mbusch77

1. Why are wider focal length lenses able to be let open longer and get shots with less star trails than my Canon 28mm 1.8 on a 5DM3? I often shoot with other people who use ultra-wide lenses. I read on wikipedia about zoom factor, and how camera shake is multiplied by this, however I'm on a tripod. Does it have anything to do with more image going onto the sensor?

2. All astro shooters, is there a better lens I could be shooting with, I'm fine switching to manual focus as I'm sharpening all my photos through manual and live mode anyway? Any Russian or german companies I may have overlooked with an EF mount convertor?

Thanks, Matt

Shellback Loc: North of Cheyenne Bottoms Wetlands - Kansas

Might get better reponse by posting this question in the Astronomical Photography Forum section...

Burtzy Loc: Bronx N.Y. & Simi Valley, CA

Logic dictates that a wider lens, taking in a greater expanse of the sky than yours, would be able to stay open longer without the star trails appearing longer simply because the individual star images would be smaller. If the other photographers are not using any sort of tracking mounts, greater enlargement of those images would reveal longer star trails reflecting the longer exposure. The universe doesn't slow down for shorter focal lengths.

MT Shooter Loc: Montana

WJShaheen Loc: Gold Canyon, AZ

Focal length = magnification. The more you "zoom in", the more apparent the unavoidable trailing of the stars becomes, depending on exposure length.
At longer focal lengths, you are simply magnifying those star trails.

jeep_daddy Loc: Prescott AZ

1. The wider the better because the more you magnify, the more evident the earth's movement has on the stars causing an elongated instead of round star point. There is a formula for lens focal lengths and f/stops that will help avoid elongated stars. It's the 500 rule that is used to determine the shutter duration used for certain focal lengths and f/stops. The rule is: 500 divided by the focal length for a full frame camera sensor. So 500 divided by say 16mm is 31.25 seconds. That's for a lens that is an f/2.8 lens. Also a rule of thumb is to never use a shutter duration longer than 30 seconds or the stars become elongated by the earth's movement. So the 31.25 shutter is approx 30 seconds at ISO 1600 but this is only a ballpark start and you may then adjust your ISO a little higher to dial it in. I wound up using ISO2000 last time I was out doing stars. If you have an f/4 lens, this is going to cut your light by a stop so you'd naturally have to up the ISO from 1600 to 3200 for starters. Also, when you use a crop sensor body, you'll have to also include the formula on your focal length to get a more accurate focal length. So for instance if you have a Canon Rebel camera with a 24mm focal length, you'll have to formulate it like this: 24x1.6=38.4
xxxxxxxx 500/38.4=13.02 or 13 second shutter. Any longer and you'll have elongated stars. If the lens is an f/4 you'll need an ISO in the 3200-6400 range. Again, this is adjusted once you are in the field and take a few test shots. I examine my histogram and look for 2 bumps on the left side but I can't explain that here.

Oh, and your formula for shooting with your camera and 28mm lens would be 500/28=18 seconds at ISO640
You can use something around ISO640 because your f/1.8 lens is very fast and lets in 1 1/3rd stops more light than a f/2.8 lens. This is approximate and your ISO can be adjusted in the field for proper exposure.

2. An inexpensive lens that is sharp and fast would be Tokina lenses. I wouldn't have believed it until a friend of mine brought hers and showed me her results. Anyway, you can buy the used pretty cheap, or new they are less than $600

https://www.bhphotovideo.com/c/product/735453-REG/Tokina_ATX168PROFXN_AT_X_16_28mm_F2_8_Pro.html
Have fun.

amfoto1 Loc: San Jose, Calif. USA

Do you also want a wider lens?

Rokinon (Samyang) 14mm AF f/2.8 is pretty amazing for $700. It matches or beats the image quality of the Canon EF 14mm f/2.8L II USM that sells for $2100.

There's also an even less expensive manual focus (and manual aperture) version of the Rokinon 14mm. I don't know if they are the same optically, though. Actually, there are two versions of this... one "chipped" to communicate with Canon camera (which allows Focus Confirmation to work, for example) and a cheaper "unchipped" version that doesn't communicate with the camera in any way.

The Rokinon lenses are made by Samyang and sometimes sell under both names. I've also seen the manual focus versions selling under Bower and Vivitar brand names. It appears to be the same lens regardless of brand.

Regardless of brand name, I've noticed buyers reporting "copy variation". It might be necessary to swap them a few times to get a "good copy". Especially watch for "softness" on one side of images, probably indicating a de-centered element (a manufacturing/quality control issue).

If you want slightly less wide, there are Zeiss 15mm and 18mm. In fact, they offer two versions of each: Classic and premium Milvus. Both are fairly pricey, but the Milvus is much more so. They are top quality build and excellent optically. In their ZE mount for Canon, these are manual focus, but aperture control is via the camera, as with native Canon EF lenses.

Canon's EF 20mm f/2.8 USM is pretty darned good, too. It's not as sharp in the corners and at the edges as some of the above, but it's better than the EF 28mm f/2.8 USM.

You can see test shots and compare image quality from these lenses and more at The-Digital-Picture.com. It's possible to set up magnified, side-by-side comparison of test target shots from any two lenses there. The last couple years Bryan has been using a 5DS-R for much of those test shots, which is just about as demanding of lens quality as any camera on the market. Any and all lens flaws will be brought out by the 50MP camera! (Note: Just be sure to view comparisons using the same camera there, which might be another 5D model or 1DS Mark III in some cases, with older full frame-capable lenses. It can be misleading to view one lens on a 21MP or 22MP camera versus another lens on a 50MP camera.)

Shooting at night, your viewfinder won't be as bright using these lenses. All are at least a stop slower than your 28/1.8. But the less wide max aperture is one reason they're sharper and if you are using Live View anyway, you can easily use Exposure Simulation to compensate. (Note: Since you are using Live View, have you considered tethering the camera to a tablet, to have an even larger image preview?)

I didn't get into any zooms because generally speaking an ultrawide prime can be sharper and better corrected. Some ultrawide zooms are very good, too (some of the best: EF 11-24mm f/4L USM, EF 16-35mm f/2.8L III USM, EF 16-35mm f/4L IS USM)... But will be big, heavy and expensive compared to the primes.

bwana Loc: Bergen, Alberta, Canada

Apply the Rule of 500 to estimate an exposure to keep star trailing at a minimum, i.e.: exposure (sec) = 500/focal length. 10 sec. for a 50mm lens, 20 sec. for a 25mm lens, etc. The '500' is a rule of thumb, not a fixed value. You can push it from 300 to 700 depending upon how much star trailing you can accept.

It is also possible to reduce trailing in software, i.e.: Photoshop. Of course a tracking mount is the optimal solution.

I've found Samyang manual lenses to be very good quality and reasonably priced. I have their 6.5, 14, 24, 35, 50, 85 and 135mm lenses. I specially like the 14 and 35mm. The 14mm is great for Auroras and the 35mm just seems to work right for Milky Way panorama subs. The 135 gives you more reach into the depths of the Milky Way's dust lanes and nebulas. The 6.5mm lens is just a lot of fisheye fun!

Clear skies!

bwa

Full Sky Aurora: 6.5mm fisheye on full frame camera

(Download)

R.G. Loc: Scotland

The earth's movement means that the whole sky is moving relative to a stationary camera. Zooming in on that movement magnifies it and zooming out does the opposite - it makes it more distant. A wider aperture means more light for the same shutter speed, so the optimum combination is a wide aperture and a wide angle of view. Or use tracking...

karno Loc: Chico ,California

Throw that gear Oman equatorial mount and letter rip