7.22
...
·
 |
|---|
|
Hi all! I have a quite unexpected update to share:  This was shot with the Same Sony a6100 and a completely different objective. The halos look pretty much the same, so, I'm starting to think that there might be nothing wrong with the Rokinon/Samyang.... That's it! |
0.00
...
·
|
|---|
|
Hello. I my self have the lens and it is very bright at F2.0 Stop down 4-5 steps and go for longer exposer time. CS. morian |
4.51
...
·
·
1
like
|
|---|
|
I use the 135 as well. Lately I've been stopping down to F/2.8 or so as I'm experimenting with step down rings, but I have used it at F/2 with my old 533MM. I also tested the 85mm F/1.4 on my old D3200 as a piggyback setup. Neither of these lenses show any kind of halo like the ones you show here. Some examples: https://www.astrobin.com/rlgr21/B/ https://www.astrobin.com/p5xcmy/J/ https://www.astrobin.com/i8ykk1/ I did test my old Nikkor AI 135mm F/2.8 at Orion though, wide open. I didn't get any halo on Alnitak or the other usual suspects there either. In fact the only time I've experienced halos like these myself is when I started using ZWO filters which were horrible. So I don't think it's far-fetched to assume that it could be either a de-centering issue or a reflective source on the sensor itself. Edit: I too found the images in the OP quite soft, make sure to check that you're actually able to focus on the stars if you haven't already. Luckily it's an easy job to fix if it needs to go a bit beyond the infinity mark, which often is the case with this particular lens. |
0.00
...
·
|
|---|
|
I did not step down anything on my Rokinon 135mm, and it has always been pretty sharp : https://www.astrobin.com/search/?q=Hamber+135mm |
|
4.51
...
·
·
1
like
|
|---|
| Stepping down the lens has less to do with sharpness than star shapes as far as I'm concerned. As long as you can find focus and get the correct backfocus, the image will be sharp. With larger sensors stopping down also helps with backfocus as any errors, both optical and in terms of backfocus, become exponentially more prominent the faster the scope/lens is. Also, there comes a point where faster isn't necessarily better and you don't gain anything from it, you may actually lose data as you will see a loss of emission signal for narrowband unless you have the right filters for it. So stepping down a few stops isn't necessarily a bad thing. But the lens, given that it is a good copy, is very usable at F/2 in my experience as well. But it can be a pain to figure out tilt and miniscule backfocus adjustments that need to be done. |
 ...
·
·
1
like
|
|---|
| I haven't followed this thread, but in answer to the original question - using a UV/IR filter will reduce star bloat, and stopping down the lens to f2.6-f2.8 will help reduce these halos. Following advice I use the Samyang 135mm (equivalent) wide open with a stop down ring giving 49mm aperture. processing the starfield separately (Starnet or StarXterminator or equivalent) will allow you to control remaining halos, whist stretching the underlying nebulosity to your taste. |
|
7.22
...
·
·
1
like
|
|---|
Tom Gray: This is a 100% crop, shot at F/2.8:  (crop close to the bottom left corner of the field, 4 hour integration, processed with StarXterminator) I'm about to start using a 2" Ha/OIII filter in front of the objective, getting a 44mm clear aperture at about f/3... all granted that I can find the Octans asterism from my Bortle 7-8ish urban backyard... I'll let you know how it goes, I don't expect those halos to go anywhere 😅 Stars from above, in context (around 40% magnification):  |
...
·
·
1
like
|
|---|
| Thanks Franco - I find OIII filters / my L-eNhance and duo/tri-band filters often cause halos. The offset of these halos suggest an issue with backspacing - this is critical with this lens - I use 0.1mm shims to try and optimise this. All said, I’m amazed with the performance of this photographic lens. |
2.11
...
·
·
1
like
|
|---|
|
Huh… I have a Rokinon 135 and haven’t tested it much, but my tests on a Sony A7R III didn’t seem to halo like that. Nothing even close. The camera should have a UV/IR cut in the sensor. I would stop the lens down for imaging, and have. I’ll have a look at my aperture star tests. Not the same camera, but seems curious. I’m guessing there is also no protective filter on the front of the lens by what you wrote. Was there an off-axis light source like the moon or an urban light? |
|
7.22
...
·
|
|---|
James Peirce: The halos have been consistent on all takes I've made so far from very different locations, so I'd rule out any off-axis light source. Additionally, the halos are very symmetric. Finally, if you check the street picture I shared a few posts above, it seems that I get the same halos with different lenses as well. I need to test more, I have 4 different lenses to compare and see what I get when pointing into a car headlight. |
|
7.22
...
·
|
|---|
Tom Gray: I'm using a mirrorless Sony camera, no backspacing issues here... |
|
2.11
...
·
·
1
like
|
|---|
Franco Grimoldi:James Peirce: With different lenses, too? That’s nuts, and points to the camera, if this has been well-tested. I would have otherwise suspected the lens. It would be interesting to get some direct confirmation against other copies of that camera. But I wouldn’t have expected that from a modern mirrorless camera. I saw you mentioned it had not been modified. I don’t have an obvious-sounding thought on this. I would check to skies sure light isn’t able to leak in at the flange. If that were the case, though, I would have suspected some other complications. But one more thing to rule out. |
 ...
