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SharpStar Askar ACL200 200-mm f/4 astrographic telephoto lens
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SharpStar Askar ACL200 200-mm f/4 astrographic telephoto lens
Reviewed by Michael Covington
Michael Covington is the author of Digital SLR Astrophotography and other books. By day, he develops artificial intelligence software in Athens, Georgia.
DISCLOSURE: The lens reviewed here was lent by the manufacturer for review, and the reviewer was then allowed to purchase it for 30% below list price. Apart from that, the reviewer has no financial or business relationship with the manufacturer and was unacquainted with them until shortly before requesting to review this lens.
All photos here are by Michael A. Covington, including technical illustrations. Larger versions of the sample astrophotos can be displayed in a new tab/window by clicking on the review image.
A telephoto lens just for us
Telephoto lenses — can't live with 'em, can't live without 'em. They are basic tools of wide-field astrophotography, but even the best ones often disappoint us. Too many of them aren't sharp all the way to the corners when shooting star fields, and much of their cost comes from features we don't need, such as autofocus, zoom, and electronic aperture control.
Wouldn't it be nice if someone made a good telephoto lens just for astrophotography? It's being done. You've probably heard of the first major product of this type, the William Optics RedCat 51, a 4-element, 250-mm, f/4.9 lens specifically for astrophotography.
Now China sends in a formidable competitor. The Askar ACL200 is a 200-mm f/4 lens with 6 elements, two of them made of ED glass, and is very ruggedly built. Using a 48-mm T-ring, it fits any DSLR and, with extension tubes, dedicated astrocameras. Figure 1 shows its features, and Figure 2 is an example of what it delivers. The manufacturer is SharpStar, officially known as Jiaxing Ruixing Optical Company, of Jiaxing City, near Shanghai. See http://www.askarlens.com/.
Figure 1. Askar ACL200 has coarse and fine focus and aperture rings, all lockable, and provision
for 2 sizes of filters.
Figure 2. Mu Cephei nebula. Askar 200-mm lens at f/4, stack of 16 2-minute exposures with
H-alpha-modified Nikon D5500 at the Deerlick Astronomy Village.
Using it
The ACL200 is strikingly easy to use for astrophotography. Focusing is purely manual, of course. There are two focusers, coarse and fine, both lockable, and the lens will focus appreciably past infinity (to accommodate filters) as well as down to 10 meters (for nature photography).
Unlike the RedCat, the ACL200 does not include a Bahtinov mask. Of course, you can easily add one. But I found it best to focus for maximum visibility of faint stars on the camera screen in Live View.
The tripod shoe below the lens has 1/4" and 3/8" tripod sockets, and, more importantly, the whole shoe is a Vixen-size dovetail (Figure 3). Many equatorial mounts will take it directly, with no additional hardware. In Figure 4 you see it on my Celestron AVX mount.
A newer version of the lens, just now coming on the market, has a Vixen saddle on top as well as a Vixen dovetail below. That way you can mount a small guidescope on top of the lens. The new lens collar, with shoe and saddle, is available as an upgrade to go in place of the one supplied on the original-model lens.
Figure 3. The built-in tripod shoe is also a Vixen dovetail that fits directly into
your equatorial mount.
Figure 4. The dovetail fits directly into many telescope mounts with
no additional hardware.
If you put the ACL200 on an equatorial mount, you may need a lighter-than-normal counterweight. With my AVX, no Celestron counterweight was light enough, so I used a 2-kilogram counterweight made for the iOptron CEM40, whose shaft is about the same diameter.
Note that the ACL200 may be too heavy for lightweight camera trackers. It weighs 1.8 kilograms (4.0 pounds), not counting the weight of the camera. That's more than twice as much as a Nikon 180-mm f/2.8 ED AI lens, for example, or a Canon EF 200-mm f/2.8 L, even though those lenses are one stop larger in aperture.
You can install a 48-mm filter inside the rear section of the lens (Figure 5). I have not tried this. That is the filter size used with 2-inch eyepieces and many astrophotographic systems.
Figure 5. You can install a 48-mm filter internally inside the rear section of the lens mount.
Finally, the lens attaches to your DSLR camera with a 48-mm T-ring — not the standard camera-store 42-mm T-ring, but just like it except for the diameter. As with conventional T-rings, the back focus is 55 mm. If you wish, you can use 48-mm threaded adapters to fit the lens to a dedicated astrocamera.
