Best film-era lenses for deep-sky astrophotography

PixelPete · 05-08-2021, 02:59 AM

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Which are the best film-era lenses to use for deep sky astrophotography on a modern DSLR (in this case my Pentax K-70)?

I have just got into deep-sky astrophotoraphy and am at present using my modern DSLR zoom lenses. I have heard that prime lenses work better and there are many 135mm examples on eBay at around £30 - £50. There are some 200mm ones that cost a bit more. I've seen good results using modern 135mm lenses, but there are many film-era lenses out there for much less money.

I've read all the lens reviews on this forum, but the problem is that a good lens for normal photography is not necessarily good for astro. So I'm looking for views of people who have used these lenses for DSO work. The ones I've seen are (all 135mm, K mount manual):

SMC Pentax-M f/3.5
Chinon f/2.8
Takumar f/2.8
Sigma Mini-Tele f/3.5
Hoya HMC f/2.8

These all scored better than 7 in the Pentax Forum Lens Review database.

johnha · 05-08-2021, 03:13 AM

I'd have a look at the Astrophotography Social Group here on PF. I had a similar question a few weeks ago and the group were very helpful.

My short answer based on some research is that the M200/4 is a really good lens which can be found very cheaply (I paid £20 for mine a couple of years ago). In order to avoid diffraction spikes by stopping down, you can reduce the aperture by using a series of step down rings to 37mm instead - maintaining a circular aperture.

stevebrot · 05-08-2021, 08:27 AM

Originally posted by johnha

My short answer based on some research is that the M200/4 is a really good lens which can be found very cheaply

I own that lens, but never though of it in terms of astro...hmmmmm...better give it a go, eh?

Steve

**Bob 256** · 05-08-2021, 08:56 AM - **1 Like**

First, you need to determine what type of astrophotography you're going to use a lens for. Astrophotography basically falls into three ranges; wide field, narrow field, and planetary. The last usually incorporates an actual telescope because it uses high power (large focal lengths) to shoot very narrow field shots of planets, close star groups, etc., and probably isn't what your after based on your inquiry.

That leaves the first two. 135mm lenses more often fall into the second category where you're trying to shoot nebulae, star clusters, and narrower field (though not very-narrow field) objects. 135mm is good for two reasons, they take in a fair amount of sky and can be had in low f-stop versions for not that much money. Having a lower f-stop is advantageous because of the need for light gathering in shooting dim sky objects using practical exposure times and ISO values. A 135mm may not be the best choice, however (read on).

A lot of the shots you see today, are of the wide-field type and show a vast section of the night sky. These are the first type I mentioned previously. They require short focal length lenses (mostly below 35mm) and many astrophotographers use ultra-wide lenses for this type of astrophotography. Again, you can probably find a low-f-stop, wide angle lens but you might have to pay more for it. IRIX wide field lenses are good choices for these wide-field types, though there are many others which can work well.

Anyway, it's better to start with an idea of what type of shots you're after rather than pick a given focal length and then try to make it fit something it may not be suited for.

In most all cases, you should probably stop the lens down a bit from its widest opening in order to gain sharpness. All lenses are a little "soft" at their widest opening (unless they are a fixed opening lens like a telescope, and then they are designed for best performance "wide open"). Picking a lens offering a low f-stop to begin with, gives you more room to do this (e.g., f1.4 becomes f2.8 instead of f4 becoming f5.6).

Take a look at some astro shots and see which ones you like best, and then try to identify a lens that will do the job in terms of its angular coverage considering what camera you're using (APS-C, Full Frame, etc). That will lead you to the best focal length to consider. Then you can see what's available and visit some reviews to see what is sharpest for what you can afford. Don't pass by the used market. There are some great opportunities there for obtaining a good astro lens.

You didn't mention how you're planning to track the stars and this is a whole subject unto itself. DSLRs can make short non-guided shots possible (using higher ISOs), but that rapidly proves more difficult as the focal length is increased. 135mm is definitely into the "iffy" range where you start having a need for guiding the camera to follow the stars for longer exposure times. A lot of (though not all) wide field shots can be made without guiding. Just something else to consider.

Last edited by Bob 256; 05-08-2021 at 09:11 AM.

**ProfessorBuzz** · 05-08-2021, 09:56 AM

Great comments Bob 256. Some of my better Astro shots were taken with 35 f/1.4 stopped down and 50mm f/1.7 stopped down.

A tracking mount really becomes necessary in the 200mm+ zone, and guiding beyond that.

