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01-10-2019, 07:08 AM   #1
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Manual Astro Prime - Wide-ish and Fast?

All,

I'm looking for a good manual prime for starfield photography. Something shorter than, say 30mm and faster than 2.5 or so. I like my Tamron 28-75, but I'm about to receive a iOptron tracking mount, and would love something small, manual, and relatively light to "set and forget" while tracking. I've considered something like the Sigma art lenses, but I'd almost prefer something older, in the Takumar age range - not least due to lens expense, or newer but not "current," like the Sigma 24mm F1.8 EX. Let me know if you have any suggestions or experience. I have a Pentax K-3, and a new Vanguard 263AB tripod.

01-10-2019, 08:35 AM   #2
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I'm evaluating a Sigma 20mm f1.8 EX DG right now - sharp from minimum focal distance to infinity...
01-10-2019, 08:36 AM - 1 Like   #3
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QuoteOriginally posted by pepperberry farm Quote
I'm evaluating a Sigma 20mm f1.8 EX DG right now - sharp from minimum focal distance to infinity...
Let me know how it goes!
01-10-2019, 08:39 AM - 1 Like   #4
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With a tracking mount why would you be so concerned with speed of the lens, assuming it is an equatorial? I would think that a properly aligned equatorial with a wide APS-C lens on it would easily be able to track without any pixel peeping detectable error for 5 minutes. An Alt-Az mount would be a different story. Also if you toss in stacking you can push the ISO up one or 2 stops without issue. If looking at takumar aged lenses that are wides and ultrawides they likely won't be fast.

I've used my old S-M-C 17mm fisheye Takumar for wide astro shots even without astro tracer. I will typically stop it down to f/8 to help with the CA (it really needs this) but even then I haven't gotten awful shots shooting at 15 seconds without astrotracer. I haven't used that lens with astrotracer but probably should once just to see if it will do the full 5 minutes well but there is no 17mm fisheye setting.

When I have gone wide (astro wide not normal photography wide) I have used my 50mm f/1.4 down to my 17mm f/4 fisheye all with pretty good results. When shooting constellations I have used my S-M-C 50mm f/1.4 takumar, S-M-C 28mm f/3.5 takumar, and DA 35mm f/2.4 all with good results and on proper tracking mount the results would likely be even better. Going wider there is that 17mm fisheye which is probably the worst lens I have for astro since it is so slow and needs to be stopped down so much to deal with CA. For that I have been seriously considering something newer possibly the Venus Optics Laowa 12mm F2.8 Zero-D or Irix 15mm F2.4 as it seems like they would fit that role.

01-10-2019, 08:50 AM   #5
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QuoteOriginally posted by MossyRocks Quote
With a tracking mount why would you be so concerned with speed of the lens, assuming it is an equatorial? I would think that a properly aligned equatorial with a wide APS-C lens on it would easily be able to track without any pixel peeping detectable error for 5 minutes. An Alt-Az mount would be a different story. Also if you toss in stacking you can push the ISO up one or 2 stops without issue. If looking at takumar aged lenses that are wides and ultrawides they likely won't be fast.

I've used my old S-M-C 17mm fisheye Takumar for wide astro shots even without astro tracer. I will typically stop it down to f/8 to help with the CA (it really needs this) but even then I haven't gotten awful shots shooting at 15 seconds without astrotracer. I haven't used that lens with astrotracer but probably should once just to see if it will do the full 5 minutes well but there is no 17mm fisheye setting.

When I have gone wide (astro wide not normal photography wide) I have used my 50mm f/1.4 down to my 17mm f/4 fisheye all with pretty good results. When shooting constellations I have used my S-M-C 50mm f/1.4 takumar, S-M-C 28mm f/3.5 takumar, and DA 35mm f/2.4 all with good results and on proper tracking mount the results would likely be even better. Going wider there is that 17mm fisheye which is probably the worst lens I have for astro since it is so slow and needs to be stopped down so much to deal with CA. For that I have been seriously considering something newer possibly the Venus Optics Laowa 12mm F2.8 Zero-D or Irix 15mm F2.4 as it seems like they would fit that role.
Do you always use primes, or do you use zooms as well?

