 15-11-2015, 11:41 PM
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Never thought of doing that. I'll may have to see what the local shop can do there.



I think I managed 135mm, but it was more the lens weight that caused me grief (balance - centre of gravity). I'll have to try the polar scope - I just drift aligned to get it close as I had the camera hooked up to the laptop.

Do you have a picture of your counterweight setup?
Here you go. Note hole is big enough for polar scope to remain in place!
Cheers!
Andrew
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Old 16-11-2015, 08:25 AM
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I wonder if I really would be able to tell the difference between the 2, quality wise for similar conditions?
In which case, there's only one way to find out
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Old 16-11-2015, 03:53 PM
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Andrew: Thanks for the pic. Did you make the adapter yourself?

Dunk: yeah....

However, at this point, I think I'll go for the 40mm. While it's more expensive than the 50mm, I can afford it now without breaking the bank. If I "need" to get a 50mm later, the lower cost will be easier to justify. How's that for some warped logic?

Now to find the best source for buying the 40mm....
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Old 18-11-2015, 11:43 AM
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Andrew: Thanks for the pic. Did you make the adapter yourself
I could have if I owned a lathe, but I don't, so I drew a picture and took it to a local machine shop. Cost me $90.
Cheers,
Andrew.
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