How to chose your tele for AP?

Hi everyone,

I decided I want to get myself a nice tele for AP, since I cant keep borrowing my friend's vintage lense of course, and that one is too short for my full frame anyways.
I found lot of suggestions around, but little explanation on how to choose, expecially if someone can't afford the new super pricy f2.8 primes.

I have many questions so I'll get started.
- How do you know if a tele fits astrophotography, in this case DSO, or not?
What are the charateristics you should check?

- Are zoom lenses viable or just not worth?

- What focal lenght (on full frame and APS-C) one can possibly use with good results on a small tracker with and without autoguiding? (In my case Star Adventure) ?

- Are teleconverters a good idea? If yes, even on zooms?

- Is something above f/4 still good?

Last, feel free to provide a little list of your best choices.

Thank you
Federico

FMelis said:

Hi everyone,
I decided I want to get myself a nice tele for AP, since I cant keep borrowing my friend's vintage lense of course, and that one is too short for my full frame anyways.
I found lot of suggestions around, but little explanation on how to choose, expecially if someone can't afford the new super pricy f2.8 primes.
I have many questions so I'll get started.
- How do you know if a tele fits astrophotography, in this case DSO, or not?
What are the charateristics you should check?

Click to expand...

You want to make sure the lens is mostly free of distortions. Some, such as light fall-off in the corners, chromatic aberrations, and barrel/pincushion distortions can be fixed in processing. Others, like Coma, are much harder. You should generally look for a lens that creates round stars and is sharp to the edges.

FMelis said:

- Are zoom lenses viable or just not worth?

Click to expand...

Yes. There are zoom lenses today that are just as good as some primes. You really need to examine each option on a case-by-case basis.

FMelis said:

- What focal lenght (on full frame and APS-C) one can possibly use with good results on a small tracker with and without autoguiding? (In my case Star Adventure) ?

Click to expand...

From everything I have seen, the Star Adventurer on its own is best kept to lenses under 200mm but it can handle up to 300mm lenses with a guide system. Without that, the periodic error is too high. Some people say you can push it harder than that, but I would imagine the "keeper" rate would drop quite a bit, as would your exposure times.

FMelis said:

- Are teleconverters a good idea? If yes, even on zooms?

Click to expand...

Teleconverters are generally okay as long as they have been tested to work well with the lens you are using. With AP we don't need auto-focus, so that drawback isn't something we worry about losing. Roger Clark here uses them with good results

FMelis said:

- Is something above f/4 still good?

Click to expand...

If you're above f/4 you can still get great results, you just need longer exposure times. You will want to make sure you have a solid mount with low tracking error, and are willing to take longer and more exposures. Most telescopes have apertures above f/4 and they do fine - f/2.8 is really a unique realm of high-end lenses that telescopes generally can't compete in. For example, Roger Clark here uses the Canon EF 300mm f/2.8L IS II USM Lens. I'll let you look up the price tag ;-)

FMelis said:

Last, feel free to provide a little list of your best choices.
Thank you
Federico

Click to expand...

Tell us what camera you plan on using so we can narrow it down.

1llusive said:

FMelis said:

Hi everyone,
I decided I want to get myself a nice tele for AP, since I cant keep borrowing my friend's vintage lense of course, and that one is too short for my full frame anyways.
I found lot of suggestions around, but little explanation on how to choose, expecially if someone can't afford the new super pricy f2.8 primes.
I have many questions so I'll get started.
- How do you know if a tele fits astrophotography, in this case DSO, or not?
What are the charateristics you should check?

Click to expand...

You want to make sure the lens is mostly free of distortions. Some, such as light fall-off in the corners, chromatic aberrations, and barrel/pincushion distortions can be fixed in processing. Others, like Coma, are much harder. You should generally look for a lens that creates round stars and is sharp to the edges.

1llusive said:

- Are zoom lenses viable or just not worth?

Click to expand...

Yes. There are zoom lenses today that are just as good as some primes. You really need to examine each option on a case-by-case basis.

1llusive said:

- What focal lenght (on full frame and APS-C) one can possibly use with good results on a small tracker with and without autoguiding? (In my case Star Adventure) ?