·
·
2
likes
|
|---|
|
If you think its the camera, you can always go out and rent a camera. It is easy to do in most locations if you are near an urban center. There is a lot of confusion on this thread regarding the use of the terms "star bloat" and halos. From your original post, I would agree that you are concerned about the halos. Star bloat comes from either overexposure, where too many photons on the sensor are causing electrons to bleed across pixels, or the optics are unsharp and peripheral, photons are causing a larger than normal star. This happens with bright star vs. faint stars all the time even in perfect images. Halos are from internal reflections from the optical surfaces. And one of those surfaces could be the cover glass of the sensor itself. I would agree with those that state that your image looks a bit "soft". You seem to be a bit out of focus. I would also agree with you that your image star quality is quite good even out to the corners. Added filters between the camera sensor and the lens can cause the internal reflections. I would not rule out the camera, as your night street shot seems to implicate. It is also interesting that the worst halo seems to be color-dependant. Only one headlight has halos. Don't give in to those who insist that you stop down the lens to correct every problem. That is for those not willing to put in the time to work out the best image solution with the widest open optic. You paid for the glass, its stupid to needlessly discard so much of it. Do the math. Your lens wide open is a 67.5mm objective. That is not that big! Stopping down to f4 turns it into a 33mm optic! Thats smaller than most finder scopes! Just think about that! Fact is your star shape is pretty good to the edges and that is the most you could expect with the f-stop reduced anyway. And if you find you must stop down your lens, buy aperature rings to do it. Unless you love the 18 spikes coming from the brighter stars. In any case, the camera can be easily ruled out my just renting another camera and shooting some bright stars. Bright blue ones to be sure! For those that don't like the Rokinon hype, well, I have one and I have seen too many nice images to deny its utility. So don't give up just yet! |
|
7.22
...
·
·
1
like
|
|---|
Alan Brunelle: Thanks for the input and support, Alan, much appreciated! I'm fully aware that I have plenty of room for improvement: . Better camera, ideally a dedicated astrocamera. I don't plan to modify my Sony as it's my main "real world" camera and I love it. . Better balancing on dec/RA: my current setup prevents me from getting a good balance if I point too far away from the pole (such as Orion). I have a declination bracket coming from China that should solve this. The Star Adventurer is, by far, not ready to take a Rokinon 135mm hanging from a camera directly attached to the mount. . Better polar alignment: I'm doing visual-only alignment and can't make easy corrections once I started shooting. . Better focus: I do have a Bahtinov mask, sometimes I feel I'm lacking a bit of travel, only sometimes. . Longer exposures: I just got an intervalometer to get over the 30" limitation from the camera. Of course, it's been cloudy AF since then. . Start guiding on RA (this would imply start using a computer, a whole different approach...). . Better mount: to be able to guide on both axis and also dither. . Most important of all: much, much more practice. Right now I'm doing one imaging session per month, at best. That's why I got the Ha/OIII filter, hoping to be able to start shooting from home on any clear night. I'll try to get out and get some halo photos with my four pieces of glass. |
|
0.00
...
·
·
1
like
|
|---|
|
It's fairly obvious that it's the camera, and not the Rok 135mm. Your picture of the cars shows the exacts same halo pattern. Something is wrong with that sensor, or the glass over it, or the glass-sensor interface. |
|
4.51
...
·
·
1
like
|
|---|
Alan Brunelle: I know OP is shooting OSC, but like I explained above stopping down isn't only because of correcting optical errors. If you shoot with filters, and don't have high speed filters that are only suitable for really fast optics, then you are actually hurting your images by imaging at F/2. You will see a loss of emission signal as opposed to imaging at closer to F/3. That's just how it is. But I also stated that F/2 should work well if it's a good lens. |
...
·
|
|---|
Jan Erik Vallestad:Alan Brunelle: Yes, that would make sense. Actually, I have to ask whether it is necessary to stop down when using a standard (narrow) bandwidth filter, or whether the filter simply will just act as an f-stop aperature anyway. The filter might just take care of the f-stop by it presence. Any light from the light cone outer 1/3rd or more should be effectly blocked by these very dense filters. This would make sense probably for the parts of the emission nebula itself, but may be wonky on the stars. On the other hand, if one wants to spend a lot of money on very tight narrow band filters, one could buy a 70mm filter and apply it to the front of the lens, as most photographers do. A no sacrifice solution for lots of $$$, if even available. I find my 135mm Rokinon to certainly be less than perfect. It can be made suitable for many applications after some effort by working on backfocus and tilt. But at best, there are still star artifacts when viewed up close in the corners, etc. However, these are hardly visible when the image is viewed at normal dimensions. Then, of course, BXT or other methods can make the image essentially perfect. For this, it is up to the user as to how good is good enough. On the other hand, not all of these lenses are perfect, with some stinkers to be found. I sent one back that I bought from a large US-based general retail supplier after finding poor performance. I suspect, for a couple reasons, that lens to have been returned previously. My guess for maybe the same faults. I then bought from a rather large throughput, but photo-dedicated seller of cameras and lenses and got better results. So care and common sense in finding reputable sellers is probably a thing to do. I think stopping down can make sense in some cases. For getting nice stars, fine. Narrow band filters, fine. But maybe get HS filters, if possible? A quick knee-jerk solution of just stopping down risks unnecessarily leaving too much performance on the table. Examples: 1. Stopping down to solve problems from a bad lens. Better to return the bad lens and get one that works well wide open. No? All evidence is these lenses can well work wide open. Why settle for a poor optic? 2. Stopping down to solve tilt issues. Leaving performance on the table is just lazy. 3. Stopping down to solve backfocus issues. Same as #3. Etc.... My biggest beef for the Rokinon 135, is that this lens is perhaps one of the biggest sellers to outdoor photographers, including astrophotographers, and the makers have not found it within their wisdom to upgrade the lens to a weather/water resistant design. Examples of lenses that do so are the Sigma 105, f1.4 and many others. I would have paid a bit more for such an upgrade. |
