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What are best 85mm to 200mm lenses for milky way panoramas?

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#1 nathanm

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Posted 01 July 2020 - 11:05 AM

I have been taking milky way panoramas, typically using 24mm or 35mm f/1.4  Samyang/Rokinon lenses, a Canon DSLR and a gigapan or roundshot motorized panorama head.   At each position in the panorama I take multiple photos and stack them.

 

It has occurred to me that I would get better quality using longer focal length lenses - 50mm, 85mm or even longer.   Obviously it will take more frames to get the same sky coverage, but the quality will be much higher.   

 

Ironically, if you expose long enough to reach the same limiting magnitude, then my calculations show it can actually take less time to take a panorama with an 85mm than a 24mm.  That's because light gathering power for astrophotos depends on the square of the clear aperture, not the f-stop.

 

You have to take more positions to get the same sky coverage, but need fewer shots to stack at each position.

 

My question is this - which short to medium telephoto  lenses can be used wide open, or if not wide open, then how much do you need to stop them down?

 

Typically daytime photography treats the maximum aperture - i.e. wide open - as a bit of a desperation move, and the best quality occurs 1 or 2 full f-stops lower.  However, every stop you stop down makes a lens less competitive for astrophotography.

 

That's usually not true for the fast telephoto sports lenses - like 300mm f/2.8 or 600mm f/4, which are typically used wide open, but those are too long for making panoramas.

 

Obvious candidates are:

 

Samyang/Rokinon 85mm f/1.2 XP/SP    - I wonder what coma / edge quality is like at f/1.2 and f/1.4 or f/2?

 

Samyang/Rokinon 85mm f/1.4 - this is the ordinary, non premium version, presumably the SP/XP is better?

 

Sigma ART 85mm f/1.4 - I have no idea what it is like with respect to edge / corner quality

 

Zeiss Otus 85mm f/1.4   -  I have tried this and it has way too much coma at f/1.4, less at f/2 but I am not sure even that is good enough.

 

Zeiss Otus 100mm f/1.4 - I haven't tried this one.  But there is a lot of coma in the 55mm Otus, and 85mm so I am not hopeful

 

Sigma ART 105mm f/1.4    - I have seen photos online suggesting this needs to be at least f/2, and maybe more

 

Samyang/Rokinon 135mm f/2    -   I have seen photos online that suggest it might be OK at f/2.   If so it would be a great contender.

 

Canon 200mm f/2  - somewhat surprisingly to me, I have seen photos online suggesting this is very usable wide open.  It's the baby brother to the 300mm f/2.8 so that might explain why it was built with good wide open performance.

 

I am open to other lenses too, so long as I can use with a Canon camera.

 

 


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#2 2ghouls

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Posted 01 July 2020 - 11:54 AM

First, I'd say with any of these lenses there is going to be some copy-to-copy variability, esp. with the Samyang/Rokinons. Also, what people call acceptable, good, great is subjective. I'd like to do a really complete testing website for these kinds of questions, but haven't gotten around to it yet. Anyways, from your list, here's my quick takes on the ones I've used:

 

- Rokinon 85mm (not great till you close down to f/4)

- Sigma Art 105 f/1.4 (acceptable to me at f/2) Sample: https://astrob.in/full/smb8x7/B/

- Rokinon 135 f/2 (good at f/2.8, but I need more time with it)

- Canon 200 f/2.8L* (good at f/2.8 for narrowband, f/4 for for broadband)

 

*Not sure if you really meant the Canon 200mm f/2 as it is much more expensive than f/2.8 and everything else on your list.

 

If you were on an equatorial mount and constructing these mosaics with platesolving, I think the sweet spot for what you want to do is 105 or 135. I would add the Sigma Art 135 f/1.8 to your list, which I think will beat the Rokinon 135 f/2. BUT given you are doing this without sidereal tracking, I would stick to the 85mm max or even consider the Sigma Art 40mm which has been getting great reviews for astro. The reason being to get pinpoint stars at 135mm without tracking, you would need very short exposures, which cancels out the SNR boost from bigger aperture you mentioned.