**W412ren** · 05-08-2021, 10:30 AM

Good advice from @Bob 256

Definitely look at images (poke around on Flickr for example) and then choose your focal lengths.
I've used 20/24/35/50/135/200/400 manual lenses for astro at different times.
Now replaced the short and long ends with a DA*11-18 and telescope and the others are now the Pentax-A series models.

Usage examples on APSC: (There are obviously a lot of other combinations)

200mm will get you Orion's Sword or crop in for M42 and can work on The Pleiades
135/200mm will get Andromeda (even 50mm will get you a very tiny one )
135/200mm will work on eclipses
50mm will fit Orion in the frame and is quite good for isolating a part of the sky and including some landscape
24mm fits Cygnus, the plough and can be useful for star trails.

The 35mm I use on the K-1 in place of the 24mm.

PixelPete · 05-08-2021, 01:08 PM

Bob thanks for the very comprehensive introduction to astrophotograhy.
I have already been all through all that. I am at the stage, as I said in my original post, where I'm looking at film-era prime lenses and am asking for views of those who have used them. A good lens does not necessarily mean a good astro lens.
As I said, I'm looking at 135mm primes, as they are good value, are plentiful and are a good compromise and will also look at 200mm ones now.
In answer to your questions, I started out wanting to photograph the Milky Way, but here in Eastern England, at this time of year, it ain't happening. I then saw the images people were producing of deep sky object - galaxies, nebulae, etc., on quite reasonable telephoto lenses, which interested me. I've had a go at a few with my Pentx 55-300 zoom, which were quite promising.
I looked at Orion, but from here it's quite low in the sky and is only visible for an hour after dark. I'm now looking to the Heart & Soul Nebulae, which will stay visible all night. I just need a clear night now.
Stellarium is good for giving the angle of view for various objects. Photopils gives me the focal lengths I need to match the angles of view.
On the subject of tracking, I have successfully used the O-GPS1 Astrotracer on focal lengths up to 300mm. Obviously I can't get 5 min exposures, but I can get ones that are around 45 times as long as for untracked shots (using Photopils again). That meant that at 300mm i was able to get 20 second exposures. I took about 40 and stacked them in Deep Sky Stacker. I also need to re-align the shot after 15 to 20 mins, depending on the target.

**Bob 256** · 05-08-2021, 02:43 PM

Originally posted by PixelPete

Bob thanks for the very comprehensive introduction to astrophotograhy.
I have already been all through all that.............................

From that, it sound's like you're well beyond the basics. I understand now that you are indeed looking for a good lens in the 135mm range. Some of the previous suggestions have been excellent. If you are planning on manual operation of your lens, you might also consider a used medium format lens with mount adapter. I have a pentax 6x7 300mm lens, which gives excellent performance on my K-1 camera. One advantage of a medium format lens is that you're using the center "sweet spot" of a larger lens and edge sharpness is greatly improved (as well as edge color fringing). A lens in the range you're after isn't that expensive used (example below), and some are really good at image quality. The downside is the need to adapt the mount and they are somewhat more bulky than a lens designed for a 35mm camera. Also, many of these don't have a tripod collar or mount so you might have to devise a means to hold the lens/camera combination.

Good luck in your sky shooting.

[Near MINT] Pentax SMC Takumar 6x7 150mm F2.8 Lens for 6x7 67 67II From JAPAN | eBay

PixelPete · 05-09-2021, 01:10 AM

Originally posted by johnha

I'd have a look at the Astrophotography Social Group here on PF. I had a similar question a few weeks ago and the group were very helpful.

My short answer based on some research is that the M200/4 is a really good lens which can be found very cheaply (I paid £20 for mine a couple of years ago). In order to avoid diffraction spikes by stopping down, you can reduce the aperture by using a series of step down rings to 37mm instead - maintaining a circular aperture.

I found the social group. I'll have to investigate further.

The M200/4 looks promising, but is around £75 at the moment. I'll keep an eye on fleabay.

Thanks for the suggestions.

---------- Post added 05-09-21 at 01:35 AM ----------

Originally posted by W412ren

Good advice from @Bob 256

Definitely look at images (poke around on Flickr for example) and then choose your focal lengths.
I've used 20/24/35/50/135/200/400 manual lenses for astro at different times.
Now replaced the short and long ends with a DA*11-18 and telescope and the others are now the Pentax-A series models.

Usage examples on APSC: (There are obviously a lot of other combinations)

200mm will get you Orion's Sword or crop in for M42 and can work on The Pleiades
135/200mm will get Andromeda (even 50mm will get you a very tiny one )
135/200mm will work on eclipses
50mm will fit Orion in the frame and is quite good for isolating a part of the sky and including some landscape
24mm fits Cygnus, the plough and can be useful for star trails.

