[koekie]

For my new K-70 I am looking for one more lens: a fast standard zoom to cover a couple of things: walkaround/landscape, general low light shooting, and astrophotography.

The Pentax 16-50 is a bit too expensive imo, and the apparent SDM issues ain't too attractive either.

Either the Sigma or the Tamron 17-50 f/2.8 seems like the obvious choice.

However, on this forum you can clearly see evidence of coma in the corners when shooting the stars with the Sigma at wide angle. I suppose it will be the same story with the Tamron? Some external reviews seem to suggest that the Tamron performs slighly better at 17mm than the Sigma. But that doesn't automatically mean less coma, as this review shows. Any people here with experience with these two lenses, and specifically with astrophotography?

Obviously getting a more 'purpose built' astro lens like any of the wide angle Samyangs or the Sigma 18-35mm is the best option. But I am a bit reluctant to spend all that extra money just for an astro lens, especially considering the fact that I am just about to take my first babysteps into astrophotography.

Any suggestions?

[lithedreamer]

Are you trying to get star trails or pin point sharp stars?

[koekie]

Are you trying to get star trails or pin point sharp stars?

Oh ye good you have asked. Definitely trying to get pin point stars. Not really interested in star trails.

[Mapleleaf-Mick]

Does the K70 have Astro Tracer? If not, you won't get pinpoint stars. You can buy or make a platform with tracer to resolve this problem. My recommendation is the Samyang 16mm F1.8. Beautiful wide angle lens. Good for landscapes and architecture as well.

Michael

[BigMackCam]

Does the K70 have Astro Tracer?

It does

[koekie]

Does the K70 have Astro Tracer? If not, you won't get pinpoint stars. You can buy or make a platform with tracer to resolve this problem. My recommendation is the Samyang 16mm F1.8. Beautiful wide angle lens. Good for landscapes and architecture as well.

Michael

I have the gps module, so in theory pin point stars should be possible through the star tracer option, bulb mode, mirror lockup, and possibly a remote/2 sec timer. If I can get the precise calibration right, of course.

I wasn't aware Samyang had a 16mm at f/1.8. Think you mean the 16mm 2.0?

Basically my question is if there will be a significant difference between using the Tamron or the Sigma 17-50 for pin point star shooting.

I am aware that there are several fast wide angle lenses from Samyang, but I am wondering if the results from the Sigma/Tamron will be good enough and if one of these edges ahead when it comes down to coma in the corners.

[Obin Robinson]

Any suggestions?

Yes. Get yourself a Pentax 67 lens and adapter. Mount the camera to a basic equatorial mount. Your results with a Pentax 67 lens will be superior to any APS-C zoom lens. If you want to see what Pentax glass is capable of check this link:
http://www.narrowbandimaging.com/widefield_page.htm

obin

[Adam]

I've never been a fan of zooms for astrophotography. Many things make getting clear star photos difficult, and I think that having a lens that isn't as bright or sharp as it could be can make a successful shoot even harder. You need the lens to perform really well wide-open, so that should be your top criteria if you decide to go for a zoom. Going by that, the DA 16-85mm may indeed be more viable than one of the F2.8 zooms if you plan to shoot mainly at the wide end.

I'd personally recommend the Samyang 16mm F2 for your wide-angle shots, and any fast wide or normal prime for your deep space shots. The Samyang 24mm, 35mm, and 50mm F1.4 would all be viable candidates. And since AF doesn't matter for astrophotography (you could even argue that manual focus lenses are better since they allow for more precise adjustments), there's no harm in going for these lenses and saving some money.

[Obin Robinson]

And since AF doesn't matter for astrophotography (you could even argue that manual focus lenses are better since they allow for more precise adjustments), there's no harm in going for these lenses and saving some money.

This is correct. Astrophotography is extremely sensitive to focus issues. Having focus off by as slight as .001" can affect whether stars are pinpointed or slightly bloated. Use a focusing tool to get the best focus:

SharpStar2 Precision Focusing Tool by Lonely Speck – Lonely Speck

To achieve perfect focus I use special software as well but for a camera lens the Sharpstar will work.

obin

[koekie]

Yes. Get yourself a Pentax 67 lens and adapter. Mount the camera to a basic equatorial mount. Your results with a Pentax 67 lens will be superior to any APS-C zoom lens. If you want to see what Pentax glass is capable of check this link:
A Gallery of Widefield Images From Pentax 6x7 Camera Lens Adaptor System

obin

Stunning images, that's for sure! Interesting suggestion too, but I guess it's coming at least one year too early Basically I am still a beginner at serious photography, and especially in stuff like astrophotography. So I guess it makes more sense to try and get the best results with the more common and regular APS-C lenses which are easier to use. Using medium format lenses sounds interesting, but I guess I'd better take the time to try and learn the craft before looking into anything like 67 lenses + adapter.

I've never been a fan of zooms for astrophotography. Many things make getting clear star photos difficult, and I think that having a lens that isn't as bright or sharp as it could be can make a successful shoot even harder. You need the lens to perform really well wide-open, so that should be your top criteria if you decide to go for a zoom. Going by that, the DA 16-85mm may indeed be more viable than one of the F2.8 zooms if you plan to shoot mainly at the wide end.