#3 AstroBrett

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Posted 01 July 2020 - 12:17 PM

I have the Samyang 85mm f/1.4 and the stars aren't really useable until stopped down to f/4, and if you don't like multiple diffraction spikes, you will need to use an aperture mask. Otherwise, it is a good performer. I understand from other users that the quality control is highly variable, so if you buy new, get it from a vendor that will accept returns. 

 

Brett



#4 erictheastrojunkie

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Posted 01 July 2020 - 12:31 PM

Skip the Samyang/Rokinon 85mm, as others have mentioned it's a pretty lousy lens until f3.5-f4, mine was ok at f3.5. 

 

The Sigma Art 85mm is incredible, if you are looking for a lens at this focal length this one should be at the top of your list, despite its size and weight. Very very sharp across the frame, no coma wide open, slight LoCA that's gone by f2. IMO it's the best 85mm currently available. 

 

The Sigma Art 105mm is incredible as well, even better than the Art 85mm and the Art 135mm, I've seen A LOT of examples of it shot wide open with no aberrations. It's a monster though, hence the dedicated lens collar.

 

In the 135mm focal length I think there isn't worth spending (more) money on than the Samyang/Rokinon 135mm, it's truly an awesome lens and has much less copy to copy variation compared to the other Samy/Roki lenses. I've had 3 copies over the years, all 3 were fantastic, the lens is completely usable at f2 (I stopped mine down to f2.8 to get rid of vignetting). 



#5 nathanm

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Posted 01 July 2020 - 12:36 PM

Yes, I meant the Canon 200mm f/2, and yes it is a lot more expensive, but it is not an impossible choice.

 

When making a mosaic / panorama, you typically are averaging the edges of some frames into the centers (or near centers) of other frames.  This tends to reduce coma quite a bit, but alternatively, it lowers average quality across the image.

 

Another factor with a longer lens is that if you have the same sky coverage, a panorama made with a longer lens has a LOT more bits.  Which means the pixel size in the final print or photo is going to be much smaller.  This also makes coma less noticable.

 

It's far from clear to me that the SNR is ruined by short exposures - that's only true if the read error is a large component of error and it is generally pretty small for modern DSLR.  I also have a cooled QHY 128c, which has very low read error.   

 

The problem with me for using a tracking mount is that I like to have foregrounds - i.e. landscape astrophotography.  So far the hassle of stacking and aligning a fixed mount has been worth it.   Alternatively, you can have an easier time with the stars, but then have the hassle of trying to compose the foreground with an equatorial mount.



#6 robbieg147

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Posted 01 July 2020 - 04:10 PM

The Canon 200 F2 is a awesome lens, but so is the Canon 200 F2.8 at a fraction of the cost. The F2 has IS but this is of no use for AP. I often use my 2.8 wide open for general photography it is so sharp, to buy the F2 for AP only is daft in my opinion when such a great lens (the 2.8) is available for a fraction of the price.



#7 nathanm

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Posted 01 July 2020 - 05:04 PM

I am sure that if I bought a 200mm f/2 Canon lens I would use it for more than astrophotography.   Other people do use the lens for lots of things - strangely, while looking for reviews of the lens I found one by a boudoir photographer - which is a long, long way from astro.

 

The main question I have about the Canon (or other) 200mm f/2.8 lens is how much coma does it have wide open, and how that compares to the 200mm f/2.

 

Stopping a lens down one stop, or going to a lens that is one stop slower and is wide open makes your exposure go up by a factor of 4, not 2.  That's because stars are point sources and exposure depends on the area of the clear aperture.

 

So it changing by 1 stop is a pretty big penalty.   a panorama that would take 30 - 40 minutes winds up being 2-3 hours which of course is possible to do but weather and lots of things can intervene.



#8 nathanm

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Posted 01 July 2020 - 05:23 PM

This site has a review of the Sigma ART 105mm f/1.4.

 http://www.atscope.c...s/Sigma105.html

 

They have corner and edge shots at f/1.4 and assuming that the photos from the site were what I got, I would say they are not usable.

 

However the site also has corner and edge shots at f/2, and they are enough better that I would call them usable but barely.

 

The same site has 200mm f/2 canon edge shots that to me look usable at f/2.

 

This picture shows coma testing using artificial stars for the 40mm Sigma ART, which looks pretty terrible if the artificial stars are to be believed.  https://www.flickr.c...in/33460966778/

 

The 135mm f/2 Samyang/Rokinon looks useable at f/2 here https://www.flickr.c...in/20005540154/    There seem to be lots of favorable reviews of the lens.