Optical design and performance
The lens design is not quite like anything I've seen elsewhere. It's inspired by classic telephoto designs with a positive achromat in front and a negative achromat in the rear, like a refractor with a Barlow lens. However, the ACL200 has two big positive groups in front, each of which has an ED-glass element, and a negative group at the rear. Obviously the designers were thinking for themselves, and they have achieved a good result.
This lens is apochromatic, more highly corrected for chromatic aberration than ordinary lenses. That was obvious to me as soon as I focused on a star in Live View mode with high magnification. Other lenses, even very good ones, show red or green fringes around star images that are slightly out of focus. Not this one — the star is always a white disk or point. I found that all the more impressive because I was using a camera with extended hydrogen-alpha response, so it picked up light outside the region of the spectrum that lenses are designed for.
I saw not a hint of decentering or miscollimation. Telephoto lenses are often poorly collimated by astronomical standards, for two reasons. First, manufacturing tolerances are considerably looser than for telescopes, and used to be looser yet. Second, the collimation of a lens suffers when it spends several years hanging around a busy journalist's neck and occasionally banging into objects. And those are the lenses we commonly buy secondhand. Compared to many other telephoto lenses I've tested, this ACL200 is unusually precisely made and assembled. Of course, that's just one; I can't tell how much variation is possible.
I took short exposures of star fields to compare the ACL200 at f/4 with my vintage Nikon 180/2.8 ED AI, also at f/4. Image analysis with PixInsight showed the two lenses to be equally sharp. The difference is that the ACL200 gave star images that were basically round all the way to the corners of an APS-C frame. (In the corners, they did have slight, faint coma.) Star images with the Nikon lens were compact but irregularly shaped, becoming triangular at the corners. Bear in mind that this is an old lens, but the shape of the star images reflects its optical design. Overall, the ACL200 wins.
I did not have a chance to test with a full-frame sensor, but Cloudy Nights user "Astrojedi" did — click here for his results, which also show almost perfect star images all the way to the corners, certainly much better than any conventional telephoto lens.
Curiously, the ACL200 did not become sharper at f/5.6 or f/8. It really is optimized for f/4. At f/4, there are no diffraction effects from diaphragm blades because the opening is circular; stars have no spikes. Diffraction effects kick in as soon as you stop it down.
Conclusions
My ACL200 has become a workhorse. It is one of the few astronomical instruments I've owned that can be relied on to do a truly excellent job of what it's designed for. Below are a couple more pictures to show what I've done with it. (The Pleiades picture shows that it's free of internal reflections.) Like Figure 2, Figures 5 and 6 were taken with the lens and camera riding on a Celestron AVX mount with PEC but no autoguiding — a very portable setup.
Figure 5. North America nebula. Askar 200-mm lens at f/4, stack of 20 2-minute exposures with
H-alpha-modified Nikon D5500 at the Deerlick Astronomy Village.
Figure 6. Pleiades, strongly stretched to show scattered nebulosity.
Askar 200-mm lens at f/4, stack of 16 2-minute exposures with
H-alpha-modified Nikon D5500 at the Deerlick Astronomy Village.
I strongly recommend the ACL200 for wide-field astrophotography. It also has some uses for (fully manual) nature and landscape photography. The optical performance is exceptional, and the physical construction is unusually well suited for astronomical use. Its main drawback is its heavy weight (too heavy for lightweight star trackers). It costs appreciably more than the secondhand telephoto lenses we often use, but less than a good 180- or 200-mm lens new. Further, you do not need to buy a tripod collar or dovetail, nor large-diameter filters.
- bill w, dswtan, Jim Waters and 20 others like this
108 Comments
Thanks for the great review, Michael. I got my ACL200 in mid-January of this year, and I completely concur with all of your findings. I use it on a motor-driven Orion SkyView Pro EQ, which makes for an easy setup. With my mirrorless Olympus OM-D E-M1' s M-4/3rds sensor, stars are tack-sharp and perfectly round all the way into the corners. I absolutely love this lens... and will be getting an upgrade lens-collar for it, when they become available in mid July.
+1 for the ACL200. :-) Haven't used it much yet, since it arrived along with bright nights here in Denmark, but it is really easy to use and also makes for a perfect option in a portable setup. I use it on an EQ3-2 with an dual axis motor and it is nice that I can polar align through the polar scope while the lens is mounted. I am looking forward to do a lot of wide field with this lens.
