Telescope or telephoto lens - advice / recommendation welcome

crowley213 said:

All,

Still a newbie in astrophotography I am looking for some advice / recommendation regarding telescope vs telephoto lens.

At this moment I can either use my Fuji X-T3 w/ 50-140mm f/2.8 plus 2xTC or my wife's (!) Nikon D750 w/ 70-200mm f/2.8 VR (1st gen) plus TC-17EII when I want to shoot deep space objects instead of more wide field milky way.

The results with these combinations are not that bad, at least for me as a beginner, but they are also not really satisfying, especially considering the loss in IQ using a teleconverter.

Therefore I am looking now for a "better" solution and in here I would be thankful for some information!

Important information upfront: At this moment I am using the Star Adventurer 2i star tracker, means I am looking for a solution that can be handled by this tracker.

Solutions I take into consideration at this moment:

- William Optics ZenithStar Z61II (approx. $590 plus $210 for flattener)

- William Optics RedCat (approx. $820)

- Sigma 150-600 C (approx. $900)

- Tamron 150-600 G2 (approx. $1,200)

From my (till limited) point of view:

- The lenses would also give me the possibility to use them for birding, even there would be better solutions for that type of shooting, e.g. Nikon 200-500 or Sigma 150-600 S)

- The lenses would give me more focal length, but IQ at 500-600mm is also not perfect

- The lenses are a little heavier (300-500gr)

- The William Optics telescopes are highly praised / recommended in reviews

- The ZenithStar 61 is 360mm with f/5.9, the RedCat 250mm with f/4.9, means I would exchange focal length for light gathering capability

- Both telescopes seem to be usable without problem with my tracker or the iOptron Sky Guider Pro which is similar reg. capacities

My questions now:

- What is the technical difference in between the both telescopes, honestly I do not really understand that aspect?

- For pure astrophotography, would the telescopes be better regarding IQ than a lens at the same focal length?

- What would be your recommendation, based on your experience?

Again, thankful for every information, hint and advice!

Herbert

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Jared Willson said:

The Zenithstar is a 61mm doublet meaning there is a pair of lenses at the front of the telescope and that's it. Best for visual use, though it can certainly adapt to photographic use. It would need a field flattener with either of the two cameras you are considering, and likely would vignette significantly with the D750.

The Redcat 51 is designed for imaging. It is a Petzval design meaning it has an integrated field flattener so stars at the edges of the field will be well corrected. It is also designed to fully illuminate a full frame camera.

Of the two, I would definitely recommend the Redcat for your intended use. Not even close. I know it has a bit less aperture, but it is well regarded for wide field astrophotography. The ZenithStar is primarily intended as a light weight visual scope.

Telescopes may or may not be better than photographic lenses of the same focal length. In general, telescopes are much simpler designs and are therefore a bit more likely to actually perform at their best--less chance of elements being decentered or tilted if you only have a couple or three elements. Also, telescopes are generally not designed to be as fast as camera lenses, so, again, the tolerances are easier to manage. Basically, the curves in the glass are less steep. That's an oversimplification, but still generally true. Finally, telescopes can be optimized to work at infinity focus whereas camera lenses involve compromises that let them perform well at a range of focal distances.

Camera lenses, one would think, would struggle to compete then for astrophotography. However, there are economies of scale that really help photographic lenses. Because they are manufactured in vastly higher numbers, R&D costs, tooling, etc. are recouped over a much larger volume of production. That means even moderately priced photographic lenses may have a fair amount of design work and exotic glass with aspheric surfaces. Telescopes in the price range you are thinking about never have aspheric glass. That can make a difference in edge performance.

Generally, telescopes that are sold for imaging are usually very good for imaging. You can get a dud, but the designs are solid and usually executed well. A photographic lens may or may not perform well as an astrograph. You need to find other photographs taken with that lens to make a determination. There might be a lot of coma or astigmatism in the corners. The field may not be all that flat. There is simply more variability with camera lenses since this isn't explicitly what they are designed for.

I can't speak to the specific photographic lenses you are considering. Don't know enough about them to know whether they will be any good for astrophotography. Generally, though, only pro grade telephoto zooms do well at the longer focal lengths. Unless you desperately want a double duty birding/astrophotography lens, stick with the RedCat.

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crowley213 said:

Jared Willson said:

The Zenithstar is a 61mm doublet meaning there is a pair of lenses at the front of the telescope and that's it. Best for visual use, though it can certainly adapt to photographic use. It would need a field flattener with either of the two cameras you are considering, and likely would vignette significantly with the D750.

