Trouble choosing between a number of lenses

[GeoAmy]

I currently have a Canon EOS 2000D which so far I only have a kit lens for. I’ve narrowed my next lens down to a few options and was hoping to get an idea of the best options for a total beginner to astrophotography. They are all second hand in order to keep them within my price point (hard max of £200). Thank you in advance! The ones I’m considering are:

• Canon EF 50mm f/1.8 II (also an STM variety, unsure of the difference)

• Canon EF 50mm f/1.4 USM

• Canon EF-S 24mm f/2.8 STM (also a 40mm EF mount variety)

• Canon EF 20mm f/2.8 USM (also a 100mm variety)

• Canon EF 17-40mm f/4L USM

• Canon EF 85mm f/1.8 USM

• Sigma 18-50mm f/2.8 EX DC

• Sigma 17-50mm f/2.8 EX DC OS HSM

• Sigma 10-20mm f/3.5 DC HSM

• Sigma 50mm f/1.4 EX DG HSM

• Samyang 16mm f/2 ED AS UMC CS

• Samyang 14mm f/2.8 ED AS IF UMC

• Samyang 14mm T/3.1 ED AS IF UMC II

• Samyang 24mm T/1.5 VDSLR ED AS IF UMC II

• Samyang 16mm T/2.2 ED AS UMC CS

[Elp]

Out of all of them the one which crops up time and time again for widefield AP is the Samyang 14mm. The two in your list, one is the photographic one, the T stop one is for videography so clickless aperture stops but similar if not the same lens. Wider lens means shallower depth of field so easier to focus, and can take longer exposure before star trailing. If you want to use it in an urban setting though I wouldn't recommend it, the lens is too curved and will overexpose from stray light sources before your fov does.

[GeoAmy]

This is great info, thank you! I'll be using it out in the countryside mostly but there will likely be some instances where I'm in the back garden of a house in a cul-de-sac so a bit more residential. Is there one that you think would be a good option to use in both settings? In terms of the quality of images I want to produce, I don't expect anything incredible because I am very much a beginner. I'm more interested in getting a lens that performs well but isn't ONLY for astro work if that makes sense, even £200 is a lot of money for me so I'm trying to pick a versatile lens.

[Louis D]

1 hour ago, GeoAmy said:

Sigma 50mm f/1.4 EX DG HSM

I haven't tried it for astrophotography, but I have one that I used for years for stage photography under available light.  Stopped down to f/2 to f/2.2, it is sharp edge to edge with little to no light falloff with a crop sensor EOS DSLR.  Autofocus is also quiet, fast, and instantly manual overridable.  Not that any of that matters for astrophotography.  However, it could do double duty for school stage performances by your kids.  I probably shot over 125,000 exposures with it over a decade of dance studio performances by my daughter and the rest of the dancers, so it's also quite durable.

[GeoAmy]

Definitely sounds like a good lens to have in the kit regardless then! Thanks for replying

[Elp]

From my experience researching I haven't really seen reviews with regard to the other lenses you've mentioned as the vast majority of people don't use them for astro which is the ultimate test for a lenses capability. If you're using for other purposes a 50mm is generally considered the most useful as its the closest to a human eye perspective. You'd have to research each lens separately for astrophotography, usually user feedback from dpreview is the best source for information if not here or Cloudy Nights forums. From my experience, fixed primes are usually better but only specific ones.

[alacant]

11 hours ago, GeoAmy said:

The ones I’m considering

Hi

Unless you really do want to do wide sky shots, there's one on your list which stands out several kilometers above the rest;)

[Elp]

19 minutes ago, alacant said:

Hi

Unless you really do want to do wide sky shots, there's one on your list which stands out several kilometers above the rest;)

Is there a prize on offer for guessing?

[ollypenrice]

Sampling rate is an important consideration in astrophotography. It defines how many arcseconds of sky are projected onto each pixel. While this will affect the resolution of detail in terrestrial photography, it is far more important in AP because stars are very awkward things for lenses to control. All the lenses above will leave you undersampled (pixels too large to separate details which can be separated by the optics) but keeping to the longer end will give a smoother result. That argues in favour of 50mm.

Prime lenses have fewer elements than zooms, generally meaning cleaner stellar images. I'd always go for a prime in AP.

The Canon Nifty Fifty on your list has form in AP - and very good form. How its Sigma rival compares, I don't know, but the Canon has done good things.

While it would be nice to shoot astro shots wide open to get more light in the time, it is usually difficult in reality because stellar distortions creep in. Rather than stopping down with the diaphragm, which will create artifacts around stars, you can consider stopping down with a front aperture mask instead, either cut from card with a compass-cutter or made up using stacked filter rings.