#9 robbieg147

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Posted 01 July 2020 - 06:07 PM

Not sure i see how one stop increases the exposure by 4 for the same lens?

 

eg:   200mm at F2 area = 100*100*pi = 31400/4mm sq

 

        200mm at F2.8 area = 71.4*71.4*pi = 16007/4mm sq

 

Which is a factor of 2?

 

I agree if comparing say a 9mm at f2 to 35mm at f2 there would be a huge difference in area, but focal lengths are normally chosen on what you want to fit in the frame.


Edited by robbieg147, 01 July 2020 - 06:12 PM.


#10 nathanm

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Posted 01 July 2020 - 06:10 PM

Sorry, I spaced...  yes it is a factor of 2.   I had the 105 mm Sigma ART lens  versus 200 mm f/2 Canon in my mind and just wrote the wrong thing.  

 

At the same focal length it is a factor of 2.

 

If you change focal length, then that matters for stars when it doesn't matter for regular daytime photography.    

 

So the 200mm  Canon at f/2 is much better than the 105mm Sigma stopped down to f/2.   You do however need to shoot more pictures to cover the same amount of sky.    And you need shorter exposure for the longer lens if you are not tracking.


Edited by nathanm, 01 July 2020 - 06:14 PM.


#11 robbieg147

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Posted 01 July 2020 - 06:26 PM

Another way would be to have a array of say 4 canon f2.8 lenses that would be twice as fast as the 200 F2 and a lot cheaper.



#12 nathanm

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Posted 01 July 2020 - 06:40 PM

I think you meant that in jest, but your idea has merit

 

People have built outfits that shoot a stitched panorama with multiple cameras rather than moving one camera to multiple viewpoints.  

 

Here is an example.  This project uses multiple 400mm f/2.8 Canon lenses  https://petapixel.co...s-worth-100000/

 

So putting 4X canon 200mm f/2.8 lenses would look like the baby brother of this set up.

 

However, while that would help in covering a given sky area more quickly than serial positioning, it would require a serious project.   One would need to align and mount four 200mm f/2.8 lenses, and then built a custom panorama robot mount to move all four together through the sky - analogous to what the project above does, but smaller.  Plus you need 4 camera bodies.   

 

So while one could do that, it would actually be a lot cheaper to buy the 200mm f/2 lens.  There is a reason Canon makes them - people do buy them!



#13 Uggbits

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Posted 01 July 2020 - 08:05 PM

Of the lenses on your list I can only speak to the Sigma 105 1.4. The whole thing sharpens up if you stop down to even f1.8. Looking at the concern you mentioned, the image quality improves in the corners when stopped down, but not by as much as I have observed with other lenses.

 

I find that in usual use the corner star quality isn't much of an issue, as the corners tend to have a reduced emphasis after aligning (I use a portable unguided setup with the lens). If you ever used an APSC sensor I doubt you would see the corner issues. The main issue with the lens in my experience is chromatic aberration, which isn't awful, but isn't great. For my outings so far (and test shots I took) I haven't been compelled to stop down. I gain enough by shooting at 1.4 that the extra signal makes up for a very slight loss in resolution and increase in distortion/chormatic aberration. It isn't perfect, but I can' think of any lenses operating under f2 (other than the Sigma 135 and 40mm) that produce better star-field images wide open.

 

My usage is based on keeping imaging sessions brief on work-nights, so I expect that on more substantial imaging sessions I will use f2.

 

Cheers,

Dan



#14 whwang

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Posted 01 July 2020 - 09:10 PM

Hi,

 

Regarding Art 85/1.4, you may check this out:

https://www.flickr.c...57667599730890/

(using the right-arrow to check different apertures)

 

To cover the same area of sky and to reach the same stellar limiting magnitude, a mosaic taken with a long lens and a single-shot taken with a wide-angle lens require similar total integration times.  However, depending on how you automate the process, the former has larger (or much larger) dead time between mosaic panels.  The images from the former also takes longer to process.  My experience is that the processing time goes up with almost N-square (N being the number of panels in a mosaic) rather than simply N. With very good software optimized for astro mosaic and some luck, it can be NlogN, but it will never be just N.