Click to expand...

From everything I have seen, the Star Adventurer on its own is best kept to lenses under 200mm but it can handle up to 300mm lenses with a guide system. Without that, the periodic error is too high. Some people say you can push it harder than that, but I would imagine the "keeper" rate would drop quite a bit, as would your exposure times.

Click to expand...

Hi Illusive,
I've been trying to push the Star Adventurer and I think I get pretty decent tracking at 200mm on APSC, probably I can get away with 300 on FF?
I've seen Roger doing 1 minute or 2 with a 300mm and even 420 (with the converter) on APSC, no guiding (I'm aware his astrotrac has less error, but still 420!)
Also I have seen some dudes pushing quite longer exposures with the autoguiding:
for example this guy at 400mm:

1llusive said:

1llusive said:

- Are teleconverters a good idea? If yes, even on zooms?

Click to expand...

Teleconverters are generally okay as long as they have been tested to work well with the lens you are using. With AP we don't need auto-focus, so that drawback isn't something we worry about losing. Roger Clark here uses them with good results

Click to expand...

Yep, I've seen his work with the converters, mostly on his 2.8 tho!
I'll see if it's worth on cheaper, slower lenses or not

1llusive said:

1llusive said:

- Is something above f/4 still good?

Click to expand...

If you're above f/4 you can still get great results, you just need longer exposure times. You will want to make sure you have a solid mount with low tracking error, and are willing to take longer and more exposures. Most telescopes have apertures above f/4 and they do fine - f/2.8 is really a unique realm of high-end lenses that telescopes generally can't compete in. For example, Roger Clark here uses the Canon EF 300mm f/2.8L IS II USM Lens. I'll let you look up the price tag ;-)

Click to expand...

That's a big problem here, getting longer exposures wouldn't be possible on a small tracker. I don't know how far you can push the exposure with the autoguiding, but I guess not so much with longer lenses.
Very long focal lenghts like a telescope wouldn't be possible either.
I'm aware of the 300 2.8 price, and it's really too much, even used ones, not to mention the 400 2.8!
The 300 f4 used seems affordable to me (the Nikon old one).

1llusive said:

FMelis said:

Last, feel free to provide a little list of your best choices.
Thank you
Federico

Click to expand...

Tell us what camera you plan on using so we can narrow it down.

Click to expand...

Nikon d810

What's your budget, and what do you want to photograph?

The good ol' AF Nikkor 180ED is cheap, and a lot of fun. good for lots of targets, but might not be right for the ones you want. It'll also ride comfortably on a tracker. I use a D600 rather than a D810, but I've had no problem using that lens on my iOptron sky tracker pro; I do use the counterweight kit with that combo, but it works fine. Focus ring needs to be taped down, as it will shift as the lens points higher in the sky.

if you need something a little longer, the new 300f4 is pretty sporty, if a little pricey. it's still light enough you could use it on the low to mid range tracking mounts with a fair amount of success, though your polar alignment is going to be extra critical here.

if you're really on a budget, the latest revision of the 70-300 zoom isn't totally worthless. it's going to have some aberration in the corners when run at 300f5.6, but it's not awful. it's also light and cheap.

Personally, I wouldn't bother trying much of anything heavier or longer than any of these without stepping up to the next tier of mount; it's not that it can't be done at all, but it's not going to be easy or fun, IMO.

Matt Fulghum said:

What's your budget, and what do you want to photograph?

The good ol' AF Nikkor 180ED is cheap, and a lot of fun. good for lots of targets, but might not be right for the ones you want. It'll also ride comfortably on a tracker. I use a D600 rather than a D810, but I've had no problem using that lens on my iOptron sky tracker pro; I do use the counterweight kit with that combo, but it works fine. Focus ring needs to be taped down, as it will shift as the lens points higher in the sky.

if you need something a little longer, the new 300f4 is pretty sporty, if a little pricey. it's still light enough you could use it on the low to mid range tracking mounts with a fair amount of success, though your polar alignment is going to be extra critical here.

if you're really on a budget, the latest revision of the 70-300 zoom isn't totally worthless. it's going to have some aberration in the corners when run at 300f5.6, but it's not awful. it's also light and cheap.

