[LennyBloke]

I read that one of the key things in choosing a lens for astrophotography is a fast maximum aperture, so when it comes to a "standard" 50mm lens the Pentax choices range from f1.2 to f2.0 and are all generally well regarded lenses, but is it worth pushing the boat out and spending the extra on the f1.2 version for that small difference in light gathering power or will the comments in the reviews ("soft wide open", "dreamy") make the lens unsuitable at maximum aperture thus making the f1.4 versions more suitable?

I'd really appreciate the views from those of you who have tried the 1.2's

[Kendigitize]

I use the Fa 50mm 1.4 for astro photography and the results are amazing. I use it at about f2.

The problem I have is I want a larger field of view, so I use my M-28mm 2.8 and get great results too.

From what I've read, a 24mm f2 is the best lens/focal length combo as well as the Rokinon (and other names) 14mm 2.8

[Sagitta]

No experience with the 1.2 myself, but I've always heard that the 1.2 is a touch fuzzy wide open compared to the 1.4, which could be problematic if you intend to use it to shoot stars. If you have to stop the 1.2 down to get decent results, you may as well grab the slower lens and use the difference in price elsewhere. (I'd shoot for a Bower/Rikonon/Vivitar 85mm f/1.4 if I had that extra $250 to blow...)

EDIT: Have the M-1.4 myself, rarely use it because I tend to either want to shoot narrower or wider... 50mm is kind of an awkward in between size for me for astro shooting.

EDIT II: Do you have a means to track? IE, a scope mount or the O-GPS1? If you can track, then that changes the game completely, as your slower lenses become much more useful than they would have been before. If you don't, you can pick up an O-GPS1 and a 50mm 1.4 or 1.7 together for the cost of that 1.2.

[JimmyDranox]

I have done some ''tests'' with SMC M50/2. I call it tests, because the result was not what I want. The biggest problem was coma. Stars was pinpoint only in the center at F2, and turn in coma shape as I go to the edges. Of course, I can crop the frame, but I don't want to do this, nor to resize it, maybe 4-5 times smaller, and to lose information. I had to close the aperture to F4, to get round stars at the edge.

A friend of mine has bought a 50/1,2. Same result.

Recently, I tried a Sigma 50/1,4 EX DG HSM. Not the ''Art''. More or less, things are the same. From what I've seen so far, the new Sigma 50/1,4 Art can be used better, at about F2. But it's not on Pentax mount yet.

[VisualDarkness]

Go with the Otus, your wallet will feel lighter.
Carl Zeiss Otus 55 mm f/1.4 ZE/ZF.2 review - Coma, astigmatism and bokeh - Lenstip.com

[JimmyDranox]

No. Ottus is worse than Sigma ''Art'' regarding coma.

Sigma A 50 mm f/1.4 DG HSM review - Coma, astigmatism and bokeh - Lenstip.com

And, surprise, the best Pentax fix lens for wide field astrophoto,, from all the lenses they tested, judging after coma, is the ''plastic fantastic'' DA 35mm/2,4.

Pentax smc DA 35 mm f/2.4 AL review - Coma and astigmatism - Lenstip.com

Funny. I have this lens, is one of the sharpest, but I've never tried it for astrophoto.

[Kendigitize]

I have the DA 35mm and have tried several times using it for astrophotography. I was never happy with the results. I use a M28mm 2.8 instead if the 50 1.4 is too close.

[JimmyDranox]

What you don't like at the35mm?

[1r0nh31d3]

forgive my ignorance as I do not know all the ins/outs of astrophotography but my understanding is that you are shooting from a tripod with long exposure times. If you're already shooting from a tripod with a long exposure (from research this can be a few minutes or even into +1hr) isn't the speed of lenses you're comparing somewhat irrelevant? If you need more light, extend your shutter time.

Am I missing something crucial about astrophotography?

[JimmyDranox]

If you want to shot long exposure you need a tracking mount, to compensate for the apparent movement of stars. If you have this, could be OK. Could be, because if the exposure is longer than few minutes, tracking errors can became visible, and you need autoguiding systems, or very expensive astronomical mount, very well oriented after the rotational axis of the Earth.

And must count that 1 minute exposure at F2, is equal with 4 minutes of exposure at F4.

If you don't have an astronomical equatorial mount, motorized and eventually with autoguiding, or a tracking unit like O-GPS, or you don't know to use it properly, the longest exposure with a 50mm lens and an APS-C camera is shorter than 4 seconds. Tested by myself. On a FF camera, with the same 50mm lens, this time can be maximum 10 seconds.

[Kendigitize]

Those are the basics. Once you go above 25sec, you're going to have star trails because of the earth rotation. If your looking for star trails, that's great. If your trying to get a nice shot of the milky way, not so much. A faster lens will pick up really faint stars. My settings when I use the 28mm are f2.8 or one stop up, ISO800 and 14sec exp.

Here's a great link on everthing you need to know about astro photo basics and lens selection.

How-To: Picking a Great Lens for Milky Way Photography

Jimmy-
I just was never happy with the sharpness of the stars when I used the 35mm 2.4. I use palm trees and mountains when setting up the shots and the lanscape is just a little to "soft" for me.

[JimmyDranox]

Yes, I understand. You want some more DOF, and you need a wider lens for this.

[LennyBloke]

Thanks for the comments guys!

I'll be using the O-GPS1 Astrotracer (when we get some clear skies again), and I've already sourced a 16mm f2 (the Milky Way link is a good one) - I'm just looking at alternative lenses for less wide shots. I'm happy that the A100/2.8 gives very good results but I was looking for recommendations on a fast 50 - ideally from someone who has tried the 50/1.2 against other lenses. I realise that I will need to do a lot of testing to find my preferred settings, but guidance from those who have been through this is a great starting point -

[LennyBloke]

After the excitement of seeing the Milky Way for the first time I took a few shots with the K5iiS + DA*55/1.4 + O-GPS1 and stacked them in DSS then attempted to add some contrast and amend the colour in LightRoom.....




.... it's not a patch on most of the results I've seen on here, but I'm chuffed as a first effort

[VisualDarkness]

That's really really good Lenny!