The 35mm I use on the K-1 in place of the 24mm.

Thanks for that. It's useful information.

---------- Post added 05-09-21 at 01:45 AM ----------

Originally posted by Bob 256

From that, it sound's like you're well beyond the basics. I understand now that you are indeed looking for a good lens in the 135mm range. Some of the previous suggestions have been excellent. If you are planning on manual operation of your lens, you might also consider a used medium format lens with mount adapter. I have a pentax 6x7 300mm lens, which gives excellent performance on my K-1 camera. One advantage of a medium format lens is that you're using the center "sweet spot" of a larger lens and edge sharpness is greatly improved (as well as edge color fringing). A lens in the range you're after isn't that expensive used (example below), and some are really good at image quality. The downside is the need to adapt the mount and they are somewhat more bulky than a lens designed for a 35mm camera. Also, many of these don't have a tripod collar or mount so you might have to devise a means to hold the lens/camera combination.

Good luck in your sky shooting.

[Near MINT] Pentax SMC Takumar 6x7 150mm F2.8 Lens for 6x7 67 67II From JAPAN | eBay

Thanks @Bob 256 . That's a good idea about medium format lenses.

kypfer · 05-09-2021, 02:43 AM - **1 Like**

Originally posted by PixelPete

Which are the best film-era lenses to use for deep sky astrophotography on a modern DSLR (in this case my Pentax K-70)?

I have just got into deep-sky astrophotoraphy and am at present using my modern DSLR zoom lenses. I have heard that prime lenses work better and there are many 135mm examples on eBay at around £30 - £50. There are some 200mm ones that cost a bit more. I've seen good results using modern 135mm lenses, but there are many film-era lenses out there for much less money.

I've read all the lens reviews on this forum, but the problem is that a good lens for normal photography is not necessarily good for astro. So I'm looking for views of people who have used these lenses for DSO work. The ones I've seen are (all 135mm, K mount manual)

Just remember, "modern" lenses have developed a lot since the days of the 135mm prime, and on the K-70 especially, with it's excellent low-light sensitivity, an extra stop is not necessarily a significant advantage, especially if the older lens in question needs to be stopped down a notch or two to sharpen the image.
Having said that, from experience, don't discount the Tamron Adaptall-2 135mm and 200mm medium telephoto lenses, the 135mm f/2.5 especially is an excellent performer, in my opinion … I've yet to give the 200mm a good "astro workout".
Enjoy

angerdan · 05-09-2021, 03:37 AM

Originally posted by PixelPete

Which are the best film-era lenses to use for deep sky astrophotography on a modern DSLR (in this case my Pentax K-70)?

vijaykishan · 05-16-2021, 03:08 AM

Originally posted by Bob 256

First, you need to determine what type of astrophotography you're going to use a lens for. Astrophotography basically falls into three ranges; wide field, narrow field, and planetary. The last usually incorporates an actual telescope because it uses high power (large focal lengths) to shoot very narrow field shots of planets, close star groups, etc., and probably isn't what your after based on your inquiry.

That leaves the first two. 135mm lenses more often fall into the second category where you're trying to shoot nebulae, star clusters, and narrower field (though not very-narrow field) objects. 135mm is good for two reasons, they take in a fair amount of sky and can be had in low f-stop versions for not that much money. Having a lower f-stop is advantageous because of the need for light gathering in shooting dim sky objects using practical exposure times and ISO values. A 135mm may not be the best choice, however (read on).

A lot of the shots you see today, are of the wide-field type and show a vast section of the night sky. These are the first type I mentioned previously. They require short focal length lenses (mostly below 35mm) and many astrophotographers use ultra-wide lenses for this type of astrophotography. Again, you can probably find a low-f-stop, wide angle lens but you might have to pay more for it. IRIX wide field lenses are good choices for these wide-field types, though there are many others which can work well.

Anyway, it's better to start with an idea of what type of shots you're after rather than pick a given focal length and then try to make it fit something it may not be suited for.

In most all cases, you should probably stop the lens down a bit from its widest opening in order to gain sharpness. All lenses are a little "soft" at their widest opening (unless they are a fixed opening lens like a telescope, and then they are designed for best performance "wide open"). Picking a lens offering a low f-stop to begin with, gives you more room to do this (e.g., f1.4 becomes f2.8 instead of f4 becoming f5.6).