Personally, I wouldn't bother trying much of anything heavier or longer than any of these without stepping up to the next tier of mount; it's not that it can't be done at all, but it's not going to be easy or fun, IMO.

Click to expand...

I would be weary of the new 300 f/4 PF - it uses a Fresnel lens design to cut the weight in half. The downside is the Fresnel elements are very prone to flare from bright point sources. Stars may trigger that. I haven't seen anyone try though.

Otherwise, you're right, it should be good, and the lower weight helps with tracking.

In my case the longest tele for astrophotography is a CZ 2/135mm lens.

When going for more reach small telescopes fit the bill. Have no problem imaging at f/5 or so when using larger apertures (talking lens diameter here). Usually exposing 64x1min and stacking when working telescopically.

Usually a good 80mm refractor (with field flattened or reducer) outperform the ordinary 4/300mm lenses around - but are optimal for one thing only - infinity.

You're right about the optics, but I'd not want to try and run an 80mm telescope on a star adventurer. Seems like it'd be tough to get enough stability.

Matt Fulghum said:

You're right about the optics, but I'd not want to try and run an 80mm telescope on a star adventurer. Seems like it'd be tough to get enough stability.

Click to expand...

I'll reply to everything here for the sake of simplicity.

My main photography is landscape, so firstly I need a tele for that, a good zoom one like the 70-200 2.8 or the 80-400 4.5/5.6 (most likely the second).
I would try to use such tele for AP aswell, but I understand it won't be super good for that. I've seen some people using the 80-400 with great results but still, not the best choice for AP.
-
This being said: I will surely invest some money specifically for AP, because I'm loving it and I want to improve.
I think buying a small telescope would be awesome and probably outperfoming any tele, BUT I never ever seen anybody tracking a telescope on a Star Adventurer, not even with guiding, so I don't really know if its doable with nice results or not.
-
I've seen people tracking 400 or 500 mm on APSC guided with really great results tho, myself I have tested 500 mm on my FF (no guiding) and it seems like it's doable with around 1 minute exposures; you need a pretty fast lense tho..
Long and fast primes are very expensive tho, probably I could afford an old version used 300 f/4, but wouldnt it be a bit short on Full Frame?

FMelis said:

I think buying a small telescope would be awesome and probably outperfoming any tele, BUT I never ever seen anybody tracking a telescope on a Star Adventurer, not even with guiding, so I don't really know if its doable with nice results or not.

Click to expand...

A friend has used a TS65 (420mm focal length) + dSLR on the Star Adventurer guided and has had pin sharp stars on 10 minute exposures. He mounted the guidescope on the counterbalance bar to reduce the overall weight.

FMelis said:

Long and fast primes are very expensive tho, probably I could afford an old version used 300 f/4, but wouldnt it be a bit short on Full Frame?

Click to expand...

As you don't need any lens/camera connections for autofocus or aperture data to be passed, you can use any brand of prime lens with the appropriate adapter.

I got a lovely 200mm f/4 Pentax SMC (full frame capable) on ebay for about £70. Works a treat on both my Pentax K5 and my Canon modded dSLR (with an PK-EF adapter)

GFamily said:

FMelis said:

I think buying a small telescope would be awesome and probably outperfoming any tele, BUT I never ever seen anybody tracking a telescope on a Star Adventurer, not even with guiding, so I don't really know if its doable with nice results or not.

Click to expand...

A friend has used a TS65 (420mm focal length) + dSLR on the Star Adventurer guided and has had pin sharp stars on 10 minute exposures. He mounted the guidescope on the counterbalance bar to reduce the overall weight.

Click to expand...

Damn 10 minute exposures at 420 seems amazing!
The only issue then would be the weight, I will keep this in mind in the future when I choose to get a telescope

GFamily said:

GFamily said:

Long and fast primes are very expensive tho, probably I could afford an old version used 300 f/4, but wouldnt it be a bit short on Full Frame?

Click to expand...

As you don't need any lens/camera connections for autofocus or aperture data to be passed, you can use any brand of prime lens with the appropriate adapter.