The Redcat 51 is designed for imaging. It is a Petzval design meaning it has an integrated field flattener so stars at the edges of the field will be well corrected. It is also designed to fully illuminate a full frame camera.

Of the two, I would definitely recommend the Redcat for your intended use. Not even close. I know it has a bit less aperture, but it is well regarded for wide field astrophotography. The ZenithStar is primarily intended as a light weight visual scope.

Telescopes may or may not be better than photographic lenses of the same focal length. In general, telescopes are much simpler designs and are therefore a bit more likely to actually perform at their best--less chance of elements being decentered or tilted if you only have a couple or three elements. Also, telescopes are generally not designed to be as fast as camera lenses, so, again, the tolerances are easier to manage. Basically, the curves in the glass are less steep. That's an oversimplification, but still generally true. Finally, telescopes can be optimized to work at infinity focus whereas camera lenses involve compromises that let them perform well at a range of focal distances.

Camera lenses, one would think, would struggle to compete then for astrophotography. However, there are economies of scale that really help photographic lenses. Because they are manufactured in vastly higher numbers, R&D costs, tooling, etc. are recouped over a much larger volume of production. That means even moderately priced photographic lenses may have a fair amount of design work and exotic glass with aspheric surfaces. Telescopes in the price range you are thinking about never have aspheric glass. That can make a difference in edge performance.

Generally, telescopes that are sold for imaging are usually very good for imaging. You can get a dud, but the designs are solid and usually executed well. A photographic lens may or may not perform well as an astrograph. You need to find other photographs taken with that lens to make a determination. There might be a lot of coma or astigmatism in the corners. The field may not be all that flat. There is simply more variability with camera lenses since this isn't explicitly what they are designed for.

I can't speak to the specific photographic lenses you are considering. Don't know enough about them to know whether they will be any good for astrophotography. Generally, though, only pro grade telephoto zooms do well at the longer focal lengths. Unless you desperately want a double duty birding/astrophotography lens, stick with the RedCat.

Click to expand...

Jared,

Thank you very much for your informative and detailed explanation.

Do I understand correct that a doublet like the Zenithstar is the most simple version of such a telescope while better ones have more glass?

Would you consider 250mm focal length on a DX format camera sufficient for a beginner to get into DSO?

Click to expand...

crowley213 said:

Still a lot to read, check and consider, definitely a topic with quite a lot of aspects.

Herbert

Click to expand...

mostlyboringphotog said:

crowley213 said:

Jared Willson said:

The Zenithstar is a 61mm doublet meaning there is a pair of lenses at the front of the telescope and that's it. Best for visual use, though it can certainly adapt to photographic use. It would need a field flattener with either of the two cameras you are considering, and likely would vignette significantly with the D750.

The Redcat 51 is designed for imaging. It is a Petzval design meaning it has an integrated field flattener so stars at the edges of the field will be well corrected. It is also designed to fully illuminate a full frame camera.

Of the two, I would definitely recommend the Redcat for your intended use. Not even close. I know it has a bit less aperture, but it is well regarded for wide field astrophotography. The ZenithStar is primarily intended as a light weight visual scope.

Telescopes may or may not be better than photographic lenses of the same focal length. In general, telescopes are much simpler designs and are therefore a bit more likely to actually perform at their best--less chance of elements being decentered or tilted if you only have a couple or three elements. Also, telescopes are generally not designed to be as fast as camera lenses, so, again, the tolerances are easier to manage. Basically, the curves in the glass are less steep. That's an oversimplification, but still generally true. Finally, telescopes can be optimized to work at infinity focus whereas camera lenses involve compromises that let them perform well at a range of focal distances.

Camera lenses, one would think, would struggle to compete then for astrophotography. However, there are economies of scale that really help photographic lenses. Because they are manufactured in vastly higher numbers, R&D costs, tooling, etc. are recouped over a much larger volume of production. That means even moderately priced photographic lenses may have a fair amount of design work and exotic glass with aspheric surfaces. Telescopes in the price range you are thinking about never have aspheric glass. That can make a difference in edge performance.

Generally, telescopes that are sold for imaging are usually very good for imaging. You can get a dud, but the designs are solid and usually executed well. A photographic lens may or may not perform well as an astrograph. You need to find other photographs taken with that lens to make a determination. There might be a lot of coma or astigmatism in the corners. The field may not be all that flat. There is simply more variability with camera lenses since this isn't explicitly what they are designed for.

