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Apo Refractor vs ED Telephoto lens? + Diy nikon lens filter idea

astrophotography beginner equipment dso dslr refractor
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#1 Naraya

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Posted 22 September 2019 - 05:10 AM

I thought I've already made up my mind that i'm upgrading my achro-ST-80 to an Evostar 72ed. But somehow after all this time, i just cannot convince myself to spend 280 pounds on a refractor purely on astrophotography.

 

So i looked at this Nikon 55-300mm ed lens, its the same price and most importantly i can use this in day-to-day photography.

 

I used to think there was no reason to buy a telephoto lens as using a filter is absolutely crucial in my huge megacityBut then i stumbled across this astrobin photo, it's beautiful: great contrast, color, and little to no CA, but the stars do look a little too"winged"

 

but most importantly he found out you can just strap a 2" filter on the lens by using his simple "rig"

 

"I rigged the filters to fit on the very front of the lens using some cardboard and tape. That's a way of life over here smile.gif."

 

 

Would you think the lens could perform as good as the Evostar? I know camera lenses have a lot of shortcomings when it comes to astrophotography (especially the distortion). But i would sacrifice some of that so i could use it for the day as well.

 

 

Moreover, does anyone think the filter "rig" is a good idea? Im 99% there will be no vignetting problem since a 2" filter will cover the whole front lens system. But theres always some kind of problem unbeknownst to me

 

*Note* One of the biggest factors of why i'm considering the lens is due to a major vacation to Europe in Christmas. Visiting beautiful cities and environments would make the telephoto a great tool. 

 

I'll also have the chance to visit a few bortle-3 skies (long as the cloud gods are particularly happy) and it'll be the first time bringing a telescope to the northern winter skies, and also imaging without a filter for once.

whee.gif

Thanks,

Naraya


Edited by Naraya, 22 September 2019 - 05:11 AM.


#2 Hesiod

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Posted 22 September 2019 - 05:47 AM

Well, you could just screw the filter to the lens' filter thread...besides "astronomical" formats, filters are also available in standard photographical formats, e.g. from Astronomik.

I also suppose you have already checked for the availability of "clip" filters for your camera.

I am not familiar with Nikon lenses, but with PP software may address to a certain extent the bad star shapes (in the worst case can erase the stars, or apply a selective gaussian blur to make them round and colorful again).

I would not be bothered by vignetting either: first can resort to calibration, and in the worst case can crop a bit (which would not be a bad idea in any case, to hid the most hideous stars).

Rather, I would be somewhat "fearful" of tilts, which could worsen the star shapes.

 

In any case, as long as you use a color sensors, filters are not a necessity but just a facilitation.They improve somewhat the S/N ratio on certain targets, and should deal with the worst of light pollution's gradients, but with enough integration and dabbling a bit more with PP can shot without.



#3 SilverLitz

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Posted 22 September 2019 - 06:52 AM

In my limited experience, a camera lens noticeably slower than the equivalent f/ telescope.  This is the difference between t/stop (light transmission) and f/stop (geometric, FL/aperture).  The camera lens, especially zooms, has many times more lens elements which decrease its light transmission efficiency.  Telescopes are MUCH nicer to focus and have focal locks, as well.  Getting precise focus with a camera lens is a PITA and takes a lot longer, as they lack the micro focus knobs and are optimized for ~10 ft distance, not infinity.

 

I came to this conclusion by comparing my Canon 70-200 f/2.8L + 2x extender iii (400mm at f/8) compared to my ES ED102CF (714 at f/7) while imaging full moons on clear nights.  The proper exposure for the camera lens + extender was ~1/160, while it was ~1/400 for the telescope, both at ISO100.



#4 Naraya

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Posted 22 September 2019 - 07:47 AM

Well, you could just screw the filter to the lens' filter thread...besides "astronomical" formats, filters are also available in standard photographical formats, e.g. from Astronomik.

I also suppose you have already checked for the availability of "clip" filters for your camera.

I am not familiar with Nikon lenses, but with PP software may address to a certain extent the bad star shapes (in the worst case can erase the stars, or apply a selective gaussian blur to make them round and colorful again).