 

Another factor is that one actually can rarely be satisfied with just getting the same limiting magnitude when switching to a long lens.  Believe me, If your 200mm image and 35mm image have the same limiting magnitude, the 200mm one will look much more ugly, despite having the same limiting magnitude. This is because many objects (especially in Milky Way shots) are extended rather than point-like. The nebulas in your 200mm image will look very noisy comparing to the same nebula in your 35mm lens, if you give the 200mm one 33x shorter exposure.  Because of this, what usually happens is we still give the long lens image almost equally long integration.  Furthermore, when you actually start to do this (long integration with long lenses), you may be tempted to give it even longer integration.  The reason is that once the focal length gets long and the resolution becomes higher, we start to see even fainter nebulas hidden by the dense star field.  Such faint nebulas are difficult to reveal with short lenses regardless of integration time.  Once you see those faint stuff in your long lens images, it is very hard for you to ignore them and stay with short exposure.  Long integration with long lenses is almost inevitable.

 

In short, there are multiple reasons that a mosaic with long lens will take much longer time than what you imagined.  My personal suggestion to you is to start with 85mm for very wide Milky Way panorama, if your previous experience is mainly on 24 to 35 mm.  You can still try a smaller mosaic with a 200mm lens (like to mosaic a constellation) though.

 

Check out my gallery to see what has been done before.

 

Cheers,

Wei-Hao


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#15 nathanm

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Posted 02 July 2020 - 02:55 PM

These links show that the Zeiss 135 mm f/2 APO Sonnar is very good at f/2

 

https://www.flickr.c...in/14897466108/

https://www.flickr.c...in/photostream/

https://www.flickr.c...in/15215805623/

 

BUT, it is not the current product:  135mm f/2 Milvus.   Does anybody know how the Milvus compares?



#16 nathanm

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Posted 02 July 2020 - 03:56 PM

With respect to the advice from Wei-Ho, thanks!    I am sure you're correct, but I will see what I can get with longer lenses.   If I don't get better results then I can always return to wide angle lenses.



#17 ChristopherBeere

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Posted 02 July 2020 - 04:07 PM

You dont need to stop the Arts down. I use the 40 and 105 wide open.

 

If you are mosaicing wide fields your biggest enemy is going to be the distortion required to flatten the celestial sphere.


Edited by ChristopherBeere, 03 July 2020 - 01:14 AM.


#18 Uggbits

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Posted 02 July 2020 - 06:24 PM

I think you meant that in jest, but your idea has merit

 

People have built outfits that shoot a stitched panorama with multiple cameras rather than moving one camera to multiple viewpoints.  

 

Here is an example.  This project uses multiple 400mm f/2.8 Canon lenses  https://petapixel.co...s-worth-100000/

 

So putting 4X canon 200mm f/2.8 lenses would look like the baby brother of this set up.

 

However, while that would help in covering a given sky area more quickly than serial positioning, it would require a serious project.   One would need to align and mount four 200mm f/2.8 lenses, and then built a custom panorama robot mount to move all four together through the sky - analogous to what the project above does, but smaller.  Plus you need 4 camera bodies.   

 

So while one could do that, it would actually be a lot cheaper to buy the 200mm f/2 lens.  There is a reason Canon makes them - people do buy them!

Just wanted to back up to this point for a second. The Dragonfly telescope has each lens aligned to the same point, and they all see the same field: the total FOV for that system is only 2.6x1.9 degrees. The main benefit in that system is not to use the multiple short focal length refractors to shoot simultaneous panels for a mosaic, but to operate with a very high effective light gathering area and exceptional signal to noise ratio. By doing this they can go very deep with a reasonably short integration time.

 

Cheers,

Dan 



#19 nathanm

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Posted 02 July 2020 - 07:03 PM

Yes, that is true that Dragonfly achieves parallelism by all looking the same place, each with its own separate SBIG camera.  Then they stack those images to improve SNR.

 

You could use such an array to make a milky way panorama.  You would only need one sub-image from each position, because "one" would really be a stack of 48 subs.

 

Evryscope http://evryscope.astro.unc.edu/ has 22 Rokinon 85mm f/1.4 lenses, each with its own KAI29050 CCD sensor  (note some papers say 22 lenses others say 27).