I suppose speed isn't as important, as I will have an EQ tracking mount - not sure about whether it's what you mean - here's what I ordered: SkyGuider<sup>TM</sup> Pro Camera Mount Full Package

So, if I want to try wider shots of, say, the milky way, or large portions of the sky, I would want to go to wider than 24mm?
01-10-2019, 09:26 AM - 1 Like   #6
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QuoteOriginally posted by jawats Quote
All,

I'm looking for a good manual prime for starfield photography. Something shorter than, say 30mm and faster than 2.5 or so. I like my Tamron 28-75, but I'm about to receive a iOptron tracking mount, and would love something small, manual, and relatively light to "set and forget" while tracking. I've considered something like the Sigma art lenses, but I'd almost prefer something older, in the Takumar age range - not least due to lens expense, or newer but not "current," like the Sigma 24mm F1.8 EX. Let me know if you have any suggestions or experience. I have a Pentax K-3, and a new Vanguard 263AB tripod.
Samyang/Rokinon lenses are worth checking out IMO.

Samyang: <= 35mm <= F1.8 Third Party Prime Lenses | PentaxForums.com

These won't disappoint in terms of image quality, and the F1.4/1.8 aperture gives a lot of flexibility when it comes to exposure.

Adam
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01-10-2019, 10:02 AM - 1 Like   #7
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QuoteOriginally posted by jawats Quote
I would want to go to wider than 24mm
On APSC, I like at least 18mm for a non-stiched image of the Milky Way.
I've recently purchased a 10-20mm which I hope delivers good results next time I shoot the MW.
It's really nice to add some foreground to provide context.

I've used the 18-50mm, 18-55, and 18-135mm to shoot the MW at 18mm, usually at f/4 ish, around 2 minutes, with the O-GPS unit on my K-S2 and have received acceptable results!
01-10-2019, 10:12 AM - 1 Like   #8
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I've been thinking along this myself as I really fancy trying astrophotography with the K1. I've got one of the Sigma 24mm F1.8's so was thinking about giving that a try as a starter. I've got the Sigma 14mm F2.8 so will also try that.

01-10-2019, 10:13 AM - 1 Like   #9
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QuoteOriginally posted by jawats Quote
Do you always use primes, or do you use zooms as well?
For the most part I have used primes exclusively. In general they are faster, sharper, and have less CA than zooms. Although doing astro you sometimes find out that a lens that is otherwise great is really awful for astro shots. This is more true with older 3rd party glass. My very first astro attempt was with a K2000 and 18-55 DA, no tracking and and I had no idea what I was doing. A couple weeks later the kid broke that lens so I never did more astro with it.

QuoteOriginally posted by jawats Quote
I suppose speed isn't as important, as I will have an EQ tracking mount - not sure about whether it's what you mean - here's what I ordered: SkyGuider<sup>TM</sup> Pro Camera Mount Full Package
That is an equatorial which is great choice. It doesn't look like it has goto functionality, get everything aligned and then it can automatically point your camera at things for you instead of you finding them, but looks to be a good place to start from. An Alt-Az mount is a different type of tracking mount where it will do x and y movements of the camera but not rotation. They are typically easier to setup and align but because of the lack of rotation errors crop up. The built in astrotracer functionality in newer Pentax cameras (either with built in GPS or through the O-GPS1 addon) act like an Alt-Az mount but in camera and more limited time wise. I hope this helps clear things up some.

QuoteOriginally posted by jawats Quote
So, if I want to try wider shots of, say, the milky way, or large portions of the sky, I would want to go to wider than 24mm?
Probably. For the milky way you probably want a HFOV greater than 90 degrees if not over 100 maybe evenapproaching the 180 some fisheyes can get to. That will allow you the ability to get huge expansive landscapes with the milky way arching overhead or in a portrait layout have a long milky way comming down from way up in the sky to the foreground. Here is a thread over in the astro group showing a wide astro shot as well as a narrow one. The first one is 3 images from a Samyang 16 mm F2 stitched together (I would assume they were landscape images stitched into a portrait image). If doing shots of things like the milky way you can always do a composite where you shoot the sky tracked and then turn off tracking and shoot the foreground. This gets you the best of both worlds.

Enjoy your new gear and have fun with it.
01-10-2019, 10:13 AM   #10
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QuoteOriginally posted by FozzFoster Quote
On APSC, I like at least 18mm for a non-stiched image of the Milky Way.
I've recently purchased a 10-20mm which I hope delivers good results next time I shoot the MW.
It's really nice to add some foreground to provide context.