Take a look at some astro shots and see which ones you like best, and then try to identify a lens that will do the job in terms of its angular coverage considering what camera you're using (APS-C, Full Frame, etc). That will lead you to the best focal length to consider. Then you can see what's available and visit some reviews to see what is sharpest for what you can afford. Don't pass by the used market. There are some great opportunities there for obtaining a good astro lens.

You didn't mention how you're planning to track the stars and this is a whole subject unto itself. DSLRs can make short non-guided shots possible (using higher ISOs), but that rapidly proves more difficult as the focal length is increased. 135mm is definitely into the "iffy" range where you start having a need for guiding the camera to follow the stars for longer exposure times. A lot of (though not all) wide field shots can be made without guiding. Just something else to consider.

That's a lot of useful information right there. IMHO, the thing that I look for for wide field is coma and fringing, these two IMHO practically have a major influence on stacking.

**Bob 256** · 05-16-2021, 11:21 AM

Originally posted by vijaykishan

That's a lot of useful information right there. IMHO, the thing that I look for for wide field is coma and fringing, these two IMHO practically have a major influence on stacking.

Do you mean stacking or stitching? In stacking, all the images should line up the same even though they are affected by coma and color fringing which means the outer periphery of your image could show these defects depending on how bad they are in the lens used. Of course, it would be desirable to have a lens with minimal coma and color fringing just from an image quality standpoint, and many wide and super-wide angle lenses are deficient in that regard.

Stitching depends on getting star images to overlap and blend so if you try to stitch several super-wide images, your stitching software is going to have a difficult job because of the distortion (and to a less extent coma) in the wide angle images. Using a lens with a narrower field (and less distortion) makes stitching more accomplishable with less work for the software and potentially better results (plus star locations are shifted less resulting in more accurate sky field representations).

vijaykishan · 05-17-2021, 01:28 AM

Originally posted by Bob 256

Do you mean stacking or stitching? In stacking, all the images should line up the same even though they are affected by coma and color fringing which means the outer periphery of your image could show these defects depending on how bad they are in the lens used. Of course, it would be desirable to have a lens with minimal coma and color fringing just from an image quality standpoint, and many wide and super-wide angle lenses are deficient in that regard.

Stitching depends on getting star images to overlap and blend so if you try to stitch several super-wide images, your stitching software is going to have a difficult job because of the distortion (and to a less extent coma) in the wide angle images. Using a lens with a narrower field (and less distortion) makes stitching more accomplishable with less work for the software and potentially better results (plus star locations are shifted less resulting in more accurate sky field representations).

I did mean stacking. The effort that goes into that is IMHO non-trivial hence it is better to have a lens that has as minimal coma as possible, lestheavy cropping becomes necessary. Heavy fringing is another challenge esp whenone is trying to clean them up, as some software usually cull stars that are inthe same range.

On the stitching, you are right, using a normal/short-tele to pan helps.OTOH, star(s) movement (relative to the camera) depends on where the photo isbeing clicked and in which direction the camera pointed at (hence the exposuretime without trackers). If one is in the Northern.H and pointing the cameratowards north the experience would be significantly different at the equatorpointing directly up.

05-08-2021, 02:59 AM	#1
PixelPete New Member Join Date: Jul 2016 Posts: 12	Best film-era lenses for deep-sky astrophotography Staff note: This post may contain affiliate links, which means Pentax Forums may earn a small commission if a visitor clicks through and makes a purchase. If you would like to support the forum directly, you may also make a donation here. Which are the best film-era lenses to use for deep sky astrophotography on a modern DSLR (in this case my Pentax K-70)? I have just got into deep-sky astrophotoraphy and am at present using my modern DSLR zoom lenses. I have heard that prime lenses work better and there are many 135mm examples on eBay at around £30 - £50. There are some 200mm ones that cost a bit more. I've seen good results using modern 135mm lenses, but there are many film-era lenses out there for much less money. I've read all the lens reviews on this forum, but the problem is that a good lens for normal photography is not necessarily good for astro. So I'm looking for views of people who have used these lenses for DSO work. The ones I've seen are (all 135mm, K mount manual): SMC Pentax-M f/3.5 Chinon f/2.8 Takumar f/2.8 Sigma Mini-Tele f/3.5 Hoya HMC f/2.8 These all scored better than 7 in the Pentax Forum Lens Review database.