I would not be bothered by vignetting either: first can resort to calibration, and in the worst case can crop a bit (which would not be a bad idea in any case, to hid the most hideous stars).

Rather, I would be somewhat "fearful" of tilts, which could worsen the star shapes.

 

In any case, as long as you use a color sensors, filters are not a necessity but just a facilitation.They improve somewhat the S/N ratio on certain targets, and should deal with the worst of light pollution's gradients, but with enough integration and dabbling a bit more with PP can shot without.

Could you give an example to filters that screw directly to the lens filter thread? Also i do think filters are a necessity in my case, there's just too much noise for my current photoshopping skills.



#5 Alen K

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Posted 22 September 2019 - 07:53 AM

As you noted yourself, star quality in the corners on that lens, at least at the focal length used in that Astrobin image, is not quite so good. You could stop it down but then the aperture gets even smaller. The refractor is no doubt going to give better images, assuming you use a field flattener. If you pair it with the 0.85x reducer/flattener advertised for it, the focal ratio becomes a respectably fast f/4.9.

 

That said, the fact that you can use the telephoto for terrestrial photography as well is obviously a point in its favor. Personally, I like to use vintage primes for AP but I don't usually use those for daytime photography. I chose them specifically as inexpensive AP lenses. 

 

Re the filter, you can get adapter rings: https://www.amazon.c...r/dp/B009T1D4FO

 

Re transmission, the difference may not be as great as you'd think given modern multi-layer coatings. Assuming every lens surface is so coated and a loss of 0.25% at each surface (seems to be a typical number) the refractor with flattener will lose about 2% while the telephoto will lose less than 8%. 

 

Re focusing, sure, a refractor with a 10x reduction mechanism on the focuser is much easier to focus. But with Live View I have never had a problem focusing a telephoto. With a zoom lens a bigger problem can be zoom creep. There are workarounds for that. (Focus can creep too. Same solutions.)


Edited by Alen K, 22 September 2019 - 08:35 AM.


#6 Naraya

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Posted 22 September 2019 - 08:42 AM

As you noted yourself, star quality in the corners on that lens, at least at the focal length used in that Astrobin image, is not quite so good. You could stop it down but then the aperture gets even smaller. The refractor is no doubt going to give better images, assuming you use a field flattener. If you pair it with the 0.85x reducer/flattener advertised for it, the focal ratio becomes a respectably fast f/4.9.

 

That said, the fact that you can use the telephoto for terrestrial photography as well is obviously a point in its favor. Personally, I like to use vintage primes for AP but I don't usually use those for daytime photography. I chose them specifically as inexpensive AP lenses. 

 

Re the filter, you can get adapter rings: https://www.amazon.c...r/dp/B009T1D4FO

 

Re transmission, the difference may not be as great as you'd think given modern multi-layer coatings. Assuming every lens surface is so coated and a loss of 0.25% at each surface (seems to be a typical number) the refractor with flattener will lose about 2% while the telephoto will lose less than 8%. 

 

Re focusing, sure, a refractor with a 10x reduction mechanism on the focuser is much easier to focus. But with Live View I have never had a problem focusing a telephoto. With a zoom lens a bigger problem can be zoom creep. There are workarounds for that. (Focus can creep too. Same solutions.)

Not planning to buy a flattener-as least for a little while (budget restraints). Also i'm still kinda confused how to mount it, do you just get the correct thread size for the camera lens (i think its 52) and make sure it's -48 since the 2 inch filter thread is m48?


Edited by Naraya, 22 September 2019 - 08:58 AM.


#7 Hesiod

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Posted 22 September 2019 - 09:16 AM

Check here
https://www.astronomik.com/
Filters do not remove the noise but lessen the effects of light pollution on targets with dominant/exclusive emission in a somewhat narrow band out of the yellow-green wavelenghts (e.g. the green-blues and reds of bright nebulae).
On full spectrum, "white" targets such as galaxies filters are IME much less useful: may help against the greenish hue you could have after the WB (but this is not the most effective way), but will also cut away useful signal

#8 Naraya

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Posted 22 September 2019 - 09:22 AM

Check here
https://www.astronomik.com/
Filters do not remove the noise but lessen the effects of light pollution on targets with dominant/exclusive emission in a somewhat narrow band out of the yellow-green wavelenghts (e.g. the green-blues and reds of bright nebulae).
On full spectrum, "white" targets such as galaxies filters are IME much less useful: may help against the greenish hue you could have after the WB (but this is not the most effective way), but will also cut away useful signal

Sorry, by "noise" I meant signal from light pollution, from my bortle 8 (or 9 actually?) sky a 30 second unfiltered exposure would make it seem like i'm photographing the sun.