Thank you for the great review. I'm happy to see the additional filter holder. This is very important especially for those who use regular 2" light pollution or narrowband filters. Looks like the lens performs pretty well fully open which is not always the case with other lenses.
Thank you very much for your review. I totally agree with you, a perfect astrographic telephoto lens. Here is my setup and my firstlight (only 1 hour without darks and without flats, but platesolve, autofocus and guiding with Asiair Pro on my GEM28) I have replaced the original M69-M48 adapter with a short version to add a filter drawer for easy filter change.
https://www.astrovis.at/teleskope.php
Best regards
Horst
aorion314 here, who has this device for purchase in the US, and what is a fair price new for this lens any input would be appreciated.
I keep hoping Astronomics (our sponsor) will get it, but it's in short supply. Agena Astro sells it. I'm not sure who else.
I got mine from Agena Astro, in January:
https://agenaastro.c...ens-acl200.html
They're currently out of stock, but that may be because the updated version ACL200 may not yet be available. Proposed availability for purchasing the updated collar separately, is "mid-July":
http://www.askarlens...class1/239.html
Camera Concepts & Telescope Solutions apparently has them in stock, but these may not be the newer version with the updated collar.
https://www.cameraco...ens-acl200.html
Same availability from a few European sites... but again, these may be the "original" version. I would call or e-mail any potential vendor, prior to placing an order.
You can buy the new version here
https://www.teleskop...fotografie.html
Last night I was able to pre-order the updated collar (with dovetail) from Agena. They are out of the lens itself but expect to have the new-style collars in shortly.
aorion314, looks like the best option/price is to wait awhile till stocks of new product in usa, this item should well with my Canon 6da sitting on top of my Losmandy g11 and my soon to be arriving SVX140, thanks to all for the input, respectfully submitted.
Hi,
I have the Askar ACL200 in its first version format and used it successfully with my Nikon 5600. I do sometimes get spikes around bright stars like Antares so possibly need a stepdown ring. However a bigger issue at the moment is that I cannot seem to get focus at infinity with my recently arrived Nikon Z6 (original).
Has anyone else used this combination? Is there a spacer or adjustment that helps.
I also find the Nikon Z6 does not seem to quite reach focus at infinity with the Redcat if someone has that instead..
sorry, I work with Canon.
Btw, I changed the way to work with different filters (Lpro, eXtreme). Filter drawers don‘t work well with DSLR‘s, either the nose disturbs or the opening is in a position, that I can not remove the filter. With this rotation adapter (see image above) I can easily disconnect the camera, switch the EOS part of the adapter with filter and connect the camera again. Quick and easy.
Something is wrong with what you have between the lens (either Askar or Redcat) and the camera body. What exactly are you using? How far off is it from correct infinity focus, and in which direction?
I'm not familiar with the Z6, but I would expect that you would use a 48mm Nikon F T-ring followed by a Nikon F to Z lens adapter. At least, that should be one way to do it.
If the failure to reach focus is slight, you might try the fine as well as coarse focus. But since you are having problems with two lenses, I think the problem is in the adapters.
Hi Michael,
Yes I am using a quite thin adapter, the BAADER T-ring for Nikon Z cameras, T rings for this camera are a little hard to get here..perhaps this ring is too thin for this mirrorless camera for these lenses. The focus issue is worse for the ACL200. I will have to try in daytime to try and work out how far it is out but I know it is fine for my DSLR. I do have another T ring coming by post so perhaps that will solve this issue.
Update on ACL200 and Nikon Z.
Not getting close to a manual correct focus at either near or far distances using BAADER T-ring at day and autofocus is not available with the Nikon. I had hoped to hear from someone with a Nikon Z but perhaps a wider T-ring will do the job, I have ordered the wide Nikon Z 48mm T-ring from Telescope Adapters.
It's not wide vs. narrow, it's lens-to-sensor distance. How far, in mm, is it from the back flange of the lens (before the T-threads) to the sensor in the camera? (At least roughly.) It should be 55 mm.
If it will not focus on anything, not even near objects, that suggests the lens is too close to the sensor.
If this is the T-ring you are using
https://www.baader-p...-2-and-s52.html
with the 48mm insert, you are also going to need some kind of spacer to increase the lens-to-sensor distance. I am surprised Baader does not provide that.