05-08-2021, 10:30 AM	#6
W412ren Loyal Site Supporter Join Date: Jul 2011 Location: Fareham, Hampshire Photos: Albums Posts: 570	Good advice from @Bob 256 Definitely look at images (poke around on Flickr for example) and then choose your focal lengths. I've used 20/24/35/50/135/200/400 manual lenses for astro at different times. Now replaced the short and long ends with a DA*11-18 and telescope and the others are now the Pentax-A series models. Usage examples on APSC: (There are obviously a lot of other combinations) 200mm will get you Orion's Sword or crop in for M42 and can work on The Pleiades 135/200mm will get Andromeda (even 50mm will get you a very tiny one ) 135/200mm will work on eclipses 50mm will fit Orion in the frame and is quite good for isolating a part of the sky and including some landscape 24mm fits Cygnus, the plough and can be useful for star trails. The 35mm I use on the K-1 in place of the 24mm.

05-08-2021, 02:43 PM	#8
Bob 256 Site Supporter Join Date: Jun 2008 Location: Idaho Photos: Gallery Posts: 2,375	Originally posted by PixelPete Bob thanks for the very comprehensive introduction to astrophotograhy. I have already been all through all that............................. From that, it sound's like you're well beyond the basics. I understand now that you are indeed looking for a good lens in the 135mm range. Some of the previous suggestions have been excellent. If you are planning on manual operation of your lens, you might also consider a used medium format lens with mount adapter. I have a pentax 6x7 300mm lens, which gives excellent performance on my K-1 camera. One advantage of a medium format lens is that you're using the center "sweet spot" of a larger lens and edge sharpness is greatly improved (as well as edge color fringing). A lens in the range you're after isn't that expensive used (example below), and some are really good at image quality. The downside is the need to adapt the mount and they are somewhat more bulky than a lens designed for a 35mm camera. Also, many of these don't have a tripod collar or mount so you might have to devise a means to hold the lens/camera combination. Good luck in your sky shooting. [Near MINT] Pentax SMC Takumar 6x7 150mm F2.8 Lens for 6x7 67 67II From JAPAN \| eBay Last edited by Bob 256; 05-08-2021 at 02:49 PM.

05-09-2021, 01:10 AM	#9
PixelPete New Member Join Date: Jul 2016 Posts: 12 Original Poster	Originally posted by johnha I'd have a look at the Astrophotography Social Group here on PF. I had a similar question a few weeks ago and the group were very helpful. My short answer based on some research is that the M200/4 is a really good lens which can be found very cheaply (I paid £20 for mine a couple of years ago). In order to avoid diffraction spikes by stopping down, you can reduce the aperture by using a series of step down rings to 37mm instead - maintaining a circular aperture. I found the social group. I'll have to investigate further. The M200/4 looks promising, but is around £75 at the moment. I'll keep an eye on fleabay. Thanks for the suggestions. ---------- Post added 05-09-21 at 01:35 AM ---------- Originally posted by W412ren Good advice from @Bob 256 Definitely look at images (poke around on Flickr for example) and then choose your focal lengths. I've used 20/24/35/50/135/200/400 manual lenses for astro at different times. Now replaced the short and long ends with a DA*11-18 and telescope and the others are now the Pentax-A series models. Usage examples on APSC: (There are obviously a lot of other combinations) 200mm will get you Orion's Sword or crop in for M42 and can work on The Pleiades 135/200mm will get Andromeda (even 50mm will get you a very tiny one ) 135/200mm will work on eclipses 50mm will fit Orion in the frame and is quite good for isolating a part of the sky and including some landscape 24mm fits Cygnus, the plough and can be useful for star trails. The 35mm I use on the K-1 in place of the 24mm. Thanks for that. It's useful information. ---------- Post added 05-09-21 at 01:45 AM ---------- Originally posted by Bob 256 From that, it sound's like you're well beyond the basics. I understand now that you are indeed looking for a good lens in the 135mm range. Some of the previous suggestions have been excellent. If you are planning on manual operation of your lens, you might also consider a used medium format lens with mount adapter. I have a pentax 6x7 300mm lens, which gives excellent performance on my K-1 camera. One advantage of a medium format lens is that you're using the center "sweet spot" of a larger lens and edge sharpness is greatly improved (as well as edge color fringing). A lens in the range you're after isn't that expensive used (example below), and some are really good at image quality. The downside is the need to adapt the mount and they are somewhat more bulky than a lens designed for a 35mm camera. Also, many of these don't have a tripod collar or mount so you might have to devise a means to hold the lens/camera combination. Good luck in your sky shooting. [Near MINT] Pentax SMC Takumar 6x7 150mm F2.8 Lens for 6x7 67 67II From JAPAN \| eBay Thanks @Bob 256 . That's a good idea about medium format lenses.