I got a lovely 200mm f/4 Pentax SMC (full frame capable) on ebay for about £70. Works a treat on both my Pentax K5 and my Canon modded dSLR (with an PK-EF adapter)

Click to expand...

Im actually using my friend's vintage lenses at moment because I dont own any tele at all yet, like a Tamron 80-210, but its very short on full frame and it wont focus at infinity over 160mm)

The problem with this option is I'm shooting Nikon and, unlike with Canon, many lenses have issues focusing at infinity, like the M42 or Pentax-K lenses.
I would need a glass adaptor for that but it kills the image quality, so I must find old Nikkor lenses, and they are not so cheap; or I would need to get a Canon for AP, but I don't really have the money to afford that any soon.

FMelis said:

GFamily said:

FMelis said:

I think buying a small telescope would be awesome and probably outperfoming any tele, BUT I never ever seen anybody tracking a telescope on a Star Adventurer, not even with guiding, so I don't really know if its doable with nice results or not.

Click to expand...

A friend has used a TS65 (420mm focal length) + dSLR on the Star Adventurer guided and has had pin sharp stars on 10 minute exposures. He mounted the guidescope on the counterbalance bar to reduce the overall weight.

Click to expand...

Damn 10 minute exposures at 420 seems amazing!
The only issue then would be the weight, I will keep this in mind in the future when I choose to get a telescope

FMelis said:

FMelis said:

Long and fast primes are very expensive tho, probably I could afford an old version used 300 f/4, but wouldnt it be a bit short on Full Frame?

Click to expand...

As you don't need any lens/camera connections for autofocus or aperture data to be passed, you can use any brand of prime lens with the appropriate adapter.

I got a lovely 200mm f/4 Pentax SMC (full frame capable) on ebay for about £70. Works a treat on both my Pentax K5 and my Canon modded dSLR (with an PK-EF adapter)

Click to expand...

Im actually using my friend's vintage lenses at moment because I dont own any tele at all yet, like a Tamron 80-210, but its very short on full frame and it wont focus at infinity over 160mm)
The problem with this option is I'm shooting Nikon and, unlike with Canon, many lenses have issues focusing at infinity, like the M42 or Pentax-K lenses.
I would need a glass adaptor for that but it kills the image quality, so I must find old Nikkor lenses, and they are not so cheap; or I would need to get a Canon for AP, but I don't really have the money to afford that any soon.

Click to expand...

Use what you have access to - and practice. Learning astrophotography is a bit like learning to play the piano - the instrument is important but will not bring pleasant results if lacking skill and not mastering the instrument - so hone your skills, then you are ready to master that Steinway (or great lenses in this case) when they become available.

Guess most of us had a modest start in astrophotography - remember humble gear and lousy results from the film era - but the skill gained is not easily forgotten. Knowledge and skill are still my greatest assets when it comes to astrophotography.

And for longer focal lenghts:

50mm lenses are easy to master.

135mm lenses become challenging.

500mm lenses are devils.

And telescopes are still worse - but still lots of rewarding fun for the persistent ones! :-D

FMelis said:

Hi everyone,
I decided I want to get myself a nice tele for AP, since I cant keep borrowing my friend's vintage lense of course, and that one is too short for my full frame anyways.

I found lot of suggestions around, but little explanation on how to choose, expecially if someone can't afford the new super pricy f2.8 primes.

I have many questions so I'll get started.
- How do you know if a tele fits astrophotography, in this case DSO
- What focal lenght (on full frame and APS-C) one can possibly use with good results on a small tracker with and without autoguiding?
Last, feel free to provide a little list of your best choices.

Click to expand...

Before you buy a lens, what targets are you specifically most interested interested in ? "DSO's can be HUGE, or minuscule. You don't a need a long telephoto for many objects which also makes tracking far easier.


These were all taken using an 85mm lens on my APS-c Nikon so figure ~ a 135mm FOV on a FF.







Without guiding, you are going to struggle at 200-300 mm+


These were taken with the old manual Nikon AIS 180ED lens on my APS-c Nikon.







And while a faster prime is normally always better, I've gotten good results using the venerable Nikon 70-300 VRii zoom. Tracking can make up for lens speed to a point.





Beyond 300mm, I just use one of my telescopes on my big GEM.