Edited by Naraya, 22 September 2019 - 09:56 AM.


#9 Alen K

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Posted 22 September 2019 - 09:59 AM

Not planning to buy a flattener-as least for a little while (budget restraints). Also i'm still kinda confused how to mount it, do you just get the correct thread size for the camera lens (i think its 52) and make sure it's -48 since the 2 inch filter thread is m48?

If you are talking only about putting the LPS filter on that particular camera lens, since it has a 58mm filter thread (not 52mm) you buy a 58mm-to-48mm step-down ring similar to what I linked to (less than $10), thread it into the front of the lens, then thread the filter onto that. 



#10 Naraya

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Posted 22 September 2019 - 10:18 AM

If you are talking only about putting the LPS filter on that particular camera lens, since it has a 58mm filter thread (not 52mm) you buy a 58mm-to-48mm step-down ring similar to what I linked to (less than $10), thread it into the front of the lens, then thread the filter onto that. 

ah, ok thanks. Still wondering about the CA and color correction though, if it at least performs better than most achros it's a buy for me.



#11 Hesiod

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Posted 22 September 2019 - 10:49 AM

For sure it will performs better than any f/5 achro in its focal range...

As for the light pollution, the filter is nice as long as your target is a red/blue nebula, but much less useful on "white" galaxies or star clusters.

When I shot from home it is natural that single subs look awful, and I do not even bother to look at them, but pay attention only to the histogram: if it is in the right place, and the subs look "white", does not matter, it means only that I have to stack (many) more of them.

 

This was my program for the weekend (4 nights of signal, aiming at 20 hours) but sadly the clouds had other plan so was forced to use only 3 hours from Friday, and opted to process them anyway to get more familiar with the software

gallery_215679_11012_4554231.jpg

 

The picture was taken from my home (amidst the Pianura Padana, norther Italy, one of the worst light-polluted areas of Europe) with a crap unmodded camera (eos1100d) through a f/6 telescope: while not a good picture, the PacMan silhouette can be seen, even if it was totally invisible in the single subs



#12 dpaigen

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Posted 22 September 2019 - 02:59 PM

Vacations:

I've taken a 70-300 on vacation and found that 300 is too long for anything except wildlife.  And I would find 55 to be too narrow for many shots.  I recently chaperoned an 8th grade trip to Washington DC & NYC.  I took a 18-140 and was very happy with my choice.  I could get group shots with 25 people in them and also long range compositions of monuments and buildings (this is with a crop sensor).

 

If your plans include museums consider adding a 35 or 50mm prime and a CPL.  Both are small and light.  The extra stops you get with a prime are extra helpful in dim lighting (like an art museum) and the CPL can make reflections in glass display cases disappear, just shoot at an angle.

 

Astro:

While I do not have personal experience with either of these lenses, the AP community seems to think very highly of the nikon 180mm f/2.8 manual focus and the nikon 300mm f/4.5 manual focus.  You can pick those up on ebay for around $300 and $100, respectively.

 

That Evostar72 looks nice, though.  Or you could pick up the used nikon 300 and a new Skystar 90 (500mm) for the same price.



#13 Alen K

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Posted 22 September 2019 - 07:28 PM

Vacations:

I've taken a 70-300 on vacation and found that 300 is too long for anything except wildlife.  And I would find 55 to be too narrow for many shots.  I recently chaperoned an 8th grade trip to Washington DC & NYC.  I took a 18-140 and was very happy with my choice.  I could get group shots with 25 people in them and also long range compositions of monuments and buildings (this is with a crop sensor).