Another factor, though, is tracking. Do you intend to use a tracking mount to 'unwind' the rotation of the earth? There are many available, the cheapest option being a home made 'barn door tracker' - it will Google. On a fixed tripod the case for a shorter focal length arises from its ability to expose for longer without trailing.

12 hours ago, Elp said:

Wider lens means shallower depth of field so easier to focus, 

Why is a shallower depth of field easier to focus? I can see that it 'snaps into focus' more readily but, conversely, the focal plane is much shallower and, therefore, more critical. I'd have thought that the two characteristics cancelled each other out, at best, and more probably mean that a deeper focal plane/slower F ratio is easier to focus.

Olly

Edited December 2, 2023 by ollypenrice
typo

[Rallemikken]

12 hours ago, GeoAmy said:

best options for a total beginner to astrophotography

I bought a Canon EF 40mm F/2.8 STM AF Lens for my 5D MkII. Lens is good, but it has a huge drawback: You will have a hard time finding focus; the focus ring is electronically controlled and very difficult to handle. Very hard to finetune focus in manual mode. Go for a lens were the focus ring operates with the camera powered off.

[Elp]

All I know is my 9mm and 24mm are much easier to focus across the whole field (you can see it when you set focus peaking to on, but the mode is useless for AP). But experience with longer FLs suggest if the optics are well corrected across the FOV correct focus at one plane is focus.

[Leo S]

It's not on the list, but I'd say consider the Tamron 35mm f1.4 SP. As well as being excellent value for money, it's very usable wide open.

[happy-kat]

I have the 40mm f2.8 pancake too and I find it needs stopping down to f4 ibetter for star shapes, through I do miss for Astro not having manual focus ability. It's a great walk around lens on my 1100d, nice size too.

The 85mmm f1.8 has strong chromatic aberration making is not so great for astro, I've tried mine.

The nifty filthy does come up second hand quite often, not sure if it is manual or fly-by-wire.

[ollypenrice]

1 hour ago, Elp said:

All I know is my 9mm and 24mm are much easier to focus across the whole field (you can see it when you set focus peaking to on, but the mode is useless for AP). But experience with longer FLs suggest if the optics are well corrected across the FOV correct focus at one plane is focus.

Regarding focus, the usual advice is to focus on a star located at one of the four points where the one third lines intersect. (These are four imaginary lines, each parallel with one of the edges of the chip and one third of the way over to the opposite edge.) This is supposed to give the best compromise between centre and corners.

Olly

[GeoAmy]

Amazing advice (as usual!), thank you all so much! I get very anxious about pretty much everything and so I struggle with worrying about making the wrong decision. I'm already about 3 weeks in to trying to work out the best option, but I really appreciate everyone taking the time to share their experiences and the pros/cons of different lenses.

1 hour ago, ollypenrice said:

All the lenses above will leave you undersampled (pixels too large to separate details which can be separated by the optics) but keeping to the longer end will give a smoother result

A lot of what I had read said that shorter than about 24mm is the best for AP which is why I'd kept the options to the shorter end. Having a quick look, there are a couple of Canon EF 100mm f/2.8 USM and a Sigma 105mm f/2.8 EX DG. Would one of these give a better trade off?

1 hour ago, ollypenrice said:

Do you intend to use a tracking mount to 'unwind' the rotation of the earth?

I'm hoping to, it all depends on what Santa brings 😂 joking aside, if I don't get one for Christmas then I'll go down the barn door route

[Elp]

I think anything approaching 85-100mm will need tracking for reliable images, for deep sky that's is. Starfields and the moon you can keep exposures short.

Edited December 2, 2023 by Elp

[ollypenrice]

7 minutes ago, GeoAmy said:

Amazing advice (as usual!), thank you all so much! I get very anxious about pretty much everything and so I struggle with worrying about making the wrong decision. I'm already about 3 weeks in to trying to work out the best option, but I really appreciate everyone taking the time to share their experiences and the pros/cons of different lenses.

A lot of what I had read said that shorter than about 24mm is the best for AP which is why I'd kept the options to the shorter end. Having a quick look, there are a couple of Canon EF 100mm f/2.8 USM and a Sigma 105mm f/2.8 EX DG. Would one of these give a better trade off?

I'm hoping to, it all depends on what Santa brings 😂 joking aside, if I don't get one for Christmas then I'll go down the barn door route

There's a lot to be said for being undersampled when starting out since the undersampling will absorb errors in tracking and focus. You'll also catch more light per pixel which speeds things up. Up to 50mm or so, you're in very tolerant terrain. Going up to a hundred mm increases most of the difficulties. One of the instruments I use is a 135mm Samyang but it is not an easy setup to use. Quite the opposite.