 

Evryscope takes the "go wide" approach and it has them pointed in different directions.  However a single exposure is only a single exposure, so they take several and stack.

 

One of the Evryscope scientific papers http://evryscope.ast...u/publications/  is of possible great interest to astrophotographers.

 

The paper https://arxiv.org/abs/2001.00879v1 is about "robotiler" which is an automatic system for making sure that the lenses are aligned properly with the sensors - specifically that the mechanical tolerance in the Rokinon lenses is not great so many are actually tilted with respect to the sensor.

 

This is consistent with a trend that I have found on CloudyNights that the Samyang/Rokinon lenses are haunted by the reputation for having poor quality control.  Perhaps the "bad" ones are only bad because of alignment?  The paper also says that they found one lens could not be aligned and suspect a crack in an element.  One out of 22-27 (so a ~4% failure rate) is also consistent with the quality control complaints.

 

I am not sure how to correct lens alignment for a Rokinon lens attached to a camera - presumably there is a way to shim the mounting flange.     

 

Correcting lens alignment between a lens and an astro CCD camera, like SBIG or something from QHY would seem to be quite straightforward.   

 

With the task of aligning 22 lenses, and then periodically checking them, I can see why they made the robotiler motorized and had an automatic method for doing the alignment but for a single camera/sensor it would seem like a manual tilt method would work.



#20 chanrobi

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Posted 02 July 2020 - 11:00 PM

Just wanted to back up to this point for a second. The Dragonfly telescope has each lens aligned to the same point, and they all see the same field: the total FOV for that system is only 2.6x1.9 degrees. The main benefit in that system is not to use the multiple short focal length refractors to shoot simultaneous panels for a mosaic, but to operate with a very high effective light gathering area and exceptional signal to noise ratio. By doing this they can go very deep with a reasonably short integration time.

 

Cheers,

Dan 

Wow crazy, didn't even know about this!

 

I used to work at that observatory!!
 



#21 erictheastrojunkie

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Posted 03 July 2020 - 02:01 AM

This site has a review of the Sigma ART 105mm f/1.4.

 http://www.atscope.c...s/Sigma105.html

 

They have corner and edge shots at f/1.4 and assuming that the photos from the site were what I got, I would say they are not usable.

 

However the site also has corner and edge shots at f/2, and they are enough better that I would call them usable but barely.

 

The same site has 200mm f/2 canon edge shots that to me look usable at f/2.

 

This picture shows coma testing using artificial stars for the 40mm Sigma ART, which looks pretty terrible if the artificial stars are to be believed.  https://www.flickr.c...in/33460966778/

 

The 135mm f/2 Samyang/Rokinon looks useable at f/2 here https://www.flickr.c...in/20005540154/    There seem to be lots of favorable reviews of the lens.

Both of these examples for the Art 105mm and Art 40mm are miserable, I have no idea if they got poor copies or what, but neither are indicative of the actual quality of those lenses. There isn't a lens wider than 100mm that's better than the 40mm, it's the current sharpness, coma, and LoCA champion in terms of wide angle lenses, it's the best lens I've ever used out of 65+ lenses at this point. You can see several reviews of these lenses here, the lenstip reviews include LoCA and Coma analysis:

https://www.lensrent...gma-art-lenses/

https://www.lenstip....ywu&test_ob=535

https://www.lenstip....ywu&test_ob=548

 

There are a lot of really good examples of astro done with both of those lenses here and around the web, in terms of cost/value you will be hard pressed to do better than them. 



#22 whwang

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Posted 03 July 2020 - 04:43 AM

I know some people disagree (and I respect them), but personally I would never expect those F1.4 lenses to be usable on astro at F2.8 or wider.  I always stop my Art lenses down to at least F3.3.  Based on the test reports on internet, some Otus may go wider than Art by half a stop, but that's probably it.

 

If you see a lens performing poorly at F1.4 for astro and decide that it's not a good one based on this, then you need to adjust your expectation.  Otherwise you will never find a good lens.

 

The above are for lenses shorter than 135mm.  On longer lenses, you can expect some very good ones to be usable at F2.8 or even F2.