I can't speak to the specific photographic lenses you are considering. Don't know enough about them to know whether they will be any good for astrophotography. Generally, though, only pro grade telephoto zooms do well at the longer focal lengths. Unless you desperately want a double duty birding/astrophotography lens, stick with the RedCat.

Click to expand...

Jared,

Thank you very much for your informative and detailed explanation.

Do I understand correct that a doublet like the Zenithstar is the most simple version of such a telescope while better ones have more glass?

Would you consider 250mm focal length on a DX format camera sufficient for a beginner to get into DSO?

Click to expand...

250mm lens will project exactly the same size image on the sensor regardless of the sensor size, A larger sensor will show more of the surrounding area but for DSO object it self, it still looks the same size.

So if the choice is between FF and DX, I would choose DX if it has more pixel density (24MP DX camera has pixel density of 36MP FF camera) - if DX is what you have and have a 250mm lens, it will do. My choice is 4/3rd camera ;-)

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DavidWright2010 said:

It was this posted image by Zoran that convinced me to try the Sigma: horsehead and flame.

I haven't yet achieved the same level of performance, maybe because my sky is more polluted:


Sigma 150-600 (C) lens, modded Nikon D5600,

This is only 11 minutes of light - with more light I'm still having trouble with LP and big gradients in the background sky.

David

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82Virago said:

If you really want to get tucked into Astro, I say go for the telescope.

I am a fan of shooting with what you have, and budget wise a lens can do double duty but there are always trade offs.

I started with what i had a 300mm f4 and 1.4 teleconverter. I am happy with the results but the lens is infinite rotation manual focus with no markings. Dialling in sharp focus is a challenge. A scope typically has 2 stage focusing with lock.

Telephotos are not optimized for star shapes, not a huge deal, but a factor.

I would only use a zoom lens if it was all I had, I wouldn't buy one for the purpose of astro.

The RedCat seems like a nice little scope but at 250mm is pretty 'short'. If want to 'go deep into space', you will find something like M51 as a tiny dot in your finished image.

It is good for the large nebula, and M31. Personally I would look at 400mm range. The tracker will handle 400mm no problem.

I haven't tried the evostar72 I bought yet, still working on the adaptors. I am not convinced a field flattener is critical when odds are heavy cropping is still going to take place. That can help on the budget side. At least for now.

There is no limit to what a person could spend for better images, so I concentrate on what I can achieve now for my budget.

Cheers

Click to expand...

JaXImagea said:

I faced the same question a couple of years ago. Since most of my photography is of the normal variety, I started with lenses vice telescope. The cons of lenses are mentioned in this thread. I have taken some nice shots with the Nikon 70-200 2.8, sigma 150-600S and lately with the 500mm PF. I have friend that shoots with the 200-500 and gets great results. A quick comment, depending on where you live, you might only get 20-40 good nights in an entire year. So for me (south central Indiana) I use my gear a lot more shooting traditional photos. After a bit of success, my current goals are to work towards longer exposures (>3 minutes) and narrowband imaging. You might want to consider upgrading your mount. I know you didn’t ask but I started with an Atlas EQ-G and never had all the issues/limitations some have with simpler mounts. Oh, and you can probably sell you current tracker for close to what you paid for it on Cloudy Nights.

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Astrophotographer 10 said:

I had a Redcat 51 Its quite good, not too heavy but may not work perfectly out of the box for full frame. I found mine (and I think many are like this) needed to be corrected for tilt. That shows up as bad stars in one or two corners. The Redcat has a tilt adapter but it will take some time to learn how to use it and to do the adjustment.

Full frame is the better choice for astro photos as its got a larger area to collect light. But it can be demanding on things like tilt.

The Redcat is very sharp. Pretty easy to focus as well.

Star Adventurer is meant really for cameras and a light lens. A telescope, even a small one like a 61mm is going to need some accurate balance and accurate polar alignment.

It will need that as well with the Redcat but if you are in the northern hemisphere Polar alignment is fairly easy. Not so in the southern hemisphere.

Greg.

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crowley213 said:

Jared Willson said:

The Zenithstar is a 61mm doublet meaning there is a pair of lenses at the front of the telescope and that's it. Best for visual use, though it can certainly adapt to photographic use. It would need a field flattener with either of the two cameras you are considering, and likely would vignette significantly with the D750.

The Redcat 51 is designed for imaging. It is a Petzval design meaning it has an integrated field flattener so stars at the edges of the field will be well corrected. It is also designed to fully illuminate a full frame camera.

Of the two, I would definitely recommend the Redcat for your intended use. Not even close. I know it has a bit less aperture, but it is well regarded for wide field astrophotography. The ZenithStar is primarily intended as a light weight visual scope.