05-17-2021, 01:28 AM	#14
vijaykishan Pentaxian Join Date: Mar 2021 Photos: Gallery Posts: 999	Originally posted by Bob 256 Do you mean stacking or stitching? In stacking, all the images should line up the same even though they are affected by coma and color fringing which means the outer periphery of your image could show these defects depending on how bad they are in the lens used. Of course, it would be desirable to have a lens with minimal coma and color fringing just from an image quality standpoint, and many wide and super-wide angle lenses are deficient in that regard. Stitching depends on getting star images to overlap and blend so if you try to stitch several super-wide images, your stitching software is going to have a difficult job because of the distortion (and to a less extent coma) in the wide angle images. Using a lens with a narrower field (and less distortion) makes stitching more accomplishable with less work for the software and potentially better results (plus star locations are shifted less resulting in more accurate sky field representations). I did mean stacking. The effort that goes into that is IMHO non-trivial hence it is better to have a lens that has as minimal coma as possible, lestheavy cropping becomes necessary. Heavy fringing is another challenge esp whenone is trying to clean them up, as some software usually cull stars that are inthe same range. On the stitching, you are right, using a normal/short-tele to pan helps.OTOH, star(s) movement (relative to the camera) depends on where the photo isbeing clicked and in which direction the camera pointed at (hence the exposuretime without trackers). If one is in the Northern.H and pointing the cameratowards north the experience would be significantly different at the equatorpointing directly up. Last edited by vijaykishan; 05-17-2021 at 01:36 AM. Reason: corrected some grammer

05-08-2021, 03:13 AM	#2
johnha Veteran Member Join Date: Apr 2012 Location: Lancashire, UK Photos: Albums Posts: 1,155	I'd have a look at the Astrophotography Social Group here on PF. I had a similar question a few weeks ago and the group were very helpful. My short answer based on some research is that the M200/4 is a really good lens which can be found very cheaply (I paid £20 for mine a couple of years ago). In order to avoid diffraction spikes by stopping down, you can reduce the aperture by using a series of step down rings to 37mm instead - maintaining a circular aperture.

05-08-2021, 08:27 AM	#3
stevebrot Otis Memorial Pentaxian Join Date: Mar 2007 Location: Vancouver (USA) Photos: Gallery \| Albums Posts: 42,007	Originally posted by johnha My short answer based on some research is that the M200/4 is a really good lens which can be found very cheaply I own that lens, but never though of it in terms of astro...hmmmmm...better give it a go, eh? Steve

05-08-2021, 08:56 AM - 1 Like	#4
Bob 256 Site Supporter Join Date: Jun 2008 Location: Idaho Photos: Gallery Posts: 2,375	First, you need to determine what type of astrophotography you're going to use a lens for. Astrophotography basically falls into three ranges; wide field, narrow field, and planetary. The last usually incorporates an actual telescope because it uses high power (large focal lengths) to shoot very narrow field shots of planets, close star groups, etc., and probably isn't what your after based on your inquiry. That leaves the first two. 135mm lenses more often fall into the second category where you're trying to shoot nebulae, star clusters, and narrower field (though not very-narrow field) objects. 135mm is good for two reasons, they take in a fair amount of sky and can be had in low f-stop versions for not that much money. Having a lower f-stop is advantageous because of the need for light gathering in shooting dim sky objects using practical exposure times and ISO values. A 135mm may not be the best choice, however (read on). A lot of the shots you see today, are of the wide-field type and show a vast section of the night sky. These are the first type I mentioned previously. They require short focal length lenses (mostly below 35mm) and many astrophotographers use ultra-wide lenses for this type of astrophotography. Again, you can probably find a low-f-stop, wide angle lens but you might have to pay more for it. IRIX wide field lenses are good choices for these wide-field types, though there are many others which can work well. Anyway, it's better to start with an idea of what type of shots you're after rather than pick a given focal length and then try to make it fit something it may not be suited for. In most all cases, you should probably stop the lens down a bit from its widest opening in order to gain sharpness. All lenses are a little "soft" at their widest opening (unless they are a fixed opening lens like a telescope, and then they are designed for best performance "wide open"). Picking a lens offering a low f-stop to begin with, gives you more room to do this (e.g., f1.4 becomes f2.8 instead of f4 becoming f5.6). Take a look at some astro shots and see which ones you like best, and then try to identify a lens that will do the job in terms of its angular coverage considering what camera you're using (APS-C, Full Frame, etc). That will lead you to the best focal length to consider. Then you can see what's available and visit some reviews to see what is sharpest for what you can afford. Don't pass by the used market. There are some great opportunities there for obtaining a good astro lens. You didn't mention how you're planning to track the stars and this is a whole subject unto itself. DSLRs can make short non-guided shots possible (using higher ISOs), but that rapidly proves more difficult as the focal length is increased. 135mm is definitely into the "iffy" range where you start having a need for guiding the camera to follow the stars for longer exposure times. A lot of (though not all) wide field shots can be made without guiding. Just something else to consider. Last edited by Bob 256; 05-08-2021 at 09:11 AM.