Proper target selection to fit your available lens options is more cost effective, than trying to buy longer and longer lens.

Trollmannx said:

FMelis said:

GFamily said:

FMelis said:

I think buying a small telescope would be awesome and probably outperfoming any tele, BUT I never ever seen anybody tracking a telescope on a Star Adventurer, not even with guiding, so I don't really know if its doable with nice results or not.

Click to expand...

A friend has used a TS65 (420mm focal length) + dSLR on the Star Adventurer guided and has had pin sharp stars on 10 minute exposures. He mounted the guidescope on the counterbalance bar to reduce the overall weight.

Click to expand...

Damn 10 minute exposures at 420 seems amazing!
The only issue then would be the weight, I will keep this in mind in the future when I choose to get a telescope

Tristimulus said:

Tristimulus said:

Long and fast primes are very expensive tho, probably I could afford an old version used 300 f/4, but wouldnt it be a bit short on Full Frame?

Click to expand...

As you don't need any lens/camera connections for autofocus or aperture data to be passed, you can use any brand of prime lens with the appropriate adapter.

I got a lovely 200mm f/4 Pentax SMC (full frame capable) on ebay for about £70. Works a treat on both my Pentax K5 and my Canon modded dSLR (with an PK-EF adapter)

Click to expand...

Im actually using my friend's vintage lenses at moment because I dont own any tele at all yet, like a Tamron 80-210, but its very short on full frame and it wont focus at infinity over 160mm)
The problem with this option is I'm shooting Nikon and, unlike with Canon, many lenses have issues focusing at infinity, like the M42 or Pentax-K lenses.
I would need a glass adaptor for that but it kills the image quality, so I must find old Nikkor lenses, and they are not so cheap; or I would need to get a Canon for AP, but I don't really have the money to afford that any soon.

Click to expand...

Use what you have access to - and practice. Learning astrophotography is a bit like learning to play the piano - the instrument is important but will not bring pleasant results if lacking skill and not mastering the instrument - so hone your skills, then you are ready to master that Steinway (or great lenses in this case) when they become available.

Guess most of us had a modest start in astrophotography - remember humble gear and lousy results from the film era - but the skill gained is not easily forgotten. Knowledge and skill are still my greatest assets when it comes to astrophotography.

And for longer focal lenghts:

50mm lenses are easy to master.

135mm lenses become challenging.

500mm lenses are devils.

And telescopes are still worse - but still lots of rewarding fun for the persistent ones! :-D

Click to expand...

Unluckily I don't have access to anything higher than 24mm.
I can only use my friends 80-210 and 500 f8 vintage lenses when we shoot astrophotography together (he doesnt have a mount).
The first lens is too short on my full frame (will only focus at 160ish and not longer) and the second is too slow for unguided Star Adventurer tracking, and of course I don't want to keep using someone else's lenses or wait for someone else's whenever I want to shoot.
There is a lot to learn indeed, and I need/want to get out and shoot as much as possible, even alone, and do my own stuff!

swimswithtrout said:

FMelis said:

Hi everyone,
I decided I want to get myself a nice tele for AP, since I cant keep borrowing my friend's vintage lense of course, and that one is too short for my full frame anyways.

I found lot of suggestions around, but little explanation on how to choose, expecially if someone can't afford the new super pricy f2.8 primes.

I have many questions so I'll get started.
- How do you know if a tele fits astrophotography, in this case DSO
- What focal lenght (on full frame and APS-C) one can possibly use with good results on a small tracker with and without autoguiding?
Last, feel free to provide a little list of your best choices.

Click to expand...

Before you buy a lens, what targets are you specifically most interested interested in ? "DSO's can be HUGE, or minuscule. You don't a need a long telephoto for many objects which also makes tracking far easier.

These were all taken using an 85mm lens on my APS-c Nikon so figure ~ a 135mm FOV on a FF.

Without guiding, you are going to struggle at 200-300 mm+

These were taken with the old manual Nikon AIS 180ED lens on my APS-c Nikon.

And while a faster prime is normally always better, I've gotten good results using the venerable Nikon 70-300 VRii zoom. Tracking can make up for lens speed to a point.