#23 nathanm

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Posted 03 July 2020 - 12:55 PM

Well, to reply to whwang, modern lens designers using aspherical elements ought to be able to do better than f/3.3. 

 

Some of the replies on this thread show people agree with that - ChristopherBeere uses the f/1.4 Sigma Art lenses wide open, for example.  

 

You could just have very high quality standards.  I think I do too, but I am aware that there are many issues in making a big mosaic that can hurt or help the quality.   For example, you typically are superimposing multiple images with different alignments and averaging them, that generally helps a lot.  Using long focal length lenses allows downsampling which tends to improve quality.  You also have distortion from the map projection (mentioned by ChristopherBeere), which can really hurt quality.

 

For daytime photography the Zeiss Otus line is spectacular including at f/1.4.   However, even on super expensive lenses like that, lens designers often don't seem to care much about astrophotography and point sources.    But some do which is why Samyang, Rokinon, Sigma Art series are generally much better than the Otus lenses.

 

For now, my list of lenses that seem to be decent wide open includes

 

at 200mm

--------------

Canon 200mm f/2  - looks good in all the examples I have seen

Canon 200mm f/2.8 

 

at 135mm

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Samyang 135mm f/2  - looks good in the examples online I have seen

Zeiss 135mm f/2  - look good

 

But the Zeiss tests I have seen are for Apo Sonnar, and I would like to confirm that the Milvus as good.

 

Canon 135mm f/2 not good at f/2, not sure about f/2.8

 

Don't know yet abut

Sigma art 135mm f/1.8

 

At 100- 105mm

---------------------

105mm f/1.4 Sigma Art - some photos I found online look bad at f/1.4 and better at f/2.  Others like ChristopherBeere, swear it is good wide open

 

Don't know about 100mm f/1.4 Zeiss Otus - but skeptical because of other otus lenses

 

for 85mm

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Zeiss Otus is bad at f/1.4 - not sure about f/2

Zeiss Milvus f/1.4 - I doubt it it is good if Otus isn't

 

Samyang/Rokinon 85mm f/1.4  - not good at f/1.4.  I don't havegood test photos at f/2

 

Samyang/Rokinon 85mm f/1.2 SP/XP  - not sure

Sigma Art 85mm f/1.4  - not sure

 

Canon 85mm f/1.4 - not good in any version (but a good daytime lens)

 

55mm

---------

Zeiss Otus bad at f/1.4,  not sure about f/2

 

So, to sum up, so far there is strong evidence from multiple sources is that 135mm and 200mm focal lengths both have some choices which are good wide open.

 

Is that true for 105mm ?  Possibly.

 

The data I have seen so far on Sigma 105mm art says it is good at f/2 which is not wide open but is a lot faster than f/3.3.   As noted above, others say it is good at f/1.4.  It might come down to the individual lens, or when it was made - the only actual star tests I have are from when the lens first came out.

 

Focal lengths shorter than 105mm seem less likely but possibly one of the 85mm lenses will be good wide open.   I suspect several of them will be decent at f/2.


Edited by nathanm, 03 July 2020 - 01:00 PM.


#24 garret

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Posted 03 July 2020 - 03:12 PM

 

Don't know yet abut

Sigma art 135mm f/1.8

Read an extensive test of this lens with photo of stars here: https://www.the-digi...M-Art-Lens.aspx

The MTF chart (10 samples tested) are made by Lensrentals with their special $100K MTF measuring device called 'OLAF'



#25 nathanm

nathanm

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Posted 03 July 2020 - 05:33 PM

Well, I have seen those tests but it is unclear to me that an MTF chart adequately captures coma for astrophotography purposes.

 

Also from Roger Cicala of lens rentals, here is MTF chart for the Zeiss 85mm f/1.4 is here https://www.lensrent...tus-mtf-charts/

 

They say it is fantastic and the best of its focal length.  Yet I know that the 85mm f/1.4 Zeiss Otus shows "flock of seagull" stars at the edges at f/1.4 because I own the lens!

 

It is a wonderful lens for daytime landscapes, which is where I use it.

 

The problem is that an MTF chart plots important things about a lens but it does not tell you everything.

 

The review does post one star picture but there are few bright stars near the corner.  Those that are there are a ways from the corner and don't look great to me.

 

I would find a more direct star test more convincing.




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