05-08-2021, 09:56 AM	#5
ProfessorBuzz Loyal Site Supporter Join Date: Feb 2018 Posts: 1,903	Great comments Bob 256. Some of my better Astro shots were taken with 35 f/1.4 stopped down and 50mm f/1.7 stopped down. A tracking mount really becomes necessary in the 200mm+ zone, and guiding beyond that.

05-08-2021, 01:08 PM	#7
PixelPete New Member Join Date: Jul 2016 Posts: 12 Original Poster	Bob thanks for the very comprehensive introduction to astrophotograhy. I have already been all through all that. I am at the stage, as I said in my original post, where I'm looking at film-era prime lenses and am asking for views of those who have used them. A good lens does not necessarily mean a good astro lens. As I said, I'm looking at 135mm primes, as they are good value, are plentiful and are a good compromise and will also look at 200mm ones now. In answer to your questions, I started out wanting to photograph the Milky Way, but here in Eastern England, at this time of year, it ain't happening. I then saw the images people were producing of deep sky object - galaxies, nebulae, etc., on quite reasonable telephoto lenses, which interested me. I've had a go at a few with my Pentx 55-300 zoom, which were quite promising. I looked at Orion, but from here it's quite low in the sky and is only visible for an hour after dark. I'm now looking to the Heart & Soul Nebulae, which will stay visible all night. I just need a clear night now. Stellarium is good for giving the angle of view for various objects. Photopils gives me the focal lengths I need to match the angles of view. On the subject of tracking, I have successfully used the O-GPS1 Astrotracer on focal lengths up to 300mm. Obviously I can't get 5 min exposures, but I can get ones that are around 45 times as long as for untracked shots (using Photopils again). That meant that at 300mm i was able to get 20 second exposures. I took about 40 and stacked them in Deep Sky Stacker. I also need to re-align the shot after 15 to 20 mins, depending on the target.

05-09-2021, 02:43 AM - 1 Like	#10
kypfer Pentaxian Join Date: Jan 2018 Location: Jersey C.I. Posts: 3,593	Originally posted by PixelPete Which are the best film-era lenses to use for deep sky astrophotography on a modern DSLR (in this case my Pentax K-70)? I have just got into deep-sky astrophotoraphy and am at present using my modern DSLR zoom lenses. I have heard that prime lenses work better and there are many 135mm examples on eBay at around £30 - £50. There are some 200mm ones that cost a bit more. I've seen good results using modern 135mm lenses, but there are many film-era lenses out there for much less money. I've read all the lens reviews on this forum, but the problem is that a good lens for normal photography is not necessarily good for astro. So I'm looking for views of people who have used these lenses for DSO work. The ones I've seen are (all 135mm, K mount manual) Just remember, "modern" lenses have developed a lot since the days of the 135mm prime, and on the K-70 especially, with it's excellent low-light sensitivity, an extra stop is not necessarily a significant advantage, especially if the older lens in question needs to be stopped down a notch or two to sharpen the image. Having said that, from experience, don't discount the Tamron Adaptall-2 135mm and 200mm medium telephoto lenses, the 135mm f/2.5 especially is an excellent performer, in my opinion … I've yet to give the 200mm a good "astro workout". Enjoy