Olly

[vlaiv]

2 hours ago, ollypenrice said:

All the lenses above will leave you undersampled (pixels too large to separate details which can be separated by the optics) but keeping to the longer end will give a smoother result. That argues in favour of 50mm.

I think it is the other way around.

Most, if not all lenses are nowadays over sampled with small pixel size. This happens because of lens construction and the fact that they need to zoom from infinity all the way down to few feet. That is enormous range to control for spherical aberration (which exists between far and near objects regardless of optics - that is why we say that telescope lens are optimized at infinity focus - they have or should have zero spherical aberration at that focus position).

In any case, most lenses need to be stopped down to about F/8 to F/16 for blur to start coming from physics of light rather than aberration of lens itself.

Here is an example of what I'm saying - one of highest regarded astrophotography lens - Samyang 135mm F/2:

Above is contrast in Sagittal and Meridional direction (in direction of optical center and perpendicular to that). Red line is 10 line pairs per mm and gray line is 30 line pairs per mm.

That corresponds to:

Line pair being 100um or line being 50um (one pixel being 50um)

and

Line pair being 33.333um or line being 16.666um (again one pixel being 16.666um).

Even a these pixel sizes we see drop of contrast (blurring), let alone at pixel size that is say 4-5 smaller than this as is often the case with modern sensors.

You are however right - if we had perfect aperture with parameters that lens has (say 30-40mm aperture at F/2 or similar) - it would be very much under sampled with pixel sizes that are currently in use but lens are far from perfect optics.

 

[GeoAmy]

I've decided to go for the Samyang 14mm. Thanks again for all your input, this is a really great community and I'm glad I came across it

[vlaiv]

1 minute ago, GeoAmy said:

I've decided to go for the Samyang 14mm. Thanks again for all your input, this is a really great community and I'm glad I came across it

If I may throw in a wrench?

There are two important points to go in favor of longer focal length lenses rather than short ones.

You can always recreate the image of short focal length lens with long focal length lens by using mosaics. You can never do the opposite - no way to achieve result of long focal length lens with short one. Sure, you can crop, but you will lack the sharpness of the longer focal length lens.

On the other hand - using longer focal length lens to achieve the result of short focal length lens will give you better results / sharper image than using short focal length lens.

Above aberrations in lens optics I mentioned are about the same in each lens - but focal length of the lens determines how pixels relate to size of the object in the sky. This means that the same optics blur from short focal length lens will be larger compared to target size than blur from long focal length lens. Image from long focal length lens will be sharper because of that when scaled to size of short focal length lens.

Only drawback is challenge of processing the data the right way - you need to do some binning and assemble mosaics to replicate results of short lens with long one.

Second thing is size of objects in the night sky versus field of view.

If you want bigger selection of night time objects to capture - you should consider how big they will look in the image.

This is M31 - largest galaxy in the sky - it takes up only a fraction of field of view when using 50mm lens.

When using 14mm lens - FOV is literally x3 bigger in width and height and that makes this target x3 smaller in that fov - it will be a tiny blob.

14mm lens is suitable only for milky way wide field shots and constellations. If you want to pursue general astrophotography - you might want a bit more focal length to be able to capture some of distinct objects rather than just going for sky panorama images.

[GeoAmy]

8 minutes ago, vlaiv said:

14mm lens is suitable only for milky way wide field shots and constellations.

That's more than enough for now, I'm not kidding when I say I'm a total beginner. I haven't shot anything that didn't make use of the camera's auto settings so I think the simpler I can keep things to begin with, the better. I would rather opt for something that has form for AP but is going to be relatively forgiving while I learn the ropes and based on all of the advice here, this is the best lens for that at the price I've found it for

[happy-kat]

If making a barn door I'd keep it 50mm or less. I could use my 40mm fine on a manual barn door anything longer tracking got worse

[Elp]

The cheapest cost of entry commercial tracker I've come across is the Omegon LX, purely mechanical too which is a bonus. I didn't use it much (as I got the azgti soon after) but 2-3 minute subs with the SY14 was no problem.

[900SL]

Prime lenses are generally better than zooms

A good beginner astrophotography lens needs to be wide angle, wide aperture (unless tracking) and with low coma, chromatic abberation and astigmatism

You can find good recommendations on youtube. The 14mm Samyang is a good starter, but be aware the QC isn't great on these, so you may have decentered lens, abberations etc. Check carefully on receipt

Edited December 2, 2023 by 900SL

[900SL]

Also be aware that you can't photograph the Milky Way in significant light pollution, or the core at northern locations during certain months