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lens for night sky/milky way....

scarr1
Posted 17/08/2016 - 11:57 Link
would a Pentax A 28mm 2.8 be any good for the night sky/milky way? I'm just thinking that as it has an aperture ring, it may be easier to compose in the dark.
I currently have a k3, and have a sigma 10-20, Pentax 18-135, and also the two plastic fantastic's...35mm 2.8 and 50mm 1.8.
I've had the best images from the 35mm 2.8 (the 50mm seems too narrow FOV).
or is there any other (cheapish) alternatives/recommendations.
JAK
Posted 17/08/2016 - 12:34 Link
I'm not saying don't get it if you want it, it's a fine lens if in good condition. However, you have the 18-135 which covers that focal length and exposures including the aperture can be set manually on that using the M setting. So it won't be any easier to set it, but the A 28mm is a prime lens so should have better resolution, albeit designed for film cameras not digital.
If you do decide to get it, make sure the aperture lever is snappy and the optics are clear with no fungal threads visible.
So ultimately, do you need it? Probably no. Would you like it? Probably yes!
John K
Edited by JAK: 17/08/2016 - 12:41
LennyBloke
Posted 17/08/2016 - 13:21 Link
If the 35 you have is the f2.4 (not the macro 2. then I believe the design is based on the FA 35mm f2.0 which IMO is superb for astro photography. One of the more common problems with some lenses is they suffer from Coma - an elongation of points of light towards the edge of the image, but the 35 is one of the better lenses for avoiding this.

I haven't tried an A 28/2.8 for astro work, but the fact that it has a manual focus ring probably means you can set it to infinity (and hopefully that will be the "hard stop" at the end of the focus throw) without having to worry about it moving (the AF lenses are easy to knock the focus out a little). I don't know of a lens that doesn't benefit from stopping down at least half a stop (preferably a full stop).

One of the advantages that Primes usually have over zooms is that they have a faster aperture, and it is the fact that you can gather more light that give you the ability to get more detailed images. My favourite lenses have included the FA35/2.0, F50/1.4 and K135/2.5 - all fast, and high quality
LennyBloke
scarr1
Posted 17/08/2016 - 13:35 Link
It is the DA 35 2.4 i have, not 2.8 (my mistake).
Thats the one that seems to give me the best images.
I dont really "want" the A 28mm (i recently sold the one i had!!), just thought it may have been a better option..ie, a little bit wider than the 35.
Blythman
Posted 17/08/2016 - 14:52 Link
Well regarded primes are the Samyang lenses. Was trying to make my mind up between the 14mm and the 24mm. While looking into those I noticed they have just announced a 20mm. So, I think I'll hang back and see how that is reviewed. Pity the Sigma 18-35 isn't a goer on full frame, because I like it on my crop cameras. Anyway as a stop gap on FF I've just bought a Sigma Super Wide II 24mm on eBay. Will see what that's like if it turns up (had no comms since I paid on Sunday). I'll be able to compare a cheap but well regarded old prime with my Sigma 24-70.
Alan


PPG
Flickr
Edited by Blythman: 17/08/2016 - 14:52
LennyBloke
Posted 17/08/2016 - 15:59 Link
One thing I would say about some Samyang lenses (I had the 16mm f2.0) is they don't always have a hard-stop on the focus at infinity - my copy (and certainly some others) went well past, making it very difficult to achieve precise focus - although this will depend on your technique & your eyesight too. Most of my Pentax primes are pretty accurate on the infinity point (the longer primes tend to allow focus past infinity), something that's very useful if you're a bit of a Bat
LennyBloke
Blythman
Posted 17/08/2016 - 16:29 Link
Pays to focus them in daylight Lenny. And then just use something like a bit of tape as markers to line up in the dark. My Sigma 18-35 seems to focus beyond infinity too. Managed it in the dark just manually focusing on a distance point
Alan


PPG
Flickr
LennyBloke
Posted 17/08/2016 - 21:51 Link
Blythman wrote:
Pays to focus them in daylight Lenny. And then just use something like a bit of tape as markers to line up in the dark. My Sigma 18-35 seems to focus beyond infinity too. Managed it in the dark just manually focusing on a distance point

Yep - had heard this before, but the difference in distance between the Moon and Jupiter is quite large so you really do need to re-focus!


LennyBloke

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