The reason is that mirrorless camera bodies such as the Nikon Z are much shallower than SLR camera bodies.
I regret that I am not familiar with the Nikon Z. But we should be able to figure this out.
Hi Michael,
I have got a bit more info from the supplier of the T-Ring, as you may have guessed this was my first full frame mirrorless camera and while I thought a closer focus would be needed, I did not realize the spacing differences would be so different from my apc DSLR. It does appear there is a relevant BAADER spacer. For those in a similar situation, having to buy an additional 48mm insert (comes with 42mm) and in addition a spacer may make this particular Nikon Z T ring an expensive option among T rings for those already invested in APC cameras but considering a Nikon Z.
"The Baader T-ring should give a distance of 8.3mm + the camera’s flange distance of 16mm = 24.3mm, leaving an additional 30.7mm to make up with a spacer. This M48 24-35mm Variable Adapter should allow you to reach that correct distance - https://www.testar.c...dapter-24-35mm"
Lockdown in the main Australian state (NSW) for importing stuff to Canberra may stop me from solving this for quite a while but when I do get remedial gear and imageable weather I will post a pic here with the Nikon Z and the ACL200 assuming no one else has done so by then.
I would actually maintain that a T-ring that does not give a flange-to-sensor distance of 55 mm is not truly a T-ring -- is not following the Tamron (Tokina? one or the other) standard that gave us T-rings in the first place. (They were a system of telephoto lenses that would fit multiple brands of SLRs in the 1960s, and of course they standardized the flange-to-film distance so that the lenses would focus the same way on all cameras.) Of course, if it is 48mm rather than 42mm it already isn't following the standard. But they should warn you about the depth!
Also, since this is a need that arises regularly, they should make a spacer that is exactly the right depth, rather than telling you to use an adjustable one.
Does anyone know how this lens performs with a full frame sensor?
In my article there is a link to some tests another person posted here on Cloudy Nights. The answer: Quite well.
Success in a Nikon Z6 ACL200 image.
The BAADER M48 variable adapter in combination with the BAADER T ring and M48mm insert will connect and allow focus to be achieved for a Nikon Z6 ACL200 combination.
My image certainly will not sell any more units, but I said I would update when I found means in getting it to focus. This is just an unguided manually focused test image after AstraPixel Processer from 30 minutes of cloud and moon impacted imaging on July 18 under the city skies of Canberra. The image is just a central, roughly 25% crop portion reduced to 49% quality to get it under 500k. But I think it is enough to show this combination will focus.
The other seemingly lost in the mail T ring option of a wide T-Ring from Telescope adapters arrived on the 19th and I hope to try it before too long.
Attached Thumbnails
I am new to astrophotography and have read this review. I have been shopping this lens but it is between 650-900 USD. Considering it has no auto focus and is an f4 lens, please help me understand the upside to this vs a 200mm prime lens with a 2.8 aperture and ED. These are all over ebay for around 200 USD. Please help me know what the main differences are? I get that this lens is sharp but if you stop down a 2.8 to 4, it will be sharp too. I am not anti this lens, please help me understand the value
This lens is apparently sharp wide open so you can avoid starburst effect of aperture blades if you prefer to not have them. It has a very flat field, at least what I have seen from images. It also seems to have very good control of chromatic aberration. It also has an internal filter holder and the ring has the ability to hold a guidescope.
All that being said my first unit of this lens was a complete dud and had horrible comet stars on one side of an APS-C frame, for both a mirrorless APS-C with t-ring, and dedicated astro cam with spacers, both cameras being proven good performers. Here's to hoping the replacement is better. I hope my experience is a one off, and there are not quality control issues on this device.
Poynting, sounds like you got a unit with a lens element either decentered or loose in its mount.
cos, autofocus is not used in astrophotography, and autofocus lenses are often hard to focus manually.
The optical quality of this lens is, in my experience, considerably better (in astrophotography) than conventional telephoto lenses, even those of high quality. For instance, this one beats the Canon 300/4 lens I used to have and the Canon 200/2.8 L lens that I tested. Terrestrial photographers are not concerned with star-image quality.
Please listen in below short video:
https://youtube.com/...k?feature=share
How about when you lightly shake the lens. On the first unit I hear the strange noise of the ring, second unit I hear the same noise and notice like a loose lens sound rattling when I lightly shake it. I cannot have had bad luck twice in a row right?