I'd personally recommend the Samyang 16mm F2 for your wide-angle shots, and any fast wide or normal prime for your deep space shots. The Samyang 24mm, 35mm, and 50mm F1.4 would all be viable candidates. And since AF doesn't matter for astrophotography (you could even argue that manual focus lenses are better since they allow for more precise adjustments), there's no harm in going for these lenses and saving some money.

Ye I also considered the 16-85mm, as I have been reading about its sharpness and excellent performance all across the board. However, I kind of figured that the 2/3 stops of less light coming in (f/2.8 vs f/3.5) would automatically make it less ideal than the Sigma/Tamron 17-50 2.8 for wide angle astrophotography.

So basically you are saying that the better performance/sharpness of the he DA 16-85 at the fl of 16mm is preferrable over 17mm at the Sigma/Tamron, even though these two lenses have a slightly larger aperture and thus will let a bit more light in? Interesting point for sure! And perhaps the good ISO performance of the K-70 helps a bit here too, compensating for the f/3.5 aperture at 16mm?

Perhaps I should consider the Sigma 17-70 as well. According to the reviews here, its just as sharp at 17mm, while being a bit faster and atm roughly 150 euros cheaper than the 16-85. Although it seems kind of hard to imagine that that Sigma 17-70 would be better at the wide angle than the Tamron/Sigma 17-50 right?

Well I already have the two Pentax plastic fantastic lenses. The Samyang equivalents are probably better, but pricewise you can't beat these two small Pentax lenses. And a review on lenstip showed that the 35mm 2.4 is excellent when it comes down to coma in the corners. They are both quite fast too.

This is correct. Astrophotography is extremely sensitive to focus issues. Having focus off by as slight as .001" can affect whether stars are pinpointed or slightly bloated. Use a focusing tool to get the best focus:

SharpStar2 Precision Focusing Tool by Lonely Speck – Lonely Speck

obin

Ye I already read about the sharpstar on Lonely Speck. Certainly seems like an interesting tool. But isn't the use of the 10x 'ok-button' live view zoom method on a bright star (+ meticulously adjusting focus manually until you have the star as small and sharp as possible) ok too? Probably this is not always the most precise method, but it also seems a bit more fun just using the camera + lens to get the best focus possible.

[Adam]

So basically you are saying that the better performance/sharpness of the he DA 16-85 at the fl of 16mm is preferrable over 17mm at the Sigma/Tamron, even though these two lenses have a slightly larger aperture and thus will let a bit more light in? Interesting point for sure! And perhaps the good ISO performance of the K-70 helps a bit here too, compensating for the f/3.5 aperture at 16mm?

It could well be, because half a stop isn't the end of the world. Plus, 16mm is noticeably wider than 17mm.

[koekie]

It could well be, because half a stop isn't the end of the world. Plus, 16mm is noticeably wider than 17mm.

True that, seems like I really need to consider the 16-85 more seriously now

But isn't the Sigma 17-70 still a better choice then? In a review here on this website, the comparison between the Sigma 17-70 and the Pentax 16-85 led to a clear conclusion: if you don't need the WR of the Pentax, go for the Sigma. Reasons: comparable IQ, faster aperture, better macro, nicer bokeh, and cheaper.

However, I doubt the Sigma 17-70 is better/sharper (perhaps less coma in the corner?) at 17mm than the higher end Sigma/Tamron 17-50 right? But you seemed to suggest the 16-85 might be a better option than the Sigma/Tamron 17-50. So now it's getting interesting

So mainly considering the astro wide angle performance, how should I decide between these 3 or actually 4 lenses?

[Digitalis]

the Sigma 18-35mm is the best option.

It certainly is...


Pentax K5IIs - Sigma 18-35mm f/1.8 @18mm - ISO 800 f/1.8 20s

But there are many, many, caveats that get in the way of me recommending this as an ideal all purpose lens, chiefly the AF issues that are completely unpredictable.

[koekie]

It certainly is...


Pentax K5IIs - Sigma 18-35mm f/1.8 @18mm - ISO 800 f/1.8 1/30th

But there are many, many, caveats that get in the way of me recommending this as ideal all purpose lens, chiefly the AF issues that are completely unpredictable.

Great picture, I already came across that one somewhere around here

Yup, the AF issues are exactly what kept me from even considering this lens. If you invest such a price on a lens, then mechanically it should be near flawless imo. Sadly, it's not. Also a bit heavy as a walkaround daytime lens, and too expensive to just use it as a manual focus single purpose astro lens.

What would you suggest? I know a wide angle Samyang gets better astro results, but I really want to try save some cash by buying the Sigma/Tamron 17-50, the Sigma 17-70 or the Pentax 16-85 for daytime stuff and wide angle astrophotography.

Edit: this post is perhaps an indication that the Sigma 17-70 is slightly better for wide angle astrophotography. I can't really see a whole lot of coma in the corners, certainly not as much as the picture of the 17-50 shows.

[Digitalis]

What would you suggest?

I would suggest you buy the sigma 17-50mm and look into getting a second fast wide angle prime lens for the astro work. Cheap multi element zoom lenses have too many compromises involved and Astrophotography is unforgiving on common optical faults such as astigmatism, vignetting and coma - so getting a fast prime dedicated for astro would work better, and produce the results you aspire to achieve.