05-09-2021, 03:37 AM	#11
angerdan Pentaxian Join Date: Feb 2015 Photos: Gallery \| Albums Posts: 2,639	Originally posted by PixelPete Which are the best film-era lenses to use for deep sky astrophotography on a modern DSLR (in this case my Pentax K-70)? Which criterias are making a lens good for deep sky astrophotography? And what separates them from the best lenses for this subject? Some answers could be hidden here: Pentax full frame lenses for infrared photography - PentaxForums.com Astrophotography + SMC Pentax-FA* 24mm F2 AL [IF] - PentaxForums.com Astophotography: K-200 F4 or K-200 F2.5 - PentaxForums.com Night photo/Astrotracer best lens advice - PentaxForums.com Which lens for Astrophotography? - PentaxForums.com Astro lens shoot out... what and why - PentaxForums.com Star photography - PentaxForums.com Which lenses are your using for startrails and night sky - PentaxForums.com Good Cheap Lens for Astrophotography - PentaxForums.com Seeking astrophotography lens recommendations - PentaxForums.com Lens for starry nights - PentaxForums.com Maybe lenses which have a higher IR transmission are more suitable. Infrared lens for Pentax - PentaxForums.com Infrared compatible lenses - PentaxForums.com Infrared ok lenses - ie no hotspots - PentaxForums.com Lenses usable for infrared photography? - PentaxForums.com Which Lens for InfraRed - PentaxForums.com What's the reason you're asking only for film era lenses? Who Needs Modern Lenses? - Page 2 - PentaxForums.com Who Needs Modern Lenses? - PentaxForums.com There are many lenses after 2004 which are good and excellent performers in general. <= F5.6 <= 1105g Lenses with Autofocus compatible with the Pentax K-70 \| PentaxForums.com

05-16-2021, 03:08 AM	#12
vijaykishan Pentaxian Join Date: Mar 2021 Photos: Gallery Posts: 999	Originally posted by Bob 256 First, you need to determine what type of astrophotography you're going to use a lens for. Astrophotography basically falls into three ranges; wide field, narrow field, and planetary. The last usually incorporates an actual telescope because it uses high power (large focal lengths) to shoot very narrow field shots of planets, close star groups, etc., and probably isn't what your after based on your inquiry. That leaves the first two. 135mm lenses more often fall into the second category where you're trying to shoot nebulae, star clusters, and narrower field (though not very-narrow field) objects. 135mm is good for two reasons, they take in a fair amount of sky and can be had in low f-stop versions for not that much money. Having a lower f-stop is advantageous because of the need for light gathering in shooting dim sky objects using practical exposure times and ISO values. A 135mm may not be the best choice, however (read on). A lot of the shots you see today, are of the wide-field type and show a vast section of the night sky. These are the first type I mentioned previously. They require short focal length lenses (mostly below 35mm) and many astrophotographers use ultra-wide lenses for this type of astrophotography. Again, you can probably find a low-f-stop, wide angle lens but you might have to pay more for it. IRIX wide field lenses are good choices for these wide-field types, though there are many others which can work well. Anyway, it's better to start with an idea of what type of shots you're after rather than pick a given focal length and then try to make it fit something it may not be suited for. In most all cases, you should probably stop the lens down a bit from its widest opening in order to gain sharpness. All lenses are a little "soft" at their widest opening (unless they are a fixed opening lens like a telescope, and then they are designed for best performance "wide open"). Picking a lens offering a low f-stop to begin with, gives you more room to do this (e.g., f1.4 becomes f2.8 instead of f4 becoming f5.6). Take a look at some astro shots and see which ones you like best, and then try to identify a lens that will do the job in terms of its angular coverage considering what camera you're using (APS-C, Full Frame, etc). That will lead you to the best focal length to consider. Then you can see what's available and visit some reviews to see what is sharpest for what you can afford. Don't pass by the used market. There are some great opportunities there for obtaining a good astro lens. You didn't mention how you're planning to track the stars and this is a whole subject unto itself. DSLRs can make short non-guided shots possible (using higher ISOs), but that rapidly proves more difficult as the focal length is increased. 135mm is definitely into the "iffy" range where you start having a need for guiding the camera to follow the stars for longer exposure times. A lot of (though not all) wide field shots can be made without guiding. Just something else to consider. That's a lot of useful information right there. IMHO, the thing that I look for for wide field is coma and fringing, these two IMHO practically have a major influence on stacking.

05-16-2021, 11:21 AM	#13
Bob 256 Site Supporter Join Date: Jun 2008 Location: Idaho Photos: Gallery Posts: 2,375	Originally posted by vijaykishan That's a lot of useful information right there. IMHO, the thing that I look for for wide field is coma and fringing, these two IMHO practically have a major influence on stacking. Do you mean stacking or stitching? In stacking, all the images should line up the same even though they are affected by coma and color fringing which means the outer periphery of your image could show these defects depending on how bad they are in the lens used. Of course, it would be desirable to have a lens with minimal coma and color fringing just from an image quality standpoint, and many wide and super-wide angle lenses are deficient in that regard. Stitching depends on getting star images to overlap and blend so if you try to stitch several super-wide images, your stitching software is going to have a difficult job because of the distortion (and to a less extent coma) in the wide angle images. Using a lens with a narrower field (and less distortion) makes stitching more accomplishable with less work for the software and potentially better results (plus star locations are shifted less resulting in more accurate sky field representations).

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