Beyond 300mm, I just use one of my telescopes on my big GEM.

Proper target selection to fit your available lens options is more cost effective, than trying to buy longer and longer lens.

Click to expand...

I don't have anything longer than 50.
I've been shooting at around 50mm and180mm on a DX and at 500mm on my FF, last two and the DX from a friend who shoots with me.
50 definitely too short, I only like it for nightscapes, 180 on APSC still too short for my liking and the 500 one way too dark and long without guiding.
This was the first night at around 180 on apsc:







I don't want anything shorter than that, in fact some more would be better, so around 300-400 on my FF.
I like nightscapes but I dont like much huge objects alone, I've tried some, and not planning to buy anything longer than 50 and shorter than 300 in the near future, the only exception being the Nikon 80-400 that I will need for my landscape photography.
I've seen Roger Clark and other people using up to 420mm on APSC without guiding with good results (Clark has a better mount tho and can get away with shorter exposures because of the 2.8 at 300).

FMelis said:

I've been shooting at around 50mm and180mm on a DX and at 500mm on my FF,

50 definitely too short, I only like it for nightscapes, 180 on APSC still too short for my liking and the 500 one way too dark and long without guiding.

This was the first night at around 180 on apsc:



I don't want anything shorter than that, in fact some more would be better, so around 300-400 on my FF......I've seen Roger Clark and other people using up to 420mm on APSC without guiding with good results (Clark has a better mount tho).

Click to expand...

The primary axiom of astrophotography is mount, mount, MOUNT !!!

Without the proper mount, you're just wasting time and money trying to use anything longer than 300mm on your FF, the equivalent FOV of the 180mm on an APS-c, using your Star Adventurer,

You need to upgrade your mount, not your lens' if you're truly serious about AP.

FMelis said:

This was the first night at around 180 on apsc:...

I don't want anything shorter than that, in fact some more would be better, so around 300-400 on my FF.
I like nightscapes but I dont like much huge objects alone, I've tried some, and not planning to buy anything longer than 50 and shorter than 300 in the near future, the only exception being the Nikon 80-400 that I will need for my landscape photography.
I've seen Roger Clark and other people using up to 420mm on APSC without guiding with good results (Clark has a better mount tho and can get away with shorter exposures because of the 2.8 at 300).

Click to expand...

At 420 mm, my system is f/4. When windy, I do 30 second exposures.

People are obsessed with exposure time, and often with dynamic range.

With modern cameras 30 second exposures are just fine. Double the exposure time and the dynamic range drops by 2. An 8-minute exposure has 4 stops less dynamic range as a 30 second exposure. I would argue that a 4 stop loss in dynamic range is worse than a few percent increase in read noise contribution due to short exposure time with a short exposure.

Roger

FMelis said:

Hi everyone, I decided I want to get myself a nice tele for AP, since I cant keep borrowing my friend's

I have many questions so I'll get started.

- What focal length (on full frame and APS-C) one can possibly use with good results on a small tracker without autoguiding? (In my case Star Adventure) ?

Thank you
Federico

Click to expand...

On a Star Adventure, you need to keep it to 200mm max and much less for consistency. If you're willing to toss out 30-40% of your time and effort beyond a 45-60" exposure using a "slow" f4 or worse you can try a 300mm lens.



These bargain mounts are all designed around using a ~100mm lens max.. Start stretching that boundary too much and all of the ugly warts start popping up.

rnclark said:

People are obsessed with exposure time, and often with dynamic range.

With modern cameras 30 second exposures are just fine.

Click to expand...

At f2.8 . Most of us shoot at f5 to f7 at the longer lengths the OP specifies.

rnclark said:

Double the exposure time and the dynamic range drops by 2. An 8-minute exposure has 4 stops less dynamic range as a 30 second exposure. I would argue that a 4 stop loss in dynamic range is worse than a few percent increase in read noise contribution due to short exposure time with a short exposure.

Roger

Click to expand...

Again you're assuming that "everyone" has access to an f2.8 lens. Most of "us" are limited to f5/ f5.6 as a starting point using a 400mm+ lens/reduced APO and many/most shoot at f6/ f7.