 

If your plans include museums consider adding a 35 or 50mm prime and a CPL.  Both are small and light.  The extra stops you get with a prime are extra helpful in dim lighting (like an art museum) and the CPL can make reflections in glass display cases disappear, just shoot at an angle.

Re 55-300mm, good point. It's not what most would consider a general-purpose "walking around" lens. Similar to you I use an 18-135mm for that. But if someone DOES have an interest in wildlife, then having 300mm available could be handy.

 

Using a fast prime for indoor shots in poor lighting is good advice. However, I find that in locations like a museum where you may not always be able to stand where you want, it is nice to have the flexibility of a short zoom. Since my camera has IBIS, I effectively get many extra stops of exposure. A short zoom with VR would be equivalent. Or something like the AF-S Nikkor 14-24mm f/2.8G ED, which may also be good for wide-field astrophotography. 

 

The advice to use a CPL to make reflections disappear is good. However, AFAIK all CPLs are rotatable (all of mine certainly are), so I don't think it is necessary to shoot at an angle. In a museum, for instance, one is not usually in a hurry and there is time to rotate the polarizer before taking the shot. 

 

(BTW, apropos to the thread here is a nice page from Nikon concerning Nikkor lenses applied to astrophotography.)


Edited by Alen K, 22 September 2019 - 07:38 PM.


#14 Naraya

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Posted 23 September 2019 - 04:41 AM

 

Astro:

While I do not have personal experience with either of these lenses, the AP community seems to think very highly of the nikon 180mm f/2.8 manual focus and the nikon 300mm f/4.5 manual focus.  You can pick those up on ebay for around $300 and $100, respectively.

 

That Evostar72 looks nice, though.  Or you could pick up the used nikon 300 and a new Skystar 90 (500mm) for the same price.

Actually, that's a really, really good idea. 

I'll go with either the 180mm or the 300mm, (probably 300mm). And with the remaining money i could purchase accessories or a narrowband filter

 

But then again, the only listing in my country of the 300mm  shows quite a lot of signs of wear, a picture of fungi growing on the lens and a (kind-off) shady seller. 

 

And one of the listings of the 180mm comes from a very reputable and popular seller

 

A question though, since there are no 72-48mm step down rings, could i buy the 72-58, then buy a 58-48? Could this introduce vignetting problems?

 

 

 

 

Thanks a lot for suggesting me this btw,

it's funny how i went from evostar 72ed vs evoguide 50ed to evostar 72ed vs 55-300m and then finally here lol.gif

just comes to show how i love this community smile.gif


Edited by Naraya, 23 September 2019 - 08:06 AM.


#15 bobzeq25

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Posted 23 September 2019 - 09:44 AM

Actually, that's a really, really good idea. 

I'll go with either the 180mm or the 300mm, (probably 300mm). And with the remaining money i could purchase accessories or a narrowband filter

 

But then again, the only listing in my country of the 300mm  shows quite a lot of signs of wear, a picture of fungi growing on the lens and a (kind-off) shady seller. 

 

And one of the listings of the 180mm comes from a very reputable and popular seller

 

A question though, since there are no 72-48mm step down rings, could i buy the 72-58, then buy a 58-48? Could this introduce vignetting problems?

 

 

 

 

Thanks a lot for suggesting me this btw,

it's funny how i went from evostar 72ed vs evoguide 50ed to evostar 72ed vs 55-300m and then finally here lol.gif

just comes to show how i love this community smile.gif

The 180 will work better with your mount.

 

Stepping things down to 48mm will cause vignetting, you remove it with flats.  Stopping that lens down will slow it from 2.8 to 3.75, but also make the stars look better, particularly at the edges.


Edited by bobzeq25, 23 September 2019 - 09:45 AM.


#16 Alen K

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Posted 23 September 2019 - 09:47 AM

Actually, that's a really, really good idea. 

I'll go with either the 180mm or the 300mm, (probably 300mm). And with the remaining money i could purchase accessories or a narrowband filter

 

But then again, the only listing in my country of the 300mm  shows quite a lot of signs of wear, a picture of fungi growing on the lens and a (kind-off) shady seller. 