Telescopes may or may not be better than photographic lenses of the same focal length. In general, telescopes are much simpler designs and are therefore a bit more likely to actually perform at their best--less chance of elements being decentered or tilted if you only have a couple or three elements. Also, telescopes are generally not designed to be as fast as camera lenses, so, again, the tolerances are easier to manage. Basically, the curves in the glass are less steep. That's an oversimplification, but still generally true. Finally, telescopes can be optimized to work at infinity focus whereas camera lenses involve compromises that let them perform well at a range of focal distances.

Camera lenses, one would think, would struggle to compete then for astrophotography. However, there are economies of scale that really help photographic lenses. Because they are manufactured in vastly higher numbers, R&D costs, tooling, etc. are recouped over a much larger volume of production. That means even moderately priced photographic lenses may have a fair amount of design work and exotic glass with aspheric surfaces. Telescopes in the price range you are thinking about never have aspheric glass. That can make a difference in edge performance.

Generally, telescopes that are sold for imaging are usually very good for imaging. You can get a dud, but the designs are solid and usually executed well. A photographic lens may or may not perform well as an astrograph. You need to find other photographs taken with that lens to make a determination. There might be a lot of coma or astigmatism in the corners. The field may not be all that flat. There is simply more variability with camera lenses since this isn't explicitly what they are designed for.

I can't speak to the specific photographic lenses you are considering. Don't know enough about them to know whether they will be any good for astrophotography. Generally, though, only pro grade telephoto zooms do well at the longer focal lengths. Unless you desperately want a double duty birding/astrophotography lens, stick with the RedCat.

Click to expand...

Jared,

Thank you very much for your informative and detailed explanation.

Do I understand correct that a doublet like the Zenithstar is the most simple version of such a telescope while better ones have more glass?

Would you consider 250mm focal length on a DX format camera sufficient for a beginner to get into DSO?

Still a lot to read, check and consider, definitely a topic with quite a lot of aspects.

Herbert

Click to expand...

crowley213 said:

82Virago said:

If you really want to get tucked into Astro, I say go for the telescope.

I am a fan of shooting with what you have, and budget wise a lens can do double duty but there are always trade offs.

I started with what i had a 300mm f4 and 1.4 teleconverter. I am happy with the results but the lens is infinite rotation manual focus with no markings. Dialling in sharp focus is a challenge. A scope typically has 2 stage focusing with lock.

Telephotos are not optimized for star shapes, not a huge deal, but a factor.

I would only use a zoom lens if it was all I had, I wouldn't buy one for the purpose of astro.

The RedCat seems like a nice little scope but at 250mm is pretty 'short'. If want to 'go deep into space', you will find something like M51 as a tiny dot in your finished image.

It is good for the large nebula, and M31. Personally I would look at 400mm range. The tracker will handle 400mm no problem.

I haven't tried the evostar72 I bought yet, still working on the adaptors. I am not convinced a field flattener is critical when odds are heavy cropping is still going to take place. That can help on the budget side. At least for now.

There is no limit to what a person could spend for better images, so I concentrate on what I can achieve now for my budget.

Cheers

Click to expand...

Yes, my main concern regarding the RedCat is the 250mm focal length, I am not sure if that would be sufficient on a longer term. Therefore I also consider the Zenithstar 61, which has 360mm focal length and gets quite good reviews, also together with the SA tracker.

I am not sure if for example the Zenithstar 73 would not already be to big / heavy for the SA. I saw one posting in another forum where one guy used that combo, but my impression was that this works at or above the limitations of the SA.

Maybe I just go for the RedCat or the Zenithstar 61 for the beginning and see where the journey will get me over time.

Herbert

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crowley213 said:

Again, thank you all very much for you information and suggestions.

After careful evaluation I finally decided to go for the William Optics Zenithstar 61 II APO telescope.

While I already received the telescope two days ago, a real beauty in red, it will take at least until mid or end of May until the recommended flattener, the WO Flat 61A, will be available again. Considering that the use of my Nikon D750 seems not to make sense without the flattener, and my Fuji X-T3 is still at the Fuji service for a repair, I will not be able to try out the telescope for astrophotography to its full extend at this moment.

On the other side, in the meantime I can use the telescope for astronomical and terrestrial viewing, as I purchased also some diagonals and a good eyepiece, and I also plan to do some trials regarding afocal photography with my little Fuji X100T. I am sure there is a lot the figure out and I will have a lot of fun... considering the steep learning curve in this interesting and complex hobby.

Herbert

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