I've used the 18-50mm, 18-55, and 18-135mm to shoot the MW at 18mm, usually at f/4 ish, around 2 minutes, with the O-GPS unit on my K-S2 and have received acceptable results!
Excellent - that's about the range I was thinking! Thank you.

---------- Post added 01-10-19 at 10:15 AM ----------

QuoteOriginally posted by MossyRocks Quote
For the most part I have used primes exclusively.....
Thank you for the advice, Mossy. I will be checking into 20mm and wider primes, most likely. Have you ever used old Pentax / Tak glass?

---------- Post added 01-10-19 at 10:18 AM ----------

QuoteOriginally posted by FozzFoster Quote
On APSC, I like at least 18mm for a non-stiched image of the Milky Way.
I've recently purchased a 10-20mm which I hope delivers good results next time I shoot the MW.
It's really nice to add some foreground to provide context.

I've used the 18-50mm, 18-55, and 18-135mm to shoot the MW at 18mm, usually at f/4 ish, around 2 minutes, with the O-GPS unit on my K-S2 and have received acceptable results!
I've also looked at the wider Tamron and Sigma zooms, but I think I prefer primes at this point, for the astrophotograhy.
01-10-2019, 10:30 AM - 1 Like   #11
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QuoteOriginally posted by jawats Quote
I think I prefer primes at this point
I've used a Sigma 24mm f/1.8 Marco lens for shooting the MW too.. very nice results! but the field of view at 24mm is too tight for me on APSC... much prefer at least 18mm!
01-10-2019, 11:18 AM   #12
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QuoteOriginally posted by jawats Quote
Have you ever used old Pentax / Tak glass?
Yes. The 17mm fisheye is the S-M-C Takumar, my 28mm f/3.5 and 50mm f/1.4 are also old old screw mount S-M-C Takumars as well. I was still exclusively using my old Spotmatic F until about 15 months ago. I have lots of good old M42 screw mount glass up to a 300mm f/4 Super Takumar all of it primes and most of it old Takumars.I have some really cheap bad glass too but we don't talk about that (looking at you 400mm f/6.3 teleastinar).
01-10-2019, 11:27 AM   #13
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QuoteOriginally posted by MossyRocks Quote
Yes. The 17mm fisheye is the S-M-C Takumar, my 28mm f/3.5 and 50mm f/1.4 are also old old screw mount S-M-C Takumars as well. I was still exclusively using my old Spotmatic F until about 15 months ago. I have lots of good old M42 screw mount glass up to a 300mm f/4 Super Takumar all of it primes and most of it old Takumars.I have some really cheap bad glass too but we don't talk about that (looking at you 400mm f/6.3 teleastinar).
Ha! Excellent. Well, I will eyeball the Taks at wider than 20mm, and see what's out there.

Also saw a good deal on a Samyang 14mm today.
01-10-2019, 02:37 PM   #14
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QuoteOriginally posted by jawats Quote
Ha! Excellent. Well, I will eyeball the Taks at wider than 20mm, and see what's out there.
Overall, there is not a lot. You have to remember that with the Taks, they were film lenses - full frame and as such, 15mm was really very wide, and with Pentax - that was it.Your best bet for wide and relatively fast are the Samyangs (along with various rebadge brands), Irix, and the like.

You also have to take in to account that the wider you go in terms of field of view (smaller focal lengths), the smaller the actual physical aperture will be. That will reduce the amount of light you will be able to capture. They all may be f2.8 but the size of the physical apertures will vary across the various focal lengths. What additional light you will be taking in via the tracking mount, you will be giving back a bit of that, based on the physical aperture.

It's all about finding a reasonable balance across the focal length and aperture.

01-10-2019, 03:43 PM   #15
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QuoteOriginally posted by interested_observer Quote
Overall, there is not a lot. You have to remember that with the Taks, they were film lenses - full frame and as such, 15mm was really very wide, and with Pentax - that was it.Your best bet for wide and relatively fast are the Samyangs (along with various rebadge brands), Irix, and the like.

You also have to take in to account that the wider you go in terms of field of view (smaller focal lengths), the smaller the actual physical aperture will be. That will reduce the amount of light you will be able to capture. They all may be f2.8 but the size of the physical apertures will vary across the various focal lengths. What additional light you will be taking in via the tracking mount, you will be giving back a bit of that, based on the physical aperture.

It's all about finding a reasonable balance across the focal length and aperture.

So would it then be better just to experiment with my Tamron 28-75 2.8 and see what I need after tooling around with it for a time?
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