 

And one of the listings of the 180mm comes from a very reputable and popular seller

 

A question though, since there are no 72-48mm step down rings, could i buy the 72-58, then buy a 58-48? Could this introduce vignetting problems?

Fungus is not good. If it hasn't eaten the coatings you could take the lens apart and clean it off. But if it HAS eaten the coatings...

 

The clear aperture of a 48mm filter is about 43mm (at least the ones I have - some may be a bit larger). That means on a 300mm lens you will be shooting at about f/7. (The 180mm would be about f/4.) There may also be some vignetting (drop off towards the corners) that you wouldn't normally see because the filter opening acts like a field stop that normally wouldn't be there. But the real issue is the ~f/7 focal ratio for the 300mm, which is a little slow. But not impossibly so. (Btw, this also applies to the Nikon zoom mentioned in the OP when operated at 300mm.)


Edited by Alen K, 23 September 2019 - 07:52 PM.


#17 Naraya

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Posted 24 September 2019 - 09:46 AM

The 180 will work better with your mount.

 

Stepping things down to 48mm will cause vignetting, you remove it with flats.  Stopping that lens down will slow it from 2.8 to 3.75, but also make the stars look better, particularly at the edges.

that's reassuring, however how bad would the vignetting problem be? I'd think a blocking 24mm of the lens' diameter would cause severe forms of vignetting.



#18 Alen K

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Posted 24 September 2019 - 09:55 AM

that's reassuring, however how bad would the vignetting problem be? I'd think a blocking 24mm of the lens' diameter would cause severe forms of vignetting.

Vignetting is not caused per se by reducing the aperture. When you adjust the f-stop ring you are also reducing the aperture and that actually improves the vignetting in most cases. In this case it is caused by reducing the aperture outside of the objective lens. In any case, the vignetting is nothing that you can't handle in an image-processing program. Taking flat frames would be the best way to handle it, as usual. 


Edited by Alen K, 24 September 2019 - 09:56 AM.


#19 Naraya

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Posted 30 September 2019 - 05:47 AM

Quick update:

I've just gotten this lens last Friday, and it that short time span I've had so much fun using it for daylight photography! (still need proper filters for astro). The sharpness, bokeh and focuser truly holds up to it's legendary status. I'll have tons of fun using this.


Edited by Naraya, 30 September 2019 - 05:48 AM.


#20 Naraya

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Posted 30 September 2019 - 07:15 AM

I also just thought about the problem of dew i'll get in Europe, would anyone recommend one of these Svbony ones. Still quite confused about which size to get too and if a fully charged mobile power bank is enough to power it for about 2 hours.



#21 Astrodymium

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Posted 30 September 2019 - 07:43 AM

I also just thought about the problem of dew i'll get in Europe, would anyone recommend one of these Svbony ones. Still quite confused about which size to get too and if a fully charged mobile power bank is enough to power it for about 2 hours.

I have two of them. I have yet to test them with my setup but I'm sure they'll work fine; converting electricity to heat is 100% efficient anyways. 

 

Measure the circumference of your camera lens and choose the corresponding dew heater size. Any power bank that has more than 2000 mAh (measured at 5 volts or more) will run the strip for two hours. I would not use them at full power though, because it's not necessary to prevent dew from forming.

 

The good thing about these Svbony dew heaters are that they come with a USB dial that controls how much current is drawn.


Edited by Astrodymium, 30 September 2019 - 07:47 AM.


#22 Naraya

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Posted 30 September 2019 - 08:49 AM

I have two of them. I have yet to test them with my setup but I'm sure they'll work fine; converting electricity to heat is 100% efficient anyways. 

 

Measure the circumference of your camera lens and choose the corresponding dew heater size. Any power bank that has more than 2000 mAh (measured at 5 volts or more) will run the strip for two hours. I would not use them at full power though, because it's not necessary to prevent dew from forming.

 

The good thing about these Svbony dew heaters are that they come with a USB dial that controls how much current is drawn.

Alright, in case the battery runs out could i use the macbook pro to power it?

 

Another question, how do i mount this into the SA safely? The lens does not have a bracket or support and i'm afraid that might damage the camera.




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